[Make-wifi-fast] Uplink vs downlink latency

[Isaac Konikoff]

Hi Tim,

I know this will probably be in your write-up, but I am curious if you are
sniffing the traffic to verify that OFDMA is actually happening by pinning
the aid to the monitor interface and using a wireshark display filter
radiotap.he.data_1.ppdu_format==0x2 to see the HE_MU frames. From my
testing it is not something that is automatically in use all the time...it
is used as needed per each AP's decision algorithm. I seem to be able to
cause OFDMA to happen sometimes when using small payloads with bursty
traffic and periods of quiet, but it is not something that I can turn on
and just say OFDMA is happening.

Also, in my flent tcp_download vs tcp_upload tests I see similar latency
values that are both relatively low. I will have to run the rtt_fair_var to
see how it compares.

Nice use of flent! Looking forward to your write-up.
Isaac


On Wed, Apr 29, 2020 at 2:40 PM Tim Higgins <tim at smallnetbuilder.com> wrote:

> Hi all,
>
> I finally have my testbed working the way I want and am starting to run
> tests to see if OFDMA does anything useful.
>
> This will all be covered in detail in an upcoming SmallNetBuilder article.
> But I wanted to sanity check something with this esteemed group.
>
> The tests are basically the flent rtt_fair_var up and down tests ported to
> the octoScope platform I use for WiFi testing.
> The initial work was done on flent, with a lot of hand-holding from Toke.
> (Thank you, Toke!)
>
> Using 4 Intel AX200 STAs on Win10. iperf3 is running traffic using TCP/IP
> with unthrottled bandwidth. I've taken Bjørn's idea and have each STA using
> a different DSCP priority level, but with TCP/IP traffic, not UDP. I'm
> sticking to using CS0-7 equivalents and confirmed that the iperf3 --dscp
> values properly translate to the intended WiFi priority levels.  Each STA
> has a different priority, either CS0,3,5 or 6 (best effort, excellent
> effort, video and voice).
>
> Ping is used to measure latency and always runs from AP to STA. Only
> TCP/IP traffic direction is reversed between the down and uplink tests.
>
> One thing that jumps out immediately is that uplink latencies are *much*
> lower than downlink, with either OFDMA on or off. Attached are three
> examples. The CDFs are average latency of the 4 STAs.
>
> The NETGEAR R7800 is a 4x4 AC Qualcomm-based. I'm using this as a baseline
> product.
>
> The NETGEAR RAX15 is 2x2 AX Broadcom-based. You can see what I mean when I
> say OFDMA doesn't help.
>
> Does this much difference between up and downlink latency pass the sniff
> test?
>
> ===
> Tim
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