Transcription
Chapter 6Medium Access ControlProtocols and Local AreaNetworksPart I: Medium Access ControlPart II: Local Area Networks
Chapter Overviewl Broadcast Networksl l l l All information sent to allusersNo routingShared mediaRadiol l l Cellular telephonyWireless LANsl Medium Access Controll l l Local Area Networksl Copper & Opticall l Ethernet LANsCable Modem AccessTo coordinate access toshared mediumData link layer since directtransfer of framesl l l High-speed, low-costcommunications betweenco-located computersTypically based onbroadcast networksSimple & cheapLimited number of users
Chapter 6Medium Access ControlProtocols and Local AreaNetworksPart I: Medium Access ControlMultiple Access CommunicationsRandom AccessSchedulingChannelizationDelay Performance
Chapter 6Medium Access ControlProtocols and Local AreaNetworksPart II: Local Area NetworksOverview of LANsEthernetToken Ring and FDDI802.11 Wireless LANLAN Bridges
Chapter 6Medium Access ControlProtocols and Local AreaNetworksMultiple AccessCommunications
Multiple Access Communicationsl Shared media basis for broadcast networksl l l Inexpensive: radio over air; copper or coaxial cableM users communicate by broadcasting into mediumKey issue: How to share the medium?3124Shared multipleaccess medium5M
Approaches to Media SharingMedium sharing techniquesStaticchannelizationl l l l Partition mediumDedicatedallocation to usersSatellitetransmissionCellular TelephoneDynamic mediumaccess controlSchedulingl l l l Random accessPolling: take turnsRequest for slot intransmissionscheduleToken ringWireless LANsl l l l LoosecoordinationSend, wait, retry ifnecessaryAlohaEthernet
Channelization: SatelliteSatellite Channeluplink findownlink fout
Channelization: Cellularuplink f1 ; downlink f2uplink f3 ; downlink f4
Scheduling: PollingData from1 from 2DataPoll 1HostcomputerInbound lineData to MPoll 2Outbound line12M3Stations
Scheduling: Token-PassingRing networkstokenData to MtokenStation that holds token transmits into ring
Random AccessMultitapped BusCrash!!Transmit when readyTransmissions can occur; need retransmission strategy
Wireless LANAd Hoc: station-to-stationInfrastructure: stations to base stationRandom access & polling
Selecting a Medium AccessControll Applicationsl l l l l Scalel l l What type of traffic?Voice streams? Steady traffic, low delay/jitterData? Short messages? Web page downloads?Enterprise or Consumer market? Reliability, costHow much traffic can be carried?How many users can be supported?Current Examples:l l Design MAC to provide wireless DSL-equivalent access torural communitiesDesign MAC to provide Wireless-LAN-equivalent access tomobile users (user in car travelling at 130 km/hr)
Delay-Bandwidth Productl Delay-bandwidth product key parameterl l l Coordination in sharing medium involves usingbandwidth (explicitly or implicitly)Difficulty of coordination commensurate withdelay-bandwidth productSimple two-station examplel l l Station with frame to send listens to medium andtransmits if medium found idleStation monitors medium to detect collisionIf collision occurs, station that begin transmittingearlier retransmits (propagation time is known)
Two-Station MAC ExampleTwo stations are trying to share a common mediumAtransmitsat t 0Distance d meterstprop d / ν secondsABCase 1ABCase 2A detectscollision att 2 tpropABABB does nottransmit beforet tprop & AcaptureschannelB transmitsbefore t tpropand detectscollision soonthereafter
Efficiency of Two-StationExamplel Each frame transmission requires 2tprop of quiet timel l l Station B needs to be quiet tprop before and after time whenStation A transmitsR transmission bit rateL bits/frameL11Efficiency ρ max L 2t prop R 1 2t prop R / L 1 2aL1MaxThroughput Reff R bits/secondL / R 2t prop 1 2aNormalizedDelay-BandwidthProducta t propL/ RPropagation delayTime to transmit a frame
Typical MAC EfficienciesTwo-Station Example:1Efficiency 1 2al CSMA-CD (Ethernet) protocol:1Efficiency 1 6.44 aToken-ring networkl If a 1, thenefficiency close to100%As a approaches1, the efficiencybecomes low1Efficiency 1 aʹ′a latency of the ring (bits)/average frame length
Typical Delay-Bandwidth ProductsDistance1m10 Mbps100 Mbps1 Gbps3.33 x10-023.33 x10-013.33 x 100Network TypeDesk area network100 m 3.33 x 1001 3.33 x 1002 3.33 x 1003 Local area network10 km 3.33 x 1002 3.33 x 10033.33 x 1004 Metropolitan areanetwork1000 km 3.33 x 1004 3.33 x 1005 3.33 x 1006 Wide area network100000 km 3.33 x 1006 3.33 x 1007 3.33 x 1008 Global areanetworkl l Max size Ethernet frame: 1500 bytes 12000 bitsLong and/or fat pipes give large a
MAC protocol featuresl l l l l l l l Delay-bandwidth productEfficiencyTransfer delayFairnessReliabilityCapability to carry different types of trafficQuality of serviceCost
MAC Delay Performancel Frame transfer delayl l l Throughputl l l From first bit of frame arrives at source MACTo last bit of frame delivered at destination MACActual transfer rate through the shared mediumMeasured in frames/sec or bits/secParametersR bits/sec & L bits/frameX L/R seconds/frameλ frames/second average arrival rateLoad ρ λ X, rate at which “work” arrivesMaximum throughput (@100% efficiency): R/L fr/sec
Chapter 6Medium Access ControlProtocols and Local AreaNetworksRandom Access
ALOHAl l Wireless link to provide data transfer between maincampus & remote campuses of University of HawaiiSimplest solution: just do itl l l l A station transmits whenever it has data to transmitIf more than one frames are transmitted, they interfere witheach other (collide) and are lostIf ACK not received within timeout, then a station picks randombackoff time (to avoid repeated collision)Station retransmits frame after backoff timeFirst transmissiont0-Xt0Backoff period BRetransmissiontt0 XVulnerableperiodt0 X 2tpropTime-outt0 X 2tprop B
ALOHA Modell Definitions and assumptionsl X frame transmission time (assume constant)l S: throughput (average # successful frame transmissions perX seconds)l G: load (average # transmission attempts per X sec.)l Psuccess : probability a frame transmission is successfulS GPsuccessXPrior intervalXframetransmissionl l Any transmission thatbegins duringvulnerable periodleads to collisionSuccess if no arrivalsduring 2X seconds
Abramson’s Assumptionl l l l l What is probability of no arrivals in vulnerable period?Abramson assumption: Effect of backoff algorithm is thatframe arrivals are equally likely to occur at any time intervalG is avg. # arrivals per X secondsDivide X into n intervals of duration Δ X/np probability of arrival in Δ interval, thenG n p since there are n intervals in X secondsPsuccess P[0 arrivals in 2X seconds] P[0 arrivals in 2n intervals] (1 - p)2nG 2n 2G (1 ) eas n n
Throughput of ALOHAS GPsuccess Ge 2 Ge-2 0.1840.20.180.160.140.120.10.080.060.040.020l l Collisions are meansfor coordinatingaccessMax throughput isρmax 1/2e (18.4%)Bimodal behavior:Small G, S GLarge G, S 0G4210.50.25l 0.12500.00781250.0156250.031250.0625Sl Collisions cansnowball and dropthroughput to zero
Slotted ALOHAl l l l Time is slotted in X seconds slotsStations synchronized to frame timesStations transmit frames in first slot after framearrivalBackoff intervals in multiples of slotsBackoff periodkX(k 1)XVulnerableperiodt0 X 2tpropBtt0 X 2tprop BTime-outOnly frames that arrive during prior X seconds collide
Throughput of Slotted ALOHAS GPsuccess GP[no arrivals in X seconds] GP[no arrivals in n intervals]G n G (1 p ) G (1 ) Ge G84210.50.250.1250.06250.0312500.01563S
Application of Slotted Alohacycle.Reservationmini-slotsl l l X-second slotReservation protocol allows a large number ofstations with infrequent traffic to reserve slots totransmit their frames in future cyclesEach cycle has mini-slots allocated for makingreservationsStations use slotted Aloha during mini-slots torequest slots
Carrier Sensing Multiple Access(CSMA)l A station senses the channel before it starts transmissionl l l l l If busy, either wait or schedule backoff (different options)If idle, start transmissionVulnerable period is reduced to tprop (due to channel capture effect)When collisions occur they involve entire frame transmission timesIf tprop X (or if a 1), no gain compared to ALOHA or slottedALOHAStation A beginstransmission att 0Station A captureschannel at t tpropAA
CSMA Optionsl Transmitter behavior when busy channel is sensedl l l 1-persistent CSMA (most greedy)l Start transmission as soon as the channel becomes idlel Low delay and low efficiencyNon-persistent CSMA (least greedy)l Wait a backoff period, then sense carrier againl High delay and high efficiencyp-persistent CSMA (adjustable greedy)l Wait till channel becomes idle, transmit with prob. p; orwait one mini-slot time & re-sense with probability 1-pl Delay and efficiency can be balancedSensing
1-Persistent CSMA Throughput0.60.53l 0.50.4a 0.010.450.30.20.16l a 0.10.164321684210.50.250.130.060.0300.02Sa 1GBetter than Aloha& slotted Alohafor small aWorse than Alohafor a 1
Non-Persistent CSMA Throughputa 0.010.810.9l 0.80.70.60.510.50.4a 0.10.30.20.140.1a 164321684210.50.250.130.060.0300.02SGl Higher maximumthroughput than1-persistent forsmall aWorse than Alohafor a 1
CSMA with Collision Detection(CSMA/CD)l l l Monitor for collisions & abort transmissionl Stations with frames to send, first do carrier sensingl After beginning transmissions, stations continuelistening to the medium to detect collisionsl If collisions detected, all stations involved stoptransmission, reschedule random backoff times, andtry again at scheduled timesIn CSMA collisions result in wastage of X secondsspent transmitting an entire frameCSMA-CD reduces wastage to time to detect collisionand abort transmission
CSMA/CD reaction timeA begins totransmit at At 0BABA detectscollision at At 2 tprop- δBB begins totransmit att tprop- δ;B detectscollision att tpropIt takes 2 tprop to find out if channel has been captured
CSMA-CD Modell Assumptionsl Collisions can be detected and resolved in 2tpropl Time slotted in 2tprop slots during contention periodsl Assume n busy stations, and each may transmit withprobability p in each contention time slotl Once the contention period is over (a stationsuccessfully occupies the channel), it takes X secondsfor a frame to be transmittedl It takes tprop before the next contention period starts.(a)BusyContentionBusyIdleContentionBusyTime
Contention Resolutionl l How long does it take to resolve contention?Contention is resolved (“success’) if exactly 1 stationtransmits in a slot:Psuccess np(1 p)l By taking derivative of Psuccess we find max occurs at p 1/nmaxsuccessPl n 111 n 11 n 11 n (1 ) (1 ) nnneOn average, 1/Pmax e 2.718 time slots to resolve contentionAverage Contention Period 2t prop e seconds
CSMA/CD onBusyTimel At maximum throughput, systems alternates betweencontention periods and frame transmission timesρ maxl X11 X t prop 2et prop 1 (2e 1)a 1 (2e 1)Rd /ν Lwhere:R bits/sec, L bits/frame, X L/R seconds/framea tprop/Xν meters/sec. speed of light in mediumd meters is diameter of system2e 1 6.44
CSMA-CD Application: Ethernetl First Ethernet LAN standard used CSMA-CDl l l 1-persistent Carrier SensingR 10 Mbpstprop 51.2 microsecondsl l l 512 bits 64 byte slotaccommodates 2.5 km 4 repeatersTruncated Binary Exponential Backoffl After nth collision, select backoff from {0, 1, , 2k – 1},where k min(n, 10)
Throughput for Random AccessMACs1CSMA/CD1-P CSMA0.8Non-P CSMAρmax0.6Slotted ALOHA0.4ALOHA0.2a00.01l l 0.11For small a: CSMA-CD has best throughputFor larger a: Aloha & slotted Aloha better throughput
Chapter 6Medium Access ControlProtocols and Local AreaNetworksScheduling
Scheduling for Medium AccessControll Schedule frame transmissions to avoidcollision in shared mediumü ü ü û l More efficient channel utilizationLess variability in delaysCan provide fairness to stationsIncreased computational or procedural complexityTwo main approachesl l ReservationPolling
Reservations Systemsl Centralized systems: A central controller acceptsrequests from stations and issues grants to transmitl l l Frequency Division Duplex (FDD): Separate frequency bandsfor uplink & downlinkTime-Division Duplex (TDD): Uplink & downlink time-share thesame channelDistributed systems: Stations implement a decentralizedalgorithm to determine transmission orderCentralController
Reservation Cycle nrl l l 1 2ddTimeCycle (n 1)3MTransmissions organized into cyclesCycle: reservation interval frame transmissionsReservation interval has a minislot for each station to requestreservations for frame transmissions
Example: GPRSl General Packet Radio Servicel l l l Packet data service in GSM cellular radioGPRS devices, e.g. cellphones or laptops, sendpacket data over radio and then to InternetSlotted Aloha MAC used for reservationsSingle & multi-slot reservations supported
Polling Systemsl l l Centralized polling systems: A central controllertransmits polling messages to stations according to acertain orderDistributed polling systems: A permit for frametransmission is passed from station to station accordingto a certain orderA signaling procedure exists for setting up orderCentralController
Application: Token-Passing RingstokenFree Token PollFrame Delimiter is TokenFree 01111110Busy 01111111Listen modeInputfromringDelayTransmit modeOutputtoringReady station looks for free tokenFlips bit to change free token to busyDelayFrom deviceTo deviceReady station inserts its framesReinserts free token when done
Application Examplesl Single-frame reinsertionl l Single token reinsertionl l IBM Token Ring @ 4 MbpsMultitoken reinsertionl l l IEEE 802.5 Token Ring LAN @ 4 MbpsIEEE 802.5 and IBM Ring LANs @ 16 MbpsFDDI Ring @ 50 MbpsAll of these LANs incorporate token prioritymechanisms
Comparison of MAC approachesl Aloha & Slotted Alohal l l l l Simple & quick transfer at very low loadAccommodates large number of low-traffic bursty usersHighly variable delay at moderate loadsEfficiency does not depend on aCSMA-CDl l l Quick transfer and high efficiency for low delay-bandwidthproductCan accommodate large number of bursty usersVariable and unpredictable delay
Comparison of MAC approachesl Reservationl l l l l On-demand transmission of bursty or steady streamsAccommodates large number of low-traffic users withslotted Aloha reservationsCan incorporate QoSHandles large delay-bandwidth product via delayed grantsPollingl l l l Generalization of time-division multiplexingProvides fairness through regular access opportunitiesCan provide bounds on access delayPerformance deteriorates with large delay-bandwidthproduct
Chapter 6Medium Access ControlProtocols and Local AreaNetworksChannelization
Channelization Approachesl Frequency Division Multiple Access (FDMA)l l l Time Division Multiple Access (TDMA)l l l Frequency band allocated to usersBroadcast radio & TV, analog cellular phonePeriodic time slots allocated to usersTelephone backbone, GSM digital cellular phoneCode Division Multiple Access (CDMA)l l Code allocated to usersCellular phones, 3G cellular
Guardbandsl FDMAl l l Frequency bands must be non-overlapping toprevent interferenceGuardbands ensure separation; form of overheadTDMAl l l Stations must be synchronized to common clockTime gaps between transmission bursts fromdifferent stations to prevent collisions; form ofoverheadMust take into account propagation delays
Channelization: CDMAl Code Division Multiple Accessl l Channels determined by a code used in modulation anddemodulationStations transmit over entire frequency band all ofthe time!Frequency12W3Time
Global System for MobileCommunications (GSM)l l l l European digital cellular telephone system890-915 MHz & 935-960 MHz bandPCS: 1800 MHz (Europe), 1900 MHz (N.Am.)Hybrid TDMA/FDMAl l Carrier signals 200 kHz apart25 MHz give 124 one-way ward960MHz
Chapter 6Medium Access ControlProtocols and Local AreaNetworksDelay Performance
M/G/1 Queueing Model forStatistical MultiplexerPoisson Arrivalsrate λl Arrival Modell l l l l serverl Independent frameinterarrival times:Average 1/λExponential distribution“Poisson Arrivals”Infinite Bufferl bufferNo BlockingGeneral servicetime XFrame Length Modell l l l l Independent frametransmission times XAverage E[X] 1/µGeneral distributionConstant, exponential, Load ρ λ/µl Stability Condition: ρ 1We will use M/G/1 model as baseline for MAC performance
M/G/1 Performance Results(From Appendix A)Total Delay Waiting Time Service TimeAverage Waiting Time:E[W ] ρ2(1 ρ )Average Total Delay:(1 σ X22E[ X ]E[T ] E[W ] E[ X ]Example: M/D/1E[W ] ρ2(1 ρ )E[ X ]) E[ X ]
Chapter 6Medium Access ControlProtocols and Local AreaNetworksPart II: Local Area NetworksOverview of LANsEthernetToken Ring and FDDI802.11 Wireless LANLAN Bridges
Chapter 6Medium Access ControlProtocols and Local AreaNetworksOverview of LANs
What is a LAN?Local area means:l Private ownershipl l Short distance ( 1km) between computersl l l l low costvery high-speed, relatively error-free communicationcomplex error control unnecessaryMachines are constantly movedl l l l freedom from regulatory constraints of WANsKeeping track of location of computers a choreSimply give each machine a unique addressBroadcast all messages to all machines in the LANNeed a medium access control protocol
Typical LAN Structurel l l k InterfaceCard (NIC)Unique MAC“physical” address
Medium Access Control SublayerIn IEEE 802.1, Data Link Layer divided into:Medium Access Control Sublayerl 1.l l l l Coordinate access to mediumConnectionless frame transfer serviceMachines identified by MAC/physical addressBroadcast frames with MAC addressesLogical Link Control Sublayer2.l Between Network layer & MAC sublayer
MAC Sub-layerOSIIEEE 802Network layerLLCNetwork layer802.2 Logical link controlData linklayer802.11802.3802.5MACCSMA-CD Token Ring WirelessLANPhysicallayerVarious physical layersOtherLANsPhysicallayer
Logical Link Control Layerl IEEE 802.2: LLC enhances service provided by MACCAAUnreliable Datagram ServiceReliable frame service CLLCLLCLLCMACMACMACMACMACMACPHYPHYPHYPHYPHYPHY
Chapter 6Medium Access ControlProtocols and Local AreaNetworksEthernet
A bit of history l l l l l l l l 1970 ALOHAnet radio network deployed in Hawaiian islands1973 Metcalf and Boggs invent Ethernet, random access in wired net1979 DIX Ethernet II Standard1985 IEEE 802.3 LAN Standard (10 Mbps)1995 Fast Ethernet (100 Mbps)1998 Gigabit Ethernet2002 10 Gigabit EthernetEthernet is the dominant LAN standardMetcalf’s Sketch
IEEE 802.3 MAC: EthernetMAC Protocol:l CSMA/CDl Slot Time is the critical system parameterl l l l l l upper bound on time to detect collisionupper bound on time to acquire channelupper bound on length of frame segment generated bycollisionquantum for retransmission schedulingmax{round-trip propagation, MAC jam time}Truncated binary exponential backoffl l for retransmission n: 0 r 2k, where k min(n,10)Give up after 16 retransmissions
IEEE 802.3 Original Parametersl l l Transmission Rate: 10 MbpsMin Frame: 512 bits 64 bytesSlot time: 512 bits/10 Mbps 51.2 µsecl l 51.2 µsec x 2x105 km/sec 10.24 km, 1 way5.12 km round trip distancel Max Length: 2500 meters 4 repeatersl Each x10 increase in bit rate, must beaccompanied by x10 decrease in distance
IEEE 802.3 Physical LayerTable 6.2 IEEE 802.3 10 Mbps medium alternativesMediumMax. Segment k coaxThin coaxTwisted pairOptical fiber500 m200 m100 m2 kmBusBusStarPoint-topoint linktransceiversThick Coax: Stiff, hard to work with(b)Hubs & Switches!T connectors flaky
Ethernet Hubs & SwitchesSingle collision domain(a)l l l l l l (b)High-Speed backplaneor interconnection fabricl Twisted Pair CheapEasy to work withReliableStar-topology CSMA-CDl l l Twisted Pair CheapBridging increases scalabilitySeparate collision domainsFull duplex operation
Fast EthernetTable 6.4 IEEE 802.3 100 Mbps Ethernet medium alternativesMediumMax. sted pair category 3UTP 4 pairsTwisted pair category 5UTP two pairsOptical fiber multimodeTwo strands100 m100 m2 kmStarStarStarTo preserve compatibility with 10 Mbps Ethernet:l Same frame format, same interfaces, same protocolsl Hub topology only with twisted pair & fiberl Bus topology & coaxial cable abandonedl Category 3 twisted pair (ordinary telephone grade) requires 4 pairsl Category 5 twisted pair requires 2 pairs (most popular)l Most prevalent LAN today
Gigabit EthernetTable 6.3 IEEE 802.3 1 Gbps Fast Ethernet medium alternativesMediumMax. SegmentLengthTopologyl l l l l 1000baseSX1000baseLX1000baseCX1000baseTOptical fibermultimodeTwo strandsOptical fibersingle modeTwo strandsShieldedcopper cableTwisted paircategory 5UTP550 m5 km25 m100 mStarStarStarStarSlot time increased to 512 bytesSmall frames need to be extended to 512 BFrame bursting to allow stations to transmit burst of short framesFrame structure preserved but CSMA-CD essentially abandonedExtensive deployment in backbone of enterprise data networks andin server farms
10 Gigabit EthernetTable 6.5 IEEE 802.3 10 Gbps Ethernet medium alternatives10GbaseSRTwo opticalfibersMultimode atMedium850 nm64B66B codeMax. SegmentLengthl l l l l 300 m10GBaseLR10GbaseEWTwo optical fibersTwo optical fibersSingle-mode at1310 nmSingle-mode at1550 nmSONETcompatibility64B66B10 km40 km10GbaseLX4Two optical fibersmultimode/singlemode with fourwavelengths at1310 nm band8B10B code300 m – 10 kmFrame structure preservedCSMA-CD protocol officially abandonedLAN PHY for local network applicationsWAN PHY for wide area interconnection using SONET OC-192cExtensive deployment in metro networks anticipated
Typical Ethernet DeploymentServer farmServerSwitch/routerServerEthernetswitch100 Mbps linksHub10 Mbps linksDepartment AServerServerGigabit Ethernet linksGigabit Ethernet linksEthernetswitch100 Mbps linksServerHub10 Mbps linksDepartment BSwitch/routerEthernetswitch100 Mbps linksServerHub10 Mbps linksDepartment C
Chapter 6Medium Access ControlProtocols and Local AreaNetworksToken Ring and FDDI
IEEE 802.5 Ring LANl l Unidirectional ring network4 Mbps and 16 Mbps on twisted pairl l Token passing protocol provides accessü ü û l Differential Manchester line codingFairnessAccess prioritiesBreaks in ring bring entire network downReliability by using star topology
Fiber Distributed Data Interface(FDDI)l l l l l l l l Token ring protocol for LAN/MANCounter-rotating dual ring topology100 Mbps on optical fiberUp to 200 km diameter, up to 500 stationsStation has 10-bit “elastic” buffer to absorb timingdifferences between input & outputMax frame 40,000 bits500 stations @ 200 km gives ring latency of 105,000bitsFDDI has option to operate in multitoken mode
Chapter 6Medium Access ControlProtocols and Local AreaNetworks802.11 Wireless LAN
Wireless Data Communicationsl Wireless communications compellingü ü ü Easy, low-cost deploymentMobility & roaming: Access information anywhereSupports personal devicesü ü Supports communicating devicesü û û û PDAs, laptops, data-cell-phonesCameras, location devices, wireless identificationSignal strength varies in space & timeSignal can be captured by snoopersSpectrum is limited & usually regulated
Ad Hoc CommunicationsCABl DTemporary association of group of stationsl l l Within range of each otherNeed to exchange informationE.g. Presentation in meeting, or distributed computergame, or both
Hidden Terminal Problem(a)ACData FrameA transmits data frameB(b)Data FrameAl BC senses medium,station A is hidden from CData FrameCC transmits data frame& collides with A at BNew MAC: CSMA with Collision Avoidance
IEEE 802.11 Wireless LANl Stimulated by availability of unlicensedspectruml l l l l l U.S. Industrial, Scientific, Medical (ISM) bands902-928 MHz, 2.400-2.4835 GHz, 5.725-5.850 GHzTargeted wireless LANs @ 20 MbpsMAC for high speed wireless LANAd Hoc & Infrastructure networksVariety of physical layers
Physical LayersLLC PDULLCMACheaderMAC SDUCRCMAClayerPhysical layerconvergenceprocedurePLCP PLCPpreamble headerl PLCP PDU802.11 designed tol l Support LLCOperate over many physical layersPhysical mediumdependentPhysicallayer
IEEE 802.11 Physical LayerOptions802.11Frequency Bit Rate Modulation SchemeBand2.4 GHz 1-2 Mbps Frequency-Hopping SpreadSpectrum, Direct SequenceSpread Spectrum802.11b2.4 GHz11 MbpsComplementary CodeKeying & QPSK802.11g2.4 GHz54 MbpsOrthogonal FrequencyDivision Multiplexing& CCK for backwardcompatibility with 802.11b802.11a5-6 GHz54 MbpsOrthogonal FrequencyDivision Multiplexing
Distance 10 Mbps 100 Mbps 1 Gbps Network Type 1 m 3.33 x 10-02 3.33 x 10-01 3.33 x 100 Desk area network 100 m 3.33 x 1001 3.33 x 1002 3.33 x 1003 Local area network 10 km 3.33 x 1002 3.33 x 1003 3.33 x 1004 Metropolitan area network 1000 km 3.33 x 1004 3.33 x 1005 3.33 x 1006 Wide area network 100000 km 3.33 x 1006 3.33 x 1007 3.33 x 1008 .
