Wide Area Networks

Chapter 10Wide Area NetworksContentsThe need for Wide area networks (WANs)Point-to-point approachesStatistical multiplexing, TDM, FDM approachesDial-up, T/ DS linksX.25, Frame relay, ATMSONETDWDMWANs and TCP/ IP stack2DefinitionWANs are physical or logical networks that provide data communications to a large number of independent users. These users are usually spread over a larger geographic area than a LAN3The need for WANsLANs are very effective at connecting computers within officesLinks are short, so dedicated link to each PC is not too expensiveBut many organizations have offices in many states and countriesWeb pages, email servers are located world-wideAs users spread over large distances, link costs become very high

4The need for WANs (contd.)Broadcast lowers costs of LAN equipment

But as number of users increases, CSMA slows down the network significantlyAs number of network users increases, need mechanisms to merge traffic from multiple users

5Roads and computer networksThere are many similarities between the challenges and design solutions used in road networks and computer networksNeighborhood networks are like LANs

Interstate networks are like WANs

6Local intersection as LAN node

Stop sign promotes carrier sensingWhite car will wait till black car passes7

Interstate exit as WAN nodeMerging lane: Entry ramp for local trafficExisting traffic does not stop for merging trafficShared lanesMerging lane: Exit ramp for local traffic8Categories of WANsPoint-to-pointDial-upT/ DSStatistical multiplexingX.25, Frame relay, ATMTDMSONETFDM/ WDMFiber opticsMPLS9

Point-to-point WANsEarliest WANs used dial-up networkingUse phone line to connect to a remote computer

Leverage existing communication networkEnd stations perform routingPhone linesInternet in 196910T/ DS carriersPhone companies realized business opportunity in providing data servicesCombined (multiplexed) data carrying capacity of multiple phone lines to provide high speeds

Offered as T/ DS carriersT =DS =11WAN built using T-carriers

T/ DS carriersFormally, t-carriers are the physical line, DS is the signal carried by the lineBoth terms used interchangeably in the industryOffer point-to-point connection like dial-up

No. of phone lines aggregatedT-carrier nameDS nameData rate1DS-064 kbps24T-1DS-11.544 mbps96T-2DS-26.312 mbps672T-3DS-344.736 mbps13Statistically multiplexed WANsPoint-to-point is very inefficient when network growsNo switching within network

Inefficient use of bandwidthStatistical multiplexing allows WANs to aggregate trafficReduces burstiness

14Reducing burstiness15Virtual circuits

16ConnectionVirtual-circuit IDA-A1B-B12B-B23X.25/ Frame relay/ ATMShared network services offered by telcosMultiple end users can share the same infrastructure

Aggregation similar to interstate systemEnd users connect to shared network using point-to-point links such as T1/ T317X.25/ Frame relay/ ATMWhen data packets enter shared network, carrier assigns label based upon destinationShared network uses labels to direct packets to correct destinations

Each label is called a virtual channelData link layer technologiesMany virtual channels can be carried over a single physical link, limited only by link capacity18X.25/ Frame relay/ ATMX.25Standardized by CCITT in 1976Data rates: 56 kbps 2 mbpsFrame relaySpecified/ standardized in 1990 (Cisco)/ 1992 (CCITT)Data rates: 56 kbps 45 mbpsATMStandardized: 1992 by CCITTData rates: 1.544 mbps 622.080 mbpsPricing: ~ $400/ mbps/port (domestic) upto $4,000/ mbps/port (internationally)19TDM WANsAvailable line data rate divided into time slotsPhysical layer technologyEach virtual channel given one or more slotsCommercially available as SONET servicesSynchronous Optical NETworkSynchronous Digital Hierarchy (SDH) in EuropeOffered as optical carrier (OC) servicesPricing generally dependent on distance: ~ $15/ mbps/ mile20TDM WANsX.25/ Frame relay/ ATM often transported over SONET linksSONET data rates first standardized in 1988 by CCITTSONET service namesData rateData + overheadOC-150.112 mbps51.84 mbpsOC-3150.336 mbps155.52 mbpsOC-12601.344 mbps622.08 mbpsOC-482.405,376 gbps2.488,320 gbpsOC-1929.621,504 gbps9.953,280 gbpsOC-76838.486,016 gbps39.813,120 gbps21FDM WANsOptical fiber has very high bandwidthCapable of supporting extremely large data rates

No single user needs such high bandwidthsAvailable line bandwidth split into multiple lower bandwidth channelsLike lanes on interstate highwaysVehicles are not wide enough to use entire road width22FDM WANsDWDM channel frequencies standardized by ITU-T as ITU grid in 20013 bands: L band, C band, S band50 channels/ band = 150 channels totalData rates up to 10 gbps possible per DWDM channelDWDM commonly used in network coreConsidered below physical layerEach FDM channel on a DWDM link may transport a SONET signal, which in turn may transport multiple ATM channels23WANs and TCP/ IP stackWhere are WAN technologies positioned on the TCP/ IP stack?Typically, multiple WANs traversed by packet from source to destinationRouters interface between WANsHence WANs typically considered a data link layer technology24WANs and TCP/ IP stackTraceroute to Google25

SummaryWANs are long distance links that aggregate traffic from multiple networksWANs generally have very high data ratesWAN types include point-to-point, statistically multiplexed, TDM and FDMCarriers define virtual circuits for each source-destination pair of nodesWANs operate at the data link layerCase study UAVsRemote wars were fought with soldiersNow, increasingly de[end upon satellite based WAN networksUAVsHands-on exerciseOPNETDownload academic version of softwareApprox. 50 MBRun scenarioCollect statisticsNetwork design exerciseChoosing appropriate WAN technologiesAdding routers to the network