Apple Catalina Appears to Introduce Massive Jitter - SOLVED!

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.

Mark.

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 
> balancing.
>
> (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.
>
>         --karl--
>
> 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:
>>
>> https://developer.apple.com/forums/thread/97805
>>
>> ... I was able to fix the problem by disabling Bluetooth.

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