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

ianswett <> Thu, 31 October 2019 19:06 UTC

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Date: Thu, 31 Oct 2019 12:06:16 -0700
From: ianswett <>
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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.

>  When a PTO timer expires, the PTO period MUST be set to twice its current
 value. This exponential reduction in the sender's rate is important because
 the PTOs might be caused by loss of packets or acknowledgements due to severe
-congestion.  The life of a connection that is experiencing consecutive PTOs is
-limited by the endpoint's idle timeout.
+congestion.  Even when there are ack-eliciting packets in-flight in multiple
+packet number spaces, the exponential increase in probe timeout occurs across
+all spaces to prevent excess load on the network.  For example, a timeout in
+the Initial packet number space doubles the length of the timeout in the
+Handshake packet number space.

The Initial and Handshake timeouts should always be the same length, because neither uses the peer's max_ack_delay.  But they could be started from different points in time.  

As long as you send both at once, then the Initial PTO dominates.

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