255-700-585
2-3
PacketStar
®
PSAX 3-Port DS3/E3 ATM Protection Module User Guide
, Issue 1
Release 10.0.0
Chapter 2 Module Description
Protection Features
ing ISC cells from a working module, the protection module sends a message
to the CPU indicating the working module failure. A likely cause of this con-
dition is that processing on the working module is interrupted or suspended.
Other causes of this condition are the removal of the working module from
the chassis or a failure of the module.
Switchover Events
During the switchover of traffic from the working module to the protection
module, various events occur depending on the reason why the switchover
was initiated. These events are described in the following scenarios:
•
Working module failure or removal
After the protection module detects the failure or removal of the working
module, automatic switchover occurs. The protection module notifies the
CPU
n
module that the working module has failed or been removed.
The protection module was configured at the time the working module
was originally configured. The protection module instructs the LIM3–1
module to transfer traffic from the working module to the protection mod-
ule, which is now placed into Active mode. No need exists for the CPU
n
module to download configuration information from the working module.
The CPU
n
module then brings the connections into service on the protec-
tion module. In this scenario, the connection downtime is only the amount
of time needed for electrical switching on the LIM3–1 module.
•
Manual switchover initiated by the user
The user can manually switch traffic from the working module to the pro-
tection module. This action might be taken in preparation for removing the
working module from the chassis for maintenance purposes or testing the
working module for diagnostic purposes. When the user executes the
switchover command, the CPU
n
module downloads the working module
and connection configurations to the protection module, and then instructs
the LIM3–1 module to transfer traffic from the working module to the pro-
tection module. In this scenario, the connection downtime is only the
amount of time needed for electrical switching on the LIM3–1 module.
Figure 2-2 illustrates the data flow in a 1:1 scheme during normal operation,
and the data flow while the protection module is in Active mode following
the failure of the working module.
