V.42Bis And V.42; Xmodem, Ymodem, And Zmodem; Fax And Facsimile; Fax Card - ZyXEL Communications 2864 Series User Manual

V.42bis and V.42

V.42bis and V.42 are data compression and error correction standards set by the
ITU-T. V.42bis has a better data compression efficiency than MNP-5 and is a more
advanced compression scheme. V.42bis is used with V.42 for error correction.

Xmodem, Ymodem, and Zmodem

These are file transfer protocols. They do error checking and ensure data integrity of
the file transferred. Some variations of these protocols also appear, like Xmodem-1k,
Ymodem-G, etc.
The "G" types 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 and there is no speed overrun on the computer's serial port.
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 com-
pression, and 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.

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 com-
puter loaded with fax software can send or receive faxes through a fax card. The com-
puter 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 differ-
ent for each fax card manufacturer.
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