Blackboard

Segments and sequence numbers

The same two segments may be combined for retransmission:

Acknowledgement and, if needed, Retransmission

Computing the value of the retransmission timer

Details of the Estimated RTT computation

Initial Sender Sequence number (ISS) and Initial Receiver Sequence number (IRS)

A sample TCP header

Most of these values aren't terribly meaningful in isolation -- they make sense relative to the connection status.

3-Way Handshake

Also, the less common "simultaneous open".

SYN and FIN and how they fit into the sequence number space

TCP close