Isdn Non-Facility Associated Signaling (Nfas); Nfas Interface Id - AudioCodes Mediant 2000 User Manual

SIP User's Manual
11.4

ISDN Non-Facility Associated Signaling (NFAS)

In regular T1 ISDN trunks, a single 64 kbps channel carries signaling for the other 23 B-
channels of that particular T1 trunk. This channel is called the D-channel and usually
resides on timeslot # 24. The ISDN Non-Facility Associated Signaling (NFAS) feature
enables the use of a single D-channel to control multiple PRI interfaces.
With NFAS it is possible to define a group of T1 trunks, called an NFAS group, in which a
single D-channel carries ISDN signaling messages for the entire group. The NFAS group's
B-channels are used to carry traffic such as voice or data. The NFAS mechanism also
enables definition of a backup D-channel on a different T1 trunk, to be used if the primary
D-channel fails.
The NFAS group can comprise up to 10 T1 trunks. Each T1 trunk is called an 'NFAS
member'. The T1 trunk whose D-channel is used for signaling is called the 'Primary NFAS
Trunk'. The T1 trunk whose D-channel is used for backup signaling is called the 'Backup
NFAS Trunk'. The primary and backup trunks each carry 23 B-channels while all other
NFAS trunks each carry 24 B-channels.
The device supports up to 9 NFAS groups. Each group must contain different T1 trunks.
The NFAS group is identified by an NFAS GroupID number (possible values are 1 to 9). To
assign a number of T1 trunks to the same NFAS group, use the ini file parameter
NFASGroupNumber_x = groupID (where x is the physical trunk ID (0 to the maximum
number of trunks) or the Web interface (refer to ''Configuring the Trunk Settings'' on page
73).
The parameter 'DchConfig_x = Trunk_type' defines the type of NFAS trunk. Trunk_type is
set to 0 for the primary trunk, to 1 for the backup trunk, and to 2 for an ordinary NFAS trunk.
'x' depicts the physical trunk ID (0 to the maximum number of trunks). You can also use the
Web interface (refer to ''Configuring the Trunk Settings'' on page 73).
For example, to assign the first four T1 trunks to NFAS group #1, in which trunk #0 is the
primary trunk and trunk #1 is the backup trunk, use the following configuration:
NFASGroupNumber_0 = 1
NFASGroupNumber_1 = 1
NFASGroupNumber_2 = 1
NFASGroupNumber_3 = 1
DchConfig_0 = 0
DchConfig_1 = 1
DchConfig_2 = 2
DchConfig_3 = 2
The NFAS parameters are described in ''PSTN Parameters'' on page 311.

11.4.1 NFAS Interface ID

Several ISDN switches require an additional configuration parameter per T1 trunk that is
called 'Interface Identifier'. In NFAS T1 trunks, the Interface Identifier is sent explicitly in
Q.931 Setup / Channel Identification IE for all NFAS trunks, except for the B-channels of
the Primary trunk (refer to note below).
The Interface ID can be defined per member (T1 trunk) of the NFAS group, and must be
coordinated with the configuration of the Switch. The default value of the Interface ID is
identical to the number of the physical T1 trunk (0 for the first trunk, 1 for the second T1
trunk, and so on, up to the maximum number of trunks).
Version 5.8
11. Advanced PSTN Configuration
;Primary T1 trunk
;Backup T1 trunk
;24 B-channel NFAS trunk
;24 B-channel NFAS trunk
477 October 2009