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U of I CS 438 - Transport Layer

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Transport LayerChapter 3: Transport LayerChapter 3 outlineTransport services and protocolsTransport vs. network layerInternet transport-layer protocolsSlide 7Multiplexing/demultiplexingHow demultiplexing worksConnectionless demultiplexingConnectionless demux (cont)Connection-oriented demuxConnection-oriented demux (cont)Connection-oriented demux: Threaded Web ServerSlide 15UDP: User Datagram Protocol [RFC 768]UDP: moreUDP checksumSlide 19Principles of Reliable data transferSlide 21Slide 22Reliable data transfer: getting startedSlide 24Rdt1.0: reliable transfer over a reliable channelRdt2.0: channel with bit errorsrdt2.0: FSM specificationrdt2.0: operation with no errorsrdt2.0: error scenariordt2.0 has a fatal flaw!rdt2.1: sender, handles garbled ACK/NAKsrdt2.1: receiver, handles garbled ACK/NAKsrdt2.1: discussionrdt2.2: a NAK-free protocolrdt2.2: sender, receiver fragmentsrdt3.0: channels with errors and lossrdt3.0 senderrdt3.0 in actionSlide 39Performance of rdt3.0rdt3.0: stop-and-wait operationPipelined protocolsPipelining: increased utilizationGo-Back-NGBN: sender extended FSMGBN: receiver extended FSMGBN in actionSelective RepeatSelective repeat: sender, receiver windowsSelective repeatSelective repeat in actionSelective repeat: dilemmaSlide 53TCP: Overview RFCs: 793, 1122, 1323, 2018, 2581TCP segment structureTCP seq. #’s and ACKsTCP Round Trip Time and TimeoutSlide 581Transport Layer2Chapter 3: Transport LayerOur goals: understand principles behind transport layer services:multiplexing/ demultiplexingreliable data transferflow controlcongestion controllearn about transport layer protocols in the Internet:UDP: connectionless transportTCP: connection-oriented transportTCP congestion control3Chapter 3 outline3.1 Transport-layer services3.2 Multiplexing and demultiplexing3.3 Connectionless transport: UDP3.4 Principles of reliable data transfer3.5 Connection-oriented transport: TCPsegment structurereliable data transferflow controlconnection management3.6 Principles of congestion control3.7 TCP congestion control4Transport services and protocolsprovide logical communication between app processes running on different hoststransport protocols run in end systems send side: breaks app messages into segments, passes to network layerrcv side: reassembles segments into messages, passes to app layermore than one transport protocol available to appsInternet: TCP and UDPapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicallogical end-end transport5Transport vs. network layernetwork layer: logical communication between hoststransport layer: logical communication between processes relies on, enhances, network layer servicesHousehold analogy:sending lettersprocesses = peopleapp messages = letters in envelopeshosts = housestransport protocol = sorting and collecting mail within housenetwork-layer protocol = postal service6Internet transport-layer protocolsreliable, in-order delivery (TCP)congestion control flow controlconnection setupunreliable, unordered delivery: UDPno-frills extension of “best-effort” IPservices not available: delay guaranteesbandwidth guaranteesapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicallogical end-end transport7Chapter 3 outline3.1 Transport-layer services3.2 Multiplexing and demultiplexing3.3 Connectionless transport: UDP3.4 Principles of reliable data transfer3.5 Connection-oriented transport: TCPsegment structurereliable data transferflow controlconnection management3.6 Principles of congestion control3.7 TCP congestion control8Multiplexing/demultiplexingapplicationtransportnetworklinkphysicalP1applicationtransportnetworklinkphysicalapplicationtransportnetworklinkphysicalP2P3P4P1host 1host 2host 3= process= socketdelivering received segmentsto correct socketDemultiplexing at rcv host:gathering data from multiplesockets, enveloping data with header (later used for demultiplexing)Multiplexing at send host:9How demultiplexing workshost receives IP datagramseach datagram has source IP address, destination IP addresseach datagram carries 1 transport-layer segmenteach segment has source, destination port number host uses IP addresses & port numbers to direct segment to appropriate socketsource port # dest port #32 bitsapplicationdata (message)other header fieldsTCP/UDP segment format10Connectionless demultiplexingCreate sockets with port numbers:sin1.sin_port = 1234;bind(socket1, &sin1, …);sin2.sin_port = 1235;bind(socket2, &sin2, …);UDP socket identified by two-tuple:(dest IP address, dest port number)When host receives UDP segment:checks destination port number in segmentdirects UDP segment to socket with that port numberIP datagrams with different source IP addresses and/or source port numbers directed to same socket11Connectionless demux (cont)sin.sin_port = 6428; bind(sock, &sin, …);ClientIP:BP2client IP: AP1P1P3serverIP: CSP: 6428DP: 9157SP: 9157DP: 6428SP: 6428DP: 5775SP: 5775DP: 6428SP provides “return address”(returned by recvfrom)12Connection-oriented demuxTCP socket identified by 4-tuple: source IP addresssource port numberdest IP addressdest port numberrecv host uses all four values to direct segment to appropriate socketServer host may support many simultaneous TCP sockets:each socket identified by its own 4-tupleWeb servers have different sockets for each connecting clientnon-persistent HTTP will have different socket for each request13Connection-oriented demux (cont)ClientIP:BP1client IP: AP1P2P4serverIP: CSP: 9157DP: 80SP: 9157DP: 80P5P6P3D-IP:CS-IP: AD-IP:CS-IP: BSP: 5775DP: 80D-IP:CS-IP: B14Connection-oriented demux: Threaded Web ServerClientIP:BP1client IP: AP1P2serverIP: CSP: 9157DP: 80SP: 9157DP: 80P4P3D-IP:CS-IP: AD-IP:CS-IP: BSP: 5775DP: 80D-IP:CS-IP: B15Chapter 3 outline3.1 Transport-layer services3.2 Multiplexing and demultiplexing3.3 Connectionless transport: UDP3.4 Principles of reliable data transfer3.5 Connection-oriented transport: TCPsegment structurereliable data


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U of I CS 438 - Transport Layer

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