Re: [quicwg/base-drafts] When/how often to send ACK frames (#230)

[ianswett <[e-mail]>]

Knowing the delayed ack timer allows you to set timers for TLP and RTO without creating spurious retransmits, because the ack timer can be incorporated into the min timeout when there's only one packet outstanding.    See the recovery doc(https://tools.ietf.org/html/draft-tsvwg-quic-loss-recovery-00), section 3.1.

Currently most TCP implementations have to use a very conservative min TLP timeout and RTO because they assume the peer likely uses a 100 or 200ms delayed ack timer.

I don't think knowing the ratio tells you much of interest, and it's fairly easy to just observe, but Mirja's right that some congestion control schemes deal better with stretch acks than others.  That being said, ideally congestion controls should deal with them anyway, since they are created by other network elements, so I don't see a large need to communicate this to the peer.

For related info, see https://tools.ietf.org/html/draft-wang-tcpm-low-latency-opt-00

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