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Re: [babel] New Version Notification for draft-ietf-babel-rtt-extension-06.txt

Juliusz Chroboczek <jch@irif.fr> Wed, 17 April 2024 19:40 UTC

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Date: Wed, 17 Apr 2024 21:40:10 +0200
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From: Juliusz Chroboczek <jch@irif.fr>
To: Toke Høiland-Jørgensen <toke@toke.dk>
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Subject: Re: [babel] New Version Notification for draft-ietf-babel-rtt-extension-06.txt
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> Well, the issue we're trying to resolve in Bird by using kernel
> timestamps is that if the application blocks for a long time without
> processing incoming packets, that will be part of the RTT which can (it
> seems) lead to some pretty inflated RTT values.

Why would the application block?  Isn't that a bug in the application?

> Or drop this entirely if we really believe that it doesn't make any
> difference?

On the write side, it definitely makes a difference: if memory serves,
kernel timestamping happens after queueing, so any local congestion is
going to make the two timestamps very different.

On the receive side, it probably doesn't.

>>> We don't explicitly expire RTT state if the sanity checks keep failing,
>>> so I don't believe we're compliant with the last paragraph of section
>>> 3.3.

> > I have misgivings about this paragraph myself.  Shall I remove it?
> 
> I'm not sure I understand the issue it is trying to solve, TBH; why was
> it added?

Right, I'll remove it.

-- Juliusz

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