User manual
Call Waiting
A service feature that provides an indication to a terminal already engaged in an established
call that one or more calls are awaiting connection.
Call Waiting Tone
A tone advising the user of the call waiting supplementary service who is engaged on a call
that someone is attempting to call his number.
Caller ID
A network service feature that permits the recipient of an incoming call to determine,
even before answering, the number from which the incoming call is being placed.
CO (Central Ofce)
Local telephone company ofce where all local loops in a given area connect and circuit switching
of subscriber lines occurs.
Codec
Coder-Decoder. Device that typically uses pulse code modulation (PCM) to transform analog signals
into a digital bit stream and digital signals back to analog.
Congestion Tone
A tone advising the caller that the groups of lines or switching equipment necessary for
the setting-up of the required call or for the use of a specic service are temporarily engaged.
CPE (Customer Premises Equipment)
Communications equipment that resides on the customer’s premises.
dB
Abbreviation for decibel. One tenth of the common logarithm of the ratio of relative powers,
equal to 0.1 B (bel).
dBm
Abbreviation. dB referenced to one milliwatt. dBm is used in communication work as a measure
of absolute power values. Zero dBm equals one milliwatt.
Dial Tone
A tone advising that the exchange is ready to receive call information and inviting
the user to start sending call information.
DID
(Direct Inward Dial) DID trunks are one-way trunks that allow you to dial into
a PBX without operator intervention.
DOD
(Direct Outward Dial) DOD trunks are also one-way trunks that allow you to connect directly to the CO.
DS0
Digital Signal Level 0. The base for the digital signal X series; transmits digital signals
over a single channel at 64 Kbps.
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User Manual
Public Switched Telephone Network (PSTN) Simulators