Re: [quicwg/base-drafts] Only send one immediate ACK after reordering (#3357)

ianswett <> Fri, 31 January 2020 16:24 UTC

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Subject: Re: [quicwg/base-drafts] Only send one immediate ACK after reordering (#3357)
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Currently in the drafts, N is 2, so there are very few cases where sending more ACKs would be beneficial.

The worst case I can construct is If the first ACK is lost, then the loss detection could be delayed by the max_ack_delay IF exactly one more packet was received.  That seems quite acceptable and loss of ack-only packets is rare in my experience.

Drafts like the ack-frequency extension do change the dynamics some, but they also increase the relative cost of sending immediate ACKs more than once.  For example, instead of sending an ACK-only packet every 10 or 20 packets, a receiver could switch to sending an ACK for every packet, which could massively slow down the connection and increase load on the network.

I'm going to run a production experiment with this change as well to confirm that it performs as well or better, but that may take a few months.

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