Problems with an ADSL connection are often within your premises. For example, it could be a bad joint in the wire, the phone line is running alongside power cables, a faulty ADSL filter, or perhaps a low-quality phone handset.

The way to check if the issue is on your premises is with an Isolation test, and is essentially the same procedure that your telephone company will ask you to do for a bad telephone connection.

  1. Before starting the test, check the current SNR Margin, Loop Attenuation, Up and Down speeds as described in How can I know if I have a good connection?.
  2. Unplug all phones, fax machines, modems, etc. from the phone line used for your ADSL connection. Now plug in ONLY the ADSL modem and test the connection. Check the SNR Margin, Loop Attenuation, Up and Down speeds; as described in How can I know if I have a good connection?.
  3. If there is NO appreciable difference, then none of the devices which you have temporarily disconnected from your phone line are having a negative effect and any issues are either within the phone cabling on your premises and/or somewhere between your premises and the telephone exchange.
  4. If there is a difference between these values and your normal values, then reconnect one device at a time, rechecking SNR with each one until you identify the culprit (or culprits).
  5. Note that loose cables and faulty connections can also cause problems, as can faulty ADSL filters so you might like to try different combinations of device / extension socket / cable to determine which of these is the culprit.

Note that the Isolation test only tests the devices connected to your wall sockets. If Telstra test your phone line, they will test it at the point it enters the building (ie the cabling between your premises and the exchange). That still leaves the wiring inside your house, office or apartment building which hasn’t been tested and it may be worthwhile finding a contractor to check it and hopefully repair it for you if the Telstra technician reports markedly better results at the premises entry point compared to the sockets inside the premises.