Re: [quicwg/base-drafts] Change PTO to be per packet number space (#3066)

ianswett <> Mon, 04 November 2019 18:09 UTC

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Subject: Re: [quicwg/base-drafts] Change PTO to be per packet number space (#3066)
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ianswett commented on this pull request.

 The PTO value MUST be set to at least kGranularity, to avoid the timer expiring
+A sender computes its PTO timer every time an ack-eliciting packet is sent.
+When ack-eliciting packets are in-flight in multiple packet number spaces,
+the timer MUST be set for the packet number space with the earliest timeout,
+except for ApplicationData, which MUST be ignored until the handshake
+completes; see Section 4.1.1 of {{QUIC-TLS}}.  Not arming the PTO for
+ApplicationData prioritizes completing the handshake and prevents the server
+from sending a 1-RTT PTO packet before it has the keys to process a 1-RTT
+packet.  This simplifies to setting the PTO on the lowest active packet number
+space if packets from two different packet number spaces are sent when the PTO

The Handshake PTO would expire at t=3, because of the backoff, which may have been what you meant.

The second Initial PTO would expire at t=5, as you said.

One note is that the text does recommend you send a packet in other packet number spaces when possible
"In addition to sending data in the packet number space for which the timer
expired, the sender SHOULD send ack-eliciting packets from other packet
number spaces with in-flight data, coalescing packets if possible."

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