Packet Loss, Python Scripts, and the Dreaded Technicolor DPC3848V

Are Youtube videos pausing more often than they used to? Do websites speed up after restarting your modem? You might be suffering from cable modem packet loss!

After switching to a popular Canadian ISP, I experienced all of the above. Packet loss is a common network problem. It can be due to poor WiFi coverage, bad cabling, and umpteen other things. But, if you are one of the unlucky souls to receive a Technicolor DPC3848V, the problem might be your cable modem itself!

Technicolor modem spotted in its natural habitat. Snail photo: Zdeněk Macháček

Searching this model number reveals many forum users reporting the same issues. Here’s the frustrating part – the problem is a function of runtime. Tech support will ask you to restart your modem, but this only fixes the problem long enough to get you off of the phone. Then it’s back to slow, laggy internet!

The main tool I used to troubleshoot this problem was an installation of smokeping, which will happily run on any raspberry pi or Linux machine on your network – it is even available in most repositories. Smokeping will constantly ping whatever hosts or IP’s you configure, and graph the results. This is important – when problems are intermittent or take hours to develop, you cant reasonably sit at a PC running the ping command all day. Let smokeping do that for you.

Once you get smokeping configured, it will give you easy to read graphs in a web interface. Here’s how a smokeping graph looks when things are running well:

…and when things aren’t running so well:

While troubleshooting this issue, I had multiple technicians come by. Important note: none of them cared one lick about my graphs. They have their company tools, and that is all that they will trust. One of them even claimed to not know what packet loss was…?! Perhaps they are asked to play dumb, for the sake of unloading these terrible modems. Who knows.

Anyways, when technicians don’t understand “packet loss”, well, things don’t progress smoothly. It took 4 separate visits to correct the issue. While this lengthy troubleshooting dragged on, I couldn’t sit idly by. I fired up my code editor, opened the developer console in firefox, loaded up the admin page for the modem, and got to work reverse-engineering the admin webpage traffic. My first goal was to automate a reboot from my PC, and I was able to get this working in a python script without too much hassle – you can see the code here. With this simple script, I used cron to reboot the machine every morning. I managed to get some basic configuration working as well – you could use it to automate changing your wireless network name & password as often as you like. See for details.

Obviously, automating reboots is a very hacky fix – the only thing that fixed the issue permanently was insisting on a new brand of modem. Once the new modem was installed, the difference was night and day:

With my internet now working, I was able to stop reverse-engineering junky products and get back to what matters most: mindless internet consumption. Hopefully, this article helps someone – and, with any luck – that technician figured out what “packet loss” is!