Avaya BCM 4.0 Networking Guide de configuration télécharger pdf (Page 717)

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Appendix B ISDN overview 717

BCM 4.0 Telephony Device Installation Guide

Figure 228 T reference point

A T loop can be used in combination with an S loop to provide D-packet service for a point-of-sale

terminal adapter (POSTA) or other D-packet device. D-packet service is a 16 kbps data

transmission service that uses the D-channel of an ISDN line. The T and S loops must be on the

same physical module.

Clock source for ISDN

Systems with ISDN interfaces need to synchronize clocking with the ISDN network and any ISDN

terminal equipment connected to the network. Systems synchronize clocking to the first

functionally available network connection. If there are excessive errors on the reference network

connection, the next available network connection is used for clock synchronization. The clock

synchronization process generates alarm codes and event messages. Clock synchronization is

supported by the DTM, BRI module, and FEM.

The BCM derives timing from the network using T reference points (loops). Terminal equipment

on S reference points (loops) derive timing from the BCM system.

When you configure the network connections to the BCM, you should take into account the

system preferences for selecting loops for synchronization:

• lower numbered loops have preference over higher numbered loops

• the loop preference order is: 201, 202, 203, 204 etc.

• the system skips S and analog loops, when selecting a network connection for synchronization

Systems with only S loops act as timing masters for the attached terminal equipment (TE), and are

not synchronized to the network. ISDN TE without access to a network connection (BRI lines) has

limited or no functionality.

If your system has both a BRI S/T configured as BRI, and a DTM configured as PRI, it is

recommended that you use PRI as the primary clock source. See “PRI hardware” on page 715.

ISDN BRI NT1 equipment

The NT1 (network termination type 1) connects an S interface (four-wire) to a U interface

(two-wire). In most cases, it connects loops from a BRI module to the network connection, which

uses the U interface.

The NT1 converts and reformats data so it can be transmitted to and from the S or T connection. In

addition, it manages the maintenance messages travelling between the network and the NT1, and

between the NT1 and the BCM system.

ISDN

BCM

network

connection

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