Table of Contents
Advertisement
Using NFAS for ISDN PRI
The Lucent ComOS implementation of NFAS supports both standard NFAS and NFAS
with D channel backup, but recommends NFAS with backup.
Understanding Standard NFAS
If you have NFAS without backup, you gain one B channel. The drawback is that if the
primary interface fails, you have no backup D channel and no calls are possible on any
of the lines in the group until the primary interface reactivates.
To enable NFAS without backup, you define an NFAS group and configure one T1 line
as the primary interface and the remaining T1 lines as slave interfaces. See "Standard
NFAS" on page 10-20 for an example configuration.
Understanding NFAS with D Channel Backup
To enable NFAS with D channel backup, you define an NFAS group and configure one
T1 line as the primary interface, another T1 line as the secondary interface, and the
remaining T1 lines as slave interfaces. The primary T1 interface carries signaling
messages for its own interface, the secondary interface, and all slave interfaces in the
NFAS group.
When you reset the slot of a PortMaster 4 configured for NFAS with backup, the
D channels on the primary and secondary interfaces initialize in "out of service" mode.
The switch then puts the D channel on the primary interface in "in service" mode and
the D channel on the secondary interface in "standby" mode. As call traffic commences
on the T1 interfaces, the primary D channel handles signaling messages for all channels
in the interface group, which typically include the primary T1 interface, the secondary
T1 interface, and other T1 interfaces configured as slave interfaces.
If the primary interface fails, all calls in process are dropped on all interfaces serviced by
that D channel. The D channel on the secondary interface switches to "in service" mode
and begins to carry signaling messages for channels on the secondary T1 interface and
all other slave interfaces previously serviced by the primary T1 interface. Call traffic does
not resume until the D channel on the secondary interface switches to "in service" mode
and begins carrying signaling messages.
Meanwhile, the switch attempts repeatedly to activate the primary interface. When the
primary interface restarts, the D channel on that interface goes into "standby" mode and
does not preempt the "in service" function from the secondary interface. Message
signals for the reactivated primary T1 interface are carried by the D channel on the
secondary T1 interface.
Multichassis Capacity
The ComOS implementation of NFAS is designed for use across multiple PortMaster 4
slots configured as a group on the same Ethernet. A group is an arbitrary number
between 1 and 99 that you assign to an interface. You can define multiple groups of T1
interfaces on the same Ethernet segment, but each group must be supported by its own
primary and secondary D channel pair.
10-16
PortMaster 4 Configuration Guide
Advertisement
Table of Contents
Troubleshooting
