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ISDN Overview

2-5

Call Control on the D Channel

ITU-T recommendation Q.931 outlines standards for out-of-band call control at

the network layer for ISDN communication. Its primary responsibility is to set up

and take down ISDN calls on the B channels.

ISDN Interfaces

One of the key concepts in ISDN is a set of universal interfaces that allow you to

purchase equipment and services from any ISDN provider. All providers can

therefore implement ISDN similarly. ITU-T created a set of interfaces, some

physical, some logical, to accomplish this goal.

ITU-T divides ISDN interfaces into two categories: functional groups and

reference points. The next sections describe these two groups.

Functional Groups

Functional groups perform speciﬁc tasks that are necessary for you to access an

ISDN network. These groups combine physical devices and functional points in

an ISDN network, as follows:

• Terminal Equipment 1 (TE1) — ISDN-compatible devices, for example, the

router with an ISDN/BRI module

• Terminal Equipment 2 (TE2) — Non-ISDN-compatible devices, such as

analog phones, PCs, computers

• Network Terminator 1 (NT1) — The point where the phone company’s

wires end at your premises

• Network Terminator 2 (NT2) — The point where any switching services

occur at your premises

• Line Terminator (LE) — The point where your network lines terminate at

the phone company’s central ofﬁce

• Exchange Terminator (ET) — Located at the phone company’s central

ofﬁce, it performs the switching exchange functions

• Terminal Adapter (TA) — Provides ISDN connectivity to non-ISDN

devices

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Avaya Configuring Dial Services Manual de usuario Pagina 47