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Re: [babel] Do we want to adopt draft-jonglez-babel-rtt-extension?

Dave Taht <dave.taht@gmail.com> Sun, 10 March 2019 20:48 UTC

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From: Dave Taht <dave.taht@gmail.com>
Date: Sun, 10 Mar 2019 13:47:50 -0700
Message-ID: <CAA93jw5=fXOqesvkk1MeYKMHDKmHYw+LwBV2XsE0c4J62pPOQA@mail.gmail.com>
To: Toke Høiland-Jørgensen <toke=40toke.dk@dmarc.ietf.org>
Cc: Juliusz Chroboczek <jch@irif.fr>, Babel at IETF <babel@ietf.org>
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Subject: Re: [babel] Do we want to adopt draft-jonglez-babel-rtt-extension?
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I support adoption.

On Sat, Mar 9, 2019 at 7:27 AM Toke Høiland-Jørgensen
<toke=40toke.dk@dmarc.ietf.org> wrote:
>
> Juliusz Chroboczek <jch@irif.fr> writes:
>
> > Dear all,
> >
> > Of all the Babel protocol extensions, the ones that are used in production
> > are all IETF WG documents.  Except draft-jonglez-babel-rtt-extension.
> >
> >   https://tools.ietf.org/html/draft-jonglez-babel-rtt-extension
> >
> > Draft-jonglez-babel-rtt-extension consists of one non-mandatory sub-TLV
> > that can be carried on Hello and IHU packets.  It contains enough data to
> > apply Mills' algorithm (the one used in the HELLO routing protocol and
> > later in NTP) in order to compute an estimate of RTT with microsecond
> > granularity.  The draft only specifies how to compute RTT -- using RTT for
> > something useful is left to the implementation -- but it gives an example
> > of using RTT in order to derive link cost.
> >
> > The algorithm is described in more detail in
> >
> >     https://arxiv.org/pdf/1403.3488.pdf
> >
> > The actual motivation is overlay networks, where a single hop might span
> > continents, and least-hop routing yields suboptimal results.  The
> > algorithm has been used in production for a few years now by a French
> > company called Nexedi.
> >
> > The same subprotocol could probably be used in other kinds of networks,
> > most notably congested wireless networks.  More experimentation is needed.
> >
> > Personal opinion -- the algorithm as described in the draft has one flaw:
> > since the IHU sub-TLV does not carry a Transmit timestamp, the IHU sub-TLV
> > is only useful in cases where the same Packet contains a Hello TLV.  I'm
> > not sure if people would be happy with a flag day, so fixing that would
> > require either eating up another sub-TLV number, or putting the Transmit
> > timestamp at the very end of the sub-TLV (which would make for an ugly
> > format).
> >
> > Do we want to adopt this draft?  I can easily upload a new revision before
> > Monday's cutoff date.
>
> I was planning to eventually implement this anyway, so sure, I support
> adoption :)
>
> -Toke
>
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Dave Täht
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