ZyXEL U-1496S Plus User Guide - Page 12
Xmodem, Ymodem, And Zmodem
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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