How Modems Work; Modem Connection Process - IBM Aptiva Hardware Handbook

The dialing sequence you type on your computer might
look like this: *70,,,5554343. The commas (,,,) pause
the modem until the command is carried out, then the
telephone number is dialed automatically.
Call waiting will be disabled only for the duration of
your modem's current call and only from the calling end.
For incoming calls, you may find it helpful to change the
value of register S10 to a higher number. For more infor-
mation on S registers, see page 35.
Your modem communications software determines how
your modem operates with Call Waiting. For specific
instructions, see the user's guide or online Help that
came with the communications software.
If your computer came with fax software already
installed, the fax software documentation was included
in the box your computer came in.
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How modems work

How modems work
If you are having problems connecting to other
modems, or are interested in learning more about how
modems work, the information in this section can help
you. This section discusses the modem connection pro-
cess, data modems, connecting to other data modems,
fax modems, and choosing fax software applications.

Modem connection process

For two modems to connect, they must be of the exact
same type and function. A data modem can only con-
nect to a data modem and a fax modem can only con-
nect to a fax modem. Many modern modems are
designed with both data and fax capabilities. The data
components of these data/fax modems can communi-
cate with data modems, and the fax components can
communicate with fax modems.
The connection process is controlled by software built
into the modem. This connection process is called a pro-
tocol. The protocol of one modem communicates with
the protocol of another and they "negotiate" to achieve
a connection. These protocols must be compatible for
the modems to connect.
The result of this negotiation determines the speed at
which the two modems connect. Normally a 14,400 bits
per second (bps) modem connects with a 9,600 bps
modem at the lower speed of 9,600. But, because of
phone line noise, they may connect at 2,400 bps.
If you use a modem communications software applica-
tion (such as Windows Terminal or HyperACESS Lite for