AT&T MERLIN LEGEND System Reference Manual page 252

Features
Considerations
Feature Interactions
Auto Dial
Callback
Call Waiting
Conference
The factory setting for the Hold Disconnect Interval is the long interval
(450 ms) since it is the interval used by most telephone companies.
If the Hold Disconnect Interval of the system does not match that of the
central office, the system may have the following problems with calls on hold:
If the interval is shorter than the setting at the local central office, callers
on hold may be disconnected.
If the interval is longer than the central office's, the LED next to the line
button continues to flash after a caller on hold hangs up.
If two users—for example, stations A and B—who share a Personal Line or
with Shared System Access buttons, put a call on hold and a third user—for
example, station C—who also shares the line or System Access button, picks
up the call, the LED next to the button continues to flash at stations A and B
(it does not change to steadily lit) and does not indicate that station C is
active on the call. If station C hangs up, the LED next to the button goes off
on all stations.
Both sides of an inside call cannot be put on hold. Therefore, if a user
presses the Hold button while waiting on hold on an inside call, the call is
disconnected.
The Hold button is pressed to enter the Pause special character in a telephone
number programmed on an Auto Dial button.
Pressing the Hold button while waiting for a queued call is the same as hanging
up—the call is disconnected. If a system operator presses another line button,
an Auto Dial button, or a DSS button while waiting on the line for a queued call,
the call is disconnected—Automatic Hold does not work.
A person with all calls on hold cannot hear the Call Waiting tone.
The conference originator receives the hold reminder when the conference is on
hold for more than one minute as a result of using the Hold button or while
adding other participants. If DLC Operator Automatic Hold is programmed and
used by a DLC system operator while setting up a conference, the entire
conference goes on hold.
Both sides of an inside call cannot be put on hold. Therefore, if a user presses
the Hold button while waiting on hold for a conference initiated by another user
(an inside call) or if the user presses the Conference button while waiting on
hold on an inside call, the entire conference call is disconnected.
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