My DSL internet connection has been very unreliable and slow recently. I called my service provider this morning and they told me that they will be sending someone to my home this weekend to fix it.

They told me that he would be inspecting the hardware between my home and their office, and if no problem is found there, they said that he will be checking the wiring inside my house. In the case that the problem is found in the home, I'm told that I'm looking at a minimum 85 USD charge.

I would like to know how to make the most of this service call.

Is there anything I should be checking in my home or researching prior to the service call? Are there certain questions I should be asking or certain information I should provide to the technician to have the best chance of getting this fixed?

Let me provide some more details about the problem I'm trying to solve.

My home is a two-story house with a basement in the suburbs of Denver, Colorado, USA. I've had no trouble with any of the utilities since moving in about 40 days ago. I am paying for 20 Mbps service from Century Link.

A few weeks ago, I had a similar problem. The technician told me that his computer indicated that my modem didn't have a good connection. The problem seemed to be fixed when we tried connecting the modem to a different phone jack. However, the problem came back today. They said that they were going to do something on their end, but whatever they did actually made it worse!

  • In response to the answers below, I would like to add that there are no landline phones installed in my house and I am paying Century Link just for internet service. Feb 6 '14 at 1:16
  • So they hooked up brand new lines for this? Or did they use what was there (meaning you have empty land lines somewhere)?
    – DMoore
    Feb 6 '14 at 3:31

Since all the telephone companies were deregulated, the practice is to have a demarcation point (which I'm really surprised no one else has mentioned yet). Most homes built within the last 20 years or so will have one, which will be a box or jack (often marked "DEMARC") marking the change in responsibility between their network and your in-house wiring.

Demarc box Demarc jack

Presumably, being a DIY site, you'd like to avoid being charged $85+ for something you can fix yourself, so there are really two steps to take:

  • Isolate the problem to either their equipment or something before the demarc, or your in-house wiring
  • If after demarc, isolate the problem to a particular jack

Connect your modem to the demarc

Best thing to do is disconnect all your house wiring from the demarc (usually it plugs in) and connect your modem to it, then run speed tests or whatever else. You may also want to try a different cable just to eliminate that.

Plug your PC/laptop directly into the modem if you can, to eliminate router/wireless, or at least plug your PC directly into to the router.

If you still have the problem, then it's either a problem with the wiring before the demarc, or your modem (both of which are the company's responsibility), or something on your PC/router (which they'll charge you for, and off-topic for this site).

If your Demarc is outside, you'll have to be a bit more creative, but at least you can just have one jack connected at a time (see the in-house wiring bit below).

Create a Demarc

If you have a wire that comes in and is directly hardwired to the house wiring, I'd suggest cutting it off and putting a demarc jack in (like the second picture).

Use a second jack to hardwire the rest of your house to, then a regular station cord to patch between the two. This also lets you disconnect the patch cable in order to do work on in-house wiring without worrying about shorting anything out or shocking yourself.

In-house wiring

If it's working at the demarc, the you've isolated the problem to the house. This could be much harder to diagnose.

If you have the same number of wires as jacks, then you have centralized wiring. If not, you probably have a harder-to-diagnose mess.

Wiring Topologies

The new way: Star topology

If you're lucky, each jack will have its own cord coming back to a central location, where they'll probably all be connected together. Detach all but the one you're using (this may take some trial and error) and try the modem there. If it works, then there's a fault in another wire and you can isolate that one-by-one, or just leave it disconnected. Repeat for another jack or two in the house.

The old way: Branching/Daisy-chaining

Technically for phones to work, the ring and tip wires just need to be connected in parallel. Many times the jacks are all or partially daisy-chained, or even worse, there are junction points hidden in the walls, in whatever way works to make the shortest wiring possible. One of the problems with this is if there's a fault, it's extremely hard to find.

You pretty much have to follow the same steps -- trying to isolate lines -- but you'll have to disconnect wiring in the boxes around the house (and hope there are no hidden junctions). It may be simpler to just run a new jack and new wiring from the demarc to the spot you need, and leave everything else disconnected.

  • This is highly regional. Most areas do not have DEMARC at homes. In a business yes. Also I am not sure I would tell a home owner to disconnect anything in their home either - especially if they are asking a question on how to troubleshoot. In home wiring is like 5% of the reason behind these and 90% of the 5% is telco equipment gone bad or set up wrong. Understand where you are going but skipped this stuff on purpose.
    – DMoore
    Feb 6 '14 at 3:41
  • In my case the demarc is just a piece of bakelite with a few brass bolts. my sister's house is the same. The main difference is her house only has one phone jack connected; which is less than 6 inches away. Feb 6 '14 at 4:55

Not much you can do other than make it easy on the technician to access all of your phone jacks, POTS runs, and where it enters the house.

In my experience, however, the problem is likely on their end.

If you want to test it yourself, find the line closest to the point it comes in to your house (the point just after it leaves the Century Link Box) and wire a jack there and plug in your modem. If that fixes the problem, then you can assume it is on your end and you might as well fix that yourself if you don't want to pay their hourly.

Also note that other devices plugged into the land-line can interfere with your DSL. So also make sure every other device is unplugged and test your DSL connection again.


Well not to get into DSL troubleshooting but might as well throw this out first:

  • When getting DSL service you may need to have filters on all phone jacks - even those not used.
  • However you may or may not (you shouldn't) need a filter on the jack supplying your modem a feed.
  • If you have a dual jack for your modem then I would try first unplugging phone from other line, plugging in phone if none, and getting rid of splitter (and also doing each of these with and without filter).
  • switch out modems - I can't tell you how much time and troubleshooting goes on when there is a modem slightly going out. Also make sure your modem isn't getting too hot or in an enclosed space.

As a home owner I would do the following:

  • trace modem phone line all the way to outside house. Make sure that the cable isn't cut or crimped bad anywhere.
  • make sure that I have all of my current phone jacks are working
  • make sure these areas are accessible to the tech
  • make sure a phone is plugged into each jack and then also unplug each jack (do this one by one)
  • unplug modem before I go to bed. Plug it in again in the morning. Usually having modem unplugged for that long will take your connection off the telco's bad/abuser list. If you have a pretty good connection at first and it goes downhill quickly - probably the modem - 90% of the time. The other 10% might be something in your house or in your neighborhood.

Common Issues:

  • You moved in 40 days ago so you have little history with house wiring. I am going to assume something was wrong with the phone wiring when you got the house. For instance when I was renovating my basement I cut off a phone wire that wasn't needed. My DSL went haywire. I informed telco of this and they said it shouldn't have mattered. It did. As soon as I rewired it and hooked up a phone w/ filter it worked fine. So I just got rid of DSL instead of troubleshooting their bugs.
  • There isn't an issue like the one described above but the equipment or line can't handle throughput. This sends errors to telco equipment. Then automatically telco filters or turns off your connection - or at least slows it down. You are mad, tech doesn't even realize your connection has been turned down and so on... (I managed an ISP call center for 5 years)
  • Something happened to phone line. Animal bit through it, you accidentally hit it or pulled it when doing something, who knows.
  • bad modem - if you own the modem they could charge you for call. If you rent it it is on them. Make sure tech has a good modem he brings with him on call. This may seem obvious but not all techs work for that company and he might need to pick one up.

Bottom line is unless you changed their equipment in your home since install they should fix it for free. You are a new account and they did not run the proper tests to make sure you were working correctly or they have bugs in their network. And sometimes these bugs are fixed with rewiring the house or adding new equipment or shutting down unused lines properly. But unless you did something to their stuff it shouldn't be on you.

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