Aktuelle Entwicklungen in der Standardisierung für drahtlose lokale Netzwerke
Maximilian RiegelSiemens AG, ICM Networks2002-10-02
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 2 © Siemens, 2002
Outline
WLAN Standardization overview The IEEE802.11 WLAN Standard
– Architecture– Physical layer– Spectrum issues– MAC layer functions– Configurations– Handover– Power Management– Privacy and access control
WLAN Security WLAN – UMTS Interworking
– Tight coupling– Market and application considerations– Loose coupling– Standardization activities
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 3 © Siemens, 2002
Wireless LAN Standardization
MAC
PHY
Current standardization topics
HiperLAN/2
DFS & TPC
5 GHz54 Mbit/s
ETSI BRAN
UMTS Integration 802.11f: Inter Access Point Protocol
IEEE 802.11
IEEE 802.11
2,4 GHz2 Mbit/s
802.11b2,4 GHz11Mbit/s
802.11g2,4 GHz54Mbit/s
802.11a5 GHz
54Mbit/s
802.11e: QoS Enhancements
802.11i: Security Enhancements
802.11hDFS & TPC
WIGWireless
Interworking Group
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 4 © Siemens, 2002
The ubiquitous WLAN
Today’s road worriers require access to the Internet everywhere.
WLAN is more than just cable replacement, it provides hassle-free broadband Internet access everywhere.
Coverage in ‘hot-spots’ sufficient. IEEE802.11b meets the expectations for easiness, cost
and bandwidth.
PublicWLAN
Airport
Railway Station
Campus
Plant
Semi-publicWLAN
OfficeHospital
Congress hall,Hotel
Corporate WLAN
Office
HomeWLAN
Remote Access
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 5 © Siemens, 2002
Wireless IEEE802.11 Standard
Approved June 1997– 802.11b approved Sept. 1999
Operation in the 2.4GHz ISM band– USA: FCC part 15.247-15.249– Europe: ETS 300-328 – Japan: RCR-STD-33A
Supports three PHY layer types: DSSS, FHSS, Infrared
MAC layer common to all 3 PHY layers Supports peer-to-peer and
infrastructure configurations IEEE802.11b high data rate extension with 11 Mbps
using existing MAC layer IEEE802.11a for operation in the 5 GHz band with up to
54 Mbit/s using the same MAC layer
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 6 © Siemens, 2002
httptcpip
pppBluetooth
Netscape
ip802.2802.11
802.2802.11 802.3
802.2802.3
802.2802.3
httptcpip
pppBluetooth
apache
ip802.2802.3
ip
IEEE802.11
local distribution network internet
Client Access Point Access Router Server
Wireless LAN IEEE802.11Basic Architecture
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 7 © Siemens, 2002
IEEE802.11 Protocol Architecture
Station Management– interacts with both MAC Management
and PHY Management MAC Layer Management Entity
– power management
– handover
– MAC MIB MAC Entity
– basic access mechanism
– fragmentation
– encryption PHY Layer Management
– channel tuning
– PHY MIB Physical Layer Convergence Protocol (PLCP)
– PHY-specific, supports common PHY SAP
– provides Clear Channel Assessment signal (carrier sense) Physical Medium Dependent Sublayer (PMD)
– modulation and encoding
MAC Sublayer
PLCP Sublayer
PMD Sublayer
MAC LayerManagement
PHY LayerManagement
StationManagement
LLC = 802.2
MAC
PHY
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 8 © Siemens, 2002
IEEE 802.112.4 GHz & 5 GHz Physical Layers
TimeF
requency
2.4 GHz Frequency Hopping Spread Spectrum– 2/4 FSK with 1/2 Mbps– 79 non overlapping frequencies
of 1 MHz width (US)
FrequencyP
ower
Frequency
Pow
er
spreading
2.4 GHz Direct Sequence Spread Spectrum– DBPSK/DQPSK with 1/2 Mbps – Spreading with 11 Bit barker Code – 11/13 channels in the 2.4 GHz band
2.4 GHz High Rate DSSS Ext. (802.11b)– CCK/DQPSK with 5.5/11 Mbps
Frequency
Pow
er
5 GHz OFDM PHY (802.11a)– Basic parameters identical to
HiperLAN2 PHY– European regulatory issues unsolved
Baseband IR, 1 and 2Mbps, 16-PPM and 4-PPM
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 9 © Siemens, 2002
IEEE802.11g: Further Speed Extension for the 2.4GHz Band
Mandatory: CCK w/ short preample (802.11b) and OFDM (802.11a applied to 2.4
GHz range). Optional: PBCC proposal for 22 Mbit/s from Texas Instruments Optional: CCK-OFDM proposal for up to 54 Mbit/s from Intersil
Upcoming
Upcoming
Upcoming
Upcoming
Range vs. throughput rate comparison of CCK (802.11b), OFDM(“802.11a”), PBCC, CCK-OFDM(Batra, Shoemake; Texas Instruments; Doc: 11-01-286r2)
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 10 © Siemens, 2002
Freq./GHz
5.200 5.300 5.400 5.500 5.600 5.700 5.800 5.9005.100
Europe
USA
Japan5.150 5.250
5.150 5.350 5.725 5.825
Indoor 200 mW / Outdoor 1 W EIRP Outdoor 4 W EIRP
Max peak Tx power
5.3505.150 5.470 5.725
Outdoor 1W EIRP Indoor 200 mW EIRP
Max mean Tx power
DFS & TPC DFS & TPC
DFS: Dynamic Frequency Selection
TPC: Transmit Power Control
Spectrum Designation in the 5 GHz range
Many European countries are currently opening 5 GHz range for radio LANs.
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 11 © Siemens, 2002
IEEE802.11h: Spectrum and Transmit Power Management
TPC (Transmission power control) – supports interference minimisation, power consumption reduction,
range control and link robustness.– TPC procedures include:
• AP‘s define and communicate regulatory and local transmit power constraints
• Stations select transmit powers for each frame according to local and regulatory constraints
AP 1AP 2
AP 3
STA
DFS (Dynamic Frequency Selection)– AP‘s make the decision– STA‘s provide detailed reports
about spectrum usage at theirlocations.
Upcoming
Upcoming
Upcoming
Upcoming
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 12 © Siemens, 2002
… when will 5 GHz WLANs come?
IEEE802.11b (2.4 GHz) is now taking over the market. There are developments to enhance IEEE802.11b for
– more bandwidth (up to 54 Mbit/s)– QoS (despite many applications do not need QoS at all)– network issues (access control and handover).
5 GHz systems will be used when the 2.4 GHz ISM band will become too overcrowded to provide sufficient service.– TCP/IP based applications are usually very resilient
against ‘error proune’ networks.
Issues of 5 GHz systems:– Cost: 5 GHz is more expensive than 2.4 GHz– Power: 7dB more transmission power for same distance– Compatibility to IEEE802.11b/g necessary
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 13 © Siemens, 2002
DIFSContention Window
Slot time
Defer Access
Backoff-Window Next Frame
Select Slot and Decrement Backoff as long as medium is idle.
SIFS
PIFSDIFS
Free access when mediumis free longer than DIFS
Busy Medium
CSMA/CA Explained
Reduce collision probability where mostly needed.– Stations are waiting for medium to become free.– Select Random Backoff after a Defer, resolving contention
to avoid collisions. Efficient Backoff algorithm stable at high loads.
– Exponential Backoff window increases for retransmissions.
– Backoff timer elapses only when medium is idle. Implement different fixed priority levels
IFS: Inter Frame Space
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 14 © Siemens, 2002
IEEE802.11e: MAC Enhancementsfor Quality of Service (EDCF)
– differentiated DCF access to the wireless medium for prioritized traffic categories (4 different traffic categories)
– output queue competes for TxOPs using EDCF wherein• the minimum specified idle duration time is a distinct value
• the contention window is a variable window
• lower priority queues defer to higher priority queues
EDCF (Enhanced Distributed Coordination Function)
Upcoming
Upcoming
Upcoming
Upcoming
Mapping toAccess Category
Transmit Queues
Per-queuechannel accessfunctions withinternal collisionresolution
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 15 © Siemens, 2002
Beacon
Contention Free Period Contention Period
CFP repetition interval
D1+Poll
U1+ACK
D2+Poll
Stations
AccessPoint
U2+ACK
CF end
IEEE802.11Point Coordination Function (PCF)
Optional PCF mode provides alternating contention free and contention operation under the control of the access point
The access point polls stations for data during contention free period
Network Allocation Vector (NAV) defers the contention traffic until reset by the last PCF transfer
PCF and DCF networks will defer to each other PCF improves the quality of service for time bounded data
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 16 © Siemens, 2002
IEEE802.11e: MAC Enhancements for Quality of Service (HCF)
– only usable in infrastructure QoS network configurations– allow a uniform set of frame exchange sequences to be
used during both the contention period (CP) and contention free period (CFP)
– uses a QoS-aware point coordinator, called a hybrid coordinator
• by default collocated with the enhanced access point (EAP)
• uses the point coordinator's higher priority to allocate transmission opportunities (TxOPs) to stations
– provides limited-duration contention free bursts (CFBs) to transfer QoS data.
– meets predefined service rate, delay and/or jitter requirements of particular traffic flows.
– ...– „Quite complex method still under definition“
HCF (Hybrid coordination function)
Upcoming
Upcoming
Upcoming
Upcoming
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 17 © Siemens, 2002
Peer-to-Peer Network
IEEE802.11 Ad Hoc Mode
Independent networking– Use Distributed Coordination Function (DCF)– Forms a Basic Service Set (BSS)– Direct communication between stations– Coverage area limited by the range of individual stations
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 18 © Siemens, 2002
BSS-A
Distribution System (DS)
BSS-B
Server
IEEE802.11 Infrastructure Mode
Access Points (AP) and stations (STA) BSS (Basic Service Set): a set of stations controlled by
a single coordination function Distribution system interconnects multiple cells via
access points to form a single network Extends wireless coverage area and enables roaming
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 19 © Siemens, 2002
IEEE802.11 Handover
Station decides that link to its current AP is poor
Station uses scanning function to find another AP– or uses information from
previous scans
Station sends Reassociation Request to new AP
If Reassociation Response is successful – then station has roamed to the new AP– else station scans for another AP
If AP accepts Reassociation Request– AP indicates Reassociation to the Distribution System– Distribution System information is updated– normally old AP is notified through Distribution System
Access Point A
Access Point B
Station 4
Access Point C
Station 1
Station 2
Station 3
Station 5Station 6
Station 7
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 20 © Siemens, 2002
IEEE802.11f: Inter-Access Point Protocol (IAPP)
IAPP defines procedures for– automatic configuration handling of access points– context transfer between APs when stations move
Distribution SystemServer
IAPP-MOVE
IAPP-ADD
Upcoming
Upcoming
Upcoming
Upcoming
RADIUS Server
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 21 © Siemens, 2002
TIM
TIM-Interval
Time-axis
Busy Medium
Tx operation
AP activity
TIM TIM TIM DTIMDTIM
DTIM interval
PS Station
Broadcast
PS-Poll
Broadcast
IEEE802.11 Power Management
Stations wake up prior to an expected DTIM (Delivery Traffic Indication Message).
If TIM indicates frame buffered – station sends PS-Poll and stays awake to receive data– else station sleeps again
Broadcast frames are also buffered in AP.– all broadcasts/multicasts are buffered– broadcasts/multicasts are only sent after DTIM.– DTIM interval is a multiple of TIM interval
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 22 © Siemens, 2002
IEEE802.11 Privacy and Access Control
Goal of 802.11 is to provide “Wired Equivalent Privacy” (WEP)– Usable worldwide
802.11 provides for an authentication mechanism– To aid in access control.– Has provisions for “OPEN”, “Shared Key” or proprietary
authentication extensions.
Shared key authentication is based on WEP privacy mechanism– Limited for station-to-station traffic, so not “end to end”.– Uses RC4 algorithm based on:
• a 40 bit secret key
• and a 24 bit IV that is send with the data.
• includes an ICV to allow integrity check.
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 23 © Siemens, 2002
Shortcomings of plain WEP security
WEP unsecure at any key length– IV space too small, lack of IV replay protection– known plaintext attacks
No user authentication– Only NICs are authenticated
No mutual authentication– Only station is authenticated against access point
Missing key management protocol– No standardized way to change keys on the fly– Difficult to manage per-user keys for larger groups
WEP is no mean to provide security for WLAN access,– … but might be sufficient for casual cases.
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 24 © Siemens, 2002
Associate
EAP Identity Request
EAP Identity Response
EAP Request
EAP Response
EAP Success
Access Request
Access Challenge
Access Request
Access Accept
AuthenticationServer
IEEE802.11i: Enhanced security
Enhanced encryption– WEP2 w/ increase IV space to 128bit, key length 128bit– optional: Advanced Encryption Standard (AES)
Authentication and key management by adoption of IEEE802.1X Standard for Port Based Network Access Control
Upcoming
Upcoming
Upcoming
Upcoming
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 25 © Siemens, 2002
A last word about WLAN security:
Even IEEE802.11i may not be sufficient for public hot-spots:
Only VPN technologies (IPSEC, TLS, SSL) will fulfil end-to-end security requirements in public environments.
VPN technologies might even be used in corporate WLAN networks.
http
ipppp
Netscape
ip802.2 802.2
802.3802.2802.3
802.2802.3
http
ipppp
Bluetooth
apache
ip802.2802.3
ip
WEP802.11 802.11
tcp tcp
802.11802.11
IPSEC, TLS, SSLtcp tcp
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 26 © Siemens, 2002
PSTN
PLMN access
PLMN coreVLR
HSSAUC
SGSN
SCPLNPIN
GGSN
TDM / ATM / IPMSCSMSCS
BTSBTS BSC
BTSBTS
Node BNode B
Node BNode B
RNC
internet
wlan local access network
WLAN – UMTS Interworking: Ancient approach: ‘tight coupling’
WLAN as just another radio access technology of UMTS All UMTS services become available over WLAN.
but: PLMN is burdened with high bandwidth WLAN traffic. Wi-Fi does not provide all the functionality needed (QoS, security).
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 27 © Siemens, 2002
UMTS and Wireless LAN are different.
GSM/GPRS/UMTS
anytime / everywhere voice, realtime messaging QoS precious bandwidth carrier grade operator driven huge customer base high revenues
WLAN IEEE802.11
sometimes / somewhere standard web applications best effort cheap bandwidth corporate technology market driven casual users low revenues
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 28 © Siemens, 2002
WLAN is much cheaper than 2G/3G
* based on current IP volume prices of 40€ /GByte.Time based pricing results in similar costs,e.g. MobileStar Pulsar pricing plan: $0,10/min
0
2
4
6
8
10
GPRS GSM-HSCSD WLAN*
0,01
0,1
1
10
GPRS GSM-HSCSD
WLAN
Transfer-Cost [€]Duration [min]
logarithmic scale€
-99,6%
Transfer cost/duration of an 1 Mbytes .ppt/.doc/.xls File...
4 min 4 min 5 sec
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 29 © Siemens, 2002
Becoming a WLAN operator is easy.
Legal aspects:– Usage of license free spectrum (2,4 GHz ISM band)– No telecommunication license necessary, as long as
• not providing telephony services,
• not providing network access across borders of private premises.
Cost issues:– The lower bound:
Investment: WLAN Access Point /w DSL Router (~ 350 €)Monthly operation cost: ~ 60 € for DSL Flat Rate
– Most commercial installations are much more expensive due to charging and billing.
It is very easy and extremely cheap to become a WLAN operator, but most people did not yet know about it.
...but wait until they have installed WLAN in their living rooms!
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 30 © Siemens, 2002
PSTN
PLMN access
PLMN coreVLR
HSSAUC
SGSN
SCPLNPIN
TDM / ATM / IPMSCSMSCS
BTSBTS BSC
BTSBTS
Node BNode B
Node BNode B
RNC
internet
wlan local access network
WLAN – UMTS Interworking: Now widely accepted: ‘loose coupling’
Only Authentication, Authorization and Accounting of WLAN access is performed by the mobile network operator.
Revenues without competing against aggressive WLAN operators. Perfect model for leveraging the huge customer base and
establishing a widely accepted platform for mobile commerce.
AuthenticationAccounting
Siemens contributed ‚loose coupling‘ to standardization.
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 31 © Siemens, 2002
mobile network
HLR
E.g.: Web based authentication and mobile network security
internet
Password:
Username:
auth
html
RADIUSclient
N
auth
DHCPServer
AAAServer
AccessGateway
MobileClient
**********
SMS containing Password
0172-3456789
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 32 © Siemens, 2002
Standards for WLAN/UMTS interworking
3GPP– R5: SA1
Requirements of 3GPP system – WLAN interworking. – R6: SA2
Continuation with architectural considerations ETSI BRAN
Subgroup on “Interworking between HiperLAN/2 and 3rd generation cellular and other public systems”. – Detailed architectural description mainly based on the
Siemens ‘loose coupling’ principle established– IEEE802.11 and MMAC are now joining this effort.
=> Wireless Interworking Group (WIG). WECA (Wireless Ethernet Compatibility Alliance)
‘Wireless ISP Roaming Initiative’– Detailed functional specification for roaming (loose
coupling) between IEEE802.11 WLAN networks available.– Mainly aimed for roaming between ISPs but also well
applicable for MNOs.
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 33 © Siemens, 2002
The end
Thank you for your attention.
Questions and comments?
Maximilian Riegel
http://www.max.franken.de/
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 34 © Siemens, 2002
Services andapplications
IP based core network
IMT-2000(UMTS)
WLANtype
cellular2nd. gen.
WirelinexDSL
DigitalBroadcast
return channel:e.g. cellular
download channel
New radiointerface
WLAN – UMTS interworking is laying the path for the future of networking…
From the ITU-R vision of Wireless Communications beyond 3G:
Seamless network of complementary access systems
M. Riegel, WLAN Standardization, 021002-wlan-informatik2002.ppt Page 35 © Siemens, 2002
Internet/Web Applications
Generic Internet Network Architecture
Internet
linkphy
iptcphttpwww
linkphy
iplinkphy
iplinkphy
iplinkphy
ip802.2802.11
linkphy
ip802.2802.11
iptcphttpwww
Peer(Client)
Peer(Web-Server)
802.2802.3
ip802.2802.3
Policy Server AAA Server
WLAN Access