IBM Aptiva, Handbook

Page: 182 / 202

168 Appendix C: Modem information
Fax modems
Fax modems send and receive facsimiles and generally
transmit and receive pictures better than text or other
data. In a fax machine, a page is read by a scanner and
broken into a series of dots representing light and dark
portions of the page. These dots compose the pictures,
graphics, letters, and numbers printed by the fax
machine.
The fax machine scans a page line-by-line and records
the number and position of each dot in a scan line. This
information is converted into a special code and
transmitted to another computer or fax machine. This
transmission uses a set of transfer and modulation
specifications called protocols.
Fax machines and modems are connected in Groups.
The Group a fax machine belongs to indicates its speed
and level of technological advancement. The original fax
machines were Group 1 machines. These are the
slowest machines and are almost obsolete today. Faster
Group 2 fax machines replaced the Group 1 machines.
Group 2 machines are also nearly obsolete today. Most
fax machines sold today are Group 3 machines.
Generally, a Group 3 fax machine can connect most
efficiently to another Group 3 machine and may also be
able to connect to many Group 2 machines. However, a
Group 2 machine cannot connect to a Group 3 machine.
The modem in your computer works with most Group 3
fax machines but not Group 2 or Group 1 fax machines.
Important:
The scan rate option in your fax software deter-
mines the size of a fax and how much time it takes
to transmit the file.
Choosing fax software
programs
If your computer did not come with fax software, you
must buy a fax software program to operate your fax
modem. Also, if you add a fax modem to your computer,
you need to purchase fax software.
You send commands to a fax modem (or the fax portion
of a data modem) using a revised version of the AT
command set. This revised version includes two
different sets of commands: Class 1 and Class 2. Some
modems support one class of command while others
support both. When buying a fax software program,
choose the highest class that your modem supports.
The modem in your computer supports class 2 fax
machines.
note:
CAS and SENDFAX are two other commonly used com-
mand sets. These command sets are not supported by the
modems already installed in IBM Aptiva PCs.