lecture14 - Alan Mislove amislove at ccs.neu.edu...

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Unformatted text preview: Alan Mislove amislove at ccs.neu.edu Northeastern University 1 CS4700/CS5700 Fundamentals of Computer Networks Lecture 14: TCP Slides used with permissions from Edward W. Knightly, T. S. Eugene Ng, Ion Stoica, Hui Zhang Alan Mislove amislove at ccs.neu.edu Northeastern University 2 What Layers are Needed in a Basic Telephone Network? Supports a single application: Telephone An end host is a telephone Each telephone makes only one voice stream Even with call-waiting and 3-way calling Application Layer Network Layer (Data) Link Layer Telephone Telephone numbering, signaling, routing TDMA Alan Mislove amislove at ccs.neu.edu Northeastern University 3 Is this Enough for a Datagram Computer Network? Supports many applications Each end host is usually a general purpose computer Each end host can be generating many data streams simultaneously In theory, each data stream can be identified as a different Protocol in the IP header for demultiplexing At most 256 streams Insert Transport Layer to create an interface for different applications Provide (de)multiplexing Provide value-added functions Application Layer Transport Layer Network Layer (Data) Link Layer telnet, ftp, email TCP, UDP IP 802.3, 802.11 Alan Mislove amislove at ccs.neu.edu Northeastern University 4 E.g. Using Transport Layer Port Number to (De) multiplex traffic IP TCP Transport A B C p1 p2 p1 p2 p3 p1 p2 ports Application HTTP ssh telnet In TCP, a data stream is identified by a set of numbers: (Source Address, Destination Address, Source Port, Destination Port) Alan Mislove amislove at ccs.neu.edu Northeastern University 5 Transport Layer in Internet Purpose 1: (De)multiplexing of data streams to different application processes Purpose 2: Provide value-added services that many applications want Recall network layer in Internet provides a Best-effort service only, transport layer can add value to that Application may want reliability, etc No need to reinvent the wheel each time you write a new application Alan Mislove amislove at ccs.neu.edu Northeastern University 6 Transport Protocols Concern only End Hosts, not Routers Lowest level end-to-end protocol. Header generated by sender is interpreted only by the destination Routers view transport header as part of the payload Adds functionality to the best-effort packet delivery IP service. Make up for the shortcomings of the core network 5 5 Transport IP Datalink Physical Transport IP Datalink Physical IP router 2 2 1 1 Alan Mislove amislove at ccs.neu.edu Northeastern University 7 (Possible) Transport Protocol Functions Alan Mislove amislove at ccs.neu.edu Northeastern University 7 (Possible) Transport Protocol Functions Multiplexing/demultiplexing for multiple applications....
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lecture14 - Alan Mislove amislove at ccs.neu.edu...

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