Re: [quicwg/base-drafts] Don't retransmit lost packets that are acked later (#3957)

[ianswett <[e-mail]>]

@ianswett commented on this pull request.

Thanks for adding this, some more comments.

> @@ -3804,6 +3804,14 @@ number length, connection ID length, and path MTU.  A receiver MUST accept
 packets containing an outdated frame, such as a MAX_DATA frame carrying a
 smaller maximum data than one found in an older packet.
 
+When a sender declares a packet as lost and either retransmits the contained
+frames or marks them for retransmission, the sender SHOULD avoid subsequent
+retransmission of this information if it later receives an acknowledgement for
+that packet. Doing so requires senders to retain information about packets after
+they are declared lost. A sender can discard this information after a period of
+time elapses, such as three times the PTO (Section 6.2 of {{QUIC-RECOVERY}}), or

3*PTO is really long in this case, and it can consume a fair bit of memory depending upon implementation details.  I'd suggest an ~RTT, since by that point you're expecting the acknowledgement of the retransmitted data.

> +When a sender declares a packet as lost and either retransmits the contained
+frames or marks them for retransmission, the sender SHOULD avoid subsequent
+retransmission of this information if it later receives an acknowledgement for
+that packet. Doing so requires senders to retain information about packets after
+they are declared lost. A sender can discard this information after a period of
+time elapses, such as three times the PTO (Section 6.2 of {{QUIC-RECOVERY}}), or
+on other events, such as reaching a memory limit.

How about "..after receiving an acknowledgement for a previously lost packet."  I think late acknowledgement is potentially confusing.

> +When a sender declares a packet as lost and either retransmits the contained
+frames or marks them for retransmission, the sender SHOULD avoid subsequent
+retransmission of this information if it later receives an acknowledgement for
+that packet. Doing so requires senders to retain information about packets after
+they are declared lost. A sender can discard this information after a period of
+time elapses, such as three times the PTO (Section 6.2 of {{QUIC-RECOVERY}}), or
+on other events, such as reaching a memory limit.

And how about starting with "A packet can be acknowledged after being declared lost." instead of "Acknowledgements can be received after a sender declares a packet as lost."

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