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DEFINITY ECS Release 8.2
Administrator’s Guide
555-233-506
Issue 1
April 2000
Features and technical reference
1332Facility and Non-Facility Associated Signaling
20
Brief Description
D-Channel Backup with NFAS
When NFAS is used, a backup D-channel can be administered to improve
reliability. The system switches to the backup D-channel if a signaling link failure
occurs on the primary D-channel span.
One D-channel is administered as the Primary D-channel and another D-channel
is administered as the Secondary D-channel. These assignments ensure that both
D-channels are in the same state at the same time and neither can be used to carry
B-channel traffic at any time. The Primary D-channel is given precedence over the
Secondary D-channel.
When D-Channel Backup is activated, all calls that have been answered are
preserved. However, some call-related information may be lost. Calls that are not
answered when D-channels are switched also may lose call-related information.
The figure below shows a possible configuration involving 3 ISDN-PRIs between
a DEFINITY ECS and another DEFINITY ECS or the public network.
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.
Figure Notes
1. DEFINITY ECS
2. Secondary D-Channel
3. Primary D-Channel
4. ISDN-PRI controlled by D-Channel
5. Network Far-End Switch DEFINITY ECS
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