tcp fast open?

Juliusz Chroboczek jch at
Mon Feb 20 14:55:45 PST 2012

> Btw, I am very interested in learning the result of AQM vs
> delayed-based CC like ledbat.

That's something that I discussed with the creators of LEDBAT a year ago
(when they convinced me to implement µTP in Transmission).  Here's what
I recall of what Shalunov told me -- but it was a long time ago, and
I was badly jetlagged, so I could be speaking nonsense.

LEDBAT reacts to loss in exactly the same way as Reno does -- it reduces
its congestion window by 1/2.  Hence, if the bottleneck is running an
agressive loss-based AQM such as BLUE, then LEDBAT will behave just the
same as NewReno.

Note that this is not the case of the variant of LEDBAT implemented in
µTP, which on loss divides its window by 1/sqrt(2) (if memory serves).
Hence, µTP will, in that case, behave like an aggregate of two Reno
flows.  However, since µTP doesn't implement slow start or fast
recovery, µTP should still end up being far less agressive than Reno.


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