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Cable Modem High Latency with Zoom and VPN Login issues


OK, this is a strange bug that you need to watch out for. With all this work-from-home, I’ve had trouble on one machine getting onto our VPN. And while we’ve not had much trouble with Zoom and so forth. We are lucky to have 300Mbps/20Mbps upload with Comcast. However last night, suddenly Zoom really slowed down. The video would hang and so forth, so here is how to diagnose this with all the new tools that Zoom has:

  1. First of all, in Zoom/Preferences/Statistics/Video is new to me but definitely your friend. You can look at the overall performance and also the Video performance. You should see something like latency of something like 100ms or less and then fps in the 24-30 fps with 640×480 being what we normally see sent.
  2. If you don’t see this, for instance, I was seeing latencies of 1,000ms (so it was like talking on satellite) and 2fps with 320×180 frames, then you know that you have a problem.
  3. Now the obvious step, reboot your computer and make sure you have the latest Zoom version. Then Option-Click your Wifi Icon, Zoom needs 1Mbps at least, but you should see what your Wifi speed is. In this machine’s case, it was running 800Mbps-1.3Gbps to the access point, so that probably wasn’t it.
  4. Then try to do a direct connection and see what happens. In this case, that really didn’t help, so you are left with a problem with your switch, cable modem, or maybe the internet is dead.
  5. So the best thing to do is to run a speed tester that also measures ping and latency like Cloudflare or the Malaysia Unifi Test (no relation to Ubiquiti) but the main point is that you should see latencies/ping on the order of 50ms and jitter something like 20ms. In this case, I could see that 1,000ms delay. That is enough for Zoom to allow audio, but video really falls apart. The audio works, but the 1ms delay means that another part of the problem is you keep stepping over each other in calls. As an aside, the typical Speedtest that everyone runs is nice but without latency and jitter it is pretty useless for more than raw bandwidth and things like Zoom and games need more than just raw speed. I do use it because it has histories, but to really debug, use Cloudflare because it not only shows you average latency but a distribution of pings as it is running….
  6. Now you have to figure out what the issue is. If you are lucky enough to have a Ubiquiti Dream Machine or Dream Machine Pro, this is way easier, the older dashboard would actually show you historical speeds and latencies (they use a ping test). So I could see immediately that for the last 24 hours, latency (aka ping times were over 1 second).
  7. One frustrating and confusing aside is that Unifi is in the process of changing their whole user interface, so there is the classic Dashboard which includes a measure of 24-hour network bandwidth and latency, but the new Dashboard does not have that and I can’t seem to find latency pinging.
  8. While I love Ubiquiti, their software management is pretty confusing, they have new settings panels and old ones because they are slowly porting controls and so forth. Nevertheless, the new dashboard does at least give you network speeds up and down and tell you how your network is doing. Too bad it doesn’t also measure latency and do pings (at least that I could find). So to find it in the new interface, go to Performance/Speed Test STats and you will see the measurements that it is running.

This was a super revealing chart for me, you can see that starting two days ago, latencies suddenly went from essentially zero to 1.5 seconds.

So the question is what would cause this. From experience, I’ve seen that when there is a lot of network traffic from different clients, then the Cable Modem will slow down. This could be related to the Intel Puma 6 chipset that is in the Arris modem I’m using.

The solution is pretty simple. You have to reboot your cable modem and hopefully it all comes back to the correct ping times.

If that is not the problem

Well then you have to go back and figure out what the issues are is not the modem, then you are left with where is the network slow, so you’ve validated all the way back, the next step is to start:

  1. Connect your laptop directly to your cable modem and bypass everything. If it works and you have low ping times and good speeds, then connect farther back until you find the device that is the problem. So plug it into your router and then each switch. It takes time, but perhaps one of those devices needs to be rebooted.
  2. If that isn’t it, then it could be the laptop itself, so try a different one. See how it works. If the ping times are shorter, well then it is reboot and maybe even reimage the laptop time.
  3. Finally if that isn’t it, then it I’m out of answers and time to send me a note 🙂

How to prevent this in the future monitor Zoom stats and network stats

Well the main thing is that when I’m on a Zoom call, I have the Unifi network speed charts up and running so that I can at least see what the network is doing.

Also for really mission-critical stuff, you can have the Video Performance in Zoom up and running as well this tells you how many frames you are setting and getting. While the current Zoom Dashbaord doesn’t show latency, you can at least see what the uploads are and that is useful.

That’s nice but what are latency and jitter

Ok, I just realized that while speeds may be obvious, these terms are not. Latency means, what is the delay between the time you send something and when it actually arrives there. You can have a very fast pipe like 1Gbps, but if it takes 30 minutes to get there, it is pretty useless for two way communications. What was happening on our network was that we were getting high speed, but it was taking over one second for an internet packet to go from our home to somewhere else.

Jitter means what is the variance in deliver of packages. You want a nice steady stream of data getting sent. On the internet, data is divided into packets of information and jitter measures the inter packet changes in timing. Again, it works way better to have that low. You can think of jitter as how the latency varies.

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