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: [email protected] _______________________________________________ aqm mailing list [email protected] https://www.ietf.org/mailman/listinfo/aqm
