Transcription of Mobile Communications Chapter 9: Mobile Transport Layer
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Mobile Communications Chapter 9: Mobile Transport Layer
Prof. Jochen Schiller, Communications Chapter 9: Mobile Transport LayerqMotivationqTCP-mechanismsqClassica l approachesqIndirect TCPqSnooping TCPqMobile TCPqPEPsin generalqAdditional optimizationsqFast retransmit/recoveryqTransmission freezingqSelective retransmissionqTransaction oriented TCPqTCP for wirelessProf. Jochen Schiller, HTTP (used by web services) typically uses TCPqReliable Transport between client and server requiredTCPqSteam oriented, not transaction orientedqNetwork friendly: time-out congestion slow down transmissionWell known TCP wrongly assumes congestion in wireless and Mobile networks whenqPacket lossesdue to transmission errorsqPacket loss due to change of networkResultqSevere performancedegradationClientServerConnec tionsetupDatatransmissionConnectionrelea seTCP SYNTCP SYN/ACKTCP ACKHTTP requestHTTP responseGPRS: 500ms!>15 sno dataProf. Jochen Schiller, ITransport protocols typically designed forqFixed end-systemsqFixed, wired networksResearch activitiesqHow to improve TCP performance in wireless networksqMaintain congestion control behaviorqEfficient retransmissionsTCP congestion control in fixed networksqTimeouts/Packet loss typically due to (temporary) overloadqRouters discard packets when buffers are full qTCP recognizes congestion only indirectly via missing ACKs, retransmissions unwise, since they
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS05 9.6 Early approach: Indirect TCP I Indirect TCP or I-TCP segments the connection
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