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 4
Frame Alignment: The state in which the frame of the receiving equipment is correctly phased with respect to that of the received signal.
Frequency: Frequency is measured in units called Hertz (Hz). One Hz is one cycle per second.
Frequency Diversity: In radio systems the use of one or more back up transmitters, channels, and receivers to protect against atmospheric (multipath) fading.
Frequency Shift Keying (FSK): Digital modulation using discrete frequencies (tones) to represent discrete symbols.
Full-Duplex Transmission: Transmission in both directions, simultaneously.
Full-Echo Suppressor: An echo suppressor in which the speech signals on either path control the suppression loss in the other path.
Glare: Simultaneous seizure of both ends of a two-way trunks.
Half-Duplex Transmission: Transmission in both directions, but only in one direction at a time.
Half-Echo Suppressor: An echo suppressor in which the speech signals of one path control the suppression loss in the other path but in which this action is not reciprocal. Half-echo suppressors are normally used in pairs-one at each end of the long-distance circuit.
HDB3 (High Density Bipolar 3): A modified AMI (bipolar) line code in which strings of four zeros are encoded with an AMI violation in the last bit. (Since this coding format precludes strings of zeros greater than three (3), it is referred to as HDB3 coding).
Highway: A common path or a set of parallel paths over which signals from a plurality of channels pass with separation achieved by time division.
Hook Flash: A momentary depression of the hook switch to alert an operator or equipment, but not so long as to be interpreter as a disconnect.
Hot Standby: Redundant equipment kept in an operational mode as backup for primary equipment. Automatic switching to the standby equipment occurs when the primary equipment fails.
Hybrid: A devise used to connect a two-wire, bi-directional circuit to a four-wire circuit.
Idle Character: A control character that is sent when there is no information to be sent.
Impulse Noise: Impulse noise is any burst of noise that produces a voltage of more than 12 dB above the steady state noise, and is typically of 5 microseconds duration. Sources of impulse noise include lightning surges, switching transients and surges on power lines, which induce surges in telephone circuits.
In-Band Signaling: Signaling transmitted within the same channel and band of frequencies used for the message traffic.
Insertion Loss: The transmission loss caused by inserting a component or network in a circuit. The ratio of power received at a load before insertion to that power received at a load after insertion, expressed in decibels.
Integrated Digital Network: A network in which connections established by digital switching are used for the transmission of digital signals.
Integrated Services Digital Network (ISDN): An integrated digital network in which the same digital switches and digital paths are used to establish connections for different services, for example, digital voice, high-speed data (both circuit and packet switched), slow-scan video, etc.
Intercept: Calls which, for reasons such as those listed below, cannot reach the wanted number may be intercepted and diverted to an operator, an answering machine, or a tone (announcement) to give the caller appropriate information. (a) Change of a particular number including advice of new number. (b) Renumbering of a group of numbers or a change of dialing code. (c) Wrong information in telephone directory. (d) Dialing of an unallocated code. (e) Dialing of a number or numbers allowed by the numbering plan but not yet allocated or no longer in service. (f) Rout(s) out of order. (g) Route(s) congested. (h) Subscriber’s line temporarily out of order. (i) Suspension of service owing to nonpayment.
International Direct Distance Dialing (IDDD): See Direct Distance Dialing (DDD).
Isochronous: A signal is isochronous if the time interval separating any two significant instants is theoretically equal to the unit interval or to a multiple of the unit interval. Note: In practice, variations in the time intervals are constrained within specified limits.
Jitter: Short-term variations of the significant instants of a digital signal from their ideal positions in time.
Junctor: A connecting circuit between switching stages or frames of a single switching office. A junctor may also provide signaling supervision and talking battery for connected subscriber instruments.
Key Telephone Set: A telephone set with special buttons (keys) to provide such capabilities as switching between lines, call holding, or alerting of other telephones.