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TCP: Transmission Control Protocol Overview Connection set-up and termination Interactive Bulk transfer Timers Improvements.

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Presentation on theme: "TCP: Transmission Control Protocol Overview Connection set-up and termination Interactive Bulk transfer Timers Improvements."— Presentation transcript:

1 TCP: Transmission Control Protocol Overview Connection set-up and termination Interactive Bulk transfer Timers Improvements

2 TCP: Overview Connection oriented, byte stream service Full or half duplex service Reliability (ARQ) – Sliding window with variable sized window – Stream is sent in segments (IP datagrams) – SN for bytes – Receiver buffer reorders bytes – Checksum on header and data – Discards duplicate data – Flow control

3 TCP: Overview IP HeaderTCP HeaderTCP Data TCP segment Source port #Destination port # Sequence # Acknowledgement # HLreservflagsWindow size ChecksumUrgent pointer Options if any =65495

4 TCP: Flags URG: The urgent pointer is used ACK: The acknowledgement number is valid PSH: The receiver should pass this data to the application as soon as possible RST: Reset the connection SYN: Synchronize sequence numbers to initiate a connection. FIN: The sender is finished sending data

5 TCP: Set-Up Syn=1 Ack = 0 A:SYN, MSS, SN=ISN B: SYN, MSS, SN=ISN Syn1 ack 1 B: ACK A: ACK AB Full duplex

6 TCP: Termination A:FIN B: ack of FIN B: FIN A: ack of FIN AB Both sides close

7 TCP windows sent and acked sent but not acked can send asap min{offered window from receiver, cwnd} usable window Actually,

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12 Transmission window: cwnd 1 cwnd 1 ack ack2 ack Doubling every RT!

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19 TCP Timeout and Retransmission Each packet has a retransmission timer It is initialized by the retransmission time out (RTO) value When the timer expires, a time out occurs and the data is retransmitted If a retransmission fails then the time-out doubles i.e., exponential backoff. It’s important to find a good RTO value

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34 TCP Slow start: cwnd =1 cwnd exponentially increasing Congestion avoidance: cwnd reaches ssthresh, cwnd linearly increasing

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42 TCP: Tahoe and Reno Tahoe: slow start + congestion avoidance Reno: fast retransmit + fast recovery


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