1 Computer Communications - CSCI 551 Copyright © William C. ChengCS551Reliable MulticastBill Chenghttp://merlot.usc.edu/cs551-f12Wait for ACKs from all receivers, re-send on timeout orselective ACK2Sender Reliable Error Detection Computer Communications - CSCI 551 Copyright © William C. Chengeasy resource managementwait for ACKreceiver state in sender, not scalable(+)(-)(-)ACK implosion(-)no state at sender - good for multicastReceivers NACKs lost packets3Receiver Reliable Error Detection Computer Communications - CSCI 551 Copyright © William C. Chengdoes not provide 100% reliabilityNACK implosion(+)(-)(-)4Implosion Computer Communications - CSCI 551 Copyright © William C. ChengSrc5Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc6Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc7Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc8Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc9Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc10Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc11Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc12Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc13Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc14Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc15Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc16Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc17Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc18Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc19Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc20Implosion (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrcsenderRe-transmitter21Retransmission Computer Communications - CSCI 551 Copyright © William C. Chengunicast, multicast, scoped multicast, retransmission group,etc.How to retransmit?receiverexposureProblem with sender retransmissions22Exposure Computer Communications - CSCI 551 Copyright © William C. ChengSrc23Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc24Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc25Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc26Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc27Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc28Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc29Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc30Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc31Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc32Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc33Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc34Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc35Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc36Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc37Exposure (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrcbuffer packetsRouters do transport level processing38Aside - Using the Routers Computer Communications - CSCI 551 Copyright © William C. Chengfuse ACKssend retransmissionsthis solves implosion and exposure problems, but:not scalableviolate end-to-end argument39 Computer Communications - CSCI 551 Copyright © William C. Cheng CS551Scalable ReliableMulticast[Floyd97c]Bill Chenghttp://merlot.usc.edu/cs551-f12NACK-basedOriginally designed for wb40SRM (Scalable Reliable Multicast) Computer Communications - CSCI 551 Copyright © William C. ChengReceiver reliableEvery member may multicast NACK or retransmissionNo assistance from routershow?All transmissions go to everyoneReceivers notice lossesLosses result in repair requests (to everyone)Repair requests produce repairs (to everyone)Requests and repairs are spaced and avoidedvia randomization and suppressionif there is a missing sequence number fromsubsequence datause session messages to deal with loss of last packet41SRM Retransmission Computer Communications - CSCI 551 Copyright © William C. Cheng42SRM Request Suppression Computer Communications - CSCI 551 Copyright © William C. ChengSrc43SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc44SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc45SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc46SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc47SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrcWhen noticing skipped sequence number:start a timer whose timeout is proportional to distance from Src48SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrcWhen noticing skipped sequence number:start a timer whose timeout is proportional to distance from Src49SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrcWhen noticing skipped sequence number:start a timer whose timeout is proportional to distance from Src50SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc51SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc52SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc53SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrc54SRM Request Suppression (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengSrcdelay before sendingNACK/Retransmission suppression55SRM
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