Apple Catalina Appears to Introduce Massive Jitter - SOLVED!
mark.tinka at seacom.com
Sun Nov 1 15:15:39 UTC 2020
Thanks for the input, Karl.
Hopefully someone from Apple is around here and can get some ideas on
how to fix this particular problem set.
On 10/31/20 11:37, Karl Auerbach wrote:
> Let me jump in and add a bit more information.
> I am not an RF guy - I stopped playing with radios [and TV] in the
> days when they used vacuum tubes (yes, really.)
> Many laptops share radio and antenna resources between WiFi and bluetooth.
> Bluetooth lives on the 2.4ghz band. Wifi presently uses both that
> band and also a 5ghz band. Different antennas might be used for each.
> I encountered Wi-Fi/Bluetooth contention issues a couple of years back....
> My home wifi has (or rather had) distinct SSIDs for Wifi on the 2.4
> and 5ghz bands. It was a rough attempt at manual load and distance
> (Our house is in a relatively quiet area, RF wise, so there's not
> really any seriously competing wi-fi - or for that matter cell signal,
> broadcast TV, or FM radio.)
> I began to notice that when I had one of my laptops on the 5ghz WiFi
> and was listening to music via some bluetooth speakers that my remote
> terminal keystrokes sometimes had that sluggish feel that is familiar
> when doing remote terminal command-line stuff over long paths with a
> lot of latency/jitter. And at the same time the music via Bluetooth
> often broke up or stuttered. There was a clear correlation between
> the two problems.
> I had heard from some Linux kernel developers that deep down in the
> Linux kernel the simultaneous use of Wifi on a 5ghz channel and
> bluetooth on 2.4 causes a lot of thrashing and flogging of the the
> radio system. I don't know, but I suspect that as a result there are
> queues of outbound traffic waiting for the radio or antennas to become
> operational on the channel they need. I have no idea what happens to
> inbound frames when the radio system is tuned elsewhere - I never
> measured whether the frames are lost or delayed.
> I suspect similar issues are present in *BSD, MacOS, and Windows kernels.
> So I did some simple empirical testing to compare life with the laptop
> coerced to use an SSID present only on the 2.4ghz band. The problems
> went away.
> I went back to the laptop, but coerced onto the 5ghz band for WiFi
> and, voila, there was trouble.
> I've done this with a MacBook Pro (circa 2015 model) using various
> versions of MacOS and with my rather newer Linux laptops (mostly Dell
> XPS units with Fedora.) Same sorts of behavior.
> These were all i5 based units with 2 or 4 cores - plenty of CPU power
> to simultaneously handle an SSH remote console client and a music player.
> I did not test with mobile phone or tablet platforms.
> I do not know if the single radio issue is the result of cost savings
> or some radio-engineering or antenna issue. I do suspect that these
> things could become more troublesome as WiFi 6 and/or 5G start to use
> some of the higher frequency allocations around 5.9 and 6ghz.)
> (A few weeks ago we switched our home WiFi to a WiFi 6 [Netgear
> Orbi-6] mesh system that does not appear to allow separate SSIDs for
> the 2.4 and 5ghz bands, so I can not repeat these tests without
> constructing a test network with the now unused access points. BTW, I
> did encounter the hell that is known as "reconfiguring dozens upon
> dozens of different kinds of IoT devices to use a different SSID".)
> Looking somewhat off topic - it is my sense that we will be seeing a
> lot more latency/jitter (and packet resequencing) issues in the future
> as radio systems become more agile and as we begin to use shorter
> (millimeter) wavelength frequencies with reduced ability to penetrate
> walls that, in turn, cause more frequent access-point transitions
> (with possibly distinctly different backhaul characteristics). I've
> observed that these things can cause trouble for some TCP stacks and
> some non-TCP based VoIP and streaming applications.
> On 10/30/20 12:08 PM, Mark Tinka wrote:
>> Hi all.
>> So I may have fixed this for my end, and hopefully others may be able
>> to use the same fix.
>> After a tip from Karl Auerbach and this link:
>> ... I was able to fix the problem by disabling Bluetooth.
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