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Without wishing to point out what might be obvious to some visitors to this page, a PSTN line is basically a normal, standard old telephone line, like the one we all have at home and ISDN is a digital connection which, for the last 20 years or so has been the mainstay for businesses and organisations who need multiple phone lines on one connection.

A PSTN or analogue line can be used for basic speech but also almost any other purpose. The most common uses are below:

  • Broadband – the broadband service 'sits' on the line and is separate to any speech etc
  • Fax
  • Alarm
  • Lift
  • Modem
  • Entry Phone

An ISDN line is a digital connection and used for those that require multiple lines such as businesses and other organisations. Here is a VERY short explanation – there are 2 variants:

  • ISDN2e – delivered in pairs (one line box per pair) – any organisation needing to accommodate between 2 and 8 simultaneous calls would have ISDN2e.
  • ISDN30 – delivered as a minimum of 8 channels. Each connection can be expanded up to 30 channels in 1 channel increments. There is one line box for each ISDN30 connection (eg a line box can accommodate up to 30 channels).

ISDN provides everything you would need from a modern connection including Direct Dial numbers (DDI's), caller ID etc.

However, ISDN is now playing second fiddle to SIP trunks which are much more functional and flexible and often cheaper. SIP trunks are phone lines delivered on an internet connection. For More details on SIP trunks see our page on SIP and VoIP.

Notwithstanding the above, ISDN2e or ISDN30 is still an excellent choice for many businesses – indeed, a lot of our customers use ISDN and SIP for Business Continuity reasons.

ISDN does not offer the features and functionality that SIP Offers. For more detail on the features of ISDN and, in particular, the buisness continuity options of ISDN30, please see our ISDN user guide page here - ISDN30 continuity

For more detail on SIP trunking, visit our SIP trunks and VoIP page.

We can install ISDN and PSTN lines or take over the billing and management of it for you from your existing supplier.

Here is a picture of an ISDN2e line box (2 channels):

ISDN2e line

Please call us for advice – ask for Paul, Michael or Nick – 01892 676000.


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