Eicon Networks ISDN NT1 Dokumentacja Pobierz pdf (Strona 12)

ISDN Networks

In this section you will learn

• How ISDNs are connected together

• How users are connected to a public ISDN through an ISPBX

• How configuration errors in the ISPBX can prevent successful connections

ISDN and PBX

A normal PABX (Private Automatic Branch Exchange) handles only speech calls, whereas

an Integrated Services Private Branch Exchange (ISPBX) is connected to the ISDN and

itself provides ISDN extension lines.

The ISPBX has the ability to switch incoming calls from outside directly to its extensions.

Being digital, it also has the ability to route not only speech calls but data, video, high

quality audio, and Group 4 Fax. These calls can also be connected internally from

extension to extension.

There are special characteristics about the relationship between individual users, the

ISPBX, and the public ISDN. Understanding this relationship is essential when attempting

to diagnose problems which can arise when using ISDN devices connected through an

ISPBX instead of directly to an public ISDN line.

In the diagram below, how many users of the public ISDN network are there?

You can see that there is only one ISDN interface connecting the ISPBX to the public

network. This means that there is only one D channel, which means that, as far as the

public ISDN network is concerned, there is only one user.

"What about the real users?" you ask. "If they're connected with ISDN, what are they

connected to?"

Assume that each of the three users shown has a Basic Rate Interface on the ISPBX.

Each therfore has a D channel that terminates in the ISPBX. Therefore each is connected

to an ISDN.

This network is inside the ISPBX.

The ISPBX acts as if it has both a network and a user inside.

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Eicon Networks ISDN NT1 Dokumentacja Strona 12