[e2e] TCP ACK HeuristicII

F. Bouy frasker at hotmail.com
Wed Aug 2 03:34:30 PDT 2006


I implemented a downscaled TCP NewReno with ACK heuristic based on RFC 3782. 
I notice that a timeout very likely triggers subsequent timeouts. Upon 
debugging the code, I notice ACK heuristic successfully avoid re-entering 
fast-retransmit (the three duplicates are due to unnecessary retransmission 
of three packets), but packets in flight quickly drain out because the code 
handling the duplicate ACK does not inject new packets into the network. 
Consequently, a timeout occurs.

Although it is common sense that one should inflate cwnd by three MSS 
whenever ACK heuristic determines that it was an unnecessary 
retransmissions, RFC 3782 does not state about the cwnd apart from "what not 
to do".

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