Re: [quicwg/base-drafts] Retaining the largest received packet number (#3541)

Martin Thomson <> Mon, 30 March 2020 00:46 UTC

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From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] Retaining the largest received packet number (#3541)
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I don't think we really need to cater for retransmitted ACK frames in any way.  What I'm concerned about is reordering.

Yes, using the increase of largest acknowledged as a proxy for strict ordering is a little weird, but the assumption is that frame handling is distinct from packet handling and packet numbers are not available when frames are handled.  (I think that's the principle we agreed on; that's why it's OK to use packet numbers in key updates, for example, something that I can confirm is borne out by implementation experience.)

The case you describe here has the appearance of exactly that type of reordering if the two senders also generate their own ACK frames (though this seems very strange).  But I think that the consequences of that sort of design are not our responsibility to deal with.

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