AT&T MERLIN LEGEND Release 4.0 Feature Reference page 244

Feature Reference
In addition to the above, the Fax Extension feature also provides the ability to
notify certain extensions when a fax is received by turning on the Message LED
(Fax Message-Waiting Extension).
The fax message threshold setting is the length of time (0–30 seconds) before
the system assumes that a fax has arrived. When a fax extension answers a call,
the MERLIN LEGEND system waits until the fax message threshold is exceeded
and then sends a message-waiting indication to the designated message-
waiting extensions(s). If the message-waiting telephone has a Message LED,
the Message LED turns on. Single-line telephone users without a Message LED
hear a stutter dial tone when a message is waiting. Telephones located off
premises are unable to receive message-waiting indications.
Return Call is not operable for messages received from a fax machine and
cannot be used to make a call to the fax. Return Call is a feature available on
MLX display telephones (including QCCs) that enables a user to automatically
call an extension that left a message.
The Fax Extension feature overrides the distinctive ringing pattern for calls
transferred to a fax extension. When a fax extension receives a transferred call,
the fax extension provides one long ring (similar to an internal call), instead of
three short rings.
NOTE:
Fax extensions can only send message-waiting indications. They cannot receive
message-waiting indications.
To use the Fax Extension feature, perform the following system programming
tasks for each fax machine:
1. Specify the tip/ring extension connected to the fax machine or fax
modem.
2. Specify the extension(s) that will receive the message-waiting indication.
3. Specify the number of seconds the system waits before it registers that a
fax has arrived and sends the message-waiting indication. (This is the fax
message threshold, which is a system-wide parameter.) The range is 0–
30 seconds, with a default of 10 seconds.
It is recommended that the default setting (10 seconds) be used for the fax
message threshold. If the fax message threshold is set to less than 10 seconds,
the Message LED could be activated on a receiver's telephone every time the
fax machine goes off hook to answer a call, even if a fax has not arrived. If the
fax message threshold is set to more than 10 seconds, there is a greater
likelihood that the Message LED will not be activated on a receiver's phone
whenever short faxes (that is, fax transmissions of less than 10 seconds in
duration) arrive.
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Fax Extension