Nortel DMS-100 Series Maintenance Manual page 95

Scenario 7
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. At the same time, the SMS
detects a fault on the B-link.
The B-shelf is protection switched. The C-link is system busied.
Scenario 8
All DS-1 links, which includes the protection link, are in-service. Faults are
not present on any links.
The SMS detects a fault on the C-link.
The C-shelf is protection switched.
The RCS detects a fault on the B-shelf.
The B-shelf is protection switched and the C-link is system busied.
Note: When the RCS detects a fault and a shelf is already protection
switched, the RCS sends an IDLE code to the SMS. A correct switch
request (for the B-shelf in these scenarios) follows an IDLE code to the
SMS. When the SMS receives the IDLE code, the SMS releases the
protection link. In Scenario 8, the SMS again detects the C-link fault
after the SMS releases the protection line. At the same time, the RCS
requests a switch for the B-shelf. The B-shelf is the lower lettered shelf
and has priority over the C-shelf. The B-shelf is switched. The same
condition applies to Scenario 9.
Scenario 9
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.
The SMS detects a fault on the B-shelf.
The B-shelf is protection switched and the C-link is system busied.
DMS-100 Family SMS Maintenance Manual XPM10 and up
Maintenance overview 1-79