 TCP connection set up  TCP connection tear-down  Sliding window revisited  Triggering transmission

2 TCP Header Destination Port NumberSource Port Number Sequence Number Urgent Pointer Acknowledgement Number Header Length ReservedWindow Size TCP Checksum URGURG ACKACK PSHPSH RSTRST SYNSYN FINFIN

3 TCP Connection Setup: 3-way Handshake ClientServer SYN, seq=client_isn SYN+ACK, seq=server_isn, ack=client_isn + 1 ACK, seq=client_isn + 1, ack=server_isn + 1

4 TCP Connection Setup: 3-way Handshake ClientServer SYN, seq=old_client_isn SYN+ACK, seq=server_isn, ack=old_client_isn + 1 RST wrong client_isn!!!

5 Initial Sequence Number?

6 TCP Connection Tear-Down (I) ClientServer FIN ACK FIN timeout closed

7 TCP Connection Tear-Down (II) ClientServer FIN ACK FIN timeout closed

8 TCP Connection Tear-Down (III) ClientServer FIN ACK FIN timeout closed timeout closed

9 Sliding Window Revisited  Sliding Window Size  not fixed, but varying over time  receiver advertises it

10 TCP Send Buffer TCP Sending Application LastByteAcked LastByteSent LastByteWritten

11 TCP Recever Buffer TCP Receiving Application LastByteRcvd NextByteExpected LastByteRead

12 Flow Control  What is the amount of buffer a TCP receiver must keep? LastByteRcvd – LastByteRead <= MaxRcvBuffer  What is the amount of advertized window size? MaxRcvBuffer – ((NextByteExpected-1) – LastByteRead)

13 TCP Recever Buffer TCP Receiving Application LastByteRcvd NextByteExpected LastByteRead MaxRcvBuffer Advertized

14 On the TCP Sender side  Do not overflow the receiver. How? LastByteSent – LastByteAcked <= Advertized  At any moment a TCP sender can only send: Advertized – (LastByteSent – LastByteAcked)

15 When the sender sent too fast  Receiver advertizes window size = 0!  Sender cannot send any  What would you do?  Sender keeps sending 1-byte segment  Who works more in this case?

16 TCP Recever Buffer TCP Receiving Application LastByteRcvd NextByteExpected LastByteRead MaxRcvBuffer

17 Keeping the pipe full  Time until 32-bit number space wraps around  1.5 Mbps – 6.4 hr  100 Mbps – 13 min  1.2 Gbps – 28 sec  Window size for 100 ms RTT  1.5 Mbps – 18 KB  100 Mbps – 1.2 MB  1.2 Gbps – 14.8 MB