2.1 transport - Transport Layer Dr Shengquan Wang Some...

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Transport Layer Dr. Shengquan Wang Some slides are modified from Computer Networking: A Top Down Approach, 6 th edition. Jim Kurose, Keith Ross. Addison-Wesley, March 2012.
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Outline Transport-layer services 2
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Transport-layer services Abstraction for application layer such as reliability Logical communication between two networking apps send side: breaks app messages into segments, passes to network layer rcv side: reassembles segments into messages, passes to app layer 3 applicatio n transport network data link physical applicatio n transport network data link physical logical end -en d t ra nsport
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Transport-layer protocols unreliable, unordered delivery: UDP no-frills extension of “best-effort” IP reliable, in-order delivery (TCP) connection setup flow control congestion control services not available: delay guarantees bandwidth guarantees applicatio n transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical applicatio n transport network data link physical logical end -en d tra nsport 4
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Packet encapsulation 5 UDP/TCP Header A chunk of application message <----------------- segment ----------------->
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Outline Transport-layer services Transition between application layer and transport layer 6
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Multiplexing/demultiplexing Multiplexing For the source host, the transport layer encapsulates data from each application, then pass them to the network layer Demultiplexing For the destination host, the transport layer receives segments from the network layer below, then delivers it to its corresponding application 7
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Illustration process socket use header info to deliver received segments to correct socket demultiplexing at receiver: transport application physical link network P2 P1 transport application physical link network P4 transport application physical link network P3 8 handle data from multiple sockets, add transport header (later used for demultiplexing) multiplexing at sender:
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How 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 demultiplexing host uses IP addresses & port numbers to direct segment to appropriate socket source port # dest port # 32 bits application data (message) other header fields TCP/UDP segment format 9
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Demultiplexing: UDP Create sockets with port numbers: DatagramSocket mySocket1 = new DatagramSocket(5775); DatagramSocket mySocket2 = new DatagramSocket(9157); 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 socket 10
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  • Winter '09
  • Computer Networks, Transmission Control Protocol, Internet Protocol Suite, User Datagram Protocol

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