This document is to assist in understanding and correcting issues with ADSL wiring within the customer premises. For general information on ADSL, visit How ADSL Works in our support pages.
Please note that in these diagrams, the lines leading to telephones imply a digital and/or multi-line system, and the lines leading to fax machines and modems imply an individual separate line operating on it's own telephone number. Also, modems do not need to be wired directly to the line as shown in some examples; the line can be wired to an RJ11 wall-jack and the modem connected to that jack.
Alarm systems often require a the same kind of copper connection as ADSL connections, which often results in both services being attached to the same line - usually a fax line. This can interrupt the ADSL freqency band or an entire line for many reasons (alarm tests, etc). Alarm companies often insist that the alarm be the first device on the line, however this is known to cause problems. This image shows the most common wiring situation, which is often problematic:
This setup can occur even without the ADSL filter by the fax machine, as that's not the real source of concern. Problems occur because the security/alarm system have the power to break the connection, leaving anything connected above it on the same line, like the fax machine and ADSL modem in this diagram, at its mercy.
The ideal configuration looks like this:
The POTS splitter divides the connection, leaving the security/alarm unit in-place on the same line, but separates the modem so that it doesn't rely on the unit to pass the signal through.
A POTS splitter is designed to separate the ADSL signal range from the telephony signal range. This has several benefits.
Businesses with a plain line but no security system attached to it are usually best to use a POTS splitter in this configuration:
A line filter is designed to block out the ADSL signal so that it doesn't bother another device. In a business where the ADSL connection is tied to the fax line, the fax machine can often complain and/or show poor performance from the extra frequencies it's getting. By attaching a line filter to the phone cable that runs into the fax machine, this can be resolved. This method will work, often reliably, but it is not ideal.
This doesn't, change that the modem is still getting the telephony/fax signals from the splitter, as drawn above. We always recommend that businesses consider POTS splitters over the regular splitter/filter combination.
|Description||Diagram Example||Actual Example |
|Demarcation Point - where the telephone wiring enters the premises|
|ADSL Modem - creates an internet link between the telephone infrastructure and the customer premises|
|Standard RJ11 (telephone plug) wall-jack|| |
|ADSL filter - installed on telephone lines to filter out the ADSL frequencies and improve phone audio quality|| |
|Security alarm system|| |
|POTS Splitter - separates the phone frequency range and the ADSL frequency range so they can be run on separate wires|| |
|Phone splitter - small, plastic & copper unit that plugs into a single wall-jack and gives two or more RJ11 plugs || |