AT&T MERLIN LEGEND System Reference Manual page 181

Features
Feature Interactions
Automatic Route Selection
Barge-In
Camp-on
Coverage
2-132 Direct Station Selector
When One-Touch Hold is programmed, only outside callers are automatically
put on hold when a DSS button for a user, calling group, or paging group is
pressed while another calli is active. For an inside caller, pressing a DSS
button for a user sends a manual signal to the user's telephone; pressing a
DSS button for a calling group or paging group has no effect.
Only DSS buttons corresponding to a system operator park zone can be
used to park calls: calls cannot be parked on a DSS button corresponding to
any other type of extension.
To park a call at a park zone, the system operator presses the DSS button for
the park zone while the caller is on the line. If a system operator tries to park
a call by pressing the Transfer button followed by the DSS button for the Park
zone, the call is put on hold for transfer and is not parked. This can transfer a
call to an outside number in error.
When a parked call returns from a park zone, the LED next to the button
goes off and does not flash as it does for transfer returns.
To park a call at a park zone, the system operator with a DSS presses the
DSS button for the park zone while the caller is on the line. When a DSS
button for a paging group is pressed, the transfer process is not
automatically initiated even if One-Touch Transfer (DLC only) or automatic
Extended Call Completion (QCC only) is programmed for the system. Calls
cannot be transferred to a paging group extension number.
For a QCC only, pressing the DSS button for a line/trunk number, Listed
Directory Number, or unassigned extension number while active on a call is
ignored.
The LED next to a DSS button for the ARS code is always off.
Barge-In can be activated by pressing a programmed Barge-In button after
making a call to the user's extension by using a DSS button.
When Camp-On is used to complete a call transfer and the call returns, the DSS
button for the extension where the call was transferred goes off and does not
flash as it does for a transfer return or park return.
When a system operator transfers an Individual or Group Coverage call and the
call returns, the red LED next to the DSS button for the sender does not flash as
it does for a transfer return for calls received on other types of line buttons.