[Make-wifi-fast] Must a WiFi link be fully loaded to get an accurate latency measurement?

[Aaron Wood]

I think that will depend on the wifi driver (on the tx side), and whether
or not it's not sending 802.11n/ac aggregate frames immediately (and how
long it's waiting).  Some drivers will buffer up packets for some period of
time before sending them out.  So on a lightly loading transmitter, in a
quiet RF airspace, the driver might add more latency than is necessary.

One thing I've seen is that the wifi aggregates, because they are so large
(64KB), can end up creating some odd RTT sawtooth patterns as a full
aggregate will contain packets with many send times, all received at once.

Here's an excellent summary:
https://datatracker.ietf.org/meeting/101/materials/slides-101-iccrg-an-update-on-bbr-work-at-google-00

-Aaron

On Wed, Apr 1, 2020 at 10:48 AM Tim Higgins <tim at smallnetbuilder.com> wrote:

> One of the things I've been wondering about as I work on OFDMA testing is
> how heavily a WiFi link needs to be loaded.
> As far as I can tell, all (most/many) of the flent scripts basically have
> netperf TCP/IP streams running full tilt.
>
> I guess put another way, how effective are the anti-bufferbloat methods at
> reducing latency on a moderately loaded link?
>
> In terms of WiFi, do I need to run a link at 90+ airtime congestion to see
> OFDMA work it's magic? Or would the lack of available airtime hinder it
> working?
>
> ===========
> Tim
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