[Cake] cake at longer rtts

[Jonathan Morton]

> On 18 Jan, 2017, at 05:35, Dave Taht <dave.taht at gmail.com> wrote:
> 
> It has been quite some time since I looked at cake at longer RTTs.
> 
> Here's a single flow test comparing it to sonic fiber default fifo
> (50ms delay in the ONT), to fq_codel, to cake at 110mbit.
> 
> http://www.taht.net/~d/sonic_cake_vs_fq_codel_vs_fifo_70ms.png

Seems to be more aggressive than fq_codel on the slow-start response, but very similar thereafter.  I think that’s consistent with what I believe I’ve implemented, and with some tests I’ve been running over here.

In my experience, Westwood+ performs better than CUBIC with Codel, because it estimates the true BDP better and hops directly to it when the signal arrives.  Probably BBR has similar properties, but with different semantics.

I sometimes use longer assumed-RTTs, ie. “oceanic” or “satellite”, in order to get a little more throughput.  However, this significantly reduces the latency control in ingress mode, because every slow-start is then uncontrolled for a full second.

 - Jonathan Morton