V.42bis is used with V.42 for error correction.
XMODEM, YMODEM, AND ZMODEM
These are file transfer protocols used by the host (e.g., the
communications program in the PC). It does error checking and
ensures data integrity of the file transferred. Some variations
of these protocols also appear, like Xmodem-1k, Ymodem-G, etc..
The "G" flavors of protocols do not include error checking. They
allow very high throughput rates, but can be safely used only
when the modems use MNP4 or V.42 error protocols.
Whenever possible, we recommend the use of Zmodem for added
security and high flexibility. Consult your communications
program manual for more information on transfer protocols.
FAX AND FACSIMILE
Fax is the abbreviation for facsimile. There are four major parts
in a normal facsimile machine, the scanner, encoding and decoding
device, modem, and printer. Before a page can be sent it is first
scanned, the bit-mapped data is encoded with data compression,
then it is transmitted across the phone line by an internal modem
module. The remote facsimile receives the data with its internal
modem, decodes it back to bit-mapped image data and prints it on
paper, normally with a thermal printer on thermal sensitive
paper.
FAX CARD
A fax card is an internal plug-in card which must be specifically
designed to fit into your type of computer. It has the modem
function of a facsimile machine. A computer loaded with fax
software can send or receive faxes through a fax card. The
computer is used as the input and output parts of a facsimile
machine and the fax card is used as the transmit/receive part and
may also do the encoding/decoding function, depending on the
design. The computer controls and communicates with the fax card
through a set of proprietary hardware and software interfaces
which are different for each fax card manufacturer.
MODEM AS A FAX
Normal modems can also be designed to include the fax
transmitting and receiving function, as does a fax card, since
the modem's interface with the computer is the standard serial
RS-232 interface. This interface will be used for both modem and
fax operations. With the data throughput of a serial RS-232
interface being limited, only compressed fax image data can be
carried through this serial interface. Fax image coding and
decoding must be done in the computer. Modem/Fax, also called
faxmodem, can be either an external stand alone unit or an
