Raj Jain1Wireless DataWireless DataNetworkingNetworkingRaj JainRaj JainThe Ohio State UniversityThe Ohio State UniversityColumbus, OH 43210Columbus, OH 43210Ohio Highway PatrolThese slides are available athttp://www.cis.ohio-state.edu/~jain/cis777-99/Raj Jain2q Spread Spectrumq Wireless wide area networks: CDPD and Metricomq Wireless local area networksq Wireless LAN standard: IEEE 802.11, HiperlanNote: wireless phone services and standards not covered.OverviewOverviewRaj Jain3Mobile vs WirelessMobile vs Wirelessq Mobile vs Stationaryq Wireless vs Wiredq Wireless ⇒ media sharing issuesq Mobile ⇒ routing, addressing issuesMobileWirelessRaj Jain4Raj Jain5Frequency HoppingFrequency HoppingSpread SpectrumSpread Spectrumq Pseudo-random frequency hoppingq Spreads the power over a wide spectrum⇒ Spread Spectrumq Developed initially for militaryq Patented by actress Hedy Lamarrq Narrowband interference can't jamFrequencyTime50 msRaj Jain6SpectrumSpectrumSignalNoiseSignalNoise(a) Normal (b) Frequency HoppingRaj Jain7Direct-SequenceDirect-SequenceSpread SpectrumSpread Spectrumq Spreading factor = Code bits/data bit, 10-100commercial (Min 10 by FCC), 10,000 for militaryq Signal bandwidth >10 × data bandwidthq Code sequence synchronizationq Correlation between codes ⇒Interference⇒ OrthogonalFrequencyTime5µs01001011011011010010Data0 1Raj Jain8DS SpectrumDS SpectrumTime Domain Frequency Domain(a) Data(b) CodeFrequencyFrequencyTimeRaj Jain9Wireless WAN ServicesWireless WAN Servicesq 4.8 kbps to 19.2 kbps nominalq Throughput 2 to 8 kbpsq Wired backbone using leased linesq Packetized short transmissionq Email, stock quotes, weatherq Options: Ardis, RAM Mobile Data, Cellular,Cellular Digital Packet Data (CDPD), and MetricomRaj Jain10Cellular Digital Packet DataCellular Digital Packet Data(CDPD)(CDPD)q Originally named “Celluplan” by IBMq Allows data to use idle cellular channelsq Data hops from one channel to next as the channelsbecome busy or idleVoice CallIdle ChannelData packetsRaj Jain11CDPDCDPDq Backed by 9 major service providersq Nationwide cellular packet data serviceq Connectionless and connection-oriented serviceConnectionless ⇒ No ack, no guaranteesConnection-oriented ⇒ reliable delivery,sequencing, flow controlq Point-to-point and multipoint connectionsq Quickly hops-off a channel grabbed by cellularsystem. Currently, dedicated channels.Raj Jain12Wireless LANsWireless LANsq IR ⇒ Line of sight, short range, indoorsq RF ⇒ Need licenseq Spread-Spectrum: Resistance to interference101010111012101310141015101610171018109µwaveInfraredVisibleUltravioletx-raysRaj Jain13Wireless LANsWireless LANsInfrared RadioSpread Spectrum902 MHz2.4 GHzProximRangeLANNCR WaveLANTelesystemsArLANMotorola ALTAIRWindata FreeportPhotonicsCollaborativeInfraLANProxim RangeLAN2FHDSDSFHNarrowband5.7GHzLine of SightDiffuseRaj Jain14IEEE 802.11 FeaturesIEEE 802.11 Featuresq 1 and 2 Mbpsq Supports both Ad-hoc and base-stationsq 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.q Supports multiple prioritiesq Supports time-critical and data trafficq Power management allows a node to doze offRaj Jain15Hidden Node ProblemHidden Node Problemq C cannot hear A.It may start transmitting while A is also transmitting⇒ A and C can't detect collision.q Only the receiver can help avoid collisionsA B CRaj Jain164-Way Handshake4-Way HandshakeAccessPointAccessPointMobileNodeMobileNodeReady to sendDataClear to sendAckRaj Jain17IEEE 802.11 MACIEEE 802.11 MACq Carrier Sense Multiple Access withCollision Avoidance (CSMA/CA)q Listen before you talk. If the medium is busy, thetransmitter backs off for a random period.q 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.q Destination sends: Clear to send (CTS)q Can not detect collision ⇒ Each packet is acked.q MAC level retransmission if not acked.Raj Jain18Ad-Hoc vs InfrastructureAd-Hoc vs InfrastructureRaj Jain19Peer-to-Peer orPeer-to-Peer orBase Stations?Base Stations?q Ad-hoc (Autonomous) Group:m Two stations can communicatem All stations have the same logicm No infrastructure, Suitable for small areaq Infrastructure Based: Access points (base units)m Stations can be simpler than bases.m Base provide connection for off-network trafficm Base provides location tracking, directory,authentication ⇒ Scalable to large networksq 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 Prioritiesq Initial interframe space (IFS)q Highest priority frames, e.g., Acks, useshort IFS (SIFS)q Medium priority time-critical frames use “PointCoordination Function IFS” (PIFS)q Asynchronous data frames use “Distributedcoordination function IFS” (DIFS)BusySIFSPIFSDIFSContention WindowRandom BackoffCarrier SensedTimeFrameRaj Jain22Contention-Free PeriodTime Critical ServicesTime Critical Servicesq Timer critical services use Point Coordination Functionq The point coordinator allows only one station to accessq Coordinator sends a beacon frame to all stations.Then uses a polling frame to allow a particular stationto have contention-free accessq Contention Free Period (CFP) varies with the load.TimeBeaconDCF AccessPCF AccessCFP Repetition IntervalContention PeriodRaj Jain23Power ManagementPower Managementq A station can be in one of three states:m Transmitter onm Receiver only onm Dozing: Both transmitter and receivers off.q Access point (AP) buffers traffic for dozing stations.q AP announces which stations have frames buffered.Traffic indication map included in each beacon.All multicasts/broadcasts are buffered.q Dozing stations wake up to listen to the beacon.If there is data waiting for it, the station sends a pollframe to get the data.Raj Jain24Status and FutureStatus and Futureq 802.11 including both MAC and PHY approved June1997.q More bandwidth in future by:1. Better encoding: Multilevel modulation ⇒ 8 Mbps2. Fewer channels with more bandwidth ⇒ 4 MHzchannels. Or Entire ISM band for one channel.3. Find another band. May get 150 MHz band in 5-GHzband. Fifteen 10-MHz