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Re: [babel] Open issues with draft-ietf-babel-rtt-extension

Juliusz Chroboczek <jch@irif.fr> Fri, 26 July 2019 21:38 UTC

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Date: Fri, 26 Jul 2019 23:38:24 +0200
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From: Juliusz Chroboczek <jch@irif.fr>
To: Baptiste Jonglez <baptiste.jonglez@imag.fr>
Cc: Toke Høiland-Jørgensen <toke@toke.dk>, babel@ietf.org
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Archived-At: <https://mailarchive.ietf.org/arch/msg/babel/yf6Cf9ROjTagu9bTWBmBp58ir9o>
Subject: Re: [babel] Open issues with draft-ietf-babel-rtt-extension
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>>> Baptiste outlined two solutions:
>>>
>>>   (a) require that all IHUs be sent in packets with a Hello;
>>>   (b) define a new TLV that contains just a timestamp.
>>>

> Thank you for summarizing.  You apparently didn't like my "Solution 1"
> because you don't even mention it, but I agree it's a bad idea anyway :)

Right, I missed that.  Baptiste's "Solution 1" is to duplicate the transmit
timestamp in all IHUs.

While it yields a somewhat cleaner packet format, it complicates the
implementation somewhat.  The transmit timestamp must be computed as close
as possible to packet transmission, so it gets patched in into the packet
at the very last moment.  In the current packet format, there's just one
transmit timestamp per packet, so we just keep one pointer to the space
reserved for the timestamp.  If the transmit timestamp gets duplicated,
then we need to either maintain a list of places to patch, or reparse the
packet just before we ship it out.

-- Juliusz

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