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.

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 labelled "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.

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.

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

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