分析教案通信网chapter switch technology fundamentals

Chapter SwitchTechnologyChapter3 CircuitMessagePacketvirtualTiminginChapter SwitchTechnologyTheNetworkmeshofinterconnectedroutersthefundamentalquestion:howisdatatransferredthroughcircuitswitching:dedicatedcircuitperpacket-switching:datasentthrunetindiscreteChapter SwitchTechnologyCircuit linkbandwidth,switchdedicatedresources:nosharingcircuit-like(guaranteed)callsetupChapter SwitchTechnologyCircuitnetworkresources(e.g.,bandwidth)dividedintopiecesallocatedtocallsresourcepieceidleifnotusedbyowningcall(nosharing)dividinglinkbandwidthfrequencytimeChapter SwitchTechnologyTiminginCircuitHost

Node Node

Host

betweenHost1andNodebetweenHost2andhostChapter SwitchTechnologyCircuitAnode(switch)inacircuitswitchinging

outgoingChapter SwitchTechnologyCircuitSwitching:TimedividedinframesandframesdividedinRelativeslotpositioninsideaframedetermineswhichconversationthedatabelongstoNeedssynchronizationbetweensenderandreceiverIncaseofnon-permanentneedstodynamicallybindaslottoahowtodoIfaconversationdoesnotuseitscircuitthecapacityisChapter SwitchTechnologyMessageeachend-enddatastreamasmessagesuserA,BmessagesharenetworkeachmessageusesfulllinkbandwidthresourcesusedasBandwidthdivisioninto“pieces”DedicatedallocationResourcereservation

resourcecontention:aggregateresourcedemandcanexceedamountcongestion:messagesqueue,waitforlinkusestoreandforward:messagesmoveonehopatatimetransmitoverwaitturnatnextChapter SwitchTechnologyTiminginMessageHost

Node Node

HostChapter SwitchTechnologyPacketeachend-enddatastreamdivideduserA,Bpacketssharenetworkresourceseachpacketusesfulllinkbandwidthresourcesusedasneeded,Bandwidthdivisioninto“pieces”DedicatedallocationResourcereservation

resourceaggregateresourcedemandcanexceedamountavailablecongestion:packetsqueue,waitforlinkstoreandforward:packetsmoveonehopatatimetransmitoverwaitturnatnextChapter SwitchTechnologyTimingofDatagramPacketHost

Node Node

HostPacketPacketdelaybetweenHost1andNodePacketPacketdelaybetweenHost1andNodePacketPacketPacketdelayofPacket1atNodePacketPacketPacketPacketChapter SwitchTechnologyPacket10Mbs10MbsstatisticalCB1.5queueofpacketswaitingforoutput45DEChapter SwitchTechnologyPacketAnodeinapacketswitchinging

outgoingChapter SwitchTechnologyPacketSwitching:DatafromanyconversationcanbetransmittedatanygiventimeAsingleconversationcanusetheentirelinkcapacityifitisHow lthemusemeta-data(header)todescribeChapter SwitchTechnologyPacketsChapter SwitchTechnologyLLRRRTakesL/Rsecondstotransmit(pushout)packetofLbitsontolinkorRbpsEntirepacketmustarriveatrouterbeforeitcanbetransmittedonnextlink:storeandforwarddelay=

L=7.5MbitsR=1.5Mbpsdelay=15secChapter SwitchTechnologyPacketSwitching:MessageNowbreakupthemessageinto5000packetsstoreandforwardEachpacket1,500bits,1msectotransmitapacketononelinkpipelining:eachlinkworksinDelayreducedfrom3*5=15secto5.002secChapter SwitchTechnologyDelayinpacket-switchedpacketsexperiencedelayonend-to-endpathfoursourcesofdelayateachB

nodalcheckbitdetermineoutputtimewaitingatoutputlinkfordependsoncongestionlevelChapter SwitchTechnologyDelayinpacket-switchedTransmissiondelay:R=linkbandwidth(bps)L=packetlength(bits)timetosendbitsintolink=

Propagationd=lengthofphysicals=propagationspeedinmedium(~2x108propagationdelay=A

Note:Note:sandRareverydifferentB Chapter SwitchTechnologyNodalttnodaltproctqueuettranstproptproc=processingtypicallyafewmicrosecsortqueue=queuingdelaydependsoncongestionttrans=transmission=L/R,significantforlow-speedtprop=propagationafewmicrosecstohundredsofChapter SwitchTechnologyQueueingdelayR=linkbandwidth(bps)L=packetlength(bits)a=averagepacketarrivalratetrafficintensity=La/R~0:averagequeueingdelaysmallLa/R->1:delayseChapter SwitchTechnologyPacketswitchingversuscircuit1Mbitlinkeachuser:100Kbpswhenactive10%of10packet

N

1Mbps with35users,probability>10%activelessthan.004Chapter SwitchTechnologyPacketswitchingversuscircuitswitchingpacketswitching:(numberofusers-error16-17-18-19-20-21-22-23-24-25-26-27-28-29-30-31-32-33-34-35-36-37-38-39-40-41-42-43-44-45-46-47-48-49-50-51-52-53-54-55-56-57-58-59-60-61-62-63-64-65-66-67-68-69-70-Chapter SwitchTechnologyPacketswitchingversuscircuitGreatforburstyresourcecongestion:packetdelayandprotocolsneededforreliabledatatransfer,congestionQ:Howtoprovidecircuit-likebandwidthguaranteesneededfor Chapter SwitchTechnology分组交换提供两种不同形式的服务分组交换提供两种不同形式的服务DG(Datagram数据报)是重复或失序，它提供“尽VCVirtualCircuit虚电路)DG(Datagram数据报)是重复或失序，它提供“尽Chapter SwitchTechnologyVirtual“source-to-destpathbehavesmuch ephoneperformance-networkactionsalongsource-to-destcallsetupforeachcallbeforedatacanflow,andteardowneachpacketcarriesVCidentifier(notdestinationhosteveryrouteronsource-destpathmaintains“state”foreachpassingtransport-layerconnectiononlyinvolvedtwoendlink,routerresources(bandwidth,buffers)maybeallocatedtotogetcircuit-likeChapter SwitchTechnologyVirtualcircuits:signalingusedtosetup,maintainteardownusedinATM,frame-relay,notusedintoday’sapplication5.Dataflow 6.Receivedata4.Call

3.Accept datalink

Initiate 2.ing

datalinkChapter SwitchTechnology3.3.2Datagramnetworks:theInternetnocallsetupatnetworkrouters:nostateaboutend-to-endpacketsforwardedusingdestinationhostdatalink

1.Send 2.Receive

datalinkChapter SwitchTechnologyDatagramorVCnetwork:dataexchangeamong“elastic”service,nostricttiming“smart”endsystemscanadapt,performcontrol,errorsimpleinsidenetwork,complexityat“edge”manylinkdifferentuniformservice

evolvedfrom humanconversation:needforguaranteed“dumb”endcomplexityinsideChapter SwitchTechnologyVirtualCircuitPK.Datagram分组头：DG方式的每个分组头中要包含详细的目的地选路DG方式则不需要有建立过程，但对每个分组都要独立地进行选路分组顺序： 失序Chapter SwitchTechnologyVirtualCircuitPK.Datagram（有些分组网具有再连接功能，出现故障时可自动建立新并做到不丢失用户数据可靠性较高。DG方式则适用于面向事务的询向／响应型数Chapter SwitchTechnologyDelay采用 转发方式的分组交换兼有电路交换和报文交换的优点，交换的不同在于：（packet），每个分组中有一个分组头，含有可供选路的信息和其他控制信息。Chapter SwitchTechnologyTiminginThe Chapter SwitchTechnologyTiminginCircuit Numberofhops=Per-hopprocessingdelay=PLinkpropagationdelay=LMessagesize=BbitsTotalDelay=total+total+total=4ML+B/W+(M-

Chapter SwitchTechnologyTiminginDatagramPacketPTPTPTLNumberofhops=Per-hopprocessingdelay=PLinkpropagationdelay=LPackettransmissiondelay=TMessagesize=NpacketsTotalDelay=total+total++total+total=ML+NT+(M-1)T+(M-Chapter SwitchTechnologyTiminginVirt.Circ.PacketPNumberofhops=Per-hopprocessingdelay=PLinkpropagationdelay=LPackettransmissiondelay=TMessagesize=N TTotalDelay=total +total +total+total=4ML+NT+(M-1)T+4(M- Chapter SwitchTechnologyWeareofteninterestedonlyinthedelayelapsedfromthetimethefirstbitwassentbythesendertothetimethelastbitwasreceivedbythereceiver(i.e.,weexcludethetimeinvolvedinacknowledgingconnectiontermination).Ifthisisthecase,thedelaywillbegivenasfollows:CircuitDelay=3ML+B/W+(M-DatagrampacketDelay=ML+NT+(M-1)T+(M-1)P(sameasVirtualcircuitpacketDelay=3ML+NT+(M-1)T+3(M-Chapter SwitchTechnologySolvedQ1:AandBare4hopsapartonadatagrampacket-switchednetworkwhereeachlinkislong.Per-hopprocessingdelayiss.Packetsare1500byteslong.Alllinkshavetransmissionspeedof56kbit/s.Thespeedoflightinthewireis y/s.IfBsendsa10-packetmessagetoA,howlongwillittakeAtoreceivethemessageuptothelastbit(measuredfromthetimeBstartssending)?Answer:WeknowtheNumberofhopsNumberofpacketsPer-hopprocessingdelayLinkpropagationdelayL=distance/speedoflight=100/125,000=Packetsize=1500bytes=1500*8=12,000PackettransmissiondelayT=packetsize/transmissionspeed=12,000/56000=0.214s.Delay=ML+NT+(M-1)T+(M-1)P=0.0032+2.14+0.642+0.000015=2.785s.NotethatthetotaldelayisdominatedbythetransmissiondelaywhichdependsonlinkAlinkwithahighertransmissionspeedcanreducethedelayChapter SolvedQ2:Allisthesame,exceptthatlinktransmissionspeednowis1Gbit/s.HowlongwillittakeAreceivethemessageuptothelastbit(measuredfromthetimeBstartsAnswer:Asbefore,weknowtheNumberofhopsNumberofpacketsPer-hopprocessingdelayLinkpropagationdelayL=distance/speedoflight=100/125,000=Packetsize=1500bytes=1500*8=12,000PackettransmissiondelayT=packetsize/transmissionspeed=12,000/109Delay=ML+NT+(M-1)T+(M-1)P=3200+120+36+15=3371s=Notethatthetotaldelayisnowdominatedbythepropagationdelaywhichcannotbeimprovedbecauseitisconstrainedbythespeedoflight.Hence,itisunlikelythatfuture willsignificantlyreducethedelayofB’smessageatthispoint(unlesswebreakthespeedoflight)!Chapter SwitchTechnologySolvedQ3:RepeatQ1andQ2,assumingthatthenetworkusescircuitswitchinginsteadofdatagrampacketswitching.B’smessageisthesamelengthasbefore.Answer:Q1NumberofhopsMessagesizeB=10*1500*8=120,000bits(itisnotLinktransmissionspeedW=Per-hopprocessingdelayLinkpropagationdelayL=distance/speedoflight=100/125,000=0.0008s,Delay=3ML+B/W+(M-1)P=0.0096+2.14+0.000015=2.1496sNotethatthedelayimprovedoverthecaseofdatagrampacketswitchingforthesamelinkspeed.Why?StoreandforwarddelayiseliminatedandpropagationdelayisQ2:LetlinktransmissionspeedbeW=Delay=3ML+B/W+(M-1)P=9600+120+15=9735s=Notethatthedelayisworsethaninth