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Voice over Wireless LAN 4.1 Design Guide
Cisco Validated Design I
January 18, 2010
Americas Headquarters
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Text Part Number: OL-14684-01
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Voice over Wireless LAN 4.1 Design Guide© 2007 Cisco Systems, Inc. All rights reserved.
C O N T E N T S
CHAPTER
1
Voice over WLAN Introduction
1-1
About the Guide 1-1
Document Purpose and Audience
Document Organization 1-1
1-1
VoWLAN Solution Overview 1-2
VoWLAN Solution Network Design Overview
Solution Benefits 1-3
Customer Requirements 1-4
Healthcare 1-4
Retail 1-4
Recommendations 1-5
CHAPTER
2
WLAN Quality of Service
QoS Overview
1-2
2-1
2-1
Wireless QoS Deployment Schemes 2-2
QoS Parameters 2-2
Upstream and Downstream QoS 2-3
QoS and Network Performance 2-4
802.11 DCF 2-4
Interframe Spaces 2-5
Random Backoff 2-5
CWmin, CWmax, and Retries
2-6
Wi-Fi MultiMedia 2-7
WMM Access 2-7
WMM Classification 2-8
WMM Queues 2-10
EDCF 2-11
U-APSD 2-14
TSpec Admission Control
2-15
QoS Advanced Features for WLAN Infrastructure 2-18
IP Phones 2-20
Setting the Admission Control Parameters 2-21
Impact of TSpec Admission Control 2-22
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IEEE 802.11e, IEEE 802.1P, and DSCP Mapping 2-23
QoS Baseline Priority Mapping 2-25
Deploying QoS Features on LWAPP-based APs
WAN QoS and the H-REAP 2-27
2-26
Guidelines for Deploying Wireless QoS 2-27
Throughput 2-27
QoS Example LAN Switch Configuration 2-27
AP Switch Configuration 2-27
WLC Switch Configuration 2-28
Traffic Shaping, Over the Air QoS, and WMM Clients 2-28
WLAN Voice and the Cisco Unified Wireless IP Phone 7921G and 7920
CHAPTER
3
Voice over WLAN Radio Frequency Design
2-29
3-1
General Voice AP Guidelines 3-1
High Availability 3-1
VoWLAN Call Capacity 3-2
2.4 GHz Network Design 3-2
Co-channel Interference Considerations 3-3
Bit Rate Impact on Co-channel Interference 3-6
20 Percent Cell Overlap 3-7
Co-channel Interference and 20 Percent AP Cell Overlap
Example Deployments 3-10
Example Single Floor Building Deployment 3-10
Example Multi-Floor Building 3-13
Location-based Services Design Considerations 3-17
The Importance of Auto-RF 3-17
5 GHz Network Design 3-17
IEEE 802.11a Physical Layer 3-17
IEEE 802.11a Channels 3-18
IEEE 802.11a Operating Frequencies and Data Rates
IEEE 802.11a and VoWLAN Deployments 3-19
An Example Single Floor Building 3-20
Planning Tools
CHAPTER
4
3-7
3-18
3-22
Voice over WLAN Security
4-1
WLAN Security Overview 4-1
802.1X/EAP and Dynamic WEP
WEP 4-2
LEAP 4-2
4-2
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EAP-FAST 4-3
WPA 4-3
WPA-Personal 4-4
WPA-Enterprise 4-4
WPA-Enterprise vs WPA-Personal
WPA2 4-6
WPA2-Personal 4-6
WPA2-Enterprise 4-6
EAP Timing
4-6
Network Segmentation
CHAPTER
5
4-5
4-7
Voice over WLAN Roaming
7-1
Client Roaming Decision 7-1
Cisco Compatible Extensions Client Roam Triggers
7-2
Roaming Selection of a New AP 7-2
Channel Scanning 7-2
Typical Scanning Behavior 7-3
Cisco Compatible Extensions Channel Scanning 7-3
Evaluating the List of Potential Roam Targets 7-5
Reauthenticating to a New AP 7-5
Authentication Types 7-5
Reauthenticating When Roaming 7-6
Roaming with Open Authentication/Static WEP 7-6
Roaming with IEEE 802.1X/EAP Authentication 7-6
Fast Secure Roaming 7-7
IP Layer Configuration
7-11
Infrastructure Impacts of Client Roaming
Measuring Roam Latency 7-12
Monitoring Client Roaming 7-13
CHAPTER
6
7-11
Voice over WLAN Campus Test Architecture
Campus Design Overview 6-1
Voice and Data VLAN Separation
6-1
6-3
Campus IP Routing Design 6-3
EIGRP Routing Protocol 6-3
Minimizing EIGRP Reconvergence Time
EIGRP Stub 6-4
Distribution Summarization 6-5
6-3
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Route Filters 6-7
CEF Switching 6-8
Adjusting EIGRP timers 6-8
Campus Layer 2 Spanning Tree Protocol Design for Data Center 6-9
Data Center Layer Introduction 6-9
Spanning Tree Triangle Looped Topology 6-9
Lab Implementation Deviations from Standard Design Principals in the Data Center
6-10
Campus Quality of Service (QoS) 6-11
Campus QoS Services Required 6-11
Campus QoS and Interface Queuing 6-12
QoS and Wired IP Phones 6-13
AutoQoS and VoIP 6-14
QoS Policing 6-14
Campus Multicast 6-15
Multicast Traffic Flows and Router Functions
Campus Security 6-16
Catalyst Integrated Security Features (CISF)
Port Security 6-16
DHCP Snooping 6-17
Dynamic ARP Inspection 6-18
IP Source Guard 6-19
Network Time Services
6-15
6-16
6-20
UniDirectional Link Detection (UDLD)
6-21
Configuration 6-21
Software versions used in test network 6-21
Lab Network used for Configuration Examples 6-21
Campus EIGRP Routing Configuration 6-22
Campus EIGRP Routing Configuration Common to all Routers 6-22
EIGRP Configuration Specific to Core Routers 6-23
EIGRP Configuration Specific to Distribution Routers 6-23
EIGRP Configuration Specific to Access Routers 6-24
Campus Layer 2 Spanning Tree Protocol Design for Data Center Configuration 6-24
Campus QoS Configuration 6-26
Campus Routed Multicast configuration 6-27
Campus Multicast Configuration Common to all Multicast-enabled Routers 6-27
Campus Multicast Configuration for Core Routers 6-27
Campus Multicast Configuration for Distribution Routers 6-28
Campus Multicast Configuration for Access Routers 6-29
Campus Multicast Configuration for Layer 2 Switches used for Data Center 6-29
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Campus Multicast configuration for Layer 2 Distribution-Layer switches used for Datacenter
6-29
Campus Multicast Configuration for Layer 2 ACcess-Layer Switches used for Data Center 6-30
Campus Multicast Configuration for Layer 2 Switches used for Data Center Verification 6-30
Access Switch Catalyst Integrated Security Features (CISF) Configuration 6-30
Router Time Services Configuration 6-31
Uni-Directional Link Detection (UDLD) Configuration 6-32
CHAPTER
7
Voice over WLAN Unified Communications Test Architecture
Cisco Unified Communications Manager Introduction
10-1
10-1
Cisco Unified Communications Manager Design Overview 10-2
Deployment Models 10-2
Single Site 10-2
Multisite WAN with Centralized Call Processing 10-3
Multisite WAN with Distributed Call Processing 10-3
Clustering Over the IP WAN 10-3
Cisco Unified Communications Manager Configuration
Call Admission Control 10-4
Device Mobility 10-5
Roaming Sensitive Settings 10-6
Device Mobility Related Settings 10-6
Network Infrastructure 10-7
UCM and Phone versions 10-7
CHAPTER
8
10-4
Voice over WLAN Wireless LAN Controller Design and Configuration
Network Configuration
Data Rates 8-1
8-1
8-1
Radio Resource Management 8-3
RRM Architecture Overview 8-4
Logical RF Sub-groups 8-5
Channel Scanning 8-5
RF Group 8-5
Dynamic Channel Assignment 8-5
Tx Power Level Assignment 8-8
Coverage Hole Algorithm 8-9
Monitor Intervals 8-10
Dynamic Channel Allocation 8-10
Client Roaming 8-11
Voice Call Admission Control 8-12
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General Cisco Unified Wireless Network Configuration
Quality of Service Policy 8-13
Mobility Groups 8-14
AP Groups 8-14
Multicast Traffic 8-14
CHAPTER
8-13
Voice over WLAN Troubleshooting and Management Tools
9
WLC Tools
9-1
9-1
WCS Tools 9-3
Monitoring 9-4
Alarms 9-5
Reports 9-5
Third Party Tools 9-7
AirMagnet Surveyor Pro 9-7
VoWLAN Analysis 9-8
CACE Technologies and Wireshark
Cisco Spectrum Expert 9-10
WildPackets OmniPeek 9-11
CHAPTER
10
9-9
Cisco Unified IP Phone 7921 Implementation for Voice over WLAN
Cisco Unified Wireless IP Phone 7921 Overview
10-1
10-1
Network Connectivity Test Configuration for Cisco Unified Wireless IP Phone 7921 10-2
WLAN Controller Network Connectivity Test Configuration 10-2
Creating a Voice WLAN 10-2
Network Infrastructure Base Configuration 10-4
Configuring the DHCP Server to Support Cisco Unified Communications Manager Option
150 10-4
Configuring the DNS with Cisco Unified Communications Manager Entries 10-8
Cisco Unified Communications Manager Base Configuration 10-10
Verifying Cisco Unified Communications Manager Name 10-10
Verifying Auto-Registration Enabled 10-11
Verifying Cisco Unified Wireless IP Phone 7921 Firmware 10-12
Cisco Unified Wireless IP Phone 7921 Base Configuration 10-13
Resetting the IP Phone 10-13
Configuring a WLAN Profile 10-14
Trace Analysis for a Base Configuration 10-14
Cisco Unified Wireless IP Phone 7921 Security 10-16
Controller WLAN Security Configuration 10-17
Setting the WLAN Controller IEEE 802.1X Timeout for EAP-FAST
10-20
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Cisco Unified Communications Manager Security Configuration 10-20
Network infrastructure Security Configuration 10-21
Cisco Unified Wireless IP Phone 7921 Security Configuration 10-23
Configure a WLAN Profile to use EAP-FAST Authentication 10-23
Cisco Unified Wireless IP Phone 7921 RF Considerations 10-24
Choosing Between IEEE 802.11b/g and IEEE 802.11a 10-24
Cisco Unified Wireless IP Phone 7921 RF Configuration 10-25
Behavior in Presence of 2.4 GHz IEEE 802.11 b/g and 5 GHz
WLAN RF—Controller Configuration 10-26
10-25
Cisco Unified Wireless IP Phone 7921 QoS 10-27
Cisco Unified Wireless IP Phone 7921 QoS Configuration 10-27
Cisco WLC QoS configuration 10-27
Cisco Unified Communications Manager QoS Configuration 10-29
Infrastructure QoS Configuration 10-29
End-to-End QoS Mapping 10-31
Cisco Unified Wireless IP Phone 7921 Troubleshooting 10-33
Configuration Checklist 10-33
Verify Coverage with Cisco Unified Wireless IP Phone 7921G 10-34
Cisco Unified Wireless IP Phone 7921 Web Page Access 10-34
Enabling or Disabling IP Phone Web Access from Cisco Unified Communications
Manager 10-35
Access the Cisco Unified Wireless IP Phone 7921s Web Pages 10-35
References
CHAPTER
11
10-36
Voice over WLAN Vocera Implementation
11-1
Vocera Overview 11-1
Vocera System Software 11-1
Vocera Communications Badge 11-2
Vocera Architecture 11-2
Main Components 11-2
Software Utilities 11-3
Badge Overview 11-3
Badge-to-Badge Communication 11-4
Badge Telephony Communication 11-4
Vocera Broadcast 11-5
Badge Location Function 11-6
WLAN Controller Base Configuration
Create Voice WLAN 11-7
Vocera Configuration
11-7
11-8
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Server and Badge Configuration 11-8
Vocera Telephony Integration 11-8
DHCP 11-10
Cisco Unified Communications Manager Configuration
Dial Plan and Translation 11-14
Vocera Security
11-10
11-15
Vocera Radio Frequency Considerations
11-16
Vocera QoS 11-16
Vocera QoS Configuration 11-17
WLC QoS Configuration 11-17
Infrastructure QoS Configuration 11-18
End-to-end QoS Mapping 11-20
APPENDIX
A
Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle
Services A-1
The Cisco Lifecycle Services Approach A-1
Lifecycle Services Methodology—Prepare Phase A-3
Wireless LAN Business Requirements Development A-4
Wireless LAN Technical Requirements Development A-4
Wireless LAN Operations Technology Strategy Development A-4
Wireless LAN High Level Design Development A-4
Lifecycle Services Methodology—Plan Phase A-4
Wireless LAN Deployment Project Management A-5
Architecture Review and Assessment A-5
Wireless LAN Operations Readiness Assessment A-5
IP Communications over Wireless LAN Assessment A-5
Wireless Security Posture Assessment A-6
Lifecycle Services Methodology—Design Phase A-6
Wireless LAN Staff Plan Development A-6
Wireless Security Design Development A-7
Wireless LAN Detailed Design Development A-7
Wireless LAN Detailed Design Validation A-7
Wireless LAN Operations Design Development A-7
Wireless LAN Staging Plan Development A-7
Wireless LAN Implementation Plan Development A-7
Wireless LAN Operations Implementation Plan Development A-8
Wireless LAN Acceptance Test Plan Development A-8
Wireless LAN Migration Plan Development A-8
Wireless LAN Site Readiness Assessment (RF Site Survey) A-8
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Security Implementation Plan Development A-8
Lifecycle Services Methodology—Implement Phase A-9
Cisco Security Agent Implementation A-9
Security Implementation Engineering A-9
Security Network Admission Control Implementation A-9
Wireless LAN Staging A-10
Wireless Control System Implementation A-10
Wireless LAN Controller Implementation A-10
Wireless LAN Operations Implementation A-10
Wireless LAN Migration A-10
Staff Training A-10
Wireless LAN Acceptance Test and Network Deployment Verification Audit
Lifecycle Services Methodology—Operate Phase A-11
Wireless LAN Systems Monitoring A-11
Wireless LAN Incident Management A-11
Wireless LAN Problem Management A-12
Wireless LAN Change Management A-12
Wireless LAN Configuration Management A-12
Wireless LAN Supplier Management A-12
Wireless LAN Security Administration A-12
Lifecycle Services Methodology—Optimize Phase A-13
Wireless LAN Business Requirements Alignment A-13
Wireless LAN Technology Assessment A-13
Wireless LAN Operations Assessment A-13
Wireless Security Assessment A-13
A-11
GLOSSARY
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C H A P T E R
1
Voice over WLAN Introduction
About the Guide
Document Purpose and Audience
This guide is intended for systems design engineers who are responsible for designing, implementing,
and operating the Cisco Voice over Wireless LAN ( VoWLAN) solution.
Document Organization
This guide contains the following chapters:
Section
Description
This chapter
Provides an overview of the VoWLAN 4.1 solution.
Chapter 2, “WLAN Quality of Service.”
Provides an overview of WLAN QoS and its implementation in the
Cisco Unified Wireless Network.
Chapter 3, “Voice over WLAN Radio Frequency
Design.”
Provides an overview of the RF network requirements of VoWLAN
deployments and a discussion of the RF deployment issues.
Chapter 4, “Voice over WLAN Security.”
Provides an overview of WLAN Security as it applies to VoWLAN
deployments.
Chapter 5, “Voice over WLAN Roaming.”
Provides an overview of WLAN roaming fundamentals.
Chapter 6, “Voice over WLAN Campus Test
Architecture.”
Provides the configuration and design information for campus
network design and configuration used in this design guide.
Chapter 7, “Voice over WLAN Unified
Communications Test Architecture.”
Provides configuration and design information for Unified
Communications Architecture design and configuration used in this
guide
Chapter 8, “Voice over WLAN Wireless LAN
Controller Design and Configuration.”
Provides configuration and design information for Cisco Unified
Wireless Network design and configuration used in this guide
Chapter 9, “Voice over WLAN Troubleshooting and
Management Tools.”
Provides troubleshooting and management tools for the VoWLAN
solution.
Voice over Wireless LAN 4.1 Design Guide
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Chapter 1
Voice over WLAN Introduction
VoWLAN Solution Overview
Section
Description
Chapter 10, “Cisco Unified IP Phone 7921
Implementation for Voice over WLAN.”
Provides design and configuration information for the Cisco Unified
Wireless IP Phone 7921G in the context of a VoWLAN
environment.
Chapter 11, “Voice over WLAN Vocera
Implementation.”
Provides details for the Vocera Communication system used in this
design guide.
Appendix A, “Deploying and Operating a Secure Voice Describes how to deploy and operating a secure voice over wireless
LAN solution.
over Wireless LAN Solution with Cisco Lifecycle
Services.”
VoWLAN Solution Overview
The mobile user needs the same applications and services with the same accessibility, security,
quality-of-service ( QoS), and high availability delivered to wired users. Many users now enjoy the
benefits of mobile access to their key enterprise applications through the Cisco Unified Wireless
Network, but these applications are primarily based on data communications. Equally important within
an enterprise is voice communication. The purpose of this design guide is to assist customers and
systems engineers design, implement, and operate VoWLAN applications in an enterprise campus. To
demonstrate these features this guide uses the Cisco 7921G VoWLAN Handset and Vocera B1000A
badges, and builds upon the mobility, campus, unified communication, and location design guides from:
http://www.cisco.com/en/US/netsol/ns742/networking_solutions_program_category_home.html
VoWLAN Solution Network Design Overview
The Cisco campus design (see Figure 1-1) is the platform used for testing and design of the VoWLAN
solution. This Cisco campus design uses a typical hierarchical, access, distribution, core design. The
following additional modules were included to this design for the VoWLAN solution:
•
Services module to provide the Cisco Unified Wireless Network
•
Data center module
•
Voice WAN Gateway module
•
Internet Gateway module
The VoWLAN solutions installed and tested for this design were the Cisco 7921G with the Cisco Unified
Communications Manager, and the Vocera Communications System.
Voice over Wireless LAN 4.1 Design Guide
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Chapter 1
Voice over WLAN Introduction
VoWLAN Solution Overview
Figure 1-1
VoWLAN Solution Network Overview
Core Layer
6504
6504
Distribution Layer
6504
6504
6504
6504
WISM WLAN Controllers
Access Layer
3845
Voice/WAN Gateway Block
ASA
ASA
Internet Gateway Block
4948
4948
Data Center Block
4503
Client Access Block
IP
M
PSTN
3750-E
Internet
M
M
M
M
W
N
S
E
222959
3845
Solution Benefits
Enterprises today are faster paced than ever before. Staying ahead of competition, success, and growth
are dependent upon efficient employees, collaboration, and a timely business process. Today, we see that
enterprises have a strong drive for efficiency, are looking to eliminate delays, and are dependent on team
collaboration to support complex business processes. While maintaining a secure corporate data and
voice infrastructure, enterprises are encouraging a mobile work style to get more done. Additionally,
enterprises are not just streamlining processes through technology, but are also looking to increase their
revenue and reduce costs with the latest technological trends.
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Chapter 1
Voice over WLAN Introduction
VoWLAN Solution Overview
Customer Requirements
The following are the customer requirements for deploying the VoWLAN solution:
•
Reduce mobile cellular minutes—VoWLAN calls are free and employees would now use their
VoWLAN handset on campus instead of their cell phone.
•
Integrate Mobile and Enterprise Telephony systems—Mobile WiFi handsets can now be integrated
with IP-PBX features and numbering plans and thus not have to return to their desk phone for certain
features.
•
No difficulty with cellular coverage since enterprises can deploy adequate access points to improve
coverage.
•
Provide mobile handsets for users that are not personal phones, in many enterprises it is
inappropriate to be taking personal calls. A cell phones merges the personal and work phone into
the same device, and despite the good will of the employee, many people do not feel that calling you
on your cell phone is the same as calling you at work.
•
In many industries the employee turn over makes the provision of a cell phones and expensing of
cell phone calls difficult; therefore, the management of cell phone usage difficult. At the same time,
communication with mobile employees is critical to business success. It is simpler and more cost
efficient to provide a VoWLAN handset.
•
Provide communications when other communications infrastructure is unavailable either due to
emergency or lack of local services.
The need for a VoWLAN solution has grown because of the demand in different industry organizations
as well. Industry organizations can take this solution and customize according to their needs. Two
examples of industry organization that are looking to meet everyday requirements with VoWLAN are
healthcare and retail organizations.
Healthcare
Many healthcare organizations today are burdened by multiple disjointed communication systems. A
typical hospital may have several in-house phone systems, overhead paging systems, and pagers, and
typically more than one data network. As the Forrestor 2006 survey –below- illustrates, these
communication inefficiencies exacerbate staff shortages and impact care delivery. According to a study
done by Forrester (2006):
•
65% of healthcare employees spend about 20-60 minutes / day just trying to reach staff.
•
66% search more than one channel to reach staff
•
84% said that time spent trying to reach staff impacts patient care. "Every minute engaged in
tracking and locating others reduces a nurses availability for the patient."
Retail
Retail organizations can realize many benefits from deploying the VoWLAN solution, including:
•
Improved customer service by freeing personnel from having to provide personalized service only
from fixed locations
•
Increased profits through operational efficiency and improved customer satisfaction
•
Improved communication by giving phone services and voicemail to each store employee
•
Improved responsiveness by making business applications, like inventory management, mobile with
wireless phones
Voice over Wireless LAN 4.1 Design Guide
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Chapter 1
Voice over WLAN Introduction
VoWLAN Solution Overview
The Cisco VoWLAN solution can meet these requirements . Many businesses are turning to WLAN
networking to give employees immediate access to the business applications and communication tools
they need. By adding voice over IP capability to their wireless networks, they can further improve
collaboration and responsiveness, and unlock the door to new cost savings. The Cisco wireless network
is ready to support voice applications. VoWLAN allows businesses and other organizations to bring the
mobility and flexibility of WLAN networking to their voice communications systems. With robust
quality-of-service, diverse client support, and manageability, the solution enables the enterprise to take
immediate advantage of IP communications to a campus workforce. The Cisco Enterprise Mobility
solution streamlines business processes by providing anytime, anywhere access to critical information,
and safeguarding information and network integrity in the new era of wireless threats. It delivers
applications that transform business operations to deliver compelling benefits and are enabled on a
simple, secure, and scalable unified platform for the lowest total cost of ownership. This VoWLAN
solution is designed for businesses of all sizes that need to improve business processes, safeguard
information and improve customer, partner and employee experience and loyalty.
Recommendations
During the research and development of this design guide, the following key findings were made:
•
Planning, RF design, and site survey are critical parts of an optimal VoWLAN deployment.
•
Auto-RF should be enabled in most cases for VoWLAN, but to allow Auto-RF to perform its role
effectively, it requires a best practice RF design and site survey for VoWLAN. Just as in a static RF
deployment, extra effort is required to maximize VoWLAN success.
•
A simple choice between Auto-RF and no-Auto-RF is not required. There are a number of different
options that may be a best fit for customers requirements. For example, there are the options when
the Transmit Power Control (TPC) algorithms are run, and there are options upon the sensitivity
settings for the Dynamic Channel Allocation (DCA), TPC, and Coverage Hole algorithms.
•
Location and VoWLAN deployments are not incompatible. The required spacing of APs for
VoWLAN deployment is very similar to that of a Location-Based Services (LBS) deployment.
Additional APs may be required to meet the perimeter requirements of LBS. These additional APs
are unlikely to add capacity to the WLAN system (particularly in the 2.4GHz band), and the
additional APs are unlikely to have great impact upon the overall co-channel interference
characteristics of the deployment.
•
Depending on the shape of the WLAN deployment there may be little difference between a
VoWLAN deployment and an LBS deployment, but is advisable to follow the LBS practice of
ensuring there is perimeter placement of APs. This provides optimal location accuracy and likely
assists in optimal Auto-RF behavior.
•
The best strategy to address the co-channel issues that increase due to the higher density
deployments of VoWLAN and LBS in 2.4GHz systems is to migrate as many devices as possible to
the 5GHz spectrum which has more non-overlapping channels, and therefore less co-channel issues
and higher capacity.
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Chapter 1
Voice over WLAN Introduction
VoWLAN Solution Overview
Table 1-1 lists the devices, roles, and releases of the products used in the VoWLAN 4.1 solution.
Table 1-1
Device and Roles
Device
Role
Software
6504
Campus Core
12.2(18)SXF9
6504
Campus Distribution
12.2(18)SXF9
6504
WLAN
12.2(18)SXF9
WiSM
WLAN
4.1.185
3845
Voice WAN gateway
12.4(15)T1
ASA
Internet gateway
7.2(2)
4948
Data center
12.2(25)EWA8
4503
Access
12.2(37)SG
3750-E
Access
12.2(37)SE1
2821
Branch Router
12.4(15)T1
MC7800
Unified CM
CM 6.0.1
7960
VoIP Handset
SCCP41.8-3-1S
7921G
VoWLAN Handset
CP7921G-1.0.4
MCS7800
Vocera Server
Vocera Server 4.0 [Build 1279]
Vocera Telephony Server 4.0 [Build 1279]
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WLAN Quality of Service
This chapter describes quality-of- service (QoS) in the context of WLAN implementations. This chapter
describes WLAN QoS in general, but does not provide in-depth coverage on topics such as security,
segmentation, and voice over WLAN (VoWLAN), although these topics have a QoS component. This
chapter also provides information on the features of the Cisco Centralized WLAN Architecture.
This chapter is intended for those who are tasked with designing and implementing enterprise WLAN
deployments using the Cisco Unified Wireless technology.
QoS Overview
QoS refers to the capability of a network to provide differentiated service to selected network traffic over
various network technologies. QoS technologies provide the following benefits:
•
Provide building blocks for business multimedia and voice applications used in campus, WAN, and
service provider networks
•
Allow network managers to establish service-level agreements (SLAs) with network users
•
Enable network resources to be shared more efficiently and expedite the handling of mission-critical
applications
•
Manage time-sensitive multimedia and voice application traffic to ensure that this traffic receives
higher priority, greater bandwidth, and less delay than best-effort data traffic
With QoS, bandwidth can be managed more efficiently across LANs, including WLANs and WANs.
QoS provides enhanced and reliable network service by doing the following:
•
Supporting dedicated bandwidth for critical users and applications
•
Controlling jitter and latency (required by real-time traffic)
•
Managing and minimizing network congestion
•
Shaping network traffic to smooth the traffic flow
•
Setting network traffic priorities
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Wireless QoS Deployment Schemes
Wireless QoS Deployment Schemes
In the past, WLANs were mainly used to transport low-bandwidth, data-application traffic. Currently,
with the expansion of WLANs into vertical (such as retail, finance, and education) and enterprise
environments, WLANs are used to transport high-bandwidth data applications, in conjunction with
time-sensitive multimedia applications. This requirement led to the necessity for wireless QoS.
Several vendors, including Cisco, have supported proprietary wireless QoS schemes for voice
applications. To speed up the rate of QoS adoption and to support multi-vendor time-sensitive
applications, a unified approach to wireless QoS is necessary. The IEEE 802.11e working group within
the IEEE 802.11 standards committee has completed the standard definition, but adoption of the 802.11e
standard is in its early stages, and as with many standards there are many optional components. Just as
occurred with 802.11 security in 802.11i, industry groups such as the Wi-Fi Alliance and industry
leaders such as Cisco are defining the key requirements in WLAN QoS through their Wi-Fi MultiMedia
(WMM) and Cisco Compatible Extensions programs, ensuring the delivery of key features and
interoperation through their certification programs.
Cisco Unified Wireless products support WMM, a QoS system based on IEEE 802.11e that has been
published by the Wi-Fi Alliance, and WMM Power Save, as well as Admission Control.
An example deployment of wireless QoS based on the Cisco Unified Wireless technology features is
shown in Figure 2-1.
Figure 2-1
QoS Deployment Example
LWAPP
LWAPP
Si
WMM downstream QoS
WMM upstream and downstream QoS
153865
IP
QoS Parameters
QoS is defined as the measure of performance for a transmission system that reflects its transmission
quality and service availability. Service availability is a crucial element of QoS. Before QoS can be
successfully implemented, the network infrastructure must be highly available. The network
transmission quality is determined by latency, jitter, and loss, as shown in Table 2-1.
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Table 2-1
QoS Parameters
Transmission
Quality
Description
Latency
Latency (or delay) is the amount of time it takes for a packet to reach the receiving
endpoint after being transmitted from the sending endpoint. This time period is called
the end-to-end delay and can be divided into two areas:
•
Fixed network delay—Includes encoding and decoding time (for voice and
video), and the finite amount of time required for the electrical or optical pulses
to traverse the media en route to their destination.
•
Variable network delay—Generally refers to network conditions, such as
queuing and congestion, that can affect the overall time required for transit.
Jitter
Jitter (or delay-variance) is the difference in the end-to-end latency between packets.
For example, if one packet requires 100 ms to traverse the network from the source
endpoint to the destination endpoint, and the next packet requires 125 ms to make the
same trip, the jitter is calculated as 25 ms.
Loss
Loss (or packet loss) is a comparative measure of packets successfully transmitted
and received to the total number that were transmitted. Loss is expressed as the
percentage of packets that were dropped.
Upstream and Downstream QoS
Figure 2-2 illustrates the definition of radio upstream and radio downstream QoS.
Figure 2-2
Upstream and Downstream QoS
Network Upstream
Radio Upstream
LWAPP
LWAPP
Network Downstream
Radio Downstream
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Si
Figure 2-2 shows the following:
•
Radio downstream QoS—Traffic leaving the AP and traveling to the WLAN clients. Radio
downstream QoS is the primary focus of this chapter, because this is still the most common
deployment. The radio client upstream QoS depends on the client implementation.
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802.11 DCF
•
Radio upstream QoS—Traffic leaving the WLAN clients and traveling to the AP. WMM provides
upstream QoS for WLAN clients supporting WMM.
•
Network downstream—Traffic leaving the WLC traveling to the AP. QoS can be applied at this point
to prioritize and rate-limit traffic to the AP. Configuration of Ethernet downstream QoS is not
covered in this chapter.
•
Network upstream—Traffic leaving the AP, traveling to the WLC. The AP classifies traffic from the
AP to the upstream network according to the traffic classification rules of the AP.
QoS and Network Performance
The application of QoS features might not be easily detected on a lightly loaded network. If latency,
jitter, and loss are noticeable when the media is lightly loaded, it indicates either a system fault, poor
network design, or that the latency, jitter, and loss requirements of the application are not a good match
for the network. QoS features start to be applied to application performance as the load on the network
increases. QoS works to keep latency, jitter, and loss for selected traffic types within acceptable
boundaries. When providing only radio downstream QoS from the AP, radio upstream client traffic is
treated as best-effort. A client must compete with other clients for upstream transmission as well as
competing with best-effort transmission from the AP. Under certain load conditions, a client can
experience upstream congestion, and the performance of QoS-sensitive applications might be
unacceptable despite the QoS features on the AP. Ideally, upstream and downstream QoS can be operated
either by using WMM on both the AP and WLAN client, or by using WMM and a client proprietary
implementation.
Note
Even without WMM support on the WLAN client, the Cisco Unified Wireless solution is able to provide
network prioritization in both network upstream and network downstream situations.
Note
WLAN client support for WMM does not mean that the client traffic automatically benefits from WMM.
The applications looking for the benefits of WMM assign an appropriate priority classification to their
traffic, and the operating system needs to pass that classification to the WLAN interface. In purpose-built
devices, such as VoWLAN handsets, this is done as part of the design. However, if implementing on a
general purpose platform such as a PC, application traffic classification and OS support must be
implemented before the WMM features can be used to good effect.
802.11 DCF
Data frames in 802.11 are sent using the distributed coordination function (DCF), which is composed of
the following two main components:
•
Interframe spaces (SIFS, PIFS, and DIFS).
•
Random backoff (contention window) DCF is used in 802.11 networks to manage access to the RF
medium.
A baseline understanding of DCF is necessary to deploy 802.11e-based enhanced distributed
coordination function (EDCF). For more information on DCF, see the IEEE 802.11 specification at the
following URL: http://ieeexplore.ieee.org/xpl/standardstoc.jsp?isnumber=14251&isYear=1997.
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802.11 DCF
Interframe Spaces
802.11 currently defines three interframe spaces (IFS), as shown in Figure 2-3:
•
Short interframe space (SIFS)—10 µs
•
PCF interframe space (PIFS)—SIFS + 1 x slot time = 30 µs
•
DCF interframe space (DIFS)—SIFS + 2 x slot time = 50 µs
The interframe spaces (SIFS, PIFS, and DIFS) allow 802.11 to control which traffic gets first access to
the channel after carrier sense declares the channel to be free. Generally, 802.11 management frames and
frames not expecting contention (a frame that is part of a sequence of frames) use SIFS, and data frames
use DIFS.
Figure 2-3
Interframe Spaces
DIFS
PIFS
SIFS
Busy medium
Contention window
Backoff window
Next frame
(t)
Defer access
Select slot and decrement backoff
as long as the medium is idle
91228
Slot time
Random Backoff
When a data frame using Distributed Coordination Function (DCF), shown in Figure 2-4, is ready to be
sent, it goes through the following steps:
Step 1
Generates a random backoff number between 0 and a minimum contention window (CWmin).
Step 2
Waits until the channel is free for a DIFS interval.
Step 3
If the channel is still free, begins to decrement the random backoff number, for every slot time (20 µs)
that the channel remains free.
Step 4
If the channel becomes busy, such as another station getting to 0 before your station, the decrement stops
and Steps 2 through 4 are repeated.
Step 5
If the channel remains free until the random backoff number reaches 0, the frame can be sent.
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802.11 DCF
Figure 2-4 shows a simplified example of how the DCF process works. In this simplified DCF process,
no acknowledgements are shown and no fragmentation occurs.
Figure 2-4
Distributed Coordination Function Example
DIFS
Station A
DIFS
DIFS
Frame
Station B
Station C
Defer
Defer
Station D
Defer
Station E
Frame
Defer
Defer
Defer
Defer
Frame
Frame
Defer
Backoff time remaining
91229
Backoff time
The DCF steps illustrated in Figure 2-4 are as follows:
Step 1
Station A successfully sends a frame; three other stations also want to send frames but must defer to
Station A traffic.
Step 2
After Station A completes the transmission, all the stations must still defer to the DIFS. When the DIFS
is complete, stations waiting to send a frame can begin to decrement the backoff counter, once every slot
time, and can send their frame.
Step 3
The backoff counter of Station B reaches zero before Stations C and D, and therefore Station B begins
transmitting its frame.
Step 4
When Station C and D detect that Station B is transmitting, they must stop decrementing the backoff
counters and defer until the frame is transmitted and a DIFS has passed.
Step 5
During the time that Station B is transmitting a frame, Station E receives a frame to transmit, but because
Station B is sending a frame, it must defer in the same manner as Stations C and D.
Step 6
When Station B completes transmission and the DIFS has passed, stations with frames to send begin to
decrement the backoff counters. In this case, the Station D backoff counter reaches zero first and it
begins transmission of its frame.
Step 7
The process continues as traffic arrives on different stations.
CWmin, CWmax, and Retries
DCF uses a contention window (CW) to control the size of the random backoff. The contention window
is defined by two parameters:
•
aCWmin
•
aCWmax
The random number used in the random backoff is initially a number between 0 and aCWmin. If the
initial random backoff expires without successfully sending the frame, the station or AP increments the
retry counter, and doubles the value random backoff window size. This doubling in size continues until
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the size equals aCWmax. The retries continue until the maximum retries or time-to-live (TTL) is
reached. This process of doubling the backoff window is often referred to as a binary exponential
backoff, and is illustrated in Figure 2-5 where the aCWmin if 25-1, and increases to 26-1, on the next
backoff level, up to the aCWmax value of 210-1.
Figure 2-5
Growth in Random Backoff Range with Retries
1023 1023 1023
511
aCWmax
255
63
31
retries
91230
127
aCWmin
Wi-Fi MultiMedia
This section describes three Wi-Fi MultiMedia (WMM) implementation topics:
•
WMM Access
•
WMM Classification
•
WMM Queues
WMM Access
WMM is a Wi-Fi Alliance certification of support for a set of features from an 802.11e draft. This
certification is for both clients and APs, and certifies the operation of WMM. WMM is primarily the
implementation of the EDCF component of 802.11e. Additional Wi-Fi certifications are planned to
address other components of the 802.11e.
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WMM Classification
WMM uses the 802.1P classification scheme developed by the IEEE (which is now a part of the 802.1D
specification).
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This classification scheme has eight priorities, which WMM maps to four access categories: AC_BK,
AC_BE, AC_VI, and AC_VO. These access categories map to the four queues required by a WMM
device, as shown in Table 2-2.
Table 2-2
Table 2 802.1P and WMM Classification
Priority
802.1P Priority
802.1P Designation
Access Category (AC)
WMM Designation
Lowest
1
BK
AC_BK
Background
2
-
0
BE
AC_BE
Best Effort
3
EE
4
CL
AC_VI
Video
5
VI
6
VO
AC_VO
Voice
7
NC
Highest
Figure 2-6 shows the WMM data frame format. Note that even though WMM maps the eight 802.1P
classifications to four access categories, the 802.11D classification is sent in the frame.
The WMM and IEEE 802.11e classifications are different from the classifications recommended and
used in the Cisco network, which are based on IETF recommendations. The primary difference in
classification is the changing of voice and video traffic to 5 and 4, respectively. This allows the
6 classification to be used for Layer 3 network control. To be compliant with both standards, the Cisco
Unified Wireless solution performs a conversion between the various classification standards when the
traffic crosses the wireless-wired boundary.
Figure 2-6
WMM Frame Format
2
2
Frame
control
Dur
6
6
6
2
0 or 6
0 or 2
A1
A2
A3
Seq
control
A4
QoS
control
15-7
6-5
0
ack
policy
Acknowledge ------- 00
Do not acknowledge ------- 01
4
EOSP
n
Body
3
0
End of service
period
4
FCS
2-0
UP
132599
Note
802.1D
priority
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WMM Queues
Figure 2-7 shows the queuing performed on a WMM client or AP. There are four separate queues, one
for each of the access categories. Each of these queues contends for the wireless channel in a similar
manner to the DCF mechanism described previously, with each of the queues using different interframe
space, CWmin, and CWmax values. If more than one frame from different access categories collide
internally, the frame with the higher priority is sent, and the lower priority frame adjusts its backoff
parameters as though it had collided with a frame external to the queuing mechanism. This system is
called enhanced distributed coordination function (EDCF).
Figure 2-7
WMM Queues
Application
Best effort
Video
Voice
132600
Background
Figure 2-8 shows the principle behind EDCF where different interframe spacing and CWmin and
CwMax values (for clarity CwMax is not shown) are applied per traffic classification. Different traffic
types can wait different interface spaces before counting down their random backoff, and the CW value
used to generate the random backoff number also depends on the traffic classification. For example, the
CWmin[3] for Voice is 23-1, and CWmin[5] for Best effort traffic is 25-1. High priority traffic has a small
interframe space and a small CWmin value, giving a short random backoff, whereas best-effort traffic
has a longer interframe space and large CWmin value that on average gives a large random backoff
number.
Access Category (AC) Timing
SIFS
7 slots
CWmin[5]
3 slots
2 slots
2 slots
CWmin[5]
CWmin[4]
CWmin[3]
Background
Best effort
Video
132598
Figure 2-8
Voice
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EDCF
The EDCF process is illustrated in Figure 2-9, using data from Figure 2-8.
Figure 2-9
EDCF Example
AIFS[0]
AIFS[0]
AIFS[0]
AIFS[0]
AIFS[6]
AIFS[6]
AIFS[6]
AIFS[6]
Frame
Best effort
Defer
Defer
Frame
Defer
Frame
Defer
Defer
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Voice
The EDCF process follows this sequence:
Note
1.
While Station X is transmitting its frame, three other stations determine that they must send a frame.
Each station defers because a frame was already being transmitted, and each station generates a
random backoff.
2.
Because the Voice station has a traffic classification of voice, it has an arbitrated interframe space
(AIFS) of 2, and uses an initial CWmin of 3, and therefore must defer the countdown of its random
backoff for 2 slot times, and has a short random backoff value.
3.
Best-effort has an AIFS of 3 and a longer random backoff time, because its CWmin value is 5.
4.
Voice has the shortest random backoff time, and therefore starts transmitting first. When Voice starts
transmitting, all other stations defer.
5.
After the Voice station finishes transmitting, all stations wait their AIFS, then begin to decrement
the random backoff counters again.
6.
Best-effort then completes decrementing its random backoff counter and begins transmission. All
other stations defer. This can happen even though there might be a voice station waiting to transmit.
This shows that best-effort traffic is not starved by voice traffic because the random backoff
decrementing process eventually brings the best-effort backoff down to similar sizes as high priority
traffic, and that the random process might, on occasion, generate a small random backoff number
for best-effort traffic.
7.
The process continues as other traffic enters the system. The AC settings shown in Table 2-3 and
Table 2-4 are, by default, the same for an 802.11a radio, and are based on formulas defined in
WMM.
Table 2-3 refers to the parameter settings on a client, which are slightly different from the settings for
an AP. This is because an AP is expected to have multiple clients and must send frames more often.
Table 2-3
WMM AP Parameters
AC
CWmin
CWmax
AIFSN
TXOP Limit
(802.11b
TXOP Limit
(802.11a/g)
AC_BK
aCWmin
aCWmax
7
0
0
AC_BE
aCWmin
4*(aCQmin+1)-1
3
0
0
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Table 2-3
WMM AP Parameters (continued)
AC
CWmin
CWmax
AIFSN
TXOP Limit
(802.11b
TXOP Limit
(802.11a/g)
AC_VI
(aCWmin+1)/2-1
aCWmin
1
6.016 ms
3.008 ms
AC_VO
(aCWmin+1)/4-1
(aCWmin+1)/2-1
1
3.264 ms
1.504 ms
Table 2-4
WMM Client Parameters
Access
Category
CWmin
CWmax
AIFSN
TXOP Limit
(802.11b
TXOP Limit
(802.11a/g)
AC_BK
aCWmin
aCWmax
7
0
0
AC_BE
aCWmin
4*(aCQmin+1)-1
3
0
0
AC_VI
(aCWmin+1)/2-1
aCWmin
2
6.016 ms
3.008 ms
AC_VO
(aCWmin+1)/4-1
(aCWmin+1)/2-1
2
3.264 ms
1.504 ms
The overall impact of the different AIFS, CWmin, and CWmax values is difficult to illustrate in timing
diagrams because their impact is more statistical in nature. It is easier to compare the AIFS and the size
of the random backoff windows, as shown in Figure 2-8.
When comparing voice and background frames as examples, these traffic categories have CWmin values
of 23-1 (7) and 2 5-1 (31), and AIFS of 2 and 7, respectively. This an average delay of 5 (2+7/1) slot times
before sending a voice frame, and an average of 22 slot (7+31/2) times for background frame. Therefore,
voice frames are statistically much more likely to be sent before background frames.
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Figure 2-10 shows the WMM information in a probe response. Apart from the WMM AC information
contained in this element, the client also learns which WMM categories require admission control. As
can be seen in this example, the voice AC has admission control set to mandatory. This requires the client
to send the request to the AP, and have the request accepted, before it can use this AC. Admission control
is discussed in more detail later in this chapter.
Figure 2-10
Probe Response WMM Element Information
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U-APSD
Unscheduled automatic power-save delivery (U-APSD) is a feature that has two key benefits:
•
The primary benefit of U-APSD is that it allows the voice client to synchronize the transmission and
reception of voice frames with the AP, thereby allowing the client to go into power-save mode
between the transmission/reception of each voice frame tuple. The WLAN client frame transmission
in the access categories supporting U-APSD triggers the AP to send any data frames queued for that
WLAN client in that AC. A U-APSD client remains listening to the AP until it receives a frame from
the AP with an end-of-service period (EOSP) bit set. This tells the client that it can now go back into
its power-save mode. This triggering mechanism is considered a more efficient use of client power
than the regular listening for beacons method, at a period controlled by the delivery traffic indication
map (DTIM) interval, because the latency and jitter requirements of voice are such that a WVoIP
client would either not be in power-save mode during a call, resulting in reduced talk times, or would
use a short DTIM interval, resulting in reduced standby times. The use of U-APSD allows the use
of long DTIM intervals to maximize standby time without sacrificing call quality. The U-APSD
feature can be applied individually across access categories, allowing U-APSD can be applied to the
voice ACs in the AP, but the other ACs still use the standard power save feature.
•
The secondary benefit of this feature is increased call capacity. The coupling of transmission
buffered data frames from the AP with the triggering data frame from the WLAN client allows the
frames from the AP to be sent without the accompanying interframe spacing and random backoff,
thereby reducing the contention experience by call.
Figure 2-11 shows an example frame exchange for the standard 802.11 power save delivery process.
Figure 2-11
Standard Client Power-Save
Beacon
with TIM
ACK
AP
DATA
(more=1)
DTIM Period
DATA
ACK
(more=0)
Beacon
with TIM
ACK
(t)
Sleep
PS-Poll
ACK
PS-Poll
ACK
PS-Poll
Sleep
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Client
Client Full Power
Access Delay
The client in power-save mode first detects that there is data waiting for it at the AP via the presence of
the traffic indicator map (TIM) in the AP beacon. The client must power-save poll (PS-Poll) the AP to
retrieve that data. If the data sent to the client requires more than one frame to be sent, the AP indicates
this in the sent data frame. This process requires the client to continue sending power-save polls to the
AP until all the buffered data is retrieved by the client.
This presents two major problems. The first is that it is quite inefficient, requiring the PS-polls, as well
as the normal data exchange, to go through the standard access delays associated with DCF. The second
issue, being more critical to voice traffic, is that retrieving the buffered data is dependent on the DTIM,
which is a multiple of the beacon interval. Standard beacon intervals are 100 ms, and the DTIM interval
can be integer multiples of this. This introduces a level of jitter that is generally unacceptable for voice
calls, and voice handsets switch from power-save mode to full transmit and receive operation when a
voice call is in progress. This gives acceptable voice quality but reduces battery life. The Cisco Unified
Wireless IP Phone 7921G addresses this issue by providing a PS-Poll feature that allows the Cisco
Unified Wireless IP Phone 7921G to generate PS-Poll requests without waiting for a beacon TIM. This
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allows the 7921G to poll for frames when it has sent a frame, and then go back to power-save mode. This
feature does not provide the same efficiency as U-APSD, but improves battery life for Cisco Unified
Wireless IP Phone 7921Gs on WLANs without U-APSD.
Figure 2-12 shows an example of traffic flows with U-APSD. In this case, the trigger for retrieving traffic
is the client sending traffic to the AP. The AP, when acknowledging the frame, tells the client that data
is queued for it, and that it should stay on. The AP then sends data to the client typically as a TXOP burst
where only the first frame has the EDCF access delay. All subsequent frames are then sent directly after
the acknowledgment frame. In a VoWLAN implementation there is only likely to be one frame queued
at the AP, and VoWLAN client would be able to go into sleep mode after receiving that frame from the
AP.
Figure 2-12
U-APSD
ACK
AP
DATA
DATA
(more=1) (more=0)
ACK
DATA
(more=0)
(t)
Sleep
Trigger Frame
+ data
ACK
Client Full Power
ACK
Sleep
Trigger Frame
+ data
ACK
Sleep
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Client
Client Full Power
EDCA Delay
This approach overcomes both the disadvantages of the previous scheme in that it is much more efficient.
The timing of the polling is controlled via the client traffic, which in the case of voice is symmetric, so
if the client is sending a frame every 20 ms, it would be expecting to receive a frame every 20 ms as well.
This would introduce a maximum jitter of 20 ms, rather than an n * 100 ms jitter.
TSpec Admission Control
Traffic Specification (TSpec) allows an 802.11e client to signal its traffic requirements to the AP. In the
802.11e MAC definition, two mechanisms provide prioritized access. These are the contention-based
EDCF option and the controlled access option provided by the transmit opportunity (TXOP). When
describing TSpec features where a client can specify its traffic characteristics, it is easy to assume that
this would automatically result in the use of the controlled access mechanism, and have the client granted
a specific TXOP to match the TSpec request. However, this does not have to be the case; a TSpec request
can be used to control the use of the various ACs in EDCF. Before a client can send traffic of a certain
priority type, it must have requested to do so via the TSpec mechanism. For example, a WLAN client
device wanting to use the voice AC must first make a request for use of that AC. Whether or not AC use
is controlled by TSpec requests is configurable with voice and video ACs controlled by TSpec requests,
and best-effort and background ACs can be open for use without a TSpec request. The use of EDCF ACs,
rather than the 802.11e Hybrid Coordinated Channel Access (HCCA), to meet TSpec requests is possible
in many cases because the traffic parameters are sufficiently simple to allow them to be met by allocating
capacity, rather than creating a specific TXOP to meet the application requirements.
Note
Unlike the Cisco Unified Wireless IP Phone 7921G, which does have support for TSpec, the Cisco
Unified Wireless IP Phone 7920 WVoIP handset does not support TSpec admission control.
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Wi-Fi MultiMedia
Add Traffic Stream
The Add Traffic Stream (ADDTS) function is how a WLAN client performs an admission request to an
AP. Signalling its TSpec request to the AP, an admission request is in one of two forms:
•
ADDTS action frame—This happens when a phone call is originated or terminated by a client
associated to the AP. The ADDTS contains TSpec and might contain a traffic stream rate set (TSRS)
IE (Cisco Compatible Extensions v4 clients).
•
Association and re-association message—The association message might contain one or more
TSpecs and one TSRS IE if the STA wants to establish the traffic stream as part of the association.
The re-association message might contain one or more TSpecs and one TSRS IE if an STA roams
to another AP.
The ADDTS contains the TSpec element that describes the traffic request. See Figure 2-13 and
Figure 2-14 for examples of an ADDTS request and response between a Cisco Unified Wireless IP Phone
7921G WLAN handset and a Cisco AP. Apart from key data describing the traffic requirements, such as
data rates and frame sizes, the TSpec element also tells the AP the minimum physical rate that the client
device will use. This allows the calculation of how much time that station can potentially consume in
sending and receiving in this TSpec, and therefore allowing the AP to calculate whether it has the
resources to meet the TSpec. TSpec admission control is used by the WLAN client (target clients are
VoIP handsets) when a call is initiated and during a roam request. During a roam, the TSpec request is
appended to the re-association request.
Figure 2-13
ADDTS Request Decode
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Figure 2-14
ADDTS Response Decode
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QoS Advanced Features for WLAN Infrastructure
QoS Advanced Features for WLAN Infrastructure
The Cisco Centralized WLAN Architecture has multiple QoS features, in addition to WMM support.
Primary among these are the QoS profiles in the WLC. Four QoS profiles can be configured: platinum,
gold, silver, and bronze, as shown in Figure 2-15.
Figure 2-15
QoS Profile Options
Each of the profiles shown in Figure 2-16 allows the configuration of bandwidth contracts, RF usage
control, and the maximum IEEE 802.1P classification allowed.
Figure 2-16
QoS Profile Settings
It is generally recommended that the Per-User Bandwidth Contracts settings be left at their default
values, and that the IEEE 802.11 WMM features be used to provide differentiated services.
For WLANs using a given profile, the IEEE 802.1P classification in that profile controls two important
behaviors:
•
Determines what class of service (CoS) value is used for packets initiated from the WLC.
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The CoS value set in the profile is used to mark the CoS of all LWAPP packets for WLAN using that
profile. So a WLAN with a platinum QoS profile, and the IEEE 802.1P mark of 6, will have its
LWAPP packets from the ap-manager interface of the controller marked with CoS of 5. The
controller adjusts the CoS to be compliant with Cisco QoS baseline recommendations. The reason
why it is important to maintain the IEEE CoS marking in the configuration is covered in the next
point. If the network is set to trust CoS rather a DSCP at the network connection to the WLC, the
CoS value determines the DSCP of the LWAPP packets received by the AP, and eventually the
WMM classification and queuing for WLAN traffic, because the WLAN WMM classification of a
frame is derived from the DSCP value of the LWAPP packet carrying that frame.
•
Determines the maximum CoS value that can be used by clients connected to that WLAN.
The IEEE 802.1P classification sets the maximum CoS value that is admitted on a WLAN with that
profile.
WMM voice traffic arrives with a CoS of 6 at the AP, and the AP automatically performs a CoS-to-DSCP
mapping for this traffic based on a CoS of 6. If the CoS value in the WLC configuration is set to a value
less than 6, this changed value is used by the WLAN QoS profile at the AP to set the maximum CoS
marking used and therefore which WMM AC to use.
The key point is that with the Unified Wireless Network, you should always think in terms of
IEEE 802.11e classifications, and allow the Unified Wireless Network Solution to take responsibility for
converting between IEEE classification and the Cisco QoS baseline.
The WLAN can be configured with various default QoS profiles, as shown in Figure 2-17. Each of the
profiles (platinum, gold, silver, or bronze) is annotated with its typical use. In addition, a client can be
assigned a QoS profile based on its identity, through AAA. For a typical enterprise, WLAN deployment
parameters, such as per-user bandwidth contracts and over-the-air QoS, should be left at their default
values, and standard QoS tools, such as WMM and wired QoS, should be used to provide optimum QoS
to clients.
Figure 2-17
WLAN QoS Profile
In addition to the QoS profiles, the WMM policy per WLAN can also be controlled, as shown in
Figure 2-18. The three WMM options are as follows:
•
Disabled—The WLAN does not advertise WMM capabilities, or allow WMM negotiations
•
Allowed—The WLAN does allow WMM and non-WMM clients
•
Required—Only WMM-enabled clients can be associated with this WLAN.
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Figure 2-18
WLAN WMM Policy
IP Phones
Figure 2-19 shows the basic QoS Basis Service Set (QBSS) information element (IE) advertised by a
Cisco AP. The Load field indicates the portion of available bandwidth currently used to transport data
on that AP.
QBSS Information Element
1 Octet
Element ID
(11)
1 Octet
Length
4 bytes
Load
153873
Figure 2-19
There are actually three QBSS IEs that need to be supported in certain situations:
•
Old QBSS (Draft 6 (pre-standard))
•
New QBSS (Draft 13 IEEE 802.11e (standard))
•
New distributed CAC load IE (a Cisco IE)
The QBSS used depends on the WMM and Cisco Unified Wireless IP Phone 7920 settings on the
WLAN.
Cisco Unified Wireless IP Phone 7920 support, shown in Figure 2-18, is a component of the WLC
WLAN configuration that enables the AP to include the appropriate QBSS element in its beacons.
WLAN clients with QoS requirements, such as the Cisco Unified Wireless IP Phone 7920 and Cisco
Unified Wireless IP Phone 7921G, use these advertised QoS parameters to determine the best AP with
which to associate.
The WLC provides Cisco Unified Wireless IP Phone 7920 support through the client call admission
control (CAC) limit, or AP CAC limit. These features provide the following:
•
Client CAC limit—The Cisco Unified Wireless IP Phone 7920 uses a call admission control setting
that is set on the client. This supports legacy Cisco Unified Wireless IP Phone 7920 code-pre 2.01.
•
AP CAC limit—The Cisco Unified Wireless IP Phone 7920 uses CAC settings learned from WLAN
advertisement.
The various combinations of WMM, client CAC limit, and AP CAC limit result in different QBSS IEs
being sent:
•
If only WMM is enabled, IE number 2 (IEEE 802.11e standard) QBSS Load IE is sent out in the
beacons and probe responses.
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Note
•
If Cisco Unified Wireless IP Phone 7920 client CAC limit is to be supported, IE number 1 (the
pre-standard QBSS IE) is sent out in the beacons and probe responses on the bg radios.
•
If Cisco Unified Wireless IP Phone 7920 AP CAC limit is to be supported, the number 3 QBSS IE
is sent in the beacons and probe responses for bg radios.
The various QBSS IEs use the same ID, and therefore the three QBSSs are mutually exclusive. For
example, the beacons and probe responses can contain only one QBSS IE.
Setting the Admission Control Parameters
Figure 2-20 shows a sample configuration screen for setting the voice parameters on the controller.
Figure 2-20
Voice Parameter Setting
The admission control parameters consist of the maximum RF Bandwidth that a radio can be using and
still accept the initiation of a VoWLAN call through a normal ADDTS request.
The reserved roaming bandwidth is how much capacity has been set aside to be able to respond to the
ADDTS requests during association or re-association, which are VoWLAN clients with calls in progress
that are trying to roam to that AP.
To enable admission control based upon these parameters to, use the Admission Control (ACM)
checkbox. This enables admission control, based upon the APs capacity, but does not take into account
the possible channel loading impact of other APs in the area. To include this “channel load” in capacity
calculations, check the Load-Based AC checkbox as well as the Admission Control (ACM) checkbox.
The Metrics Collection option determines whether data is collected on voice or video calls for use by the
WCS.
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Figure 2-21 shows an example of one of the voice statistics reports available on the WCS, which shows
the calls established on the radio of one AP, and the number of calls that roamed to that AP. This report
and other voice statistics can be scheduled or ad-hoc, and either graphically displayed or posted as a data
file.
Figure 2-21
Voice Statistics from WCS
Total Voice Calls for 802.11a/n Interface of AP AP0012.d92b.5cc2
6
Number of Calls
5
4
3
2
0
221947
1
5/29/07
8:30 PM
5/29/07
8:50 PM
5/29/07
8:40 PM
5/29/07
9:00 PM
Time
Total Calls
Note
Total Roaming Calls
Call admission control is performed only for voice and video QoS profiles.
Impact of TSpec Admission Control
The purpose of TSpec admission control is not to deny clients access to the WLAN; it is to protect the
high priority resources. Therefore, a client that has not used TSpec admission control does not have its
traffic blocked; it simply has its traffic re-classified if it tries to send (which it should not do if the client
is transmitting WMM-compliant traffic in a protected AC).
Table 2-5 and Table 2-6 describe the impact on classification if access control is enabled and depending
on whether a traffic stream has been established.
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Table 2-5
Upstream Traffic
Traffic Stream Established
No Traffic Stream
No admission control
No change in behavior; the packets
go into the network as they do todayUP is limited to max= WLAN QoS
setting.
No change in behavior; the packets
go into the network as they do todayUP is limited to max= WLAN QoS
setting.
Admission control
No change in behavior; the packets
go into the network as they do todayUP is limited to max= WLAN QoS
setting.
Packets are remarked to BE (both
CoS and DSCP) before they enter the
network for WMM clients. For
non-WMM clients, packets are sent
with WLAN QoS.
Table 2-6
Downstream Traffic
Traffic Stream Established
No Traffic Stream
No admission control
No change
No change
Admission control
No change
Remark UP to BE for WMM client.
For non-WMM clients, use WLAN
QoS.
IEEE 802.11e, IEEE 802.1P, and DSCP Mapping
WLAN data in a Unified Wireless network is tunneled via LWAPP (IP UDP packets). To maintain the
QoS classification that has been applied to WLAN frames, a process of mapping classifications to and
from DSCP to CoS is required.
For example, when WMM classified traffic is sent by a WLAN client, it has an IEEE 802.1P
classification in its frame. The AP needs to translate this classification into a DSCP value for the LWAPP
packet carrying the frame to ensure that the packet is treated with the appropriate priority on its way to
the WLC. A similar process needs to occur on the WLC for LWAPP packets going to the AP.
A mechanism to classify traffic from non-WMM clients is also required, so that their LWAPP packets
can also be given an appropriate DSCP classification by the AP and the WLC.
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Figure 2-22 shows a numbered example of the traffic classification flow for a WMM client, an AP, and
a WLC.
Figure 2-22
WMM and IEEE 802.1P Relationship
802.11e DSCP Payload
802.1p
DSCP
LWAPP Encapsulated
DSCP Payload
2
802.1p
DSCP Payload
1
LWAPP
LWAPP
LWAPP Tunnels
Si
Ethernet
Switch
WLAN Controller
LWAPP
AP
802.11e DSCP Payload
DSCP
LWAPP Encapsulated
DSCP Payload
802.1p
DSCP Payload
222682
4
3
In Figure 2-22, the following occurs:
Step 1
A frame with a 802.1p marking and a packet with an IP DSCP marking arrive at the WLC wired
interface. The IP DSCP of the packet is used to determine the DSCP of the LWAPP packet leaving the
WLC, and the 802.1p value of the frame depends on the QoS translation table ( see Table 2-7), the QoS
profile for the WLAN, and the Wired QoS Protocol configured for that QoS profile (Figure 2-16). If the
Wired QoS Protocol is configured as "None", then no 802.1p value is set, but if the protocol is set to
802.1p, then the 802.1p used depends on the translation table capped at a maximum value of 802.1p table
value shown in Figure 2-16.
Step 2
The IP DSCP of the LWAPP packet reaching the AP will translate to an 802.11e CoS marking based on
Table 2-7.
Step 3
The 802.11e CoS marking of a frame arriving at the AP translates to an LWAPP DSCP value based on
Table 2-7, capped at the maximum value for that QoS profile.
Step 4
The DSCP of the packet leaving the WLC will be equal to the DSCP of the packet that left the WLAN
client, but the 802.1p value depends on the QoS translation table (Table 2-7), QoS profile for the WLAN,
and the Wired QoS Protocol configured for that QoS profile (Figure 2-16). If the Wired QoS Protocol is
configured as "None", then no 802.1p value is set, but if the protocol is set to 802.1p, then the 802.1p
used depends on the translation table.
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IEEE 802.11e, IEEE 802.1P, and DSCP Mapping
The multiple classification mechanisms and client capabilities require multiple strategies:
Note
•
LWAPP control frames require prioritization, and LWAPP control frames are marked with a DSCP
classification of CS6.
•
WMM-enabled clients have the classification of their frames mapped to a corresponding DSCP
classification for LWAPP packets to the WLC. This mapping follows the standard IEEE
CoS-to-DSCP mapping, with the exception of the changes necessary for QoS baseline compliance.
This DSCP value is translated at the WLC to a CoS value on IEEE 802.1Q frames leaving the WLC
interfaces.
•
Non-WMM clients have the DSCP of their LWAPP tunnel set to match the default QoS profile for
that WLAN. For example, the QoS profile for a WLAN supporting Cisco Unified Wireless IP Phone
7920s would be set to platinum, resulting in a DSCP classification of EF for data frames packets
from that AP WLAN.
•
LWAPP data packets from the WLC have a DSCP classification that is determined by the DSCP of
the wired data packets sent to the WLC. The IEEE 80211.e classification used when sending frames
from the AP to a WMM client is determined by the AP table converting DSCP to WMM
classifications.
The WMM classification used for traffic from the AP to the WLAN client is based on the DSCP value
of the LWAPP packet, and not the DSCP value of the contained IP packet. Therefore, it is critical that
an end-to-end QoS system is in place.
QoS Baseline Priority Mapping
The LWAPP AP and WLC perform QoS baseline conversion, so that WMM values as shown in Table 2-7
are mapped to the appropriate QoS baseline DSCP values, rather than the IEEE values.
Table 2-7
Access Point QoS Translation Values
Access Point QoS
Translation Values AVVID
Traffic Type
AVVID IP DSCP
QoS Profile
AVVID 802.1p
IEEE 802.11e UP
Network control
56 (CS7)
Platinum
7
7
Inter-network control
(CAPWAP control,
802.11 management)
48 (CS6)
Platinum
6
7
Voice
46 (EF)
Platinum
5
6
Interactive video
34 (AF41)
Gold
4
5
Streaming video
32 (CS4)
Gold
4
5
Mission critical
26 (AF31)
Gold
3
4
Call signaling
24 (CS3)
Gold
3
4
Transactional
18 (AF21)
Silver
2
3
Network management
16 (CS2)
Silver
2
3
Bulk data
10 (AF11)
Bronze
1
2
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Table 2-7
Access Point QoS Translation Values (continued)
Best effort
0 (BE)
Silver
0
0
Scavenger
8 (CS1)
Bronze
0
1
In cases where the AP is translating CoS values, autonomous APs for example, the translation shown in
Table 2-8 is used.
Table 2-8
WMM to AVVID Packet Re-Marking for APs when AVVID Priority Type Configured
Downstream L2 Packet Re-Marking1
Upstream L2 Packet Re-Marking
Typical Application
AVVID CoS
WMM UP
802.1d
Designation
WMM UP
AVVID CoS
Best Effort Data
0
0
BE
0
0
Medium Priority Data
1
2
BK
1
1
High Priority Data
2
3
-
2
1
Call Signaling
3
4
EE
3
2
Video Conferencing
4
5
CL
4
3
Voice Bearer
5
6
VI
5
4
Reserved
6
7
VO
6
5
7
7
Reserved
7
7
NC
2
1. In the downstream direction, the AP takes AVVID CoS markings on the wired interface and maps them to the UPs shown.
In the upstream direction, the AP takes UPs received on the dot11 interface and maps them to AVVID CoS on the wired
interface. Using this remapping results in the best match of WMM AC to AVVID CoS.
2. The only network control traffic that should get mapped to CoS = 7 is spanning tree traffic that is used when WGBs are
deployed or when outdoor bridges are deployed, connecting the LANs between 2 or more buildings. Even though 802.11
MAC management traffic is carried on UP=7 in autonomous APs, is it not bridged onto the wired port of the AP.
Deploying QoS Features on LWAPP-based APs
When deploying WLAN QoS on the APs, consider the following:
•
The wired LWAPP AP interface does read or write Layer 2 CoS (IEEE 802.1P) information, the
WLC and the APs depend on Layer 3 classification (DSCP) information to communicate WLAN
client traffic classification. This DSCP value may be subject to modification by intermediate routers,
and therefore the Layer 2 classification received by the destination might not reflect the Layer 2
classification marked by the source of the LWAPP traffic.
•
The APs no longer use NULL VLAN ID. As a consequence, L2 LWAPP does not effectively support
QoS because the AP does not send the IEEE 802.1P/Q tags, and in L2 LWAPP there is no outer
DSCP on which to fall back.
•
APs do not re-classify frames; they prioritize based on CoS value or WLAN profile.
•
APs carry out EDCF-like queuing on the radio egress port only.
•
APs do FIFO queueing only on the Ethernet egress port.
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WAN QoS and the H-REAP
For WLANs that have data traffic forwarded to the WLC, the behavior is same as non-hybrid remote
edge access point (H-REAP) APs. For locally-switched WLANs with WMM traffic, the AP marks the
dot1p value in the dot1q VLAN tag for upstream traffic. This occurs only on tagged VLANs; that is, not
native VLANs.
For downstream traffic, the H-REAP uses the incoming dot1q tag from the Ethernet side and uses this
to queue and mark the WMM values on the radio of the locally-switched VLAN.
The WLAN QoS profile is applied both for upstream and downstream packets. For downstream, if an
IEEE 802.1P value that is higher than the default WLAN value is received, the default WLAN value is
used. For upstream, if the client sends an WMM value that is higher than the default WLAN value, the
default WLAN value is used. For non-WMM traffic, there is no CoS marking on the client frames from
the AP.
Guidelines for Deploying Wireless QoS
The same rules for deploying QoS in a wired network apply to deploying QoS in a wireless network. The
first and most important guideline in QoS deployment is to know your traffic. Know your protocols, the
sensitivity to delay of your application, and traffic bandwidth. QoS does not create additional bandwidth;
it simply gives more control over where the bandwidth is allocated.
Throughput
An important consideration when deploying IEEE 802.11 QoS is to understand the offered traffic, not
only in terms of bit rate, but also in terms of frame size, because IEEE 802.11 throughput is sensitive to
the frame size of the offered traffic.
Table 2-9 shows the impact that frame size has on throughput: as packet size decreases, so does
throughput. For example, if an application offering traffic at a rate of 3 Mbps is deployed on an 11 Mbps
IEEE 802.11b network, but uses an average frame size of 300 bytes, no QoS setting on the AP allows
the application to achieve its throughput requirements. This is because IEEE 802.11b cannot support the
required throughput for that throughput and frame size combination. The same amount of offered traffic,
having a frame size of 1500 bytes, does not have this issue.
Table 2-9
Throughput Compared to Frame Size
300
600
900
1200
1500
Frame Size (bytes)
11g–54 Mbps
11.4
19.2
24.6
28.4
31.4
Throughput Mbps
11b–11 Mbps
2.2
3.6
4.7
5.4
6
Throughput Mbps
QoS Example LAN Switch Configuration
AP Switch Configuration
The QoS configuration of the AP switch is relatively trivial because the switch must trust the DSCP of
the LWAPP packets that are passed to it from the AP. There is no CoS marking on the LWAPP frames
coming from the AP. The following is an example of this configuration.
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Note
This configuration addresses only the classification, and that queueing commands may be added,
depending on local QoS policy.
interface GigabitEthernet1/0/1
switchport access vlan 100
switchport mode access
mls qos trust dscp
spanning-tree portfast
end
In trusting the AP DSCP values, the access switch is simply trusting the policy set for that AP by the
WLC. The maximum DSCP value assigned to client traffic is based on the QoS policy applied to the
WLANs on that AP.
WLC Switch Configuration
The QoS classification decision at the WLC-connected switch is a bit more complicated than at the
AP-connected switch, because the choice can be to either trust the DSCP or the CoS of traffic coming
from the WLC. In this decision there are a number of points to consider:
•
Traffic leaving the WLC can be either upstream (to the WLC or network) or downstream (to the AP
and WLAN clients). The downstream traffic is LWAPP encapsulated, and the upstream traffic is
from AP and WLAN clients, either LWAPP encapsulated or decapsulated WLAN client traffic,
leaving the WLC.
•
DSCP values of LWAPP packets are controlled by the QoS policies on the WLC; the DSCP values
set on the WLAN client traffic encapsulated by the LWAPP tunnel header has not been altered from
those set by the WLAN client.
•
CoS values of frames leaving the WLC are set by the WLC QoS policies, regardless of whether they
are upstream, downstream, encapsulated, or decapsulated.
The following example illustrates choosing to trust the CoS of settings of the WLC. This allows a central
location for the management of WLAN QoS, rather than having to manage the WLC configuration and
an additional policy at the WLC switch connection. Other customers, intending to have a more precise
degree of control, might implement QoS classification policies on the WLAN-client VLANs.
interface GigabitEthernet1/0/13
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 11-13,60,61
switchport mode trunk
mls qos trust cos
end
Traffic Shaping, Over the Air QoS, and WMM Clients
Traffic shaping and over-the-air QoS are useful tools in the absence of WLAN WMM features, but they
do not address the prioritization of IEEE 802.11 traffic directly. For WLANs that support WMM clients
or Cisco Unified Wireless IP Phone 7920 handsets, the WLAN QoS mechanisms of these clients should
be relied on; no traffic shaping or over-the-air QoS should be applied to these WLANs.
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WLAN Voice and the Cisco Unified Wireless IP Phone 7921G and 7920
The Cisco Unified Wireless IP Phone 7921G and the Cisco Unified Wireless IP Phone 7920 are Cisco
VoWLAN handsets. Their use is one of the most common reasons for deploying QoS on a WLAN.
For more information on each of these handsets, see the following:
•
Cisco Unified Wireless IP Phone 7921G Version 1.0(2)—
http://www.cisco.com/en/US/products/hw/phones/ps379/products_data_sheet0900aecd805e315d.h
tml
•
Cisco Unified Wireless IP Phone 7920 Version 3.0—
http://www.cisco.com/en/US/products/hw/phones/ps379/products_data_sheet09186a00801739bb.
html
Deploying VoWLAN infrastructure involves more than simply providing QoS on WLAN. A voice
WLAN implementation must consider site survey coverage requirements, user behavior, roaming
requirements, and admission control. These are covered in the following guides:
•
Design Principles for Voice Over WLAN—Refer to the following listing of whitepapers:
http://www.cisco.com/en/US/netsol/ns340/ns394/ns348/networking_solutions_white_papers_list.h
tml
•
Cisco Wireless IP Phone 7920 Design and Deployment Guide—
http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7920/5_0/english/design/guide/7920dd
g.html
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3
Voice over WLAN Radio Frequency Design
The purpose of this chapter is to discuss, in general terms, the considerations in radio frequency (RF)
planning and design for VoWLAN. Handset capabilities, local conditions, and regulations impose
additional opportunities and constraints. This chapter illustrates the RF-related processes and
considerations by presenting typical deployment scenarios.
General Voice AP Guidelines
The packet loss and jitter requirements of VoIP and the increased mobility of VoWLAN handset users
place demands on connection quality, coverage, and user expectations that are beyond that a of a typical
WLAN data deployment. While later generations of WLAN equipment and software might provide
further VoWLAN improvements, RF planning, design, and implementation is the foundation of a
successful VoWLAN deployment. A VoWLAN deployment without a solid RF foundation is the
proverbial house built on sand. Correctly designing, planning, implementing, operating, and maintaining
the WLAN RF environment is critical for a successful VoWLAN deployment. The processes, guides,
heuristics, and tools used for a WLAN data deployment are unlikely to deliver a successful VoWLAN
deployment. The general 7920 and 7921G VoWLAN guidelines are:
Note
•
The optimal VoWLAN network requires overlaps of 20 percent (2.4 GHz), and approximately 15 to
20 percent (5 GHz), where a WLAN Data design may use an AP cell overlap of 5 to 10 percent.
•
The optimal VoWLAN cell boundary recommendation is -67 dBm
The RF characteristics of VoWLAN handsets do vary, and can greatly impact the WLAN design and
capacity. If you are planning a deployment of a VoWLAN handset with RF deployment requirements that
are at odds with those presented in this chapter, the handset guidelines should be followed. Although
handset recommendations do vary, the general principles and issues discussed in this chapter still apply
with some changes in cell sizes.
High Availability
One of the requirements of many systems—including VoWLAN—is for high availability (HA). In a
VoWLAN deployment, the same HA strategies, as used in wired networks, can be applied to the wired
components of the VoWLAN solution. One area unique to the VoWLAN availability is RF coverage
HA—providing RF coverage that is not dependent upon a single WLAN radio. The primary mechanism
for providing RF HA is cell boundary overlap as set out in the VoWLAN requirements. An overlap of
20 percent means that 80 percent of a given AP cell is also covered by other APs at the recommended
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signal levels, while in the other 20 percent of the cell VoWLAN calls may have degraded quality, but
would still be available. The RF HA coverage is augmented by the Cisco Unified Wireless Network
Coverage Hole algorithm which detects if WLAN clients are experiencing poor signal-to-noise ratio
(SNR) values and causes the power of APs to increase as needed in order to rectify SNR issues.
Note
In systems planning to rely on Coverage Hole algorithm, the planning needs to consider that if an AP is
going to increase its power level to adjust for a hole, clients also need to increase their power to adjust
for a hole. Therefore, the maximum power of the VoWLAN handset, which can be lower than the
maximum power of an AP, needs to be considered in the AP power level used in the initial planning of
the deployment. For example, if the VoWLAN handset has a maximum power of 40mW and the AP
planning was based on an AP power of 40mW, increasing the AP power to cover an RF hole does not
help a VoWLAN client in that hole. For the hole coverage to be effective, the RF planning needs to be
based on an AP of 20mW or less.
Higher levels of overlap may be applied as required in order to increase the RF HA; however, increasing
overlap requires that you consider the potential changes to your network operation due to the resulting
increase in co-channel interference and the tuning of Auto-RF algorithms.
VoWLAN Call Capacity
An important parameter in VoWLAN planning is call capacity—the number of simultaneous VoWLAN
calls that can be supported in an area. This value can vary depending upon the RF environment, the
VoWLAN handset features, and the WLAN system features. For example, the VoWLAN maximum
capacity for a Cisco Unified IP Phone 7921G using a WLAN that provides optimized WLAN services
(such as the Cisco Unified Wireless Network), the capacity is expected to be 14 simultaneous VoWLAN
calls per 2.4 GHz channel and 20 simultaneous VoWLAN calls per 5 GHz channel. These capacity values
are based on assuming no competing high priority WLAN traffic and normal background noise. Note
that because the 5 GHz spectrum generally features less noise and interference, there can be greater
capacity with the higher carrier frequency implementation. The additional non-overlapping channels
available in the 5 GHz spectrum also provides a great deal more call capacity for a given area.
Note
The call capacities are quoted per non-overlapping channel because the channel capacity is the limiting
factor—not the number of access points (AP). This is explained in more detail in the following section.
The purpose of providing these maximum call capacity figures is general planning purposes. The call
capacity specified by the actual VoWLAN handset should be used for deployment since this is the
supported capacity of that handset.
2.4 GHz Network Design
A total of 14 channels are defined in the IEEE 802.11b/g channel set. Each channel is 22 MHz wide, but
the channel separation is only 5 MHz. This leads to channel overlap such that signals from neighboring
channels can interfere with each other. In a 14-channel DS system (11 usable channels in the U.S.), there
are only three non-overlapping (and thus, non-interfering) channels: 1, 6, and 11—each with 25 MHz of
separation. This channel spacing governs the use and allocation of channels in a multi-AP environment,
such as an office or campus. APs are usually deployed in a cellular fashion within an enterprise, where
adjacent APs are allocated non-overlapping channels. See Figure 3-1.
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Figure 3-1
2.4GHz Channel Allocations
Channels
2
3
4
5
6
7
8
9
10
11
12
13
14
87181
1
2.402 GHz
22 MHz
2.483 GHz
IEEE 802.11b provides rates of 1, 2, 5.5, and 11 Mbps. IEEE 802.11g provides data rates of 6, 9, 12, 18,
24, 36, 48, and 54 Mbps in the 2.4-GHz band, in the same spectrum as IEEE 802.11b. IEEE 802.11g is
backward-compatible with IEEE 802.11b with a single AP providing WLAN access for both IEEE
802.11b and IEEE 802.11g clients.
Co-channel Interference Considerations
As mentioned in the preceding section, there are only three non-overlapping channels in U.S. 2.4 GHz
spectrum. This presents a challenge when trying to deploy APs, and ensure that APs on the same channel
cannot see the signal from an AP using the same channel. It is well known that the AP coverage radius
changes with the client bit rates supported, and the boundary created by this RADIUS is often considered
the AP’s boundary.
The reality is somewhat more complicated because the AP influences the WLAN RF environment
around it for a much greater distance than just the bit-rate boundary. This is because the RF energy from
the AP, although too low to be demodulated in to a WLAN frame, is strong enough to cause an IEEE
802.11 radio to defer sending. In addition to the AP’s influence of the RF environment, the clients
associated with that AP extend the range of the RF energy associated with that AP’s cell even further.
The IEEE 802.11 MAC is a Carrier Sense Multiple Access-Collision Avoidance (CSMA-CA) algorithm,
and the Carrier Sense will perform a Clear Channel Assessment (CCA) before attempting to send an
IEEE 802.11 Frame. If the CCA fails, it prevents the IEEE 802.11 radio to delay attempting
transmission. The CCA mechanism is specified for each IEEE 802.11 physical layer; it is typically
triggered either by a simple raw energy level, and physical layer convergence protocol (PLCP) header
power levels, or carrier detection. The CCA of an IEEE 802.11 radio does not vary with the bit rates
being used and is not, generally, user-configurable.
The impact of CCA deferrals on an AP WLAN from IEEE 802.11 radios that are not part of that AP
WLAN is called co-channel interference. As co-channel interference results in delays in sending frames,
it causes increased jitter and delay experienced by VoWLAN calls. Although WLAN QoS prioritizes
WLAN traffic, this occurs after the CCA and therefore prioritization does not overcome the jitter and
delay introduced by CCA.
The guidance for the Cisco Unified IP Phone 7921G VoWLAN handset is for a power level boundary of
-67 dBm, and a separation between adjacent AP channels of -86 dBm. The -67 dBm requirement is to
minimize packet loss, and the -86 dBm requirement is to minimize co-channel interference from other
AP cells on the same channel. Figure 3-2 shows an example of the two boundaries created by the -67
dBm and -86 dBm requirements, based on standard RF loss formulas for an open office environment.
This RF environment that would give an AP a client radius of 43 feet gives an AP co-channel interference
radius of 150 feet using standard antenna gain (2 dB) and an AP output power of 16 dBm (40mW).
Different RF environments, AP powers, and antennas will result in different client and co-channel
interference radii, but the principles discussed in this chapter will generally hold.
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Note
The recommended cell boundary for the Vocera badge is at -65 dBm and therefore would yield slightly
different results from those below.
Note
The output power chosen for the AP must align with the VoWLAN handset capabilities and deployment
requirements. For example the Cisco Unified Wireless IP Phone 7921G has a maximum output power of
40 mW. An AP power greater than 40 mW should not be used for a Cisco Unified Wireless IP Phone
7921G deployment. In circumstances where the Cisco Unified Wireless Network Hole Coverage
mechanism is expected to provide VoWLAN coverage in event of an AP outage, an AP power of less
than 40 mW (using the Cisco Unified Wireless IP Phone 7921G as an example) should be used for AP
planning to allow the APs covering an RF hole to be operating in a range suitable for the VoWLAN
handset. One additional advantage of using a lower AP transmit power is a proportional decrease in the
co-channel interference radii. Our example of 40 mW transmit power gives a co-channel radius of the
150 feet and a client radius of 43 feet. Decreasing the power to 20 mW reduces the co-channel radius to
130 feet and the client radius to 38 feet, and also reduces the co-channel interference proportional to the
co-channel interference generated by an AP.
Figure 3-2
Bit Rate and Co-channel Interference Boundaries of an AP
AP co-channel
interference
radius
222638
AP client
radius
The RF co-channel interference radius of an AP is not the whole picture because a WLAN client is just
as capable as an AP of producing co-channel interference as illustrated in Figure 3-3.
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Figure 3-3
Bit-rate
radius
AP energy
radius
222639
Client energy
radius
Single Client Co-channel Interference Radius
Given that a client or clients might be anywhere on the bit-rate radius perimeter, the client co-channel
interference radius is better illustrated by Figure 3-4. Given the 43 foot bit-rate radius and 150 foot AP
co-channel interference radius of the previous calculations the new client co-channel interference radius
is 193 feet.
Note
The 193 feet would represent close to a worst case because the WLAN client is not normally in an
equivalent location to an AP and would likely suffer greater signal attenuation due to obstacles.
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Figure 3-4
Complete Client Co-channel Interference Radius
Client co-channel
interference
radius
AP co-channel
interference
radius
222640
AP client
radius
Bit Rate Impact on Co-channel Interference
The AP client radius in our example results in a nominal bit rate for the Cisco Unified IP Wireless IP
Phone 7921G of approximately 24 Mbps or greater, depending upon noise. The AP client radius can be
extended further by decreasing by supporting lower bit rates. This is not recommended for the following
reasons:
•
Lowering the bit rate extends the AP client radius, but also increases the client co-channel
interference radius, increasing the area that only has the VoWLAN call capacity of a single AP.
•
The lower bit rates reduce the overall call cell capacity, as lower bit rate packets consume more time,
and transmit less packets.
VoWLAN call quality is sensitive to data-rate shifting. The decision to a data-rate shift is normally the
result of being unable to send at the date rate previously used which is determined by sending multiple
times without receiving an acknowledgement for that frame. This increases the delay and jitter
experienced by a VoWLAN call.
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20 Percent Cell Overlap
The recommended AP cell overlap for VoWLAN deployments at 2.4GHz, is 20 percent. The purpose of
the 20 percent overlap is to ensure that a VoWLAN handset can detect and connect to alternative APs,
when it is close to the cell boundary. This should allow a VoWLAN client to change AP associations
with a minimum of interruption to a call, by minimizing the amount of data rate shifting and
retransmission at a cell boundary for a given VoWLAN client. This 20 percent overlap requirement
means that APs are spaced closer together than the two-times-70 feet distance suggested by the cell
boundary. The area of overlap between two circles of radius equals 1 is given by:
This calculation is taken from http://mathworld.wolfram.com/Circle-CircleIntersection.html
In this equation, d is the distance between the centers of each circle. Solving for an area of 20 percent
gives a d value of 1.374 for a standard radius of 1, or 59 feet between APs for our 67 dBm boundary.
Note
Other common d values are 10 percent (1.611), 15 percent (1.486), 25 percent (1.269), and 30 percent
(1.198)
Figure 3-5 illustrates this AP overlap, where the colors, red, green, and yellow represent channels 1, 6,
and 11 respectively.
APs with 20 Percent Overlap
222947
Figure 3-5
Co-channel Interference and 20 Percent AP Cell Overlap
Figure 3-6 shows the APs with 20 percent overlap and their co-channel interference boundaries. The
co-channel interference boundary for one of the APs using channel 1 (red) overlaps with an AP using
the same channel. In this situation, co-channel interference will occur in a 2.4 GHz VoWLAN
deployment.
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AP with 20 Percent Overlap and Co-channel Interference Boundaries
222948
Figure 3-6
It should be noted that the combined effect of the 20 percent overlap requirement for reliable roaming
between AP cells and the impact of co-channel interference is a reduced per VoWLAN call capacity over
a given area.
Note
It is not an effective strategy to reduce the overlap in order to reduce co-channel interference. As users
satisfaction can be greatly affected by poor roaming performance. In contrast, call capacity can be
addressed in planning and design.
Existing WLAN data deployments (initially using lower-power cell-boundaries and less overlap) that are
changed to match recommended power boundaries and overlap for VoWLAN or Location might
experience application issues for timing-sensitive applications. It is difficult to predict which
applications might be affected by the WLAN changes, because the actual effect depends on the
application implementation. Generally, custom applications (requiring keepalive timeouts) are most
likely to be affected and should be validated in the new environment to ensure that their timers require
no adjustment.
For the sake of comparison, a WLAN data deployment is illustrated in Figure 3-7. This example features
an AP client radius of 110 feet, -a 75 dBm client power boundary-, and a 10 percent overlap. The
increased client radius and reduced overlap is possible because WLAN data clients are generally more
tolerant of packet loss and jitter.
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WLAN Data Single Floor Data Example
222949
Figure 3-7
Note
The co-channel radius is larger for the WLAN Data example. See Figure 3-8. The energy detect levels
are the same, but the AP client radius 67 feet larger. This means that the capacity of the single floor will
still be the equivalent of three channels, even though 6 APs are used.
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Single Floor WLAN Data with Co-channel Radius
222950
Figure 3-8
Example Deployments
The AP layout within a building depends greatly upon the building construction and shape, as well as
the WLAN coverage requirements in that building. Due to differing effects of implementation-specific
variables, there is not a single recommended deployment for the number of APs that should be deployed
nor a single solution for determining the effect of co-channel interference. Therefore, we illustrate the
design process with examples to illustrate deployment options. In the subsequent descriptions, we focus
upon the following examples:
•
Example Single Floor Building Deployment
•
Example Multi-Floor Building
Example Single Floor Building Deployment
Figure 3-9 shows a simple rectangular building example, based upon a standard size building floor at the
Cisco San Jose Campus (285 feet x 185 feet). As we can see from Figure 3-9, 20 APs are required to
give complete coverage. A WLAN data deployment with the same AP boundary and plan may have been
able to use only 15 APs, as shown in Figure 3-10, but this has small coverage gaps. One of the
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characteristics of VoWLAN deployments is that users are more mobile and find coverage gaps that were
not found by WLAN data clients. As a result, a 20 AP deployment is needed. A detail that has not been
shown in Figure 3-9 and Figure 3-10 is the location of building exits. It is critical to have coverage
around the building exits, if not between buildings. Employees will step outside for many reasons and
expect VoWLAN calls to be maintained. One of the issues of Figure 3-10 is that the coverage gaps would
occur at building exits.
Single Floor Deployment with 20 APs
222951
Figure 3-9
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Single Floor Deployment with 15 APs
222952
Figure 3-10
Figure 3-11 shows the co-channel interference radius of an example AP. As can be seen from the figure,
the co-channel interference radius extends for the entire building. This means that the APs using channel
1 (red) are effectively sharing some channel capacity. The seven channel 1 APs have increased the
coverage over single AP by seven times, but has not increased the capacity by the same ratio and might
not increase the capacity significantly in comparison with single AP. The same is true for the APs on
other channels. Due to co-channel interference the call capacity of the floor is equivalent to something
above the capacity of 3 independent APs, but not approaching the capacity of 20 APs. This is the primary
reason for addressing VoWLAN call capacity in terms on the number of calls per channel, rather than
the number of calls per AP. Channel capacity is the limiting factor.
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Single Floor Co-channel Interference
222953
Figure 3-11
Example Multi-Floor Building
In a multi-floor building, RF energy can travel between floors and, as part of RF planning, the channels
are staggered from floor-to-floor to minimize the co-channel interference between floors, as show in
Figure 3-12.
Note
Figure 3-12 and Figure 3-13 do not represent a recommended channel implementation and are provided
only to illustrate this description.
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Figure 3-12
Multi-floor Channel Assignments
Floor 3
Floor 2
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Floor 1
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As the signal path between the floors is different from that on the same floor (there is often a piece of
reinforced concrete in the between floor path), this must be taken into account when considering the
co-channel interference radius of an AP. If we use a typical between floor loss of 7 dB, the co-channel
interference radius of an AP between floors is reduced to 120 feet. Figure 3-13 shows an example of the
co-channel interference radius of APs on different floors. Where floor 2 is the same layout as our single
floor example earlier, and floor 1 and floor 3 shows the co-channel interference radius on the floors
above and below. As can be seen from Figure 3-13, the co-channel interference between floors is still
significant and it is reasonable to assume that the capacity across the three floors may be the equivalent
of six or seven APs, but is not close to that of the 60 APs that have been deployed.
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Figure 3-13
Multi-floor Building Showing Co-channel Interference
Floor 3
Floor 2
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Floor 1
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Location-based Services Design Considerations
The signal level requirements of IEEE 802.11 location-based services are similar to those on VoWLAN,
but the AP placement requirements are different. For example, our AP placements shown in Figure 3-9
illustrate APs positioned close to what would be required in a Location-based Service (LBS)
deployment. In this environment, there are many APs deployed on the perimeter—as well as at the core
of the building. An additional column of APs (four) might be required. The VoWLAN AP count and the
Location AP count may not always be this similar. The AP placement requirements of LBS may result
in the addition of more APs—depending on the shape and size of the building. The addition of more APs
for LBS will introduce an additional level of co-channel interference due to the additional IEEE 802.11
management traffic associated with additional AP; however, given the existing co-channel interference,
the difference is not likely to be significant. The key point, as with the VoWLAN deployment, is that the
addition of extra APs does not contribute to additional capacity in the 2.4GHz band due to co-channel
interference.
The Importance of Auto-RF
As developed in the preceding sections, the VoWLAN call capacity is constrained by the effect of
co-channel interference in the 2.4GHz band. This constraint should be considered in the planning, design
and operation of the VoWLAN network. In our examples we determined that the call capacity of our
deployment is the equivalent of three times the capacity of a single AP. These estimates assume that
Auto-RF in being used, and that an AP will change channels to minimize interference and provide an
optimal channel plan. Unfortunately, there is only so much Auto-RF can do to address the effects of
co-channel interference in the 2.4 GHz channel because the limiting factor in the 2.4 GHz band is the
three, non-overlapping channels. Auto-RF can tune AP power levels that might reduce co-channel
interference by reducing power levels, but this power level adjustment must be balanced against the
signal-level and coverage requirements of the VoWLAN deployment. Auto-RF is discussed further in a
subsequent chapter of this document. The best mechanism to achieve greater capacity and a greater
return on the investment of deployed APs is to use the 5 GHz band of IEEE 802.11a.
5 GHz Network Design
This section describes the following considerations for implementing a 5 GHz VoWLAN deployment:
•
IEEE 802.11a Physical Layer, page 3-17
•
IEEE 802.11a Channels, page 3-18
•
IEEE 802.11a Operating Frequencies and Data Rates, page 3-18
•
IEEE 802.11a and VoWLAN Deployments, page 3-19
IEEE 802.11a Physical Layer
IEEE 802.11a defines requirements for the physical layer (of the OSI model), operating in the 5 GHz
UNII frequency band, with data rates ranging from 6 Mbps to 54 Mbps. It uses Orthogonal Frequency
Division Multiplexing (OFDM), which is a multi-carrier system (52 sub-carriers are used, modulated
with BPSK, QPSK, QAM or 64-QAM to provide different data rates). OFDM allows sub-carrier
channels to overlap, providing a high spectral efficiency. The modulation technique used by OFDM is
more efficient than spread spectrum techniques used with IEEE 802.11b; it is the same as is used in
802.11g.
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IEEE 802.11a Channels
The basic IEEE 802.11a channels are shown in Figure 3-14. This shows the center frequency of the
channels. The spectrum of each channel is 10 MHz on either side of the dotted line (20 MHz total), with
5 MHz of separation between channels spectrum.
5 GHz Channel Set
30 MHz
5150
5180
Lower Band Edge
30 MHz
5200
5220
5240
5260
5280
5300
5320
5350
Upper Band Edge
87182
Figure 3-14
For the U.S.-based IEEE 802.11a standard, the 5 GHz unlicensed band covers 300 MHz of spectrum and
supports 23 channels. As a result, the 5 GHz band is actually a conglomeration of three bands in the U.S.:
5.150-to-5.250 GHz (UNII 1), 5.250-to-5.350 GHz (UNII 2), and 5.725-to-5.875 GHz (UNII 3).
IEEE 802.11a Operating Frequencies and Data Rates
Operating in the unlicensed portion of the 5 GHz radio band, IEEE 802.11a is immune to interference
from devices that operate in the 2.4 GHz band, such as microwave ovens, many cordless phones, and
Bluetooth (a short-range, low-speed, point-to-point, personal-area-network wireless standard). Because
the IEEE 802.11a standard operates in a different frequency range, it is not compatible with existing
IEEE 802.11b or IEEE 802.11g-compliant wireless devices, but it does mean that 2.4-GHz and 5-GHz
equipment can operate in the same physical environment without interference.
IEEE 802.11a provides data rates of 6, 9, 12, 18, 24, 36, 48, with a maximum data rate of 54 Mbps,
though generally at shorter ranges compared to 2.4GHz network, for a given power and gain. However
it has up to 23 non-overlapping frequency channels (depending on the geographic area) as compared to
the three non-overlapping channels for the 2.4GHz band, which results in increased network capacity,
improved scalability, and the ability to create microcellular deployments without interference from
adjacent cells.
The 5 GHz band in which IEEE 802.11a operates is divided into several sub-bands. Each of the
Unlicensed National Information Infrastructure (UNII) bands presented in Table 3-1 were originally
intended for different uses, but all can now be used for indoor IEEE 802.11a deployments with
applicable power restrictions. Originally, the FCC defined what is known as the UNII-1, UNII-2, and
UNII-3 bands, each consisting of four channels. The channels are spaced 20 MHz apart with an RF
spectrum bandwidth of 20 MHz, thereby providing four non-overlapping channels.
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Table 3-1
Operating Frequency Range for IEEE 802.11a
Band
Channel ID
Center Frequency (MHz)
UNII-1
36 
40 
44 
48
5180 
5200 
5220 
5240
UNII-2
52 
56 
60 
64 
100 
104 
108 
112 
116 
120 
124 
128 
132 
136 
140
5260
5280
5300
5320
5500
5520
5540
5560
5580
5600
5620
5640
5660
5680
5700
UNNII-3
149 
153 
157 
161
5745 
5765 
5785 
5805














There are different limitations imposed on each of the UNII bands. Depending on the band, restrictions
include transmit power, antenna gain, antenna styles, and usage. The UNII-1 band is designated for
indoor operation, and initially required devices to use permanently attached antennas. The UNII-2 band
was designated for indoor or outdoor operation, and permitted the use of external antennas. The UNII-3
band, originally intended for outdoor bridge products that use external antennas, can now be used for
indoor or outdoor IEEE 802.11a WLANs as well. The channels in UNII-1 (5.150 to 5.250 GHz) are 36,
40, 44, and 48. The channels in UNII-2 (5.250-5.350 GHz) are 52, 56, 60, 64 and require Dynamic
Frequency Selection (DFS) and Transmitter Power Control (TPC). The channels in the new frequency
range (5.470-5.725 GHz) are 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140 and require DFS and
TPC. The channels in UNII-3 are 149, 153, 157, 161, 165 (5.725-5.825) and do not require DFS and
TPC. Not all channels in a given range can be used in all of the regulatory domains. Table 3-1 shows the
various channels in the UNII-1, -2, and -3 bands, along with the additional 11 new channels.
Note
The 1100 AP does not have an 802.11A radio and the 1000 series AP does not support DFS channels.
IEEE 802.11a and VoWLAN Deployments
Although there are 23 non-overlapping channels in the 5 GHz band, it is generally recommended to use
the lower four channels and upper four channels of the 5 GHz spectrum as the base for VoWLAN, as
they do not have a DFS and TPC requirements. Then add to the base of eight channels by determining
which other channels are unlikely to be affected by DFS and TPC. The timing requirements of DFS and
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TPC can adversely affect VoWLAN call quality. If your region or location is such that you are certain
DFS and TPC will not be triggered, then the use of specific channels should not be an issue. If you are
not certain, you should investigate. The Cisco Spectrum Expert analyzer is a good tool for starting this
assessment to determine whether there are any 5 GHz signals in the area that would trigger DFS and TCP.
Note that these channels must also be supported by the WLAN clients (data and VoWLAN). It is simpler
to stay with the eight non-DFS channels, but every additional channel that can be safely deployed
increases the capacity of the design. In addition to avoiding the DFS and TPC channels, it is also
recommended that adjacent channels be avoided in the AP channel lay out—to avoid interference from
the sidebands in each channel. The channel spacing and channel mask characteristics are such that the
sidebands produced by an IEEE 802.11a client might interfere with the adjacent channels. It is best to
avoid this potential issue in the AP layout. The general power levels and AP separation recommendations
use in this guide for VoWLAN in the 5 GHz implementation are the same as the 2.4 GHz
implementation: a power level boundary of ~67 dBm and a separation between adjacent AP channels of
-86 dBm. Given the lower noise floor in the 5 GHz bands, the overlap recommendation may be reduced
to 15 percent. A 20 percent or higher overlap can still be used if desired. It provides a higher availability
design and takes into account that the use of the 5GHz spectrum is increasing; therefore, the noise floor
can be expected to rise.
The range in the 5 GHz band is different to that in the 2.4 GHz band. However, when using the
recommended power levels and typical antennas in our example, we obtained distances similar to those
used in the 2.4 GHz example. Therefore, the same AP locations and overlap have been used for both the
2.4 GHz and 5 GHz bands. The primary difference between the two deployments is the additional
capacity available due to the additional non-overlapping channels. This difference is sufficient for the 5
GHz band to be recommended for VoWLAN deployments.
Note
The TPC mechanism discussed above is different from the TPC algorithm that is part of Auto-RF.
An Example Single Floor Building
Figure 3-15. shows an AP layout using the eight different channels and designed to maximize the
distance between re-used channels. However, in most cases, more channels should be available. Because
the 2.4GHz and 5 GHz AP client radius and co-channel interference radii are fundamentally the same in
this example, the multiple floor examples need not be repeated here. The major difference between the
two bands is the increase in capacity that is made available by the added channels associated with the 5
GHz band. The more channels that can be found for use in the 5 GHz band, the closer the capacity of the
system can correlate to the number of APs deployed.
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5 GHz Network Design
5 GHz Single Floor Layout
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Figure 3-15
Figure 3-16 illustrates an example of the same AP layout as Figure 3-15 combined with the co-channel
interference radius of a single AP. This illustrates that even though the co-channel interference is smaller,
and the number of channels available is greater, co-channel interference is sufficiently large to affect
overall call capacity on the floor. It would be very difficult to attempt to calculate the amount of
co-channel interference across the entire floor, given that there are 20 APs and eight channels in use. It
is safe to say, given that there are eight channels in use, that the VoWLAN call capacity of the floor
would be equivalent eight times the call capacity of a single AP.
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Planning Tools
5 GHz Single Floor Layout with Co-channel Radius
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Figure 3-16
Planning Tools
The examples shown in this chapter use simple drawing tools and do not address the complex physical
construction and building layout that must be considered in WLAN planning. We recommend that
WLAN planning tools be used to plan the WLAN layout. These tools will assist in both ordering and
placing equipment in an optimum. As with any project, the cost of fixing errors increases by orders of
magnitude in a project. An error missed in planning can be 10 times more costly to fix in the
implementation stage and 100 times more costly to fix in the operation stage. Investments in planning
and planning tools generally pay for themselves many times over.
The Cisco Unified Wireless Network Wireless Control System (WCS) provides a WLAN planning tool,
as do third-party vendors such as AirMagnet. Figure 3-17 depicts an example of the WCS planning page
that uses the same floor plans that would be later used by the WCS to automatically lay out APs based
on common WLAN deployment models.
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Figure 3-17
Example WCS Planning Page
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4
Voice over WLAN Security
The security of a wireless LAN (WLAN) system is always a critical consideration in every WLAN
deployment. Control of the WLAN access relies on the principles of Authentication, Authorization, and
Accounting (AAA), augmented by encryption to ensure privacy. This chapter focuses on the
authentication and encryption aspects of WLAN security, as they relate to VoWLAN deployments. For
a more complete and system view of WLAN security, refer to the following guides:
•
Secure Wireless Design Guide—
http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/secwlandg10/secwire_1_0_book.
html
•
Mobility Design Guide—
http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/emob41dg/emob41dg-wrapper.ht
ml
WLAN Security Overview
WLAN traffic is visible to any WLAN device within radio frequency (RF) range, and is a shared access
medium. This creates a number of security challenges:
•
How do you provide privacy for users of your WLAN, from non-users?
•
How to provide privacy for users of your WLAN from each other?
•
How to support privacy of multicast and broadcast traffic?
•
How to identify which user is which on the WLAN?
Each generation of WLAN security have addressed these challenges in slightly different ways. But the
key mechanisms are based on the same strategies used to secure communication over an untrusted
medium( i.e., Authentication, Authorization and Accounting (AAA) , and encryption). The original
802.11 standard defined an encryption mechanism, Wired Equivalent Privacy (WEP), but did not define
a AAA mechanism. The level of authentication offered in the 802.11 standard was at a group level,
everyone in the group had to have the same encryption key. This key was used to encrypt unicast and
multicast traffic. WLAN security solutions have augmented this group authentication by authenticating
the client’s MAC address. This is not considered a significant improvement in security as:
•
It does not provide any additional per user privacy; the WEP key is still shared by all users.
•
Offers a weak level of authentication as the 802.11 MAC addresses are sent unencrypted; the MAC
address identifies the WLAN client and not the users.
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•
MAC address authentication can be difficult to administer for large groups of users, as the database
of client MAC addresses must be maintained. The management for WEP keys is difficult, if a WEP
needs to be changed all devices must be updated.
802.1X/EAP and Dynamic WEP
In order to provide an enterprise-level WLAN security, Cisco introduced the 802.1X/EAP authentication
mechanisms to provide mutual authentication of WLANs and WLAN clients. During the authentication
process, a unique per-user per session shared key is also derived and a portion of this key is used as
per-session WEP encryption key. The Extensible Authentication Protocol (EAP) mechanism used by
Cisco was called LEAP Lightweight Extensible Authentication Protocol (LEAP), which allowed users
to perform an MSCHAPv2 authentication against a RADIUS server. Additional EAP mechanisms such
as PEAP and EAP-TLS followed LEAP, all providing mechanism for dynamic WEP key generation.
However, LEAP is considered the best suited of these for VoWLAN handsets as it requires fewer
network transactions for authentication and has lower CPU requirements than the other EAP
mechanisms.
Note
EAP-FAST, if available, is the recommended EAP type for use of VoWLAN deployments. For more
information about EAP-FAST, refer to EAP-FAST, page 4-3.
WEP
While the introduction of a dynamic WEP mechanism was a great improvement upon static WEP key
implementations, weakness found in the WEP encryption mechanism means that the security of both
static and dynamic WEP are compromised. Dynamic WEP is still the superior security mechanism to
static WEP, but the security weaknesses in WEP are such that WEP, either static or dynamic, should not
be relied upon to secure a WLAN network.
LEAP
LEAP has been found to have security weakness where weak passwords can be derived through analysis
of the LEAP authentication transactions. The security weakness of LEAP is such that it should only be
used where the use of strong passwords, a 10-character or higher random string, can be enforced. This
means that LEAP may be suitable for VoWLAN handsets as they typically can have a strong passwords
policy enforced, as the network administrator would control the handset’s passwords. LEAP may be
unsuitable for WLAN PCs, as LEAP would typical use the Windows password and these passwords are
generally user-generated and a strong password policy can be difficult to enforce.
Note
Although LEAP is considered secure for VoWLAN handsets when correctly deployed, it is
recommended that a different EAP supplicant, such as EAP-FAST, be used if available.
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EAP-FAST
The recommended replacement for LEAP is EAP-Flexible Authentication via Secure Tunneling
(EAP-FAST). The EAP-FAST protocol was specifically design to take into account the limited
processing power of application specific devices (ASDs) such as VoWLAN handsets. It is designed to
provide the same tunneling protection as a tunneled authentication protocol such as PEAP, without
requiring the Public Key Infrastructure (PKI) overhead associated with setting up the TLS tunnel used
in PEAP. As a tunneled protocol EAP-FAST is capable of supporting multiple inner authentication
mechanism such as MSCHAPv2 or GTC, the supported inner authentication mechanism depends upon
the client implementation.
WPA
The weaknesses in WEP and the demand for a solution drove the Wi-Fi Alliance ( http://www.wi-fi.org/)
to develop WLAN security improvements, based on an 802.11i draft. These improvements are defined
as Wi-Fi Protected Access (WPA). WPA addressed the main weakness in WEP encryption by replacing
it with the Temporal Key Integrity Protocol (TKIP) which reuses the core encryption engine of WEP
(RC4). The reuse of RC4 allowed TKIP to be implemented in the majority of systems through a firmware
upgrade, rather than requiring a hardware upgrade. In addition to TKIP, WPA implemented one other
major improvement to WEP encryption, an additional message integrity check (MIC) mechanism. In
addition to the encryption and message integrity improvements WPA introduced cryptographic
improvements where the key shared between the WLAN client and the WLAN AP is not used directly
for encryption, but instead it is used as the basis for a 4-way cryptographic handshake, that derives the
encryption key, and passes the multicast (group) key. This 4-way handshake is used in both
WPA-Personal and WPA-Enterprise. Figure 4-1 shows the basic 4-way handshake mechanism used in
WPA-Enterprise. The difference between the WPA-Enterprise behavior and the WPA-Personal behavior
is that the 4-way handshake with WPA-Enterprise uses a key derived during the EAP authentication as
the base key of the 4-way. Whereas WPA-Personal 4-way handshake users a shared key configured in
the WLAN client, Supplicant, and the WLC Authenticator (see Figure 4-1).
Figure 4-1
4-Way Handshake
Supplicant
Authenticator
LWAPP
Enterprise
Network
LWAPP
PMK
PMK
EAP Success
1
EAP Success
ANonce
2 PTK
SNonce (MIC)
PTK
Ready to use MIC, GTK
4
OK, use
221278
4 way handshake
3
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The keys used for encryption are derived from the PMK that has been mutually derived during the EAP
authentication. This PMK is sent to the authenticator in the EAP success message, but is not forwarded
to the supplicant because the supplicant has derived its own copy of the PMK:
Step 1
Step 2
The authenticator sends an EAPOL-Key frame containing an authenticator nonce (ANonce), which is a
random number generated by the authenticator).
a.
The supplicant generates an supplicant nonce (SNonce), which is a random number generated by the
supplicant).
b.
The supplicant derives a pair-wise temporal key (PTK) from the ANonce and SNonce (supplicant
nonce, which is a random number generated by the client/supplicant).
The supplicant sends an EAPOL-Key frame containing an SNonce, the RSN information element from
the (re)association request frame, and a MIC (generated from the PMK).
a.
Step 3
If the validation is successful, the authenticator sends an EAPOL-Key frame containing the group
temporal key (GTK), the multicast, and the broadcast encryption key.
a.
Step 4
The authenticator derives the PTK from the ANonce and SNonce and validates the MIC in the
EAPOL-Key frame.
Upon validating the MIC from this frame, the supplicant installs its PTK and the GTK.
The supplicant sends an EAPOL-Key frame to confirm that the temporal keys are installed.
a.
Upon validating the MIC from this frame, the authenticator installs the PTK for this client.
At this point the supplicant and authenticator have verified that they both have a matching PMK, and
both share the same PTK and GTK.
WPA-Personal
WPA-personal uses the same cryptographic tools, as WPA-Enterprise but uses a shared key to
authenticate WLAN clients. This shared key is the key that used in the 4-way handshake that creates the
encryption key for that session. The shared key mechanism of authentication used in WPA-Personal does
not provide a per-user or per device authentication, every device and every AP that is part of that WLAN
uses the same shared key. The key used for encryption is unique per user and per session thanks to the
randomizing that occurs during the 4-way handshake, but the shared key used to authenticate is the same
for everyone. The primary advantage of WPA-personal in a VoWLAN deployment is that it does not
require the use of a AAA server, and this can be an advantage in branch deployments.
Note
Strong keys should be used as there are tools available that can successfully perform a dictionary attack
on WPA-personal.
WPA-Enterprise
WPA-enterprise uses the base WPA frame protection features, and cryptographic features as
WPA-personal, but adds 802.1X/EAP-based authentication to the certification. In WPA-enterprise the
shared key that is used to generate the cryptographic key through 4-way handshake is derived during the
EAP Authentication. The EAP authentication process provides the AAA features missing in
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WPA-personal, allowing each user/device to be individually authenticated, a policy based on the
authentication ID applied (authorization), and the collection of statistics based on authentication ID
(accounting). Figure 4-2 shows an example of EAP protocol flow.
Figure 4-2
EAP Protocol Flow
RADIUS
802.1x
LWAPP
LWAPP
Enterprise
Network
EAP Identity Request
EAP Identity Response
EAP Request – EAP Type
EAP Response – EAP Type
Forward Identify to ACS Server
EAP Request – EAP Type
EAP Response – EAP Type
EAP Success
EAP Success
221274
Authentication conversation is between client and Authentication Server
WPA-Enterprise vs WPA-Personal
Generally, the use of WPA-enterprise is preferred over WPA-personal in enterprise deployments;
therefore, the naming convention, WPA-personal is targeted more at the home users. Shared key security
systems do not provide the AAA features required for the enterprise, and can introduce operational
issues due to the overhead in updating the shared keys if a WLAN client is lost, stolen, or as part of a
regular key rotation regime. The reward for successfully cracking, guessing, or stealing the shared key
is very high, as it the key for all users. In some deployments WPA personal may be used for VoWLAN
deployments, as the enterprise security requirement for AAA need to be balanced against the VoWLAN
handset requirements, and characteristics. Voice systems have very high availability requirements, and
these may be difficult to achieve in branch and remote environments, when there is a dependency upon
a centralized authentication system. This could be addressed by distributing authentication databases to
branches through local AAA servers or the embedded AAA services of a WLC; or by deploying a
VoWLAN system that does not rely on centralized authentication, such as WPA-personal. The security
requirements of VoWLAN also need to be considered in light of the access given to the VoWLAN
handsets (i.e., the VoWLAN handset need not be given access to the entire enterprise network) is able
to make and receive phone calls, and have limited application access. In addition, a handset such as a
Cisco 7921G has application level AAA performed by the UC Manager where the handset is
authenticated, authorized, and accounting information is collected.
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EAP Timing
WPA2
The security features developed in WPA were based on the recommendations of the 802.11i workgroup
that was tasked with replacing original security features defined in the 802.11 standard. The market
demands for a replacement for WEP, where WPA was released prior to the ratification of the 802.11i
standard. There are also slight differences between WPA and the related sections of the 802.11i standard;
these differences should be transparent to users. The sections from the 802.11i standard used by WPA
primarily addresses the need for a securing the WLAN while maintaining sufficient backward
compatibility with WEP for the deployed hardware to be upgraded, though software and firmware
changes. While the security changes from 802.11i adopted by WPA are important, the key component in
802.11i was the incorporation of the Advanced Encryption Standard (AES) into WLAN security this
would align its encryption mechanism with the new industry standard for encryption. The underlying
mechanism of AES-Counter Mode CBC-MAC (AES-Counter Mode describes the encryption
mechanism, and CBC-MAC describes frame protection mechanism) is very different to those of WPA
and WEP, and generally requires hardware upgrades to be supported. The hardware requirements to
support AES encryption in WPA2 mean that migration from WPA is dependent upon a hardware
refreshes. In many cases, updating the network infrastructure is an easier task than updating the WLAN
client infrastructure and a complete migration to WPA2 is dependent upon a generational change in the
WLAN client infrastructure. The desire to migrate from WPA to WPA2 is also tempered by the
knowledge that currently there are no known serious security exposures in WPA.
WPA2-Personal
WPA2-Personal uses the same shared key and 4-way handshake of WPA, but uses the AES-Counter
Mode CBC-MAC Protocol to encrypt and protect frames.
WPA2-Enterprise
WPA2-Enterprise uses the same 802.1X/EAP authentication and 4-way handshake of WPA, but uses the
AES-Counter Mode CBC-MAC Protocol to encrypt and protect frames.
EAP Timing
The EAP authentication mechanism, its supporting infrastructure and protocols, has to make some
assumptions about what is a reasonable amount of time to wait for a WLAN client during the EAP
authentication process. These assumptions are based on the typical timing from PC clients, and may not
be valid for lower CPU devices such as VoWLAN handsets. For example, an EAP timer adjustment is
recommended when using EAP-FAST authentication for the 7921G phone. If not implemented the
7921G is likely to fail authentication even though its credentials are correct.
To adjust the EAP request timeout to 20: [WiSM]]-slot3-1) config advanced eap request-timeout 20
show advanced eap command:
EAP-Identity-Request Timeout (seconds)........... 1
EAP-Identity-Request Max Retries................. 20
EAP Key-Index for Dynamic WEP.................... 0
EAP Max-Login Ignore Identity Response....... enable
EAP-Request Timeout (seconds).................... 20
EAP-Request Max Retries.......................... 2
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Network Segmentation
Note
Only adjust the EAP timers on the advice of the VoWLAN handset vendor, or when following
recommendation from Cisco TAC.
Network Segmentation
The VoIP network shares the base network infrastructure of an enterprise network, but should be
separated whenever possible from the general purpose data network. The topic of segmenting and
securing the VoIP network is beyond the scope of this design guide, but the VoWLAN network should
be separated from the WLAN data network. This can be done in the Cisco Unified Wireless Network,
through the assignment of a VoWLAN interface on the WLC, which is a type of VLAN separation. This
should be sufficient to provide integration into the large enterprise VoIP segmentation scheme, whether
that be VLAN segmentation, IP address segmentation, or VRF segmentation.
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5
Voice over WLAN Roaming
At its most basic level, roaming in an enterprise IEEE 802.11 network occurs when an IEEE 802.11
client changes its access point (AP) association from one AP to another AP within the same WLAN.
Roaming is a client decision. The client is responsible for deciding it needs to roam, and then detecting,
evaluating, and roaming to an alternative AP.
Note
Roaming is a client decision. WLAN standards bodies (such as the IEEE) and industry bodies (such as
the Wi-Fi Alliance) do not specify when a client should roam, or how the client determines to which
alternative AP it should roam. Each vendor’s roaming algorithms are proprietary and are not generally
published.
Client Roaming Decision
IEEE 802.11 clients typically decide to roam when the connection to the current AP becomes degraded.
Roaming necessarily has some impact on client traffic because a client scans other IEEE 802.11 channels
for alternative APs, reassociates, and authenticates to the new AP. Prior to roaming, a client may take
some actions to improve its current connection without necessitating a roam:
•
Data retries—The IEEE 802.11 MAC specifies a reliable transport. Every unicast frame sent
between a wireless client and an AP is acknowledged at the MAC layer. The IEEE 802.11 standard
specifies the protocol used to retry the transmission of data frames for which an acknowledgment
was not successfully received.
•
Data rate shifting—IEEE 802.11a, IEEE 802.11b, and IEEE 802.11g each support a variety of
possible data rates. The data rates supported for a given frequency band (such as 2.4GHz or 5GHZ)
are configured on the WCS/WLC and are pushed down to the APs using that frequency band. Each
AP in a given WLAN then advertises the supported data rates in its beacons. When a client or AP
detects that a wireless connection is becoming degraded, it can change to a lower supported
transmission rate (lower transmission rates generally provide superior transmission reliability).
Although the roaming algorithms differ for each vendor or driver version (and potentially for different
device-types from a single vendor), there are some common situations that typically cause a roam to
occur:
•
Maximum data retry count is exceeded—Excessive numbers of data retries are a common roam
trigger.
•
Low received signal strength indicator (RSSI)—A client device can decide to roam when the receive
signal strength drops below a threshold. This roam trigger does not require active client traffic in
order to induce a roam.
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•
Low signal to noise ratio (SNR)—A client device can decide to roam when the difference between
the receive signal strength and the noise floor drops below a threshold. This roam trigger does not
require active client traffic in order to induce a roam.
•
Proprietary load balancing schemes—Some wireless implementations have schemes where clients
roam in order to more evenly balance client traffic across multiple APs. This is one case where the
roam may be triggered by a decision in the WLAN infrastructure and communicated to the client via
vendor-specific protocols.
Cisco Compatible Extensions Client Roam Triggers
WLAN controllers (WLC) are configured with a default set of RF roaming parameters that are used to
set the RF thresholds adopted by the client to decide when to roam. The default parameters can be
overridden by defining a custom set. These Cisco Compatible Extensions parameters are defined on the
WLC once per IEEE 802.11 frequency band (2.4GHz or 5GHz).
WLAN clients running Cisco Compatible Extensions version 4 or later are able to use the following
parameters (which are communicated to the client via the enhanced neighbor list feature described in
“Cisco Compatible Extensions Channel Scanning” section on page 5-3):
•
Scan threshold—The minimum RSSI that is allowed before the client should roam to a better AP.
When the RSSI drops below the specified value, the client must be able to roam to a better AP within
the specified transition time. This parameter also provides a power-save method to minimize the
time that the client spends in active or passive scanning. For example, the client can scan slowly
when the RSSI is above the threshold and scan more rapidly when below the threshold.
•
Transition time—The maximum time allowed for the client to detect a suitable neighboring AP to
roam to and to complete the roam, whenever the RSSI from the client’s associated AP is below the
scan threshold. The scan threshold and transition time parameters guarantee a minimum level of
client roaming performance. Together with the highest expected client speed and roaming
hysteresis, these parameters make it possible to design a WLAN network that supports roaming
simply by ensuring a certain minimum overlap distance between APs.
•
Minimum RSSI field—A value for the minimum RSSI required for the client to associate to an AP.
•
Hysteresis—A value to indicate how much greater the signal strength of a neighboring AP must be
in order for the client to roam to that AP. This parameter is intended to reduce the amount of roaming
between APs if the client is physically located on or near the border between two APs.
Roaming Selection of a New AP
Channel Scanning
Wireless clients learn about available APs by scanning other IEEE 802.11 channels for available APs on
the same WLAN/SSID. Scanning other IEEE 802.11 channels can be performed actively or passively as
follows:
•
Active scan—Active scanning occurs when the client changes its IEEE 802.11 radio to the channel
being scanned, broadcasts a probe request, and then waits to hear any probe responses (or periodic
beacons) from APs on that channel (with a matching SSID). The IEEE 802.11 standards do not
specify how long the client should wait, but 10 ms is a representative period. The probe-request
frames used in an active scan are one of two types:
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– Directed probe—The client sends a probe request with a specific destination SSID; only APs
with a matching SSID will reply with a probe response
– Broadcast probe—The client sends a broadcast SSID (actually a null SSID) in the probe
request; all APs receiving the probe-request will respond, with a probe-response for each SSID
they support.
•
Passive scan—Passive scanning is performed by simply changing the clients IEEE 802.11 radio to
the channel being scanned and waiting for a periodic beacon from any APs on that channel. By
default, APs send beacons every 100 ms. Because it may take 100 ms to hear a periodic beacon
broadcast, most clients prefer an active scan.
During a channel scan, the client is unable to transmit or receive client data traffic. There are a number
of approaches clients take to minimize this impact to client data traffic:
•
Background scanning—Clients may scan available channels before they need to roam. This allows
them to build-up knowledge of the RF environment and available APs so they may roam faster if it
becomes necessary. Impact to client traffic can be minimized by only scanning when the client is
not actively transmitting data, or by periodically scanning only a single alternate channel at a time
(scanning a single channel incurs minimal data loss)
•
On-roam scanning—In contrast with background, on-roam scanning occurs after a roam has been
determined necessary. Each vendor/device may implement its own algorithms to minimize the roam
latency and the impact to data traffic. For example, some clients might only scan the
non-overlapping channels.
Typical Scanning Behavior
Although most client roaming algorithms are proprietary, it is possible to generalize the typical behavior.
Typical wireless client roam behavior consists of the following activities:
•
On-roam scanning—This ensures clients have the most up-to-date information at the time of the
roam.
•
Active scan—An active scan is preferred over a passive scan, due to lower latency when roaming.
There are some informational attributes that may be used to dynamically alter the roam algorithm:
•
Client data type—For example, voice call in progress
•
Background scan information—Obtained during routine periodic background scans
Ways in which attributes can be used to alter the scan algorithm include:
•
Scan a subset of channels—For example, information from the background scan can be used to
determine which channels are being used by APs in the vicinity.
•
Terminate the scan early—For example, if a voice call is in progress, the first acceptable AP might
be used instead of waiting to discover all APs on all channels.
•
Change scan timers—For example, if a voice call is in progress, the time spent waiting for probe
responses might be shortened during an active scan.
Cisco Compatible Extensions Channel Scanning
While WLAN clients ultimately determine when to associate (or reassociate) to an AP, Cisco APs
provide information to clients to facilitate AP selection by providing information (such as channel load
in its beacons and probe responses) or by providing a list of neighboring APs.
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WLC software release 4.0 and later support the following Cisco Compatible Extensions, Layer-2
client-roaming enhancements:
Note
•
AP assisted roaming—This feature helps clients save scanning time. Whenever a Cisco Compatible
Extensions v2 client associates with an AP, it sends an information packet to the new AP listing the
characteristics of its previous AP. The AP uses this information to build a list of previous APs, which
it sends (via unicast) to clients immediately after association to reduce roaming time. The AP list
contains the channels, BSSIDs of neighbor APs that support the client’s current SSID(s), and time
elapsed since disassociation.
•
Enhanced neighbor list—The enhanced neighbor list is an enhanced version of the neighbor list
which is sent as part of the Cisco Compatible Extensions v2 AP Assisted Roaming feature. It is
always provided unsolicited by the AP to the client immediately following a successful association
or reassociation. As the AP periodically checks to ensure its neighbor list is up to date, it may also
send an unsolicited update to the corresponding clients. The enhanced neighbor list may include, for
each AP, the RF parameters discussed in the “Cisco Compatible Extensions Client Roam Triggers”
section on page 5-2. In addition, it may include, for each AP in the list, additional information about
AP timing parameters, information about the AP support for the clients subnet, and the strength and
SNR of the last transmission from the client received by the AP.
•
Enhanced neighbor list request (E2E)—The End-2-End (E2E) specification is a Cisco and Intel joint
program that defines new protocols and interfaces to improve the overall voice and roaming
experience. It applies only to Intel clients in a Cisco Compatible Extensions environment.
Specifically, it enables Intel clients to request a neighbor list at will. When this occurs, the AP
forwards the request to the WLC. The WLC receives the request and replies with the current Cisco
Compatible Extensions roaming sublist of neighbors for the AP to which the client is associated.
To see whether a particular client supports E2E, click Wireless > Clients on the WLC GUI, click the
Detail link for the desired client, and look at the E2E Version field under Client Properties.
•
Directed roam request—This feature enables the WLC to send directed roam requests to the client
in situations when the WLC can better service the client on an AP different from the one to which
the client is associated. In this case, the WLC sends the client a list of the best APs that it can join.
The client can either honor or ignore the directed roam request. Non-Cisco Compatible Extensions
clients and clients running Cisco Compatible Extensions v3 or prior must not take any action. No
configuration is required for this feature.
WLC software release 4.0 supports Cisco Compatible Extensions versions 1 through 4. Cisco
Compatible Extensions support is enabled automatically for every WLAN on the WLC and cannot be
disabled. The WLC stores the Cisco Compatible Extensions version of the client in its client database
and uses it to generate and respond to Cisco Compatible Extensions frames appropriately. Clients must
support Cisco Compatible Extensions v4 (or Cisco Compatible Extensions v2 for AP-assisted roaming)
in order to utilize these roaming enhancements.
Note
AP 1030s in Remote Edge AP (REAP) mode, and hybrid-REAP APs in H-REAP locally switched mode
do not support Cisco Compatible Extensions Layer 2 roaming.
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Reauthenticating to a New AP
Evaluating the List of Potential Roam Targets
Once the wireless client has a list of potential APs to which it can roam, the client will use a
client-specific algorithm to choose a specific AP to which it will roam. Factors that may be considered
include:
•
Receive signal strength indicator (RSSI)
•
Signal to noise ratio (SNR)
•
Number of clients on the AP
•
Transmit and receive bandwidth being used by the AP
•
RF channel load information from beacon and probe responses sent by the AP (see Chapter 2,
“WLAN Quality of Service” for more information).
Reauthenticating to a New AP
When a wireless client initially joins a WLAN it must authenticate before being granted access to the
network. This section describes the following considerations and processes:
Note
•
Authentication Types, page 5-5
•
Reauthenticating When Roaming, page 5-6
Detailed security information including WLAN authentication details is available in the CVD Secure
Wireless Design Guide.
Authentication Types
Authentication schemes for WLAN access include the following:
•
Open Authentication—This is null authentication, any client is permitted to access the WLAN.
•
Wired Equivalent Privacy (WEP) Shared Key (Static WEP)—Static WEP requires sender and
receiver to have the same pre-provisioned key in order to decode messages from each other
•
Wi-Fi Protected Access (WPA)-Personal and WPA2-Personal—A shared key, which is not the
encryption key, is configured on both the WLAN and the WLAN client, and this key is used in the
WPA 4-way handshake to generate a per-session encryption key.
•
IEEE 802.1X/Extensible Authentication Protocol (EAP) Authentication used in WPA-Enterprise or
WPA2-Enterprise—Depending on the customer requirements, various EAP authentication protocols
such as Protected EAP (PEAP), EAP-Transport Layer Security (EAP-TLS), and EAP-Flexible
Authentication via Secure Tunneling (EAP-FAST) can be used in secure wireless deployments.
Regardless of the protocol, they all currently use IEEE 802.1X, EAP, and Remote Authentication
Dial-In User Service (RADIUS) as their underlying transport. These protocols allow network access
to be controlled based on the successful authentication of the WLAN client, and just as importantly,
allow the WLAN network to be authenticated by the user. Figure 5-1 shows the basic flow of an
IEEE 802.1X/EAP authentication.
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Reauthenticating to a New AP
Figure 5-1
EAP Protocol Flow
RADIUS
802.1x
LWAPP
LWAPP
Enterprise
Network
EAP Identity Request
EAP Identity Response
EAP Request – EAP Type
EAP Response – EAP Type
Forward Identify to ACS Server
EAP Request – EAP Type
EAP Response – EAP Type
EAP Success
EAP Success
222663
Authentication conversation is between client and Authentication Server
In Figure 5-1, the section labeled Authentication conversation is between client and Authentication
Server (highlighted in red) depicts the step when authentication of the client by the
authentication—Authentication, Authorization, and Accounting (AAA)/RADIUS—server occurs. This
authentication involves multiple packets being relayed by the WLC from the client to the AAA/RADIUS
server and back again. This portion of the authentication also requires CPU-intensive cryptographic
processing at both the client and the AAA/Radius server. This part of the authentication is where latency
can easily exceed one second and is the focus of the fast roaming algorithms discussed in the following
section.
Reauthenticating When Roaming
Roaming with Open Authentication/Static WEP
When a client roams using open authentication (no keys) or using shared keys, authentication adds little
roam latency, This is because no additional packets need to be exchanged between the client and the
AAA server.
Roaming with IEEE 802.1X/EAP Authentication
When a client roams using IEEE 802.1X with Dynamic WEP WPA-Enterprise or WPA2-Enterprise, an
IEEE 802.1X authentication generally must occur with an AAA/RADIUS server. As discussed above,
authenticating with an AAA/RADIUS server can take more than one second. A one-second interruption
to latency sensitive applications such as VoIP when roaming is unacceptable and therefore fast secure
roaming algorithms have been developed to reduce the roam latency.
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Reauthenticating to a New AP
Fast Secure Roaming
Fast roaming algorithms include Cisco Centralized Key Management (CCKM) and Proactive Key
Caching (PKC). CCKM and PKC allow a WLAN client to roam to a new AP and re-establish a new
session key—known as the Pairwise Transient Key (PTK)—between the client and AP without requiring
a full IEEE 802.1X/EAP reauthentication to a AAA/RADIUS server.
Both CCKM and PKC are Layer-2 roaming algorithms in that they to not consider any Layer-3 issues
such address IP address changes. In the Cisco Unified Wireless Network, clients are allocated IP
addresses from subnets that originate at the WLC—not the AP. In this way, it is possible to group large
numbers of WLAN clients for a given SSID into the same Layer-2 subnet. This maximizes the scope of
the Layer-2 domain—and the Fast Secure Roaming domain. Additionally, multiple-WLC deployments
support client roaming across APs managed by WLCs in the same mobility group on the same or
different subnets. This roaming is transparent to the client because the session is sustained and a tunnel
between the WLCs allows the client to continue using the same DHCP-assigned or client-assigned IP
address as long as the session remains active.
Fast Secure Roaming with Cisco Centralized Key Management
CCKM is a Cisco standard supported by Cisco Compatible Extensions clients to provide fast secure
roaming.
CCKM requires support in the client. Cisco Compatible Extensions provides client-side specifications
for support of many client functions, including fast secure roaming. Table 5-1 summarizes the EAP types
supported in each version of Cisco Compatible Extensions.
Table 5-1
Cisco Compatible Extension EAP Support
Cisco Compatible Extensions Version
EAP Types Supported
Cisco Compatible Extensions v2
CCKM with LEAP
Cisco Compatible Extensions v3
CCKM with LEAP, EAP-FAST
Cisco Compatible Extensions v4
CCKM with EAP, EAP-FAST, EAP-TLS and
LEAP
CCKM establishes a key hierarchy upon initial WLAN client authentication and uses that hierarchy to
quickly establish a new key when the client roams. The following sections describe the initial
establishment and roam phases.
CCKM Roaming—Initial Key Hierarchy Establishment
The initial key hierarchy establishment process is illustrated in Figure 5-2 through Figure 5-5. In
WPA-Enterprise and WPA2-Enterprise, the outcome of a successful EAP authentication (the protocol
portion highlighted in red in Figure 5-1) is a Pairwise Master Key (PMK). Figure 5-2 shows the
establishment of this PMK at the client and the AAA/RADIUS server, and the subsequent forwarding of
of the PMK to the WLC.
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Reauthenticating to a New AP
CCKM Initial Key (Part 1 of 4)
Client
Access Point
RADIUS
Controller
LWAPP
L3
LWAPP
EAP Authentication
EAP Authentication
PMK
PMK
PMK
222657
Figure 5-2
The WLC and the client both derive a Network Session Key (NSK) from the PMK. After the NSK is
established, the WPA-prescribed 4-way handshake is performed between the client and the WLC. At the
conclusion of the 4-way handshake, a Base Transient Key (BTK) and Key Request Key (KRK) are
established. See Figure 5-3.
For more detail on the 4-way handshake, see the CVD Secure Wireless Design Guide.
WPA and WPA2 differ only slightly from CCKM at this point. WPA/WPA2 uses the PMK directly
(instead of deriving a NSK), and after the 4-way handshake establishes a Pairwise Transient Key (PTK)
thus concluding the establishment of the WPA/WPA2 unicast key.
CCKM Initial Key (Part 2 of 4)
Client
Access Point
RADIUS
Controller
LWAPP
L3
LWAPP
EAP Authentication
NSK
PMK
EAP Authentication
NSK
Cryptographic Nonces
4-way Handshake
BTK, (KRK)
BTK, (KRK)
PMK
PMK
222658
Figure 5-3
Both the client and the WLC hash the BTK, an initial Rekey Number (RN) = 1, and the BSSID to derive
a PTK. The WLC then forwards the PTK to the AP over the LWAPP tunnel. See Figure 5-4.
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Reauthenticating to a New AP
Figure 5-4
CCKM Initial Key (Part 3 of 4)
Client
Access Point
RADIUS
Controller
LWAPP
L3
LWAPP
EAP Authentication
NSK
EAP Authentication
PMK
NSK
PMK
PMK
Cryptographic Nonces
4-way Handshake
BTK, (KRK)
BTK, (KRK)
BSSID
PTK
(RN=1)
PTK
222659
RN=1
PTK
The client and AP communicate using the PTK to encrypt the data sent between them. See Figure 5-5.
Figure 5-5
CCKM Initial Key (Part 4 of 4)
Client
Access Point
RADIUS
Controller
LWAPP
L3
LWAPP
EAP Authentication
NSK
PMK
EAP Authentication
NSK
PMK
PMK
Cryptographic Nonces
4-way Handshake
BTK, (KRK)
BSSID
RN=1
PTK
PTK
(RN=1)
PTK
EPTK (Data)
222660
BTK, (KRK)
CCKM Roaming—Client Roam
CCKM exists to provide very fast roaming.
In the absence of CCKM, a WPA/WPA2 client must perform a full EAP authentication to a remote
AAA/RADIUS server, followed by a WPA/WPA2 4-way handshake whenever it roams. This process can
take more than one second. With CCKM, the roaming client and WLC can use pre-established keying
material to immediately establish a PTK—normally within a few ten of milliseconds.
When the client roams to a new AP, the client sends a reassociate-request with the next sequential
rekey-number. Protection against spoofed reassociate-requests is provided by the Message Integrity
Check (MIC) that the client adds to the reassociate-request (the MIC is generated using the KRK as
cryptographic input). The reassociate request is forwarded by the AP to the WLC and the MIC is
validated. See Figure 5-6.
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Reauthenticating to a New AP
Figure 5-6
CCKM Roam Key (Part 1 of 2)
Client
Access Point
RADIUS
Controller
LWAPP
L3
LWAPP
BTK, (KRK)
BTK, (KRK)
Reassoc. Req
MICKRK RN=n+1
Verify MIC
222661
PTK
BSSID
The WLC calculates the next PTK, and forwards it to the AP. The client and the AP can now
communicate using the new PTK to encrypt the data sent between them. See Figure 5-7.
CCKM Roam Key (Part 2 of 2)
Client
Access Point
LWAPP
L3
LWAPP
BTK, (KRK)
RADIUS
Controller
BTK, (KRK)
Reassoc. Req
MICKRK RN=n+1
Verify MIC
PTK
BTK, (KRK)
BSSID
PTK
(RN=n+1)
PTK
EPTK (Data)
222662
Figure 5-7
Fast Roaming with Proactive Key Caching
PKC is an IEEE 802.11i extension that allows for the proactive caching (before the client roaming event)
of the WPA/WPA2 PMK that is derived during a client IEEE 802.1 x/EAP authentication at the AP (see
Figure 5-8). If a PMK (for a given WLAN client) is already present at an AP when presented by the
associating client, full IEEE 802.1X/EAP authentication is not required. Instead, the WLAN client can
simply use the WPA 4-way handshake process to securely derive a new session encryption key for
communication with that AP.
Note
PKC is an IEEE 802.11i extension and so is supported in WPA2—not WPA.
The distribution of these cached PMKs to APs is greatly simplified in the Cisco Unified Wireless
deployment. The PMK is simply cached in the WLC(s) and made available to all APs that connect to
that WLC, and between all WLCs that belong to the mobility group of that WLC in advance of a client
roaming event.
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IP Layer Configuration
Figure 5-8
PKC Roam
Authentication
PMK
Encryption LWAPP
PTK n
PTK n
LW
AP
P
PTK n+1
PMK
LWAPP
LWAPP
LWAPP
PTK n+x
Mobility
group
Enterprise
Network
190653
PTK n+1
LWAPP
PTK n+x
IP Layer Configuration
When a client roams from one AP to another, it must determine if it requires a new IP address, or if it
can continue to use its old IP address. Actions that might be required by the client include:
•
Acquiring a valid IP address via DHCP
•
IP duplicate address detection
•
Mobile IP signaling (if required)
•
Virtual private network (VPN) Internet Key Exchange (IKE) signaling (if required)
In a Cisco WLC deployment, client IP addresses do not change when they roam within the same mobility
group. WLC deployments support client roaming across APs managed by one or more WLCs in the same
mobility group on the same or different subnets. This roaming is transparent to the client because the
session is sustained and a tunnel between the WLCs allows the client to continue using the same
DHCP-assigned or client-assigned IP address as long as the session remains active.
Clients roaming without a Cisco fast secure roaming protocol (CCKM or PKC), will typically send a
DHCP request asking for their current IP address. In a Cisco WLC environment, the WLC infrastructure
will ensure the client stays on the same subnet and can continue to use its old IP address. Next, the client
will typically perform duplicate address detection by pinging its own IP address and ensuring there are
no replies from WLAN clients using that same address. If a client is running mobile IP or VPN, those
protocols would run after the IP address is verified unique.
Infrastructure Impacts of Client Roaming
When a wireless client authenticates and associates with an AP, the WLC of the AP places an entry for
that client in its mobility database. This entry includes the client MAC and IP addresses, security context
and associations, QoS context, WLAN, and associated AP. The WLC uses this information to forward
frames and manage traffic to and from the wireless client.
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Infrastructure Impacts of Client Roaming
When the wireless client moves its association from one AP to another, the WLC updates the client
database with the new associated AP. If necessary, new security context and associations are established
as well.
Multiple-WLC deployments support client roaming across APs managed by WLCs in the same mobility
group on the same or different subnets. This roaming is transparent to the client because the session is
sustained and a tunnel between the WLCs allows the client to continue using the same DHCP-assigned
or client-assigned IP address as long as the session remains active. Figure 5-9 illustrates the roaming in
this context.
Figure 5-9
WLAN Infrastructure—Roam
Client Database
MAC, WLAN, IP, Sec, ANCHOR...
Controller 1
Mobility
Announcement
Controller 2
Subnet B
Subnet A
LWAPP
LWAPP
LWAPP
AP A
AP B
AP C
AP D
190687
LWAPP
Measuring Roam Latency
A roam can be segmented into the following components;
•
Client roam decision
•
Choosing a new AP to which a client roams
•
Reauthenticating to the new AP
•
IP layer configuration
•
Infrastructure impacts of client roam
Each of these components have the potential to add latency to a roam. However, there is no industry
consensus on how to measure roam latency.
The most realistic measure of roam latency is from the last packet sent by the roaming client on the old
AP to the first packet received by the roaming client on the new AP. This ensures all the above
components are measured and ensures that 2-way communication is as show in Table 5-2.
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Infrastructure Impacts of Client Roaming
Table 5-2
Roam
Action
Summary of Roam Latency Measurement Process
Measurement Point
Description
Start
Last packet sent by roaming Ensures 2-way communication is still established when the
client on old AP
roam latency measurement commences; it is common for
frames to continue to be forwarded to the roaming client on the
old AP after the client has started the roam.
End
First packet received by
roaming client on new AP
This again ensures 2-way communication by ensuring that the
client’s new location has been learned by the network
infrastructure and that the client is receiving packets as well as
sending them.
When comparing roam latency for different WLAN implementations, take care that the same criteria for
measuring roam latency is used in each case.
Monitoring Client Roaming
In addition to the Cisco Compatible Extensions v4 channel scanning capabilities, Cisco Compatible
Extensions v4 clients also send a Roam Reason Report to report the reason why they roamed to a new
AP. It also allows network administrators to build and monitor a roam history.
Use the following commands to view information about Cisco Compatible Extensions Layer-2 client
roaming.
To view the current RF parameters configured for client roaming for the IEEE 802.11a or IEEE
802.11b/g network, enter the following command:
show {IEEE 802.11a | IEEE 802.11bg} l2roam rf-params
To view the Cisco Compatible Extensions Layer-2 client roaming statistics for a particular AP, enter the
following command:
show {IEEE 802.11a | IEEE 802.11bg} l2roam statistics ap_mac
This command provides the following information:
•
The number of roam reason reports received
•
The number of neighbor list requests received
•
The number of neighbor list reports sent
•
The number of broadcast neighbor updates sent
To view the roaming history for a particular client, enter the following command:
show client roam-history client_mac
This command provides the following information:
•
The time when the report was received
•
The MAC address of the AP to which the client is currently associated
•
The MAC address of the AP to which the client was previously associated
•
The channel of the AP to which the client was previously associated
•
The SSID of the AP to which the client was previously associated
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Infrastructure Impacts of Client Roaming
•
The time when the client disassociated from the previous AP
•
The reason for the client roam
•
To obtain debug information for the Cisco Compatible Extensions Layer 2 client roaming, use the
following command:
debug l2roam {detail | error | packet | all} enable
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6
Voice over WLAN Campus Test Architecture
This chapter describes the campus deployments of voice over wireless LAN (VoWLAN). The campus
network used for the VoWLAN end-to-end testing was built based on the design recommendations
documented in the existing campus CVD Routed Access Design Guide
Additional information on the existing campus CVD, including detailed test results, can be found under
the campus heading at:
http://www.cisco.com/en/US/netsol/ns742/networking_solutions_program_category_home.html.
Elements from the following design guides were also used and documented in the network built for this
this chapter:
•
Enterprise QoS Solution Reference Network Design Guide Version 3.3—
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND
-Book.html
•
Cisco AVVID Network Infrastructure IP Multicast Design (SRND)—
http://www.cisco.com/application/pdf/en/us/guest/tech/tk363/c1501/ccmigration_09186a008015e
7cc.pdf
•
Cisco Unified Communications SRND Based on Cisco Unified Communications Manager 6.x—
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/6x/uc6_0.html
•
Enterprise Mobility 4.1 Design Guide—
http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/emob41dg/emob41dg-wrapper.ht
ml
•
Data Center Infrastructure Design Guide 2.5—
http://www.cisco.com/en/US/docs/solutions/Enterprise/Data_Center/DC_Infra2_5/DCI_SRND_2_
5_book.html
Campus Design Overview
The campus design used for the VoWLAN testing is shown in Figure 6-1. Most readers will be familiar
with the hierarchical, access, distribution, core design used in this network. In the past, it was common
to run Layer 2 links between the access layer and the distribution layer, and to use Spanning Tree
Protocol (STP) to create a redundant, loop-free topology. Current design best practice replaces this Layer
2 STP configuration with a configuration that instead routes IP packets at the access layer. Routing in
the access layer allows for faster re-convergence around failure, and simplifies the network by
eliminating the need for STP and Hot standby Routing Protocol (HSRP). The campus CVD design
documents referenced above provide additional information and detailed test results on the advantages
of a routed access layer over a Layer 2 connection.
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Campus Design Overview
Data center devices have some unique network connectivity requirements that make it necessary to
continue to connect to the access layer using Layer 2 and not routed IP. The unique requirements of the
data center network connections are described in Campus Layer 2 Spanning Tree Protocol Design for
Data Center , page 6-9.
Figure 6-1
VoWLAN Campus Architecture
Core Layer
6504
6504
Routed (EIGRP)
10 Gig
Distribution Layer
6504
6504
6504
6504
6504
6504
L2 Trunk
6
L2 Trunk
WISM = Virtual Access Layer
Routed (EIGRP)
1 Gig
Layer 2 using HSRP/STP
10 Gig
Routed (EIGRP)
10 Gig
Access Layer
T1 Data to branches
T1 voice to PSTN
FXS analogue Phone GW
ASA
ASA
Internet Gateway Block
Default Route to Internet
4948
4948
Data Center Block
Cisco Unified Communications
Manager infrastructure
Windows Network infrastructure
(ACS, WCS, AD, DNS, DHCP etc)
3750-E
4503
Client Access Block
APs, phones, workstations
222852
3845
3845
Voice/WAN Gateway Block
The architecture shown in Figure 6-1 differs from the existing campus CVD Routed Access Design
Guide in that multiple access layer blocks are connected to a single distribution block. In a production
deployment, the campus CVD Routed Access Design Guide topology should be followed. This would
result in each access layer block connecting to a dedicated distribution block, where policy appropriate
to that type of access layer could be applied. Following the campus CVD Routed Access Design Guide
would result in the voice/WAN gateway, the Internet Gateway, and the data center access blocks all
connecting to dedicated distribution blocks rather than sharing a distribution block, as is shown in
Figure 6-1.
In accordance with the campus design recommendations, all router interconnections use fiber optic
transport due to the superior link failure detection capabilities fiber links have when compared to wired
Ethernet connections.
The Configuration section provides sample configurations that can be used as a basis for implementing
the policies discussed in the following sections.
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Campus IP Routing Design
Voice and Data VLAN Separation
Separate voice and data VLANs are used for the following reasons;
•
Address space conservation and voice device protection from external networks—Private
addressing of phones on the voice or auxiliary VLAN enables address conservation and ensures that
phones are not accessible directly via public networks. PCs and servers are typically addressed with
publicly routed subnet addresses; however, voice endpoints should be addressed using RFC 1918
private subnet addresses.
•
QoS trust boundary extension to voice devices—QoS trust boundaries can be extended to voice
devices without extending these trust boundaries and, in turn, QoS features to PCs and other data
devices.
•
Protection from malicious network attacks—Subnet access control, can provide protection for voice
devices from malicious internal and external network attacks such as worms, denial-of- service
(DoS) attacks, and attempts by data devices to gain access to priority queues.
•
Ease of management and configuration—Separate VLANs for voice and data devices at the access
layer provide ease of management and simplified QoS configuration.
Campus IP Routing Design
Most of the information in this section was taken directly from the campus CVD Routed Access Design
Guide. The campus CVD Routed Access Design Guide advocates the use of Layer 3 routing to the access
layer in order to obtain the highest possible network availability. Test results in the HA Campus
Recovery Analysis document (available at
http://www.cisco.com/en/US/netsol/ns815/networking_solutions_program_home.html) confirm the
advantages of Layer 3 design over Layer 2 designs.
EIGRP Routing Protocol
The campus documents referenced above describe the use of both OSPF and EIGRP as appropriate
choices for the campus routing protocol. The test results show convergence for both of these routing
protocols to be essentially equivalent. For this chapter, we chose to implement EIGRP due to its superior
ease of deployment.
Minimizing EIGRP Reconvergence Time
The length of time it takes for EIGRP or any routing protocol to restore traffic flows, after a network
outage, within the campus is bounded by the following three main factors:
•
The time required to detect the loss of a valid forwarding path
•
The time required to determine a new best path
•
The time required to update software and associated hardware forwarding tables
In the cases where the switch has redundant equal-cost paths, all three of these events are performed
locally within the switch and controlled by the internal interaction of software and hardware. In the case
where there is no second equal-cost path nor a feasible successor for EIGRP to use, the time required to
determine the new best path is variable and primarily dependent on EIGRP query and reply propagation
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Campus IP Routing Design
across the network. To minimize the time required to restore traffic in the case where a full EIGRP
routing convergence is required, it is necessary to provide strict bounds on the number and range of the
queries generated.
Although EIGRP provides a number of ways to control query propagation, the two main methods are
route summarization and the EIGRP stub feature. In the routed access hierarchical campus design, it is
necessary to use both of these mechanisms.
EIGRP Stub
Configuring EIGRP stub on the Layer 3 access switches prevents the distribution switch from generating
downstream queries.
Access Switch EIGRP Routing Process Stub Configuration
A4R-Top#sh run | beg router eigrp 100
router eigrp 100
passive-interface default
no passive-interface TenGigabitEthernet1/0/1
no passive-interface TenGigabitEthernet2/0/1
network 10.0.0.0
no auto-summary
eigrp router-id 10.33.9.19
eigrp stub connected
By configuring the EIGRP process to run in “stub connected” state, the access switch advertises all
connected subnets matching the network 10.0.0.0 0.255.255.255 range. It also advertises to its neighbor
routers that it is a stub or non-transit router, and thus should never be sent queries to learn of a path to
any subnet other than the advertised connected routes. With the design in Figure 6-2, the impact on the
distribution switch is to limit the number of queries generated to 3 or less for any link failure.
Figure 6-2
EIGRP Stub Limits the Number of Queries Generated to 3
10.22.50.0/24
Stub Neighbors are
not sent queries
132708
On link failure Query
Neighbors for route to
10.22.50.0/24
To confirm that the distribution switch is not sending queries to the access switches, examine the EIGRP
neighbor information for each access switch and look for the flag indicating queries being suppressed.
D3L#sh ip eigrp neigh det te 2/6
IP-EIGRP neighbors for process 100
H
Address
Interface
Hold Uptime
(sec)
SRTT
(ms)
RTO
Q Seq
Cnt Num
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3
10.33.3.3
Te2/6
2 00:00:15 1004
Version 12.2/1.2, Retrans: 0, Retries: 0
Stub Peer Advertising ( CONNECTED REDISTRIBUTED ) Routes
Suppressing queries
5000
0
36
Configuring the access switch as a stub; router enforces hierarchical traffic patterns in the network. In
the campus design, the access switch is intended to forward traffic only to and from the locally connected
subnets. The size of the switch and the capacity of its uplinks are specified to meet the needs of the
locally-connected devices. The access switch is never intended to be a transit or intermediary device for
any data flows that are not to or from locally-connected devices. The hierarchical campus is designed to
aggregate the lower speed access ports into higher speed distribution uplinks, and then to aggregate that
traffic up into high-speed core links. The network is designed to support redundant capacity within each
of these aggregation layers of the network, but not to support the re-route of traffic through an access
layer. Configuring each of the access switches as EIGRP stub routers ensures that the large aggregated
volumes of traffic within the core are never forwarded through the lower bandwidth links in the access
layer, and also ensures that no traffic is ever mistakenly routed through the access layer, bypassing any
distribution layer policy or security controls.
Each access switch in the routed access design should be configured with the EIGRP stub feature to aid
in ensuring consistent convergence of the campus by limiting the number of EIGRP queries required in
the event of a route recalculation, and to enforce engineered traffic flows to prevent the network from
mistakenly forwarding transit traffic through the access layer.
For more information on the EIGRP stub feature, see the following URL:
http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/eigrpstb.html
Distribution Summarization
Configuring EIGRP stub on all of the access switches reduces the number of queries generated by a
distribution switch in the event of a downlink failure, but it does not guarantee that the remaining queries
are responded to quickly. In the event of a downlink failure, the distribution switch generates three
queries; one sent to each of the core switches, and one sent to the peer distribution switch. The queries
generated ask for information about the specific subnets lost when the access switch link failed. The peer
distribution switch has a successor (valid route) to the subnets in question via its downlink to the access
switch, and is able to return a response with the cost of reaching the destination via this path. The time
to complete this event depends on the CPU load of the two distribution switches and the time required
to transmit the query and the response over the connecting link. In the campus environment, the use of
hardware-based CEF switching and GigE or greater links enables this query and response to be
completed in less than a 100 msec.
This fast response from the peer distribution switch does not ensure a fast convergence time, however,
EIGRP recovery is bounded by the longest query response time. The EIGRP process has to wait for
replies from all queries to ensure that it calculates the optimal loop free path. Responses to the two
queries sent towards the core need to be received before EIGRP can complete the route recalculation. To
ensure that the core switches generate an immediate response to the query, it is necessary to summarize
the block of distribution routes into a single summary route advertised towards the core.
D3L#sh run | begin TenGigabitEthernet2/1
interface TenGigabitEthernet2/1
description from D3L to CL
ip address 10.33.1.11 255.255.255.254
ip hello-interval eigrp 100 1
ip hold-time eigrp 100 3
ip authentication mode eigrp 100 md5
ip authentication key-chain eigrp 100 eigrp-chain
ip pim sparse-mode
ip summary-address eigrp 100 10.33.48.0 255.255.240.0 5
logging event link-status
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load-interval 30
carrier-delay msec 0
mls qos trust dscp
The summary-address statement is configured on the uplinks from each distribution switch to both core
nodes. In the presence of any more specific component of the 10.33.0.0/16 address space, it causes
EIGRP to generate a summarized route for the 10.33.0.0/16 network, and to advertise only that route
upstream to the core switches.
CL#sh ip route 10.33.50.0
Routing entry for 10.33.48.0/20
Known via "eigrp 100", distance 90, metric 3328, type internal
Redistributing via eigrp 100
Last update from 10.33.1.11 on TenGigabitEthernet2/5, 4w3d ago
Routing Descriptor Blocks:
* 10.33.1.13, from 10.33.1.13, 4w3d ago, via TenGigabitEthernet2/6
Route metric is 3328, traffic share count is 1
Total delay is 30 microseconds, minimum bandwidth is 1000000 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
10.33.1.11, from 10.33.1.11, 4w3d ago, via TenGigabitEthernet2/5
Route metric is 3328, traffic share count is 1
Total delay is 30 microseconds, minimum bandwidth is 1000000 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
With the upstream route summarization in place, whenever the distribution switch generates a query for
a component subnet of the summarized route, the core switches reply that they do not have a valid path
(cost = infinity) to the subnet query. The core switches are able to respond within less than 100 msec if
they do not have to query other routers before replying back to the subnet in question.
Figure 6-3 shows an example of summarization toward the core.
Figure 6-3
Summarization toward the Core Bounds EIGRP Queries for Distribution Block Routes
Summarized Route Only
10.33.48.0/20
Return Infinite Cost
10.22.50.0/24
Valid Route to
10.120.4.0/24
Return Route Cost
Stub Neighbors are
not sent queries
132709
On link failure Query
Neighbors for route to
10.22.50.0/24
Using a combination of stub routing and summarizing the distribution block routes upstream to the core
both limits the number of queries generated and bounds those that are generated to a single hop in all
directions. Keeping the query period bounded to less than 100 msec keeps the network convergence
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similarly bounded under 200 msec for access uplink failures. Access downlink failures are the worst case
scenario because there are equal-cost paths for other distribution or core failures that provide immediate
convergence.
Route Filters
The discussion on EIGRP stub above noted that in the structured campus model, the flow of traffic
follows the hierarchical design. Traffic flows pass from access through the distribution to the core and
should never pass through the access layer unless they are destined to a locally attached device.
Configuring EIGRP stub on all the access switches aids in enforcing this desired traffic pattern by
preventing the access switch from advertising transit routes. As a complement to the use of EIGRP stub,
Cisco recommends applying a distribute-list to all the distribution downlinks to filter the routes received
by the access switches. The combination of “stub routing” and route filtering ensures that the routing
protocol behavior and routing table contents of the access switches are consistent with their role, which
is to forward traffic to and from the locally connected subnets only.
Cisco recommends that a default route (0.0.0.0 mask 0.0.0.0) be the only route advertised to the access
switches.
D3L#sh run | begin router eigrp 100
router eigrp 100
...
network 10.0.0.0
distribute-list only-default out TenGigabitEthernet2/4
distribute-list only-default out TenGigabitEthernet2/6
...
eigrp router-id 10.33.9.8
!
...
!
ip access-list standard only-default
permit 0.0.0.0
remark redistribute default route to access layer stub-routers
No mask is required in the configuration of this access list because the assumed mask, 0.0.0.0, permits
only the default route in the routing updates.
In addition to enforcing consistency with the desire for hierarchical traffic flows, the use of route filters
also provides for easier operational management. With the route filters in place, the routing table for the
access switch contains only the essential forwarding information. Reviewing the status and/or
troubleshooting the campus network is much simpler when the routing tables contain only essential
information.
A4L#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is 10.33.3.24 to network 0.0.0.0
C
C
C
C
2.0.0.0/32 is subnetted, 1 subnets
2.2.2.2 is directly connected, Loopback2
10.0.0.0/8 is variably subnetted, 5 subnets, 3 masks
10.33.49.0/24 is directly connected, Vlan49
10.33.48.0/24 is directly connected, Vlan48
10.33.3.4/31 is directly connected, TenGigabitEthernet1/1
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C
10.33.3.24/31 is directly connected, TenGigabitEthernet1/2
C
10.33.9.20/32 is directly connected, Loopback1
D*EX 0.0.0.0/0 [170/3584] via 10.33.3.24, 3w4d, TenGigabitEthernet1/2
[170/3584] via 10.33.3.4, 3w4d, TenGigabitEthernet1/1
If the network does not contain a default route, it may be acceptable to use an appropriate full network
summary route in its place; that is, 10.0.0.0/8, or a small subset of summary routes that summarize all
possible destination addresses within the network.
CEF Switching
Per-destination load balancing is enabled by default when you enable CEF, and is the load balancing
method of choice for most situations. Per-destination load balancing allows the router to use multiple
paths to achieve load sharing. Packets for a given source-destination host pair are guaranteed to take the
same path, even if multiple paths are available.
When you enable CEF or dCEF globally, all interfaces that support CEF are enabled by default.
Adjusting EIGRP timers
The recommended best practice for campus design is to use point-to-point fiber connections for all links
between switches. Link failure detection via 802.3z and 802.3ae remote fault detection mechanism
provide for recovery from most campus switch component failures. Cisco recommends in the Layer 3
campus design that the EIGRP hello and dead timers be reduced to 1 and 3 seconds, respectively (see
Figure 6-4). The loss of hellos and the expiration of the dead timer provides a backup to the L1/2 remote
fault detection mechanisms. Reducing the EIGRP hello and hold timers from defaults of 5 and 15
seconds provides for a faster routing convergence in the rare event that L1/2 remote fault detection fails
to operate, and hold timer expiration is required to trigger a network convergence because of a neighbor
failure.
Reducing EIGRP Hello and Dead Timers
interface TenGigabitEthernet4/3
description 10 GigE to Distribution 1
ip address 10.122.0.26 255.255.255.254
. . .
ip hello-interval eigrp 100 1
ip hold-time eigrp 100 3
. . .
interface TenGigabitEthernet2/1
description 10 GigE to Core 1
ip address 10.122.0.27 255.255.255.254
. . .
ip hello-interval eigrp 100 1
ip hold-time eigrp 100 3
Ensure Timers are
consistent on both
ends of the link
132710
Figure 6-4
...
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Campus IP Routing Design
Campus Layer 2 Spanning Tree Protocol Design for Data Center
Much of the information in this section is summarized from the Data Center Infrastructure 2.5
Design Guide. For details, refer to this guide at:
http://www.cisco.com/en/US/docs/solutions/Enterprise/Data_Center/DC_Infra2_5/DCI_SRND_2_
5_book.html.
Data Center Layer Introduction
In the test network used for this document, the data center is used to connect network infrastructure
devices such as Cisco Unified Communications Manager, Cisco Unified Unity, ACS, WCS, DNS,
DHCP.
While the rest of the campus network uses Layer 3 routing (EIGRP) all the way to the access layer, the
unique requirements of data center deployments require a Layer 2 connection to the data center. A Layer
2 access topology provides the following unique capabilities required in the data center:
•
VLAN extension—The Layer 2 access topology provides the flexibility to extend VLANs between
switches that are connected to a common aggregation module. This makes provisioning of servers
to a particular subnet/VLAN simple, and without the worry of physical placement of the server in a
particular rack or row.
•
Layer 2 adjacency requirements—NIC teaming, high availability clusters, and database clusters are
application examples that typically require NIC cards to be in the same broadcast domain (VLAN).
The list of applications used in a clustered environment is growing, and Layer 2 adjacency is a
common requirement.
•
Custom applications—Many developers write custom applications without considering the Layer 3
network environment. This can create challenges in a Layer 3 IP access topology. These servers
usually depend on Layer 2 adjacency with other servers and may require rewriting of code when
changing IP addresses.
•
Service modules—A Layer 2 access permits services provided by service modules or appliances to
be shared across the entire access layer. Examples of this are when using the FWSM, CSM, and
SSLSM. The active-standby modes of operation used by service modules require Layer 2 adjacency
with the servers that use them.
Spanning Tree Triangle Looped Topology
The triangle looped topology utilized in the network used for this document is currently the most widely
implemented in the enterprise data center. This topology provides a deterministic design that makes it
easy to troubleshoot while providing a high level of flexibility (see Figure 6-5).
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Figure 6-5
Triangle Looped Access Topology
Distribution
D1L
D1R
6504
6504
L3
L2 Trunk
HSRP Primary
STP root (Priority 24576)
HSRP Backup
STP backup (Priority 28672)
Spanning tree is blocked for
all VLANs on links to D1R
4948
4948
A3R
A3L
Data Center
222853
Spanning tree is forwarding for
all VLANs on links to D1R
In a triangle looped access layer design, it is desirable to align the spanning tree root, HSRP default
gateway, and active service modules on the same aggregation switch, as shown in Figure 6-5. Aligning
the access layer switch uplink that is in the forwarding state directly to the same switch that is the
primary default gateway and active service module/appliance optimizes the traffic flows. Otherwise,
traffic flows can hop back and forth between aggregation switches, creating undesirable conditions and
difficulty in troubleshooting.
Lab Implementation Deviations from Standard Design Principals in the Data Center
In the network used for this chapter, multiple access layer blocks are connected to a single distribution
block. This was done to reduce the number of distribution layer switches required. In a production
deployment, the data center access-block would connect to a dedicated distribution block. In a
production network, the distribution block dedicated to the data center access-block would run a variety
of service modules supporting data center access. Example service modules include:
•
Firewall Services Modules (FWSM)
•
Secure Sockets Layer Services Modules (SSLSM)
•
Content Switching Module (CSM)
•
Intrusion Detection
•
Network Analysis Module (NAM)
•
Distributed denial-of-service attack protection (Cisco Guard)
While some combination of these would be expected in a production distribution layer block, our test
network is not specifically focused on data center testing, and we have implement the network without
any of these service modules.
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Campus Quality of Service (QoS)
Campus Quality of Service (QoS)
Much of the information in this section is summarized from the Enterprise QoS Solution Reference
Network Design Guide Version 3.3. For details refer to this guide at:
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Bo
ok.html.
QoS refers to the set of tools and techniques used to manage network resources. QoS technologies allow
different types of traffic to contend inequitably for network resources. Using QoS, some network traffic
such as Voice, video, or critical data may be granted priority or preferential services from network
devices; this prevents lower priority background traffic from degrading the quality of these strategic
applications.
Until recently, QoS was not a great concern in the enterprise campus due to the large amount of available
bandwidth as well as the asynchronous nature of data traffic and the ability of applications to tolerate
the effects of buffer overflows and packet loss. However, with new applications such as voice and video,
which are sensitive to packet loss and delay it is important to utilize quality of service features to protect
high priority traffic.
Campus QoS Services Required
Access switches require the following QoS policies:
•
Appropriate (endpoint-dependant) trust policies, and/or classification and marking policies
•
Policing and markdown policies
•
Queuing policies
Distribution and core switches require the following QoS policies:
•
DSCP trust policies
•
Queuing policies
•
Optional per-user microflow policing policies (only on supported platforms)
These recommendations are summarized in Figure 6-6.
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Figure 6-6
Typical Campus Oversubscription Ratios
Core
Si
Si
Si
Si
Distribution
222855
Access
Access Edges: Trust, Classification, Marking, Policing, and Queuing Policies
Interswitch Links: DSCP-Trust and Queuing Policies
Optional (C6500-PFC3 Only): Per-User Microflow Policing on Uplinks from Access Layer
Campus QoS and Interface Queuing
Many campus links are underutilized. Some studies have shown that 95 percent of campus access layer
links are used at less than 5 percent of their capacity. This means that you can design campus networks
to accommodate oversubscription between access, distribution and core layers. Oversubscription allows
for uplinks to be used more efficiently and more importantly, reduces the overall cost of building the
campus network.
Common campus oversubscription values are 20:1 for the access-to-distribution layers and 4:1 for the
distribution-to-core layers, as shown in Figure 6-7.
Figure 6-7
QoS Requirement within the Campus
Core
Si
Si
Typical 4:1
Oversubscription
Distribution
Si
Si
Typical 20:1
Oversubscription
222854
Access
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The potential for congestion exists in campus uplinks because of oversubscription ratios and speed
mismatches in campus downlinks (for example, GigabitEthernet to FastEthernet links). The only way to
provision service guarantees in these cases is to enable advanced interface queuing at these points.
For a given input or output interface, Cisco IOS can manage multiple queues. Traffic of a particular
priority is mapped into the appropriate queue for that traffic class. Cisco IOS queue scheduling
algorithms can then be configured to service those queues, giving more priority to servicing the queues
containing higher priority traffic. In this way, higher priority traffic is protected from queue overruns
caused by lower priority traffic.
QoS and Wired IP Phones
This section is specific to wired Ethernet-attached IP phone. Wireless LAN IP phones such as the Cisco
7921G use a different QoS procedure and are discussed in Chapter 10, “Cisco Unified IP Phone 7921
Implementation for Voice over WLAN.”
Cisco wired IP phones perform an intelligent exchange of information between the phone and the
switchport it is plugged into using Cisco Discovery Protocol (CDP). When the switch discovers a Cisco
IP phone, it can extend QoS trust to it dynamically.
Figure 6-8 shows a conditional trust boundary extension granted to an IP phone that has passed a CDP
exchange.
Figure 6-8
Conditionally Trusted Endpoint Trust Boundary Extension and Operation
1
“I see you’re an IP phone.”
“So I will trust your CoS.”
IP Phone
Phone VLAN = 110
IP
PC VLAN = 10
TRUST BOUNDARY
4
“CoS 5 = DSCP 46”
“CoS 3 = DSCP 24”
“CoS 0 = DSCP 0”
“Voice = 5, Signaling = 3”
All PC traffic is reset to CoS 0.
2
3
PC sets CoS to 5 for all traffic.
1 Switch and phone exchange CDP; trust boundary is extended to IP phone.
3 Phone rewrites CoS from PC Port to 0.
4 Switch trusts CoS from phone and maps CoS
DSCP for output queuing.
222856
2 Phone sets CoS to 5 for VoIP and to 3 for Call-Signaling traffic.
The sequence shown in Figure 6-8 is the following:
Step 1
Switch and phone exchange CDP; trust boundary is extended to IP phone.
Step 2
Phone sets CoS to 5 for VoIP and to 3 for call signaling traffic.
Step 3
Phone rewrites CoS from PC to 0.
Step 4
Switch trusts CoS from phone and maps CoS to DSCP for output queuing.
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Campus Quality of Service (QoS)
AutoQoS and VoIP
When the main business objective of the QoS deployment is to enable QoS for IP Telephony only (i.e.,
without Scavenger-class QoS), then the network administrator may choose to take advantage of the
Cisco AutoQoS VoIP feature.
AutoQoS VoIP is essentially an intelligent macro that enables an administrator to enter one or two simple
AutoQoS commands to enable all the appropriate features for the recommended QoS settings for VoIP
and IP telephony for a specific platform and/or a specific interface.
AutoQoS VoIP automatically configures the best-practice QoS configurations (based on previous Cisco
Enterprise QoS SRNDs) for VoIP on Cisco Catalyst switches and IOS routers. By entering one global
and/or one interface command (depending on the platform), the AutoQoS VoIP macro then would
expand these commands into the recommended VoIP QoS configurations (complete with all the
calculated parameters and settings) for the platform and interface on which the AutoQoS VoIP macro is
applied.
For example, on Cisco Catalyst switches, AutoQoS performs the following automatically:
•
Enforces a conditional-trust boundary with any attached Cisco IP phones
•
Enforces a trust boundary on Catalyst switch access ports and uplinks/downlinks
•
Modifies CoS-to-DSCP (and IP Precedence-to-DSCP) mappings, as required
•
Enables Catalyst strict priority queuing for voice (CoS 5/DSCP EF) and preferential queuing for
Call-Signaling traffic (CoS 3/DSCP CS3) * Enables best-effort queuing for all other data (CoS
0/DSCP 0) traffic
•
Modifies queue admission criteria (such as CoS-to-queue mapping)
•
Modifies queue sizes and queue weights, where required
QoS Policing
At the time of writing, classification using a port trust state (for example, mls qos trust [cos | dscp |
ip-precedence] and a policy map (for example, service-policy input policy-map-name) are mutually
exclusive on the Catalyst 2970/3560/3750. The last one configured overwrites the previous
configuration. This limitation is to be addressed; consult the latest Catalyst 2970/3560/3750 QoS
documentation for updates on this limitation.
Because of the above limitation, policing will not be discussed in the configuration section of this
document. For detailed guidance on policing configuration, refer to the Enterprise QoS Solution
Reference Network Design Guide Version 3.3 at the following URL:
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Bo
ok.html
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Campus Multicast
Campus Multicast
For complete details on the recommended campus multicast design, see the Cisco AVVID Network
Infrastructure IP Multicast Design SRND at the following URL:
http://www.cisco.com/application/pdf/en/us/guest/tech/tk363/c1501/ccmigration_09186a008015e7cc.p
df.
When designing multicast networking, a routed access design has advantages over a design that has
Layer 2 to the distribution layer. In the Layer 2 design, there are two routers on the same subnet as the
multicast hosts. This results in the following;
•
One of the routers needs to be elected the PIM DR and IGMP querier
•
One of the routers needs to be elected the HSRP active node
•
One of the routers needs to be elected the Layer 2 root bridge
For each specific VLAN The root bridge, the HSRP active node, and the PIM DR should all be on the
same distribution switch.
In the routed access design, this need for synchronized configuration is removed because there is only
one router on the local segment, which by default results in synchronization of the unicast and multicast
traffic flows. Additionally, with the migration of the multicast router from the distribution to the access,
there is no longer a need to tune the PIM hello timers to ensure rapid convergence between the
distribution nodes in the case of a failure. The same remote fault indicator mechanisms that trigger rapid
unicast convergence drive the multicast software and hardware recovery processes, and there is no need
for Layer 3 detection of path or neighbor failure across the Layer 2 access switch. The presence of a
single router for each access VLAN also removes the need to consider non-reverse path forwarding
(non-RPF) traffic received on the access side of the distribution switches. A multicast router drops any
multicast traffic received on a non-RPF interface. If there are two routers for a subnet, the DR forwards
the traffic to the subnet, and the non-DR receives that traffic on its own VLAN interface where it fails
the RPF check and so must be dropped
Multicast Traffic Flows and Router Functions
In the Layer 3 access design, there is a single router on the access subnet and no non-RPF traffic flows.
Although the current generation of Cisco Catalyst switches can process and discard all non-RPF traffic
in hardware with no performance impact or access list configuration required, the absence of non-RPF
traffic simplifies operation and management.
The following summarizes the campus multicast configuration implementation:
•
The access layer switches have IGMP snooping enabled.
•
The RPs are located on the two core layer switches ( RPs should be close to the multicast sources.
In our lab the core routers represented the best location.).
•
PIM-SM is configured on all access layer, distribution layer, and core-layer switches.
•
Anycast RP is configured for fast recovery of IP multicast traffic.
•
PIM-SM and MSDP are enabled on all core layer switches. (auto RP is not used due to its reliance
on PIM-sparse-dense)
•
Each access layer switch points to the anycast RP address as its RP.
•
MSDP is used to synchronize source active (SA) state between the core switches.
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Campus Security
Campus Security
The Campus Security section is focused on the Catalyst Integrated Security Features (CISF) features
found in the access layer switches connecting end-user devices to the network.
Much of the information in this section is summarized from Cisco Unified Communications SRND Based
on Cisco Unified Communications Manager 6.x at the following URL:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/6x/uc6_0.html
Refer to the above document as well as the relevant access-layer switch documentation for more details.
Catalyst Integrated Security Features (CISF)
Layer 2 switched environments can prove easy targets for security attacks. These attacks exploit normal
protocol processing such as a switches’ ability to learn MAC addresses, end-station Media Access
Control (MAC) address resolution through Address Resolution Protocol (ARP) or Dynamic Host
Configuration Protocol (DHCP) IP address assignments.
The rich set of integrated security features on Cisco Catalyst Switches (CISF) protect your critical
network infrastructure with easy-to-use tools that effectively prevent the most common—and potentially
damaging— Layer 2 security threats.
Port Security
Function
Shuts down MAC address-flooding attacks .
How It Works
A classic attack on a switched network is a MAC content-addressable memory (CAM) flooding attack.
This type of attack floods the switch with so many MAC addresses that the switch does not know which
port an end station or device is attached to. When the switch does not know which port a device is
attached to, it broadcasts the traffic destined for that device to the entire VLAN. In this way, the attacker
is able to see all traffic that is coming to all the users in a VLAN.
Port security limits the number of MAC addresses allowed to access individual switch ports thus
protecting against MAC flooding attacks from hacker tools such as macof (see Figure 6-9).
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Figure 6-9
Limited Number of MAC Addresses Prevents Rogue Network Extensions
148494
Only two MAC
addresses
allowed on the
port: Shutdown
DHCP Snooping
Function
Prevent rogue DHCP server attacks, DHCP starvation attacks, create client binding information used by
additional CISF tools
Using DHCP Snooping
Untrusted
Rogue server
Untrusted
Bad DHCP
responses:
offer, ack, nak
Trusted
OK DHCP
responses:
offer, ack, nak
148495
Figure 6-10
DHCP Snooping: Prevent Rogue DHCP Server Attacks
How It Works
Dynamic Host Configuration Protocol (DHCP) Snooping prevents a non-approved DHCP or rouge
DHCP server from handing out IP addresses on a network by blocking all replies to a DHCP request
unless that port is allowed to reply. When enabled, DHCP Snooping treats all ports in a VLAN as
untrusted by default. An untrusted port is a user-facing port that should never make any reserved DHCP
responses. If an untrusted DHCP-snooping port makes a DHCP server response, it will be blocked from
responding. Therefore, rogue DHCP servers will be prevented from responding. However, legitimately
attached DHCP servers or uplinks to legitimate servers must be trusted.
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DHCP Snooping: Prevent DHCP Starvation Attacks
How It Works
DHCP address scope starvation attacks from tools such as Gobbler are used to create a DHCP
denial-of-service (DoS) attack. Because the Gobbler tool makes DHCP requests from different random
source MAC addresses, you can prevent it from starving a DHCP address space by using port security
to limit the number of MAC addresses. However, a more sophisticated DHCP starvation tool can make
the DHCP requests from a single source MAC address and vary the DHCP payload information. With
DHCP Snooping enabled, untrusted ports will make a comparison of the source MAC address to the
DHCP payload information and fail the request if they do not match
DHCP Snooping: Binding Information
How It Works
Another function of DHCP Snooping is to record the DHCP binding information for untrusted ports that
successfully get IP addresses from the DHCP servers. The binding information is recorded in a table on
the Cisco Catalyst switch. The DHCP binding table contains the IP address, MAC address, lease length,
port, and VLAN information for each binding entry. The binding information from DHCP Snooping
remains in effect for the length of the DHCP binding period set by the DHCP server (that is, the DHCP
lease time). The DHCP binding information is used to create dynamic entries for Dynamic ARP
Inspection (DAI) to limit ARP responses for only those addresses that are DHCP-bound. The DHCP
binding information is also used by the IP source guard to limit sourcing of IP packets to only those
addresses that are DHCP-bound.
Dynamic ARP Inspection
Function
Adds security to ARP using DHCP snooping table.
How It Works
Dynamic Address Resolution Protocol (ARP) Inspection (DAI) is a feature used on the switch to prevent
Gratuitous ARP attacks on the devices plugged into the switch and on the router.
Gratuitous ARP can be exploited by malicious programs that want to illegitimately take on the identity
of another station. When a malicious station redirects traffic to itself from two other stations that were
talking to each other, the hacker who sent the GARP messages becomes the man-in-the-middle. Hacker
programs such as ettercap do this with precision by issuing "private" GARP messages to specific MAC
addresses rather than broadcasting them. In this way, the victim of the attack does not see the GARP
packet for its own address. Ettercap also keeps its ARP poisoning in effect by repeatedly sending the
private GARP messages every 30 seconds.
Dynamic ARP Inspection (DAI) is used to inspect all ARP requests and replies (gratuitous or
non-gratuitous) coming from untrusted (or user-facing) ports to ensure that they belong to the ARP
owner. The ARP owner is the port that has a DHCP binding which matches the IP address contained in
the ARP reply. ARP packets from a DAI trusted port are not inspected and are bridged to their respective
VLANs.
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Figure 6-11
Using DHCP Snooping and DAI to Block ARP Attacks:
ARP 10.1.1.1
saying
10.1.1.2 is MAC C
None matching
ARPs in the
bit bucket
DHCP snooping enabled;
Dynamic ARP Inspection
enabled
ARP 10.1.1.2
saying
10.1.1.1 is MAC C
10.1.1.2
MAC B
148496
10.1.1.3
MAC C
10.1.1.1
MAC A
IP Source Guard
Function
Prevents IP host spoofing.
How It Works
IP address spoofing is commonly used to perform DoS attacks on a second party. A simple example of
this occurs when an attacker pings a third-party system while sourcing the IP address of the second party
that is being attacked (see Figure 6-12). The ping response will be directed to the second party from the
third-party system. Aggressive SYN-flooding originating from spoofed IP addresses is another common
type of attack used to overwhelm a server with TCP half-sessions.
The IP Source Guard (IPSG) feature, when invoked, dynamically creates an ACL based on the contents
of the DHCP Snooping binding table. This ACL ensures that traffic is sourced from the IP address issued
at DHCP binding time and prevents any traffic from being forwarded by other spoofed addresses. While
DHCP Snooping is a prerequisite for IP Source Guard, DAI is not. However, Cisco recommend that you
enable DAI in addition to IP Source Guard to prevent ARP-poisoning man-in-the-middle attacks in
addition to IP address spoofing.
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Network Time Services
Figure 6-12
Using IP Source Guard to Prevent Address Spoofing:
10.1.1.1
MAC A
Non-matching
traffic dropped
DHCP snooping enabled;
Dynamic ARP Inspection enabled;
IP Source Guard enabled
Traffic sent with
IP 10.1.1.2
Mac C
10.1.1.3
MAC C
Received traffic
source IP 10.1.1.2
Mac B
10.1.1.2
MAC B
148497
Traffic sent with
IP 10.1.1.3
Mac B
Network Time Services
An essential element of network management, troubleshooting, and security operations is to have all
network elements (including routers switches and servers) synchronized to a common clock source.
Network Time Protocol (NTP) is most commonly used to synchronize clocks in network equipment.
NTP provides accuracies typically within a millisecond on LANs and up to a few tens of milliseconds
on WANs.
By synchronizing the clocks across the network it is possible to examine the exact sequence in which
events occurred. This ability to analyze and correlate the sequence of events across multiple network
elements makes it much easier to determine the root cause of network problems or security issues.
The configuration section of this document shows the commands used in our network to have NTP
synchronize to an external time source. In most production the external time source used would be
redundant, dedicated hardware that synchronizes via a GPS receiver to a clock source that is itself
directly synchronized to an atomic clock.
NTP links
•
http://support.ntp.org/bin/view/Main/WebHome
•
http://en.wikipedia.org/wiki/Network_Time_Protocol
•
http://www.cisco.com/en/US/tech/tk869/tk769/technologies_white_paper09186a0080117070.shtml
•
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_white_paper0900aecd8037fdb5.s
html
•
http://www.symmetricom.com/
•
http://www.meinberg.de/english/products/
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UniDirectional Link Detection (UDLD)
UniDirectional Link Detection (UDLD)
Use UDLD to protect against one-way up/up connections. In fiber topologies where fiber optic
interconnections are used, which is common in a campus environment, physical misconnections can
occur that allow a link to appear to be up/up when there is a mismatched set of transmit/receive pairs.
When such a physical misconfiguration occurs, protocols such as EIGRP or STP can cause network
instability. UDLD detects these physical misconfigurations and disables the ports in question
Configuration
Software versions used in test network
Table 6-1
Software Releases Used in Testing
Platform
Role
SW Version
6504
Campus Core
12.2(18)SXF9
6504
Campus Distribution
12.2(18)SXF9
6504
WLAN
12.2(18)SXF9
3845
Voice WAN gateway
12.4(15)T1
ASA
Internet gateway
7.2(2)
4948
Data center
12.2(25)EWA8
4503
Access
12.2(37)SG
3750-E
Access
12.2(37)SE1
2821
Branch Router
12.4(15)T1
Lab Network used for Configuration Examples
Throughout the configuration section of this chapter, many configuration examples are shown from
actual routers and switches used in the lab build-out used to test and write this document. Figure 6-13
provides a detailed view of the lab network, that will assist in understanding the configuration examples
below.
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Configuration
Figure 6-13
TSE VoWLAN campus Architecture Detailed
VPN/TermServ = 172.28.217.25
CUCM = 10.33.32.20
DNS/DHCP = 10.33.32.5
Domain = sj.tseuc.local
Lo0 = 10.33.9.1
Lo1 = 10.33.9.2
CL
6504
.2
10 Gig
1 Gig
RP = Lo0
MSDP Peer = Lo1
7 .252
1
2 3 4
.4 .6
Core
5
CR
6504
.253 7
1 .32
.22
6
.24 5 4 3 2
.26 .28 .30
6
.10
.8
Lo0 = 10.33.9.1
Lo1 = 10.33.9.3
.12
10.33.1.x/31
Lo1 = 10.33.9.4
HSRP Primary .3
.23
STP root
1
D1L
6504
2
3
6
11
10 13 12 4 5
Lo1 = 10.33.9.5
D1R .5
6
L2 Trunk
.13
Distribution
.5
.9
.21
2
.247 3
.246
1
.9
1
2
3
6504
L2 Trunk
Lo1 = 10.33.9.7
.29
2 1
.33
Lo1 = 10.33.9.8
.31
.11
D2R
2
6504
3
Distribution
WISM = Virtual Access Layer
.29
.25
1
D2L
6504
6
4
10 11 12 13 5
.17
Lo1 = 10.33.9.6
.7
.27
.25
Lo1 = 10.33.9.9
D3L
1
.250
.33
.13
1
D3R
2
.251
6504
6 4
6
4
6504
Distribution
.5
Summary = 10.33.64.0/20
10.33.64.0/24 = data 10.33.66.0/25 = mgmt
10.33.65.0/24 = voice
10.33.2.x/30
.13
.9
.17
10.33.3.x/30
Layer 2 using HSRP/STP
.14
0/1
0/0
.10
.18
Lo1 = 10.33.9.13
0/0
0/1
.22
.30
.26
Lo1 = 10.33.9.14
1/1
1/0
.6
.34
Lo1 = 10.33.9.15
1/0
10.33.39.4
3845
3845
Voice/WAN Gateway
A1L
Summary = 10.33.16.0/20
10.33.16.0/24 = data
10.33.17.0/24 = voice
10.33.18.0/24 = data
10.33.19.0/24 = voice
T1 Data to branches
T1 voice to PSTN
FXS analogue Phone GW
A2R ASA
ASA
49
50
1/1
49
A1R
10.33.39.5
A2L
Internet Gateway
Default Route to Internet
50
A3R
4948
Data Center
4948 A3L
Summary = 10.33.32.0/20
10.33.32.0/24 = data
10.33.33.0/24 = voice
10.33.39.0/24 = Mgmt
CUCM infrastructure
Network infrastructure
(ACS, WCS, AD, DNS, DHCP etc)
.14
Lo1 = 10.33.9.19
Te1/0/1
Te2/0/1
A4R 3750-E
.10
.18
Lo1 = 10.33.9.20
1
2
4503 A4L
Summary = 10.33.48.0/20
10.33.48.0/24 = data
10.33.49.0/24 = voice
10.33.50.0/24 = data
10.33.51.0/24 = voice
APs, phones, workstations
222858
.6
Lo1 = 10.33.9.12
Campus EIGRP Routing Configuration
Campus EIGRP Routing Configuration Common to all Routers
Table 6-2 shows the configuration commands that are common to all routers/switches in the example
network. The IP addressing is based on the network diagram shown in Figure 6-1.
Table 6-2
Configuration Common to all Routers
Configuration Command (Switch D3L used for
example configuration)
Description of Configuration 
ip cef distributed
Enable CEF
key chain eigrp-chain 
key 100 
key-string cisco
Configure EIGRP authentication paramaters 
(Ensure a more secure key is used in production deployments
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Configuration
Table 6-2
Configuration Common to all Routers (continued)
interface loopback1 
description unique /32 interface on every
router 
ip address 10.33.9.8 255.255.255.255
Provides a unique IP address for every router. Can be used by
services like NTP and multicast. Also a good telnet address.
spanning-tree mode rapid-pvst
Enable spanning tree as a fail-safe practice
router eigrp 100 
passive-interface Loopback1 
network 10.0.0.0 
no auto-summary 
eigrp router-id 10.33.9.8
* Enable EIGRP; this example uses AS 100, but any valid AS
number can be substituted 
* Passive all interfaces not intended to form EIGRP
neighbors. Add any other non-routing interfaces. 
* Define the networks to route using EIGRP 
* Ensure all subnets are routed unless explicitly summerized 
* Explicitly configure the EIGRP router id as a best
practice. Use the Loopback1 address for this.
A similiar configuration is required on all
links between core and distribution or
distribution and access layers 
interface TenGigabitEthernet2/2 
description from D3L to CR 
ip address . 10.33.1.31 255.255.255.254 
ip hello-interval eigrp 100 1 
ip hold-time eigrp 100 3 
ip authentication mode eigrp 100 md5 
ip authentication key-chain eigrp 100
eigrp-chain 
load-interval 30 
carrier-delay msec 0 
mls qos trust dscp 
logging event link-status
* Use of /31 addressing on point to point links optimizes use
of IP address space in the campus 
* Tune EIGRP timers on interfaces between the Core and
Distribution layers for faster convergence. Reduce EIGRP
hello and hold timers to 1 and 3 seconds. In a point-point L3
campus design the EIGRP timers are not the primary mechanism
used for link and node failure detection (physical detection
of fiber breaks are). They are intended to provide a
fail-safe mechanism only. 
* enable eigrp authentication on this interface 
* Reduce load-interval to set the length of time (in seconds;
default is 300) for which data is used to compute load
statistics on this interface 
* Reduce carrier delay to 0. Tuning carrier delay no longer
has an impact on GigE or 10GigE interfaces but is recommended
to be configured as a best practice for network operational
consistency 
* Configure trust DSCP to provide for maximum granularity of
internal QoS queuing
Note
The base EIGRP configuration shown in the section above is common to all routers.
EIGRP Configuration Specific to Core Routers
There is no special routing policy applied to the core routers; their configuration is left as simple as
possible so as to not interfere with their primary function of routing packets.
EIGRP Configuration Specific to Distribution Routers
Table 6-3
EIGRP Configuration Specific to Distribution Routers
Configuration Command (Switch D3L used for example
configuration)
Description of Configuration 
ip access-list standard only-default 
permit 0.0.0.0
Access-list used by eigrp to only send default route to
access layer
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Configuration
Table 6-3
EIGRP Configuration Specific to Distribution Routers (continued)
router eigrp 100 
distribute-list only-default out
TenGigabitEthernet2/4 
distribute-list only-default out
TenGigabitEthernet2/6
Apply a distribute list filtering all routes other than
select default(s) to the access switches
On the interfaces to the core routers only 
Interface TenGigabitEthernet2/1 
ip summary-address eigrp 100 10.33.48.0
255.255.240.0 5
Advertise a summary address for the entire distribution
block upstream to the core 
The "5" parameter is the administrative distance which
is used to advertise a summary without installing it in
the routing table.
EIGRP Configuration Specific to Access Routers
Table 6-4
EIGRP Configuration Specific to Access Routers
Configuration Command (Switch A4R used for
example configuration)
Description of Configuration 
router eigrp 100 
* Configure EIGRP as an EIGRP stub router; advertising
passive-interface default 
connected routes upstream to the distribution. 
no passive-interface TenGigabitEthernet2/0/1  * Make passive-interface the default and explicitly remove it
no passive-interface TenGigabitEthernet2/0/1  from the links to the distribution
eigrp stub connected summary
Campus Layer 2 Spanning Tree Protocol Design for Data Center Configuration
Table 6-5
Layer 2 Configuration Specific to Distribution Switch/Routers
Configuration Command (Switch D1L used Description of Configuration 
for example configuration)
vtp domain datacenter 
vtp mode transparent
Define a VTP domain, and make all switches in it transparent mode
spanning-tree mode rapid-pvst 
no spanning-tree optimize bpdu
transmission 
spanning-tree extend system-id 
spanning-tree pathcost method long 
spanning-tree vlan 1-4094 priority
24576
Configure Rapid Per-VLAN Spanning tree. Make one of the Distribution
layer switches the STP root by configuring it with priority 24576.
Make the other Distribution layer switch the backup STP root by
configuring it with priority 28672
router eigrp 100 
passive-interface
Ensure routing updates are not sent out the Layer 2 VLANs
vlan 32 
name DataCenter-Data32
define each VLAN
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Table 6-5
Layer 2 Configuration Specific to Distribution Switch/Routers
interface Vlan32 
Configure each of the VLANs servicing the datacenter access layer with
description DataCenter-Data32 
IP address. Make the same router STP root and HSRP primary by
ip address 10.33.32.2 255.255.255.0  configuring it with priority 120. Make the other Distribution layer
no ip redirects 
switch the HSRP secondary by configuring it with priority 115
standby 1 ip 10.33.32.1 
standby 1 timers 1 3 
standby 1 priority 120 
standby 1 preempt delay minimum 60
interface TenGigabitEthernet3/6 
Configure the Layer 2 interface between the 2 Distribution layer
description Layer2_connection_TO_D1R  switches and between the Distrbution layer switches and the Data
switchport 
Centers access layer switches. Trunk the Data Center VLANs
switchport trunk encapsulation dot1q 
switchport trunk native vlan 2 
switchport trunk allowed vlan
2,32-35 
switchport mode trunk 
no ip address 
logging event link-status
Table 6-6
Layer 2 Configuration Specific to Data Center L2 Access Switches
Configuration Command (Switch A3R used for example
configuration)
Description of Configuration 
vtp domain datacenter 
vtp mode transparent
Define a VTP domain, and make all switches in it
transparent mode
spanning-tree mode rapid-pvst 
spanning-tree loopguard default 
spanning-tree portfast bpduguard default 
no spanning-tree optimize bpdu transmission 
spanning-tree extend system-id 
spanning-tree pathcost method long
Configure spanning tree. The priority statements on the
distribution layer switches will ensure the one of them
will always be the root
vlan 32 
name DataCenter-Data32
define each VLAN
interface GigabitEthernet1/1 
description All Ports assigned to access VLAN 32 
switchport access vlan 32 
switchport mode access 
no cdp enable 
spanning-tree portfast
Assign each access port to a VLAN
interface TenGigabitEthernet1/49 
description to_D1L 
switchport trunk encapsulation dot1q 
switchport trunk native vlan 2 
switchport mode trunk 
logging event link-status
Configure each of the uplinks to the distribution layer
interface Vlan32 
ip address 10.33.32.4 255.255.255.0 
exit 
ip default-gateway 10.33.32.1 
ip route 0.0.0.0 0.0.0.0 10.33.32.1
Give 1 of the VLANs an IP address so the switch can be
managed via Telnet and SNMP, and so that the switch can
connect to the NTP server 
Define a default gateway and default route so the
switch can communicate with IP devices on different
subnets
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Configuration
Campus QoS Configuration
The auto qos voip commands shown below are macros. They generate many configuration statements
that configure CoS-to-DSCP mappings, interface queue discard thresholds, the mapping of specific CoS
and DSCP values to a particular queue and threshold, and queue buffer sizes as well as generating the
specific interface QoS trust policies. The commands generated can be observed by entering the debug
auto qos command before beginning the configuration.
Table 6-7
Campus QoS Configuration Common to all Switch/Routers
Configuration Command
Description of Configuration
debug auto qos
Enable debugging for auto-QoS. When debugging is enabled, the
switch displays the QoS configuration that is automatically
generated when auto-QoS is enabled.
For uplinks/downlinks (interfaces
connected directly to other
switch/routers) 
interface interface-id 
auto qmls qos trust dscp 
end
* Specify the switch port identified as connected to a trusted
switch or router, and enter interface configuration mode 
* Configure inter-switch links to trust the DSCP settings that
have been marked by auto-qos at the network edge. 
* Return to privileged EXEC mode.
Table 6-8
Campus QoS Configuration for Access Layer Switch/Routers
Configuration Command
Description of Configuration
debug auto qos
Enable debugging for auto-QoS. When debugging is enabled, the switch
displays the QoS configuration that is automatically generated when
auto-QoS is enabled.
For interfaces connected directly to
Cisco IP Phones 
cdp enable 
interface interface-id 
auto qos voip cisco-phone 
exit
* Enable CDP globally. By default, it is enabled. 
* Specify the switch port connected to the Cisco IP Phone, and enter
interface configuration mode. 
* Enable auto-QoS on the port, and specify that the port is connected
to a Cisco IP Phone. The QoS labels of incoming packets are trusted
only when the Cisco IP Phone is detected. 
* Return to global configuration mode. 
* Repeat for as many ports as are connected to Cisco IP Phones.
For interfaces connected to directly
Cisco LWAPP APs 
interface interface-id 
auto qos voip trust 
mls qos trust dscp 
exit
* Specify the switch port connected to the Cisco LWAPP, and enter
interface configuration mode. 
* Enable auto-QoS on the port, and specify that the port is to trust
QoS and prioritize voice traffic. 
* With the auto qos voip trust macro, in addition to setting
interface queuing parameters, the switch automatically sets the
ingress classification to trust the CoS value received in the packet
on a nonrouted port or to trust the DSCP value received in the packet
on a routed port. We use this macro to have the interface queuing
parameters automatically set, but an LWAPP AP sets its QoS values in
DSCP bits not CoS bits, so we need to change the generated mls qos
trust cos to mls qos trust dscp 
* Return to global configuration mode. 
* Repeat for as many ports as are connected to Cisco LWAPP APs.
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Configuration
Campus Routed Multicast configuration
This section provides the configuration required for the campus network with the exception of the
connection to the datacenter where slightly different configuration is required for the Layer 2
connections from the distribution to the access layers.
Campus Multicast Configuration Common to all Multicast-enabled Routers
The voice/WAN Gateway routers and the Internet Gateway routers are not multicast enabled.
Table 6-9
Campus Multicast Configuration Common to all Routers
Configuration Command (sample multicast
groups used for illustration purposes)
Description of configuration
ip multicast-routing
Globally enable multicast
interface Te1/0/1 
ip pim sparse-mode
Enable PIM on all multicast-enabled interfaces 
(including VLAN interfaces)
interface Loopback2 
description Garbage-CAN RP 
ip address 2.2.2.2 255.255.255.255
Define a local loopback address to provide a sink hole route point
for invalid multicast groups
ip access-list standard GOOD-IPMC 
permit 239.1.2.3 0.0.0.0 
permit 230.230.0.0 0.0.255.255 
permit 239.192.240.0 0.0.3.255 
permit 239.192.248.0 0.0.3.255
Explicitly define what multicast groups to be forwarded to the RP 
-- permit LWAPP multicast tunnel 
-- Permit Vocera traffic 
-- Permit music on hold traffic 
-- Permit IPTV medium-rate traffic
ip pim rp-address 10.33.9.1 GOOD-IPMC
override
Send all traffic permitted by the GOOD-IPMC access-list to the
anycast RP address
ip pim rp-address 2.2.2.2
Send all multicast traffic that does not match the multicast
groups defined in GOOD-IPMC access-list to the locally-defined
Garbage-Can RP.
Campus Multicast Configuration for Core Routers
Table 6-10
Campus Multicast Configuration for Core Routers
Configuration Command (Switch CL
used for example configuration)
Description of Configuration 
interface Loopback0 
description shared MSDP local
peer address 
ip address 10.33.9.1
255.255.255.255
Loopback0 is the shared IP address that is used by all routers providing
RP functionality. All RPs can use this address concurrently. The MSDP
protocol keeps the RPs in synch with SA information. The DRs use whichever
RP its unicast routing protocol finds closest. The unicast routing
protocol will automatically provide failover if a RP fails.
interface Loopback1 
description unique router
address (for MSDP/RP and other
uses) 
ip address 10.33.9.2
255.255.255.255 
ip pim sparse-mode
Loopback1 is the unique IP address used to keep the redundant RPs in synch
by exchanging Source Active (SA) information via the MSDP protocol.
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Table 6-10
Campus Multicast Configuration for Core Routers (continued)
ip msdp peer 10.33.9.3
connect-source Loopback1
Multicast Source Distribution Protocol (MSDP) is the protocol that ensures
that all RPs which are sharing a single IP address receive updates from
each other (as muticast sources join one or other of the RPs). 
The command defines the peer routers MSDP address (its loopback1) and uses
this routers loopback1 as the source IP address
ip msdp cache-sa-state
Cache SA-pairs learnt from MSDP peer (even when there is no registered
receiver for that multicast group); this sacrifices some router memory in
order to reduce join latency.
ip msdp originator-id Loopback1
Tells an MSDP speaker that originates an SA message to use the IP address
of the Loopback1 as the RP address in the SA message
ip access-list extended
PERMIT-SOURCES 
permit ip 10.33.66.0 0.0.0.255
239.1.2.3 0.0.0.0 
permit ip 10.33.65.0 0.0.0.255
230.230.0.0 0.0.255.255 
permit ip 10.33.32.0 0.0.0.255
239.192.240.0 0.0.3.255 
permit ip 10.33.32.0 0.0.0.255
239.192.248.0 0.0.3.255
Example list of multicast source/groups permitted to register with the RPs
-- permit LWAPP multicast tunnel from controller management interfaces 
-- Permit Vocera traffic from WLAN Voice VLAN on controller 
-- Permit music on hold from the Data Center access VLAN 
-- Permit IPTV medium-rate traffic from the Data Center access VLAN
ip pim accept-register list
PERMIT-SOURCES
Configure the RPs to only accept register messages from sources explicity
defined in the PERMIT-SOURCES access list
Figure 6-14 provides a logical view of the MSDP configuration of the core switches.
Figure 6-14
Logical View of MSDP Configuration
MSDP
Lo0-10.33.9.1
L01-10.33.9.3
RP = Lo0/10.33.9.1
MSDP Peer = Lo1/10.33.9.x
222859
Lo0-10.33.9.1
L01-10.33.9.2
Campus Multicast Configuration for Distribution Routers
No multicast-specific configuration is required on distribution routers.
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Campus Multicast Configuration for Access Routers
Table 6-11
Campus Multicast configuration for Access Routers and
Configuration Command (Switch A4R
used for example configuration)
Description of Configuration 
ip pim spt-threshold infinity
Reduces multicast state (S,G) from the leaf routers by keeping traffic
on the shared tree. (Optional)
interface VLAN 50 
ip pim query-interval 250 msec
Increase the speed with which the router will detect other multicast
routers on the same subnet; and then elect a designated router for IGMP
queries and to send source registration messages to the rendezvous
point (RP).
IP igmp snooping VLAN 50
immediate-leave
Enables IGMP Fast-leave processing; upon receiving an “IGMP leave
group” message, the switch immediately removes the interface from its
Layer 2 forwarding table. Only enable this on vlans where only one host
is connected to each Layer 2 LAN interface.
Campus Multicast Configuration for Layer 2 Switches used for Data Center
This section provides the configuration required for the datacenter where slightly different configuration
is required for the Layer 2 connections from the distribution to the access layers.
Campus Multicast configuration for Layer 2 Distribution-Layer switches used for Datacenter
Table 6-12
Campus Multicast configuration for Layer 2 Distribution-Layer Switches used for Data Center
configuration command 
(Switch D1L used for example config)
Description of configuration
ip multicast-routing
Globally enable multicast
spanning-tree vlan 32 root primary 
interface VLAN 32 
standby 1 priority 120 
ip pim dr-priority 120
The root STP bridge, the HSRP active node, and the PIM DR should
all be on the same distribution switch for each specific VLAN.
interface VLAN 32 
ip pim query-interval 250 msec
Increase the speed with which the router will detect other
multicast routers on the same subnet; and then elect a designated
router for IGMP queries and to send source registration messages to
the rendezvous point (RP).
interface vlan32 
ip igmp snooping fast-leave
Enables IGMP Fast-leave processing; upon receiving an “IGMP leave
group” message, the switch immediately removes the interface from
its Layer 2 forwarding table. Only enable this on vlans where only
one host is connected to each Layer 2 LAN interface.
interface VLAN 32 
ip pim sparse-mode
Enable PIM on all multicast-enabled VLANs
interface Loopback2 
description Garbage-CAN RP 
ip address 2.2.2.2 255.255.255.255
Define a local loopback address to provide a sink hole route point
for invalid multicast groups
ip access-list standard GOOD-IPMC 
permit 239.1.2.3 0.0.0.0 
permit 230.230.0.0 0.0.255.255 
permit 239.192.240.0 0.0.3.255 
permit 239.192.248.0 0.0.3.255
Explicitly define what multicast groups to be forwarded to the RP 
-- permit LWAPP multicast tunnel 
-- Permit Vocera traffic 
-- Permit music on hold traffic 
-- Permit IPTV medium-rate traffic
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Table 6-12
Campus Multicast configuration for Layer 2 Distribution-Layer Switches used for Data Center (continued)
ip pim rp-address 10.33.9.1 GOOD-IPMC
override
Send all traffic permitted by the GOOD-IPMC access-list to the
anycast RP address
ip pim rp-address 2.2.2.2
Send all multicast traffic that does not match the multicast groups
defined in GOOD-IPMC access-list to the locally-defined Garbage-Can
RP.
Campus Multicast Configuration for Layer 2 ACcess-Layer Switches used for Data Center
No multicast-specific configuration is required on L2 access layer switches.
Campus Multicast Configuration for Layer 2 Switches used for Data Center Verification
Table 6-13
Verifying the L2 Multicast Configuration for the Data Center
configuration command
Description of configuration
show spanning-tree summary 
show standby brief
show ip pim interface
These commands can be used to check that spanning-tree root,
HSRP active, and PIM DR are all on the same router for a given
VLAN
Access Switch Catalyst Integrated Security Features (CISF) Configuration
The configuration below is applied to all access layer switches that will have end-users or APs connected
to them. The port security configuration permits a maximum of 2 MAC addresses; this is enough for a
Cisco IP phone with an attached PC to be connected. An LWAPP AP tunnels all client traffic to the
LWAPP controller, so the switch it is connected to will only ever see the MAC and IP address of the AP
on that port.
Table 6-14
Switch Security Configuration
Configuration command
Description of Configuration
DHCP Snooping 
ip dhcp snooping vlan 50 51 
no ip dhcp snooping information option 
ip dhcp snooping
Globally enable DHCP Snooping 
These commands will put every VLAN 50 and VLAN 51 port into
"untrusted" state. If the path to the DHCP server is out one
of these switch ports, that port should be manually set to
"trusted"
Dynamic Arp Inspection (DAI) 
ip arp inspection 
vlan 50,51 
ip dhcp snooping database
tftp://10.33.32.10/tftpboot/cisco/a4r-dhcpd
b
Globally enable Dynamic ARP Inspection (DAI), and make sure
the DHCP snooping database is backed up. (DAI requires an
accurate DHCP snooping database, and backing up to TFTP
ensures its preservation - even if the switch reboots)
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Table 6-14
Switch Security Configuration (continued)
Port Security 
interface commands to enable Port Security
interface GigabitEthernet1/0/1 
switchport access vlan 50 
switchport mode access 
switchport voice vlan 51 
switchport port-security 
switchport port-security maximum 2 
switchport port-security violation restrict 
switchport port-security aging time 2 
switchport port-security aging type
inactivity
IP Source Guard 
interface GigabitEthernet1/0/1
ip verify source
Interface command to enable IP Source Guard
interface GigabitEthernet1/0/1 
ip dhcp snooping limit rate 10
Interface command to limit the number of DHCP messages an
interface can receive per second
Router Time Services Configuration
Table 6-15
Campus Router Time Services Configuration
Configuration Command
Description of Configuration
service timestamps debug datetime msec
localtime 
service timestamps log datetime msec
localtime
Add timestamps with millisecond resolution to debug and log
messages; use the local timezone to represent the time
clock timezone PST -8 
clock summer-time PDT recurring 
clock update-calendar
* Internally, the router uses Universal Coordinated Time (AKA
GMT); these commands configure the router to display time in a
local time. 
* The timezone command uses a user-defined label and the local
offset from UTC as parameters. 
* The summer-time command configures the router to
automatically adjust the local-time displayed in accordance
with daylight saving conventions; the default is for North
America conventions, other regions daylight saving conventions
can be explicitly configured if required
ntp source Loopback1 
ntp server 10.33.32.16
* Source NTP Queries from Loopback1 interface instead of the
interface that sends them. This ensures the NTP server always
sees the same source IP and is useful if the NTP server limits
the number of NTP Peers that can associate, of if it has
Access Control Lists controlling what devices can sync with
it. 
* The NTP Server command defines the IP address of the NTP
server.
show ntp status 
show clock details
Useful show commands for verifying correct NTP operation
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Configuration
Uni-Directional Link Detection (UDLD) Configuration
Table 6-16
UniDirectional Link Detection (UDLD) Configuration
configuration command
Description of configuration
uldp enable
Globally enables ULDP on all fiber-optic ports
UDLD is not supported on the ASAs or 3800s used in this document, and is enabled by default on the
4948s.
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Voice over WLAN Unified Communications Test
Architecture
Cisco Unified Communications Manager Introduction
Cisco Unified Communications Manager (Cisco UCM) is the call-processing component of the Cisco
Unified Communications System (previously known as Cisco CallManager). The Cisco UCM extends
enterprise telephony features and capabilities to IP phones, media processing devices, gateways, mobile
devices and multimedia applications. Additional services such as unified messaging, multimedia
conferencing, collaborative contact centers, and interactive multimedia response systems interact with
the IP telephony solution through Cisco UCM APIs. The Cisco UCM is installed on Cisco Media
Convergence Server (MCS) 7800 Series of server platforms and selected third-party servers. An example
of Cisco UCM and several possible services and endpoints is shown in Figure 7-1.
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Figure 7-1
Cisco Unified Communications Manager Example
g
Cluster
V
IP
M
Gateways
Cisco Unified
Presence Server
M
M
M
Microsoft
OCS
M
MeetingPlace/
MP Express
IBM
Sametime
Cisco Unified
Personal
Communicator
Cisco IP
Communicator
Unity/Unity
Connection
IP
Cisco and
Third-Party
Phones
Video
Endpoints
Contact Center
IPCC
IPCC
IP IVR
222960
IPCC
IPCC
Enterprise Express
This Cisco UCM design is based on the existing Cisco Unified Communications Solution Reference
Network Design (based on Cisco UCM Release 6.x):
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/6x/uc6_0.html
Cisco Unified Communications System Release Summary Matrix for IP Telephony:
http://www.cisco.com/en/US/docs/voice_ip_comm/uc_system/unified/communications/system/ver
sions/IPTMtrix.html
Cisco Unified Communications Manager Design Overview
Deployment Models
There are several deployment models for Cisco UCM based on the following factors:
•
Number of call processing agent clusters
•
Number of IP phones
•
Locations of the call processing cluster(s) and IP phones
Single Site
The single-site model for Cisco Unified Communications consists of a call processing agent cluster
located at a single site, or campus, with no telephony services provided over an IP WAN.
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Multisite WAN with Centralized Call Processing
The model for a multisite WAN deployment with centralized call processing consists of a single call
processing cluster that provides services for many remote sites and uses the IP WAN to transport Cisco
Unified Communications traffic between the sites.
Multisite WAN with Distributed Call Processing
The model for a multisite WAN deployment with distributed call processing consists of multiple
independent sites, each with its own call processing cluster connected to an IP WAN that carries voice
traffic between the distributed sites
Clustering Over the IP WAN
It is possible to deploy a single UCM cluster across multiple sites that are connected by a QoS-enabled
IP WAN. For specific WAN requirements, refer to the Cisco Unified Communications Solution
Reference Network Design:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/6x/uc6_0.html
Each deployment model has benefits and network requirements that should be considered. Further
descriptions of the Cisco Unified Communications Manager Deployment models are available within the
Cisco Unified Communications Solution Reference Network Design.
The design considerations presented in this chapter were based on the use of a Multisite WAN with
Centralized Call Processing deployment. This model consists of a centralized call processing cluster and
one or more remote sites using an IP WAN to transport voice and call control.
Figure 7-2 is an example of a Multisite WAN with Centralized Call Processing with one branch location.
Figure 7-2
Multisite with Centralized Call Processing
Cisco Unified
Communications Manager
Cluster
M
M
M
PSTN
M
M
V
IP WAN
SRST-enabled
Router
IP
IP
IP
IP
Headquarters
IP
222961
Branch A
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Wireless phones (and softphones) are inherently mobile so controlling the admission of their calls into
a network is critical to maintaining the quality of calls by avoiding traffic collisions leading to loss, jitter
and delay perceptible to the user. The next two sections will discuss CAC and Device Mobility and how
Device Mobility configuration is important to maintaining accurate CAC decisions.
Call Admission Control
This chapter discusses Call Admission Control (CAC) by the Cisco UCM for those devices on the
physical IP LAN/WAN, in the context of a single cluster design. This applies to wireless phones (Cisco
7920/7921) from the point of entry into the physical network. CAC must also be considered on the
wireless network and is discussed in detail in the Chapter 2, “WLAN Quality of Service.”
CAC in the context of this chapter is a concept that applies to real-time (voice) traffic only, not data
traffic. If an influx of data traffic oversubscribes a particular link in the network, queuing, buffering, and
packet drop decisions resolve the congestion. The extra traffic is simply delayed until the interface
becomes available to send the traffic, or, if traffic is dropped, protocol timeouts or user-initiated actions
will trigger the re-transmission of the information.
Network congestion cannot be resolved in this manner when real-time traffic, sensitive to both latency
and packet loss, is present, without jeopardizing the quality of service (QoS) expected by the users of
that traffic. For real-time delay-sensitive traffic such as voice, it is better to deny network access under
congestion conditions than to allow traffic onto the network to be dropped and delayed, resulting in
sporadic impairments perceived by the users.
QoS protects voice from being overrun by data. CAC on the other hand, protects voice from voice. If a
link can support X calls, allowing X + 1 calls will have a negative impact on calls being carried by that
link. CAC is therefore a deterministic and informed decision that is made before a voice call is
established and is based on whether the required network resources are available to provide suitable QoS
for the new call.
Considering Figure 7-3, because it is based on a packet-switched network (the IP network), no circuits
are established to setup an IP telephony call. Instead, the IP packets containing the voice samples are
simply routed across the IP network together with other types of data packets. QoS is used to
differentiate the voice packets from the data packets, but bandwidth resources, especially on IP WAN
links, are not infinite. Therefore, network administrators dedicate a certain amount of "priority"
bandwidth to voice traffic on each IP WAN link. However, once the provisioned bandwidth has been
fully used, the IP telephony system must reject subsequent calls to avoid oversubscription of the priority
queue on the IP WAN link, which would cause quality degradation for all voice calls.
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CAC Example
Circuit-Switched
Networks
Packet-Switched
Networks
PSTN
PSTN
Physical
Trunks
PBX
Third call
rejected
IP WAN link provisioned
for 2 VoIP calls (equivalent
to 2 “virtual” trunks)
No physical limitation
on IP links.
Third call can go through,
but voice quality of all
calls degrades.
->Call admission
control prevents this
problem.
IP WAN
Link
STOP
V
Router/
Gateway
IP
Cisco Unified CM
M
IP
IP
126670
Figure 7-3
Most CAC control mechanisms fall into two categories:
•
Topology-unaware call admission control—Based on a static configuration within the call
processing agent
•
Topology-aware call admission control—Based on communication between the call processing
agent and the network about the available resources
Topology-unaware CAC is based on the UCM construct of CAC static locations, with each branch site
belonging to a unique location. All devices in a site are assigned to the same location. Based on the
amount of bandwidth available, each site would support a specific number of calls over the IP WAN.
Topology-aware CAC limits the number of calls across the IP WAN using real-time communications
about the availability of network resources between the UCM and the network. This CAC mechanism
works well in environments with constant topology changes as it can dynamically adjust to the changes,
or with non hub-and-spoke WAN topologies. Resource Reservation Protocol (RSVP) is the primary
industry-standard signaling protocol that enables an application to reserve bandwidth dynamically
across an IP network. Using RSVP, applications can request a certain amount of bandwidth for a data
flow across a network (for example, a voice call) and can receive an indication of the outcome of the
reservation based on actual resource availability.
For this version of the design guide, static locations-based CAC (topology-unaware) was used. For an
in-depth discussion of CAC, refer to Cisco Unified Communications Solution Reference Network Design
at the following URL:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/6x/uc6_0.html
Device Mobility
Mobility of wireless phones includes not just moving between access points within a building but also
moving between buildings and locations. If a wireless phone user is defined with a UCM region and
location specific to their home location (for example, San Jose) takes their phone to a branch office in
somewhere else (for example, in RTP), it is important that device mobility is configured so the WAN
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links between these location are not oversubscribed. Without device mobility, when the users phone
registers in the branch location (RTP), the UCM configuration for the phone assumes they have
registered in San Jose. If the user dials a PSTN number in RTP, UCM may use a gateway in San Jose and
also not deduct bandwidth that the phone is using over the WAN link between RTP and San Jose,
possibly causing and over-subscription environment.
Device mobility allows UCM to make device configuration decisions based on the subnet of the device
that is registering. Some of the device mobility elements include:
•
Device Mobility Info—Configures IP subnets and associates device pools to the IP subnets.
•
Device Mobility Group—Defines a logical group of sites with similar dialing patterns (for example,
US_dmg and EUR_dmg).
•
Physical Location—Defines the physical location of a device pool. In other words, this element
defines the geographic location of IP phones and other devices associated with the device pool.
UCM uses a new set of parameters under the device pool configuration to accommodate device mobility.
These parameters are of the following two main types:
•
Roaming Sensitive Settings
•
Device Mobility Related Settings
Roaming Sensitive Settings
The parameters under these settings override the device-level settings when the device is roaming within
or outside a device mobility group. The parameters included in these settings are:
•
Date/Time Group
•
Region
•
Media Resource Group List
•
Location
•
Network Locale
•
SRST Reference
•
Physical Location
•
Device Mobility Group
The roaming sensitive settings primarily help in achieving proper CAC and voice codec selection,
because the location and region configurations are used based on the device's roaming device pool. The
roaming sensitive settings also update the media resource group list (MRGL) so that appropriate remote
media resources are used for music on hold, conferencing, transcoding, and so forth, thus utilizing the
network efficiently. The roaming sensitive settings also update the Survivable Remote Site Telephony
(SRST) gateway. Mobile users register to a different SRST gateway while roaming.
Device Mobility Related Settings
The parameters under these settings will override the device-level settings only when the device is
roaming within a device mobility group. The parameters included in these settings are:
•
Device Mobility Calling Search Space
•
AAR Calling Search Space
•
AAR Group
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The device mobility related settings affect the dial plan because the calling search space dictates the
patterns that can be dialed or the devices that can be reached. Device mobility group, as explained earlier,
defines a logical group of sites with similar dialing patterns (for example, sites having the same PSTN
access codes and so forth). With this guideline, all sites have similar dialing patterns in the site-specific
calling search spaces. Sites having different dialing behavior are in a different device mobility group. A
user roaming within a device mobility group may preserve his dialing behavior at the remote location
even after receiving a new calling search space. A user roaming outside the device mobility group may
still preserve his dialing behavior at the remote location because he uses his home calling search space.
However, if a device mobility group is defined with sites having different dialing patterns (for example,
sites having different PSTN access codes), then a user roaming within that device mobility group might
not preserve his same dialing behavior at all locations. A user might have to dial digits differently at
different locations after receiving a new calling search space at each location.
For an in-depth discussion of device mobility, refer to Cisco Unified Communications Solution
Reference Network Design:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/6x/uc6_0.html
Network Infrastructure
Refer to the Cisco Unified Communications Solution Reference Network Design for additional network
infrastructure recommendations.
UCM and Phone versions
This design guide use the following Cisco UCM and phone versions:
•
Cisco UCM 6.0.1
•
7960—SCCP41.8-3-1S
•
7921—CP7921G-1.0.34
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Voice over WLAN Wireless LAN Controller
Design and Configuration
Wireless LAN Controller (WLC) configuration can vary from VoWLAN handset to VoWLAN handset
and specific configuration settings can also depend on the requirements of the overall WLAN data
network. Variations are principally targeted to the WLAN configuration on the WLC. There are also
certain key Cisco Unified Wireless configuration considerations that directly affect the overall VoWLAN
design and implementation—in particular, IEEE 802.11 wireless network configurations can have an
effect.
Chapter 3, “Voice over WLAN Radio Frequency Design,” addresses the guidelines for AP location, AP
density, and Auto-RF features. This chapter focuses on Auto-RF configuration and WLC network
configuration.
RF design cannot be ignored. Implementing an architecture featuring the correct location and density of
APs for a WLAN network is the equivalent of correctly installing the cable plant for a wired network.
In wired network, problems in the cable plant cannot be completely overcome by advanced features.
Similarly, in the WLAN network, Auto-RF is unlikely to overcome a flawed AP deployment. This
chapter addresses wireless network and Auto-RF configuration.
Network Configuration
The radio configuration of each AP should be left to Auto-RF , unless there are know issues at the site
that preclude the effective use of Auto-RF.. The configuration for the AP network is performed under
the IEEE 802.11b/g/n and IEEE 802.11a/n subsections of the wireless menu.
Data Rates
The goal in setting the data rates for the VoWLAN network is to match the data rates of VoWLAN
handsets as closely as possible. For example, if the VoWLAN RF network design was based on a 24
Mbps data-rate, lower data-rates should be excluded if possible. This would only be possible when not
supporting IEEE 802.11 1Mbps and 2Mbps and IEEE 802.11b 5.5Mbps and 11Mbps clients. Any
lowering of the data-rate below that used in the RF design extends the AP cell size, increases co-channel
interference, and reduces call capacity. Higher data rates than the site survey rate can be enabled, but a
VoWLAN client might not take advantage of these rates because some VoWLANs prefer not to data rate
shift. An example of the 24 Mbps and above configuration is shown in Figure 8-1.
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Network Configuration
Figure 8-1
Channel Data Rate Setting
The general global parameters (see Figure 8-2) for a channel can normally be kept at the default values.
Some VoWLAN handsets might require the delivery traffic indication Map (DTIM) to be increased to
maximize battery life, but this change should only be done based on design recommendation specific to
the handset. The DTIM period sets the number of beacon intervals that a WLAN client will sleep before
waking up to see whether any traffic has been buffered for it (when in power save mode). Multicast and
broadcast traffic must be buffered—as well as any unicast traffic—when destined for power saving
clients. This can affect application performance, so DTIM should only be adjusted to the levels
recommend by the VoWLAN handset vendor. DTIM settings are global for the band and are not changed
on a per WLAN basis; therefore, changing the DTIM value will affect each WLAN on a given AP radio.
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Figure 8-2
General Global Parameters
Radio Resource Management
Radio Resource Management (RRM) can adjust AP channels (dynamic channel assignment) and power
(dynamic transmit power control) to maintain the RF coverage and quality:
•
It adjusts the power level of the APs to maintain a baseline signal strength with neighboring APs at
-70 dBm (configurable, and default value changed from -65dBm to -70dBm in the 4.1.185 code
Release).
•
It adjust the power levels of the APs to increase the SNR of WLAN clients that are detected with
poor SNRs.
•
It adjusts the channel of the AP when it notices nearby interference sources on the channel which
the AP is currently located.
•
It continues to optimize the RF coverage for the best reception and throughput for the wireless
network.
RRM addresses the issue that RF environments are not static. As different RF variables change (people
in the room, amount of devices stored in the facility, leaves on trees for outside deployment, interference
from different RF sources, and so on), the RF coverage changes with them.
Because these variables change continuously, monitoring for the RF coverage and adjusting it
periodically is necessary, and RRM is an automatic mechanism for adjusting for changes in RF variables.
For more detailed information on RRM (Auto-RF), see the following URL:
http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008072c759.shtml
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RRM Architecture Overview
Each WLC is configured with a RF-Network Name (the RF-Group Name, which is by default the same
as the Mobility Group Name). WLCs with the same RF-Network Name can be part of the same RF
Group. The RF-Network Name configuration is found in the Controller General Configuration menu, as
shown in Figure 8-3.
Figure 8-3
RF-Network Name
In each RF group (if Group Mode is enabled in the Auto-RF configuration, Figure 8-4), the WLCs elect
a leader and form an RF domain. The function of the leader is to collect the network-wide neighbor
information from a group of WLCs and do the channel/power computation for an optimal system-wide
map. If Group Mode is not enabled, the WLCs run computations based only on the neighbor data
gathered from the APs connected to that WLC via LWAPP, trying to optimize the signal to -70 dBm
between APs.
The APs transmit RRM neighbor packets at full power at regular intervals. These messages contain a
field that is a hash of the RF group name, BSSID, and time stamp:
•
The APs accept only RRM neighbor packets sent with this RF network name.
•
When neighboring APs receive neighbor messages, they validate them before forwarding them to
the WLC.
•
If they can validate the message hash and confirm that it belongs to the same RF group, the packet
is sent to the WLC; otherwise, the AP drops the neighbor packet.
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•
The APs forwards validated messages to the WLC, filling in the LWAPP packet status field with the
SNR and RSSI of the received neighbor packet.
Logical RF Sub-groups
Within an AP group there may be clusters of APs that do not see each other, even if they are connected
to the same WLC or connected to different WLCs that are part of the same RF group. In this case, theses
APs form a logical RF sub-group whose RF parameters are calculated separately( i.e., the Auto-RF
algorithms are calculated per RF sub-group).
Channel Scanning
The APs goes "off-channel" for a period not greater than 60 ms to listen to the other channels. Packet
headers collected during this time are sent to the WLC, where they are analyzed to detect rogue APs,
whether service set identifiers (SSIDs) are broadcast or not, rogue clients, ad-hoc clients, and interfering
APs. By default, each AP spends approximately 0.2 percent of its time off-channel. This is statistically
distributed across all APs so that no two adjacent APs are scanning at the same time. Packets received
by the AP from clients are forwarded to the WLC with the LWAPP status field filled-in, which provides
the WLC with radio information including RSSI and signal-to-noise ratio (SNR) for all packets received
by the AP during reception of the packet. For more detailed information on RRM (Auto-RF), see the
following URL:
http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008072c759.shtml
RF Group
Figure 8-4 shows the RF Group configuration section of Auto-RF. In this area the Group Mode is enabled
(if it is not enabled. the WLC considers only its own AP information in its RRM calculations). The
display also identifies the Group Leader (the WLC responsible for the RF Group).
Figure 8-4
RF Group Configuration
Dynamic Channel Assignment
The next section in the Auto RF configuration section is RF Channel Assignment, shown in Figure 8-5.
This feature controls Dynamic Channel Assignment (DCA).
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Figure 8-5
RF Channel Assignment
The DCA algorithm, run by the RF Group Leader (the Channel Assignment Leader), is applied on a
per-RF (sub) Group basis to determine optimal AP channel settings for all the RF (sub) Group APs. With
the DCA process, the RF Group Leader (a WLC) considers a group of RF metrics to determine whether
a change in AP channel scheme is appropriate.
•
Avoid Foreign AP Interference—APs report the percentage of the medium taken up by interfering
IEEE 802.11 transmissions (this can be caused by overlapping signals from foreign APs, as well as
non-neighbors).This field allows the co-channel interference metric to be included in DCA
algorithm calculations. This field is enabled by default.
•
Avoid Cisco AP Load—Every AP measures the percentage of total time occupied by transmitting or
receiving IEEE 802.11 frames This field allows the utilization of APs to be considered when
determining which AP’s channels need changing. AP load is a frequently changing metric and its
inclusion might not be always desired in the RRM calculations. As such, this field is disabled by
default. The Cisco AP Load parameter is a measure of channel load seen by the APs in the RF Group.
It includes the co-channel interference generated by neighboring APs and clients.
•
Avoid non-IEEE 802.11b Noise—APs calculate noise values on every serviced channel. This field
allows each AP’s non-IEEE 802.11 noise level to be a contributing factor to the DCA algorithm. This
field is enabled by default.
•
Signal Strength Contribution—Every AP listens for Neighbor Messages on all serviced channels
and records the RSSI values at which these messages are heard. This AP signal strength information
is the most important metric considered in the DCA calculation of channel energy. The signal
strength of neighboring APs is always included in DCA calculations. This is a display-only field and
cannot be modified.
These values are used by the RF Group Leader to determine whether another channel schema will result
in an improvement of at least 5 dB (SNR) for the worst performing AP. A weighting is given to APs on
their operating channels to bias them into maintaining their channels. As a result, adjustments are kept
local; the weighting dampens changes preventing a domino effect in which a single change triggers
system-wide channel alterations. Preference is also given to APs based on utilization (derived from each
AP’s load measurement report). A less-used AP has a higher likelihood of having its channel changed
(as compared to a heavily used neighbor) in the event a change is needed.
Note
Whenever an AP channel is changed, clients are briefly disconnected. Clients can either reconnect to the
same AP (on its new channel), or roam to a nearby AP depending on client roaming behavior. Fast,
secure roaming—offered by both Cisco Centralized Key Management (CCKM) and Proactive Key
Caching (PKC)—will help reduce this brief disruption, assuming clients are compatible.
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The following WLC commands provide visibility of the RF data collected by each AP:
show ap auto-rf IEEE 802.11b
show ap auto-rf IEEE 802.11a
ap-name
ap-name
The following is an example output using the show ap auto rf command:
Cisco Controller> show ap auto-rf IEEE 802.11b AP0012.d92b.5cfa
Number Of Slots.................................. 2
AP Name.......................................... AP0012.d92b.5cfa
MAC Address...................................... 00:12:d9:2b:5c:fa
Radio Type..................................... RADIO_TYPE_IEEE 80211b/g
Noise Information
Noise Profile................................ PASSED
Channel 1.................................... -97 dBm
Channel 2.................................... -96 dBm
Channel 3.................................... -95 dBm
Channel 4.................................... -99 dBm
Channel 5.................................... -96 dBm
Channel 6.................................... -96 dBm
Channel 7.................................... -93 dBm
Channel 8.................................... -95 dBm
Channel 9.................................... -100 dBm
Channel 10................................... -96 dBm
Channel 11................................... -96 dBm
Interference Information
Interference Profile......................... PASSED
Channel 1.................................... -128 dBm @ 0 % busy
Channel 2.................................... -82 dBm @ 1 % busy
Channel 3.................................... -128 dBm @ 0 % busy
Channel 4.................................... -128 dBm @ 0 % busy
Channel 5.................................... -76 dBm @ 1 % busy
Channel 6.................................... -128 dBm @ 0 % busy
Channel 7.................................... -75 dBm @ 1 % busy
Channel 8.................................... -128 dBm @ 0 % busy
Channel 9.................................... -128 dBm @ 0 % busy
Channel 10................................... -128 dBm @ 0 % busy
Channel 11................................... -70 dBm @ 2 % busy
Load Information
Load Profile................................. PASSED
Receive Utilization.......................... 2 %
Transmit Utilization......................... 1 %
Channel Utilization.......................... 3 %
Attached Clients............................. 0 clients
Coverage Information
Coverage Profile............................. PASSED
Failed Clients............................... 0 clients
Client Signal Strengths
RSSI -100 dbm................................ 0 clients
RSSI -92 dbm................................ 0 clients
RSSI -84 dbm................................ 0 clients
RSSI -76 dbm................................ 0 clients
RSSI -68 dbm................................ 0 clients
RSSI -60 dbm................................ 0 clients
RSSI -52 dbm................................ 0 clients
Client Signal To Noise Ratios
SNR
0 dB.................................. 0 clients
SNR
5 dB.................................. 0 clients
SNR
10 dB.................................. 0 clients
SNR
15 dB.................................. 0 clients
SNR
20 dB.................................. 0 clients
SNR
25 dB.................................. 0 clients
SNR
30 dB.................................. 0 clients
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SNR
35 dB..................................
SNR
40 dB..................................
SNR
45 dB..................................
Nearby APs
AP 00:0b:85:51:63:60 slot 1..................
AP 00:0b:85:52:40:d0 slot 1..................
AP 00:12:44:b3:c1:f0 slot 0..................
AP 00:14:1b:59:40:20 slot 0..................
AP 00:17:df:36:99:80 slot 0..................
Radar Information
Channel Assignment Information
Current Channel Average Energy...............
Previous Channel Average Energy..............
Channel Change Count.........................
Last Channel Change Time.....................
Recommended Best Channel.....................
RF Parameter Recommendations
Power Level..................................
RTS/CTS Threshold............................
Fragmentation Tnreshold......................
Antenna Pattern..............................
0 clients
0 clients
0 clients
-36
-36
-32
-36
-59
dBm
dBm
dBm
dBm
dBm
on
6 (192.168.60.10)
on 11 (192.168.60.10)
on
6 (192.168.60.10)
on 11 (192.168.60.10)
on 11 (192.168.60.10)
unknown
unknown
0
Fri Oct 12 01:37:57 2007
1
7
2347
2346
0
Tx Power Level Assignment
The Tx Power Level Assignment is controlled by the Transmission Power Control (TPC) algorithm (see
Figure 8-6) is run at fixed 10-minute intervals by default. It is used by the RF Group Leader to determine
AP RF proximity and adjust each band’s transmit power level in order to limit excessive cell overlap and
co-channel interference. Each AP reports an RSSI-ordered list of all neighboring APs and—provided an
AP has three or more neighboring APs—the RF Group Leader will apply the TPC algorithm on a
per-band, per-AP basis in order to adjust AP power transmit levels downward such that the third loudest
neighbor AP will then be heard at a signal level of -70 dBm (default value, with the 4.1.185 code release,
but earlier code default of -65dBm may be inherited from a pre-existing configuration) or lower. Power
changes are only made when an AP's third loudest neighbor is heard at a signal level higher than the
default value of -70 dBm (there is a 6dB hysteresis used built into the TPC algorithm to prevent it from
continuously hunting for the -70dBm value).
The TPC algorithm it not aware of the physical location of the APs or of requirements to run the APs at
a higher or lower power due to some deployment issues. This needs to be considered in AP planning and
deployment.
TPC is not aware of AP location or the coverage requirements of the WLAN deployment following
should be observed for optimal power level and coverage:
•
APs should be located close to the perimeters of the building to ensure that coverage extends to these
areas.
•
APs should be distributed as evenly as possible to ensure that neighbor signals reflective of coverage
requirements
•
As the TPC algorithm is three dimensional, and an even AP distribution assists TPC, different floors
should not have the same AP layout ( i.e., APs should be staggered per floor).
•
TPC not is aware of the goals for RF coverage and cell overlap that drove your AP placement.
Therefore you should verify that your RF needs are being met by Auto-RF by performing a site
survey after deployment and Auto-RF has performed its adjustments.
•
Auto-RF should be monitored to track the adjustments made by Auto-RF. Auto-RF will be making
adjustments to assist the WLAN network to make changes, but these change can mean that
something has happened that you did not plan our design for, and this should be investigated.
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Figure 8-6
Tx Power Level Assignment Algorithm
Coverage Hole Algorithm
The Coverage Hole Algorithm is used to detect holes in coverage based on WLAN client signal
measurements and to adjust AP power to address low client-signal levels. A coverage hole is considered
to have occurred when client SNRs falls below a predetermined level. The number of clients required to
trigger action is configurable as is the signal level. The Coverage Hole Algorithm section from the
Auto-RF page is shown in Figure 8-7
Figure 8-7
Coverage Hole Algorithm
Maintaining VoWLAN coverage is critical for a successful VoWLAN service, so coverage hole
protection is an important component in a VoWLAN deployment. As with many design considerations,
a decision must be made favoring one characteristic over another:
•
If the Coverage Hole algorithm is made overly sensitive, it can trigger power increases in APs that
are caused by client characteristics rather than coverage issues. This issue can occur with older
non-Cisco compatible extension clients that might stay associated with an AP even though that
association features a poor SNR. This can result in hole coverage being triggered and AP power
being set too high. Poor planning can also trigger hole coverage. VoWLAN clients might be
operating in an area where WLAN coverage was not planned and this might cause hole coverage to
be triggered.
•
If the Coverage Hole is too insensitive, VoWLAN clients might lose calls due to a coverage holes.
Given the variables involved, there are no hard-and-fast rules for specific the Coverage Hole settings. It
is best to start with the default settings for the Coverage Hole Algorithm and to monitor any coverage
adjustments. If many APs are increasing the power levels, there might be a client issue. If a small group
of APs are making coverage adjustments there might be a RF coverage issue.
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Monitor Intervals
The Monitor Intervals section for the Auto-RF page is shown in Figure 8-8. These parameters determine
how often the AP stops serving clients to perform RRM and Wireless duties. There is no need to adjust
these values as part of the design process and they should only be adjusted when directed by Cisco
support.
Figure 8-8
Monitor Intervals
Dynamic Channel Allocation
Figure 8-9 shows the Dynamic Channel Allocation (DCA) screen of RRM. This screen allows the
selection of channels for use by the DCA algorithm. Figure 8-9 shows the channels have been selected
in the 5 GHz band for use in this example. In this case, the UNII-1 and UNII-3 bands have been chosen
to avoid in any Dynamic Frequency Selection (DFS) issues that might affect the VoWLAN network.
Channels subject to DFS may be selected if the customer is sure that DFS is not going to be triggered at
that site. DFS is required to avoid radar that operates in nominated channels.
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Figure 8-9
Channel Selection for DCA
Client Roaming
Figure 8-10 shows the Client Roaming Screen of RRM. The parameters presented in this screen are
communicated to Cisco compatible extension clients to inform them of parameters that should trigger a
client roam. The default values might be a little low for a VoWLAN deployment because the AP cell
sizes of VoWLAN deployments are usually smaller. While WLAN data clients can maintain their
connection at a point where a VoWLAN client should roam, data clients should also roam as close as
possible to the planned cell boundary to minimize the range of co-channel interference from these
clients. The minimum values for the Minimum RSSI is -80 dBm, and the minimum value for the Scan
Threshold is -70 dBm. These should be tested against typical WLAN data clients and used in VoWLAN
deployments unless they are found to interfere with normal WLAN data client operation.
Note
If the VoWLAN deployment is using lower client boundary power levels than our example, then different
thresholds should be applied.
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Figure 8-10
Client Roaming Parameters
Voice Call Admission Control
Figure 8-11 shows the Voice Call Admission Control screen of RRM. The default values (Max RF
Bandwidth value equals 75 percent) are set high to prevent rejection of calls when suitable capacity is
available.
Figure 8-11
Voice Call Admission Control
For best performance, the most accurate assessment of call capacity—Load-based AC—should be
enabled. Admission Control enabled by itself uses the APs capacity to calculate the Call Admission
Control (CAC). Load-based AC incorporates the channel capacity into the CAC determination and gives
a much more accurate assessment of the current call-carrying capacity of the AP. Settings for the Max
RF bandwidth and Reserved Bandwidth values depend on the VoWLAN handsets, the data rates used,
and the other sources of the WLAN load. However, the Max RF Reservation should not be greater than
60 percent. At levels greater than 60 percent, the IEEE 802.11 protocol itself can start to be under stress
with increases in retransmission. This can impact call quality even if WMM is being used, particularly
if the is a number of voice calls are already in progress. Testing with the Cisco Unified IP Phone 7921G
in both the 2.4 GHz and 5 GHz bands using the recommended signal levels and SNR suggests that the
minimum value for the Maximum Bandwidth Reservation parameter of between 40 to 60 percent is also
the best setting for this specific phone. Call quality starts to deteriorate when the Max RF Bandwidth is
set at or below these levels.
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General Cisco Unified Wireless Network Configuration
General Cisco Unified Wireless Network Configuration
This section focuses on VoWLAN specifics of the WLC network configuration. The connection to the
wired network is addressed in the The Enterprise Mobility 4.1 Design Guide, as are considerations
affecting the decision to implement centralized or distributed WLCs.
The centralized WLC model was used in this design guide because it is the recommended deployment
model of the The Enterprise Mobility 4.1 Design Guide, but no design features or characteristics unique
to the centralized WLC model were implemented. The Cisco Unified IP Phone 7921G handset
deployments discussed in this guide works equally well in either a centralized or distributed WLC
deployment, but only the centralized model was tested and documented in this guide.
Quality of Service Policy
The quality-of-service (QoS) per-user bandwidth and over the air QoS policy settings on the WLC
should be left at their defaults. The WLC, by default, does the appropriate conversion between IEEE
class of service (CoS) values and Cisco QoS baseline, when CoS marking is enabled (Wired Protocol
802.1p) Differentiated Services Code Point (DSCP) and CoS values. An example of the a QoS Profile
for Platinum QoS with CoS Marking is shown in Figure 8-12.
Figure 8-12
Example Platinum QoS Profile
We recommend that the QoS policy on the router/switch interfaces connected to the WLC be set to trust
the CoS settings of the WLC. This means that the wired network responds to the CoS values controlled
by the QoS policy set on the WLC. The WLC does not enforce any policy that changes the WLAN client
DSCP values. The WLC policy effects will only be seen in the CoS values associated with the WLAN
client traffic. If the routers and switches connecting to the WLC are set to trust DSCP, then a DSCP
policy must be created and maintained on those router and switch interfaces—in addition to the policies
applied on the WLC. For more information on WLAN QoS and traffic classification, refer to the
Chapter 3, “Voice over WLAN Radio Frequency Design.”
Note
CSCsi78368 means that the WLC sets incorrect CoS values in the 4.1.185 code, but this is fixed in the
WLC Release 4.2.61.0.
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General Cisco Unified Wireless Network Configuration
Mobility Groups
The APs (and associated WLCs) for an area of continuous VoWLAN coverage should be part of the same
Mobility Group. If this is not the case, call quality is likely to be affected during a VoWLAN client roam
between mobility groups because VoWLAN client state information will not be transferred between the
WLCs of the two different groups. Given that there can be up to 24 WLCs per Mobility Group, it is
unlikely that there is a requirement for multiple Mobility Groups in most enterprise deployments.
AP Groups
AP Groups were not used in this design guide. Customers might wish to implement AP Groups to map
different VLANs on a WLC to the same WLAN SSID on different APs. This would allow VoWLAN
client associated to APs in one building to use a different subnet to the VoWLAN clients from another
building. The primary purpose of using AP Groups in this manner is to minimize the size of WLAN
broadcast domains, or share WLAN client traffic across multiple VLANs. Another purpose is to have
the WLAN subnet size fit a standard size used in the general campus design. Unless broadcast or
multicast traffic has been enabled on the Cisco Unified Wireless Network, there is no need to minimize
subnet size to control the WLAN broadcast domain because the Cisco Unified Wireless Network default
prevents broadcast and multicast traffic from being sent over of the WLAN. This allows all the clients
on the same WLC’s WLAN to be on the same subnet without broadcast/multicast domain issues.
Multicast Traffic
The transmission of multicast and broadcast traffic over the WLAN is disabled by default on the Cisco
Unified Wireless Network. Unless there is a specific application requirement (such as the use of Vocera
badges), it should remained disabled. When multicast is enabled on the Cisco Unified Wireless Network,
it is enabled on every WLAN—although it might only be required on a single WLAN. Given that the
multicast traffic on a WLAN is sent out every AP radio with clients associated to that WLAN regardless
of that client(s) requirements, every effort should be made to minimize the multicast traffic on every
WLC WLAN interface. You can minimize the potential affects of multicast traffic by disabling IGMP
on interfaces not requiring multicast and filtering multicast traffic on interfaces that have IGMP enabled.
For more information on WLC multicast features, refer to Chapter 6 of the Enterprise Mobility 4.1
Design Guide at this URL:
http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/emob41dg/ch6_Mcst.html
Note
In WLC 4.2 software release, Internet Group Management Protocol (IGMP) snooping is introduced to
better direct multicast packets, and block the unwanted multicast traffic addressed above. When this
feature is enabled, an access point transmits multicast packets only if a client associated to the access
point is subscribed to the multicast group. This feature was not tested and documented this guide, but it
is recommended that customers implement the feature.
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9
Voice over WLAN Troubleshooting and
Management Tools
One of the challenges in mobility is the fact that users are mobile, and while they have an investment in
ensuring that their end device is working correctly, they have less of an investment in a piece of
geography. That is, while a user will address what they perceive as an equipment issue promptly, they
are less likely to spend time addressing what they perceive as coverage issues as they will simply move
on to another location. This means that you are more likely to get help desk calls if users cannot connect,
but coverage and performance issues are more likely to be anecdotal. Unless time and effort are invested
to ensure coverage issues are address proactively, user satisfaction can be low before the issues make
into a operations and maintenance case. For this reason the primary focus in this chapter will be the use
of tools to translate user anecdotes into system parameters, and tools to proactively identify potential
coverage and performance issues.
WLC Tools
The WLC provides many different debug and show commands to assist in general trouble shooting. In
the case of VoWLAN two help screens in analyzing VoWLAN quality issues are shown in Figure 9-1
and Figure 9-2. Figure 9-1 shows the client traffic Stream metrics, which provides information upon the
packet delay and packet loss experience by a client on an AP. As packet delay and loss are key parameters
in VoIP call quality the traffic stream measures provide network insight in to the call quality experienced
by a client.
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Figure 9-1
Note
WLC Client Traffic Stream Metrics
In Figure 9-1, uplink statistics have not been reported by the VoWLAN client, and therefore the data is
all zeros.
Figure 9-2 shows AP radio statistics, including channel load, channel noise, client RSSI and SNR and
AP Neighbor information from RRM. This can provide more general information about the RF
environment that VoWLAN clients are operating in which parameters may be impacting VoWLAN call
quality.
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WCS Tools
Figure 9-2
AP Radio Statistics
WCS Tools
While the WLC can provide AP statistics and client traffic stream statistics, the WCS is the best place
to start VoWLAN trouble shooting. This is because the WCS provides the topological visibility through
its building and floor plan maps providing a way to translate the user complaint “I seem to have trouble
with calls in building x on floor y” into there seems to be an issue involving APs X1, X2, and X3. In
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WCS Tools
addition to providing this translation between the physical world to the network world, the WCS
provides a centralized location for viewing and aggregation of the same statistics shown by the WLC, as
well as providing reports of how key parameters have changed over time
Monitoring
Figure 9-3 shows similar AP statistics to those shown in by the WLC in Figure 9-2; the WLC allows
these to be shown in text format or graphical format.
Figure 9-3
AP Statistics
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Alarms
The WCS provides an aggregation point for alarms. Figure 9-4 shows an example of an alarm that may
provide input to a VoWLAN issue, that is, a Coverage Hole alarm. Excessive hole coverage alarms that
are unrelated to an actual AP issue may indicate a RF coverage issue users are in an area inadequately
covered due either to planning, implementation or operational issue. The Coverage Hole alarms may also
be indicative of a sticky client issue where a WLAN client is not roaming into a better coverage area.
Figure 9-4
Hole Coverage Alarm
Reports
The WCS reports provide insight into key VoWLAN parameters over time, helping to correlate network
parameters with the timing of particular incidents, and allowing trending of key parameters overtime.
Figure 9-5 shows an example of the a graph from the AP TxPower and Channel report, excessive changes
in this area may indicate a systematic RF interference issue to be investigated or an indication that the
Auto-RF configuration of the network may need to be tuned to better fit the environment and
deployment.
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Figure 9-5
Power and Channel Reports
Figure 9-6 shows an example of the voice bandwidth statistics report, these reports can used to track
possible call capacity and admission control issues.
Figure 9-6
Voice Statistics
Figure 9-7 shows an example of the client traffic stream metrics, similar to that shown in the WLC in
Figure 9-1, but it has the advantage of providing information upon roaming delay, and providing client
traffic stream information across APs, and WLCs.
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Figure 9-7
Traffic Stream Statistics
Figure 9-8 shows an example of a traffic stream metrics graph which provides tracking of key stream
parameters over time. This allows the correlation of traffic stream parameters with specific events and
the trending of these parameters over time.
Figure 9-8
Traffic Stream Metrics Graph
Third Party Tools
AirMagnet Surveyor Pro
We have already discussed the importance of site surveys in RF design session. While the WCS planning
tools and WCS RF visualization tools provide a picture of the RF environment, but these are predictions
of the RF environment, and if there is one invariable law of computing it is “Garbage in Garbage Out”.
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Despite the effort and care applied at the front end of the system the only true measure of their quality
and the prediction system is to measure the output. The means of output measurement is a site survey.
A site survey can be as simple as measuring signal strength and performance on sample client devices,
but, site survey tools such as Airmagnet provide a much richer interface view of the data collected and
value added tools to analyze the RF data. The site survey data associated with the floor plan, as shown
in Figure 9-9, allows the RF coverage maps of the WCS be validated against data in the WLAN client
domain. Given that the WCS maps are a key remote trouble shooting tool, it is also key that these maps
be validated by performing a site survey. http://www.airmagnet.com/products/survey/.
Figure 9-9
Example of an Airmagnet Survey
In addition the Airmagnet Site Survey through its AirWise feature provides and assessment of the the
VoWLAN readiness of the environment analyzing key parameters such as coverage and AP overlap, and
providing planning prediction of network changes based upon the collected survey data.
VoWLAN Analysis
One of the challenges in VoWLAN analysis is determining call quality. Most VoIP systems provide a
Mean Opinion Score (MoS) score, but these MoS scores are not always readily accessible and their
values are not consistent across devices. The VoFi analyzer from Airmagnet provides a readily
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accessible means of measuring VoWLAN voice quality overtime for multiple handsets. Figure 9-10
shows an example of a VoFi Analyzer capture for a group of 11a handsets. Section 1 shows a pie chart
of the distribution of MoS scores across handsets, section 2 shows the a histogram of calls and MoS
scores over time, and section three shows the MoS values of individual handsets over time.
Figure 9-10
VoFi 11a Analysis
For more information about VoFi11a, refer to the following URL:
http://www.airmagnet.com/products/vofi_analyzer/
CACE Technologies and Wireshark
One of the challenges in troubleshooting WLAN issues is capturing traffic on multiple channels while
maintaining accurate timing information. CACE Technologies provides USB WLAN NICs, and a USB
hub with drivers to allow the multiple WLAN NICs configured for different channels and connected to
the hub, can deliver capture data to Wireshark. Figure 9-11 shows an example of the AirPcap interfaces
for Wireshark. The interfaces are available individually and an aggregated capture from all AirPcap
adaptors is also available.
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Figure 9-11
Wireshark Capture Interfaces
Cisco Spectrum Expert
WLAN networks can suffer performance degradation caused by changes in the environment.
Interference—caused by WLAN transmissions as well as signals radiating from WLAN electronic
equipment—accounts for the majority of spectrum problems. Interfering devices may include Bluetooth
devices, fluorescent lights, microwave ovens, wireless video and audio monitors, cordless computer
mice, and millions of other device types. A standard WLAN site survey tool is designed to measure
WLAN coverage. It uses a WLAN chipset to measure the signal strength of APs as you move around the
building. Unfortunately, WLAN chips are designed to decode WLAN signals only, and can’t tell you
much about interference from other WLAN devices. (This is the same limitation experienced when using
a WLAN packet analysis tool.) A WLAN site survey tool might indicate a general area where a WLAN
signal was observed. But the tool can’t directly help you determine the nature of the interference, the
type of device causing it, or where the device is located. The Cisco Spectrum Expert analyzer has
intelligent spectrum management tools that provide a straightforward view into exactly what devices are
on the network at any given time and where they are located. With such visibility, enterprises can address
critical problems dynamically and can also set policies that eliminate or control interfering devices that
might be clogging the WLAN spectrum. At the time of writing, Cisco Spectrum Expert is a recent Cisco
acquisition, please check www.cisco.com for the most up to date information on Cisco Spectrum
Expert’s availability and capabilities
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Figure 9-12
Example Cisco Spectrum Expert Screen Capture
For more information about Cisco Spectrum Expert, refer to the following URL:
http://www.cisco.com/en/US/products/ps9393/index.html
WildPackets OmniPeek
The Omni Peak network analyzer provides comprehensive WLAN protocols decodes and an filtering as
well as VoIP analysis. Unfortunately the VoIP analysis like that of the Wireshark relies upon analyzing
the RTP stream, which on a typical WLAN would encrypted and unavailable from a WLAN capture. For
VoIP analysis the capture and analysis must be performed after the WLC.
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Figure 9-13
Example OmniPeek VoIP Analysis
For more information about OmniPeek, refer to the following URL:
http://www.wildpackets.com/products/omnipeek/overview
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10
Cisco Unified IP Phone 7921 Implementation for
Voice over WLAN
This chapter describes how to deploy the Cisco Unified Wireless IP Phone 7921G in the context of a
Voice over WLAN (VoWLAN) environment. This chapter provides a brief introduction to the Cisco
Unified Wireless IP Phone 7921G in general which is followed by detailed implementation guidance
about the following deployment topics:
•
Network Connectivity Test Configuration for Cisco Unified Wireless IP Phone 7921, page 10-2
•
Cisco Unified Wireless IP Phone 7921 Security, page 10-16
•
Cisco Unified Wireless IP Phone 7921 RF Considerations, page 10-24
•
Cisco Unified Wireless IP Phone 7921 QoS, page 10-27
•
Cisco Unified Wireless IP Phone 7921 Troubleshooting, page 10-33
Cisco Unified Wireless IP Phone 7921 Overview
The Cisco Unified Wireless IP Phone 7921G is an IEEE 802.11 dual-band wireless device that provides
comprehensive voice communications in conjunction with Cisco Unified Communications Manager and
Cisco Aironet IEEE 802.11a/b/g access points (AP) in a private business communications network. This
phone model supports G.711a, G.711u, G.729a and G.729ab audio compression coder-decoders
(CODEC). You must configure and manage a wireless IP phone like other IP phones and wireless devices
on your network. The wireless IP phone supports multiple lines and most of the IP phone features of
other Cisco Unified IP phones. Figure 10-1 shows the Cisco Unified Wireless IP Phone 7921G.
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Figure 10-1
Cisco Unified IP Phone 7921 Implementation for Voice over WLAN
Cisco Unified Wireless IP Phone 7921G
Refer to the to the following URL for the complete list of Cisco Unified Wireless IP Phone 7921G
features, specifications, and capabilities:
http://www.cisco.com/en/US/products/hw/phones/ps379/products_data_sheet0900aecd805e315d.html
Network Connectivity Test Configuration for Cisco Unified
Wireless IP Phone 7921
This section provides the minimal configuration necessary to get the Cisco Unified Wireless IP Phone
7921 connected to the network and communicating with the Cisco Unified Communications Manager.
The intent of this section is to make it as simple as possible to verify that the network infrastructure is
correctly configured for 7921 connectivity. Subsequent sections provide guidance for the addition of the
necessary security, RF, and QoS features. Specific topics addressed in this section include the following:
Warning
•
WLAN Controller Network Connectivity Test Configuration, page 10-2
•
Network Infrastructure Base Configuration, page 10-4
•
Cisco Unified Communications Manager Base Configuration, page 10-10
•
Cisco Unified Wireless IP Phone 7921 Base Configuration, page 10-13
•
Trace Analysis for a Base Configuration, page 10-14
This network connectivity test configuration should not be left active in a production network, as it
provides no security against unauthorized access.
WLAN Controller Network Connectivity Test Configuration
This section provides implementation guidance for initial WLAN Controller configuration.
Creating a Voice WLAN
Creating a WLAN with the minimum necessary configuration needed to test Cisco Unified Wireless IP
Phone 7921 connectivity can be done using the following steps on the controller GUI.
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Step 1
Click the WLANs tab in the controller GUI.
Step 2
Click the New button at the top-right corner of the page.
Step 3
For the new WLAN, define a profile name and use the Cisco Unified Wireless IP Phone 7921 default of
cisco for the SSID.
Step 4
Click Apply.
Step 5
The WLANs > Edit page loads. See Figure 10-2.
Figure 10-2
WLANs > Edit Page
\
Step 6
Check WLAN Status box to signal that this new WLAN should be enabled.
Step 7
Change the Interface drop-down box to point to a user-defined dynamic interface (you must have
predefined a dynamic interface; do not use the management interface)
Step 8
Click the Security tab.
Step 9
Change the Layer-2 Security drop-down box to None.
Step 10
Click the QoS tab.
Step 11
Change the Quality of Service (QoS) drop-down box to Platinum (voice).
Step 12
Click the Apply button at the top-right corner of the page
When the base controller WLAN configuration is complete, the WLAN window should look similar to
Figure 10-3.
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Figure 10-3
Cisco Unified IP Phone 7921 Implementation for Voice over WLAN
WLANs Page with Base Configuration
Network Infrastructure Base Configuration
The network infrastructure used by the Cisco Unified Wireless IP Phone 7921 must provide DNS and
DHCP services. These services are required for any Cisco IP phone, so they might be previously defined
in many customer networks. If they are not defined, the following two sections provide details on how
to define them.
Configuring the DHCP Server to Support Cisco Unified Communications Manager Option 150
To connect any Cisco IP phone, including the Cisco Unified Wireless IP Phone 7921, you must configure
your DHCP server to provide option 150—the address of the TFTP server used by the phones to
download the latest firmware version. Most networks use the default TFTP server provided with the
Cisco Unified Communications Manager itself, so option 150 in the phones scope must point to the
Cisco Unified Communications Manager IP address.
Step 1
Right-click appropriate DHCP Server and select Set Predefined Options. See Figure 10-4.
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Figure 10-4
Step 2
Click Add in the Predefined Options and Values pop-up window. See Figure 10-5.
Figure 10-5
Step 3
Setting Predefined Options
Selecting the Add Option
Fill out the new option and click OK. See Figure 10-6.
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Figure 10-6
Step 4
Entering the Option Type Information
Enter in the IP address of the Cisco Unified Communications Manager and click OK. See Figure 10-7.
Figure 10-7
Step 5
Cisco Unified IP Phone 7921 Implementation for Voice over WLAN
Entering IP Address in Predefined Options and Values
Configure the DHCP server to pass the newly defined option 150 to all DHCP clients. Select Server
Options, then click Configure Options. See Figure 10-8.
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Figure 10-8
Step 6
Select your newly created class from the drop-down menu, check your newly created option 150, and
click OK. See Figure 10-9.
Figure 10-9
Step 7
Choosing DHCP Server Configuration Options
Choosing Option 150 from Server Options
Select a DHCP scope and verify that option 150 now shows up in the Scope Options window. See
Figure 10-10.
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Figure 10-10
Cisco Unified IP Phone 7921 Implementation for Voice over WLAN
DHCP Scope Options Window
Configuring the DNS with Cisco Unified Communications Manager Entries
An Cisco IP phone (including the Cisco Unified Wireless IP Phone 7921) uses DHCP option 150 to learn
the IP address of an associated TFTP server. An Cisco IP phone downloads its configuration file from
the TFTP server. That configuration file contains the name of the Cisco Unified Communications
Manager publisher and subscribers. The Cisco IP phone uses DNS to resolve a Cisco Unified
Communications Manager name into an IP address that can be used with IP telephony registration
messages.
If Cisco IP phones have already been deployed, the DNS configuration will already be complete, and
this step can be skipped.
The following steps must be completed once for the Cisco Unified Communications Manager publisher,
and once for each of the Cisco Unified Communications Manager subscribers.
Step 1
From the DNS server console, right-click the relevant forward lookup zone, and select New Host (A)...
See Figure 10-11.
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Figure 10-11
Step 2
New Host (A)
Fill out the Name and IP address of the Cisco Unified Communications Manager publisher server or
subscriber server and click Add Host. See Figure 10-12.
The “Cisco Unified Communications Manager Base Configuration” section on page 10-10 describes
how to determine the Cisco Unified Communications Manager name from Cisco Unified
Communications Manager administration.
Figure 10-12
Entering New Host Name
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Step 3
Click OK to acknowledge the success message. See Figure 10-13.
Figure 10-13
Step 4
Cisco Unified IP Phone 7921 Implementation for Voice over WLAN
Acknowledging Successful Host Record Creation
Either, fill out the Name and IP address of the next Cisco Unified Communications Manager publisher
server or subscriber server and click Add Host, or click Done to exit DNS configuration. See
Figure 10-14.
Figure 10-14
Entering Cisco Unified Communications Manager Publisher Information
Cisco Unified Communications Manager Base Configuration
This section assumes a Cisco Unified Communications Manager installation pre-exists and provides
procedures for verifying the necessary settings to enable a Cisco Unified Wireless IP Phone 7921 to
successfully operate.
Verifying Cisco Unified Communications Manager Name
You must know the Cisco Unified Communications Manager server name in order to ensure that it is
correctly configured in the DNS server as described in the “Configuring the DNS with Cisco Unified
Communications Manager Entries” section on page 10-8. From Cisco Unified Communications
Manager administration window, navigate to System > Server > Find. By leaving all the Find fields
blank, the system will display all Cisco Unified Communications Manager names known to the system.
See Figure 10-15.
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Figure 10-15
Verifying Cisco Unified Communications Manager Server Names
Verifying Auto-Registration Enabled
The simplest way to enable Cisco Unified Wireless IP Phone 7921 registration to a Cisco Unified
Communications Manager is to enable auto-registration. To verify or enable auto-registration, navigate
to System > Cisco Unified CM > Find. When the Find action completes, click the relevant Cisco Unified
Communications Manager name and verify that auto-registration is enabled on that Cisco Unified
Communications Manager. See Figure 10-16.
In production environments, auto-registration is often disabled and phones are added by explicitly
defining each phone in Cisco Unified Communications Manager. Follow the procedures established at
your site for adding phones.
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Figure 10-16
Cisco Unified IP Phone 7921 Implementation for Voice over WLAN
Cisco Unified Communications Manager Auto Registration:
Verifying Cisco Unified Wireless IP Phone 7921 Firmware
The Cisco Unified Wireless IP Phone 7921 updates its firmware from the Cisco Unified Communications
Manager TFTP server. Customers are strongly encouraged to run the most recent release of Cisco
Unified Wireless IP Phone 7921 firmware. The current release on Cisco.com can be determined by going
to http://www.cisco.com, logging in, and navigating to Support > Download Software > Voice Software
> Cisco Unified Wireless IP Phone Firmware. Make a note of the most recent version of firmware
available on Cisco.com, and ensure the same version is loaded in the Cisco Unified Communications
Manager by navigating on Cisco Unified Communications Manager to Device > Device Settings >
Device Defaults. See Figure 10-17.
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Figure 10-17
Cisco Unified Communications Manager Device Defaults
Cisco Unified Wireless IP Phone 7921 Base Configuration
Baseline configuration for the IP phone consist of two procedures:
•
Resetting the IP Phone, page 10-13
•
Configuring a WLAN Profile, page 10-14
Resetting the IP Phone
If necessary, reset the Cisco Unified Wireless IP Phone 7921 to factory defaults. The factory default
option erases all user-defined entries in Network Profiles, Phone Settings, and Call History. To erase the
local configuration, follow these steps:
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Step 1
Press the Navigation Button downwards to enter SETTINGS mode
Step 2
Navigate to and select Phone Settings.
Step 3
Press **2 on the keypad. The phone briefly displays this prompt: Restore to Default?
Step 4
Press the Yes softkey to confirm or No to cancel. The phone resets after selecting Yes
Configuring a WLAN Profile
The following procedure summarizes the process of configuring the WLAN profile:
Step 1
Press the Navigation Button downwards to enter SETTINGS mode
Step 2
Navigate to and select Network Profiles (pressing the number adjacent to a menu item is equivalent to
selecting that item).
Step 3
Unlock the IP phone’s configuration menu by pressing **#. The padlock icon on the top-right of the
screen will change from closed to open.
Step 4
Navigate to the profile you want to change and press the Change softkey.
Step 5
Navigate to and select Profile Name.
Step 6
Use the IP phone’s keypad to enter a profile name. Normally this name will match the corresponding
WLAN profile name defined on the Cisco Wireless LAN Controller (Cisco WLC).
Step 7
Navigate to and select WLAN Configuration.
Step 8
Navigate to and select SSID.
Step 9
Use the IP phone’s keypad to enter a SSID name (normally this name will match the corresponding
WLAN SSID name defined on the Cisco WLC).
Step 10
Press the Back softkey until the Exit softkey appears.
Step 11
Press the Exit softkey.
Trace Analysis for a Base Configuration
This section presents annotated sections of a trace of a Cisco Unified Wireless IP Phone 7921 being
connected to a network for the first time. Five distinct sections of this trace are examined—highlighting
the different stages of the connection. See Figure 10-18. The first section shows the initial connection
and the start of the TFTP download.
Because this is the first time the Cisco Unified Wireless IP Phone 7921 has connected, its firmware is
out of date. One of the first files the phone downloads contains the name of the firmware image that the
Cisco Unified Wireless IP Phone 7921 should be running. The Cisco Unified Wireless IP Phone 7921
will see this and will download the specified firmware image. Because of the need to download a new
firmware image, the TFTP process takes longer than it would if the Cisco Unified Wireless IP Phone
7921 was already running the correct firmware.
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Figure 10-18
Initial Cisco Unified Wireless IP Phone 7921 Connect Trace (Part 1)
Figure 10-19 illustrates the end of the initial TFTP download sequence. At this point five TFTP files
containing the Cisco Unified Wireless IP Phone 7921 configuration and firmware have been
downloaded.
Figure 10-19
Initial Cisco Unified Wireless IP Phone 7921 Connect Trace (Part 2)
Figure 10-20 illustrates that the Cisco Unified Wireless IP Phone 7921 has downloaded and installed the
new firmware, and then rebooted. The TFTP download in this case is much shorter and quicker.
Figure 10-20
Initial Cisco Unified Wireless IP Phone 7921 Connect Trace (Part 3)
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Figure 10-21 illustrates the conclusion of the normal TFTP sequence, the ARPs verifying that the IP
address is unique, and a DNS lookup to resolve the name to IP address of the Cisco Unified
Communications Manager publisher and subscriber that learned via the TFTP configuration file. The
Cisco Unified Wireless IP Phone 7921 then starts a TCP connection to the subscriber Cisco Unified
Communications Manager and begins the phone registration process (shown here as the skinny protocol).
Figure 10-21
Initial Cisco Unified Wireless IP Phone 7921 Connect Trace (Part 4)
Cisco Unified Wireless IP Phone 7921 Security
The Cisco Unified Wireless IP Phone 7921 supports the following WLAN security options:
•
Security protocols
– Wi-Fi Protected Access (WPA) Versions 1 and 2; Personal and Enterprise
•
Authentication
– Lightweight Extensible Authentication Protocol (LEAP) Authentication
– Extensible Authentication Protocol-Flexible Authentication via Secure Tunneling (EAP-FAST)
– WEP/WPA/WPA2 Shared Key
•
Encryption
– Wired Equivalent Privacy (WEP)
– Temporal Key Integrity Protocol (TKIP)
– Advanced Encryption Standard (AES)
•
Fast roaming protocol
– Cisco Centralized Key Management (CCKM)
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The remainder of the Cisco Unified Wireless IP Phone 7921 security section provided in this chapter
focuses on the items listed that comprise the current best practice recommendations for secure Cisco
Unified Wireless IP Phone 7921 deployments. More information on other Cisco Unified Wireless IP
Phone 7921 security options is available in the product documentation available at
http://www.cisco.com.
Controller WLAN Security Configuration
The optimal configuration for the controller configuration for the WLAN supporting Cisco Unified
Wireless IP Phone 7921s is for the WPA security protocol with TKIP encryption and IEEE 802.1X with
CCKM key management.
The combination of WPA, TKIP, IEEE 802.1X/CCKM provides the strongest supported authentication,
encryption, and key management with CCKM for fast secure roaming between APs. Chapter 5, “Voice
over WLAN Roaming,” provides additional details addressing CCKM and describes why it is necessary
to achieve voice handset roam times between APs in less than the ITU G.114 recommended maximum
delay of 150 msec.
Note
Cisco Unified Wireless IP Phone 7921s do not support WPA2 with TKIP encryption.
Note
Cisco Unified Wireless IP Phone 7921s support WPA2 with AES encryption, but CCKM is not supported
in this combination. Even though CCKM can be configured, and the Cisco Unified Wireless IP Phone
7921s appear to connect successfully, CCKM will not be used when roaming between APs in this
combination.
The recommended configuration is shown Figure 10-22.
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Figure 10-22
Cisco WLC Security Layer 2 Recommended Configuration
The recommended configuration uses IEEE 802.1X key management; that necessitates a RADIUS
server for authentication. RADIUS server information is added to the controller by navigating Security
> RADIUS > Authentication.
Cisco WLAN Controllers also support a mode known as Local EAP. When you enable Local EAP, the
controller serves as the authentication server and the local user database, thereby removing dependence
on an external authentication server. Local EAP is designed for use in remote offices that must maintain
connectivity to wireless clients when the remote external authentication server is lost.
Figure 10-23 shows a RADIUS server definition being added to a controller. In Figure 10-23, the Server
IP Address field is the IP address of the external RADIUS server. The shared secret is defined on both
the controller and the RADIUS server; it is used to secure communications between the two. Chapter 4,
“Voice over WLAN Security,” provides details about configuring the Cisco ACS server to act as the
external RADIUS server for wireless LAN EAP authentication.
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Figure 10-23
Adding a RADIUS server to the Controller
Once the external RADIUS server definition has been added to the controller, the RADIUS server can
be selected from the drop-down box for use by individual WLANs. Figure 10-24 shows a RADIUS
server being selected from the WLANs > Security > AAA Servers tab.
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Figure 10-24
Selecting Cisco WLC Security AAA Servers
Setting the WLAN Controller IEEE 802.1X Timeout for EAP-FAST
When using EAP-FAST, the IEEE 802.1X timeout on the controller must be increased (default = 2
seconds) in order for the client to obtain the PAC via automatic provisioning. The default timeout on the
Cisco ACS server is 20 seconds, which is the recommended value. To change the IEEE 802.1X timeout
on the Cisco Wireless LAN controller, connect using Telnet or SSH to the controller and enter the
following command:
(Cisco Controller)> config advanced eap request-timeout 20
(Cisco Controller)> show advanced eap
EAP-Identity-Request Timeout (seconds)........... 1
EAP-Identity-Request Max Retries................ 20
EAP Key-Index for Dynamic WEP.................... 0
EAP-Request Timeout (seconds)................... 20
EAP-Request Max Retries.......................... 2
Cisco Unified Communications Manager Security Configuration
The Cisco Unified Wireless IP Phone 7921G supports the following voice security features:
•
Certificates
•
Image authentication
•
Device authentication
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•
File authentication
•
Signaling authentication
•
Secure Cisco Unified SRST
•
Media encryption (SRTP)
The Cisco Unified Communications Manager provides these available voice security features. For more
information, refer to the Cisco Unified Communications Manager documentation at
http://www.cisco.com/en/US/products/sw/voicesw/ps556/tsd_products_support_series_home.html
Network infrastructure Security Configuration
EAP-FAST authenticates to a RADIUS server. In this section, we configure the Cisco ACS server to
support EAP-FAST authentication.
Every network device performing EAP authentication must be defined to the ACS as an AAA Client. On
the ACS, we define the controller as an AAA Client by navigating Network Configuration > (select a
group if device groups are being used) > Add Entry. Figure 10-25 shows an example of a controller being
defined on the ACS.
Figure 10-25
Cisco ACS Configuration—Adding NAS
Every Cisco Unified Wireless IP Phone 7921 using EAP-FAST is configured with a userid and a
password.
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It is possible to configure multiple Cisco Unified Wireless IP Phone 7921s with the same userid and
password. This is useful for small test deployments, but should be avoided in productions deployments
where the loss of a single phone could require all deployed phones to be reconfigured.
Figure 10-26 shows a Cisco Unified Wireless IP Phone 7921s userid and password being configured on
the ACS. This is done by navigating User Setup > (enter the name of the new user being added) >
Add/Edit.
Figure 10-26
ACS Configuration—Adding a User
The ACS must also be configured to explicitly support EAP-FAST authentication. The Cisco Unified
Wireless IP Phone 7921G currently supports only automatic provisioning of the Protected Access
Credential (PAC), so Anonymous In-Band PAC Provisioning must be enabled. EAP-FAST is configured
by navigating System Configuration > Global Authentication Setup > EAP-FAST Configuration. See
Figure 10-27.
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Figure 10-27
ACS Configuration—EAP-FAST Settings
Cisco Unified Wireless IP Phone 7921 Security Configuration
The “Cisco Unified Wireless IP Phone 7921 Base Configuration” section on page 10-13 covered
resetting a Cisco Unified Wireless IP Phone 7921 to factory defaults (if necessary) and adding a new
WLAN Profile. Follow the instructions in that section to create a new WLAN profile for a EAP-FAST
WLAN. This section focuses on configuring EAP-FAST.
Configure a WLAN Profile to use EAP-FAST Authentication
Cisco Unified Wireless IP Phone 7921s can be configured to use EAP-FAST with a specific userid and
password as described in the following procedure.
Step 1
Press the Navigation Button downwards to enter SETTINGS mode
Step 2
Navigate to and select Network Profiles (pressing the number adjacent to a menu item is equivalent to
selecting that item).
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Step 3
Unlock the phones configuration menu by pressing **#. The padlock icon on the top-right of the screen
will change from closed to open.
Step 4
Navigate to the profile you want to change and press the Change softkey.
Step 5
Navigate to and select WLAN Configuration.
Step 6
Navigate to and select Security Mode.
Step 7
Navigate to and select EAP-FAST.
Step 8
Press the Save soft-key.
Step 9
Navigate to and select UserName.
Step 10
Use the IP phone’s keypad to enter a username (press the Select button to enter).
Step 11
Navigate to and select Password.
Step 12
Use the IP phone’s keypad to enter a password (press the select button to enter).
Step 13
Press the Back softkey until Network Profiles re-appears.
Step 14
Select the newly added profile for EAP-FAST and de-select the old profile.
Step 15
Press the Back softkey until the Exit softkey appears.
Step 16
Press the Exit softkey,
Cisco Unified Wireless IP Phone 7921 RF Considerations
A well-designed and effectively deployed RF environment is critical for a successful VoWLAN
implementation. A wireless network that appears to function well for data traffic might provide
unsatisfactory coverage for a voice deployment. This is because data applications can often tolerate
packet delays or recover from packet loss that would be disruptive to a voice call.
Refer to the datasheet at the following URL for Cisco Unified Wireless IP Phone 7921 RF specifications:
http://www.cisco.com/en/US/products/hw/phones/ps379/products_data_sheet0900aecd805e315d.h
tml
Chapter 3, “Voice over WLAN Radio Frequency Design,” provides general RF deployment guidance as
well as voice call capacity information. In particular, the following general VoWLAN guidelines, as
stated in the RF design for voice, are applicable to the Cisco Unified Wireless IP Phone 7921:
•
VoWLAN networks require overlaps of about 20 percent (for 2.4 GHz), and about 15 percent (for 5
GHz), where a WLAN data design might use an AP cell overlap of 5-to-10 percent.
•
The recommended VoWLAN cell boundary recommendation is -67 dBm, while a WLAN data cell
boundary might be acceptable at lower power levels.
Choosing Between IEEE 802.11b/g and IEEE 802.11a
It is a common customer requirement to deploy voice on the relatively interference-free IEEE 802.11a
5 GHz frequency band (see Chapter 3, “Voice over WLAN Radio Frequency Design,” for more details).
There are two ways in which voice can be restricted to just one frequency band (IEEE 802.11a or just
IEEE 802.11b/g).
•
By configuring the phone to use one frequency band
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•
By configuring the WLAN on the controller to support only one frequency band
Configuration guidance for these two option is provided in the sections that follow.
The recommended method used to limit the Cisco Unified Wireless IP Phone 7921 operation to a single
frequency band is to leave the phones at their default setting and to configure the WLAN on the
controller—or Cisco Wireless Control System (WCS)—to operate on the required frequency band.
Cisco Unified Wireless IP Phone 7921 RF Configuration
The Cisco Unified Wireless IP Phone 7921 is enabled for all IEEE 802.11 frequency bands (IEEE
802.11b/g and IEEE 802.11a) by default. The frequency band used can be changed with the following
procedure:
Step 1
Press the Navigation Button downwards to enter SETTINGS mode.
Step 2
Navigate to and select Network Profiles (pressing the number adjacent to a menu item is equivalent to
selecting that item).
Step 3
Unlock the phones configuration menu by pressing **#. The padlock icon on the top-right of the screen
will change from closed to open.
Step 4
Navigate to the profile you want to change and press the Change softkey.
Step 5
Navigate to and select WLAN Configuration.
Step 6
Navigate to and select 802.11 Mode.
Step 7
Navigate to and select the mode option you wish to use.
Step 8
Press the Save soft-key.
Step 9
Press the Back softkey until the Exit softkey appears.
Step 10
Press the Exit softkey.
The available options for IEEE 802.11 mode are shown in Table 10-1
Table 10-1
Available IEEE 802.11 Mode Options
IEEE 802.11 Mode
Description
IEEE 802.11b/g
Always use only IEEE 802.11b/g
IEEE 802.11a
Always use only IEEE 802.11a
Auto-b/g
Use IEEE 802.11b/g if available, fallback to IEEE 802.11a if not
Auto-a
Use IEEE 802.11a if available, fallback to IEEE 802.11b/g if not
Auto-RSSI
Use whatever frequency band has the strongest RSSI
Behavior in Presence of 2.4 GHz IEEE 802.11 b/g and 5 GHz
If the Cisco Unified Wireless IP Phone 7921 is enabled for both IEEE 802.11b/g and IEEE 802.11a, and
receives beacons on both of these frequency bands for the voice SSID (assuming there is sufficient
admission control capacity on each frequency band), the following notes apply.
On Cisco Unified Wireless IP Phone 7921 initial association:
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•
If the default Auto-RSSI is enabled, the phone will associate to the radio (and therefore frequency
band) it acquires having the strongest Receive Signal Strength Indicator (RSSI).
•
If Auto-b/g or Auto-a is enabled, the phone will associate to the frequency band specified and will
fall back to the non-specified frequency band only if the specified frequency is unavailable
•
If IEEE 802.11-b/g or IEEE 802.11-a is enabled, the phone will only associate to the frequency band
specified.
On Cisco Unified Wireless IP Phone 7921 roam:
•
Once the phone has associated to an AP on a particular frequency band, it will only scan for and
roam to APs on the same frequency band.
•
If the Cisco Unified Wireless IP Phone 7921 has moved beyond the boundaries of the frequency
band it initially associated with and cannot roam to another AP on that frequency band, then the
Cisco Unified Wireless IP Phone 7921 will become disassociated and will begin the association
process again (looking on both frequency bands).
WLAN RF—Controller Configuration
The recommended way to limit the Cisco Unified Wireless IP Phone 7921 operation to a single
frequency band (such as IEEE 802.11a or IEEE 802.11b/g) is to leave the phone at its default setting and
to configure the WLAN on the controller (or Cisco WCS) to operate on a single frequency band.
Figure 10-28 shows the options available to restrict a voice VLAN to specific frequency ranges.
Figure 10-28
VLAN Radio Policy
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Cisco Unified Wireless IP Phone 7921 QoS
A well-designed and effectively deployed QoS implementation is critical for a successful VoWLAN
deployment. A wireless network that appears to function well for data traffic might well provide
unsatisfactory performance for a voice deployment. This is because data applications can often tolerate
packet delays or recover from packet loss that would be disruptive to a voice call.
Chapter 2, “WLAN Quality of Service,” provides general QoS deployment guidance.
Cisco Unified Wireless IP Phone 7921 QoS Configuration
The Cisco Unified Wireless IP Phone 7921 supports the following QoS related protocols and standards;
•
IEEE 802.11e/Wi-Fi Multimedia (WMM)
•
Traffic Specification (TSPEC)
•
Enhanced Distributed Channel Access (EDCA)
•
QoS Basic Service Set (QBSS)
•
Unscheduled automatic power-save delivery (U-APSD)
•
Power-save mode
All of these features are enabled by default on the phone and will be used if enabled on the AP to which
the phone associates. The QoS chapter provides more details about each of these.
Cisco WLC QoS configuration
A dedicated voice VLAN should be defined on the controller for all VoIP handsets including the Cisco
Unified Wireless IP Phone 7921. The voice VLAN should be configured for the highest possible QoS by
editing the VLAN and selecting the QoS tab.
As shown in Figure 10-29, in the Quality of Service (QoS) drop-down box Platinum (voice) should be
selected. If only WMM-capable voice handsets, such as the Cisco Unified Wireless IP Phone 7921, are
to be deployed, then the WMM Policy drop-down box should be set to Required. If there will be a mix
of Cisco Unified Wireless IP Phone 7921 and nonWMM-capable devices, such as the Cisco Unified
Wireless IP Phone 7920, then the WMM policy should be set to Optional.
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Figure 10-29
Cisco WLC WLAN QoS Policy Options
For each of the four QoS Profiles (Bronze, Silver, Gold, and Platinum) that can be selected for a given
WLAN, there is a controller-wide option to change the characteristics of that profile.
Figure 10-30 shows an example of a QoS Profile edit screen. In most deployments, these settings should
not be changed and the default configuration shown here should be used. More information on these
options is available in the Chapter 2, “WLAN Quality of Service.”
Figure 10-30
Cisco WLC Edit QoS Profile
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Cisco Unified Communications Manager QoS Configuration
The default Cisco Unified Communications Manager configuration contains the recommended values
for Cisco Unified Communications Manager voice signaling QoS. The following relevant settings are
shown in Figure 10-31 and are appropriate for most deployments:
Figure 10-31
•
DSCP for Phone Configuration—This parameter specifies the Differentiated Service Code Point
(DSCP) IP classification for any phone configuration, including any TFTP, DNS, or DHCP access
necessary for phone configuration.
•
DSCP for Cisco Unified Communications Manager to Device Interface—This parameter specifies
the DSCP IP classification for protocol control interfaces used in Cisco Unified Communications
Manager-to-device communications.
Cisco Unified Communications Manager QoS Parameters
Infrastructure QoS Configuration
This section shows sample QoS configurations for switch interfaces used in the campus network. More
configuration details for all the switches and routers used in this design guide is available in the
Appendix , “Voice over WLAN Campus Test Architecture,” testing section of this guide.
Table 10-2 shows interface commands on a Cisco 3750G access-layer switch used to connect an IP
Phone. The Auto-QoS configuration statement is shown in red and the statements generated by
Auto-QoS follow it.
Table 10-2
Cisco 3750G—Wired IP Phone Port Configuration
Commands
Comments
interface GigabitEthernet2/0/3 
description IP phone 7960
Interface configuration mode and description.
switchport access vlan 50 
switchport mode access
Define access VLAN for data VLAN.
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Table 10-2
Cisco 3750G—Wired IP Phone Port Configuration (continued)
Commands
Comments
switchport voice vlan 51
Define Voice VLAN.
switchport
switchport
switchport
switchport
switchport
inactivity
port-security
port-security
port-security
port-security
port-security
maximum 2 

aging time 2 
violation restrict 
aging type
Define Port Security features.
spanning-tree portfast
Spanning tree port configuration.
auto qos voip cisco-phone
Auto-QoS statement entered on all voice ports
srr-queue bandwidth share 10 10 60 20 
srr-queue bandwidth shape 10 0 0 0 
queue-set 2 
mls qos trust device cisco-phone 
mls qos trust cos
Platform-specific QoS statements generated by
the Auto-QoS statement that is in red in the
preceding line.
Table 10-3 shows interface commands on a Cisco 4503 access-layer switch used to connect an AP. The
Auto-QoS configuration statement is shown in red and the statements generated by Auto-QoS follow it.
Table 10-3
Cisco 4503—AP Port
Commands
Comments
interface FastEthernet2/16 
description ports connected to APs in
Isolation Boxes
Interface configuration mode and description.
switchport access vlan 48 
switchport mode access
Define access VLAN for data VLAN all APs go
on the access VLAN.
auto qos voip trust
Auto-QoS statement entered on all AP ports.
qos trust dscp
The Auto-QoS statement above sets the switch
port to trust Layer-2 CoS. For nonrouted ports, the
CoS value of the incoming packet is trusted. For
routed ports, the DSCP value of the incoming
packet is trusted.
Note—The mls qos trust dscp command is the
equivalent command format for a 3750 switch.
This qos trust dscp command overrides that and
sets the port to trust Layer-3 DSCP instead. The
link between the AP and the switch port is not
trunked and does not mark Layer-2 CoS.
tx-queue 3 
bandwidth percent 33 
priority high 
shape percent 33 
service-policy output autoqos-voip-policy
Platform-specific QoS statements generated by
the Auto-QoS statement shown in red in
preceding line.
Table 10-4 shows interface commands on a Cisco 4503 access-layer switch used as an uplink port to a
distribution-layer switch. The Auto-QoS configuration statement is shown in red and the statements
generated by Auto QoS follow it.
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Table 10-4
Cisco 4503 Uplink Port to Distribution Layer
Commands
Comments
interface TenGigabitEthernet1/1 
description A4L to D3L
Interface configuration mode and description.
no switchport 
ip address 10.33.3.10 255.255.255.252 
ip hello-interval eigrp 100 1 
ip hold-time eigrp 100 3 
ip authentication mode eigrp 100 md5 
ip authentication key-chain eigrp 100
eigrp-chain 
ip pim sparse-mode 
logging event link-status 
load-interval 30 
carrier-delay msec 0
Interface configuration unrelated to QoS.
auto qos voip trust
qos trust dscp
tx-queue 3 
bandwidth percent 33 
priority high 
shape percent 33 
service-policy output autoqos-voip-policy
Platform-specific QoS statements generated by
the Auto-QoS statement that is in red in the line
above
Note—Because this is a Layer-3 port, the auto
qos voip trust command sets qos trust dscp not
qos trust cos as it did in Table 10-3.
End-to-End QoS Mapping
In the centralized WLAN architecture, WLAN data is tunneled between the AP and the wireless LAN
controller via LWAPP. In order to maintain the original QoS classification across this tunnel, the QoS
settings of the encapsulated data packet must be appropriately mapped to the Layer 2 (IEEE 802.1p) and
Layer 3 (IP DSCP) fields of the outer tunnel packet. See Figure 10-32.
Figure 10-32
End-to-end QoS Packet Marking Mappings
802.11e DSCP Payload
DSCP
LWAPP Encapsulated
802.11e DSCP Payload
802.1p
DSCP Payload
2
LWAPP Tunnel
LWAPP
3
4
802.11e DSCP Payload
802.1p DSCP
LWAPP Encapsulated
802.11e DSCP Payload
802.1p
DSCP Payload
222890
1
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The original IP packet DSCP and user-data—sent by the WLAN client to the AP or received by the
controller from the wired network infrastructure—are transmitted unaltered across the LWAPP tunnel
between the AP and the controller. The Layer-2 and Layer-3 QoS markings are only changed on the
headers that encapsulate the original IP packet. Table 10-5 provides additional marker mapping
elaboration for the numbered labels in Figure 10-32.
Table 10-5
End-to-end QoS Packet Marking Mappings
Label
Number1
From
To
1
AP
Controller
Outbound UP (IEEE 802.1p/IEEE
802.11e) Mapping
Outbound IP DSCP Mapping
N/A (APs do not support IEEE
WMM Client (such as Cisco Unified Wireless
802.1Q / IEEE 802.1p tags on the IP Phone 7921)—Police the IEEE 802.11e UP
wired interface).
value to ensure it does not exceed the
maximum value allowed for the QoS policy
assigned to that client; translate the value to
the DSCP value.
Regular Client—Use the IEEE 802.11e UP
value for the QoS policy assigned to that
client’s WLAN; translate the value to the
DSCP value.
2
Controller
Ethernet
Switch
Translate the DSCP value of the
incoming LWAPP packet to the
IEEE 802.1p UP value.
Note—The AP has policed the
upstream DSCP (when it mapped
from IEEE 802.1p UP to DSCP)
3
Controller
AP
Translate the DSCP value of the
incoming packet to the Cisco
Architecture for Voice, Video and
Integrated Data (AVVID) IEEE
802.1p UP value.
N/A (The original/encapsulated DSCP value
is preserved)
Note—The DSCP is un-policed; it is whatever
was set by the WLAN client.
Copy the DSCP value from the incoming
packet.
Note—No policing is performed here; it is
assumed that traffic was policed at ingress to
the network.
Note—The QoS profile is used to
police the maximum IEEE 802.1p
value that can be set
4
AP
Wireless
Client
WMM Client (such as Cisco
N/A (original/encapsulated DSCP value is
Unified Wireless IP Phone
preserved).
7921)—Translate the DSCP value
of the incoming LWAPP packet to
the IEEE 802.11e UP value.
Police the value to ensure it does
not exceed the maximum value
allowed for the WLAN QoS
policy assigned to the WLAN the
client belongs to. Place packet in
the IEEE 802.11 Tx queue
appropriate for the UP value.
Regular Client—Place packet in
the default IEEE 802.11 Tx queue
for the WLAN QoS policy
assigned to that client.
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1. Refer to Figure 10-32.
Table 10-6 provides the translations that occur between IEEE 802.11e/IEEE 802.1p UP values and IP
DSCP values. Because Cisco AVVID defines the translation from IEEE 802.1 UP to IP DSCP, and the
IEEE defines the translation from IP DSCP to IEEE 802.11e UP, two different sets of translations must
be used.
Table 10-6
QoS Packet Marking Translations
Cisco AVVID IEEE 802.1p
UP-Based Traffic Type
Cisco AVVID IP DSCP
Cisco AVVID
IEEE 802.1p UP
IEEE 802.11e UP Notes
Network Control
–
7
–
Reserved for network control only
Inter-Network Control
48
6
7 (AC_VO)
LWAPP control
Voice
46 (EF)
5
6 (AC_VO)
Controller—Platinum QoS profile
Video
34 (AF41)
4
5 (AC_VI)
Controller—Gold QoS profile
Voice Control
26 (AF31)
3
4 (AC_VI)
–
Best Effort
0 (BE)
0
3 (AC_BE) 
0 (AC_BE)
Controller— Silver QoS profile 
–
Transaction Data
18 (AF21)
2
2 (AC_BK)
–
Bulk Data
10 (AF11)
1
1 (AC_BK)
Controller— Bronze QoS profile.
Cisco Unified Wireless IP Phone 7921 Troubleshooting
This section will focus on troubleshooting that is specific to the Cisco Unified Wireless IP Phone 7921G.
For additional troubleshooting information, refer to Chapter 9, “Voice over WLAN Troubleshooting and
Management Tools.”
Configuration Checklist
When configuring your wireless LAN controller, use the following guidelines:
Step 1
Set the QoS policy to Platinum.
Step 2
Enable WMM to enable QoS and the ability to use U-APSD.
Step 3
Disable DHCP address assignment required.
Step 4
Ensure Aggressive Load Balancing is disabled.
Step 5
If you have clients from other regions that will attempt to associate with the WLAN, enable World Mode
(IEEE 802.11d).
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Verify Coverage with Cisco Unified Wireless IP Phone 7921G
Chapter 9, “Voice over WLAN Troubleshooting and Management Tools,” covers the management of the
RF deployment using the Cisco WCS, Cisco WLC, as well as using third-party site-survey and WLAN
analysis tools. This section describes how the Cisco Unified Wireless IP Phone 7921G can be used to
validate the RF design provided by those tools.
Wireless LAN performance varies from client device to client device. A client with a strong transmit
signal and a high receiver sensitivity will perform better in marginal WLAN coverage than a client with
weaker radio characteristics. For this reason, it is recommended that WLAN coverage is validated with
the actual device you intend to use (in addition to using professional site survey tools such as AirMagnet
Survey and Cisco Cisco Spectrum Expert Analysis).
After the initial deployment of wireless phones in the WLAN, it is a good practice to perform site surveys
at regular intervals to verify that the APs are providing adequate coverage and that wireless phones can
roam from one AP to another without audio problems. You should use the Cisco Unified Wireless IP
Phone 7921G to verify that the signal range and transmission power provide adequate coverage for
roaming phones.
Access the Site Survey menu on the phone by pressing Settings > Status > Site Survey
Note
When not in a call, the Cisco Unified Wireless IP Phone 7921G only scans other non-associated channels
when the current signal lowers to a certain threshold, so you might see the AP with which it is associated
in the list. To see all APs, place a call from the Cisco Unified Wireless IP Phone 7921G to a wired IP
phone where scanning occurs constantly while the phone call is active.
Figure 10-33 shows an example display output from a Cisco Unified Wireless IP Phone 7921.
Figure 10-33
Cisco Unified Wireless IP Phone 7921 Site Survey Screen Capture
Cisco Unified Wireless IP Phone 7921 coverage statistics can also be viewed by using Telnet to connect
to the Cisco Unified Wireless IP Phone 7921.
Cisco Unified Wireless IP Phone 7921 Web Page Access
You can access the web page for any Cisco Unified Wireless IP Phone 7921G that is connected to the
WLAN. Be sure the phone is powered on and connected. To access the web page for the Cisco Unified
Wireless IP Phone 7921G follow these steps:
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•
Enabling or Disabling IP Phone Web Access from Cisco Unified Communications Manager, page
10-35
•
Access the Cisco Unified Wireless IP Phone 7921s Web Pages, page 10-35
These procedure are summarized in the brief sections that follow.
Enabling or Disabling IP Phone Web Access from Cisco Unified Communications Manager
Web access for IP phones is enabled by default on Cisco Unified Communications Manager. The
following steps are required to disable or re-enable web access.
Step 1
Navigate to the Phone Configuration web page in Cisco Unified Communications Manager
Administration and set the Web Access field to Read Only or Disabled.
Step 2
Reset the phone from Cisco Unified Communications Manager to implement the change in web access
policy.
Access the Cisco Unified Wireless IP Phone 7921s Web Pages
Step 1
Step 2
Obtain the IP address of the Cisco Unified Wireless IP Phone 7921G using one of these methods:
a.
Search for the phone in Cisco Unified Communications Manager by choosing Devices > Phones.
Phones registered with Cisco Unified Communications Manager display the IP address on the Find
and List Phones web page and at the top of the Phone Configuration web page.
b.
On the Cisco Unified Wireless IP Phone 7921G, press Settings > Device Information > Network
Configuration and then scroll to the IP Address option.
Open a web browser and enter the following URL, where IP_address is the IP address of the Cisco
Unified IP Phone: https://IP-address
Note
When the Security Alert dialog box displays a notice to accept the Trust Certificate, click Yes or
Always to accept the application.
Step 3
Log in to the web pages with the username admin and enter the password Cisco for the phone web pages.
Step 4
View the informational pages and changes to configurable pages as needed.
Figure 10-34 provides an example display showing some of the information that is available from the
Cisco Unified Wireless IP Phone 7921 web pages.
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References
Figure 10-34
Cisco Unified Wireless IP Phone 7921 Stream Statistics
References
Please see the following publications for additional information:
•
Cisco Unified Wireless IP Phone 7921G Adminstration Guide 
http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7921g/5_0_1/english/administration/gu
ide/21adm501.html
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References
•
Wireless LAN Controller Documentation 
http://www.cisco.com/en/US/products/ps6366/products_installation_and_configuration_guides_lis
t.html
•
Cisco Wireless Control System Configuration Guide 
http://www.cisco.com/en/US/products/ps6305/products_installation_and_configuration_guides_lis
t.html
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References
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11
Voice over WLAN Vocera Implementation
Vocera Overview
The Vocera Communications System enables wireless voice communication that users control with
naturally spoken commands. The system is primarily targeted at hospitals, hotels, retail stores, and other
in-building environments where mobile workers must stay in contact to perform their jobs. The Vocera
Communications System consists of two key components:
•
Vocera System Software—Controls and manages call activity
•
Vocera Communications Badge—A lightweight, wearable, voice-controlled communication device
that operates over a wireless LAN (IEEE 802.11b/g)
The Vocera Badge is briefly discussed in this chapter with minimum configurations required to integrate
it with Cisco Unified Communications Manager.
The Vocera User Guide, Configuration Guide, and Infrastructure Planning Guide can be found at
http://www.vocera.com/documentation/default.aspx
Note
The first Badge release by Vocera is the B1000A and is the subject of this design guide. Vocera has since
announced the Vocera Communications Badge B2000 with an improved wireless radio which will
support WiFi Multimedia (WMM). This announcement occurred as this design guide was in the process
of being released so no testing has been done on the new B2000 Badge.
Vocera System Software
The Vocera System Software platform runs on a standard Windows server and contains the system
intelligence, including managing calls call connections, and user profiles, as well as the Nuance speech
recognition and voice-print verification software. The Administrative Console allows system
administrators to set global preferences and permissions for users. User preferences are configured on
the server via browser-based Administration and User Consoles.
The Vocera versions used for this design guide are as follows:
•
Vocera Server 4.0 [Build 1279]
•
Vocera Telephony Server 4.0 [Build 1279]
•
Vocera Badge V4.0 1273
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Vocera Architecture
Vocera Communications Badge
The Vocera Communications Badge is a small, lightweight, wearable, wireless device that provides a
voice-controlled user interface to the Vocera Communications System. The Vocera Communications
Badge enables instant, hands-free conversations among people throughout the workplace. It contains a
speaker, microphone, wireless radio, and a backlit LCD that shows caller ID, text messages and alerts.
A Vocera Communications Badge is shown in Figure 11-1.
Figure 11-1
Vocera Communications Badge
Vocera Architecture
This section addresses the following Vocera architecture topics:
•
Main Components, page 11-2
•
Badge Overview, page 11-3
•
Badge-to-Badge Communication, page 11-4
•
Badge Telephony Communication, page 11-4
•
Vocera Broadcast, page 11-5
•
Badge Location Function, page 11-6
Main Components
Primary Vocera system components consist of the following elements:
•
Vocera Server Program—Provides the central system functionality, and calls on the other
components for specific services.
•
Embedded MySQL Database—Stores user profiles (which contain personal information and Badge
settings), group and location information, and system settings.
•
NuanceTM Speech Recognition, Verifier, and Vocalizer Software—Provides the speech recognition,
voiceprint authentication, and text-to-speech engines used by the Vocera voice interface.
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•
Apache/Tomcat Web Serve—Hosts the browser-based Administration Console and User Console
applications.
Software Utilities
The Vocera system software includes the following utilities:
•
Badge Properties Editor—Allows setting values for Badge properties so the Vocera Badges can
connect to the wireless network.
•
Badge Configuration Utility—Downloads the properties set with the Badge Properties Editor, as
well as any firmware upgrades, to the Badges.
•
Vconfig Utility—Provides interactive setting of individual properties and to download individual
firmware components to a Badge.
The Vocera system can be a standalone communications system with Badge-to-Badge communication
only. Typically the system is installed in conjunction with a PBX to allow hardphone (wired)-to-Vocera
Badge communications, as well as access through the PBX to the Public Switched Telephone Network
(PSTN). For this communication to take place, an Intel Dialogic board must be installed in the Vocera
System Server. For this design guide an Intel Dialogic D/480JCT-1T1 (North America, T1/PRI) was
used. For a list of other supported analog and digital integrations refer to the Vocera Datasheet.
A high level diagram is shown in Figure 11-2.
Figure 11-2
Vocera Architecture Diagram
Cisco Unified
Communications
Manager
M
LWAPP
LWAPP
Si
V
Voice
Gateway
ISDN PRI
Vocera
Server
222963
IP
Badge Overview
The Badges are centrally maintained by the Vocera Server from a single configuration file for all Badges.
The Badge does not have a keyboard, so this single configuration file is uploaded to all Badges. The
Badge does not maintain a static DN or ID (as a typical phone would have). Instead, each Badge defines
its identity when a user logs in. As a necessary consequence of this centralized management, all Badge
properties, including the SSID and security settings that allow it to connect to the network, must be the
same. In turn, all APs to which the Vocera Badge can connect must also share the same SSID and security
settings.
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Vocera Architecture
The Vocera Badge supports the following wireless networks, and authentication and encryption
capabilities:
•
Wireless Network Support—IEEE 802.11b/g wireless network with multicast and UDP unicast
packet delivery
•
Authentication—Types supported include the following:
– Open
– Wi-Fi Protected Access-Pre-shared Key (WPA-PSK)
– WPA-Protected Extensible Authentication Protocol (PEAP)
– Lightweight Extensible Authentication Protocol (LEAP)
•
Encryption—Types supported include the following:
– 64/128 bit Wired Equivalent Privacy (WEP)
– Temporal Key Integrity Protocol (TKIP)
– Message Integrity Check (MIC)
– Cisco Temporal Key Integrity Protocol (CKIP)
Note
Vocera supports Autonomous and Lightweight Access Point Protocol (LWAPP). Refer to the “Vocera IP
Phone Deployment” chapter in Cisco Unified Wireless Network Infrastructure for more information on
deploying Vocera in a Wireless Network.
Badge-to-Badge Communication
When one Vocera user calls another user, the Badge first contacts the Vocera Server which looks up the
IP address of the callee’s Badge and contacts the Badge user to ask the user if he/she can take a call. If
the callee accepts the call, the Vocera Server will notify the calling Badge of the callee Badge’s IP
address to setup direct communication between the Badges with no further server intervention. All
communication with the Vocera Server uses the G.711 CODEC and all Badge-to-Badge communication
uses a Vocera proprietary CODEC.
Badge Telephony Communication
When the Vocera Telephony Server is installed and setup with a connection to a PBX, a user is able to
call internal extensions off of the PBX or outside telephone lines. Vocera allows users to make calls by
either saying the numbers (five, six, three, two) or by creating an address book entry in the Vocera
database for the person or function at that number (for example, pharmacy, home, pizza) the Vocera
server determines the number that is being called, either by intercepting the numbers in the extension or
by looking up the name in the database and selecting the number. The Vocera Server then passes that
information to the Vocera Telephone Server which connects to the PBX and generates the appropriate
telephony signaling (ex. DTMF). All media is via UDP using g711, but call signaling between the Vocera
Server (VS) and Vocera Telephony Server (VTS) is via a TCP connection between the two. Once a call
is established, media between the VS and VTS or between the badge and VTS is g711 via UDP.
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Vocera Broadcast
A Vocera Badge user can call and communicate to a group of Vocera Badges at the same time by using
the broadcast command. When a user broadcasts to a group, the users Badge sends the command to the
Vocera Server who looks up the members of a group, determines which members of the group are active,
assigns a multicast address to use for this broadcast session, and sends a message to each active user’s
Badge instructing it to join the multicast group with the assigned multicast address. More information
on Vocera Multicast in an LWAPP environment can be found at “Vocera IP Phone Deployment” chapter
in Cisco Unified Wireless Network Infrastructure.
Filtering a trace on IGMP Protocol allows you to see the Membership Report of a device joining the
multicast group. Figure 11-3 illustrates the Badge with an IP Address of 10.33.65.202 joins Multicast
Group 230.230.0.13 (hex e6 e6 00 0d).
Figure 11-3
Vocera Badge Joining Multicast Group
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After locating the Membership Report of a specific Badge joining the multicast group, look earlier in the
trace for the occurrence of the Vocera Server as the source and the Badge in question as the destination.
See Figure 11-4. In this example the Badge is 10.33.65.202 and the Vocera Server is 10.33.32.251. In
the data you will see the occurrence of e6 e6 00 0d (hex representation of the multicast address
230.230.0.13).
Figure 11-4
Vocera Server Sending Multicast Address to Vocera Badge
Badge Location Function
The Vocera Server keeps track of the AP to which each active Badge is associated as each Badge will
send a 30 second keepalive to the server with the associated BSSID. This allows the Vocera system to
roughly estimate the location of a Badge user. This function has a relatively low degree of accuracy
because a Badge might not be associated to the AP to which it is closest. A more accurate solution for
finding the location of a device is the Cisco Location-Based Services (LBS).
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WLAN Controller Base Configuration
WLAN Controller Base Configuration
This section addresses creating a Voice WLAN.
Create Voice WLAN
Creating a WLAN with the minimum necessary configuration needed to test Vocera connectivity can be
done in the following steps on the controller GUI.
Figure 11-5
Step 1
Click the WLANs tab in the controller GUI.
Step 2
Click the New button at the top-right corner of the page.
Step 3
Define a profile name and SSID (often the same string is used for both) for the new WLAN.
Step 4
Click Apply.
Step 5
The WLANs > Edit page loads. See Figure 11-5.
WLANs > Edit Page
Step 6
Check the WLAN Status box to signal that this new WLAN should be enabled.
Step 7
Change the Interface drop-down box to point to a user-defined dynamic interface (you must have
predefined a dynamic interface; do not use the management interface).
Step 8
Click the Security tab.
Step 9
Change the Layer-2 Security drop-down box to WPA-PSK.
Step 10
Click the QoS tab.
Step 11
Change the Quality of Service (QoS) drop-down box to Platinum (voice).
Step 12
Click the Apply button at the top-right corner of the page.
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Vocera Configuration
When the base controller WLAN configuration is complete, the WLAN page should look similar to the
page shown in Figure 11-6.
Figure 11-6
WLANs Page with Vocera VoWLAN
Vocera Configuration
This section addresses Vocera Server and Vocera Badge configuration.
Server and Badge Configuration
Since the Vocera Badge has no keyboard for the entry of network settings, the computer running the
Vocera Badge Configuration Utility must have specific TCP/IP properties defined. This computer must
also be connected to an Isolated Access Point with a specific SSID.
Refer to the Vocera Configuration Guide for information on specific TCP/IP and SSID properties
required for the Isolated Access Point.
Vocera Telephony Integration
The hardware required to integrate Vocera with a PBX differs according to whether you perform an
analog or a digital integration. A digital integration with Cisco Unified Communications Manager is
suggested as it provides a higher density of channels than an analog integration. Specific Intel Dialogic
boards are supported by Vocera and can be found in the Vocera Configuration Guide.
For this design guide the Intel® Dialogic® D/480JCT-2T1 was used with a switch protocol of NI2.
Figure 11-7 and Figure 11-8 show the Dialogic settings from the Vocera Intel® Dialogic® Configuration
Manager located on the Vocera Server.
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Vocera Configuration
Figure 11-7
Vocera Intel® Dialogic® Configuration Manager Screen 1
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Cisco Unified Communications Manager Configuration
Figure 11-8
Vocera Intel® Dialogic® Configuration Manager Screen 2
DHCP
Vocera does not allow the running of the DHCP server on the Vocera Server computer. Although the
DHCP server does not typically require significant system resources, running it on the Vocera Server
computer causes significant problems in a clustered environment, including the following:
•
Devices may inadvertently receive duplicate IP addresses.
•
Badges may not receive an IP address and get stuck displaying Requesting IP Address.
•
Badges may get invalid and unusable IP address information.
Unlike Cisco IP phones, the DHCP scope does not require option 150 to be set. Option 150 defines the
address of the Cisco Unified Communications Manager TFTP Server for Cisco IP phones (Vocera
Badges do not communicate directly with Cisco Unified Communications Manager). If DHCP is not
used, the Badges will require manual entry of network properties. Since the Badges do not have a
keyboard this process is slow and error prone, thus DHCP is highly recommended.
Cisco Unified Communications Manager Configuration
Communication between Cisco Unified Communications Manager and Vocera is accomplished in the
same manner as connecting CUCM with a PBX. It is always suggested to use the highest level of
integration that both systems can support. For example, if both systems support QSig then this would
offer a more robust integration than ISDN or analog integration. In the case of Vocera they only support
ISDN or analog integration so ISDN should be used whenever possible.
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Cisco Unified Communications Manager Configuration
Figure 11-9 shows the Cisco Unified Manager Communications gateway configuration when using
MGCP. The gateway is A1L.sj.tseuc.local with endpoint 2/0/0 (T1PRI) connected to the Vocera Dialogic
board.
Figure 11-9
Cisco Unified Communications Manager Gateway Configuration
Figure 11-10 through Figure 11-13 show the endpoint 2/0/0 configuration.
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Cisco Unified Communications Manager Configuration
Figure 11-10
Cisco Unified Communications Manager Gateway Configuration (Part 1)
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Figure 11-11
Cisco Unified Communications Manager Gateway Configuration (Part 2)
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Cisco Unified Communications Manager Configuration
Figure 11-12
Cisco Unified Communications Manager Gateway Configuration (Part 3)
Figure 11-13
Cisco Unified Communications Manager Gateway Configuration (Part 4)
Dial Plan and Translation
Vocera Badges are usually deployed for special-purpose areas such as on hospital or retail sales floors.
It is suggested that access to the Vocera Badges be restricted by putting the Badges in their own partition
that only allows those devices with a need to contact a Vocera Badge the ability to do so. The Route
Pattern Configuration shown in Figure 11-14 allows all numbers within the range of 1440 to 1449 to be
routed to the Vocera Server and assigns the Vocera partition.
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Vocera Security
Figure 11-14
Route Pattern Configuration
Vocera Security
Table 11-1 summarizes the security features supported by Vocera.
Table 11-1
Vocera-supported Security Features
Authentication
Encryption
Message Integrity Check
Open
None, WEP64,WEP128
N/A
LEAP
TKIP-Cisco, WEP64, WEP128
N/A
WPA-PEAP (MS-CHAP v2)
TKIP-WPA
MIC
WPA-PSK
TKIP-WPA
MIC
The LEAP and PEAP protocols typically require each user in a network environment to be authenticated
with a unique set of credentials. However, each Badge must have the same security properties so the
Vocera Server can automatically update all Badges when necessary. Consequently, Vocera supports
device authentication for PEAP and LEAP, not user authentication. All Badges must present the same
set of credentials for network authentication.
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Vocera Radio Frequency Considerations
Applications such as voice running on client devices require fast reassociation when they roam to a
different AP to prevent delays and gaps in conversation. Vocera Badges do not support fast, secure
roaming so in order to provide fast roaming and a reasonable level of authentication security and
encryption, WPA-PSK with TKIP should be used with the Vocera Badge (pre-B2000).
Setting the authentication and encryption is set in the WLC WLAN Layer 2 Security tab. Figure 11-15
shows the authentication and encryption setting for the Vocera WLAN.
Figure 11-15
WLAN Security Settings
Vocera Radio Frequency Considerations
Wireless IP telephony networks require careful RF planning. A thorough voice site survey is often
required to determine the proper levels of wireless coverage and to identify sources of interference. AP
placement and antenna selection choices can be greatly eased with the help of the results of a valid voice
site survey. For further information on Vocera RF considerations and configuration please refer to the
“Vocera IP Phone Deployment” chapter in Cisco Unified Wireless Network Infrastructure.
Vocera QoS
A well-designed and effectively deployed QoS implementation is critical for a successful voice over
WLAN deployment. A wireless network that appears to function well for data traffic might provide
unsatisfactory performance for a voice deployment. This is because data applications can often tolerate
packet delays or recover from packet loss that would be disruptive to a voice call.
Chapter 2, “WLAN Quality of Service,” of this document provides general QoS deployment guidance.
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Vocera QoS Configuration
VLANs provide a mechanism for segmenting networks into one or more broadcast domains. VLANs are
especially important for IP telephony networks, where the typical recommendation is to separate voice
and data traffic into different Layer-2 domains. Cisco recommends that you configure separate VLANs
for the Vocera Badges from other voice and data traffic. For example, VLANs might consist of the
following: a native VLAN for AP management traffic; data VLAN for data traffic; a voice or auxiliary
VLAN for voice traffic; and, a VLAN for the Vocera Badges. A separate voice VLAN enables the
network to take advantage of Layer-2 marking and provides priority queuing at the Layer-2 access switch
port. This ensures that appropriate QoS is provided for various classes of traffic and helps to resolve
addressing issues such as IP addressing, security, and network dimensioning. The Vocera Badges use a
broadcast feature that utilizes multicast delivery. The use a separate, common voice VLAN ensures that
a Badge remains part of the multicast group whenever it roams between controllers. Refer to the “Vocera
IP Phone Deployment” chapter in Cisco Unified Wireless Network Infrastructure.
Vocera sets the ToS byte in the following ways:
•
With a DiffServ Code Point (DSCP) marking of EF (Expedited Forwarding).
•
With an IP Precedence marking of 5.
This is not configurable within the Vocera system.
Note
The Badge broadcast is sent by the Badge at DSCP EF; when the multicast comes back to the group from
the WLC, it is marked best effort. This is a function of the WLC and can have an effect on voice quality.
If your Vocera traffic traverses a WAN circuit, you should make sure the following QoS requirements
are met:
•
Enable QoS at all WAN ingress and egress points.
•
Make sure routers providing WAN circuits give the highest priority to traffic with a DSCP marking
of EF or an IP Precedence of 5.
WLC QoS Configuration
As mentioned in the “Cisco WLC QoS configuration” section on page 10-27, a dedicated voice VLAN
should be defined on the controller for all VoIP handsets—that includes Vocera Badges. The voice
VLAN should be configured for the highest possible quality of service by editing the VLAN and
selecting the QoS tab.
As shown in Figure 11-16, Platinum (voice) should be selected on the Quality of Service (QoS)
drop-down box. Vocera Badges do not support WMM so the WMM Policy drop-down box should be set
to Optional.
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Vocera QoS
Figure 11-16
WLC QoS Configuration
For each of the four QoS Profiles (bronze, silver, gold, platinum) that can be selected for a given WLAN,
there is a controller-wide option to change the characteristics of that profile.
In most deployments, these settings should not be changed and the default configuration should be used.
More information on these options is available in Chapter 2, “WLAN Quality of Service,” of this
document.
Infrastructure QoS Configuration
This section shows sample QoS configurations for switch interfaces used in the campus network. More
configuration detail for all the switch and routers used in this design guide is available in the Chapter 11,
“Voice over WLAN Vocera Implementation.”
Table 11-2 summarizes configuration commands for an interface on a Cisco 3750G access-layer switch
used to connect an IP phone. The Auto-QoS configuration statement is shown in red and the statements
generated by Auto-QoS are shown below it.
Table 11-2
Cisco 3750G —Wired IP Phone Port
Commands
Comments
interface GigabitEthernet2/0/3
description IP phone 7960
Interface configuration mode and provide
description
switchport access vlan 50
switchport mode access
Define access VLAN for data VLAN
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Table 11-2
Cisco 3750G —Wired IP Phone Port (continued)
Commands
Comments
switchport voice vlan 51
Define Voice VLAN
switchport
switchport
switchport
switchport
switchport
port-security
port-security
port-security
port-security
port-security
Define Port Security features
maximum 2
aging time 2
violation restrict
aging type inactivity
spanning-tree portfast
Spanning tree port configuration
auto qos voip cisco-phone
Auto-QoS statement entered on all voice ports
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
queue-set 2
mls qos trust device cisco-phone
mls qos trust cos
Platform-specific QoS statements generated
by the Auto-QoS statement that is in red in the
line above.
Table 11-3 summarizes configuration commands for an interface on a Cisco 4503 access-layer switch
used to connect an AP. The Auto-QoS configuration statement is shown in red and the statements
generated by Auto-QoS are shown below it.
Table 11-3
Cisco 4503—Access Point Port
Command
Comments
interface FastEthernet2/16
Interface configuration mode and provide
description.
(description ports connected to APs in Isolation
Boxes)
switchport access vlan 48
switchport mode access
Define access VLAN for data VLAN all APs go
on the access VLAN
auto qos voip trust
Auto-QoS statement entered on all AP ports
qos trust dscp
The Auto-QoS statement above sets the switch
port to trust Layer-2 CoS (For nonrouted ports,
the CoS value of the incoming packet is trusted.
For routed ports, the DSCP value of the incoming
packet is trusted).
(mls qos trust dscp is the equivalent command
format for a Cisco 3750 switch.)
This qos trust dscp command overrides that and
sets the port to trust Layer-3 DSCP instead. The
link between the AP and the switch port is not
trunked and does not mark L2 CoS
tx-queue 3
bandwidth percent 33
priority high
shape percent 33
service-policy output autoqos-voip-policy
Platform-specific QoS statements generated by
the Auto-QoS statement that is in red in the line
above.
Table 11-4 summarizes configuration commands for an interface on a Cisco 4503 access-layer switch
used as an uplink port to a distribution-layer switch. The Auto-QoS configuration statement is shown in
red and the statements generated by Auto-QoS are shown below it.
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Table 11-4
Cisco 4503 Uplink Port to Distribution Layer
Command
Comments
interface TenGigabitEthernet1/1
Interface configuration mode and provide
description
description A4L to D3L
no switchport
ip address 10.33.3.10 255.255.255.252
ip hello-interval eigrp 100 1
ip hold-time eigrp 100 3
ip authentication mode eigrp 100 md5
ip authentication key-chain eigrp 100
eigrp-chain
ip pim sparse-mode
logging event link-status
load-interval 30
carrier-delay msec 0
Interface configuration unrelated to QoS
auto qos voip trust
Note—Because this is a Layer-3 port, the auto
qos voip trust command sets qos trust dscp not
qos trust cos as it did in Table 11-3.
qos trust dscp
Platform-specific QoS statements generated by
the Auto-QoS statement that is in red in the line
above
tx-queue 3
bandwidth percent 33
priority high
shape percent 33
service-policy output autoqos-voip-policy
Note
Nothing relevant to this topic is configurable within the Vocera devices/products.
End-to-end QoS Mapping
In the centralized WLAN architecture, WLAN data is tunneled between the AP and the WLAN
controller via LWAPP. In order to maintain the original QoS classification across this tunnel, the QoS
settings of the encapsulated data packet must be appropriately mapped to the Layer-2 (IEEE 802.1p) and
Layer-3 (IP DSCP) fields of the outer tunnel packet. See Figure 11-17.
Figure 11-17 and Table 11-5 reference the original Vocera Badge tested for this document. The original
Badge does not support WMM for over-the-air QoS, but Vocera has announced a new Badge (the B2000)
which will support WMM QoS.
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End-to-end QoS Packet Marking Mappings
DSCP Payload
DSCP
1
LWAPP
LWAPP Encapsulated
DSCP Payload
DSCP Payload
802.1p
DSCP Payload
2
LWAPP Tunnel
3
4
DSCP Payload
802.1p
802.1p DSCP
LWAPP Encapsulated
DSCP Payload
222979
Figure 11-17
The original IP packet DSCP and user-data sent by the WLAN client to the AP or received by the
controller from the wired network infrastructure are transmitted across the LWAPP tunnel between the
AP and the controller unaltered; the Layer-2 and Layer-3 QoS markings are only changed on the headers
that encapsulate the original IP packet.
Table 11-5
End-to-end QoS Packet Marking Mappings
Mapping
Number1
From
To
1
Access Point
Controller
Outbound UP (IEEE 802.1p/IEEE
802.11e) mapping
N/A (APs do not support IEEE
802.1Q / IEEE 802.1p tags on
the wired interface)
Outbound IP DSCP mapping
WMM Client: Police the IEEE
802.11e UP value to ensure it
does not exceed the maximum
value allowed for the QoS policy
assigned to that client; translate
the value to the DSCP value.
Regular Client (Vocera
Badge): Use the IEEE 802.11e
UP value for the QoS policy
assigned to that clients WLAN;
translate the value to the DSCP
value.
2
Controller
Ethernet Switch
Translate the DSCP value of the N/A (The original/encapsulated
incoming LWAPP packet to the DSCP value is preserved)
IEEE 802.1p UP value.
Note—The DSCP is un-policed;
it is whatever was set by the
Note—The AP has policed the
upstream DSCP (when it mapped WLAN client.
from IEEE 802.1p UP to DSCP)
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Table 11-5
End-to-end QoS Packet Marking Mappings
Mapping
Number1
From
To
3
Controller
Access Point
Translate the DSCP value of the Copy the DSCP value from the
incoming packet to the AVVID incoming packet.
IEEE 802.1p UP value.
Note—No policing is performed
Note—The QoS profile is used here; it is assumed that traffic
was policed at ingress to the
to police the maximum IEEE
network
802.1p value that can be set
4
Access Point
Wireless Client
WMM Client: Translate the
N/A (original/encapsulated
DSCP value of the incoming
DSCP value is preserved)
LWAPP packet to the IEEE
802.11e UP value. Police the
value to ensure it does not
exceed the maximum value
allowed for the WLAN QoS
policy assigned to the WLAN the
client belongs to. Place packet in
the IEEE 802.11 Tx queue
appropriate for the UP value.
Outbound UP (IEEE 802.1p/IEEE
802.11e) mapping
Outbound IP DSCP mapping
Regular client (Vocera Badge):
Place packet in the default IEEE
802.11 Tx queue for the WLAN
QoS policy assigned to that
client.
1. Refers to Figure 11-17.
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A P P E N D I X
A
Deploying and Operating a Secure Voice over
Wireless LAN Solution with Cisco Lifecycle
Services
To gain full advantage of converged mobile applications requires blending wired and wireless systems
within an infrastructure that is continuously reliable, highly available, and scalable. Wireless network
users expect the same level of secure connectivity, reliability, and performance for Voice over Wireless
LAN applications as they experience with a wired environment.
Companies aim to design, build, and operate a voice system that is secure, yet highly available to
designated users, and that offers the lowest possible total cost of ownership.
The Cisco Lifecycle Services Approach
The Cisco Lifecycle Services approach defines the minimum set of activities needed, by technology and
by network complexity, to help you successfully deploy and operate Cisco Wireless LAN solutions and
optimize their performance throughout the lifecycle of your network.
Figure A-1 illustrates the general Cisco Lifecycle Services methodology.
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Appendix A
The Cisco Lifecycle Services Approach
Figure A-1
Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
Lifecycle Services Methodology
Prepare
Optimize
Develop a business
case for a technology
investment
Achieve operational
excellence through
ongoing improvements
Plan
Operate
Assess readiness to
support proposed
solution
Maintain network
health through
day-to-day operations
Implement
Create a detailed
design to address
business and techical
requirements
Deploy new
technology
222552
Design
This approach is based on proven methodologies for planning, designing, implementing, operating, and
optimizing the performance of a variety of secure voice and data wireless network solutions and
technologies. It creates a framework for defining services that is independent of who performs the
service activities—Cisco, partners, or customers themselves—enabling multiple parties to provide the
support needed in a coordinated manner. Table A-1 summarizes the lifecycle methodology components
summarized in the sections that follow. Each listed recommended activity links to a brief description.
Note
Cisco and our Wireless LAN Specialized Partners offer a broad portfolio of end-to-end services based
on proven methodologies for deploying and operating a variety of secure voice and data wireless network
solutions and technologies. For more information, please see
http://www.cisco.com/en/US/products/ps8306/serv_home.html.
Table A-1
Lifecycle Methodology for Cisco Voice over Wireless LAN Solutions
General Tasks
Specific Recommended Activity
Prepare
Wireless LAN Business Requirements Development
Wireless LAN Technical Requirements Development
Wireless LAN Operations Technology Strategy Development
Wireless LAN High Level Design Development
Plan
Wireless LAN Deployment Project Management 
Architecture Review and Assessment
Wireless LAN Operations Readiness Assessment
IP Communications over Wireless LAN Assessment 
Wireless Security Posture Assessment
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Appendix A
Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
The Cisco Lifecycle Services Approach
Table A-1
Lifecycle Methodology for Cisco Voice over Wireless LAN Solutions (continued)
General Tasks
Specific Recommended Activity
Design
Wireless LAN Staff Plan Development 
Wireless Security Design Development
Wireless LAN Detailed Design Development 
Wireless LAN Detailed Design Validation 
Wireless LAN Operations Design Development 
Wireless LAN Staging Plan Development 
Wireless LAN Implementation Plan Development 
Wireless LAN Operations Implementation Plan Development 
Wireless LAN Acceptance Test Plan Development 
Wireless LAN Migration Plan Development 
Wireless LAN Site Readiness Assessment (RF Site Survey) 
Security Implementation Plan Development
Implement
Cisco Security Agent Implementation 
Security Implementation Engineering 
Security Network Admission Control Implementation 
Wireless LAN Staging 
Wireless Control System Implementation 
Wireless LAN Controller Implementation 
Wireless LAN Operations Implementation 
Wireless LAN Migration 
Staff Training 
Wireless LAN Acceptance Test and Network Deployment Verification Audit
Operate
Wireless LAN Systems Monitoring
Wireless LAN Incident Management
Wireless LAN Problem Management
Wireless LAN Change Management
Wireless LAN Configuration Management
Wireless LAN Supplier Management
Wireless LAN Security Administration
Optimize
Wireless LAN Business Requirements Alignment 
Wireless LAN Technology Assessment 
Wireless LAN Operations Assessment 
Wireless Security Assessment
Lifecycle Services Methodology—Prepare Phase
In the prepare phase, a company determines a business case and financial rationale to support wireless
LAN solution adoption. By carefully anticipating future needs and developing both a technology strategy
and a high-level architecture to meet those needs, your business is better equipped to contain costs during
deployment and operations.
Cisco recommends the following activities to support successful deployment:
•
Wireless LAN Business Requirements Development
•
Wireless LAN Technical Requirements Development
•
Wireless LAN Operations Technology Strategy Development
•
Wireless LAN High Level Design Development
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Appendix A
The Cisco Lifecycle Services Approach
Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
These activities are described briefly in the sections that follow.
Wireless LAN Business Requirements Development
Assess and document the business requirements for end-user voice over wireless LAN service delivery
that support the technology investment.
Why: Make sound financial decisions by developing a business case that establishes the financial
justification for making a technology change.
Wireless LAN Technical Requirements Development
Analyze your business and voice over wireless LAN service requirements and identify the Cisco
advanced technologies that support them. Document a technology strategy.
Why: Improve efficiency throughout the solution lifecycle by aligning your technology strategy to your
business goals.
Wireless LAN Operations Technology Strategy Development
Create an operational strategy that defines the people, processes, and tools required to support the
operations and management of the technology solution.
Why: Achieve business goals by aligning your operations strategy with your business and technical voice
over wireless LAN requirements.
Wireless LAN High Level Design Development
Create a high-level conceptual architecture of your proposed voice over wireless LAN solution that
addresses business and technical requirements and creates the foundation for wireless LAN solution
deployment. Include specifications for availability, capacity, and security to meet service requirements.
Why: Reduce rework during the design phase by identifying and validating required technologies and
features early in the wireless LAN solution lifecycle.
Lifecycle Services Methodology—Plan Phase
Successful wireless LAN deployment depends on an accurate assessment of your company's network,
security state, and overall readiness to support the proposed solution. In the plan phase, a company
ascertains whether it has adequate resources to manage a technology deployment project to completion.
To evaluate and improve network security, a company tests for vulnerability to intruders and outside
networks.
Cisco recommends the following activities to support successful deployment:
•
Wireless LAN Deployment Project Management
•
Architecture Review and Assessment
•
Wireless LAN Operations Readiness Assessment
•
IP Communications over Wireless LAN Assessment
•
Wireless Security Posture Assessment
•
Wireless Security Design Review
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Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
The Cisco Lifecycle Services Approach
These activities are described briefly in the sections that follow.
Wireless LAN Deployment Project Management
Provide for one or more project managers or program managers to manage the planning, design, and
implementation of your deployment project. Develop and implement a project management plan,
manage information and resources, and control change.
Why: Reduce risks and resolve problems quickly by using proven project management methodologies
and risk mitigation strategies.
Architecture Review and Assessment
Prepare for your technology solution deployment by assessing the readiness of your existing system
infrastructure to support a new technology. Analyze the physical and logical configuration of the
network, systems availability, systems capacity, quality of service, systems resiliency, security, and
integration with existing platforms. Identify network and application modifications that should be made
prior to implementation. Prepare for your technology solution deployment with a comprehensive site
assessment that evaluates the readiness of your current facilities infrastructure to support the new
technology. Identify any physical, environmental, and electrical modifications that should be made prior
to implementation.
Why: Reduce deployment costs by analyzing gaps early in the planning process to determine what is
needed to support the solution and to improve productivity by identifying and resolving gaps in
service-level requirements associated with availability, capacity, and security specifications.
Wireless LAN Operations Readiness Assessment
Prepare for your wireless LAN solution deployment with a comprehensive operations assessment that
evaluates the readiness of your current operations and network management infrastructure to support the
new technology. Identify any changes to people, processes, and tools that should be made prior to
implementation.
Why: Effectively plan and budget for your wireless LAN technology expenditures by gauging your
operational preparedness and ability to support current and planned applications and services. Reduce
network operations costs by identifying the operational changes required to support the operation and
management of the technology solution.
IP Communications over Wireless LAN Assessment
Understand the readiness of the existing wireless LAN to support their proposed IP communications
applications, and how migrating the proposed IP communications application may affect the existing
wireless LAN / Wired LAN. Assess the readiness of your existing wireless LAN to support your
proposed IP communications applications. Appraise the potential effects of migration on the
interoperability between the proposed IP communications application and your existing wireless LAN
and wired LAN. Review building blueprints and coverage requirements, potential interference sources,
noise floor, signal strength, and more.
Why: Avoid costly and disruptive design changes during the implementation phase through early
planning of design changes to accommodate IP communications over wireless LAN.
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Appendix A
The Cisco Lifecycle Services Approach
Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
Wireless Security Posture Assessment
Protect your network from inside and outside intruders by assessing system, application, and network
device vulnerabilities. Safely simulate activities typical of attacks on your network, without affecting
your network. Recommend changes that should be made to the network to help prevent security breaches
and reduce risk of attack.
Why: Mitigate network security threats by limiting their ability to do damage. Improve the overall
security state of the corporate trusted network and the systems and information within it by identifying
changes to address vulnerabilities.
Lifecycle Services Methodology—Design Phase
Developing a detailed design is essential to reducing risk, delays, and the total cost of your wireless LAN
deployment. A design aligned with business goals and technical requirements can improve network
performance while supporting high availability, reliability, security, and scalability. Day-to-day
operations and network management processes need to be anticipated, and, when necessary, custom
applications are created to integrate new systems into existing infrastructure. The design phase can also
guide and accelerate successful implementation with plans to stage, configure, test, and validate network
operations.
Cisco recommends the following activities:
•
Wireless LAN Staff Plan Development
•
Wireless Security Design Development
•
Wireless LAN Detailed Design Development
•
Wireless LAN Detailed Design Validation
•
Wireless LAN Operations Design Development
•
Wireless LAN Staging Plan Development
•
Wireless LAN Implementation Plan Development
•
Wireless LAN Operations Implementation Plan Development
•
Wireless LAN Acceptance Test Plan Development
•
Wireless LAN Migration Plan Development
•
Wireless LAN Site Readiness Assessment (RF Site Survey)
•
Security Implementation Plan Development
These activities are described briefly in the sections that follow.
Wireless LAN Staff Plan Development
Prepare your staff for wireless LAN solution deployment by using conventional instructional design
methodologies to create a staff plan. Determine the technical activities and tasks required to support the
voice over wireless solution, measure the ability of functional groups to perform those tasks, and develop
a curriculum plan to address skill and knowledge gaps.
Why: Reduce ongoing operating costs by identifying proficiency issues that could affect staff
productivity and performance.
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Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
The Cisco Lifecycle Services Approach
Wireless Security Design Development
Develop an in-depth, implementation-ready detailed design for your wireless LAN security solution.
Take into consideration your defined business requirements and the associated performance, availability,
resiliency, maintainability, resource-capacity, and security criteria used to measure and confirm the
delivery of the required services.
Why: Implement advanced security and intrusion detection devices and strategies effectively to keep
data private and secure and lower your total cost of ownership.
Wireless LAN Detailed Design Development
Develop an in-depth, implementation-ready detailed design for your wireless LAN solution. Derive the
design from availability, capacity, reliability, security, scalability, and performance specifications that
align with your business and technical voice over wireless requirements.
Why: Reduce expensive, time-consuming network redesign by creating a well-engineered design early
in the network lifecycle.
Wireless LAN Detailed Design Validation
Validate that your detailed design meets your business and technical voice over wireless requirements
with an in-depth, detailed test plan and support for test implementation. Include testing of features,
functionality, compatibility, and software applications.
Why: Accelerate wireless LAN solution adoption by validating that your design meets end-user service
delivery goals.
Wireless LAN Operations Design Development
Prepare your current operations and network management infrastructure to support the new technology
with a detailed design of the operations and network management processes and tools for your wireless
LAN solution.
Why: Speed migration of the new voice over wireless LAN solution by improving operations
preparedness.
Wireless LAN Staging Plan Development
Develop a step-by-step plan for staging the configuration, implementation, and connectivity testing of
the voice over wireless LAN solution in a controlled environment that emulates, but does not affect, your
production network.
Why: Reduce delays and other problems during staging with a detailed plan that addresses staging
requirements including physical, electrical, and environmental conditions on the site; network hardware
and software; and third-party devices.
Wireless LAN Implementation Plan Development
Develop a detailed, site-specific plan for implementing your voice over wireless LAN solution. Define
the activities, configurations, and commissioning test plans required to deploy and commission the
technology.
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Appendix A
The Cisco Lifecycle Services Approach
Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
Why: Reduce delays, rework, and other problems during implementation by creating a detailed
implementation plan and by accurately estimating the time and resources required to implement the new
system or solution.
Wireless LAN Operations Implementation Plan Development
Develop an operations implementation plan detailing the tasks needed to deploy and commission the
operations and network management system for your voice over wireless LAN solution to be deployed.
Include scheduling of priorities, resources, and responsibilities.
Why: Reduce delays, disruption, and other problems by accurately estimating the time and resources
required to implement new operations and network management systems.
Wireless LAN Acceptance Test Plan Development
Develop a test plan that can be used to demonstrate that the voice over wireless LAN solution to be
deployed meets operational, functional, and interface requirements at implementation.
Wireless LAN Migration Plan Development
Develop a step-by-step plan for migrating your existing wireless network and associated mobility
services to the proposed secure wireless LAN solution.
Why: Improve the speed and efficiency of the migration by developing a plan that covers the steps
necessary to migrate from the existing state to a future state while continuing to minimize the risk and
disruption to critical production systems and applications.
Wireless LAN Site Readiness Assessment (RF Site Survey)
Gauge the ability of your environment to allow secure wireless LAN access in the desired coverage area.
Assess your current state and future needs so you can make informed decisions about how to build your
wireless network architecture.
Why: Obtain the best performance out of your voice over wireless LAN solution by placing access points
in optimal locations and reduce the interference caused by other radio emitters to a minimum.
Security Implementation Plan Development
Develop a step-by-step staging plan detailing the Cisco Security Agent installation and
service-commission requirement tasks to be staged in a controlled implementation environment that
emulates your network.
Why: Reduce delays and other problems during staging with a detailed plan that addresses staging
requirements including physical, electrical, and environmental conditions on the site; network hardware
and software; and third-party devices.
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Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
The Cisco Lifecycle Services Approach
Lifecycle Services Methodology—Implement Phase
A network is essential to any successful organization, and it must deliver vital services without
disruption. In the implement phase, a company works to integrate devices and new capabilities in
accordance with the design-without compromising network availability or performance. After
identifying and resolving potential problems, the company can speed return on investment with an
efficient migration and successful implementation.
Cisco recommends the following activities to support successful deployment:
•
Cisco Security Agent Implementation
•
Security Implementation Engineering
•
Security Network Admission Control Implementation
•
Wireless LAN Staging
•
Wireless Control System Implementation
•
Wireless LAN Controller Implementation
•
Wireless LAN Operations Implementation
•
Wireless LAN Migration
•
Staff Training
•
Acceptance Test and Network Deployment Verification Audit
These activities are described briefly in the sections that follow.
Cisco Security Agent Implementation
Install, configure, and integrate Cisco Security Agent solution components in a production environment.
Why: Successfully deploy the new technology solution by following an in-depth, detailed
implementation process based on leading practices.
Security Implementation Engineering
Develop security design specifications in accordance with your security policies detailing the security
design topology, feature configuration, and policy implementation contains the detailed security design
of the systems, including network diagrams and sample software configurations for protocols, policies,
and features taking you through the initial development process, testing processes, deployment phases
as well as integration, management, and the optimization processes.
Why: More effectively mitigate network security threats by using a sound implementation methodology
to deploy a new security solution that will reduce your operating costs and total cost of ownership by
helping to ensure consistent deployment of security policies.
Security Network Admission Control Implementation
Install, configure, and integrate Network Admission Control components as specified in your
implementation plan. Complete predefined test cases.
Why: Successfully deploy the Network Admission Control components by following an in-depth,
detailed implementation process based on leading practices.
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Appendix A
The Cisco Lifecycle Services Approach
Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
Wireless LAN Staging
Stage and test your voice over wireless LAN solution in a controlled environment that does not affect
your live network, as outlined in your predefined staging plan.
Why: Staging can help you to improve efficiency and reduce costly delays and rework during
implementation by identifying and resolving issues.
Wireless Control System Implementation
Install/upgrade WCS and then configure the WCS software to support for the customer wireless
requirements. Wireless LAN controllers will be configured in WCS along with policy provisioning,
network optimization, security monitoring, and customized fault settings
Why: Realize the business and technical goals of your new system in accordance with recommendations
made in the earlier phases of the lifecycle to monitor and configure the entire wireless LAN solution
from a centralized appliance.
Wireless LAN Controller Implementation
Install and configure the wireless LAN controller and access points to be assigned to the required
Controller according to the wireless LAN detailed design. Configure the security policy including IEEE
802.1X (or VPN) authentication to the RADIUS server and backend database will be configured along
with mobility management including L2/L3 roaming (if required), RF network optimization, including
RF interference detection, TX power and channel optimization, security monitoring, including rogue AP
detection/containment, and intrusion detection, QOS settings, load balancing, policy provisioning, and
customize fault settings.
Why: Successfully deploy the new voice over wireless LAN solution by following an in-depth, detailed
implementation process based on leading practices.
Wireless LAN Operations Implementation
Install, configure, test, and commission the wireless LAN operations and network management system
you are deploying in accordance with your operations implementation plan.
Why: Reduce network operating expenses by improving the efficiency of operations processes and tools.
Wireless LAN Migration
Migrate your existing network services for the solution you are deploying as specified in your migration
plan. Include equipment, interfaces, applications, services, and hardware platforms.
Why: Reduce risks such as downtime, delays, and the need for rework by following a thorough, detailed
implementation process based on leading practices.
Staff Training
Manage and implement the staff development plan for your deployment or operations teams. Includes
scheduling classes, creating the enrollment process, providing course materials, and managing training
vendors. Can include delivery of workshops or instructor-led training classes with hands-on lab
exercises, e-learning, mentoring, materials for self-paced study, and leading-practice documentation.
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Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
The Cisco Lifecycle Services Approach
Why: Increase overall productivity and reduce ongoing wireless LAN solution operating costs through
training designed to close the skill gaps that were identified in developing your staff plan.
Wireless LAN Acceptance Test and Network Deployment Verification Audit
Perform systems-level acceptance testing by performing a survey of the RF environment for coverage,
interference, and general performance of your wireless LAN solution to objectively measure operability
and functionality of the system you are deploying to verify that it meets your business and technical
requirements and is ready for production.
Why: Systems acceptance testing help you speed the migration process; accelerate return on investment;
and reduce unnecessary risk, including disruption, delays, rework, and other problems.
Lifecycle Services Methodology—Operate Phase
Network operations represent a significant portion of IT budgets, so it's important to be able to reduce
operating expenses while continually enhancing performance. Throughout the operate phase, a company
proactively monitors the health and vital signs of the network to improve service quality; reduce
disruptions; mitigate outages; and maintain high availability, reliability, and security. By providing an
efficient framework and operational tools to respond to problems, a company can avoid costly downtime
and business interruption. Expert operations also allow an organization to accommodate upgrades,
moves, additions, and changes while effectively reducing operating costs.
Cisco recommends implementing the following processes to support successful operations:
•
Wireless LAN Systems Monitoring
•
Wireless LAN Incident Management
•
Wireless LAN Problem Management
•
Wireless LAN Change Management
•
Wireless LAN Configuration Management
•
Wireless LAN Supplier Management
•
Wireless LAN Security Administration
These activities are described briefly in the sections that follow.
Wireless LAN Systems Monitoring
Monitor, manage, and report on service-level metrics and abnormal events or trends that might adversely
affect the availability, capacity, performance, and security of your wireless LAN solution.
Why: Improve service quality and reduce disruptions and outages by proactively monitoring system
health.
Wireless LAN Incident Management
Manage and resolve real-time incidents with wireless LAN solution components using an incident
management process that creates and maintains a report of the status of an incident from isolation to
closure.
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The Cisco Lifecycle Services Approach
Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
Why: Restore normal service operation quickly by providing an in-depth incident management process
that includes case management, investigation, and diagnosis; hardware and software replacement or
updates; and service restoration, testing, and verification.
Wireless LAN Problem Management
Manage and resolve recurring incidents using an in-depth problem management process that analyzes
incident trends to identify patterns and systemic conditions.
Why: Reduce the risk of downtime and increase network and/or application availability, reliability, and
stability by analyzing the root cause of recurring wireless LAN incidents and rectifying underlying
problems through hardware and software support.
Wireless LAN Change Management
Standardize methods and procedures for authorizing, documenting, and performing wireless LAN
solution changes.
Why: Reduce operating costs and limit change-related incidents by providing a consistent and efficient
change management process.
Wireless LAN Configuration Management
Obtain an accurate, real-time logical model of your wireless LAN solution hardware, software, and
applications by using an efficient, reliable process for tracking components and component
interrelationships. Identify, control, monitor, maintain, change, and verify versions of individual and
interrelated solution components.
Why: Improve operational efficiency by maintaining an accurate, reliable solution configuration
database and managing configuration changes through an orderly, effective process.
Wireless LAN Supplier Management
Facilitate the efficient delivery of networking products and services by hardware and software vendors
through management of fulfillment, assurance, and financial processes.
Why: Increase operational productivity by aligning supplier processes and tools with your organizational
requirements.
Wireless LAN Security Administration
Protect the confidentiality, integrity, and availability of information on the wireless LAN network using
a thorough security administration process. Manage security incidents, identify and address
vulnerabilities, and secure the delivery of content.
Why: Reduce the risk of wireless LAN network disruptions by proactively identifying security breaches
and defining a remediation plan.
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Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
The Cisco Lifecycle Services Approach
Lifecycle Services Methodology—Optimize Phase
A good business never stops looking for a competitive advantage. That is why continuous improvement
is a mainstay of the wireless LAN solution lifecycle. In the optimize phase, a company is continually
looking for ways to achieve operational excellence through improved performance, expanded services,
and periodic reassessments of network value. Have business goals or technical requirements changed?
Is a new capability or enhanced performance recommended? As an organization looks to optimize its
wireless network and prepares to adapt to changing needs, the lifecycle begins anew-continually
evolving the network and improving results.
Cisco recommends the following activities:
•
Wireless LAN Business Requirements Alignment
•
Wireless LAN Technology Assessment
•
Wireless LAN Operations Assessment
•
Wireless Security Assessment
These activities are described briefly in the sections that follow.
Wireless LAN Business Requirements Alignment
Evaluate how successfully your voice over wireless LAN solution is meeting the requirements
established in your business requirements assessment. Analyze data on operational and capital costs,
return on investment, and other related factors.
Why: Help realize your voice over wireless LAN investment goals by making recommendations to
remediate gaps in solution performance relative to your objectives and requirements.
Wireless LAN Technology Assessment
Improve the performance, availability, capacity, and security of your voice over wireless LAN solution
by assessing system performance and software configurations and recommending changes.
Why: Improve network performance, availability, capacity, and security by assessing a particular system
and recommending improvements.
Wireless LAN Operations Assessment
Improve the performance and functionality of the operations and network management environment
supporting your voice over wireless LAN solution by assessing it and recommending changes.
Why: Help reduce solution operating expenses and improve solution operational productivity,
performance, and functionality by assessing your operations and network management environment and
recommending changes.
Wireless Security Assessment
Assess network security system performance. Measure your security systems for trends and exceptions
related to security policy and procedures and user access. Audit intrusion-detection data. Make
recommendations for improvement.
Why: Improve the security of your company's information assets and your company's ability to mitigate
intrusion attempts.
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Appendix A
The Cisco Lifecycle Services Approach
Deploying and Operating a Secure Voice over Wireless LAN Solution with Cisco Lifecycle Services
Cisco and our Wireless LAN Specialized Partners offer a broad portfolio of end-to-end services based
on proven methodologies for deploying and operating a variety of secure voice and data wireless network
solutions and technologies. For more information, please see
http://www.cisco.com/en/US/products/ps8306/serv_home.html.
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G L OS S A RY
A
AAA
Authentication, Authorization, and Accounting.
ACS
Cisco Access Control Server.
AES
Advanced Encryption Standard.
AP
Access point.
B
BSSID
Basic service set identifier.
C
CAM
Clean Access Manager.
CCMP
Counter Mode with Cipher Block Chaining Message Authentication Code Protocol.
CCX
Cisco Compatible Extensions.
CKIP
Cisco Key Integrity Protocol.
CMIC
Cisco Message Integrity Check.
CSA
Cisco Security Agent.
CSM
Content Switching Module.
CSSC
Cisco Secure Services Client. Cisco Key Integrity Protocol (CKIP) and Cisco Message Integrity Check
(CMIC).
D
DoS
Denial of service.
DTIM
Delivery Traffic Indication Map.
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Glossary
E
EAP
Extensible Authentication Protocol.
EAP-FAST
EAP-Flexible Authentication via Secured Tunnel.
EAP-TLS
EAP-Transport Layer Security.
EDCF
Enhanced distributed coordination function.
EIRP
Effective Isotropic Radiated Power.
ESSID
Extended service set identifier, commonly referred to as an SSID.
F
FWSM
Firewall Services Module.
I
IDS
Intrusion detection system.
IPS
Intrusion prevention system.
L
LAN
Local Area Network.
LAP
LWAPP Access Point.
LBS
Location-based service
LWAPP
Lightweight Access Point Protocol.
M
MAP
Mesh AP
MFP
Management frame protection.
MCS
Media Convergence Server.
MIC
Message integrity check.
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Glossary
N
NAC
Network Admission Control.
NAM
Network Analysis Module.
O
OFDM
Orthogonal Frequency Division Multiplexing.
P
PEAP GTC
Protected EAP Generic Token Card.
PEAP MSCHAP
Protected EAP Microsoft Challenge Handshake Authentication Protocol.
PKI
Public Key Infrastructure.
PTK
Pairwise Transient Key.
R
RADIUS
Remote Authentication Dial-In User Service.
RF
Radio frequency.
RFID
Radio-frequency identification.
RLDP
Rogue Location Discovery Protocol.
RSSI
Received signal strength indication.
S
SNR
Signal-to-noise ratio.
SSID
IEEE Extended Service Set Identifier.
SSLSM
Secure Sockets Layer Services Modules.
SSO
Single sign-on.
SVI
Switched virtual interfaces.
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Glossary
T
TKIP
Temporal Key Integrity Protocol.
TLS
Transport Layer Security.
U
UCM
Unified Communications Manager
UDLD
UniDirectional Link Detection (UDLD)
V
VoWLAN
Voice over Wireless LAN.
W
WCS
Wireless Control System.
WEP
Wired Equivalent Privacy.
Wi-Fi
Wi-Fi is the brand of the Wi-Fi Alliance, which certifies interoperability of products and services based
on IEEE 802.11 technology.
WiSM
Wireless Services Module.
WLAN
Wireless LAN.
WLC
Wireless LAN Controller.
WLCM
Wireless LAN Controller Module.
WLSM
Wireless LAN Services Module.
WMM
Wi-Fi Multimedia.
WPA
Wi-Fi Protected Access.
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