There are 3 primary rate sizes available, comprising of 8, 15 & 30 channels which can be configured for both-way exchange line working or as an S-Interface where ISDN to the desktop is required.  For basic rate (ISDN2) there are 3 sizes available, namely 2, 4 and 8 channels.

One of the major benefits of ISDN is the ability to have trunk to trunk transfer enabling incoming calls to be transferred offsite to a remote destination or mobile.

Incoming calls on ISDN can also be linked to a computer database allowing client information to appear on screen by linking the incoming call number to the clients details.

ISDN2 and ISDN30 (basic rate & primary rate) are supplied with a range of DDI (Direct Dial In) numbers which are programmed to ring the desk of an individual.