ICS 156: Networking Lab

4.3.2 Sequence Numbers and ACKs

nTCP is connection oriented - uses sequence numbers (always increasing, numbers not consecutive, reflect the number of bytes not segments!). For example: if TCP wants to send 2000 bytes and sends them in two segments of 1000 bytes each, if first segment has sequence no 102, then sequence number of second segment will be 102+1000= 1102.

nThe ACKs on the other hand reflect the sequence number of the next byte that the receiver is expecting. If the receiver received segment with sequence number 102 of length 1000, then ACK will use number: 102+ 1000 = 1102.