Understanding IWLAN – thanks to Use Cases

Understanding IWLAN – thanks to Use Cases
Understanding IWLAN –
even allowing for Safety
Which bits really matter?
Why is 802.11 suitable for automation tasks?
© Siemens AG 2010. All Rights Reserved.
What advantages does IWLAN bring to the
automation world?
Many reasons for WLAN
 WLAN frees Profibus and PROFInet from cables
 bridging of distances without cables
 e.g. between buildings
 across obstacles (streets, rivers, lakes)
 maintenance-free, e.g. compare to slip rings
 higher data rates than other wireless systems
 WLAN makes data transmission with mobile machines/devices
But
 A permanently installed cable will have a higher availability than WLAN!
 WLAN technology is slightly different….e.g. CSMA/CA and positive
acknowledgement
 WLAN channels are limited
Page 2/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 1:
Wireless Access to Control Room
Requirements
 Innovate plant maintenance of sensors and actuators
(maintenance with one person/ commissioning)
Control
Room
Boiler
Ethernet
Control
Power
Page 3/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 1:
Wireless Access to Control Room
Why does the Access Point “understand” the laptop?
The Access Point (AP) and laptop…..
 have been set to the same wireless standard
 chat on the same frequency
 use the network name
 encrypt the messages with the same “secret code”
Page 4/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 1:
IEEE 802.11 WLAN Standards (PHY)
IEEE 802.11b
IEEE 802.11g
IEEE 802.11a
IEEE 802.11h
IEEE 802.11n
Frequency Range
2.4 GHz
2.4 GHz
5 GHz
5 GHz
2.4 GHz/ 5 GHz
Range
Indoor: 30 m
Outdoor: 140 m
Indoor: 30 m
Outdoor: 140 m
Indoor: 30 m
Outdoor: 120 m
Indoor: 30 m
Outdoor: 120 m
Indoor: 70 m
Outdoor: 250 m
Indoor and
outdoor: 20 dBm
Indoor and
Indoor and outdoor:
Indoor: 23 dBm
outdoor: 20 dBm
23 dBm/ 30 dBm
(depends on antenna and env.)
TX Power
(On The Example In EU)
Indoor and outdoor:
23 dBm/ 30 dBm
Non Overlapping
Channels
3
3
4
8 + 11
2,4 GHz: 3
5 GHz: 8 + 11
Gross Data Rate
11 MBit/s
54 MBit/s
54 MBit/s
54 MBit/s
600 MBit/s
Specifics
because of DSSSmodulation robust
DFS mandatory,
up to Ch 64 only
indoor
DFS mandatory at
5 GHz
(On The Example In EU)
Page 5/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 1:
Physical Properties of the Frequency Ranges
2.4 GHz
5 GHz
Use in Networks
- common  often already occupied
+ less common
- outdoor only with DFS
Use In Devices
+ very common
- less common
Free Space Loss At Different
Frequencies („Resistance“
Of The Air)
Fresnelzone (r)
At Different Distances (d)
1m
2m
10 m
100 m
1m
2m
10 m
100 m
40 dB
+
46 dB
60 dB
80 dB
47 dB
-
53 dB
67 dB
87 dB
10 m
100 m
1000 m
10 m
100 m
1000 m
0.55 m
-
1.75 m
5.55 m
0.38 m
+
1.19 m
3.75 m
Fresnelzone (at least 40 % required)
d
r
Page 6/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 1:
Network name and Security
The SSID (Service Set Identifier)……..
 is the name of a wireless network
 can be defined freely (e.g. „bh_1“)
 must be set on the AP and the wireless client
 It can have a length limits e.g. up to 32 characters
Radio waves are able to propagate across borders of rooms or
buildings
 Therefore it is necessary to limit the access to WLAN (authentication)
and to encrypt the exchanged data
Tip: To be compatible with devices from multiple manufacturers be
careful with characters within the SSID.
Page 7/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 1:
Security in Terms of WLAN
Authentication
 authentication protects a WLAN against undesired access
 possible methods of authentication
 open system (no authentication takes place)
 shared Key
 WPA-PSK + (encryption with TKIP or AES; Passphrase)
 WPA2-PSK + + (encryption with AES (def.) or TKIP; Passphrase)
 WPA and WPA2 can be used with authentication servers e.g.
RADIUS, but this is uncommon in industrial environments
WPA2-PSK is the preferred authentication method!
Page 8/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 1:
Authentication and Encryption
Encryption
 encryption protects the data of a network
 existing encryption methods
 WEP (weak encryption, should be avoided)
 TKIP + (good encryption, uses changing keys)
 AES + + (very good encryption, better than TKIP)
AES is the preferred encryption method
Page 9/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 1:
Example Settings for WLAN:
Access point
Laptop/ PG
 IP-addresses
 WLAN at 5 GHz
 Country code
 search for WLAN
 Enable Interface
 Passphrase
 SSID: bh_1 (for instance)
 Mode: 5 GHz, 802.11a
 Channel 36
 Antenna: ANT795-4MR
 Admin-Password
 Auth. type: WPA2-PSK
 Cipher: AUTO
 Passphrase
Page 10/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 2:
Automatic Guided Vehicle with PN IO
Requirements
 Wireless communication to automatic guided vehicles
 PN IO between CPU and remote I/O
 PI IO update time 64 ms
 length of the track: 50 m
ANT795-6DN
ANT795-6DN
AP
Cl
Line of Sight
Ethernet
Antenna cable
Page 11/30
2010-02-01
50 m
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 2:
What are the Antennas for?
To bridge the 50 m distance reliably for PN IO!
 check internal/supplied antennas and compare to external
antenna options
 for Profinet IO a reliable WLAN connection is necessary
 omnidirectional antennas can bridge up to 30 m
(e.g. ANT795-4MS  “rabbit ears”)
 antennas with directional characteristics are better suited for
this example
 they concentrate the radio waves while sending AND receiving
  longer range
  less interferences because of and for other WLANs
Page 12/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 2:
About the mentioned Antenna Types
Different Antenna Types:
 omnidirectional Antennas
(e.g. ANT795-4MS – “rabbit ears”)
(horizontal pattern bird's-eye view)
 send and receive the signal in/ from radius of 360°
 directional Antennas (e.g. ANT795-6DN)
(horizontal pattern bird's-eye view)
 send and receive the signal in/ from a sector with a specific
angle (here 55 °)
 have a gain like a speaking tube but NO amplification
 they only concentrate the signal in a small lobe – when sending
AND receiving
Page 13/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 2:
Example Directional Antenna
Pattern
Directional Antenna:
 e.g. ANT795-6DN
 Frequency range: 2.4 GHz and 5.6 GHz
 Gain: 9 dBi
 3 dB beam width: 75°/ 55°
Page 14/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 2:
Reliable WLAN by Thorough Planning
Why Radio Field Planning?
 a thorough planning of the WLAN…….
 guarantees a fast and on time commissioning of the application
 saves recofiguring and modification of the original setup
 achieves customer satisfaction!
Parts of a Radio field Planning for WLAN
 Site survey
 spectrum analysis (Network analysis is not enough!)
 define mounting points for APs and antennas
 considers distances, obstacles, radio-properties
 Simulation packages (e.g. SINEMA E) and proof of concept re
performance and post commissioning comparison
Page 15/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 2:
Structure of PROFINET Stack & Telegrams
IT applications
PROFINET Applications
e.g.
 HTTP
 SNMP
 DHCP...
Processdata
Real-Time
Configuration
Diagnostics
TCP/UDP
IP
Real-Time (RT)
Ethernet
Ethernet Frame
Preambel
Sync
Source
MAC
7 Byte 1 Byte 6 Byte
Dest.
MAC
Priority
Tagging*
Ethertype
6 Byte
4 Byte
2 Byte
Ethernet-Standard
Page 16/30
2010-02-01
Frame
ID
2 Byte
Prozess data
up to 1440 Byte
Status
Information
4 Byte
FCS
4 Byte
PROFINET specific
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 2:
WLAN and Profinet IO
What special requirements has PN IO for WLAN?
 Profinet IO works with cyclic data communication
 3 retries (default) = bus fault (BF)
  the WLAN connection must be reliable!
“Domestic” WLAN could, however, be used for PN IO –
under following conditions:
 No roaming for the Ethernet Client Module (ECM)
 The PN IO update time >= 32 ms
 max. of four WLAN Clients for each AP
Page 17/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 2:
MAC Mode setting
The ECMs can be set to the following MAC modes:
 Auto find „Adopt MAC‟
ECM adopts MAC address from first frame to pass
 Set 'Adopt MAC' manually
MAC address can be edited manually
 Adopt own MAC
ECM uses its own MAC address
 Layer 2 Tunnel
ECM uses its own MAC address but also the MAC addresses of
the end devices that are connected to the ECM
Page 18/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 2:
Example Settings for WLAN:
Access Point
Ethernet Client Module
 Basic settings (IP-Address, SSID ..)
 Basic settings (IP-Address, SSID ..)
 Mode: 5 GHz, 802.11a
 Mode: 5 GHz, 802.11a
 Antenna Type: ANT795-6DN
 Antenna Type: ANT795-6DN
 Antenna cable length: 1 m
 Antenna cable length: 1 m
 Antenna mode: Antenna A
 Antenna mode: Antenna A
 Auth. type: WPA2-PSK with Passphrase
 Auth. type: WPA2-PSK with Passphrase
 Transmit Power Control: - 6 dB
 Transmit Power Control: - 6 dB
 MAC mode: Auto find 'Adopt MAC'
 Background scan mode: Scan if idle
 Background scan ch. select: Enable
 Background scan channels: 36
Page 19/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 3:
Multiple PN devices behind a WLAN Client
“Domestic WLAN”  Real-time WLAN
“Domestic WLAN” – technical details
 In a “Domestic WLAN”, each device transmits (AP and clients)
as soon as data is pending and the channel is free (“distributed
coordination”)
 “Domestic WLAN” is therefore also known as DCF (distributed
coordination function)
Cl 3
Cl 2
AP
Cl 1
Page 20/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 3:
“Domestic WLAN”  Real-time WLAN
“Real-time WLAN” – technical details
 In real-time WLAN, the access point coordinates radio traffic
 Real-time WLAN is therefore also known as iPCF (industrial point
coordination function)
 The AP assigns each client a 2 ms time slot
 Now the AP transmits data to client 1
 Client 1 receives this and answers in turn with its data
 This process is known as “polling”
Note: “Real-time” doesn‟t mean “immediately” but “at a
pre-determinable time” i.e. deterministic
Page 21/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 3:
“Domestic WLAN”  Real-time WLAN
“Real-time WLAN” – what actually happens
2 ms time slot
Cl 1
AP
Cl 3
Cl 2
The AP determines the polling sequence and it cannot be
influenced!
Page 22/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Example 3:
Example Settings for WLAN:
Page 23/30
Access Point
Ethernet Client module
 Basic settings (IP address, SSID ..)
 Basic settings (IP address, SSID ..)
 System name: AP x
 System name: Cl x
 Mode: 5 GHz, 802.11a
 Mode: 5 GHz, 802.11a
 Transmit power: 0 dB
 MAC mode: Layer 2 Tunnel
 Antenna Type: RCoax leaky wave c..
 Transmit power: -6 dB
 Antenna cable length: 1 m
 Antenna Type: ANT793-4MN
 Antenna mode: Antenna A
 Antenna cable length: 1 m
 Public key 1: [16 ASCII symbols]
 Antenna mode: Antenna A
 Auth. type: Open System
 Background scan ch. select: Enable
 Encryption: enable
 Background scan channels: 36 40 44
 iPCF enabled: enable
 Public key 1: [16 ASCII symbols]
 Strong AES-CCM encryption: enable
 Auth. type: Open System
 PNIO support enabled: enable
 Encryption: enable
 PNIO Cycle: 64 ms
 iPCF enabled: enable
 Antenna pattern: Leaky/Directional ...
 Strong AES-CCM encryption: enable
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
PROFIsafe
When used with Profibus or PROFInet
PROFIsafe is a profile for Profibus or PROFInet
 PROFIsafe uses the same ASIC as a “standard” unit but needs
safety applied at the firmware/software level.
 The diagnostics for PROFIsafe are the same as for Profibus or
PROFInet (whichever you are using).
 The installation rules/guidelines for PROFIsafe are the same as
for Profibus or PROFInet (whichever you are using).
 PROFIsafe uses a lot of the same principles of configuration &
programming that are used in the “standard” world.
Page 24/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
PROFIsafe
WLAN with functional safety?
As mentioned previously a permanently installed cable will have
better availability than a WLAN.
What should I consider when I need to use WLAN for a safety
application?
 Always cable if you can. Look at WLAN if cabling isn’t an option.
 Can be used for up to SIL 3/PL e (IEC 61508/62061/61511 &
ISO 13849)
 Does the availability of WLAN suit the safety application?
Number of retries?
 Does WLAN suit your reaction time for the safety application?
Page 25/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
PROFIsafe
Failsafe communication via PROFIsafe
 First communications standard developed in accordance with safety standard IEC 61508
with more than 840,000 PROFIsafe nodes implemented in over 85,000 systems
 PROFIsafe handles potential
faults (e.g. invalid addresses,
delays, data loss) by means of
 Serial numbering
Safetyrelated
data
Standard
data
PROFIsafe
layer
Standard
bus protocol
 Authenticity monitoring
PROFIBUS
 Additional CRC backup
 Evaluated by
Standard
data
PROFIsafe
layer
Standard
bus protocol
 Time monitoring
Safetyrelated
data
or
"Black channel"
 Developed to IEC 61784-3-3,
PROFIsafe is the international
standard
PROFINET
and
PROFIsafe supports standard and failsafe
communication via one physical bus
Page 26/30
2010-02-01
© Siemens AG 2010. All Rights Reserved.
Industry Sector
PROFIsafe
PROFIsafe Specification V2.0
Overview: Possible Errors and detection mechanism
Remedy:
Consecutive
Number
Time Out
with Receipt
Failure type:
Repetition
Deletion
Insertion
Resequencing






Codename for
Sender and
Receiver


Data Corruption


Delay
Masquerade (standard
message mimics failsafe)
Revolving memory failure
within switches
Page 27/30
2010-02-01
Data
Consistency
Check



© Siemens AG 2010. All Rights Reserved.
Industry Sector
PROFIsafe
High flexibility for applications
PLC level
PLC level
I/O level
I/O level
Separation of PLC, I/O and bus
One bus, but separation of PLC and I/O
Page 28/30
2010-02-01
One PLC, but separation of I/O and bus
PLC level
PLC level
I/O level
I/O level
One PLC, one bus and mixed I/O
© Siemens AG 2010. All Rights Reserved.
Industry Sector
PROFIsafe
PROFInet “Shared Device”
Access to one device from several controllers
 Flexible assignment of channels and modules to different controllers
 For inputs and outputs
IO Controller 1
Page 29/30
2010-02-01
IO Controller 2
© Siemens AG 2010. All Rights Reserved.
Industry Sector
PROFIsafe
“Shared Device” and F-shutdown
F-IO controller
F-shutdown
Page 30/30
2010-02-01
IO controller
F-IO controller
IO controller
 Less cabling
 Lower hardware overhead
 Simpler engineering
© Siemens AG 2010. All Rights Reserved.
Industry Sector
Thank you for your attention!
Peter Brown
HelpDesk Team Leader
Functional Safety Professional
Siemens IA&DT
Phone: +44 161 446 - 5545
Any Questions?
© Siemens AG 2010. All Rights Reserved.
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