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Stages of DSL connection-making

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Revision as of 12:19, 13 February 2010 by Aa456 (talk | contribs)
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After powering up, a DSL modem typically goes through these stages:

  1. Self-testing
  2. DSL sync
  3. Authentication
  4. In-service


Upon power-up, a modem typically performs tests to detect proper operation of its hardware and to detect problems in its software and data. This stage usually takes only a few seconds.

DSL sync

The first stage of connecting to the internet is to obtain a 'link level' DSL connection to the Central Office. Once established, the modem will use this connection to carry internet traffic.

Obtaining and maintaining a good DSL connection to the Central Office is crucial to good performance. To maximize performance, the modem tries to sense the quality of your phone line and adapt to conditions. The most basic requirement is obtaining 'DSL synchronization' (detecting and locking onto the DSL signal).

Things that can go wrong at this stage include no connection to the phone line, electrical noise from other devices on your phone line (that's partly why filters are needed), low power signal caused by being far from the Central Office, electrical noise on the line from sources outside your location, and problems at the Central Office.


Once a DSL connection has been made with the Central Office, it can be used by the modem to talk with computers there. They require your modem to identify itself with a login and password (for billing purposes and security). Your modem can do this authentication for you but of course it must have been provided with the information.

The most common problems at this stage include not having correct login and password information in your modem, or temporary network problems that prevent the Central Office from confirming what your modem provides to it.


Finally, when a DSL connection is up and your modem has been authenticated and granted access, it tells your computer that it is ready. Your computer can then send and recieve information from the internet. Requests go from your computer to your modem via ethernet or wireless, then from your modem to the Central Office via your phone line, then from the Central Office over the network to whichever web site computer you specified.

Connecting to your modem

Your modem also looks for connections to your computer(s) via its ethernet ports or, if equipped and enabled, via wireless. The establishment of such links goes through similar stages as described above for DSL. Ethernet connections are usually quite reliable and trouble-free, but wireless connections can suffer from interference with other wireless signals.

Once you have a 'link level' connection to your modem, you can use a web browser to talk with the computer inside the modem, just as if it were a web site on the internet.