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Glossary
GL-2
Cisco IP Phone Models 7905G and 7912G Administrator Guide (SIP)
OL-4277-01
CDP
Cisco Discovery Protocol. Used primarily to obtain protocol addresses of
neighboring devices and discover the platform of those devices. CDP can also
be used to show information about the interfaces your router uses. CDP is media-
and protocol-independent, and runs on all Cisco-manufactured equipment
including routers, bridges, access servers, and switches.
CED tone
CallED station identification. A 3-second, 2100-Hz tone generated by a fax
machine while answering a call, which is used in the handshaking used to set the
call; the response from a called fax machine to a CNG tone.
CELP
Code excited linear prediction compression. Compression algorithm used in low
bit-rate voice encoding. Used in ITU-T Recommendations G.728, G.729, and
G.723.1.
CLIP
Calling Line Identification Presentation. Shows your identity to callers with
Caller ID.
CLIR
Calling Line Identification Restriction. Hides your identity from callers with
Caller ID.
CNG
Comfort noise generation or calling tone. Distinctive, repeating 1100-Hz tone (on
for 0.5 seconds, off for 3 seconds) generated by a fax machine when placing a call.
codec
Coder-decoder. In Voice over IP, Voice over Frame Relay, and Voice over
ATM, a DSP software algorithm used to compress/decompress speech or audio
signals.
companding
Contraction derived from the opposite processes of compression and expansion.
Part of the PCM process whereby analog signal values are rounded logically to
discrete scale-step values on a nonlinear scale. The decimal step number then is
coded in its binary equivalent before transmission. The process is reversed at the
receiving terminal using the same nonlinear scale. Compare with compression
and expansion. See also A-law and u-law.