Definitions and Terms Digital Telephone Switching System Part 6

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 6

Packet-Mode Operation: The transmission of data by means of addressed packets whereby a transmission channel is occupied for the duration of transmission of the packet only. The channel is then available for use by packets being transferred between different data terminal equipment.
Pair-Gain system: A subscriber transmission system that serves a number of subscribers with a smaller number of wire pairs, by using concentration, multiplexing, or both.
Parity: The process of adding a redundant bit to a group of information bits to maintain either odd or even numbers of 1’s in the composite group of bits. A parity error results if an odd number of 1’s is detected when even parity is transmitted or vice versa.
Phase Distortion: Signal distortion resulting from non-uniform delay of frequencies within the passband.
Phase Jitter: The unwanted change in phase or frequency of a transmitted signal caused by modulation by another signal during transmission.
Phase Shift Keying (PSK): A form of digital modulation that uses 2n distinct phases to represent n bits of information in each signal interval.
Plesiochronous: Two signals are plesiochronous if their corresponding significant instants occur at nominally the same rate, any variation in rate being constrained within specified limits.
(1) Two signals having the same nominal digit rate, but not stemming from the same clock are usually plesiochronous.
(2) There is no limit to the phase relationship between corresponding significant instants.
PBX (Private Branch Exchange): Switching equipment used by a company or organization to provide in-house switching and access to the public network.
Post-dial Delay: Is the amount of time it takes after the calling subscriber completes dialing until ring-back tone is received.
Protection Switching: That category of restoration in which one transmission path is substituted for another to permit maintenance operations for the protection against component failure, or remedy temporary conditions such as fading. This is intended to reflect a configuration in which M paths protect N paths on the same route.
Psophometric Weighting: Noise weighting filter recommended by CCIR.

PSTN: Public Switched Telephone Network.
Pulse Amplitude Modulation (PAM): The process of representing a continuous analog waveform with a series of discrete time samples. The amplitudes of the samples are continuous and therefore analog in nature.
Pulse Code Modulation (PCM): A process in which a signal is sampled, and the magnitude of each sample with respect to a fixed reference is quantized and converted by coding to a digital signal.
QPRS: Quaternary channel modulation using partial response signaling on each channel.
QPSK: Quaternary phase shift keying (4-PSK).
Quadrature Amplitude Modulation (QAM): Independent amplitude modulation of two orthogonal channels using the same carrier frequency.
Quantization Noise: The difference between the discrete sample value represented by a digital code and the original analog sample value.
Quantizing: A process in which samples are classified into a number of adjacent intervals, each interval being represented by a single value called the quantizing value.
Reference Clock: A clock of high stability and accuracy which is used to govern the frequency of a network of mutually synchronizing clocks of lower stability. The failure of such a clock does not cause loss of synchronization.
Reframing Time: The time that elapses between a valid frame alignment signal being available at the received terminal equipment and frame alignment being established.
Regeneration: The process of recognizing and reconstructing a digital signal so that the amplitude, waveform, and timing are constrained within stated limits.
Regenerative Repeater: A device used to detect, amplify, reshape, and retransmit a digital bit stream.
Resistance: Property of a conductor that determines the current, which will flow through it, when a particular voltage is applied. In electrical circuit, the greater the resistance between two points the greater the drop in voltage.
Return Loss: The difference in dB between reflected and incident energy at a signal reflection point. (See also “Echo Return Loss” and “Singing Return Loss”).
Ringback: The signaling tone returned by switching equipment to a caller, indicating that a called party telephone is being alerted (ringing).


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