[Babel-users] Babel RTT settings for low and high latencies

[Juliusz Chroboczek]

> I hope it's okay if I say it here, but I took the liberty of writing a
> little blog entry about the parameters that were initially confusing to
> me: https://mk16.de/blog/babel-rtt-options-en/

Nice, thanks.

I think it's missing an introduction, where you explain that RTT-sensitive
routing is naturally prone to route flaps, so there's a tradeoff between
stability (rare route flapping) and reactivity (reacting quickly to
changes in RTT).

I'd also explain why you'd want a large rtt-min or a small rtt-max.
Making these values larger and smaller, respectively, makes the protoool
less precise, but drastically reduces the likelihood of route flaps.

As to the content, it looks correct to me, thanks for your work.  A minor
nuance, rtt-max does not need to be larger than all natural RTTs in your
network, it just needs to be larger than all links that you need to
discriminate between.  For example, suppose that your topology is

                       300ms
   Lille --------------------------------
     |                                   \
     | 20ms                               \
     |                                     \
   Paris                                  Tokyo
     |                                     /  
     | 20ms                               /
     |                                   /
   Marseille ----------------------------
                       350ms

then setting rtt-max to, say, 100ms should be fine, since there is no need
to distinguish between the two long-distance links: you just want to avoid
long-distance links whenever possible.

-- Juliusz