Unformatted text preview:

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 Jain2Spread SpectrumWireless wide area networks: CDPD and MetricomWireless local area networksWireless LAN standard: IEEE 802.11, HiperlanNote: wireless phone services and standards not covered.OverviewOverviewRaj Jain3Mobile vs WirelessMobile vs WirelessMobile vs StationaryWireless vs WiredWireless media sharing issuesMobile routing, addressing issuesMobileWirelessRaj Jain4Raj Jain5Frequency Hopping Frequency Hopping Spread SpectrumSpread SpectrumPseudo-random frequency hoppingSpreads the power over a wide spectrum Spread SpectrumDeveloped initially for militaryPatented by actress Hedy LamarrNarrowband interference can't jamFrequencyTime50 msRaj Jain6SpectrumSpectrumSignalNoiseSignalNoise(a) Normal (b) Frequency HoppingRaj Jain7Direct-Sequence Direct-Sequence Spread SpectrumSpread SpectrumSpreading factor = Code bits/data bit, 10-100 commercial (Min 10 by FCC), 10,000 for militarySignal bandwidth >10 × data bandwidthCode sequence synchronizationCorrelation between codes InterferenceOrthogonalFrequencyTime5s01001011011011010010Data0 1Raj Jain8DS SpectrumDS SpectrumTime Domain Frequency Domain(a) Data(b) CodeFrequencyFrequencyTimeRaj Jain9Wireless WAN ServicesWireless WAN Services4.8 kbps to 19.2 kbps nominalThroughput 2 to 8 kbpsWired backbone using leased linesPacketized short transmissionEmail, 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 IBMAllows data to use idle cellular channelsData hops from one channel to next as the channels become busy or idleVoice CallIdle ChannelData packetsRaj Jain11CDPDCDPDBacked by 9 major service providersNationwide cellular packet data serviceConnectionless and connection-oriented serviceConnectionless No ack, no guaranteesConnection-oriented reliable delivery, sequencing, flow controlPoint-to-point and multipoint connectionsQuickly hops-off a channel grabbed by cellular system. Currently, dedicated channels.Raj Jain12Wireless LANsWireless LANsIR Line of sight, short range, indoorsRF Need licenseSpread-Spectrum: Resistance to interference101010111012101310141015101610171018109waveInfraredVisibleUltravioletx-raysRaj Jain13Wireless LANsWireless LANsInfrared RadioSpread Spectrum902 MHz2.4 GHzProxim RangeLANNCR WaveLANTelesystems ArLANMotorola ALTAIRWindata FreeportPhotonicsCollaborativeInfraLANProxim RangeLAN2FHDSDSFHNarrowband5.7GHzLine of SightDiffuseRaj Jain14IEEE 802.11 FeaturesIEEE 802.11 Features1 and 2 MbpsSupports both Ad-hoc and base-stationsSpread 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 prioritiesSupports time-critical and data trafficPower management allows a node to doze offRaj Jain15Hidden Node ProblemHidden Node ProblemC 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 MACCarrier 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 communicateAll stations have the same logicNo infrastructure, Suitable for small areaInfrastructure Based: Access points (base units)Stations can be simpler than bases.Base provide connection for off-network trafficBase provides location tracking, directory, authentication  Scalable to large networksIEEE 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 PrioritiesInitial 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 ServicesTimer critical services use Point Coordination FunctionThe point coordinator allows only one station to accessCoordinator sends a beacon frame to all stations.Then uses a polling frame to allow a particular station to have contention-free accessContention Free Period (CFP) varies with the load.TimeBeaconDCF AccessPCF AccessCFP Repetition IntervalContention PeriodRaj Jain23Power ManagementPower ManagementA station can be in one of three states:Transmitter onReceiver only onDozing: Both transmitter and receivers off.Access point (AP) buffers traffic for dozing stations.AP


View Full Document

WUSTL CIS 777 - Wireless Data Networking

Documents in this Course
SONET

SONET

17 pages

SONET

SONET

22 pages

SONET

SONET

19 pages

Load more
Download Wireless Data Networking
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Wireless Data Networking and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Wireless Data Networking 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?