ZyXEL Communications Omni 288S User Manual page 131

Glossary
CEPT : Commission Européenne Postale et Telephonique. This organization regulates the
data exhange between the European postal services and participates in the drafting of
some standards.
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. It marks the position where input from the
ZyXEL LCD model's front panel will be shown on the 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.
DCD : Data Carrier Detected - a control signal line of the RS-232C interface.
DCE : Data Circuit Terminating Equipment or Communications Equipment - a modem is
a DCE.
Demodulation : Transferring analog signals into digital data bits.
Digital : Digital data consists of a series of bits. A bit may have only one of two states.
Analog data may have any value.
Digital loopback test : A modem test procedure which transfers the received digital data
back to the modulator and transmits them out.
DIP switch : Dual inline package switch. DIP switches are abundant in the world of
electronic equipment. They are used to set certain parameters on a printer, modem or
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