jbn@wdl1.UUCP (08/05/85)
This looks sound by my copy of MIL-STD-1778. The TCP concept here is that when A is in a synchronized state and gets a segment outside the window, it sends a current ACK (i.e. a duplicate of A's last ACK). See table XII, row 1, noting that in some copies of MIL-STD-1778 tables XII and XIV were switched; the proper XII is the longer one. This provides B with current sequence information. So, if B is in SYN SENT state, and gets an ACK that is not the one expected, because it's talking to a half-dead connection at A, it sends an RST, per table VIII, row 8. Receipt of this RST by A will kill the connection at A. B will then retransmit its SYN, which will now establish a new connection. This is the famous ``three way handshake'' in action. John Nagle Ford Aerospace and Communications Corp.