AT&T MERLIN LEGEND System Reference Manual page 89

Features
Considerations
Feature Interaction
Alarm
Automatic Route Selection
Pools
System Programming
2-40 Automatic Maintenance Busy
Incoming calls are received and processed normally on lines/trunks in a
maintenance-busy state.
Direct inward dialing (DID) trunks in the Hybrid/PBX mode are not affected
by Automatic Maintenance Busy because these trunks can only receive calls.
100D (DS1) modules configured as ground-start line/trunks, loop-start
lines/trunks, or tie trunks are monitored and maintained by Automatic
Maintenance Busy.
No more than 50 percent of the trunks in a trunk pool are allowed to be
placed in the maintenance state at one time, except when the central
office has failed to disconnect a trunk (preventing its use) or when an entire
trunk module is manually taken out of service (a user-imposed-
maintenance-busy state).
When more than 50 percent of trunks in a pool are in a maintenance-busy
state because of either or both of these exceptions, a system alarm oocurs
and the red LED next to the Alarm button on system operator consoles goes
on.
The red LED next to the Alarm buttons on system operator consoles goes on
and the designated Maintenance Alarm alert device sounds or flashes when
more than 50 percent of the trunks in the trunk pool are in a maintenance-busy
state.
When ARS is used to make an outside call, the system selects another trunk in
the pool when the first trunk is in the maintenance-busy state.
To provide optimum performance, Automatic Maintenance Busy should be
enabled when a Hybrid/pBX system includes trunk pools.
Enable or disable Automatic Maintenance Busy.
System -> MaintenBusy