Fax Modems; Choosing Fax Software Applications - IBM Aptiva Hardware Handbook

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Many network services have their own proprietary
protocols. To connect to these services, you often
have to buy the protocol from the service. Other net-
work services rely on V.42bis or MNP 4 and 5.
All error detection and correction protocols com-
press data to avoid slowing the transmission rate.
However, combining protocols will not increase your
transmission speed or significantly reduce transmis-
Important: sion errors.
For example, running V.42bis and X-modem together
will not give you a greater compression rate or trans-
mission speed than running V.42bis alone. Use only
one protocol.

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 pic-
tures, graphics, letters, and numbers printed by the fax
machine.
The scan rate option in your fax software deter-
Important: mines the size of a fax and how much time it takes
to transmit the file.
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 trans-
mitted to another computer or fax machine. This trans-
mission 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 slow-
est machines and are almost obsolete today. Faster
Group 2 fax machines replaced the Group 1 machines.
Most fax machines sold today are Group 3 machines.
Generally, a Group 3 fax machine can connect most effi-
ciently 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
and Group 2 fax machines.

Choosing fax software applications

If your computer did not come with preinstalled fax soft-
ware, you must buy a fax software application to oper-
ate your fax modem. Also, if you add a fax modem to
your computer, you need to purchase fax software.
How modems work 25