Draw the ISDN address structure and explain how the addressing works?

Address Structure: The ISDN address structure is demonstrated in figure. ISDN number part has a maximum of 15 digits and the ISDN sub address part a maximum of 40 digits. National destination code is as an area code in telephony network and is of variable length. Subscriber number of ISDN is the one usually listed in the directories. This is the number to be dialed to reach a subscriber in similar numbering area. An ISDN number is a unique worldwide address and unambiguously specifies an end point connection. Such end point may be:

1. Single S or T reference point,

2. One for many T reference points at similar site, and

3. One of many S reference points by using direct inward dialing feature.

A single S or signal T reference point may also be addressed through multiple ISDN numbers. This characteristic is usually used in internetworking.

FIG - ISDN Address Structure