Chapter 3 System Features
Multiservice Media Gateway Software Features
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255-700-239
PacketStar
®
PSAX 4500 Multiservice Media Gateway User Guide
, Issue 2
Release 8.0.0
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
CPU2 module that the working module has failed or been removed. After
this notification, the following sequence of events occurs depending on
which type of protection scheme is being used:
~
In the 1:1 scheme
, the protection module was configured at the time the
working module was originally configured. The protection module
instructs the LIM3–4 module to transfer traffic from the working module
to the protection module, which is now placed into Active mode. No
need exists for the CPU2 module to download configuration information
from the working module. The CPU2 module then brings the connec-
tions into service on the protection module. In this scenario, the connec-
tion downtime is only the amount of time needed for electrical switching
on the LIM3–4 module.
~
In the N:1 scheme
, the protection module instructs the LIM3–4 module
to transfer traffic from the working module to the protection module,
which is now placed into Active mode. The CPU2 module then down-
loads the module and connection configurations from the working mod-
ule to the protection module, and restores traffic flow. In this scenario,
connection downtime is slightly longer than that for the 1:1 scheme
because the module and connection configurations must be downloaded
to the protection 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 CPU2 module downloads the working module
and connection configurations to the protection module, and then instructs
the LIM3–4 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 LIM3–4 module.
Figure 3-5 illustrates the data flow in an N:1 scheme during normal opera-
tion, and the data flow while the protection modules are in Active mode fol-
lowing the failure of a working module in groups 1 and 2.
