Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions

Dave Taht <> Thu, 07 November 2019 22:25 UTC

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From: Dave Taht <>
To: Sebastian Moeller <>
Cc: Greg White <>, tsvwg IETF list <>
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Date: Thu, 07 Nov 2019 14:24:56 -0800
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Subject: Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions
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I'm not sure if I should weigh in here or not. A couple notes...

802.11e was seemingly a good idea in 2004, when men were men, APs
scarce, and txops limited to about 3000/sec.

802.11n added packet aggregation, and 802.11ac added ever more
dense encodings to wedge even more data into that txop...

but the limiting factor for wifi - particularly in dense environments
with a range of standards being broadcast remains that fatal 3000
txops/sec - and while that's a little mitgated by mu-mimo and with
wifi 6 in ofdma mode made MUCH better, having to be backward compatible
elsewhere still messes things up.

furthermore, in 802.11n the VO queue cannot aggregate. 700usec lost
on a single packet.

Use of the VI queue was often buggy in 802.11n chipsets at least as
far back as 2014 when I last poked into it. The main tested paths
have generally been BE, BK, and to a small extent VO.

I've got plenty of data showing that it's in general better (from the
AP's standpoint) to well multiplex and fully fill as best as possible
just the BE queue for each station, to ignore 802.11e, and to try to
manage the max txop size in BE in proportion to the load.

We pointed to that result in "ending the anomaly".

and 802.11e scales ever more badly to ever more devices.

>From the stations standpoint, it can be (if lightly used) to still
use the 802.11e stuff, but that should at best be sparingly used.

Some (mostly enterprise) wifi routers do fiddle with the edca params
some, in particular it does make sense at higher workloads to clamp the
size of txops to stations are allowed to transmit (via the beacon), and
I wish more wifi routers did that.

But trying to actively use the 802.11e priorities at this late date,
not huge on it. Twiddling edca extensively seems like an especially bad idea.

That said, I've been meaning to dig up my old work on the subject,
look at it in light of modern conditions, but given that most of
my aircaps still see some wireless-g APs helping mess up things up,
don't think I have huge reasons to change my current take on it.

I guess my core takeway I'd like people to think about is txops/sec
relative to how much data can be stuffed into a txop, in the real world,
rather than trying to make 802.11e do anything useful.