Non-Facility Associated Signaling
ISDN NFAS, as illustrated in Figure 4-10, allows a single D channel to control multiple
PRI interfaces. Use of a single D channel to control multiple PRI interfaces frees one B
channel on all other interfaces to carry other traffic. A backup D channel can be configured
for use when the primary NFAS D channel fails. When a backup D channel is configured,
any hard system failure causes a switchover to the backup D channel, and currently
connected calls remain connected.
Chapter 4: Performing Call Signaling over Digital Voice Ports 207
V
D Channel 64 kbps (Signaling)
24 B Channels (Voice)
23 B Channels (Voice)
V
D Channel 64 kbps (Signaling)
ISDN T1 PRI 23 B Channels (Voice)