Last night, my home internet access, provided via cable modem, went bad. It's still up, but I'm getting 10%-25% packet loss. We had a small ice storm yesterday, and I would be surprised if it wasn't a major culprit.

So this morning, I went outside to my demarc to see if there was anything that looked storm damaged. Nothing storm-related really jumped out at me, but I noticed that the grounding wire had snapped off of the coupler, and there was generally a lot of corrosion. There was no lightning in the storm, so I don't think that the lack of a ground fried the modem, and the corrosion might have been dessicated dielectric grease.

The connections were like this: the cable from Time Warner was connected to a coupler, which is where the ground was/would have been attached. There was a 6 inch cable running from the coupler to the input of a 3-way splitter. There were cables attached to all three outputs, but only one of those is attached inside the house. I don't know which is which, sadly. The splitter was marked to show -7dB on two of the outputs and -3.5dB on the third.

I figured a reasonable idea was to connect the cable modem's line directly to the main cable, and lose the splitter. Figuring that it would be easy enough just to try all three cables, I connected one of them up. It didn't seem to work, so I connected the second. It also didn't work, and I connected the third, which still didn't work. I played with a lot of things before I gave up and just put it back the way it was. At which point, my internet service came back up, with about the same signal quality as before.

So what I want to know is: is there some reason that it would work going through the splitter, but not when hooked up directly? Obviously, it's easy enough now to figure out which cable is which; I can just unplug them one at a time until my service goes out. But I tried all three. Why would it fail that way?

One handy thing that could help troubleshoot it is the signal status as reported by the cable modem. It should be accessible at http://192.168.100.1/ .

I have no access to the cable modem, sadly.

Well.. the obvious thing is to reconnect the earth on that external splitter. It might quiet things down a little, or not.

Cheers

I forgot to mention that I did that already.

Okay, I went back outside and found which cable was the right cable. It worked, albeit miserably, through the coupler and splitter, but as soon as I got rid of the splitter, it just didn't work at all. Then I got rid of the coupler and plugged the input cable directly into the splitter. That didn't really seem to help. Then I moved the output cable from the -3.5dB output to one of the -7dB outputs, and my packet loss seems to have gone away. The ping times jitter quite a bit, but throughputs are back to about 75% of what I got on Thursday. Certainly far more usable than it's been in 24 hours.

Does it make sense that the signal from Time Warner needs to be attenuated, or am I drawing an invalid conclusion?

It can do. If the signal is particularly strong then it will overwhelm the receiver inside your cable modem. They're designed to operate within a certain amplitude range of signals.

Go call for an engineer to come out.

Ha! That even works for the Motorola Surfboard modem I have.

Yeah, I already did that, too, but it's the weekend and no one has shown up yet. I did get a call back that "I see that everything is on line and seems to be functioning properly. I'm not getting any errors at this time." So I had to reopen the case, delaying my repair, which is when I decided to fiddle with it myself.