Re: [quicwg/base-drafts] Define how an "out of order" packet is detected (#3347)

Jana Iyengar <notifications@github.com> Tue, 21 January 2020 00:40 UTC

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Subject: Re: [quicwg/base-drafts] Define how an "out of order" packet is detected (#3347)
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Thinking about this some more, there are three possible definitions here for out-of-order:
1. a newly received packet is greater than largest received by more than one,
2. a newly received packet is smaller than the largest received,
3. both (1) and (2).

(1) is the obvious case where a loss happens and a subsequent packet is received. (2) is the reordering case, where an earlier packet is delivered later, and while it does not indicate loss, it does indicate that a gap was filled. It's useful to signal (2) as well immediately to prevent a sender from unnecessarily retransmitting what it believes to be a missing packet.

The definition we want for "out-of-order" is the one that is most useful for determining when to send an immediate ack. The definition in the PR captures both (1) and (2), and is probably the one we want.

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