Q. What do you mean by addressing and numbering?

Numbering and Addressing: In data and telephone networks, end equipment are more often single units than multiple devices units such as PABX or LAN. Historically, a telephone, a computer or a terminal has been predominant end equipment. Numbering system for these networks has also evolved to identify single equipment end points. In ISDN, multiple devices at the end points are more of a norm than single units, in view of multiple services environment. It then becomes essential to identify a specific end equipment, for example facsimile or computer, to render the service. Identifying specific equipments in a two-level process; first the end point is identified as in case of telephone or data networks and then equipment at the end point. ISDN addressing structure provides for this requirement. Component of the ISDN address which is used to identify end points is called ISDN number, and component for identifying the specific equipment at the end point is known as ISDN sub address.

Numbering plan for ISDN is evolved using the following guidelines:

1. It is based on and is an enhancement of, telephone numbering plan. It's independent of the nature of the services (for example voice, facsimile or data) or performance characteristics of the connection (for example 32 kbps voice or 64 kbps voice).

2. It is independent of routing, that is the numbering or addressing doesn't specify the intermediate exchanges through which services is to be put through.

3. It is a sequence of decimal digits. No alphabet or other characters are permitted as part of address.

4. Its design is such that interworking between ISDNs requires only use of ISDN number and no other additional addressing signals ordigits.