Re: [quicwg/base-drafts] Skip a packet number when sending one PTO packet (#2952)

MikkelFJ <notifications@github.com> Tue, 06 August 2019 05:31 UTC

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Subject: Re: [quicwg/base-drafts] Skip a packet number when sending one PTO packet (#2952)
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mikkelfj commented on this pull request.



> @@ -601,7 +601,9 @@ removed from bytes in flight when the Initial and Handshake keys are discarded.
 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.
+expensive consecutive PTO expiration due to a single lost datagram.  When only
+sending a single packet on PTO, senders can skip a packet number to elicit a
+faster acknowledgement.
 

I don't understand this: while packet numbers are usually incremental, that does not carry any semantics to my knowledge. PN's are skipped to guard against optimistic ACK attacks. It would be unfortunate if that praxis affects retransmission?

That said, I think it would be great if PN's could be assumed to be incremental, but there is no good solution to the optimistic ACK attack so far.

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