Nfas Interface Id - 3Com VCX V7122 User Manual

The ISDN Non-Facility Associated Signaling (NFAS) feature enables 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 comprises several 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 VCX V7122 supports multiple NFAS groups. Each group should contain different T1
trunks.
The NFAS group is identified by an NFAS GroupID number (possible values are 1, 2, 3 and
4). To assign a number of T1 trunks to the same NFAS group, use the parameter
'NFASGroupNumber_x = groupID'. 'x' stands for the physical trunkID (0–7).
The parameter 'DchConfig_x = Trunk_type' is used to define 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' stands for the physical trunkID (0–7).
For example, to assign the first four VCX V7122 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

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 (see note 1 below).
The Interface ID can be defined per each 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 VCX V7122 trunk, 1 for the second VCX V7122 T1 trunk etc. up to 7).
To define an explicit Interface ID for a T1 trunk (that is different from the default), use the
following parameters:
3Com VCX V7122 SIP VoIP Gateway User Manual
;Primary T1 trunk
;Backup T1 trunk
;24 B-channel NFAS trunk
;24 B-channel NFAS trunk
Table 29 on page 127.
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