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Mediant 2000 SIP User's Manual
8.4
Using ISDN NFAS
In regular (non-NFAS) 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 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 Mediant 2000 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 to 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 to 7).
For example, to assign the first four Mediant 2000 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
Note:
8.4.1
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 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 Mediant 2000 trunk, 1 for the second Mediant 2000 T1 trunk etc. up to 7).
Version 4.4
;Primary T1 trunk
;Backup T1 trunk
;24 B-channel NFAS trunk
;24 B-channel NFAS trunk
Table 6-6
In the current version the NFAS parameters cannot be configured via the
'Trunk Settings' screen in the Embedded Web Server. Use ini file
configuration instead.
141
8. Gateway Capabilities Description
on page 122.
July 2005
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