Chapter 5: Installation
EST3X Technical Reference Manual 133
Removing the plug re-establishes connection to the premises telephones.
Inserting the plug opens the jumper and connects the 3-MODCOM, which
provides a series connection to the telephones.
Refer to the 3-MODCOM, 3-MODCOMP Modem Communicator Installation
Sheet (P/N 387476) for a diagram of the jack wiring.
• 3-MODCOM dialers can be used for most applications that use telephone
lines. The exceptions are:
• The central station telephone number cannot be dialed directly (using
access numbers and area code where necessary) without operator
interception of the call
• Multiparty service (a party line) exists
• Operator assistance is required to complete a telephone call and a foreign
exchange cannot be introduced
• Connection is not established within 38 seconds following completion of
dialing
• The 3-MODCOM dialer circuit is compatible with any switched telephone
network that employs direct dialing (local) and Direct Distance Dialing (DDD),
without operator interception of the call.
• Operator interception occurs in some areas where message billing is not
completely automatic. Where operator interception is involved, you must
obtain a foreign exchange (FX) connection from the central station exchange
to the exchange serving the customer. The FX provides a local number for
calling the central station without toll billing. A WATS or ground-start line
connection must not be used for this purpose because the line cannot be
supervised.
• The 3-MODCOM includes a feature that prevents jamming by an incoming
telephone call. The feature is based on a telephone service option referred to
as called party disconnect. This option lets the receiver of a call disconnect by
hanging up the telephone for a period of time, even if the caller stays on the
line. The time required for disconnect varies in different areas, but is usually
between 18 and 90 seconds. Called party disconnect is available in most
areas. To determine whether the called party disconnect control is available in
the area to be served, consult the local telephone company.
In areas not having called party disconnect, the 3-MODCOM module is
vulnerable to jamming by an incoming call. To minimize the possibility of
jamming, we recommend that the customer order a separate, unlisted number
for exclusive use of the 3-MODCOM module. The customer should keep this
number confidential. In the case of the two-line dialer, two premises
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