Overview of IEEE 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 increasinglypopular 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 WG Wireless Local Area Network 802.15 WG Wireless Personal Area Network 802.11a... 802.11n 802.15.1... 802.15.5 802.16 WG Broadband Wireless Access 802.20 WG Mobile Wireless Access 802.16a... 802.16e
IEEE 802.11 protocol model TCP IP UDP IETF 802.11a PHY 802.2 Logical Link Control (LLC) 802.11 Medium Access Control (MAC) (Amended with 802.11e, 802.11i, ) 802.11b PHY 802.11g PHY 802.11n PHY 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 Backbone network STA AP STA STA STA STA STA STA BSS = Basic Service Set, STA = Station, AP = Access Point
Mobility Handovers possible within a subnet i.e. in an Extended Service Set (ESS) Inter-Access Point Protocol (IAPP) Inter-subnet handovers require higher level functionalities, e.g. Mobile IP Backbone network 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
802.11 MAC Layer (2) 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) CTS ACK RTS RTS CTS Data ACK
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 EncryptionStandard
802.11 PHY Layers Standard 802.11a 802.11b 802.11g Frequency Band 5 GHz 2.4 GHz 2.4 GHz Spectrum available 455 MHz 83.5 MHz 83.5 MHz Channel Width ~18 MHz ~22 MHz ~22 MHz Channel Spacing 20 MHz 5 MHz 5 MHz Independent Channels 18 3 / 4 3 / 4 Range Lower Higher Higher Radio OFDM DSSS DSSS / OFDM Max. Data Rate 54 Mbps 11 Mbps 54 Mbps Compatibility NO YES Status Available Dominant Available 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 increases Mbps 12 10 8 6 4 2 Mbps 30 25 20 15 10 5 1 2 4 802.11a 802.11b (TTKK) Whole network Single user users 8 16 32 64 (Atheros) m 30 60
Interoperability: Wi-Fi Alliance Standards fall short without certified interoperability A major force behind the success of 802.11 WLANs is Wi-Fi Alliance (former WECA) 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 scenarios 1. Common billingand customer care 2. 3GPP system based access control and charging 3. Access to 3GPP system PS based services 4. Service continuity 5. Seamless service provision 6. 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) Intranet / Internet 3GPP Visited Network Wa 3GPP AAA Proxy Wf CGw/CCF WLAN UE Ww WLAN Access Network Wn WAG Wg Wd Wu Scenario 3 Wp Packet Data Gateway Wi Wm 3GPP AAA Server Wo OCS 3GPP Home Network Wx D' / Gr' Wf HSS HLR CGw/ CCF UE = User Equipment WAG = WLAN Access Gateway AAA = Authentication, Authorization, and Accounting CGw = Charging Gateway CCF = Charging Control Function HSS = Home Subscriber System HLR = Home Location Register OCS = Online Charging System Source: 3GPP TS 23.234 v2.4.0
3GPP-WLAN Interworking (3) Node B RNC SGSN 3GPP based Core Network GGSN Node B UTRAN HSS RNC WAG PDG UTRAN 3GPP AAA AP IP (IMS, Internet) AC Signalling 3GPP AAA Signalling and User Data HSS Roaming Partner
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 access method to 3GPP-based networks of mobile operators
Thank You! Questions? timo.smura@hut.fi