Nortel DMS-100 Series Maintenance Manual page 102

1-86 Maintenance overview
An automatic switch request for the A-shelf overrides a manual switch for
the B-, C- or D-shelves. An automatic switch request for the B-, C- or
D-shelf never overrides a manual switch request. Refer to scenarios 3 and 4.
If a fault is present on the A-link, a protection switch cannot occur or be
maintained for the B-, C- or D-shelves. If a fault is present on the A-link,
DDL messaging is lost. Without DDL messaging, messages between the
RCS or the SMS that request a protection switch for the B-, C- or D-shelves
are not sent. Refer to scenario 5.
Scenarios of manual protection switching
Scenario 1
The C-shelf is protection switched because of a C-link fault detection.
Faults are not present on any other primary link. The protection link is
INSV.
Scenario 2
The C-shelf is protection switched because of C-link fault detection. Faults
are not present on any other primary links. The protection link is INSV.
Scenario 3
The C-shelf is manually protection switched. Faults are not present on any
primary links. The protection link is INSV.
297-8231-550 Standard 09.01 August 1998
An automatic protection switch is requested for the A-shelf. The SMS is
manually switched for another shelf. The protection link is dropped
from the B-, C- or D-shelf and switched to the A-shelf. Automatic
protection switching for the A-shelf overrides manual protection
switching for the B-, C-, or D-shelves. Refer to scenario 7.
A manual switch to the B-shelf is requested.
The B-shelf is protection switched.
The C-link is system busied.
A manual switch to the C-shelf is requested.
The protection link is manually switched to the C-shelf.
A fault is detected on the A-link.
The protection link is dropped from the C-shelf. The protection link is
switched to the A-shelf.