[Bloat] [aqm] [iccrg] AQM deployment status?
swmike at swm.pp.se
Sun Sep 29 05:37:56 EDT 2013
On Sun, 29 Sep 2013, Bob Briscoe wrote:
> The shallow marking threshold certainly keeps standing queuing delay
> low. However, that's only under long-running constant conditions. During
> dynamics, not waiting a few hundred msec to respond to a change in the
> queue is what keeps the queuing delay predictably low. Dynamics are the
> norm, not constant conditions.
Well, my original question was in the context of a 3-5ms tail drop queue
(such as are frequently available in lower end switches). My understanding
from earlier experience is that TCP will severely saw-tooth under these
conditions and only way I could see marking as being valuable was if the
RTT was less than buffer depth (or at least very low).
There was a discussion earlier on bloat-l regarding what the impact of a
10ms CoDel queuing scheme will have on 200ms RTT existing non-ECN TCP
performance. Deep queues were invented to handle this specific use-case.
One way would absolutely be for TCP to not send a lot of packets
back-to-back but instead pace them out at the rate that actually makes the
TCP rate be exact in a millisecond resolution instead of as it is today,
perhaps tens or hundreds of milliseconds. I believe some implementations
already do this.
Mikael Abrahamsson email: swmike at swm.pp.se
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