Nortel DMS-100 Series Maintenance Manual page 98

1-82 Maintenance overview
another fault on an INSV link, a protection switch occurs. Refer to
scenarios 4 and 5.
If the RCS detects a fault on a ManB link other than the A-link, a protection
switch does not occur. The SMS can detect another fault on an INSV link
other than the A-link. If this link has greater priority than the defective
ManB link, a protection switch does not occur. For example, the D-link has
priority over the C-link. The RCS is designed to give some links priority
over other links. If the RCS detects a fault on a ManB link, other than the
A-link, a protection switch does not occur. The SMS can detect another
fault on an INSV link other than the A-link. If this link is of lower priority
than the defective ManB link, a protection switch occurs for the defective
INSV link. Refer to scenarios 6, 7, and 8.
Note: The A-link has a fault and the A-link is ManB. A protection switch
cannot occur for the B-, C- or D-shelves when this condition occurs. 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 are not sent. Refer to scenario 9 that follows.
Scenarios of protection switching for ManB and PBsy primary
links
The following scenarios of protection switching apply to ManB and PBsy
primary DS-1 links:
Scenario 1
The C-link is ManB. The protection link is INSV and available. A fault is
not present on the C-link.
Scenario 2
The A-link is ManB. The protection link is INSV and available. A fault is
not present on the A-link.
297-8231-550 Standard 09.01 August 1998
The RCS detects a fault on the C-link.
The protection link is not switched for the ManB link.
The RCS detects a fault on the A-link.
The protection link is switched to the A-shelf.
Note: Call processing does not occur for the A-shelf until the A-link is
INSV.