>Basically, assuming nothing is lost, the receipt
>of an acknowledgement with sequence number
>0 "frees up" that sequence number allowing the
>sender to reuse it for the next unsent packet.
>
>Tom

Alright. When are serial numbers assigned? Are they assigned when the packets are created, so that the sequence would be:
A0
B1
C0
D1...

Or, are they assigned just before the packet is sent out, allowing for network problems? So this would be possible given the right network conditions?:
A0
B1
C1

Only the sequence

A0
B1
C0
D1

is possible. You can look at this as meaning that the sequence numbers are assigned as packets are created.

Tom