Nortel DMS-100 Series Maintenance Manual page 92

1-76 Maintenance overview
that detects the fault does not have another fault on a link. The SMS and
RCS are the ends that detect the fault.
Three tables must be datafilled to support protection switching: table
CARRMTC, table LTCPSINV and table RCSINV. How to datafill tables
CARRMTC, LTCPSINV, and RCSINV is described in the Translations
Guide.
Automatic protection switching for INSV, SysB, ManB, and PBsy
primary DS-1 links
The SMS supports automatic protection link switching for INSV, SysB,
ManB and P-side busy (PBsy) primary DS-1 links.
If a protection link is not INSV at the start, a protection switch cannot occur.
A protection switch cannot occur on a link that has had protection switching
manually disabled. If a fault is present on the A-link, protection switching
cannot occur for the B-, C- or D-shelves. A protection switch to the A-shelf
because of an A-link fault has priority over other shelves.
If a fault is present on the A-link, DDL messaging is lost. Without DDL
messaging, protection switch messages for the B-, C- or D-shelves cannot be
sent to the RCS or the SMS.
INSV and SysB primary DS-1 links If the SMS detects a fault on a
primary link, the SMS immediately attempts to switch the protection link
into service to replace the defective DS-1 link. If the RCS requests a
protection switch, the SMS attempts to activate the protection switch. If a
protection switch fails, a correct alarm condition is raised. Refer to
protection switching scenarios 1, 2, 3, 4 and 13.
Protection switching priority always goes to the A-link. A protection switch
request for the A-shelf drops any other shelf that uses the protection link
from the protection link. Refer to scenario 5.
Two or more faults can occur at the same end of a configured SMS-RCS.
When two or more faults occur, the protection link switches to the first shelf
that requests the switch. This action occurs if none of the faults are on the
A-link. Refer to scenario 6.
Both the SMS and the RCS can request a protection switch at the same time.
When the request occurs at the same time, the protection link switches for
the lowest-lettered shelf. For example, shelf B is a lower letter than shelf C.
Refer to scenarios 7, 8 and 9.
A fault can occur for RCS shelf hardware which causes the protection link
to switch to that shelf. The fault causes the protection link to become
297-8231-550 Standard 09.01 August 1998