Re: [TLS] Efficiency of ACKing scheme

Thomas Fossati <Thomas.Fossati@arm.com> Mon, 06 April 2020 16:03 UTC

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From: Thomas Fossati <Thomas.Fossati@arm.com>
To: Eric Rescorla <ekr@rtfm.com>, Hanno Becker <Hanno.Becker@arm.com>
CC: Rob Sayre <sayrer@gmail.com>, "tls@ietf.org" <tls@ietf.org>, Thomas Fossati <Thomas.Fossati@arm.com>
Thread-Topic: [TLS] Efficiency of ACKing scheme
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Date: Mon, 06 Apr 2020 16:03:19 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/zNHdrbqMbtcHFNkOBwg_hvnzmhk>
Subject: Re: [TLS] Efficiency of ACKing scheme
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On 06/04/2020, 16:20, "Eric Rescorla" <ekr@rtfm.com> wrote:
> First, let me say that in scenarios like the one you posit we have
> other problems besides ACK inefficiency. Specifically, DTLS doesn't do
> any real congestion control and so your initial window will be way too
> big if you broadcast a 40K message at once. So I don't think a huge
> amount of optimization is in order here.

While it is true that there's no explicit congestion control, that
doesn't prevent an implementation to conservatively pace the send
instead of firing off the whole 40K worth of payload at line rate.

> By contrast. we do know that DTLS retransmission is too slow and given
> that small flights are common, losing the ability to indicate that you
> lost a tail seems undesirable.

I agree this should be avoided if possible.

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