Embed Size (px)
Citation preview
Overview ofIEEE 802.11 Networks
Timo Smura 24.03.2004
Outline
• Introduction• IEEE 802.11 standards
– Protocol model– Network topologies– 802.11 MAC layer– 802.11 PHY layers
• Interoperability: Wi-Fi Alliance• 3GPP WLAN Interworking• Summary
Introduction• WLANs are increasingly popular
– In offices, homes, and public places– Due to standardized, interoperable
products and low prices– Whether mobile operators want it or not
• WLAN technology is evolving– Alphabet soup of IEEE 802.11
standards– Higher throughputs, better QoS,
security, mobility– Smaller chipsets, power consumption,
prices– Integration to mobile devices, e.g. Nokia
9500, PDAs
IEEE wireless standards
802.11 WGWireless Local Area
Network
802.15 WGWireless Personal Area
Network
802.16 WG Broadband Wireless Access
802.20 WGMobile Wireless Access
802.11a 802.11n... 802.15.1 802.15.5...
802.16a 802.16e...
IEEE 802.11 protocol model
802.2 Logical Link Control (LLC)
IP
802.11 Medium Access Control (MAC)(Amended with 802.11e, 802.11i, …)
802.11aPHY
802.11bPHY
802.11gPHY
802.11nPHY
TCP UDP
IETF
IEEE 802
IEEE 802.11
…
802.11 Network topologies• Independent BSS
– ”Ad-hoc mode”– No relaying, i.e. not a
mesh network
• Infrastructure BSS– ”Access point mode”
Backbonenetwork
BSS = Basic Service Set, STA = Station, AP = Access Point
STA
STA
STA
STA STA
STA
STA
AP
Mobility
• Handovers possible within a subnet– i.e. in an Extended Service Set (ESS)– Inter-Access Point Protocol (IAPP)
• Inter-subnet handovers require higherlevel functionalities, e.g. Mobile IP
Backbonenetwork
Subnet 1 Subnet 2
802.11 MAC Layer (1)
• CSMA/CA for multiple access– Carrier Sense Multiple Access with Collision Avoidance
• Ethernet = CSMA/CD (CSMA with Collision Detection)
– Listen before talk
• Contention-based mechanism– No QoS guarantees– Delays increase together with the number of active
users in an area– QoS enhancements specified in 802.11e
• Hidden node problem– E.g. two stations are within the range of an AP but
cannot hear each other– Solution: Request To Send / Clear To Send (RTS/CTS)
802.11 MAC Layer (2)
RTSCTSCTSDataACKACK
RTS…
802.11 MAC Layer (3)• Security
– Wired Equivalent Privacy (WEP)• Included in original 802.11 standard, flawed• Authentication and encryption based on shared keys• No message integrity checking
– 802.11i• Security enhancements to the MAC layer• 802.1x for authentication, TKIP / AES for encryption• Message integrity check
– Wi-Fi Protected Access (WPA)• Subset of 802.11i, for faster time-to-market• Includes 802.1x and TKIP
TKIP = Temporal Key IntegrityProtocol, AES = Advanced Encryption Standard
802.11 PHY LayersStandard
Frequency Band
Independent Channels
802.11a
5 GHz
18
802.11b
2.4 GHz
3 / 4
802.11g
2.4 GHz
3 / 4
Max. Data Rate 54 Mbps 11 Mbps 54 Mbps
Radio OFDM DSSS DSSS / OFDM
Spectrum available 455 MHz 83.5 MHz 83.5 MHz
Status Available Dominant Available
Channel Width ~18 MHz ~22 MHz ~22 MHz
Channel Spacing 20 MHz 5 MHz 5 MHz
Compatibility YESNO
Range Lower Higher Higher
OFDM = Orthogonal Frequency Division Multiplexing, DSSS = Direct Sequence Spread Spectrum
802.11 throughputs• Data rates of 11 Mbps and
54 Mbps are theoretical• The actual maximum
throughput is about 50% of the theoretical
• Throughput decreases as:– the range increases– the number of users
increases3025201510
5
30 60
Mbps
m
(Atheros)
1210
8642
2 4
Mbps (TTKK)
8 16 32 641
Whole network
Single user
802.11b
802.11a
users
Interoperability: Wi-Fi Alliance• Standards fall short without certified
interoperability• A major force behind the success of
802.11 WLANs is Wi-Fi Alliance (formerWECA)– more than 200 members– more than 1000 certified products
• Tasks include:– Certification of interoperable products– Developing and publishing specifications:
WPA, WISPr– ”Certification” of WLAN hotspots
Wi-Fi = Wireless Fidelity, WECA = Wireless Ethernet Compatibility Alliance, WISPr = Wireless ISP roaming
3GPP-WLAN Interworking (1)
• Six interworking scenarios1. Common billing and customer care2. 3GPP system based access control and charging3. Access to 3GPP system PS based services4. Service continuity5. Seamless service provision6. Access to 3GPP CS services
• Each scenario adds to the previous– Work in 3GPP is incremental– Scenarios 1-3 in Release 6, 4-5 in Release 7
3GPP-WLAN Interworking (2)
Ww
3GPP Home Network
WLAN Access Network
WLANUE
3GPP AAAServer
Packet DataGateway
HSS
HLR
CGw/CCF
OCS
D' / Gr'
Wf
Wo
Intranet / Internet
3GPP Visited Network
3GPP AAAProxy
CGw/CCF
WAGWn
WaWf
Wd
Wp
Wm
Wi
Wx
Sce
nario
3Wg
Wu
Source: 3GPP TS 23.234 v2.4.0
UE = User EquipmentWAG = WLAN Access GatewayAAA = Authentication, Authorization,
and AccountingCGw = Charging GatewayCCF = Charging Control FunctionHSS = Home Subscriber SystemHLR = Home Location RegisterOCS = Online Charging System
3GPP-WLAN Interworking (3)Node B
AP
AC
UTRAN
3GPP basedCore Network
Signalling
Signallingand User Data
Node B
UTRAN
RNC
RNC
SGSN GGSN
IP(IMS, Internet)
Roaming Partner
PDG
3GPPAAA
WAG
HSS
HSS
3GPPAAA
Summary
• WLANs are becoming increasingly popular– In offices, homes, and public hotspots
• WLAN standards are evolving constantly– New PHY layers with higher throughputs– MAC layer enhancements for security, QoS, …
• WLANs will be an alternative accessmethod to 3GPP-based networks of mobile operators
