AT&T MERLIN LEGEND System Reference Manual page 153

Features
Mode Differences
Hybrid/PBX
Key and Behind Switch
Considerations
2-104 Direct-Line Console
In the Hybrid/PBX mode, DLCs can be assigned with queued call consoles
(QCCs). A QCC must be connected to the first station jack on the first MLX
module (called the primary system operator position).
Pool buttons cannot be assigned on a DLC; however, trunks included in a pool
can be assigned as Personal Line buttons on a DLC.
Trunks that are not assigned to buttons on the DLC can be selected by the
system operator only by dialing the pool dial-out code from the System Access
button or, on digital DLCs, by selecting a DSS button for the pool dial-out code.
Trunks that are not assigned to a pool cannot be selected from a DLC unless
they are assigned to buttons on the console.
Shared System Access buttons cannot be assigned to DLCs.
Only DLCs (and not QCCs) are allowed in the Key and Behind Switch modes.
A DLC system operator cannot select lines that are not assigned to buttons on
the console.
The maximum number of system operator positions is determined by the
type of telephone used as a DLC (see Table 2-4). In addition, when both
DLCs and QCCs are assigned in the Hybrid/PBX mode, the maximum
combined number of both types is eight; no more than four can be QCCs.
Only multiline telephones connected to the first and fifth station jacks on a
digital or analog module can be assigned as DLCs. This includes DLC
positions used for calling group supervisors and Call Management System
(CMS) supervisors.
A maximum of two DLCs can be assigned per MLX or analog module.
A DLC cannot be located off premises.
When only DLCs (and not QCCs) are assigned, the first DLC connected to
the control unit is the primary system operator position. When the system is
first connected, all "Dial 0" calls, invalid-destination calls from Remote Access
users, and unassigned direct inward dialing (DID) calls (in the Hybrid/PBX
mode) are directed to this position.
CMS equipment is connected to analog station jacks that are assigned as
DLCs. Two DLCs on the same module must be assigned for each CMS (a
maximum of two) connected to the system.
A DLC is not operable during a power failure.