ZyXEL Communications 2864 Series, User Manual, Page: 238 / 267

Glossary-2
Bit rate: Count of data bits transmitted per time unit. The framing bits needed for
asynchronous transfer are also counted in the calculation of the bit rate. In general,
the bit rate is ten times the character rate.
bps: Unit of the bit rate; bits per second.
Carrier: The carrier is a modulated tone and is used by the modem to transfer the data.
CCITT: Comité Consultatif International Téléphonique et Télégraphique; former
name for the ITU-TSS (ITU-T), the international standard making organization for
telecommunications.
CD: See DCD.
CEPT: Commission Européenne Postale et Telephonique. This organization regu-
lates 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 ex-
ist 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.