handout12

Architectures and Supporting

Protocols for VOIP/3G

IETF at work

NGN and 3G Network Elements

Numbering and Naming (ENUM)

Session Description Protocol (SDP)

Media Gateway Control (Megaco/MGCP)

Diameter

Raimo Kantola –S- 2007 Signaling Protocols 12 - 1

Agenda

• IETF

• Networking framework – 3G, wireline

• Why control what users can do?

– Justification for 3G IMS architecture

• 3G terminal

• ENUM – naming and addressing

Raimo Kantola –S- 2007 Signaling Protocols 12 - 2

1

IETF

• IETF toolkit

– bottom-up approach

(“one problem – one protocol”)

– Protocols should be simple, reusable, scalable, robust

IESG

Internet Engineering

Steering Group

Application

Area

… simple

General

Area

¾ over 100 active WGs

¾ here are some of them

Raimo Kantola –S- 2007

Internet

Area

O&M

Area aaa dnsop

Routing

Area bgmp idmr idr manet mpls ospf

Signaling Protocols

Security

Area ipsec smime tls

Sub-IP

Area

Transport

Area avt enum iptel mmusic sip sipping sigtran

12 - 3

IETF specifications

•Every standard follows the route Proposed standard-> Draft Standard-> Standard

Raimo Kantola –S- 2007 Signaling Protocols 12 - 4

2

ETSI, etc have delegated the 3G standardisation work to 3GPP

• 3GPP – is the 3G Partnership Project

• this gives a key role to vendors

• site: www.3gpp.org

has all their documents!

• The idea is that ETSI etc will rubberstamp

3G documents as standards.

12 - 5 Raimo Kantola –S- 2007 Signaling Protocols

3G is composed of many Subsystems

UTRAN

Circuit Switched

Domain

UE

Other IP

Connectivity

Access

Network

Packet Switched

Domain

Raimo Kantola –S- 2007 Signaling Protocols

IMS

IP Multimedia

Subsystem

12 - 6

3

3G IP Multimedia core network

Subsystem (3G IMS)

AS AS

AS – Application Server

CAP - Camel Application Part

IM-SSF – IP Multimedia Service Switching

Function

ISC – IP Multimedia Service Control

S-CSCF – Serving Call Session

Control Function

HSS – Home Subscriber Server

Sh

SCIM

SIP Application

Server

ISC

MAP

Si

Cx

Raimo Kantola –S- 2007

ISC

CAP

Camel Service

Environment

ISC

OSA service capability server

Mr

Signaling Protocols

OSA API

OSA application server

MAP - Mobile Application Part

MRFC - Media Resource Function

Controller

OSA – Open Service Access

SCIM – Service Capability Interaction

Manager

SCS – Service Capability Server

12 - 7

Alternative to IMS?

• With a 3G device a user can access the open

Internet and use any services that are available on the Internet: www, e-mail, conferencing, VOIP etc.

– QoS is the Best Effort QoS of regular Internet

– Charging can be either volume based or flat rate.

– Flat rate can lead to overuse of the cellular capacity and poor QoS

• Take the CS domain signaling and call control, map TDM trunks to IP ”connections” Æ retains the existing CS –domain services control and architecture, replace TDM transport by IP (this is called UMA – universal mobile access)

Raimo Kantola –S- 2007 Signaling Protocols 12 - 8

4

Motivation for IMS

• IMS = Integration of cellular and Internet worlds.

Why, when a user already can take an Internet connection from a cellular device and use all

Internet Services?

– Controlled QoS for Interactive voice and video

– Proper Charging for QoS and Freedom of charging based on any business model for the services

– Integration of services on a single packet platform: access to all aspects of sessions from any service.

– Ease of interworking with Internet Services(?)

Q: Is this enough?

Q: Why should operators switch from circuit based voice services to IMS based voice services in 3G?

Raimo Kantola –S- 2007 Signaling Protocols 12 - 9

IMS Objectives

Support for the following:

1. establishing IP Multimedia Sessions

2. negotiation of QoS

3. interworking with the Internet and the CSN

4. roaming

5. strong conrol by the operator with respect to the services delivered to the end user

6. rapid service creation without requiring strandardization

7. access independence ( starting from release 6)

Raimo Kantola –S- 2007 Signaling Protocols 12 - 10

5

Next Generation Network (NGN) is the

ETSI effort to harmonize packet telephony

The network architecture is layered in a much more strict sense than in case of CSN

Services

Control

Switching

• IP Applications

• Virtual Home Environment

• Open Service Architecture

Network Specific

• call control

• session management

• mobility management

• Transcoding at the edge

• Switching

• Routing

In practice this means that ETSI has decided to adopt the IMS framework as a basis for services over all kinds of networks wireline or wireless.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 11

Competition in Information Economy

– Porter’s Five Forces model

Suppliers role is often nonexistent or weak.

Often not governed by markets.

Education system

University Research.

New Entrants

Copyright Brand

New entrants are a constant threat to imcumbents.

Suppliers

Information

”product”

Patent Freq license

Regulation

New innovations (technology push) tends to break old earning methods.

Replacements

Raimo Kantola –S- 2007 Signaling Protocols

Buyers

Bayers role and competition inside the industry is weakened by copyrights, patents and secrets

12 - 12

6

Competition inside an Industry

• Information creation often happens inside companies

• Competition is limited by

– Copyright: a product is available from a single source

– Patent: a problem can often be solved in many ways. A Group of patents, often cross-licenced by key players, may create a new market creating entry barriers for new entrants

– Frequency licenses. E.g. Cellular.

• The key question is granularity: how big an area is coverned by the monopoly right. The bigger the area, the more inefficiencies it can contain.

12 - 13 Raimo Kantola –S- 2007 Signaling Protocols

Price = 0

• Information is non-depletable and non-excludable: you give it to somebody, you still have it and as many times as you like

– Under free market conditions, supply is infinite

– Copy cost approaches zero

– According to law of demand and supply, price approaches marginal cost Æ price of information approaches zero.

• Free market does not support a price that makes creation of information sustainable economically.

• Copyrights, patents, (frequency) licenses and secrets are fundamental for earning money using information.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 14

7

Examples of information goods

• Internet BE service under over-provisioning is non-depletable

– Because ISP does not promise any quality

• Î Overprovisioned BE networks – economically efficient prices = flat rate

• Difficult to recover investments and make a margin Æ desire for control by operators

• In the long run, the mentality of free Internet service will lead to consolidation of operators and creation of new monopolies Æ there is no answer that would be best for all times.

12 - 15 Raimo Kantola –S- 2007 Signaling Protocols

3G Application Triggering

Application Server

Service Logic

HSS

SIP Interface iFC sFC

SIP

S-CSCF – Serving Call Session

Control Function

HSS – Home Subscriber Server

S - CSCF

SIP

S

Filter Criteria SIP

T iFC – Initial Filter Criteria sFC – Subsequent Filter Criteria

SPT – Service Point Trigger

Service processing can be delegated to

Application Servers with a fine grained control sFC is considered historical (obsolete)

The result is the same as in IN: for low penetration services, only one or a few servers need to be upgraded instead of upgrading all CSCF network elements.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 16

8

Media processing in 3G

AS

ISC

S-CSCF

Mr

MRFC

Mp

MRFP

MRFC likely to have a general purpose processor,

MRFP has many DSPs – digital signal processors.

MRFC - Media Resource Function

Controller

MRFP – Media Resource Function

Processor

All this takes place in the IP domain.

Examples:

- transcoding Wideband AMR/

Narrowband AMR codec

- Multiparty conference media processing

In practice it is convenient to implement

MRFP in the same device as the Media

Gateway between CS/PS domains

12 - 17 Raimo Kantola –S- 2007 Signaling Protocols

The role of HSS

Mobility Management

User security info. generation

User security support

Service Provisioning support

Call / Session establishment support

GUP Data Repository

Identification handling

Service authorization support

Access authorization

Application Services Support

CAMEL Services Support

HSS

Source: 23002-700.doc

Release 7

Wx C D

GMSC MSC / VLR

CS Domain

gsmSCF

Gr Gc

SGSN GGSN

PS Domain

3GPP AAA Server

Raimo Kantola –S- 2007

Applications

Signaling Protocols

Rp

Sh

Si Cx

SIP

Application

Server

OSA SCS IM-SSF

IM CN subsystem

CSCF

GUP Server

GUP –Generic

User Profile

12 - 18

9

PSTN PSTN

PSTN Go

Gi Gp

CS-

MGW

Mc

GMSC server

GGSN

PSTN

Nb

VLR

B

MSC server

G

E

Nc

VLR

B

MSC server

Mc

Mc

CS-MGW

Nb

CS-MGW

A

IuCS

BSS

BSC

Gb

IuPS

Abis

BTS BTS

Nc

C

HSS

(

HLR,AuC)

Gc

Gr

D

EIR

F Gf

Gs

IuCS

Gn

SGSN

RNC

Node B cell

Iub

IuPS

RNS

Node B

Iur

CN

Um

Uu

RNC

Basic Configuration of a PLMN

GGSN – Gateway GPRS Support Node

SGSN – Serving GPRS Support Node

HSS – Home Subscriber Server

RNC – Radio Network Controller

Node B = 3G base station

USIM – UMTS Subscriber Identity Module

On CS side breakdown of MSC to

Media Gateway and MSC server.

3G and GSM/GPRS are based on the same packet core elements.

ME

SIM-ME i/f or Cu

Raimo Kantola –S- 2007

SIM USIM source: www.3gpp.org/specs/archive/23002-580

MS

Signaling Protocols 12 - 19

The IP Multimedia Subsystem

Mb

Mb sits on top of the Packet Core

IP Multimedia Networks

PSTN

Mb PSTN

BGCF CSCF

PSTN

Mk Mk

Mw

Mj

BGCF

Mi

Mm

Cx

IMS-

MGW

Mn

MGCF

Mg

CSCF

Mb

Mr

Mw

Dx

Legacy mobile signalling Networks

BGCF – Breakout Gateway

Control Function

PCF – Policy Control Function

HSS

C, D,

Gc, Gr

SLF – Service Location Function

CSCF – Call Session Control

Function

P-CSCF – Proxy CSCF

HSS – Home Subscriber Server

SLF

MRFP

Mb

M p

Mb

Raimo Kantola –S- 2007

MRFC

P-CSCF

PCF

UE

Gm

Go

IM Subsystem

source: www.3gpp.org/specs/archive/23002-580

Signaling Protocols 12 - 20

10

Signaling Gateway maps SS7

MTP to SCTP/IP transport

IP

Signalling transport

NW

SCTP/IP

SGW

MTP

SS7

Signalling transport

NW

This allows to transfer signaling and service processing responsibility to IP based environment.

NB: The call control protocol on top may be e.g. ISUP on both interfaces, just the message transport is between MTP and IP

Raimo Kantola –S- 2007 Signaling Protocols 12 - 21

UE

UE has a tunnel to visited IMS

PDP – Packet data protocol (IPv4, IPv6 or X.25 …)

Virtual presence of UE in visited network IM subsystem

(UE’s IP-address is here)

SGSN

Visited Network

GGSN

Gi

PDP Context

Home Network

IM Subsystem

BG

Inter-Network

IM Backbone

BG

Visited Network

IM Subsystem

Internet

Intranets

Raimo Kantola –S- 2007 Signaling Protocols 12 - 22

11

3G UE can use several services at the same time

Gi

Internet/

Intranet

Home Network

GGSN

SGSN

Gp

BG

UE

PDP Context

Gp

BG

Visited Network

Visited Network

IM Subsystem

SGSN GGSN

PDP Context

- PDP context = virtual connection between the terminal and an access point to an

IP network thru GGSN

- Assigns an IP address for the terminal

For mobile office applications Intranet connectivity at this level is not popular. Instead IP VPNs are used.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 23

ETSI SoftSwitch Architecture for NGN

This is the wireline networking framework

Service

Control

Point (SCP)

INAP

Service

Switching

Point(SSP)

ISUP or other

Voice

API

Integrated

Service

Node

Circuit Switched Network

Application

Service

Application

Parlay

Interface

Adapter

API

API

Signaling

Gateway

API

Media

Gateway

Controller

SS7 over IP

SIP

MEGACO or MGCP

Media

Gateway

SIP Server

SIP

Voice over RTP

Raimo Kantola –S- 2007 Signaling Protocols 12 - 24

12

The UMTS terminal functional model

Browser Streaming

Point-to-Point data

Messaging

FTP LDAP DNS HTTP SLP SIP IMAP SMTP X.509 Radius H.323

QoS extension

QoS

Management

DiffServ RSVP TCP

IP

Packet Classifier

Socket API

DHCP RTP/RTCP

WAP

UDP

PPP

UMTS

12 - 25 Raimo Kantola –S- 2007 Signaling Protocols

IMS Interworking with the PSTN

• IMS terminals must support CSN services due to Emergency Call requirements, so

PSTN interworking can occur thru the CS domain. However, IMS Interworking with PSTN is also possible.

SGW

SIP

ISUP/IP

BGCF

SIP

MGCF

H.248

RTP

MGW

ISUP/MTP

Switching

System

PCM

Raimo Kantola –S- 2007 Signaling Protocols 12 - 26

13

The GPRS and 3G networks implement the Multimedia Messaging Service

MMS User Agent

HLR

MMS

Server

SMSC

Wireless

Network

MMS

Relay

e-mail

Server

Foreign

MMS

Relay

Wireless

Network

MMS

Server

Uses MMS over WAP

HTTP and WAP push

MMS User Agent

Raimo Kantola –S- 2007 Signaling Protocols 12 - 27

Supporting protocols for IP telephony – wired and wireless

• ENUM – addressing and naming

• Gateway control - Megaco

• Session description – SDP

• AAA - Diameter

12 - 28 Raimo Kantola –S- 2007 Signaling Protocols

14

Naming and Addressing in NGN and 3G

IMS vs. Telephone numbering

• A Name identifies a domain, a user or a service. An address

points to a user or to an interface or to an inlet/outlet in a network.

• Internet heavily relies on the Domain Name System (DNS) to translate names to addresses. The specs of using DNS for

Telephony names and addresses is called ENUM – tElephone-NUmber-Mapping.

• ENUM was originally meant for mapping IP telehone numbers (e.g. 3G IMS phonenumbers) to logical names (and

IP addresses).

• With Naming and Addressing, at the same time we need to solve the problem of Gateway (CSN/IP) location and

Number Portability across the technology boundary.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 29

ENUM uses DNS to store telephone numbers

”.” the root

.arpa

.com

.net

.fi

.e164.arpa

in-addr second-level node second-level node second-level node

Most likely ”.e164.arpa” –server is the root of the ENUM hierarchy.

Countries are starting to reserve names under it and establishing

ENUM services/country. Enum pilot in Finland in 2004-2006.

8.5.3.e164.arpa

Telephone numbers are presented in the inverted order with dots in between!

An ENUM server may cover any subtree.

1.1.5.4.9.8.5.3.e164.arpa

A node may carry any digit string with dots

(not just one digit) – this is up to operators.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 30

15

ENUM introduces NAPTR records

RFC 2915 - The Naming Authority Pointer (NAPTR) DNS Resource Record (Sep 2000)

NAPTR – Naming Authority PoinTeR = Record in DNS containing an URI.

E.g. IN NAPTR 10 10 ”u” ”sip+E2U” ”!^.*$!sip:[email protected]!”.

Internet expect uri

Record type

Order and Pref

SIP, E.164 to

URI

The URI itself!

Can be modified by Regular expression

NAPTR format is: Domain TTL Class Type Order Preference Flags Service Regexp Replacement

Domain=first well known key e.g. <something>.uri.arpa

TTL=Time-To-Live – validity time of the record (time to cache)

Class=IN=Internet

Type=NAPTR=35

Order=low nrs are processed before high, once target found, stop (excepting flags)

Pref=if same order value, all with diff pref can be processed, take lowest first.

Flags=“S”-next lookup for SRV record, “A”-next lookup for A, AAAA or A6 record, “U” – the reminder has an URI+this is the last record, P –protocol specific processing

Service=protocol-name + resolver, resolver is used to resolve the result of regexp

Regexp=replacement-rule for whatever querier is holding.

Replacement=a fully qualified domain name to query next for NAPTR, SRV or address records (“S”, “A”)

Raimo Kantola –S- 2007 Signaling Protocols 12 - 31

Example from RFC 2915

In order to convert the phone number to a domain name for the first iteration all characters other than digits are removed from the telephone number, the entire number is inverted, periods are put between each digit and the string ".e164.arpa" is put on the left-hand side. For example, the

E.164 phone number "+1-770-555-1212" converted to a domain-name it would be

"2.1.2.1.5.5.5.0.7.7.1.e164.arpa."

For this example telephone number we might get back the following

NAPTR records:

$ORIGIN 2.1.2.1.5.5.5.0.7.7.1.e164.arpa.

IN NAPTR 100 10 "u" "sip+E2U" "!^.*$!sip:[email protected]!" .

IN NAPTR 102 10 "u" "mailto+E2U" "!^.*$!mailto:[email protected]!" .

This application uses the same 'u' flag as the URI Resolution application. This flag states that the

Rule is terminal and that the output is a URI which contains the information needed to contact that telephone service. ENUM uses the Service field by defining the 'E2U' service. The example above states that the available protocols used to access that telephone's service are either the Session Initiation Protocol or SMTP mail.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 32

16

A possible ENUM hierarchy

Tier 1 maps a number of a number block to ENUM op, Tier 2 gives the NATPR records.

(this is the planned deployment model in Finland)

Tier 0 ficora_enum.fi

8.5.3.e164.arpa

Tier 1 enum.elisa.fi

$ORIGIN e164.arpa.

1 IN NS att_enum.com.

6.4 IN NS sweden_enum.se.

8.5.3 IN NS ficora_enum.fi.

$ORIGIN 4.9.8.5.3.e164.arpa.

5 IN NS enum.elisa.fi.

6 IN NS enum.elisa.fi.

358 is delegated to ficora_enum

Elisa is chosen as the ENUM operator for HUT numbers 09-45….,

From Oct 2006 will be run by Ficora

Tier 2

$ORIGIN 1.7.4.2.1.5.4.9.8.5.3.e164.arpa.

IN NAPTR 10 10 ”u” ”sip+E2U” ”!^.*$sip:[email protected]!”.

My office phone number is mapped to a (non-existing at the moment)

SIP server operated by the NETLAB

Tier 3

Corporate numbering schemas…

In Finnish ENUM pilot until oct-2006 only Tier 1 and Tier 2 present!

Raimo Kantola –S- 2007 Signaling Protocols 12 - 33

ENUM use and future

• Since DNS is used by everybody, ENUM is a likely surviver, policy routing etc additions may emerge

• Due to Number Portability, the Provision of

ENUM service and the provision of VOIP service to end-customers are two independent services.

– User may need to select the Numbering service provider separately from the VOIP service provider.

• ENUM does not support secret telephone numbers

12 - 34 Raimo Kantola –S- 2007 Signaling Protocols

17

Use of ENUM in 3G IMS

• If the callee is identified by tel URL (tel: +358-59-345-

897), the originating S-CSCF tries to map this to a SIP

URI using a NAPTR query to ENUM

– successful if the target is a VOIP number

– Æ if call is made from IMS to GSM, we first try to find the destination in an IP network. This may take a while because the query escalates up in the DNS hierarchy.

• If no mapping is found, it is assumed that the target is a

PSTN or any other CSN number and the call signaling is routed to a BGCF (Breakout Gateway Control Function) that is specialised at routing based on telephone numbers.

12 - 35 Raimo Kantola –S- 2007 Signaling Protocols

Call from PSTN to a SIP phone

2. Query

1.7.4.2.1.5.4.9.8.5.3.e164.arpa

ENUM

3. Response sip:[email protected]

1. Caller dials 4512471

Gateway

4

5. INVITE SIP

Proxy

IP Network

4 - sip:[email protected]

is translated to an IP address of the SIP proxy serving the number by another DNS query that returns an address record.

6. INVITE

SIP phone

192.151.79.187

or

+358-9-451 2471

12 - 36 Raimo Kantola –S- 2007 Signaling Protocols

18

ENUM issues and problems

• Long chain of DNS servers results in low reliability

• Secret telephone numbers seem to require two ENUM systems: the

”Operator ENUM” with no direct access by users and ”user ENUM”.

• Result is always the same for a number irrespective of from where the call is originating in a domain ÆNon-optimal routing.

• Number Portability accross technology boundary would require changes in PSTN (link between IN and ENUM)

• Using ENUM for calls from PSTN is difficult because of overlap sending: non-complete numbers are not described in ENUM records (leads to many queries with result: Not Found).

• Management of numbering data. DNS mgt tools are not optimal.

• Security (DNSSec under development…?)

• Nicklas Beijar of Netlab suggests solutions to some of the above problems in his Lic thesis 2004.

• ENUM pilot in Finland until 1.6.2005 now unofficially, from Oct 2006 commercial operation says Klaus Nieminen of Ficora.

12 - 37 Raimo Kantola –S- 2007 Signaling Protocols

IP Telephony Research in the

Networking Laboratory

• Technology evaluation

– Delay measurements breakdown (1997…)

– SIP call waiting

• Numbering and Routing Information

Interoperability with ISDN

– TRIP (Telephony Routing over IP) and ENUM protocols

– CTRIP (Circuit TRIP) protocol proposed

– Database (mySQL) solution to Number Portability

(Antti Paju)

– Nicklas Beijar’s Lic thesis (Spring 2004) on alternative solutions for NP

Raimo Kantola –S- 2007 Signaling Protocols 12 - 38

19

SDP: Session Description Protocol

• SDP was initially designed for Mbone. Mbone was/is a multicast overlay network on the Internet

• Used to describe sessions (to link the session with media tools)

• Describes conference/session addresses and ports

+ other parameters needed by RTP, RTSP and other media tools

• SDP is carried by SIP, SAP: Session

Announcement Protocol etc.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 39

Multicast

• Several parties involved

– IPv4 Multicast from 224.0.0.0 – 239.255.255.255

• Saves bandwidth cmp to n times p2p connection

• Entity that is sending does not have to know all the participants

• Multicast Routing protocols

– Dense Mode (shortest-path tree per sender)

– Sparse Mode (shared tree used by all sources)

• IGMP (Internet Group Management Protocol)

– For hosts that want to become part of a multicast group

• Mbone – part of Internet that supported multicast

• RTP – transport of real-time data such as voice or video

– Sequence number, timestamps

• RTCP – controls RTP transport (every RTP session has a parallel

RTCP session.)

• Has its direct use as a service in corporate networks and as a service enabler in public networks.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 40

20

SDP can describe

• Session name and purpose

• Time(s) the session is active

– start, stop time, repetition (relevant for conferences)

• The media comprising the session

– video, audio, etc

– transport protocol: RTP, UDP, IP, H.320 etc

• Parameters to receive media: addresses, ports, formats etc.

– H.261 video, MPEG video, PCMU law audio, AMR audio

• Approximate bandwidth needed for the session

• Contact info for person responsible

12 - 41 Raimo Kantola –S- 2007 Signaling Protocols

SDP info is <type>=<value> in strict order

<type> is a single, case sensitive character.

<value> is a text string or a nrof fields delimited by a single white space char.

SDP has one session level description and optionally n media descriptions.

Session description v= (protocol version) o= (owner/creator and session identifier).

s= (session name) i=* (session information) u=* (URI of description)

* = optional e=* (email address) p=* (phone number) c=* (connection information - not required if included in all media) b=* (bandwidth information)

One or more time descriptions (see below) z=* (time zone adjustments) k=* (encryption key) a=* (zero or more session attribute lines)

Zero or more media descriptions (see below)

Raimo Kantola –S- 2007 Signaling Protocols 12 - 42

21

SDP items continued

Time description t= (time the session is active) r=* (zero or more repeat times)

Media description m= (media name and transport address) i=* (media title) c=* (connection information - optional if included at session-level) b=* (bandwidth information) k=* (encryption key) a=* (zero or more media attribute lines)

3G document refer to a newer SDP- draft from may 2002.

Some SDP documents:

RFC 2327: SDP Session Description Protocol (dated 1998), now Proposed Std

RFC 3407: SDP Simple Capability Declaration

RFC 3264 - An Offer/Answer Model with Session Description Protocol (SDP)

RFC 3266 - Support for IPv6 in Session Description Protocol (SDP)

RFC 3556 SDP Bandwidth modifiers for RTCP

Raimo Kantola –S- 2007 Signaling Protocols 12 - 43

Megaco - Media Gateway Control protocol controls Media Gateways and Media Processing

• MGCP was promoted by Cablelabs = US CATV

R&D body as the CATV Telephony standard

• ITU-T has its own variant called Megaco=H.248

• Megaco, MGCP are master-slave protocols by which media gateways can be configured e.g to services - in case of residential media gateway,

MGCP becomes a subscriber signalling system

Raimo Kantola –S- 2007 Signaling Protocols 12 - 44

22

Gateway decomposition

SG

DSS1 or ISUP

(e.g. ISUP over IP)

Media Gateway

Control

IP based signaling

(H.323 or SIP)

H.248 = Megaco or MGCP

PCM voice Media

Gateway

RTP + RTCP flow

MG - Trunk gateway, residential gateway etc.

Many MGs can be controlled by one MGC, MGCs can be a mated pair --> higher availability performance.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 45

Megaco functions

• Establishment of connections between terminations

– PCM –timeslots for voice

– ephemeral packet stream terminations: IPaddress + source + dest UDP-port number

• Release of connections

• Separation of signaling from voice band in case of CAS and analogue subsc signaling

12 - 46 Raimo Kantola –S- 2007 Signaling Protocols

23

SCN

LS

IP

LS

SG

MGC

Megaco

SS

ISU

P/H

.323

/SIP

SS

LS

MG

SG - Signalling Gateway, MGC - Media Gateway Controller

MG - Media Gateway, SS = Signaling Server, LS = Location Server

Raimo Kantola –S- 2007 Signaling Protocols 12 - 47

Gateway decomposed

SCN

SCN - SIG

(CCS)

Call Control

MGC

Megaco

IP - SIG

= SIP

= H.323

= ISUP/IP

SCN-SIG

- CAS

MG

IP

12 - 48 Raimo Kantola –S- 2007 Signaling Protocols

24

Megaco for Residential Gateways

• Residential MG processes analogue subscriber signaling – inband, can not be separated from media plane

• Controller gives a dialling pattern for MG to look for. When detected, report to MGC. MGC gives a new pattern to look for. Etc.

• Real time processing of signals is delegated to the residential gateway, while MGC retains overall control over what is happening and what is the interpretation of the patterns.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 49

NAT Traversal

RFC 3489 Title: STUN - Simple Traversal of User Datagram Protocol (UDP) Through Network

Address Translators (NATs)

Author(s): J. Rosenberg, J. Weinberger, C. Huitema, R. Mahy

Status: Standards Track Date: March 2003

See also: http://corp.deltathree.com/technology/nattraversalinsip.pdf

Traversal Using Relay NAT (TURN) draft-rosenberg-midcom-turn-03

• The NAT story that was here is OBSOLETE

• Look at Gonzalo’s slides!

Internet is an A-subscriber’s Network! B-subscribers are not connected!

Raimo Kantola –S- 2007 Signaling Protocols 12 - 50

25

Documents of BEHAVE

Internet-Drafts:

Simple Traversal Underneath Network Address Translators (NAT) (STUN) (152616 bytes)

Network Address Port Translator (NAPT) Any-Source Multicast Requirement (14242 bytes)

NAT Behavioral Requirements for TCP (47849 bytes)

Obtaining Relay Addresses from Simple Traversal Underneath NAT (STUN) (124751 bytes)

Extension to the Simple Traversal Underneath NAT (STUN) Relay Usage for IPv4/IPv6 Transition

(15352 bytes)

NAT Behavioral Requirements for ICMP protocol (48330 bytes)

State of Peer-to-Peer(P2P) Communication Across Network Address Translators(NATs)

(81765 bytes)

Request For Comments:

Network Address Translation (NAT) Behavioral Requirements for Unicast UDP (RFC 4787)

(68693 bytes)

DO NOT USE THESE SLIDES on NAT Æ LOOK at Gonzalo’s presentation instead!

Raimo Kantola –S- 2007 Signaling Protocols 12 - 51

About NATs and VOIP

• Users behind a NAT use private addresses. They may e.g. get them from a

DHCP server in the private network. E.g. an ADSL modem with several

Ethernet ports may contain a NAT and the DHCP server. Private addresses are not unique in the Internet and can not be used for communication across the public Internet.

• When a host in the private network sends a message to the public Internet, the

NAT creates a mapping: [priv-source IP add, source port] -> [public source IP addr, source port] and will keep this mapping for a time. If within the time a packet is seen, the timeout is restarted. As a result, non-active hosts do not need to have a public IP address. When the timeout expires, the mapping is deleted. Due to a NAT, a large number of clients can use a single public IP address (how many depends on how many ports each will use simultaneously).

• In client server applications (DNS, e-mail, www etc), communication always starts from the host so NAT traversal is automatic. E.g. using DNS (a server in the public Internet), the client (even behind a NAT) can learn public IP addresses of other communicating parties such as mail server addresses. VOIP is fundamentally a peer-to-peer application, because a VOIP client must be reachable from the public Internet. Clients with private addresses are not reachable from the Internet – they must themselves take the initial step.

Moreover, VOIP may send the callers IP add+port information in application messages (in signaling).

Raimo Kantola –S- 2007 Signaling Protocols 12 - 52

26

Problems created by NATs to VOIP

• Invitation (or setup message) can not be sent to a client in a private IP network, i.e. behind a NAT. This does not depend on whether the call comes from a client or a proxy in the public Internet.

– This means that there are no B-subscribers (callees) in the Internet with NATs

• Even if the invitation goes through, sending voice packets (RTP/UDP/IP) to the B –subscriber is not possible without additional tricks, because RTP can not use the same port as signaling.

• A solution would be that ”B-subscribers” are always registered on some server in the Internet and all packets to the B-subscriber go through the server. For signaling, this might be ok (although it defiets the original purpose of NATs). For voice packets, this creates additional delay and a significant additional cost.

12 - 53 Raimo Kantola –S- 2007 Signaling Protocols

Diameter is the emerging AAA protocol for the Internet and 3G

• Applications include:

– Network Access Servers for dial-up with PPP/SLIP,

– Mobile IPv4 Foreign Agents,

– Roaming 3G and Internet users (SIP Application).

– Credit Control

– Vendor specific applications: e.g. 3G policy and charging control

• Provides Authentication of users, Authorization and Accounting of use

• Carried over TCP or SCTP

Client

REQ

NAS: Network Access

Server

Mobile IPv4 FA

S-CSCF

Answer

Agent

Relay

Proxy

Redirect Agent

Request

Answer

Server Msg e.g. stop service now

Server e.g.

-Policy server

- HSS

Raimo Kantola –S- 2007 Signaling Protocols 12 - 54

27

Overall Diameter Architecture

Network Access

Server

Application

EAP

Application

Mobile IPv4

Application

SIP

Application

Credit Control

Application

Diameter Base Protocol (RFC 3588)

EAP - Extensible Authentication Protocol

NB: The current de-facto solution to AAA is Radius – Diameter for example in 3G

IETF Diameter group has not yet adopted 3G policy and charging control (PCC)…

Raimo Kantola –S- 2007 Signaling Protocols 12 - 55

Diameter Documents

Request For Comments:

Accounting Attributes and Record Formats (RFC 2924) (75561 bytes)

Introduction to Accounting Management (RFC 2975) (129771 bytes)

Criteria for Evaluating AAA Protocols for Network Access (RFC 2989) (53197 bytes)

Authentication, Authorization, and Accounting:Protocol Evaluation (RFC 3127) (170579 bytes)

Authentication, Authorization and Accounting (AAA) Transport Profile (RFC 3539) (93110 bytes)

Diameter Base Protocol (RFC 3588) (341261 bytes)

Diameter Mobile IPv4 Application (RFC 4004) (128210 bytes)

Diameter Network Access Server Application (RFC 4005) (198871 bytes)

Diameter Credit-Control Application (RFC 4006) (288794 bytes)

Diameter Extensible Authentication Protocol (EAP) Application (RFC 4072) (79965 bytes)

Diameter Session Initiation Protocol (SIP) Application (RFC 4740) (174175 bytes)

No Internet drafts (12.1.2007)

Source: http://www.ietf.org/html.charters/aaa-charter.html

Raimo Kantola –S- 2007 Signaling Protocols 12 - 56

28

Diameter features include

- Delivery of attribute value pairs: AVPs

- Capability negotiation

- Error Notification

- Extensibility

- Sessions and Accounting

User Authentication

Service specific authentication info -> grant service or not

Resource usage information

- accounting and capacity planning is supported

Relay, proxy and redirect of requests thru a server hierarchy

12 - 57 Raimo Kantola –S- 2007 Signaling Protocols

Diameter operation model

User NAI

Local Realm

Client

Relay

Routing

Security Association

TCP/SCTP SCTP/TCP

Proxy

Policy

Roaming Relationship

Home Realm

SCTP/TCP

Home

Server

User Session

Accounting Relationship

NAI – Network Access Identifier = user’s-identity + realm

Raimo Kantola –S- 2007 Signaling Protocols 12 - 58

29

Diameter terms and definitions

Accounting

The act of collecting information on resource usage for the purpose of capacity planning, auditing, billing or cost allocation.

Authentication

The act of verifying the identity of an entity (subject).

Authorization

The act of determining whether a requesting entity (subject) will be allowed access to a resource (object).

AVP

The Diameter protocol consists of a header followed by one or more Attribute-Value-Pairs (AVPs).

AVP = header encapsulating protocol-specific data (e.g. routing information) + AAA information.

Broker

A broker is a business term commonly used in AAA infrastructures. A broker is either a relay, proxy or redirect agent, and MAY be operated by roaming consortiums. Depending on the business model, a broker may either choose to deploy relay agents or proxy agents.

Diameter Agent = Diameter node that provides either relay, proxy, redirect or translation services.

Diameter Client = a device at the edge of the network that performs access control. Examples are a Network Access

Server (NAS) or a Foreign Agent (FA).

Diameter Node = a host process that implements the Diameter protocol, and acts either as a Client, Agent or Server.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 59

More Diameter terms

Diameter Security Exchange = a process through which two Diameter nodes establish end-to-end security.

Diameter Server = one that handles AAA requests for a particular realm. By its very nature, a Diameter Server

MUST support Diameter applications in addition to the base protocol.

End-to-End Security

TLS and IPsec provide hop-by-hop security, or security across a transport connection. When relays or proxy are involved, this hop-by-hop security does not protect the entire Diameter user session. End-to-end security is security between two Diameter nodes, possibly communicating through Diameter Agents. This security protects the entire Diameter communications path from the originating Diameter node to the terminating Diameter node.

Home Realm = the administrative domain with which the user maintains an account relationship.

Interim accounting

An interim accounting message provides a snapshot of usage during a user's session. It is typically implemented in order to provide for partial accounting of a user's session in the case of a device reboot or other network problem prevents the reception of a session summary message or session record.

Local Realm

A local realm is the administrative domain providing services to a user. An administrative domain MAY act as a local realm for certain users, while being a home realm for others.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 60

30

Still more terms

Network Access Identifier or NAI [NAI] = a user's identity + realm.

The identity is used to identify the user during authentication and/or authorization, the realm is used for message routing purposes.

Proxy Agent or Proxy

- forward requests and responses,

- proxies make policy decisions relating to resource usage and provisioning. This is typically accomplished by tracking the state of NAS devices.

- proxies typically do not respond to client Requests prior to receiving a Response from the server,

- they may originate Reject messages in cases where policies are violated.

- proxies need to understand the semantics of the messages passing through them, and

- may not support all Diameter applications.

Real-time Accounting

Real-time accounting involves the processing of information on resource usage within a defined time window.

Time constraints are typically imposed in order to limit financial risk.

Relay Agent or Relay

- Relays forward requests and responses based on routing-related AVPs and realm routing table entries.

- do not make policy decisions, they do not examine or alter non-routing AVPs.

- relays never originate messages, do not need to understand the semantics of messages or non-routing AVPs,

- are capable of handling any Diameter application or message type.

- do not keep state on NAS resource usage or sessions in progress.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 61

The last terms

Redirect Agent

- refer clients to servers and allow them to communicate directly.

- do not sit in the forwarding path Æ they do not alter any AVPs transiting between client and server.

- do not originate messages and

- are capable of handling any message type, although they may be configured only to redirect messages of certain types, while acting as relay or proxy agents for other types.

- do not keep state with respect to sessions or NAS resources.

Roaming Relationships

Roaming relationships include relationships between companies and ISPs, relationships among peer ISPs within a roaming consortium, and relationships between an ISP and a roaming consortium.

Security Association

A security association is an association between two endpoints in a Diameter session which allows the endpoints to communicate with integrity and confidentially, even in the presence of relays and/or proxies.

Session = a related progression of events devoted to a particular activity. Each application SHOULD provide guidelines as to when a session begins and ends. All Diameter packets with the same Session-Identifier are part of the same session.

Sub-session represents a distinct service (e.g. QoS or data characteristics) provided to a given session. These services may happen concurrently (e.g. simultaneous voice and data transfer during the same session) or serially. These changes in sessions are tracked with the Accounting-Sub-Session-Id.

Translation Agent performs protocol translation between Diameter and another AAA protocol, such as RADIUS.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 62

31

Access is broken into sessions:

Diameter authorizes sessions

Client

Initial Request for Autentication/authorization: IRA

[Session-id] whatever

[Session-id]

:

:

whatever

[Session-id]

Server

Session Termination Request: STR [Session-id]

Session Termination Answer: STA [Session-id]

12 - 63 Raimo Kantola –S- 2007 Signaling Protocols

A diameter node has a peer table

Host identity Status

Stat/ Dyn Expiration time TLS enabled Additional Security info origin host

-from capability exchange:

CER/CEA

- Closed

- Wait-conn-ack

- wait-I-CEA

- wait-I-CEA/Elect

- wait-returns

- R-Open

- I- Open

- ….

- …

- Stop

- = state of the “dialogue” with the peer

The peer table is referenced by

Realm Routing Table.

The peer relationship may be dynamically established – will have an expiration time.

12 - 64 Raimo Kantola –S- 2007 Signaling Protocols

32

Diameter peer discovery helps scalability: order is as follows

• Search manually configured peer agent list

• Use SLPv2 (service location protocol)

• NAPTR query to DNS (”AAA+D2x where x=T|S, T=tcp, S=sctp) – gives the preferred SRV record, a new query gives the IP address

• query `_diameter._sctp´.realm and

`_diameter._tcp´.realm, where realm is the destination realm

Raimo Kantola –S- 2007 Signaling Protocols 12 - 65

Realm Routing Table describes the actions of a Diameter Node

Primary Key Secondary key

Realm-name Application-id Local Action Next-Hop

- vendor-id

- application-id

Local

Relay

[Transaction State]

Server Failover

Proxy

Redirect

Local Policy

Processing

[Session state]

Breaks end-to-end security

Home Diameter Server identity

Default Entry for Non-matching Requests

A node can act as proxy for some user connections and as a relay for others.

The Routing Table is configuration information.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 66

33

Redirect server helps to centralize Diameter request routing in a roaming consortium

NAS example.net

1. Request

6. Answer

2. Request

Redirect

Server

Use Example:

Service Location Function:

SLF in 3G to locate HSS

3. Redirect Notification

Relay example.net

4. Request

5. Answer

Home

Server example.com

12 - 67 Raimo Kantola –S- 2007 Signaling Protocols

A node must watch over its peers to achieve security

Authorized user session

Check Record-Route AVP

Client

Route-Record AVP

HMS

Authorized connection Authorized connection

Replay&integrity protection&Confidentiality/packet

Capability Request

Advertize Applications

Credit-limit

- Capability negotiation tells a node what to expect of a peer

- Authorization means taking a business risk, limited by Credit limit agreed by the peer realms.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 68

34

Diameter header is designed for max flexibility

Version=1

Command Flags

Message Length

Command-Code

Application-ID

Hop-by-Hop Identifier

End-to-End Identifier

AVPs

R(equest) – if 0 = Answer

P(roxiable) – if 0 msg must be locally processed

E(rror) – only set in Answer msgs.

T(potentially re-transmitted message

- set after failover to help remove duplicate messages

Raimo Kantola –S- 2007 Signaling Protocols

Application-ID: e.g. 3GPP application

Normally +1 increasing number on a connection

Same for Request and the corresponding Answer

Client sets to locally unique value (4 min) even over Reboots

Server copies from Request to Answer

12 - 69

Base Diameter protocol Requests and Answers

Diameter node

Abort-Session-Request: ASR

Abort-Session-Answer: ASA

Accounting-Request: ACR

Diameter node

Accounting-Answer: ACA

Capabilities-Exchange-Request: CER

Capabilities-Exchange-Answer: CEA

Device-Watchdog-Request: DWR

Device-Watchdog-Answer: DWA

Disconnect-Peer-Request: DPR

Disconnect-Peer-Answer: DPA

Re-Auth-Request: RAR

Re-Auth-Answer: RAA

Session-Termination-Request: STR

Session-Termination-Answer: STA

For each Command-code

Spec contains exact possible flags, required and optional

AVPs and their nr.

Applications introduce additional command-codes and their exact syntax.

Applications may extend these

Messages.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 70

35

Base protocol AVPs

AVPs have a common header

VMPrrrrr

AVP Code

AVP Length

Vendor-ID (opt)

Data…

V-vendor-id present

M-Mandatory AVP

P-encryption for e-2-e sec

In AVPs e.g. the following items may appear:

- IPaddress

- Time

- UTF8String

- Diameter Identity = FQDN

(fully qualified domain name)

- Diameter URI such as

”aaa://” FQDN [port] [transport] [protocol] aaa://host.example.com:1813;transport=sctp; protocol=radius

- IPFilterRule such as action dir proto from src to dst [options], where action =permit|deny dir=in|out (in = from the terminal) src/dst = <address/mask> [ports]

You can specify firewall rules in Diameter.

12 - 71 Raimo Kantola –S- 2007 Signaling Protocols

A diameter node operation is described as a set of state machines

• Peer state machine

• Authorization Session State Machines (4)

– Server maintains session state: client FSM and server

FSM

– Server does not maintain session state: client FSM and server FSM

• Accounting Session State Machines

– Client state machine

– Server state machines: stateless and stateful

– may be overridden by applications

Raimo Kantola –S- 2007 Signaling Protocols 12 - 72

36

Summary of Diameter scalability cmp.

Radius

Radius is the current standard for AAA in the Internet. E.g. when an ISP user accesses the Internet thru a modem line, the POP uses Radius to contact a DB in order to check access rights.

Radius problems are: vulnerability to certain attacks, limited set of attributes are supported and the architecture was designed based on the Client-Server Model.

Add mobile roaming users: Users can roam in many networks owned by hundreds or even thousands of Operators all over the world. The set of offered services is extended – a lot of attributes are needed to describe authorization. The visited network should know about the visitor as little as possible but still be able to route AAA –requests to the home network.

The solution is DIAMETER: introduces proxies, relays, redirect servers + a very flexible protocol message coding + base protocol and extensions architecture. Also Diameter is reliable, runs over TCP or SCTP rather than UDP, less vulnerable to attacks and fraud than Radius.

Challenge is to introduce Diameter when the existing infra is based on Radius. Interoperability of the two protocols becomes key to deployment of Diameter.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 73

Server may require

Re-authentication/authorization

Client Server

Re-Auth-Request: RAR

Re-Auth-Answer: RAA

A successful RAA must be followed by application specific

Authentication/authorization message

Use example: enforcing a credit limit on a user during a long telephone call.

12 - 74 Raimo Kantola –S- 2007 Signaling Protocols

37

NASREQ defines an authentication and authorization application

Client

Capabilities-Exchange-Request: CER

[Application-ID=1 (=NASREQ)]

Capabilities-Exchange-Answer: CEA

[Application-ID=1 (=NASREQ)]

AA-Request: AAR

<session-id> …

AA-Answer: AAA

[Diameter_multi_round_Auth]

AA-Request: AAR

AA-Answer: AAA

In Capabilities exchange peers agree to understand NASREQ commands.

Server

NAS (PoP) initiates a new session.

HMS may challenge the user.

User has to respond to challenge additional rounds|Accounting, Re-Auth…

AAR and AAA have loads of AVPs!

Raimo Kantola –S- 2007 Signaling Protocols 12 - 75

NASREQ messages (RFC 4005)

AAR AA-Request

AAA AA-Answer

RAR Re-Auth-Request

RAA Re-Auth-Answer

STR Session-Termination-Request

STA Session-Termination-Answer

ASR Abort-Session-Request

ASA Abort-Session-Answer

ACR Accounting-Request

ACA Accounting-Answer

Extended from BASE

EAP Application extends NASREQ and provides

Command-Name Abbrev.

Diameter-EAP-Request DER

Diameter-EAP-Answer DEA

Raimo Kantola –S- 2007 Signaling Protocols 12 - 76

38

Diameter SIP Application

Command Name | Abbr.

This application is used in 3G IMS

Registration-Termination-Request | RTR

Raimo Kantola –S- 2007

3GPP TS 29.228 V7.4.0 (2006-12)

IP Multimedia (IM) Subsystem Cx and Dx interfaces;

Signalling flows and message contents(Release 7)

Signaling Protocols 12 - 77

Diameter Credit Control Application

• The Diameter CC Application provides

– support for prepaid services

– real time credit control for the service

• Two mandatory messages

– CCR – Credit Control Request

– CCA – Credit Control Answer

• The CC Server can be different from the rest of Diameter AAA servers

Raimo Kantola –S- 2007 Signaling Protocols 12 - 78

39

3G IMS Diameter SIP Application

I-CSCF

Cx

User-Authorization-Req: UAR

HSS

S-CSCF

Cx

Server-Assignment-Req: SAR

HSS

Server-Assignment-Ans: SAA

User-Authorization-Ans: UAA

Multimedia-Auth-Req: MAR

Location-Info-Req: LIR

Multimedia-Auth-Ans: MAA

Location-Info-Ans: LIA

Registration-Termination-Req:RTR

Registration-Termination-Ans:RTA

Cx interface runs over SCTP

SLF

Push-Profile-Request: PPR

Push-Profile-Answer: PPA

Dx

Raimo Kantola –S- 2007

Dx

Signaling Protocols 12 - 79

UA

Registration – user not registered

Source: 29228-740.doc

Visited Network

P-CSCF

1.Register

2.Register

I-CSCF S-CSCF

3.UAR

4.UAA

Home Network

HSS

10. 401 Unauthorised

11.Register, RES

20. OK

S-CSCF selection

9. 401 Unauthorised

5.Register

6.MAR

Authe Vector Selection

7.MAA

RAND||AUTN||XRES||CK||IK

8. 401 Unauthorised,

RAND||AUTN

12.Register

13.UAR

14.UUA

15.Register

16.SAR

17.SAA

Authentication

19. OK

18. OK,

CK||IK

Raimo Kantola –S- 2007 Signaling Protocols 12 - 80

40

Registration – user currently registered

UA

Visited Network

P-CSCF

1.Register

2.Register

I-CSCF

3.UAR

4.UUA

S-CSCF selection

Home Network

HSS

5.Register

S-CSCF

6.SAR

7.SAA

Authentication

10. OK

9. OK

8. OK

• Registration may need to be refreshed from time to time.

• Location changes may require re-registration.

• Mobile Initiated de-registration looks exactly the same!

Raimo Kantola –S- 2007 Signaling Protocols 12 - 81

UA

Many ways/reasons to de-register

Visited Network

P-CSCF

1. Timer Expires

HSS

Home Network

S-CSCF

2.SAR

3.SAA

1. Timer Expires Registration timeout

Remove S-CSCF addess from HSS

6. Notify (reg)

1. RTR

2. RTA

3. Notify (reg)

4. 200 OK

5. Notify (reg)

8. 200 OK

Administrative de-registration

Both P-CSCF and the terminal have subscribed to the reg state!

3. UE Inform

5. 200 OK

2. De-register

1. Service Control

4. 200 OK

6. SAR

7. SAA

De-registration initiated by Service Platform

Raimo Kantola –S- 2007 Signaling Protocols 12 - 82

41

Mobile Terminated SIP Session Set-up is similar to MAP MT call

I-CSCF

1. INVITE

2. LIR

Home Network

HSS

S-CSCF

3. LIA

4. INVITE cmp: SendRoutingInformation of MAP

HSS knows the name (and address) of

S-CSCF – no RoutingNumber is needed from ”VLR”. So there is a difference in how routing and addressing operates in GSM and in 3G IMS.

1. INVITE

4. S-CSCF Selection

2. LIR

3. LIA

5. INVITE

Initiation of a session to a non-registered user.

6. SAR

7. SAA

8. Service Control further actions

When there is a change in the user profile HSS issues

Push-Profile-Request: PPR and

S-CSCF answers by PPA.

This transaction is unrelated to any SIP signaling.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 83

Policy and charging control architecture in 3G

• Documents

– 3GPP TS 23.203 V7.1.0 - Policy and charging control architecture (Release 7)

– 3GPP TS 29.212 V1.0.0

-

Policy and Charging

Control over Gx reference point (Release 7)

• Up-to release 6, COPS protocol was used

• Now a new Diameter Application

12 - 84 Raimo Kantola –S- 2007 Signaling Protocols

42

SIP Sessions require policy control

• Parties can release the “call session” but since they have obtained each others IP-addresses, they can continue sending media streams to each other!!

• How to push INVITE to B-party, if

B-party does not have a permanent

IP address which is most often the case!

Integration of

Proxy with

Firewall and

NAT

12 - 85 Raimo Kantola –S- 2007 Signaling Protocols

QoS – Integrated Serv. and DiffServ help resolving the QoS issue in VOIP and 3G IMS

• Integrated Services

– Different treatment to different flows

– State info stored in network, routers examine packets!!!(not good)

– Reservation merging

– RSVP protocol – for reservation of resources

• DiffServ

– Defines a small nrof traffic classes with different priority levels

– Packets tagged with level tags at the beginning(ingress)

– Routers just examine tags (diffServ code points)

– Better scaling

– Requires policy management: e.g. which packets to assign to which class.

– Managing class weights remains an issue.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 86

43

A Solution for QoS

• Best Effort Service for greedy and even malevolent users.

• Real time or background traffic classification.

– It is a good idea to let the network do the classification based on the

”nature” of the traffic flow. If flows of different burstiness properties are put to a single class, quality assurance is poor.

• Policy based management of allocated bandwidth at the edge.

– Policy enforcement at the edge is possible, because each device handles only a limited set of users.

– This is where users interfire with each other (e.g. one greedy p2p user blocks the traffic of all other users of a shared link at the edge.

• Adaptive scheduling for managing class weights and thus bandwidth allocations at least in edge (access) routers.

• Statistical multiplexing in the Core ( = ordinary BE Service).

– Makes the core simpler and thus less expensive. At the speeds, the core needs to transfer packets, the nodes do not have time per packet to more than just the simplest BE service.

12 - 87 Raimo Kantola –S- 2007 Signaling Protocols

Scope of Policy and Charging Control

• Diameter is used to create a harmonized solution for

¾Flow Based Charging, including charging control and online credit control;

¾Policy control (e.g. gating control, QoS control, etc.).

• Flow based charging control gives a fine granularity control over charging for service flows

• Policy control allows assigning QoS, Firewall etc per service

Raimo Kantola –S- 2007 Signaling Protocols 12 - 88

44

Key terms for PCC – policy and charging control

Packet flow: a sequence of packets with identical parameters such as IP-protocol, source-IP address, source port, destination IP address, destination port, etc

Service data flow: An aggregate set of packet flows.

Service data flow filter: A set of IP header parameter values/ranges used to identify one or more of the packet flows constituting a service data flow. A service data flow filter of a PCC rule that is predefined in the PCEF may use parameters that extend the packet inspection beyond the IP 5 tuple.

Service data flow template: The set of service data flow filters in a PCC rule, required for defining a service data flow.

FBC Flow Based Charging

IP-CAN IP Connectivity Access Network

OFCS

OCS

Offline Charging System

Online Charging System

PCC

PCEF

PCRF

Policy and Charging Control

Policy and Charging Enforcement Function

Policy and Charging Rules Function

PDF

PEP

SBLP

SPR

Policy Decision Function

Policy Enforcement Point

Service Based Local Policy

Subscription Profile Repository

Raimo Kantola –S- 2007 Signaling Protocols 12 - 89

Relationship of service data flow, packet flow, service data flow template and service data flow filter is implemented at PCEF service data flow downlink gate and counter packet flow C packet flow D

Raimo Kantola –S- 2007 service data flow filter

1 service data flow filter

2 service data flow filter

3 downlink part uplink part service data flow template

Signaling Protocols packet flow A packet flow B uplink gate and counter

12 - 90

45

PCC requirements

The PCC architecture discards packets that don't match any service data flow filter of the active PCC rules. It is possible for the operator to define PCC rules, with wild-carded service data flow filters, to allow for the passage and charging for packets that do not match any service data flow filter of any other active PCC rules.

The PCC architecture allows the charging control to be applied on a per service data flow basis, independent of the policy control.

The PCC architecture supports a binding method that allows the unique association between service data flows and their IP-CAN bearer.

A single service data flow template is used to detect a service data flow, for the purpose of both policy control and flow based charging.

A PCC rule may be predefined or dynamically provisioned at establishment and during the lifetime of an IP-CAN session. The latter is referred to as a dynamic PCC rule.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 91

PCC elements

Subscription Profile

Repository

(SPR)

Rx

AF

SPR example – HSS

AF example P-CSCF

PCEF example – GGSN or PDG for WLAN access

Online Charging System (OCS)

CAMEL

SCP

Service Data Flow

Based

Credit Control

Raimo Kantola –S- 2007

Gy

RFC 4006

Sp

PCC usage in the visited network is based on proxying of Gx messages between the

V-PCEF and the H-PCRF by the V-PCRF.

Policy and Charging

Rules Function

(PCRF)

Gx

Gx supports

-Initialisation and maintenance of connection

(IP-CAN session);

-Request for PCC decision from PCEF to

PCRF;

-Provision of PCC decision from PCRF to PCEF;

-Negotiation of IP-CAN bearer establishment mode (UE only or NW only);

-Termination of connection

(IP-CAN session).

Signaling Protocols

PCEF

GW

Gz

Offline

Charging

System

(OFCS)

12 - 92

46

IP-CAN session establishment for PCC

GW(PCEF) PCRF SPR OCS

1. Establish IP-CAN

Bearer Request

2. Indication of IP-

CAN session establishment

3. Profile Request

4. Profile Response

5. Policy Decision

This is a logical

Information flow that is used as a basis for protocol design

9. IP-CAN Bearer

Signaling

10. Establish IP-CAN

Bearer Response

6. Acknowledge

IP-CAN session establishment

7. Credit Request

8. Credit Response

Raimo Kantola –S- 2007 Signaling Protocols 12 - 93

IP-CAN session termination for PCC

SPR

GW(PCEF) PCRF AF OCS

1. Remove IP-CAN

Bearer Request

2. Indication of IP-

CAN Session

Termination

4. Remove all

Policy and

Charging Rules

3. Identify what

Policy and

Charging Rules are affected.

5. Notify loss of transmission.

6. Notification response.

7. Acknowledge

IP-CAN Session

Termination

10. Remove IP-CAN

Bearer Response

8. Credit Final Report

9. Credit Acknowledge

11. Cancel Subscribed Notification Request

12. Cancel Subscribed Notification Response

Also GW(PCEF) Initiated

IP-CAN Session

Termination is supported

(not shown)

Raimo Kantola –S- 2007 Signaling Protocols 12 - 94

47

Proxying rules to visited network

Raimo Kantola –S- 2007 Signaling Protocols 12 - 95

Policy and Charging Control over

Gx interface

GW: PCEF PCRF

CC Request

CC Answer

CCR and CCA extended from

CC Application

Re-Auth Request

Re-Auth Answer

RAR and RAA extended from

The Base Protocol

3GPP TS 29.212 V1.0.0 (2006-12)

12 - 96 Raimo Kantola –S- 2007 Signaling Protocols

48

Use of Diameter in 3G IMS

• 3GPP uses the Diameter SIP Application to handle roaming.

• Cx and Dx interfaces are the same. The difference is that Dx points to a Diameter Redirect Agent and Cx to a Diameter Server (HSS)

• ”Cellular” Location management maps into MAP operations in

SGSN+GGSN+ Registration/De-Registration in SIP terms maps to

Authorization-Request/-Answer in Diameter + S-CSCF obtaining

Subcr data = Diameter SAR/SAA etc.

– User-Location-Query is used to obtain S-CSCF identity

– I-CSCF can use Diameter Redirect capability in SLF (Dx interface):

Server-Location-Function to select S-CSCF/user-identity

– I-CSCF is stateless, so SLF has to be used for every query

– S-CSCF is stateful and will cache HSS address for the session.

• There is also a Diameter Application for AS to HSS interface (Sh

Interface). This is vendor specific where 3GPP is the vendor.

• The newest usage is for harmonized Policy and Charging Control

AS – Application Server

Raimo Kantola –S- 2007 Signaling Protocols 12 - 97

Authentication and charging

• For an operator, the motivation to authenticate reliably is linked with charging

– Usage based charging requires knowledge of whom to send the bill

– Transaction based charging – the same thing

• If the only method to collect money is a flat rate monthly tariff – why bother authenticating individual users and create additional cost for the operator for no gain?

Raimo Kantola –S- 2007 Signaling Protocols 12 - 98

49

Summary

• IP telephony requires many supporting protocols.

• Many IETF protocols overlap with GSM protocols (e.g.

Diameter with MAP) in terms of functionality

– This overlap was created because of the move from CS to PS services

• IETF development model is one protocol for one problem.

• Client-Server model is used whenever possible.

• The drive is towards providing PSTN like control over services and over what a user can do in the IP environment.

• Through access to the Internet, the open Internet model lives on.

Raimo Kantola –S- 2007 Signaling Protocols 12 - 99

50

Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement