ZyXEL Elite 2864 User Guide - Page 33

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 compression, 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 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. 2-7