From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ej1-x62b.google.com (mail-ej1-x62b.google.com [IPv6:2a00:1450:4864:20::62b]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 9D6453B29E for ; Thu, 14 May 2020 17:43:06 -0400 (EDT) Received: by mail-ej1-x62b.google.com with SMTP id s3so228973eji.6 for ; Thu, 14 May 2020 14:43:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=broadcom.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=NaXmYAZfOhrlCmNj3Tb598Gxymf9f1Mw9CHLqRXGRJY=; b=LxKwQJ5msBcYTTMdx33TFdvfYc0sKVQrFN8hI9TMwBSet7PErbPt5Ode2Y3HKhDE9d SHKFBXluwJvG9zlYf8bLeB8VXqbmegiju7W5XFWqvYN4KOT4uWHtWakiX+P3QAnEWTLL hnprc+kww3yAeMM2fk040hk0igyIbA8io7p30= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=NaXmYAZfOhrlCmNj3Tb598Gxymf9f1Mw9CHLqRXGRJY=; b=hOWVbdwRAeHjH4LQl3K9VMryMwdu92YoFDQ36bUwdw8aBBn/itx99Yq3UEP3xx2Spa RdMvMhWmylZw99gWu6dWeD/2XaDdxGBYptjCccv7EH3LgGo7wEp+9LREMmwoHZAP8T0b rs7pZ1g8uWLtHnuKpYGjR7Ltx+k+kf6zAPruLeFBlQIXAFX1Ebiu+L28FV8rdpgTc59U quzVP4gdcFPfMC+XN/eYuRmvYRjFd0i9N74U2FVGsg57wmVaqayGEpI4tVDjiSKKnyfb asd5JZxaPHFy/GBxwHCurbWJ2gmWgD5NKh3Jm6o9kwxT4QajxsxYOYYtTN1wY38+liNk 5ezA== X-Gm-Message-State: AOAM533nCRlghAjoE6hJr2vZVC3+eVMOm2OqFUeJkVB4g1onO1LSiqkj RdxeJPd8AdpxHiZipw8tdJwukNHVukc2FW8LUkVShQ== X-Google-Smtp-Source: ABdhPJxE/iJxTuSz665icduRpZ4B0jIa5IxDwaOWDfeRT/G5lA3ijxKfyzhIubScUnrdBgZ0XunjxRai8R3L3QR3I94= X-Received: by 2002:a17:906:81c6:: with SMTP id e6mr29939ejx.241.1589492585529; Thu, 14 May 2020 14:43:05 -0700 (PDT) MIME-Version: 1.0 References: <56a03e99-3337-bf4a-4743-deb93abb9592@smallnetbuilder.com> In-Reply-To: From: Bob McMahon Date: Thu, 14 May 2020 14:42:54 -0700 Message-ID: Subject: Re: [Make-wifi-fast] SmallNetBuilder article: Does OFDMA Really Work? To: Tim Higgins Cc: Make-Wifi-fast Content-Type: multipart/alternative; boundary="000000000000ef687605a5a2940b" X-List-Received-Date: Thu, 14 May 2020 21:43:06 -0000 --000000000000ef687605a5a2940b Content-Type: text/plain; charset="UTF-8" Also, forgot to mention, for latency don't rely on average as most don't care about that. Maybe use the upper 3 stdev, i.e. the 99.97% point. Our latency runs will repeat 20 seconds worth of packets and find that then calculate CDFs of this point in the tail across hundreds of runs under different conditions. One "slow packet" is all that it takes to screw up user experience when it comes to latency. Bob On Thu, May 14, 2020 at 2:38 PM Bob McMahon wrote: > I haven't looked closely at OFDMA but these latency numbers seem way too > high for it to matter. Why is the latency so high? It suggests there may > be queueing delay (bloat) unrelated to media access. > > Also, one aspect is that OFDMA is replacing EDCA with AP scheduling per > trigger frame. EDCA kinda sucks per listen before talk which is about 100 > microseconds on average which has to be paid even when no energy detect. > This limits the transmits per second performance to 10K (1/0.0001.). Also > remember that WiFi aggregates so transmissions have multiple packets and > long transmits will consume those 10K tx ops. One way to get around > aggregation is to use voice (VO) access class which many devices won't > aggregate (mileage will vary.). Then take a packets per second > measurement with small packets. This would give an idea on the frame > scheduling being AP based vs EDCA. > > Also, measuring ping time as a proxy for latency isn't ideal. Better to > measure trip times of the actual traffic. This requires clock sync to a > common reference. GPS atomic clocks are available but it does take some > setup work. > > I haven't thought about RU optimizations and that testing so can't really > comment there. > > Also, I'd consider replacing the mechanical turn table with variable phase > shifters and set them in the MIMO (or H-Matrix) path. I use model 8421 > from Aeroflex > . > Others make them too. > > Bob > > On Thu, May 14, 2020 at 9:43 AM Tim Higgins > wrote: > >> Hi folks, >> >> I decided to publish some details of the hoops I've been jumping through >> to try to find benefit from OFDMA. >> It's proving very hard to do. >> >> >> https://www.smallnetbuilder.com/wireless/wireless-features/33222-does-ofdma-really-work-part-1 >> >> I'll publish results from real devices next. But I'm still trying >> different things to get SOMETHING to show an improvement from OFDMA. >> >> Suggestions are welcome. >> =========== >> Tim >> _______________________________________________ >> Make-wifi-fast mailing list >> Make-wifi-fast@lists.bufferbloat.net >> https://lists.bufferbloat.net/listinfo/make-wifi-fast > > --000000000000ef687605a5a2940b Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Also, forgot to mention, for latency don't rely on ave= rage as most don't care about that.=C2=A0 Maybe use the upper 3 stdev, = i.e. the 99.97% point.=C2=A0 Our latency runs will repeat 20 seconds worth = of packets and find that then calculate CDFs of this point in the tail acro= ss hundreds=C2=A0of runs under different conditions. One "slow packet&= quot; is all that it takes to screw up user experience when it comes to lat= ency.=C2=A0

Bob

On Thu, May 14, 2020 at 2:38 PM Bob McMahon <bob.mcmahon@broadcom.com> wro= te:
I haven't looked closely at OFDMA but these latency numbers seem w= ay too high for it to matter.=C2=A0 Why is the latency so high?=C2=A0 It su= ggests there may be queueing delay (bloat) unrelated to media access.
Also, one aspect is that OFDMA is replacing EDCA with AP scheduling per t= rigger frame.=C2=A0 EDCA kinda sucks per listen before talk which is about = 100 microseconds on average which has to be paid even when no energy detect= .=C2=A0 This limits the transmits per second performance to 10K (1/0.0001.)= . Also remember that WiFi aggregates so transmissions have multiple packets= and long=C2=A0transmits will consume those 10K tx ops. One way to get arou= nd aggregation is to use voice (VO) access class which many devices won'= ;t aggregate (mileage will vary.). Then take a packets per second measureme= nt=C2=A0with small packets.=C2=A0 This would give an idea on the frame sche= duling being AP based vs EDCA.=C2=A0=C2=A0

Also, measuring ping time= as a proxy for latency isn't ideal. Better to measure trip times of th= e actual traffic.=C2=A0 This requires clock sync to a common reference. GPS= atomic clocks are available but it does take some setup work.

I hav= en't thought about RU optimizations and that testing so can't reall= y comment there.=C2=A0

Also, I'd consider replacing the mechanic= al turn table=C2=A0with variable phase shifters and set them in the MIMO (o= r H-Matrix) path.=C2=A0 I use model 84= 21 from Aeroflex. Others make them too.

Bob

On Thu, May 14, 2020= at 9:43 AM Tim Higgins <tim@smallnetbuilder.com> wrote:
=20 =20 =20
Hi folks,

I decided to publish some details of the hoops I've been jumping through to try to find benefit from OFDMA.
It's proving very hard to do.

https://www.smallnetbuild= er.com/wireless/wireless-features/33222-does-ofdma-really-work-part-1
I'll publish results from real devices next. But I'm still tr= ying different things to get SOMETHING to show an improvement from OFDMA.

Suggestions are welcome.
=20
=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D
Tim
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Make-wifi-fast mailing list
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https://lists.bufferbloat.net/listinfo/make-wif= i-fast
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