3CX - PSTN, ISDN and VoIP – Part 3 - Geek Guru

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3CX – PSTN, ISDN and VoIP – Part 3


Next up in our series exploring the different types of lines available to use with 3CX systems, ISDN lines.


ISDN stands for Integrated Services Digital Network. It’s the technological standard for transmitting voice, data and other services over standard copper telephone network cables. It can allow both circuit-switched transmission (voice and data) and packet-switched transmission (data only), unlike PSTN which is solely circuit-based. It is the technologically advanced successor to PSTN.

In some countries, ISDN is still used as a primary line to access the internet, but it is much slower than most broadband options now available in the UK, which use ADSL or Cable/Fibre networks to provide greater speeds. It is still used in some areas in the UK where standard broadband internet is not available. Each ISDN channel (or line) offers a data rate of up to 64 kb/s, which allows you to use all the features made available by your provider – ISDN generally offers features such as video conferencing, DDI (Direct Dial-In) and the ability to transfer calls externally. Call quality over ISDN lines is often very high, noticeably higher than a standard PSTN line.

Some businesses that choose to go totally VoIP keep one ISDN line (or rather pair of lines) active for emergency voice and data communications, but also providing them with support for more advanced backup services than a standard PSTN line. Backup ISDN lines can also be used to provide connectivity to various pieces of equipment such as modern G4 Fax machines that require an ISDN line to function.

The 3CX systems installed by Geek Guru are fully compatible with any number of ISDN channels, through the use of a gateway. They can be used exclusively with ISDN or combined with VoIP, PSTN or both.


ISDN lines come in two main types:


ISDN 2 / 2e

This type of ISDN connection is suitable for businesses requiring up to 8 incoming channels or lines. They are provided in pairs, so you will be paying line rental for them in multiples of two. They provide the advanced services and quality of ISDN in small chunks, so if your business is small, you don’t have to rent far more lines than necessary. These lines are powered by the local exchange, therefore they don’t need an on-site power supply to function.


ISDN 30 / 30e

Suited to large businesses or small businesses requiring 8 – 30 channels or lines, ISDN 30 provides much the same service as ISDN 2, except on a larger scale. The initial installation of this service is designed to support up to 30 lines – meaning you can upgrade to more lines without needing to pay additional installation costs. You can purchase lines one at a time, with a minimum of 8 and a maximum of 30.


ISDN lines provide more functionality and greater quality than standard PSTN lines. They can be used with most equipment, are fully compatible with the 3CX systems we offer and renting a pair of ISDN channels is generally not much more expensive than renting two standard PSTN lines (depending on provider and selected options).

Next time we’ll be taking a look at VoIP lines (also known as SIP Trunks), how they work and how we can help you get the most out of them.


If you’d like to discuss 3CX Systems, VoIP, ISDN or anything else IT or tech-related with us, give us a call and we’ll be happy to help you in any way we can!

Call us on 0845 234 0580 or email us at info@geek-guru.co.uk

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Posted on by Emily
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