Nortel BCM50 2.0, Руководство по установке

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38 Chapter 5 ISDN overview
NN40020-309 NN40020-309
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 BCM50 derives timing from the network using T reference points (loops). Terminal
equipment on S reference points (loops) derive timing from the BCM50 system.
When you configure the network connections to the BCM50, 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 36 .
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
(only in North America). In addition, it manages the maintenance messages travelling between the
network and the NT1, and between the NT1 and the BCM50 system.
The NT1 from Nortel is packaged two ways:
• a stand alone package which contains one NT1 card (NTBX80XX) and a power supply
(NTBX81XX)
• a modular package which contains up to 12 NT1 cards (NTBX83XX) and a power supply
(NTBX86AA)
ISDN standards compatibility
In North America, BCM50 ISDN equipment supports National ISDN standards for basic call and
calling line identification services. BCM50 BRI is compliant with National ISDN-1 and PRI is
compliant with National ISDN-2.
BCM50 does not support EKTS (Electronic Key Telephone System) on PRI.
In Europe, BCM50 supports ETSI Euro and ETSI QSIG standards, and PRI SL-1 protocol.