One factor you should consider when selecting a modem is whether the telephone
line where you plan to attach it uses touch-tone dialing. Touch-tone dialing
is an extra-cost service that is installed on a line-by-line basis for
residential telephones.
When automatic telephone exchanges were first invented about eighty years ago,
digits of the telephone number were signalled to the central exchange by
physically making and breaking the electrical connection between the handset
and the telephone wire. When you use a dial telephone, you can hear this in
the clicking in the receiver; you will hear as many clicks as the numbers you
have dialed, spaced at about one-tenth of a second intervals.
Touch-tone dialing was developed about twenty-five years ago to provide greater
reliability, faster dialing and characters other than numbers. With the
touch-tone system, each digit or symbol in the telephone number is coded by a
unique combination of two audio frequencies. When using touch-tone dialing,
you will hear a series of musical tones, one for each digit in the number.
Most telephone lines equipped for touch-tone dialing will also handle the older
pulse dialing method.
NOTE: Not all telephones with push-buttons use touch-tone dialing. If you hear clicks when pressing a digit button, the
telephone is actually using pulse dialing.
Since modem technology is compatible with that used in touch-tone dialing, this
method is the usual way a modem dials. Pulse dialing capabilities may be
designed into modems as an extra feature.
If your home telephone is a touch-tone telephone, then you should have no
problems using the auto-dial feature of your modem (if it's included).
If your present telephone line uses pulse dialing only, then you will
either need to upgrade to touch-tone dialing or provide a method of pulse
dialing. The preferred method is to upgrade your telephone line. If an
upgrade is impractical, then you should buy a modem with the ability to pulse
dial. If you are considering a Hayes-compatible modem, check the instruction
set for the following instructions:
- ATDT is the instruction to use touch-tone dialing
- ATPD is the instruction to use pulse dialing
A less convenient method is to use your existing telephone to do the dialing.
Most modems provide a connector to accept the plug from your telephone so that
the modem can be permanently installed in the line between your telephone and
the wall jack; this lets you use your telephone when the modem is inactive.
With the modem installed in this manner, you can manually dial before
activating the modem. Then, once you receive the carrier tone, start the modem
and continue with your communications. You will need to read the modem
manual carefully to determine the exact sequence in this method.
Technical Briefs
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