AT&T MERLIN LEGEND System Reference Manual page 175

Features
Calling Group or CMS
Supevisor Operation
2-126 Direct Station Selector
Table 2-6 Continued
LED Extension
Status Type
ARS, Remote Not applicable, red LED is always off.
On,
Access,
cont.
Listed
Directory
Number
Fast User
flashing
Note: Fast flashing is not applicable for the rest of the extension types.
Slow User
flashing
Line/trunk
number
Note: Slow flashing is not applicable for the rest of the extension types.
A supervisor with a DLC switches from normal call handling to supervisory
operation by pressing the Feature button, dialing 32, and pressing the Hold
button. The effect of pressing a DSS button while in supervisor operation is the
same as that described for normal call-handling operation. Message status
operation is described later in this section.
When the supervisory position is not in message status operation (the green
LED next to the Message Status button is off), the red LED next to each DSS
button for a calling group member's extension is used to monitor the availability
of members to take calls directed to the calling group. The LEDs for the rest of
the extension number types (such as paging groups or line/trunk numbers) are
always off and have no meaning while the position is not in message status
operation.
Meaning
The person is calling the system operator position.
A call transferred by the system operator to the
extension is returning.
A call is ringing on this line/trunk.