AT&T MERLIN LEGEND Release 4.0 Feature Reference page 186

Feature Reference
When not in Message Status operation, the red LED next to each DSS button for
a room extension is used to monitor room availability, and the DSS button is
used to restrict the extensions when the rooms are not occupied.
The meaning of the red LED next to the DSS button for each room is shown in
Table 13.
Table 13. LED Meanings for Hotel Extension Status Operation Without Message Status
Active
LED Status Extension Status
Off 0
On 2
Slow flashing 1
NOTE:
The LED next to the DSS button for all other types of extensions is always off
and has no meaning.
Message Status Operation
Message Status operation activates when the operator presses the Message
Status button (the lower-left feature button on the first DSS) while in normal
call-handling, calling group, CMS supervisory, or Extension Status operation.
The green LED next to the Message Status button is on when Message Status
operation is active.
While the position is in Message Status operation, the red LEDs next to the DSS
buttons for user extensions indicate whether or not the Message LED was
turned on by a system operator and do not light when a Message LED was
turned on by another source, such as a fax machine or another user. An LED
associated with a calling group extension or a pool dial-out code is always off
while the position is in Message Status operation.
186
Direct Station Selector: MLX
Meaning
The room is occupied, and the extension is in regular
call-handling state.
The room is vacant and available for occupancy, and
outside calls cannot be made from the extension.
The room is vacant and ready for cleaning. Outside
calls cannot be made from the extension.