Administrator's Guide

Facility and Non-Facility Associated Signaling
Issue 5 October 2002 1679555-233-506
Figure 58. ISDN-PRI Configuration
With T1 (24 channel) interfaces, 2 of the ISDN-PRIs contain a D-channel and 23
B-channels, while the other ISDN-PRI contains 24 B-channels. One of the
D-channels is the Primary D-channel, and the other is the Secondary D-channel.
Together, this pair of D-channels signals for all 70 (23+24+23) B-channels in the
3 Primary Rate Interfaces.
Since the D-channels are signaling for more than one ISDN-PRI facility,
D-Channel Backup requires the use of NFAS. At any given time, one of the two
D-channels is carrying Layer 3 signaling messages, while the other D-channel is
active at layer 2, but in standby mode only. Any layer 3 messages received over
the standby D-channel are ignored. Since only one of the D-channels can be active
at a time, load sharing between the two D-channels is not possible. The two
D-channels can provide signaling for only a predefined set of B-channels and
cannot dynamically backup other D-channels on other interfaces.
Figure Notes
1. Avaya Media Server
2. Secondary D-Channel
3. Primary D-Channel
4. ISDN-PRI controlled by D-Channel
5. Network Far-End Switch DEFINITY
Server
r781799 CJL 060996