Sequence and Acknowledgements

Sequence numbers indicate the most recent piece of data sent.

Acknowledgement numbers indicate the next byte expected.

During the initial handshake:

• Host A randomly generates a sequence number.
• Host B will acknowledge A's seq number, and generate a randomseqno of it's own.
• Host A will acknowledge B's seq number and the connection is established.

With NO DATA transmitted (e.g. keep alive packet, or a one-sided series of transactions):

• A sender that is simply ACKing and not sending data of it's own, will re-use the same Sequence Number.
• Sequence Numbers may be re-acked until other side actually sends some data.

During normal data transmission:

• Sequence numbers mark the beginning of most recent data sent. It starts at the random number chosen during the handshake and is cumulative.
• Acknowledgement numbers =seqnumber + datarecv'd since last ACK + 1.

Errors will result in the Acknowledgement number being set to the last successfully received CONTIGUOUS block of data + 1.

• A sends 10 data, with as eq of 1, but B only receives 1-7, the Ack number will be 8.
• A sends 10 data, with as eq of 1, but B only receives 1 and 4-10, the Ack number will be 2.