tcp_ack()

The tcp_ack() function is called whenever a segment with an ACK arrives.

The first small change is after the ACK is deemed to be valid. Since we no longer have to send our SYN, we can switch off the TF_SENDSYN flag.

Two state additions are required.

In the check for the state LAST_ACK, the check for LAST_ACK* is also required.

In the check for SYN_RECV, the check for ESTABLISHED* is also made. In this situation, we are receiving the final ack of a 3-Way Handshake and can move into the ESTABLISHED state. A number of changes are made for T/TCP processing:

• The cached CC value is updated on the completion of the three way handshake.
• The acked_seq variable is increased by the size of data in the segment.
• Since at least the initial SYN has been acked, switch off the SYN bit of the segment in the retransmission queue in case the segment needs to be retransmitted (the SYN doesn't need to be resent)

Appendix A.2.5 contains the code modifications to this function.