Chapter 2 Module Description
Protection Features
2-6
255-700-585
PacketStar
®
PSAX 3-Port DS3/E3 ATM Protection Module User Guide
, Issue 1
Release 10.0.0
associated with one protection module in group 2. In the 1:1 scheme, only
one working module in a protection group is associated with one protection
module. Under normal conditions, the working module in a protection group
is in active mode, exchanging traffic, and the protection module is in standby
mode.
The N:1 Traffic Protection modules can also be used in a nonprotected config-
uration in which these modules can be installed in slots
3–12
only as long as
each Protection module has a corresponding LIM3–4 module installed
directly behind the Protection module that the LIM3–4 module is serving. If
any slots in the range of slots designated for group 1 (slots
3
–
8
) and group 2
(slots
9
–
12
) are not configured for a protection group, the unused slots can be
used for other types of PSAX I/O or server modules.
Working Module
Monitoring
Traffic is switched from a working module to its associated protection module
under the following conditions:
•
Working module failure
•
Removal of the working module from the chassis
•
Manual switchover initiated by the user
•
Nonservice affecting upgrades
The protection module monitors the operation of the working module. Inter-
Slot Communication (ISC) cells are exchanged between the working and
protection module. If the protection module detects eight consecutive miss-
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. 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 CPU
n
module to download configuration information
from the working module. The CPU
n
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.
