lecture_10_TCP - CS536DataCommunica0ons andComputerNetworks...

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CS 536 Data Communica0ons and Computer Networks Lecture 10: TCP 10/02/2008 CS 536 Computer Networks 1
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Recap from last lecture Segment structure MSS Header data Estimating RTT SampleRTT is computed as the time between a packet sent and when its ack is received Use EWMA for smoothing RTT estimation EstimatedRTT = 0.875 *EstimatedRTT + 0.125 *SampleRTT Setting TCP timeouts Using a combination of SampleRTT and DevRTT TimeoutInterval = EstimatedRTT + 4*DevRTT CS 536 Computer Networks 2
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CS 536 Computer Networks Chapter 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 control 3
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CS 536 Computer Networks TCP reliable data transfer TCP creates rdt service on top of IP’s unreliable service Pipelined segments Cumulative acks TCP uses single retransmission timer Retransmissions are triggered by: timeout events duplicate acks Initially consider simplified TCP sender: ignore duplicate acks ignore flow control, congestion control 4
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CS 536 Computer Networks TCP sender events: data rcvd from app: Create segment with seq # seq # is byte-stream number of first data byte in segment start timer if not already running (think of timer as for oldest unacked segment) expiration interval: TimeOutInterval timeout: retransmit segment that caused timeout restart timer Ack rcvd: If acknowledges previously unacked segments update what is known to be acked start timer if there are outstanding segments 5
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CS 536 Computer Networks TCP sender (simplifed) NextSeqNum = InitialSeqNum SendBase = InitialSeqNum loop (forever) { switch(event) event: data received from application above create TCP segment with sequence number NextSeqNum if (timer currently not running)
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This note was uploaded on 10/24/2009 for the course CS 536 taught by Professor Sonia,f during the Spring '08 term at Purdue University-West Lafayette.

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lecture_10_TCP - CS536DataCommunica0ons andComputerNetworks...

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