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

[Jana Iyengar <[e-mail]>]

janaiyengar commented on this pull request.



> @@ -471,8 +474,10 @@ 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
+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 from the packet number space with the earliest timeout.

```suggestion
the timer MUST be set for the packet number space with the earliest timeout.
```

> @@ -471,8 +474,10 @@ 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
+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 from the packet number space with the earliest timeout.
+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.

Remove this sentence, it's unnecessary.

> @@ -522,9 +525,17 @@ removed from bytes in flight when the Initial and Handshake keys are discarded.
 ### Sending Probe Packets
 
 When a PTO timer expires, a sender MUST send at least one ack-eliciting packet
-as a probe, unless there is no data available to send.  An endpoint MAY send up
-to two full-sized datagrams containing ack-eliciting packets, to avoid an
-expensive consecutive PTO expiration due to a single lost datagram.
+in the packet number space as a probe, unless there is no data available to
+send.  An endpoint MAY send up to two full-sized datagrams containing
+ack-eliciting packets, to avoid an expensive consecutive PTO expiration due
+to a single lost datagram.
+
+In addition to sending data in the packet number space for which the timer
+expired, the sender SHOULD coalesce ack-eliciting packets from all other packet

Is this necessarily "all" spaces?

> @@ -522,9 +525,17 @@ removed from bytes in flight when the Initial and Handshake keys are discarded.
 ### Sending Probe Packets
 
 When a PTO timer expires, a sender MUST send at least one ack-eliciting packet
-as a probe, unless there is no data available to send.  An endpoint MAY send up
-to two full-sized datagrams containing ack-eliciting packets, to avoid an
-expensive consecutive PTO expiration due to a single lost datagram.
+in the packet number space as a probe, unless there is no data available to
+send.  An endpoint MAY send up to two full-sized datagrams containing
+ack-eliciting packets, to avoid an expensive consecutive PTO expiration due
+to a single lost datagram.
+
+In addition to sending data in the packet number space for which the timer
+expired, the sender SHOULD coalesce ack-eliciting packets from all other packet
+number spaces with in-flight data if sending coalesced packets is supported.
+If implementations do not send coalesced packets upon timeout when multiple
+packet number spaces have in-flight data, then they MUST only send a single

Suggestion: "If an endpoint has data in multiple packet number spaces in flight and is unable to send coalesced packet when a PTO expires, it MUST send only a single datagram on PTO expiration."

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