Re: [quicwg/base-drafts] kInitialRtt of 100 msec is too aggressive (#2184)

ianswett <notifications@github.com> Mon, 25 March 2019 22:51 UTC

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Subject: Re: [quicwg/base-drafts] kInitialRtt of 100 msec is too aggressive (#2184)
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Thanks for the additional information.  The data is from 2009(https://www.ietf.org/proceedings/75/slides/tcpm-1.pdf), but still seems largely plausible in terms of RTTs, though I'm sure some details have changed.

One thought is that the client may have a better idea of what it's RTT is than the server does when there is no resumption information available.  As such, we could pick a fairly conservative value(ie: 1s) on the server and if the client retransmits(and the server receives) the ClientHello more frequently,  the server should retransmit its response as well.  In practice, the current anti-amplification limit of 3x amount to exactly that in a lot of circumstances, so making it core to the handshake mechanism may be wise.  On the other hand, this is a special case unless we tweak the anti-amplification limit to be min(3 packets, initial server flight).

The 4 second timeout I mentioned is for the handshake.  I would expect live migrations to not occur during the handshake, or at least not expect the handshake to complete in that case, but maybe that's not true?  We experimented with bumping the timeout to 10 seconds a while back in gQUIC, but there were some performance regressions and we didn't dig in deeply enough to understand why.

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