[Ecn-sane] Using the ECN bits as signalling for explicit congestion control

Rodney W. Grimes 4bone at gndrsh.dnsmgr.net
Wed May 15 11:43:33 EDT 2019

> This popped up in my Google scholar: "ABC: A Simple Explicit Congestion
> Control Protocol for Wireless Networks" - https://arxiv.org/pdf/1905.03429
> Basically, they propose an explicit congestion control mechanism that
> uses signalling from the bottleneck router to slow down or speed up, and
> they re-purpose ECT(0) and ECT(1) as the signalling mechanism. I do
> believe the end result is rather similar to SCE, isn't it?
> The appendix contains what appears to be an extensive stability
> analysis.

It appears to indeed be similiar, though they solved
the hard problem with:
	To this end, ABC routers
	separate ABC and non-ABC flows into two queues, and
	use a simple algorithm to schedule packets from these
	queues. ABC makes no assumptions about the conges-
	tion control algorithm of non-ABC flows, is robust to
	the presence of short or application-limited flows, and
	requires a small amount of state at the router.

Thus they require a 2 queue AQM, something the SCE work
knows is the easy way out, and are trying to solv 
in ways that do not require this added complexity.

Also they seem to be miss named the actual bits and
confused the bit names with the meaning of the 4 possible
code values.  The bits, per RFC are ECT(0) and ECT(1)
and can be used to signal the 4 states non-ECN, ECN cable,
unused, and CE (by current RFC, we intened to consume
the unused as SCE)

I find it interesting that the apparent publication
date is ~16 days after the SCE ietf/104 presentation
and some months after the SCE work had become semi public.

Rod Grimes                                                 rgrimes at freebsd.org

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