Avaya Communication Manager Administrator's Manual page 1537

Figure 386: ISDN-PRI Configuration
Figure notes
1 Avaya Media Server
2 Secondary D-Channel
3 Primary D-Channel
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.
Administrator's Guide for Avaya Communication Manager
November 2003
Facility and Non-Facility Associated Signaling
4 ISDN-PRI controlled by D-Channel
5 Network Far-End Switch DEFINITY
Server
Feature Reference
1537