Wireless LANs and MANsENEE 426 | Communication Networks | Spring 2008 Lecture 9IEEE 802.11 Standards• PHY/MAC:– 802.11: MAC, 2Mbps FHSS 2.4GHz PHY, 2Mbps DSSS 2.4GHz PHY, IR PHY– 802.11a: 54Mbps OFDM 5GHz PHY– 802.11b: 11Mbps DSSS 2.4GHz PHY– 802.11g: 54Mbps OFDM DSSS 2.4GHz PHY– 802.11n: 100+Mbps MIMO OFDM PHY/MAC• Security:– 802.11i: Security Enhancements, TKIP, AES– 802.11r: Key Exchange for Fast Handoff– 802.11s: Mesh NetworkingENEE 426 | Communication Networks | Spring 2008 Lecture 9PHY: Basic RF PropertiesStandard 802.11a 802.11b 802.11gFrequency 5.1 GHz, 5.2 GHz, 5.7 GHz;40 MHz wide2.4 GHz;20 MHz wide2.4 GHz;20 MHz wideData Rate 6, 9, 12, 18, 24, 36, 48, 54 Mbps1, 2, 5.5, 11 Mbps 6, 9, 12, 18, 24, 36, 48, 54 MbpsModulation OFDM-{BPSK, QPSK, 16QAM, 64QAM}DSSS-{DBPSK, DQPSK, CCK, PBCC}OFDM-{BPSK, QPSK, 16QAM, 64QAM}TX Power {40, 200, 800} mW (US)1000 mW (US);100 mW (Europe)1000 mW (US);100 mW (Europe)ENEE 426 | Communication Networks | Spring 2008 Lecture 9PHY: 802.11 FHSS• FHSS = Frequency Hopping Spread Spectrum• Signal hops between 79 different frequencies– dwells at each one for 10 to 200ms– predefined sequence for hoppingPowerFreqChannel 1 = 2402 MHzChannel 2 = 2403 MHzChannel 79 = 2480 MHzENEE 426 | Communication Networks | Spring 2008 Lecture 9PHY: 802.11a OFDM• OFDM = Orthogonal Frequency Division Multiplexing• Problem: Mobile, urban environments cause rapidly fluctuating signal quality (multipath fading)• Solution: Slow everything down, but use simultaneous parallel frequenciesFreqNormal Wideband SignalOFDM SignalENEE 426 | Communication Networks | Spring 2008 Lecture 9PHY: 802.11b DSSS• DSSS = Direct Sequence Spread Spectrum• Use same power, but spread it out over a larger bandwidth• Causes less interference, more resistant to noisePowerFreqTypical Narrowband SignalSpread Spectrum Signal• Normal signal modulated by 11-bit Barker Code0 11011011100 0 1 0 1 1 0 1 1 1 0 0 01011011100001001000 111Original SequenceBarker CodeXOR Resultincreases frequency (bandwidth)same power, just spread outENEE 426 | Communication Networks | Spring 2008 Lecture 9PHY: 802.11g OFDM• Same as 802.11a, but at 2.4 GHz• Adds additional rates onto 802.11b, making it backward compatibleENEE 426 | Communication Networks | Spring 2008 Lecture 9MAC: 802.11 TopologiesAd HocInfrastructureWireless DistributionSystem (WDS)ENEE 426 | Communication Networks | Spring 2008 Lecture 9MAC: 802.11 DCF• DCF = Distributed Coordination Function• Regulates the RF – who can talk and when?Anyone Transmitting?TransmitPacketSimple DCFYesNoComplex DCFused when network crowdedAnyone Transmitting?Anyone Transmitting?TransmitRTSReceive CTS?Anyone Transmitting?TransmitPacketReceive ACK?DoneNoYesTimeoutYesYesNoYesTimeoutDoneENEE 426 | Communication Networks | Spring 2008 Lecture 9MAC: Network Formationbeaconprobe responseprobe requestassociation requestassociation responsebeaconSTAAPpossible authentication and key exchange (802.11i)data (possibly encrypted)ENEE 426 | Communication Networks | Spring 2008 Lecture 9MAC: Packet Format• 24 to 30-byte header (WDS has 30-byte)• 0, 4, or 8-byte encryption header– 0 bytes = no encryption– 4 bytes = WEP encryption– 8 bytes = WPA/802.11i encryption• 8-byte LLC header• Packet Data• 4 to 16-byte encryption checksum if encrypted• 4-byte CRC-32MACHeaderEncHdrLLCHdrPayload CRCEncCksmencrypted if privacy is enabledENEE 426 | Communication Networks | Spring 2008 Lecture 9MAC: MAC Header• Contains flags, addresses, sequence numbers• Addresses:– wired to wireless: src, AP/BSSID, dst (3 addresses)– wireless to wireless: src, IBSSID, dst (3 addresses)– WDS: src, src AP, dst AP, dst (4 addresses)Frame Ctl(4 bytes)Address 1(6 bytes)Address 2(6 bytes)Address 3(6 bytes)SeqNo(2 bts)Address 4(6 bytes)MAC Header FormatENEE 426 | Communication Networks | Spring 2008 Lecture 9MAC: Frame ControlVer(2 b)Type(2 b)Subtype(4 bits)Flags(8 bits)Duration / ID(16 bits)Frame Control and Duration FieldsFlags:• type (adhoc, AP, WDS), 2 bits• more fragments, 1 bit• retry, 1 bit• power management, 1 bit• more data, 1 bit• encrypted payload, 1 bit• order, 1 bitPacket TypeCommon Types:• beacon = 0x80• normal data = 0x08• probes = 0x50• authentication = 0xb0ENEE 426 | Communication Networks | Spring 2008 Lecture 9MAC: Beacons• Beacons transmitted by AP to advertise network• Can be disabled for “hidden” networks• Contain the following information:– network name (SSID)– channel / frequency– supported data rates– authentication requirements– encryption schemes usedENEE 426 | Communication Networks | Spring 2008 Lecture 9Standards and Terminology• IEEE 802.16: IEEE WMAN Standard– 802.16: original standard– 802.16d 802.16-2004: fixed WMAN standard– 802.16e: revision to support mobile WMAN• Industry Terms:– Fixed WiMAX = 802.16-2004– Mobile WiMAX = 802.16e– “WiMAX” implies certification by WiMAX Forum– WiBRO = Korean version of early 802.16e draftENEE 426 | Communication Networks | Spring 2008 Lecture 9Technology ComparisonWiMAX802.16WiFi802.11WRAN802.223GRangeBandwidthTodayTomorrowENEE 426 | Communication Networks | Spring 2008 Lecture 9WiMAX ApplicationsBACKHAUL for HOTSPOTS1RESIDENTIAL & SoHo DSL1FRACTIONAL T1 for SMALL BUSINESST1+ LEVEL SERVICE ENTERPRISE1BACKHAULMULTI-POINT BACKHAUL1RURAL RESIDENTIAL11Metro Area CoverageMOBILITY SUPPORT /CELLULAR NETWORKS33Limited Coverage2- 2005-200612- 2006-20073- 2007LegendTimeframeENEE 426 | Communication Networks | Spring 2008 Lecture 9WiMAX Deployment BandsUSA700 MHz, 2.5 & 5.8 GHzCentral/South America2.5, 3.5 & 5.8 GHzEUROPE3.5 & 5.8 GHzPossible: 2.5 GHzMIDDLE EASTAFRICA3.5 & 5.8 GHzASIA PACIFIC2.3, 2.5, 3.3, 3.5 & 5.8 GHzCANADA2.3, 2.5, 3.5 & 5.8 GHzRUSSIA 3.5 & 5.8 GHzPossible: 2.3, 2.5 GHzInitial WiMAX Forum focus on 3.5 GHz profiles – Not usable in USAENEE 426 | Communication Networks | Spring 2008 Lecture 9Expected Timeline• IEEE Standard Approval– Fixed WiMAX: early 2005– Mobile WiMAX: early 2006• Certified Products Available:– Fixed WiMAX: early 2006– Mobile WiMAX: early 2007• Widespread Deployment– Fixed WiMAX: 2007-2008– Mobile WiMAX: 2008-2009ENEE 426 | Communication Networks | Spring 2008 Lecture 9IEEE 802.16 PHY LayersPHY Freq Licensing Max Mod Duplexing Multiple AccessSC.1611-66 GHz Licensed 64-QAM TDD, FDD
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