ISDN lines

A basic ISDN line, sometimes referred to as ISDN2e, provides two 'channels', each of which can be used for separate calls, thus equivalent to having two regular lines. However they are usually linked through a telephone system in your office to give greater flexibility than 2 PSTN lines.

ISDN lines are most typically used to carry voice calls and are usually connected into a multiple user phone system through an in-house installed exchange box. On a digital line such as ISDN, analogue voices have to be converted to digital signals. Many ISDN terminal adaptors also provide 'analogue sockets' into which you can connect regular telephones services such as fax machines, answerphones or credit card machines.

As the number of ISDN lines you have determines the number of calls you can handle simultaneously (every ISDN 2e gives you a pair of lines) then you may of course need more than one ISDN line. Commonly, you might need multiple ISDN lines (called an ISDN system) feeding into your in-house installed exchange box.  In those cases, you might want to have your phone number (or numbers) deliverable across ANY of the lines, rather than tied to just one line and this requires a DDI range to be purchased. This is where there is a lead number and a range of subsidiary or linked numbers that can either be hidden or actively used to give certain extensions a direct dial number.

ISDN2e lines can joined into a system of up to 4 pairs, giving the capability of handling up to 8 calls at any one time. Once you get to 8 channels (4 ISDN lines) then it is often more economical to consider an ISDN30 system.

The functionality of ISDN2e and ISDN30 is very similar. ISDN2e is supplied in multiples of two lines. You can expand further in multiples of two, but each expansion requires an engineer’s visit and an installation cost. If you require 6 lines or less on your telephone system and it is likely that this figure will not increase, then ISDN2e is usually adequate. For larger organisations, the best solution is ISDN30. ISDN30 is delivered as ‘a site connection', you merely specify how many lines you want with eight being the minimum.

However, ISDN technology is now being replaced by SIP Trunking technology. SIP Trunking is where the connection to the national public telephone network is made over broadband and not a hard wired dedicated telephone line. Sip Trunking offers significantly lower costs and the same quality of call and comes with many other additional benefits . To find out more about SIP ……….