Avaya DEFINITY Server CSI Maintenance Manual page 1290

In an NFAS Signaling Group, the 24th port of a DS1 Interface circuit pack (for 24
channel interfaces) or the 16th port of a DS1 Interface circuit pack (for 32 channel
interfaces) is administered as a D-channel. The D-channel carries signaling
information for the other ports (B-channels) on that circuit pack. That D-channel
can also carry signaling information for any of the ports on other DS1 Interface
circuit packs in the NFAS Signaling Group. As a result, the 24th port on other
24-channel DS1 Interface circuit packs and the 16th port on other 32-channel DS1
Interface circuit packs can be used as B-channels. A D-channel in an NFAS
Group can signal for B-channels on a total of 20 DS1 Interface circuit packs. This
configuration is known as NFAS Simplex.
In addition to NFAS Simplex, there is another type of NFAS Group called NFAS
Duplex. This provides the user with more reliability, which is desirable because
NFAS permits the D-channel to signal for so many B-channels. NFAS Duplex
allows the administration of a backup D-channel, which remains in a Standby
state until the Active D-channel goes down. If the Active D-channel does go down,
the backup D-channel takes over and provides signaling for all the B-channels in
the signaling group.
The ISDN-PRI Signaling Group itself depends on three other entities: the DS1
Interface circuit pack on which the D-channel(s) resides, the ISDN-PRI Signaling
Link Port(s), and the Processor Interface Link that provides connectivity to the
processor. If there are any problems with the ISDN-PRI Signaling Group, also
investigate the ISDN-PRI Signaling Link Port(s), the DS1 Interface circuit pack(s).
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Issue 5 October 2002 555-233-119