[e2e] Some questions about TCP.

John Kristoff jtk at depaul.edu
Wed Nov 25 08:17:58 PST 2009

On Tue, Nov 24, 2009 at 07:08:04PM -0500, Noel Chiappa wrote:
> If you are seeing multiple ack-only TCP packets for the same segment, and
> those aren't due to a lost packet causing a hole, then either i) you
> retransmitted that segment several times, and either the original data
> segments, or the acks, all got wildly delayed (so long that you timed out and
> retransmitted it several times _before_ either a) the first segment got to
> the far end, or b) the first ack got back to you), or ii) it got duplicated
> somehow in the network.

There is also the TCP keep-alive mechanism, which I believe may result
in this type of behavior too, though I'm not familiar with implementation
details or the scale of its deployment.


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