Re: [tsvwg] I-D Action: draft-ietf-tsvwg-nqb-15.txt

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Alex,

is that Maxwells Demon scheduler working similar as the one on slide 5 of
https://datatracker.ietf.org/meeting/116/materials/slides-116-iccrg-alternative-best-effort-abe-for-service-differentiation-trading-loss-versus-delay  ?

The scheduler described by that publication isn't NQB, it trades low delay for packet loss during congestion. Another notable difference is, that NQB allows packets which can't be scheduled by the low delay queue, to get access to the default queue. Hence these packets are the only ones being able to access both schedulers, low delay and default. So there's no strict priority in NQB scheduling at the NQB scheduler itself, however there's exclusive access to scheduler resources for a particular kind of traffic (NQB at the expense of default/QB). In the end I think, NQB is able to seize more bandwidth than QB.

While the authors of the above material present a fair amount of measurement results giving some indication how the scheduler impacts transport while not having been editing any ID, I note that the authors of NQB, a standards track doc, didn't publish any measurement or simulation result within IETF. 

A kind of priority or "unfair advantage" (not sure it's the right term) results from shallow queues, once the default queue depth is approaching congestion free RTT. I didn't give it a deep thought, but could that say, the default queue of such an experiment is of sub-optimal depth if it is on the order of the RTT or bigger (and should be decreased)?

Regards, Ruediger


Alex wrote: 

The following thought experiment should illustrate that moving from a single queue, to two queues with a scheduler between them, can be positive sum for latency/delay:

We have two traffic types A and B. In the "control group" case, they are in the same queue. In the test case, we separate them into two queues. The queue for type A offers the same treatment the original single queue. The queue for type B has a different treatment with a shallow queue.

The scheduler between the two is  Maxwell's Demon. The demon knows exactly which time slots the packets from each type *would have used* if they had been moving through as single queue. It schedules as follows:
 * When a packet of type A would have exited the single queue, the demon lets through a packet from queue A. 
 * When a packet of type B would have exited the single queue, the demon lets through a packet from queue B.
 * If a packet from the appropriate queue is not available, it lets the slot go empty.