Troubleshooting dropped DSL connections

By raheem

I am helping a client troubleshoot issues with their DSL connection that drops about 2-3 times a day. The DSL modem had already been replaced but it just made the problem worse. I used the steps below and the links at the bottom to troubleshoot the issue.

1. Collect information – Collecting the following info will make the troubleshooting process a little simpler

1. DSL Modem username and password

2. If you are using a separate router, collect the username and password for the router

3. Your DSL provider’s technical support number as well as your account number

4. DSL phone number

5. When the DSL goes down, what lights are blinking, what lights are solid (good) and what lights are red (bad)

6. Find the IP address of your DSL modem. You can do so by typing the ipconfig command in a command prompt and hitting enter. Go to Start -> Run -> type in ‘cmd’ without the quote and hit enter. A black command prompt window will open. Type “ipconfig” (without quotes) and hit enter. The output of the ipconfig command will look similar to the image below. The Default Gateway listed is most likely to be your DSL modem’s IP address. THIS IS NOT TRUE IF YOUR COMPUTER CONNECTS TO A SEPARATE ROUTERS LIKE A LINKSYS OR NETGEAR. In my case, the default gateway is 192.168.1.1:

2. Remove unnecessary devices – The goal is to isolate the problem to specific devices. This can be done by removing other devices from your network such as routers, switches, etc. If you unable to remove devices, ensure that the laptop or desktop you are using for troubleshooting is connected directly to the DSL modem.

3. Ping your DSL modem while internet is down – Pinging is a simple communication test that verifies the connection between two devices. A successful ping test from your desktop/laptop to the DSL modem will verify that the problem is not between your computer and the DSL modem. Perform a ping test using the steps below:
1. Open a command prompt and ping your DSL router. See step 1.5 above on how to find out your DSL modem’s IP address.
2. Type “ping i92.168.1.1 (replace with your DSL modem’s ip address” (without quotes). If you receive a response like “Reply from ..” four times – then the connection from your computer to the DSL modem is good. If you get a response saying “Request Timed Out” four times, then the connection between your computer the DSL modem is problematic. In this case, change the network cable from your computer to the DSL modem and do the ping test again.

4. Check the DSL modem’s transceiver statistics – The DSL modem’s transceiver statistics can give clues as to whether the problem lies with the DSL line. Check these stats using a browser and entering the DSL modem’s IP address. You may need to enter a username or password to login. Depending on the DSL modem you have, the transceiver statistics can usually be found in the Monitoring or Advanced Monitoring sections. Below is an example of transceiver stats:

Transceiver Revision: 4.3.0.1
Vendor ID Code: 4
Line Mode: ADSL2+ Mode
Data Path: Interleaved

Transceiver Information Down Stream Path Up Stream Path
DSL Speed (Kbits/Sec) 3355 863
Margin (dB) 18.5 12.0
Line Attenuation (dB) 47.0 28.5
Transmit Power (dBm) 20.4 12.1

The two main figures are the Margin and the Line Attenuation. The margin shows the signal to noise ratio. Use the guide below to judge the margin ratio:

1 dB < 6 dB Bad
7 dB < 10dB OK
11dB < 20dB Good
20dB < 28dB Excellent

Here is the guide for the Line Attenuation figure

0 dB < 20 dB Outstanding
20 dB < 30 dB Excellent
30 dB < 40 dB V. Good
40 dB < 50 dB Good
50 dB < 60 dB Poor and may experience connectivity problems
60 dB and higher Bad

Problems with the margin and line attenuation indicate that the issue is with your DSL line/service. Try step 5 below if possible.

5. Test the NID – the NID is a phone box that is found outside your home. It contains a phone jack. You can read more about finding the NID here. Plug in the DSL modem to the NID’s phone jack and check the modem’s transceiver stats as described in above step. If the margin or line attenuation statistics improve, then the problem is with the wiring from the NID to your DSL modem. Your DSL provider will usually charge for such repairs as they are only responsible for ensuring service to the NID. Anything from the NID to your home or office is your responsibility. Even if the phone company charges extra, it’s best to get them to do such repairs.

6. Call your DSL service provider

Useful Links
How do I check modem stats & event logs? What do the numbers mean?
Troubleshooting sync issues