[Make-wifi-fast] [Babel-users] reducing delays in wifi mcast queues

Juliusz Chroboczek jch at irif.fr
Tue Sep 18 20:43:20 EDT 2018

>> Interesting.  AFAIK, ECN is only considered by AQM queues, so this implies
>> there's a queue in the way that's dropping Babel packets.

> There's fq_codel on every queue, which does FQ, and codel assumes
> everything is at least moderately TCP friendly (and/or reasonably
> responsive to ecn marks)

Jonathan seems to agree with you.

Were your tests run with more than 60 installed routes or so?

>> Or perhaps, if we know which queue that is,
>> we could modify Babel's packet scheduling to be more AQM friendly?

> How would you describe babel's packet schedulig now?

The main flaw is that it sends periodic updates as a burst of back-to-back
full-size packets.  That could trigger Codel if you had more than 60
routes or so.

> So dumping packets in there at a rate no more than 20ms each (short term
> burst of 100ms) - relative to whatever bandwidth can be achieved vs the
> other flows.

Right.  Guilty as charged.

-- Juliusz

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