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U-90E Data/Fax Modem
Carrier: The carrier is a modulated tone and is used by the modem to transfer the data.
CCITT: Comité Consultatif International Thonique et Traphique; former name for the ITU-TSS (ITU-T), the
international standard making organization for telecommunications.
CD: See DCD.
Class 2: A standard for fax transfers using a fax modem. Currently several drafts exist which are
incompatible with each other. ZyXEL modems support the draft PN-2388 of Aug. 20th 1990, and the final
2.0 standard.
CNG: Call negotiation tone. A calling fax machine sends this tone before connecting to quickly establish a
fax connection. A data modem may also have a data calling tone.
Command mode: In command mode, a modem accepts commands from the local DTE. Data transfer is
suspended while the modem is in command mode.
Compatibility: If components are compatible, they work with each other.
COM port: Another name for the serial port on a PC.
Compression: See data compression.
CRC: Cyclic redundancy check; an error checking protocol.
CTS/RTS: Control signal lines on an RS-232C serial interface. These lines are needed to use hardware
flow control.
Cursor: A special marker on a display.
Data bit: In asynchronous transfers, a character is composed of data bits (the actual information) and
framing bits (start bit, stop bit/s, parity bit). The framing bits are needed to recognize whether a character
has been successfully transmitted and where a new charater starts.
Data compression: Recoding of information. The same information is represented by less data bits.
ZyXEL modems use MNP4 and V.42 compression schemes.
Data packet: Block of data which is framed by error control groups. A block consists of up to 256 8-bit
groups. Data packets are used in synchronous transfer.
Data pump: The important module doing modulation and demodulation for a modem. The data pump is
decisive for the quality and the speed of a modem's transfer capabilities.
B
Glossary
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