Re: [quicwg/base-drafts] Should we allow ACK-only packets to be declared lost? (#3451)

Igor Lubashev <notifications@github.com> Fri, 21 February 2020 18:14 UTC

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Subject: Re: [quicwg/base-drafts] Should we allow ACK-only packets to be declared lost? (#3451)
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@mikkelfj, @ianswett Thanks, the SHOULD in "Section "13.2.1. Sending ACK Frames" being a SHOULD due to connection termination makes sense, but it would benefit for being explicit that it is the only case when packets may never get ACKed.

@ianswett Some implementations might not care about loss of ACK-only packets, while others may care about such losses. For the latter ones, knowing of such losses is as required for correct functioning as knowing of loss of packets with DATAGRAMs (what bytes count toward a congestion window is not the only implementation concern).

I do not think that there is any burden on even the simplest implementation. If the simplest implementation detects a gap, it can send a packet with an ACK. If that gap was detected due to a receipt of an non-ack-eliciting packet, a PING frame could be included with the resulting ACK (to satisfy "_An endpoint MUST NOT send a non-ack-eliciting packet in response to a non-ack-eliciting packet, even if there are packet gaps which precede the received packet._"

The bottom line is that building in a "loss ambiguity" into the protocol without a great reason is a mistake. TCP has a retransmission ambiguity, and we know it is a problem.

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