Dropped packets on 5GHz band only

[jm_ranger]

Just trying to confirm if I'm the only one with this specific issue, and if others have clues or suggestions.

Since upgrading my M1 Air to Monterey (12.0.1 and 12.1), FaceTime calls are unstable and frequently drop. Same on Zoom calls, although in that case, symptoms are audio or video freezing instead of call dropping.

i found that if I ping my router at the same time, I get lots of dropped packets, sometimes 10-20 in a row. I can also get pings to get dropped simply by running a benchmark on speedtest.net (although it might takes 10-30 seconds to appear, so I sometimes have to run the benchmark twice back-to-back to see the issue). Sometimes, the ping drops will continue for a few seconds after the speed test has completed.

But I just now realized that this only happens on the 5GHz band - it doesn't happen on 2.4GHz or when connected via a USB-Ethernet adapter.

The router runs OpenWRT, so I installed tcpdump. That shows that the dropped packets are all dropped on the "request" path, never on the reply.

The Air is the only device on the 5GHz band, although interference with other nearby networks is possible. The internet connection is 100Mbps up/down. The access point is WIFi-4 (802.11n), and gigabit on all lan & wan ports.

I was unable to reproduce on two other 5GHz wireless networks. Both were 802.11ac, one with a 15Mbps up/down connection, the other 300Mbps up/down.

I reinstalled the Air from scratch with both 11.6 and 12.1 over the Holidays, and was able to confirm that I only had the ping drops on Monterey, but hadn't figured out the link with the 5GHz band then.

My personal opinion is that there's a glitch in the MacOS wireless driver (or firmware), where it incorrectly calculates the best buffer size, creating bufferbloat.

Ideas ? Thanks.

 

[ChargerDad]

I'm experiencing something similar on 12.1 with the Macbook Pro 16 M1. On fresh boot, performance is fine, but over the course of a couple days, I will start to have issues with real time video and audio streaming on Webex like you are experiencing with zoom. If I ping my router or AP (also OpenWRT), I will notice intermittent spikes and/or drops in ping responses, from 3/4 ms to over a second with some drops. These coincide with the audio and video issues on webex meetings. A reboot fixes the issue for a couple days. I'm hoping 12.2 resolves the issue, but this is a corp laptop and they haven't released 12.2 as of yet.

 

[jmranger]

Thanks for chiming in.

Sorry to be the bearer of bad news, but 12.2 doesn't address the issue in my case.
Would you mind providing a bit more details about your setup? Which router do you have? And what you see for the Security, Channel and PHY Mode fields when option-clicking on the wireless menu, on the top right corner of the Mac screen?

In my case, it seems that I can work around the issue by configuring the router to only use 20MHz-wide channels - at the expense of a significant impact on the wifi performance. On the 2.4GHz band, while in theory, 40MHz channels are possible, there's pretty much always too many other networks around, so it always fallback to 20MHz. So the issue might not be with the 5GHz band, but with 40MHz channels instead.

I did sign-up for the MacOS Public Beta program, in part to figure out if future versions will have a fix, but also to be able to access Feedback Assistant, Apple's tool for bug reporting. My report is 10 days old, and at the "Open, no other recent similar report" state.

 

[ChargerDad]

I have a Linksys WRT32X running OpenWRT 19.07.8
Security is WPA2 Personal
Channel is 36, 80 MHz
PHY Mode: 802.11ac

Interesting on the channel width.. I really don't want to go to 20MHz, but may have to test that.

 

[jmranger]

Sorry for the delay. Thanks for the info.
So there goes my idea that this was a 802.11n-only issue.
You might want to try 40MHz first - I went to 20 since it's the first step down from 802.11n's max of 40.

It looks to me that MacOS 12 has a fancy algorithm to evaluate the available bandwidth, and that it gets it quite wrong in some cases. But not often enough for a lot of people to be impacted.