Definitions and Terms Digital Telephone Switching System Part 2

Some of the definitions and terms associated with Central Office (CO) digital telephone switching systems are defined below:

Definitions and Terms Digital Telephone Switching System Part 2

CAMA: Centralized Automatic Message Accounting (see also LAMA).
CCIS: Common Channel Interoffice Signaling.
CCS: A measure of traffic intensity expressed as so many hundred call- seconds per hour. 1 CCS = 36 erlangs. (See also Erlang).
Central Office (CO): A facility of the communication common carrier, where the switching of telephone calls is performed automatically. A switching telephone system in the public network, or in a large corporation’s network.
Centrex Service: The provision to subscribers, by means of a specially equipped public telephone exchange, of services normally available only in PABXs (i.e., internal dialing of PABX type, operator’s desk, direct access to the network, direct dialing-in, transfer of calls).
Channel Associated Signaling (CAS): A signaling method in which the signals necessary for the traffic carried by a single channel are transmitted in the channel itself or in a signaling channel permanently associated with it.
Channel Bank: Terminal equipment for a transmission system used to multiplex individual channels, by using FDM or TDM techniques.
Circuit: In telephony, sound is carried over an electrical circuit from a calling party through a communication office, where it is switched out to the called party.
Circuit Switching: The principle of establishing an end-to-end connection between users of a network. The associated facilities are dedicated to the particular connection and held for the duration of the call.
Class 5 Office: A category of Central Office (CO) that serves as the network entry point, for user access lines (trunks). Also called “end office.”
Clock: Equipment providing a time base used in a transmission system to control the timing of certain functions such as the control of the duration of signal elements, and the sampling. (See also “Master Clock”).
Codec: An assembly comprising an encoder and a decoder in the same equipment.
Coherent Demodulation: Demodulation using a carrier reference that is synchronized in frequency and phase to the carrier used in the modulation process.
Common Channel Signaling (CCS): A signaling method using a link common to a number of channels for the transmission of signals necessary for the traffic by way of these channels.

Common Control: A form of automatic control for a switching system that concentrates all control functions into one or more equipment modules shared by all connections.
Companding: The process of compressing a signal at the source and expanding it at the destination to maintain a given end-to-end dynamic range while reducing the dynamic range between the compressor and expander.
Concentration: The process of switching some number of lightly used channels or sources onto a smaller number of more heavily used channels.
Conference Call: A telephone call between more than two participants.
Crosstalk: Crosstalk is the disturbance (specifically speech disturbance) and unwanted signal transfer from one circuit into another. Intelligible crosstalk occurs when some of the words in a conversation can be understood by a person using another circuit. Intelligible crosstalk is objectionable because it interferes with privacy.
dBm: The power level in decibels relative to 1 milliwatt (mW). The standard zero (0) dBm, which has been established in telephony, results from 1 mW of power at a frequency of 1004 Hz across an impedance of 600 ohms.
dBrn: A value of decibels above reference noise that begins at a zero (0) level dBrn. Reference noise is that magnitude of circuit noise, which will produce a reading on a circuit noise meter equal to one picowatt (10-12 watts) of electric power at 1004 Hz. Thus: 0 dBrn = 10-12 watts = 10-9 milliwatts = -90 dBm.
dBrnC: The power level of noise with C-message weighting expressed in decibels relative to reference noise. Reference noise power is –90 dBm at 1004 Hz (-90 dBm = 10-12 watts = 10-9 milliwatts = 0 dBrn).
dBrnC0: The noise power measured in dBrnC, but referenced to the zero –level transmission level point.
DDD: Direct Distance Dialing. (See also under Direct Distance Dialing).
Dial Tone Delay: The time elapsed from off-hook of a telephone set to the initiation of dial tone.
Decibel (dB): The decibel is the standard unit for expressing transmission gain or loss and relative power ratios. The decibel is one tenth (1/10) the size of a Bel, which is a very large unit for convenient use. Both units are expressed in terms of the logarithm to the base 10 of a power ratio. The decibel is expressed mathematically as:
dB = 10 log (P1)/(P2) (Where P1 and P2 are the power levels compared).


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