So, you are on ADSL or ADSL2/2+ and are having some problems, someone has told you to do an isolation test and you have no idea what that is.

What is an Isolation test
An isolation test is when you remove all telephony devices in your premises from the phone line. These include ADSL filters, phones, faxes, answering machines, Foxtel Digital (or any other Digital PayTV) set top box, EFTPOS machines, back-to-base alarm systems, dialup modems, medical alerting systems etc – basically anything that plugs into the phone line. Small businesses might even have unexpected devices like soft drink vending machines plugged into the line, check thoroughly.

The purpose of removing all devices from the line other than the ADSL modem is to eliminate any source of ADSL disturbers (noise sources) that might be caused by electronics in your premises. These are a frequent source of problems.

After all devices have been removed, plug your ADSL modem directly into the first phone socket into the house, bypassing any ADSL filters/splitters (just to eliminate these as a possible problem). The first socket is generally the one in the common area of the house (kitchen or lounge/front room), but you may have to consider where the line comes into the house and trace it if necessary – especially if multiple sockets have been installed. If in doubt, try all sockets and record the results. Use the shortest phone cable you have (ie 1-2m), and try another phone cable if there is no luck with the first. Try various phone sockets in the house if what you think is the first socket doesn't work; it's not impossible for a single socket to have a fault, and if the house has a central filter fitted then some sockets may have no ADSL signal at all by design.

Monitor the Internet connection for the difficulty you were experiencing to see if it clears. If the problem is still there, refer to the notes below.

If the difficulty you were experiencing clears, then you can connect one filter and one telephony device to your phone line, and monitor your internet connection again for the difficulty you were experiencing. If the problem recurs, don't forget you have attached at least three components to the phone line circuit – filter, line cord and telephony device – four, if the filter also requires a separate cord to connect to the socket. DO NOT ASSUME. Swap out EVERY COMPONENT one by one to ensure you accurately sectionalise the fault into one piece of equipment.

What is the purpose for doing an Isolation test
If you are having issues with things like your connection dropping out (modem losing ADSL sync), noise/static on your phone line, slower speeds than usual, then this test can help isolate the issue.

All these issues are often caused by some form of interference induced into line, which could be a result of bad filters, dodgy phone cables, malfunctioning telephony equipment, or even nearby electrical devices. Ensure that "pest-it" and other electronic rodent repellers (like the devices Dick Smith and others sell) are removed from power points – these often cause problems with ADSL signals. The same goes for any electrical equipment capable of generating an electromagnetic field, such as fridges/freezers, air conditioners, compressors, cordless phones, microwave ovens, fluorescent lights etc. This alone is a good argument for not using extension cords, as they act as an antenna for electromagnetic interference induction – their flat-wire (non-twisted pair) construction is unable to reject external sources of EMI which result in line noise.

Notes

1. If after you have done all this and still having issues, it isn't always a problem with your line outside your house (Telstra's boundary), it sometimes could be an issue with your internal wiring (eg a mouse could've chewed the wires in your roof). Issues can also arise with corroded cabling/sockets, problems with hardwired equipment that can't be removed (alarm systems, wallphones, ringer bells), or internal cabling that won't support ADSL due to faulty installation – the latter is why you try all the sockets.
2. If after you have done all this and still having issues, it isn't always a problem with your line outside your house or your internal wiring. It may be possible that your modem has gone faulty and would be good if possible to test with another modem.
   If you have completed your isolation tests and still have no ADSL connection, an unstable connection, or a poor speed issue etc, it's time to escalate the problem to your ISP and let them launch an investigation for you. It's in your best interest to complete this process first though for several reasons:

• If the problem is on your end, you can clear it quickly yourself.
• Your ISP will ask you to do it anyway, both for speed and to protect you – see point 3 below.
• If a Telstra tech finds the problem is beyond the Telstra Network Boundary Point (NBP), they not only charge you a callout fee starting at $130 (plus $38 for every additional 15 minutes), but they may leave the problem as is and walk away. This is because any and all wiring, sockets, equipment and connections downstream/past the NBP are your privately owned equipment, which Telstra can not service. Doing your isolation test thoroughly eliminates this as an issue, protects you from being charged this fee, and allows you to correct any issues with your own equipment more quickly than waiting for a Telstra tech to do so.