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

[martinduke <[e-mail]>]

martinduke approved 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.
-
-A sender computes its PTO timer every time an ack-eliciting packet is sent. A
-sender might choose to optimize this by setting the timer fewer times if it
-knows that more ack-eliciting packets will be sent within a short period of
-time.
+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. The life of a connection that

"For example, a timeout in the Initial packet number space doubles the length of the timeout in the Handshake number space."

>  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.
-
-A sender computes its PTO timer every time an ack-eliciting packet is sent. A
-sender might choose to optimize this by setting the timer fewer times if it
-knows that more ack-eliciting packets will be sent within a short period of
-time.
+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. The life of a connection that

There is also some conceptual subtlety that I suspect people could mess up.

If I'm coalescing my probes, then there is *never* a timeout at the higher levels -- each time, the junior level times out and a new high-level packet is sent that resets that level.

Misinterpreting this paragraph might mean that coalescing three probes could result in three bitshifts of the PTO.

This doesn't have to be in this PR, but when I reread this draft when everything's landed, hopefully it's in here somewhere.

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