Definitions and Terms Digital Telephone Switching System Part 5

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 5

LAMA: Local Automatic Message Accounting (see also CAMA).
Line Code: A code chosen to suit the transmission medium and giving the equivalence between a set of digits generated in a terminal or other processing equipment and the pulses chosen to represent that set of digits for line transmission.
Local Central Office (CO): A central office (CO) which normally provides service to nearby subscribers and which serves as a termination point for leased trunks.
Local Exchange: A switching exchange serving no more than 10,000 subscribers. The term is often used to refer to the building, which houses the central office (CO) equipment.
Loop Resistance: The actual DC resistance of the circuit. Loop resistance must be specified if it includes the telephone set(s). (The loop resistance associated with cables must also be specified if it includes only resistance of cable and load coils).
Lost Calls Cleared (LCC): A mode of operation in which blocked calls are rejected by the network and may or may not return. [See also “Blocked Calls Cleared” (BCC)].
Lost Calls Held (LCH): A mode of operation that holds blocked call requests until a channel becomes available. The portion of call that gets blocked is lost. [See also “Blocked Calls Held” (BCH)].
Main Distribution Frame (MDF): A Central Office (CO) structure with wiring terminations to connect the switching equipment with the outside cables. Connections are made between points on the frame by jumper wires, which can be readily changed.
Master Clock: A clock, which generates accurate timing signals for the control of other clocks and possibly other equipment. (See also “Clock”).
Message switching: The practice of transporting complete messages from a source to a destination in non real time and without interaction between source and destination, usually in a store-and-forward fashion.
Modem: A contraction of the terms modulation and demodulation. A device used to generate “voice-like” data signals for transmission over telephone lines. A modem is referred to as a “data set” in Bell System terminology.
Modified Alternate Mark Inversion: An AMI signal that does not strictly conform with alternate mark inversion but includes violations in accordance with a defined set of rules. Examples of such signals are HDB (high-density binary), B6ZS, and B3ZS.
Multi Frequency (MF) Signaling: A signaling method used for interoffice applications. MF signaling uses two of six possible tones to encode 10 digits and five special auxiliary signals.

Multiplexing: The process of combining multiple signals into a single channel for transmission over common facilities.
Near-End Cross-Talk (NEXT): Unwanted energy coupled from a transmitter in one circuit into a receiver of another circuit at the same location (near end).
Network: Network is a physical structure of paths or channels over which information can be moved.
Network Management: Network management is the function of supervising a communications network to ensure maximum utilization of the network under all conditions. Supervision requires monitoring, measuring and, when necessary, action to control the flow of traffic. The objective of network management is to provide service protection and to maximize the number of paid conversations by fully utilizing available equipment and facilities during normal and abnormal periods.
Non-Blocking: A switching network that always has a free path from any idle incoming trunk or line to any idle outgoing trunk or line.
Non-Return to Zero (NRZ): A line code that switches directly from one level to another. Each level is held for the duration of a signal interval.
Objectives: Objectives are the recommended operating limits for circuits or equipment in order to keep overall performance at a desired level.
Off Hook: The state or condition that a telephone receiver is requesting service, or it is in use. A supervisory signal is also associated with the off hook condition, indicating active status of a telephone or line.
Offered Traffic: It is necessary to distinguish between traffic offered and traffic carried. The traffic carried is only equal to the traffic offered if all calls are immediately handled (by the group of circuits or group of switches being measured) without any call being lost or delayed on account of congestion. The flow of traffic offered, and of traffic carried, is expressed in erlangs. The amount of traffic offered and of traffic carried is expressed in erlang-hours.
On Hook: The inactive status of a telephone or line.
One-Way Trunk: A trunk circuit that can be seized at only one end.
Out-Of-Frame Alignment Time: The time during which frame alignment is effectively lost. That time will include the time to detect loss of frame alignment and the alignment recovery time.
PABX (Private Automatic Branch Exchange (also a PBX): Switching equipment used by a company or organization to provide in-house switching and access to the public network.


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