What could cause periodic DSL problems?

I currently have DSL through a local ISP, though the line actually belongs to Verizon. I’ve been trying to get my connection problems resolved for going on a month now, and I’m at something of a loss.

The behavior that I’m experiencing is that I cannot keep a good connection for more than about five minutes at a time. I put together a test script that pings once every ten seconds, and when I graph the results they are exceptionally regular; 4-5 minutes of good connection (response in the 15-20 ms range) followed by 2-3 minutes of no or poor connection (responses in 1500-2000 ms range, or no response).

Here are the scenarios tested, all exhibiting the same behavior:
[ol][li]Computer hooked up to router, which is hooked up to DSL modem[/li][li]Computer hooked up directly to DSL modem[/li][li]Same as 1, with a replacement DSL modem[/li][li]Same as 2, with a replacement DSL modem[/ol][/li]A field tech came out and tested from the demarc and declared everything fine. Since I wasn’t home at the time, they considered that the end of it. Verizon now says it must be an internal wiring problem, so I did one more test. I hooked the modem up to the test port on the demarc, connected the router, and then repeated the test, getting exactly the same behavior. Verizon still insists there is no problem.

I am as certain as I can be that this is a Verizon problem, so I guess what I’m looking for are suggestions as to what I can say to them that might expedite the resolution. You know, something like “I’ve seen this problem before where the oscillation overthruster at the CO had a warped core matrix. Have you looked at that?”

Any ideas?

I had problems with my DSL connection that I eventually traced to a defective router. But in my case it worked fine when the computer was connected directly to the DSL modem, and worked fine once I got the router replaced under the warranty.

What haven’t you replaced? Are you still using the same power brick with the old and new DSL modem? How about the network cables?

And I assume that the new DSL modem was provided by Verizon, right?

I would guess it’s a line problem. I would assume the verizon tech tested during a “good” phase in your cycle.

Do any of your neighbors have the same problem?

Dewey Finn, the entire DSL setup was replaced; modem, phone cable, network cable, power brick. The new modem came from my ISP, just like the previous. And to add just a wee bit more information, in the last test (modem connected to demarc) I used a different computer to test, my work laptop using wireless to the router. Same behavior as with my desktop.

Maus Magill, to the best of my knowledge none of my neighbors have DSL. Verizon just recently made it available in my area, so I expect I’m reaping the rewards of being on the leading edge. What makes me think equipment rather than line is the absolutely regular pattern, which suggests to me a failing electronic component, either at the pole or the CO, rather than a line problem.

I applaud your scripting approach – brilliant! Can you change the script to send a ping 1 or 2 seconds after receipt of last packet, or timeout, and provide a little more data, specifically:

  • mean uptime (sec), standard dev (sec), min-mean-max ping when “up” (ms)
  • mean downtime (sec), standard dev (sec), min-mean-max ping when down (ms - let a timeout = 2000 ms or what-have-you).

I suspect that there is a piece of hardware that is duty-cycling your connection, and that since you’re seeing ~5 minutes up and ~2.5 minutes down, it’s cycling you through three pieces of hardware: two good, one bad. If you’re not doing so already, consider pinging a dotted quad address rather than a named host – if the results differ, consider manually removing the “bad” DNS from your list.

If you can show them that periodicity, and explain to them that – with their help – you’ve already tested everything inside your house, then you might be able to convince them that you’re interested in helping solving their problem for the benefit of all involved.

…and that if they aren’t, you’re interested in switching to a cable modem ISP. :smiley:

Jurph, thanks for the suggestions. Unfortunately, I had to go out of town for a few days, but when I returned I had a message from Verizon that it was a problem at the CO and that the bad equipment had been replaced. All is now well, though the customer service makes me think that maybe cable would have been a better choice.

No, I’m sorry, but this stretched credibilty. Verizon does not make mistakes. You must have misheard teh message.