Wireless Data NetworkingOverviewMobile vs WirelessSlide 4Frequency Hopping Spread SpectrumSpectrumDirect-Sequence Spread SpectrumDS SpectrumWireless WAN ServicesCellular Digital Packet Data (CDPD)CDPDWireless LANsSlide 13IEEE 802.11 FeaturesHidden Node Problem4-Way HandshakeIEEE 802.11 MACAd-Hoc vs InfrastructurePeer-to-Peer or Base Stations?IEEE 802.11 ArchitectureIEEE 802.11 PrioritiesTime Critical ServicesPower ManagementStatus and FutureHIPERLANSummaryWireless: Key ReferencesRaj Jain1Wireless Data Wireless Data NetworkingNetworkingRaj Jain Raj Jain The Ohio State UniversityThe Ohio State UniversityColumbus, OH 43210Columbus, OH 43210Ohio Highway PatrolThese slides are available at http://www.cse.ohio-state.edu/~jain/cis777-99/Raj Jain2Spread SpectrumWireless wide area networks: CDPD and MetricomWireless local area networksWireless LAN standard: IEEE 802.11, HiperlanNote: wireless phone services and standards not covered.OverviewOverviewRaj Jain3Mobile vs WirelessMobile vs WirelessMobile vs StationaryWireless vs WiredWireless media sharing issuesMobile routing, addressing issuesMobileWirelessRaj Jain4Raj Jain5Frequency Hopping Frequency Hopping Spread SpectrumSpread SpectrumPseudo-random frequency hoppingSpreads the power over a wide spectrum Spread SpectrumDeveloped initially for militaryPatented by actress Hedy LamarrNarrowband interference can't jamFrequencyTime50 msRaj Jain6SpectrumSpectrumSignalNoiseSignalNoise(a) Normal (b) Frequency HoppingRaj Jain7Direct-Sequence Direct-Sequence Spread SpectrumSpread SpectrumSpreading factor = Code bits/data bit, 10-100 commercial (Min 10 by FCC), 10,000 for militarySignal bandwidth >10 × data bandwidthCode sequence synchronizationCorrelation between codes InterferenceOrthogonalFrequencyTime5s01001011011011010010Data0 1Raj Jain8DS SpectrumDS SpectrumTime Domain Frequency Domain(a) Data(b) CodeFrequencyFrequencyTimeRaj Jain9Wireless WAN ServicesWireless WAN Services4.8 kbps to 19.2 kbps nominalThroughput 2 to 8 kbpsWired backbone using leased linesPacketized short transmissionEmail, stock quotes, weather Options: Ardis, RAM Mobile Data, Cellular,Cellular Digital Packet Data (CDPD), and MetricomRaj Jain10Cellular Digital Packet Data Cellular Digital Packet Data (CDPD)(CDPD)Originally named “Celluplan” by IBMAllows data to use idle cellular channelsData hops from one channel to next as the channels become busy or idleVoice CallIdle ChannelData packetsRaj Jain11CDPDCDPDBacked by 9 major service providersNationwide cellular packet data serviceConnectionless and connection-oriented serviceConnectionless No ack, no guaranteesConnection-oriented reliable delivery, sequencing, flow controlPoint-to-point and multipoint connectionsQuickly hops-off a channel grabbed by cellular system. Currently, dedicated channels.Raj Jain12Wireless LANsWireless LANsIR Line of sight, short range, indoorsRF Need licenseSpread-Spectrum: Resistance to interference101010111012101310141015101610171018109waveInfraredVisibleUltravioletx-raysRaj Jain13Wireless LANsWireless LANsInfrared RadioSpread Spectrum902 MHz2.4 GHzProxim RangeLANNCR WaveLANTelesystems ArLANMotorola ALTAIRWindata FreeportPhotonicsCollaborativeInfraLANProxim RangeLAN2FHDSDSFHNarrowband5.7GHzLine of SightDiffuseRaj Jain14IEEE 802.11 FeaturesIEEE 802.11 Features1 and 2 MbpsSupports both Ad-hoc and base-stationsSpread Spectrum No licensing required.Three Phys: Direct Sequence, Frequency Hopping, 915-MHz, 2.4 GHz (Worldwide ISM), 5.2 GHz, and Diffused Infrared (850-900 nm) bands. Supports multiple prioritiesSupports time-critical and data trafficPower management allows a node to doze offRaj Jain15Hidden Node ProblemHidden Node ProblemC cannot hear A. It may start transmitting while A is also transmitting A and C can't detect collision.Only the receiver can help avoid collisionsA B CRaj Jain164-Way Handshake4-Way HandshakeAccessPointAccessPointMobileNodeMobileNodeReady to sendDataClear to sendAckRaj Jain17IEEE 802.11 MACIEEE 802.11 MACCarrier Sense Multiple Access with Collision Avoidance (CSMA/CA)Listen before you talk. If the medium is busy, the transmitter backs off for a random period.Avoids collision by sending a short message: Ready to send (RTS)RTS contains dest. address and duration of message.Tells everyone to backoff for the duration.Destination sends: Clear to send (CTS)Can not detect collision Each packet is acked.MAC level retransmission if not acked.Raj Jain18Ad-Hoc vs InfrastructureAd-Hoc vs InfrastructureRaj Jain19Peer-to-Peer or Peer-to-Peer or Base Stations?Base Stations?Ad-hoc (Autonomous) Group: Two stations can communicateAll stations have the same logicNo infrastructure, Suitable for small areaInfrastructure Based: Access points (base units)Stations can be simpler than bases.Base provide connection for off-network trafficBase provides location tracking, directory, authentication Scalable to large networksIEEE 802.11 provides both.Raj Jain20IEEE 802.11 ArchitectureIEEE 802.11 ArchitectureStationStationStationStationStationStationStationStationAd-hocStationAd-hocStationAd-hocStationAd-hocStationAccessPointAccessPointAccessPointAccessPointBasic Service Set2nd BSSServerServerAd-hocnetworkRaj Jain21IEEE 802.11 PrioritiesIEEE 802.11 PrioritiesInitial interframe space (IFS)Highest priority frames, e.g., Acks, use short IFS (SIFS)Medium priority time-critical frames use “Point Coordination Function IFS” (PIFS)Asynchronous data frames use “Distributed coordination function IFS” (DIFS)BusySIFSPIFSDIFSContention WindowRandom BackoffCarrier SensedTimeFrameRaj Jain22Contention-Free PeriodTime Critical ServicesTime Critical ServicesTimer critical services use Point Coordination FunctionThe point coordinator allows only one station to accessCoordinator sends a beacon frame to all stations.Then uses a polling frame to allow a particular station to have contention-free accessContention Free Period (CFP) varies with the load.TimeBeaconDCF AccessPCF AccessCFP Repetition IntervalContention PeriodRaj Jain23Power ManagementPower ManagementA station can be in one of three states:Transmitter onReceiver only onDozing: Both transmitter and receivers off.Access point (AP) buffers traffic for dozing stations.AP
View Full Document