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22 4019777 Rev B
What Are the Requirements for Telephone Service?
What Are the Requirements for Telephone Service?
This section provides hardware and software requirements for using your cable
modem for telephone service.
Number of Telephone Devices
The RJ-11 telephone-style connectors on the cable modem can each provide
telephone service to multiple telephones, fax machines, and analog modems.
The maximum number of telephone devices connected to each RJ-11 port is limited
by the total Ringing Load of the telephone devices that are connected. Many
telephone devices are marked with a Ringer Equivalent Number (REN). Each
telephone port on the cable modem can support up to a 5 REN load.
The sum of the REN load on all of the telephone devices attached to each port must
not exceed 5 REN.
Telephone Device Types
You can use telephone devices that are not labeled with a REN number, but the
maximum number of attached telephone devices cannot be accurately calculated.
With telephone devices that are not labeled, each device should be connected and
the ring signal should be tested before adding more devices. If too many telephone
devices are attached and the ring signal can no longer be heard, telephone devices
should be removed until the ring signal works properly.
Telephones, fax machines, and other telephone devices should use the center 2 pins
of the RJ-11 connectors to connect to the cable modem telephone ports. Some
telephones use other pins on the RJ-11 connectors and require adapters in order to
work.
Dialing Requirements
All your telephones should be set to use DTMF dialing. Pulse dialing is typically not
enabled by your local provider.
Telephone Wiring Requirements
The cable modem supports interior telephone wiring. The maximum distance from
the unit to the most distant telephone device must not exceed 1000 feet (300 meters).
Use 26-gauge twisted-pair, or larger, telephone wiring.
Important: Connection to an existing or a new permanently installed home
telephone wiring network must be done by a qualified installer.