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INTRODUCTION
1-5
Figure 1-1. System 85 R2V4 ISDN Configuration
Generic 2 provides a signaling method called nonfacility-associated signaling (NFAS). NFAS allows
a D-channel on one PRI facility (sometimes called a PRI pipe) to provide signaling for B-channels on
another PRI pipe. With NFAS, if two or more PRI pipes are present, an optional D-channel backup
feature is available. One D-channel is administered as the primary D-channel on one DS1 and the
secondary D-channel on another DS1. Only one D-channel per primary-secondary pair can be active
at a time. If the primary D-channel fails, the signaling function is switched automatically to the
secondary (sometimes called the backup) D-channel. Without D-channel backup, D-channel failure
results in loss of service for all calls passing through a PRI pipe.
Generic 2 offers ISDN-BRI, however, some BRI capabilities are not initially available. Figure 1-2,
Generic 2 ISDN Network Configuration, shows a Generic 2 switch in a sample network.