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 65535-20-20=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 1 2 3 4 5 6 7 8 9 10 11 sent and acked sent but not acked can send asap min{offered window from receiver, cwnd} usable window Actually,

12. Transmission window: cwnd 1 cwnd 1 ack1 2 2323 ack2 ack3 4 45674567 Doubling every RT!

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

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

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