Re: [babel] Iotdir telechat review of draft-ietf-babel-rtt-extension-05
Pascal Thubert <pascal.thubert@gmail.com> Tue, 05 March 2024 06:56 UTC
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From: Pascal Thubert <pascal.thubert@gmail.com>
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Date: Tue, 05 Mar 2024 07:56:14 +0100
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Cc: Juliusz Chroboczek <jch@irif.fr>, babel@ietf.org
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To: David Schinazi <dschinazi.ietf@gmail.com>
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Subject: Re: [babel] Iotdir telechat review of draft-ietf-babel-rtt-extension-05
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Le 5 mars 2024 à 01:58, David Schinazi <dschinazi.ietf@gmail.com> a écrit :
I like the new section, thanks for writing it!DavidHello Pascal,
I've added an applicability section following your advice. I'll be
grateful if you find the time to review it. (David, Toke, Donald, anyone
else, your comments are also welcome.)
1.1. applicability
The extension defined in Section 3 provides a sequence of accurate
but potentially noisy RTT samples. Since the round-trip time is a
symmetric measure of delay, this protocol is only applicable in
environments where the symmetric delay is a good predictor of whether
a link should be taken by routing traffic; this is the case in most
networks known to the authors, but might not necessarily be the case
in networks built over exotic link technologies.
The extension makes minimal requirements on the nodes. In
particular, it does not assume synchronised clocks, but only requires
that clock drift be negligible during the time interval between two
Hello TLVs. Since that is on the order of a few seconds, this
requirement is met even with cheap crystal oscillators such as the
ones used in consumer electronics.
The algorithm defined in Section 4 makes a number of assumptions
about the network. The assumption with most severe consequences is
that all links below a certain RTT (rtt-min in Section 4.2) can be
grouped in a single category of "good" links. While this is the case
in wide-area overlay networks, it makes the algorithm inapplicable in
networks where distinguishing between low-latency links is important.
There are other assumptions, but they are less likely to limit the
algorithm's applicability. The algorithm assumes that all links
above a certain RTT (rtt-max in Section 4.2) can be assumed to be
equally bad, and will only be used as a last resort. In addition, in
order to avoid oscillations, the algorithm is designed to react
slowly to RTT variations, thus causing suboptimal routing for seconds
or even minutes after an RTT change; while this is a desirable
property in fixed networks, as it avoid excessive route oscillations,
it might be an issue with networks with high rates of node mobility.
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- [babel] Iotdir telechat review of draft-ietf-babe… Pascal Thubert via Datatracker
- Re: [babel] Iotdir telechat review of draft-ietf-… Juliusz Chroboczek
- Re: [babel] Iotdir telechat review of draft-ietf-… Pascal Thubert
- Re: [babel] Iotdir telechat review of draft-ietf-… Juliusz Chroboczek
- Re: [babel] Iotdir telechat review of draft-ietf-… Juliusz Chroboczek
- Re: [babel] Iotdir telechat review of draft-ietf-… David Schinazi
- Re: [babel] Iotdir telechat review of draft-ietf-… Pascal Thubert
- Re: [babel] Iotdir telechat review of draft-ietf-… Toke Høiland-Jørgensen