Re: [quicwg/base-drafts] Improve ACK_ECN frame encoding (e.g., use bit-vector) (#1439)

[MikkelFJ <[e-mail]>]

I don't thank I get the entire concept here but I'm wondering:

Assume receiver does not detect or reject duplicate packets, but it does track an ACK backlog and there has some natural ACK dectection capability.

If packet 4 in the above example first sets CE, this will be visible in the backlog. A second packet 4 without CE can then see that 4 is already pending ACK and can choose to a) overwrite the CE bit, b) do nothing since a packet is present, or c) use inclusive OR on the CE bit.

If packet 4 is not in the backlog when packet 4 v2 arrives then it has already been ACK'ed leaving it to the sender, or it never received packet 4 v1. In either case it it business as usual.

Now, assume the receiver does reject duplicates by tracking more than the latest ACK backlog and that it simply drops any later receiver packets. In this case this corresponds to case b) in the above.

The question is then - if the above is reasonable - how should a second update to the CE bit be handled receiver side, when the sender is prepared to handle duplicate ACKS / CE. Is replace, drop, or OR the proper approach?

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