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Transport Layer3-1Chapter 3Transport LayerComputer Networking: A Top Down Approach 4thedition. Jim Kurose, Keith RossAddison-Wesley, July 2007. A note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.Thanks and enjoy! JFK/KWRAll material copyright 1996-2007J.F Kurose and K.W. Ross, All Rights ReservedTransport Layer3-2Chapter 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 controlTransport Layer3-3Transport services and protocols providelogical communicationbetween app processes running on different hosts As if hosts running the processes were directly connected 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 linkphysicalTransport Layer3-4Transport vs. Network layertransport layer logical communication between processes relies on, enhances, network layer servicesnetwork layer logical communication between hostsApplication LayerTransport LayerNetwork LayerData Link LayerPhysicalTransport Layer Protocols User Datagram Protocol (UDP) Unreliable Connectionless Transmission Control Protocol (TCP) Reliable Connection-orientedTransport Layer3-5Transport Layer3-6Internet transport-layer protocolsapplicationtransportnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalapplicationtransportnetworkdata linkphysicalFeatureIPUDPTCPIn-order DeliveryNoNoYesReliableNoNoYesError-checkingYesYesYesError-recoveryNoNoYesCongestion ControlNoNoYesFlow ControlNoNoYesConnection Set-upNoNoYesDelay GuaranteesNoNoNoBandwidth GuaranteesNoNoNoSecurityNoNoNoTransport Layer3-7Chapter 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 controlMultiplexing/demultiplexing Extends the host-to-host delivery service provided by the network layer to a process to process delivery service for applications running on the host. Socket The application programming interface between the application and the network One or more sockets can use the same portTransport Layer3-8Transport Layer3-9Multiplexing/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:Process Identification Sockets have unique identifiers which include port numbers and source IP addresses Range from 0 – 65535 Use of 0-1023 is restricted to well-known applications Each transport layer segment has a source port number field and a destination port number field Why don‟t transport layer segments have one or more IP address fields?Transport Layer3-10Transport Layer3-11How demultiplexing works host receives IP datagrams each packet has source IP address, destination IP address each packet 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 fieldsUDP segment formatTransport Layer3-12Connectionless demultiplexing (UDP) Create sockets with port numbers:DatagramSocket mySocket1 = new DatagramSocket(12534);DatagramSocket mySocket2 = new DatagramSocket(12535); UDP socket identified by two-tuple:(dest IP address, dest port number)DatagramPacket packet = new DatagramPacket( buf, BUF_SIZE, address, port );socket.send( packet ); IP datagrams with different source IP addresses and/or source port numbers directed to same socketConnectionless demultiplexing (UDP) When host receives UDP segment: checks destination port number in segment directs UDP segment to socket with that port numberDatagramPacket request=new DatagramPacket( new byte[1024],1024);socket.receive( request );Transport Layer3-13Transport Layer3-14Connectionless demux (cont)DatagramSocket serverSocket = new DatagramSocket(6428);ClientIP:BP2clientIP: AP1P1P3serverIP: CSP: 6428DP: 9157SP: 9157DP: 6428SP: 6428DP: 5775SP: 5775DP: 6428SP provides “return address”Transport Layer3-15Connection-oriented demux (TCP) 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-tupleTransport Layer3-16Connection-oriented demux (TCP)ClientIP:BP1clientIP: AP1P2P4serverIP: CSP: 9157DP: 80SP: 9157DP: 80P5P6P3D-IP:CS-IP: AD-IP:CS-IP: BSP: 5775DP: 80D-IP:CS-IP: BTwo different applications accessing the serverOne application accessing the serverSeparate process for each requestThreaded Web ServerTransport Layer3-17•Web servers have different sockets for each connecting client
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