[e2e] Stupid Question: Why are missing ACKs not considered as indicator for congestion?

Michael Welzl michael.welzl at uibk.ac.at
Wed Jan 31 23:14:15 PST 2007

> >On 31/01/07, Lloyd Wood <L.Wood at surrey.ac.uk> wrote:
> >>It's possible for the sender to infer that an ack has been lost, based on subsequent receiver behaviour in sending a cumulative ack including packets received that the sender didn't get individual acks for.
> >
> >No, that was my point.  We can't distinguish between ACKs which are
> >lost and those which are never sent in the first place.
> Yes, we can. If a SACK block is present, it tells you which datagrams were and weren't received.
> If a datagram was received, an ack was sent (modulo the delack mechanism), and the datagram will not be called out in the SACK block.
> If the datagram wasn't received, this will be reflected in the SACK block.
> >Also, having a unique identifier (like a timestamp) isn't the same as
> >having sequence numbers which can say "We're (not) consecutive".  The
> >latter can detect loss but the former can't.
> If you have timestamps on every ack and packet, what's the difference?

I think that these methods of ACK loss detection are interesting
ideas, and there might be a way to intelligently combine them
with what's already in


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