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Re: kMaxDatagramSize

Ian Swett <ianswett@google.com> Mon, 16 September 2019 21:01 UTC

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From: Ian Swett <ianswett@google.com>
Date: Mon, 16 Sep 2019 17:01:05 -0400
Message-ID: <CAKcm_gPqhPdyHeg9S38yU4sZo9AeqXppVbryDMCUWDcBFECUmA@mail.gmail.com>
Subject: Re: kMaxDatagramSize
To: Timo Völker <timo.voelker@fh-muenster.de>
Cc: "quic@ietf.org" <quic@ietf.org>
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In recovery, kMaxDatagramSize is used for initial congestion window,
initial congestion windows, and the growth rate of Reno.

As you state above, it's expected most connections will have a value larger
than 1200.  Possibly a recommendation of >= 1200 bytes would make more
sense?

On Mon, Sep 16, 2019 at 2:10 AM Timo Völker <timo.voelker@fh-muenster.de>
wrote:

> Hi,
>
> I wonder why kMaxDatagramSize is a constant and why the recommended value
> is 1200 (section B.1. of the recovery draft).
>
> The transport draft mentions PMTUD, which makes the QUIC maximum packet
> size variable.
> Also it mentions that, in absence of a PMTUD, we can assume a QUIC maximum
> packet size of 1232 or 1252 for IPv6 or IPv4, respectively. Why is 1200
> bytes recommended then?
>
> My assumption is that kMaxDatagramSize = QUIC maximum packet size. Is this
> just wrong? Is it OK to use a kMaxDatagramSize with kMaxDatagramSize <=
> QUIC maximum packet size?
>
> Thanks,
>
> Timo

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