Re: [quicwg/base-drafts] pto_count should be reset when dropping a packet number space (#3272)

Kazuho Oku <notifications@github.com> Thu, 28 November 2019 11:10 UTC

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Date: Thu, 28 Nov 2019 03:10:23 -0800
From: Kazuho Oku <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] pto_count should be reset when dropping a packet number space (#3272)
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> I believe the simplest way to ensure QUIC isn't overly aggressive during the handshake and to encourage packet coalescing is to specify pto_count on a connection scope, similar to the rtt variables.

I think we agree that PTO during handshake should be _as aggressive as_ after the handshake. However, I am starting to wonder if the current spec. actually works that way.

Consider the case when the server responds to ClientHello. It would be sending Initial, Handshake, and 1-RTT packet at the same time. Then, when those QUIC packets gets lost, the loss timer would be invoked three times, resulting in pto_count set to 3. Is that the intended behavior? I think in such case, pto_count should become one, after the PTO timers of each epoch is triggered.

Therefore, to me, the correct logic seems to be:
* have pto_count for each epoch
* every time the per-epoch PTO timer is triggered, increment the per-epoch pto_count by 1
* when an ACK is being received on *any* epoch, reset pto_count of all the epochs

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