Troubleshooting dsl connections

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Basic Concepts


ADSL (asymmetric digital subscriber line) operates over a normal telephone connection using ATM. The ATM signal is converted by a bridge (sometimes integrated with a router) into an ethernet connection.

DSL Status Lights

If you are using an ADSL bridge supplied as a part of a full or self-install kit, there will be a number of status lights which will assist you in determining the status of your connection

Depending upon make and model, the names for these status lights may vary, however common status lights are as follows:

  • Power: this light will indicate whether your bridge is presently plugged in and turned on
  • Sync: this light will indicate whether your bridge is able to detect a DSL-conditioned phone line. This light is sometimes labeled "ready" or "dsl." On most bridges, a red or flashing red sync light indicates that your phone line is impaired in some way.
  • Activity: This light will light up when information is being passed over the bridge. Some makes and models will have two separate activity lights, TX for tranmitting from your computer and RX for receiving from the outside world.
  • Ethernet: This light will indicate whether your bridge is able to detect an ethernet connection to a computer on your side of the DSL connection.

Types of DSL Problems

Most DSL connectivity problems resulting in a failure to use the internet fall under three categories. Troubleshooting methods vary depending upon the type of problem you are experiencing.

No Sync

One common symptom when your computer cannot connect via your DSL connection is a No-sync situation. This is when your DSL bridge does not detect your DSL circuit anymore, and cannot deliver your requests to the internet anymore.

Troubleshooting No Sync


It is possible for your connection to fail even when your bridge indicates that you have sync (your bridge detects your DSL connection).

Troubleshooting Sync-no-surf

Intermittent Sync

Some sync problems are not constant, with the connection coming up and down repeatedly at seemingly random intervals.

Troubleshooting Intermittent Sync