Apple GeoPort Telecom Adapter Kit - Manual (Page 38)

What modems do
Modems allow computers to communicate over telephone
lines. While computers manipulate information in digital
format, most telephone systems carry information as analog
(wave) signals. Therefore, in order for computers to
communicate over the PSTN (Public Switched Telephone
Network), information must be converted to and from digital
and analog formats. A modem (modulator/demodulator)
handles these format conversions. The modem of the
sending computer converts information from digital format
to an analog signal by a process called modulation. The
modem of the receiving computer converts the analog signal
back to digital format by a process called demodulation.
Modems also dial, establish connections, and control the
flow of data across the telephone line so that transmission
takes place with optimal speed and accuracy.
Setting up a connection
Before two computers can exchange data over telephone
lines, their modems must establish a connection and agree
on how data will be transmitted.
Your modem is already set to make the best possible
connection automatically. See Appendix A for a complete list
of specifications and default settings.
Note: In general, it is best to accept your modem’s
automatic settings. If you want to control the speed, error
control, and data compression settings yourself, see the
Apple Telecom AT Command Set guide or the user’s guide
that came with your data communications software.
38 Chapter 5