Re: [quicwg/base-drafts] kGranularity and max_ack_delay possibly should be added after exponential backoff (#2393)

Praveen Balasubramanian <> Mon, 25 March 2019 21:56 UTC

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Subject: Re: [quicwg/base-drafts] kGranularity and max_ack_delay possibly should be added after exponential backoff (#2393)
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TCP does not use kGranularity because minRTO already accounts for it indirectly i.e. minRTO values have never been allowed to be set lower than the timer granularity. But yes in TCP minRTO is included in the exponential backoff so it makes sense to keep the equation as is. I think we are effectively using kGranularity as minRTO here. 

In any case I think max_ack_delay is going to be the dominant value here in practice unless delayed ACKs are turned off. I wonder if another option is this:
PTO = smoothed_rtt + max(4*rttvar) + max(max_ack_delay, kGranularity)

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