Nortel DMS-100 Series Maintenance Manual page 93

system busied and the protection link remains switched for that shelf. The
primary link that serves the shelf that has faults is system busied. Calls
cannot be processed for the shelf that has faults. Refer to scenario 10.
Note: The switch to the shelf that has faults causes a fault to be detected on
the protection link. This action occurs even if the protection facility is not
defective.
If the protection link is switched and the SMS detects a problem with the
protection link, the system releases this protection link. Both protection and
primary links are system busied. Refer to scenarios 11 and 12.
Scenarios of protection switching for INSV and SysB primary
links
The following scenarios of protection switching apply to primary DS-1 links
that are INSV and SysB:
Scenario 1
All DS-1 links, which includes the protection link, are in-service. Faults are
not present on any link.
The RCS detects a fault on the C-link.
The C-shelf is protection switched.
Scenario 2
All DS-1 links, which includes the protection link, are in-service. Faults are
not present on any link.
The SMS detects a fault on the C-link.
The C-shelf is protection switched.
Scenario 3
All DS-1 links, which includes the protection link, are in-service. Protection
switching is disabled for the C-link. Faults are not present on any link.
The RCS detects a fault on the C-link.
Protection switch does not occur. The C-link is system busied.
Scenario 4
All primary DS-1 links are in-service. The protection link is out-of-service
(SysB or ManB). Faults are not present on any link.
The SMS detects a fault on the C-link.
DMS-100 Family SMS Maintenance Manual XPM10 and up
Maintenance overview 1-77