Re: [tsvwg] L4S status: #17 Interaction w/ FQ AQMs

Jonathan Morton <> Thu, 07 November 2019 16:36 UTC

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From: Jonathan Morton <>
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Date: Thu, 7 Nov 2019 18:36:35 +0200
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Subject: Re: [tsvwg] L4S status: #17 Interaction w/ FQ AQMs
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> On 7 Nov, 2019, at 2:54 pm, wrote:
> It's just that I'm aware that there is an awful lot of kit out there which has an implementation of RED (or WRED) in hardware - eg for TR-059 [1], which mandates WRED support in BRAS. That's from having worked at a silicon vendor, so it doesn't give me visibility of actual usage. I understand a lot of it isn't switched on, but if even a small fraction of it was, it would be a pretty big deployment. It would be interesting if anyone has actual numbers. .  Of course, to be relevant to this discussion, it would need to be configured to do ECN marking as well. 

My experience is that these hardware features are not actually deployed, ie. switched on, unless it is effectively mandated by backhaul usage pricing, to eliminate excess backhaul traffic that would get dropped at the DSLAM.  Then, it is as a hard-dropping policer, ie. without RFC-3168 support.

In your linked document, there is not a single mention of RFC-3168 or ECN, and even WRED is *only* mentioned in the context of upstream policing, which I would expect to be mostly irrelevant at the BRAS.

There are two DSL ISPs I know of that have deployed RFC-3168 compliant AQM in both directions (in BRAS and in CPE).  In both cases, it is a software implementation of fq_codel.

 - Jonathan Morton