Definitions and Terms Digital Telephone Switching Systems

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

Definitions and Terms Digital Telephone Switching Systems

Abbreviated Dialing: A subscriber can dial a short code which is converted in the originating exchange into a form which will establish connection with the local, national, or international number required.
Alternate Mark Inversion (AMI) signal (bipolar signal): A PCM signal, conveying binary digits, in which successive “marks” (or 1’s) are normally of alternative, positive, and negative, polarity but equal in amplitude, and in which “space” (or 0) is of zero amplitude.
Alternate Mark Inversion (AMI) violation (bipolar violation): A “mark” which has the same polarity as the previous “mark” in the transmission of AMI signals.
Amplitude Distortion: Distortion of a transmission signal caused by non-uniform passband attenuation as a function of frequency.
Amplitude Modulation (AM): Modulation in which the amplitude of an alternating current is the characteristic varied.
APSK: Amplitude and phase shift keying, is a form of digital modulation using a combination of both amplitude and phase modulation.
Asynchronous Transmission: A mode of communication characterized by start/stop transmissions with undefined time intervals between transmissions.

Attenuation Distortion: Attenuation distortion is the variation in attenuation (loss) relative to that at 1000 Hz.
Automatic Call Distribution (ACD): A switching system used to distribute automatically and evenly incoming calls to a number of stations on a first-come, first-served basis.
Automatic Number Identification (ANI): A feature required for automatic message accounting in a Central Office (CO) switching system, to identify the calling party’s number, even if that party is one of several subscribers on a multi-party line.
Availability: (1) With respect to switching systems: the number of outlets available from a particular inlet. (2) With respect to equipment in general: the percentage of time the equipment is operational.
Baud: A variable unit of data transmission speed (1 baud = 1 bit per second).
Bipolar Coding: See Alternate Mark Inversion.
Blocked Calls Cleared (BCC): A service discipline in which unserviceable requests are rejected, by the switching system, without service. Also called Lost Calls Cleared (LCC).
Blocked Calls Held (BCH): A service discipline in which unserviceable requests stay “in the system” without being serviced but having a portion of their desired service time elapse until service begins. Also called Lost Calls Held (LCH).
Busy Hour (of a group of circuits, a group of switches, or an exchange, etc.): The busy hour is the uninterrupted period of 60 minutes of which the traffic is at the maximum.
C-Message Weighting: Selective attenuation of voice-band noise in accordance with the subjective effects as a function of frequency.
Call Congestion: Blocking probability of a trunk group.
Call Forwarding: A customized feature available on switching systems that allows customers to direct all incoming calls to another number.
Call Waiting: Subscriber A whose termination is in the active state associated with a call to subscriber B is given a call waiting indication (CWI) that a caller subscriber C, is attempting to obtain connection. Subscriber A may either: (a) ignore or reject the indication and continue with the existing call; (b) terminate the existing call and answer subscriber C; or (c) hold the existing call and answer subscriber C.
Calling Number Indication: A service whereby the calling subscriber’s number can be identified by means of a visual or verbal indication at the called terminal.


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