Telco glossary NB: This document was not written by me. The authors are anonymous. Please distribute and reproduce as you see fit. There are no restrictions. ---------------------------------- AC/DC RINGING A method of telephone signaling that uses alternating current to operate a ringer and direct current to actuate a relay which stops the ringing when the called party answers. ACCESS A point of entry or a means of entry into a circuit. ACCESS CHARGE A charge imposed by the exchange access tariff that compensates the BOC for the provision of connections between end users and InterLATA Carriers (ICs) via BOC-provided facilities. ACCESS CODE (See CARRIER ACCESS CODE, FEATURE/FUNCTION ACCESS CODE, or SERVICE ACCESS CODE.) ACCESS LINE A transmission path that continuously connects a subscriber's premises to a switching center, common carrier operating center, or teleprocessing system. ACCESS LINK (see SPECIAL LATA ACCESS.) ACCESS TANDEM (AT) A BOC switching system that provides a traffic concentration and distribution function for interLATA traffic originating/terminating within a LATA. The AT provides the IC with access to more than one End Office (EO) within the LATA. More than one AT may be required to provide access to all End Offices within a LATA. (See TANDEM INTERLATA CONNECTING TRUNK.) ACOUSTIC CONNECTION A connection to a device or system made by sound waves. ADD-ON A PBX station which permits a user to add one other station (user) to a two-party conversation. ADDRESS A symbol, code or code sequence designating: 1. The location of the operating portion of a program instruction/information in a computer system. 2. In communication, the coded representation of a destination station. ADDRESS SIGNALS Signals used to convey call destination information, such as telephone station code, central office code, and area code. Some forms of address signals are called pulses, e.g., dial pulses and Multi-Frequency (MF) pulses. AI)DRESSING The means whereby a system selects: 1. The destination of a message in a communication system. 2. A specified location in the storage area of a computer system. ADJACENT CHANNEL INTERFERENCE Interference resulting when two or more modulated carrier channels are placed close together in frequency so that one or more sideband frequencies interfere with each other. ADMINISTRATIVE TRUNK GROUPS (also called Miscellaneous) A category of trunk groups that provide call status monitoring. The function may be one of revenue protection (i.e., coin overtime collection), protection of the message network from overloads (i.e., no-circuit announcements), and so on. Types of trunk groups in this category include: o Announcement o Coin Supervisory o Coin Zone o Permanent Signal o Vacant Code o Verification AERIAL CABLE A transmission facility physically strung between poles or similar over head structures. ALERTING (ALERTING SIGNAL) A special signal sent to a station, PBX, or switching system to indicate the presence of an incoming call. A common form is the signal that rings a bell in the telephone set being called. ALGORITHM 1. Specific procedure for solving a certain type of problem. 2. A set of rules to be followed in a prescribed sequence. ALPHANUMERIC (ALSO ALPHAMERIC) A code set capable of representing both alphabetic and numeric characters. ALTERNATE ROUTE A second or subsequent choice path between two points, usually consisting of two or more trunk groups in tandem. This term (or alternate routing) is also used as a verb to define the act of selecting an alternate route. AMBIENT NOISE Background noise existing in any environment, unrelated to noise induced in the transmission medium. AMPLIFIER Any device that, by enabling a relatively low level received signal to control a local source of power, delivers an amplified reproduction of the received signal. AMPLITUDE The size of magnitude of a voltage or current signal. ANALOG Signals which make use of electrical or physical analogies (i.e., varying voltages, frequencies, distance, etc.) to produce a signal of a continuous (rather than of a pulse or digital) nature. ANALOG CHANNEL A channel capable of transmitting analog signals within the specified bandwidth of the facility. Voice channels are analog channels. ANALOG SIGNAL A signal that varies in a continuous manner, such as voice or music. An analog signal may be contrasted with a digital signal that represents only discrete states. The signal put out by a data set has both analog and discrete characteristics. ANNUNCIATOR A visual or audible signaling device that indicates the condition and/or availability of associated circuit(s) or stations. ANSWER BACK (ALSO ANSWERBACK) A specific identifying code, automatically transmitted by an addressed station upon the receipt of a special request signal from the originating station (or system). AREA CODE A three-digit number identifying one of the assigned geographic areas in the North American direct assistance dialing numbering plan. AREA EXCHANGE (also see Exchange) Geopolitical areas set up for the administration of local telephone service. Usually a single metropolitan area or collection of towns and villages sharing a common area of community interest. ASCII An acronym for American Standard Code for Information Interchange, an 8-level alphanumeric code (7 bits + parity bit). ASYNCHRONOUS TRANSMISSION Without a regular time relationship; unexpected or unpredictable with respect to the timing of another element or assembly in a system. Asynchronous transmission, also called start-stop transmission, employs individually synchronized informational characters or words. This is usually accomplished with the use of start and stop elements. The gap between each character is not necessarily of a fixed length of time. ATTEMPT A call offered to a telecommunications system, whether or not it is completed. ATTENUATION The difference between transmitted and received power due to loss through equipment, lines, or other transmission devices. Usually measured in decibels. AREA CODE A three-digit number identifying one of the assigned geographic areas in the North American direct assistance dialing numbering plan. AREA EXCHANGE (also see Exchange) Geopolitical areas set up for the administration of local telephone service. Usually a single metropolitan area or collection of towns and villages sharing a common area of community interest. ASCII An acronym for American Standard Code for Information Interchange, an 8-level alphanumeric code (7 bits + parity bit). AUXILIARY SERVICE TRUNK GROUPS A category of trunk groups that provide selected services for customers or operators and terminates at announcement systems, cord switch boards, or desks. Typical applications commonly employ the following types of trunk groups: o Direct Assistance o Intercept o Official o Public Announcement o Rate-and-Route o Repair Service o Time o Weather AVERAGE BUSINESS DAY (ABD) Any day, Monday through Friday (except for national holidays), that is characterized by normal operation of the work force in a state or large metropolitan area. Occurrences of extraordinary natural conditions (floods, severe storms, earthquakes) or other extreme conditions (war, civil disturbances, major public transportation disasters) on an otherwise average business day, when neither predictable nor normally recurring, usually justify classifying such a day as other than an average business day. AVERAGE LOAD The load obtained by averaging a series of hourly loads; may be further defined as average carried load, average offered load. This term is not to be confused with load, which is inherently an average of all the instantaneous loads over a basic time interval, such as an hour. BABBLE Noise or confusion; the aggregate crosstalk from interfering channels. BACK-HAUL A communications path which takes traffic farther than the ultimate destination, then routes it back. This is done because the cost of transmission to the more remote location is much lower than a more direct route. BACKBONE (ALSO BACKBONE NETWORK) That portion of a communications network connecting primary nodes via multiplexing techniques; a primary shared telecommunications pathway by which multiple users are served via multiplexing at designed jumping-off points. BACKGROUND NOISE Random signals that can be attributed to the unpredictable movement of free elections in a telephone channel. (See AMBIENT NOISE.) BALANCE 1. To distribute traffic over a facility as uniformly as possible. 2. To adjust the impedance of circuits and balancing networks to achieve specified gain/loss objectives. BALANCED The state of impedance on a two-wire line when the impedance to ground as measured from one wire is equal to the impedance to ground as measured from the other wire. A balancing network is a combination of electronic components which stimulate the impedance of a uniform cable or open-wire circuit over a band of frequencies. BAND 1. The range of frequencies between two defined limits. 2. For WATS, one of the geopolitical boundaries established to define a WATS serving area. BAND ELIMINATION FILTER An electrical device which blinds a receiving unit from recognizing a specific range of frequencies. BAND-PASS FILTER An electrical device which allows a specific frequency or band of frequencies to enter a receiving device and attenuate all others. BIDIRECTIONAL SWITCH Any switch in which a moving contact level travels in two directions to connect to a desired fixed contact. While the most common combination is a vertical motion followed by an angular motion, other combinations are possible. BINARY Pertaining to the property which permits the selection of two distinct possibilities. A binary code makes use of two distinct characters (i.e., "0" and "1," positive and negative pulses). The flow of this information is referred to as a binary stream or binary code. BINARY CODED DECIMAL (BCD) A system of binary numbering where each decimal digit is represented by four bits. BINARY SWITCH A switch that must exist in one of only two states: on/off, zero/one, etc. BIPOLAR A code or transmission scheme incorporating both negative and positive polarity pulses. In AT&T's DDS bipolar transmission scheme, a negative-positive pulse and the absence of pulses indicates a binary zero. In this code, bipolar violation occurs when the alternating negative-positive pulsating pattern of the bipolar code is not followed. BIT A contraction of binary digit, the smallest unit of coded information. Data bits are used in combination to form characters, framing markers, parity, transmission synchronization, and so on. BIT RATE The speed at which bits are transmitted. Expressed as bits per second or bps. BIT STREAM Any reference to a binary signal stream without regard to a code. BIT SYNCHRONOUS A data transmission technique in which each bit is synchronized against an accurate clock. In asynchronous transmission this synchronization is held for one character. In synchronous transmission this synchronization is held for a block of characters. BIT, PARITY (See PARITY BIT.) BITS PER SECOND (BPS) A measure of speed in serial transmission - generally the number of signaling elements per second; synchronous with baud. Bps is also used to describe hardware transmission capabilities, as in a 1200 bps modem. BIT A contraction of binary digit, the smallest unit of coded information. Data bits are used in combination to form characters, framing markers, parity, transmission synchronization, and so on. BIT RATE The speed at which bits are transmitted. Expressed as bits per second or bps. BIT STREAM Any reference to a binary signal stream without regard to a code. BIT SYNCHRONOUS A data transmission technique in which each bit is synchronized against an accurate clock. In asynchronous transmission this synchronization is held for one character. In synchronous transmission this synchronization is held for a block of characters. BIT, PARITY (See PARITY BIT.) BITS PER SECOND (BPS) A measure of speed in serial transmission - generally the number of signaling elements per second; synchronous with baud. Bps is also used to describe hardware transmission capabilities, as in a 1200 bps modem. BLOCK The period during the transmission of information when no characters are recorded. 1. A group of words or characters which are stored, operated on, or transmitted as a unit. 2. To prevent any station on a network from receiving selected data. BLOCKED ATTEMPT An attempt that cannot be further advanced toward its destination due to an equipment shortage or failure in the network. BLOCKING The inability of the calling party to be connected to the called party be cause either: 1. All permitted trunk paths are busy. 2. A path between a given inlet and any permitted free outlet of the switching network of a switching system is unavailable. BOUNCING BUSY HOUR The daily busy hour that does not remain consistent over a number of days. BRIDGING The technique whereby additional stations may be served from a 2-point facility by extending the facility from a "bridge" at one of the terminating points of the facility. BROADBAND A communication channel having a bandwidth greater than a voice grade channel and, therefore, capable of higher speed data transmission. BUSY The condition of a line resulting in the inability to complete a call be cause it is in use or in trouble. BUSY HOUR A consecutive 6-minute interval with the highest levels of measurement or derived load used in traffic engineering. A busy hour may also be identified by the period of the day, the class of service of the traffic, and so on; e.g., morning busy hour, coin busy hour. BUSY SEASON An annual recurring and reasonably predictable period of maximum and busy hour requirements for networks that are engineered to traffic characteristics and levels. A busy season may be regular and well-defined, or may be less regular, occurring at different intervals of a generally longer busy period. It may be a period of one or more consecutive months. For the purpose of engineering network facilities, a busy season occurs within a predefined 12-month interval, not necessarily a calendar year. BUSY TONE An audible signal indicating a call cannot be completed because the called line is busy. The tone is applied 60 times per minute. BYPASS The direct connection to customer-premises equipment by an IC. This occurs when an IC connects its own facilities (or facilities leased from a non-BOC entity) directly to an end user's premises, circumventing the use of the BOC network. BYPASS TRUNK GROUP In a hierarchical network, a trunk group (usually high usage) that circumvents one or more tandems in its routing ladder. BYTE A group of binary digits which are processed as a unit by a computer or telecommunication equipment. CABLE 1. An assembly of one or more conductors within an enveloping protective sheath, constructed so as to permit the use of the conductors singly or in groups. 2. An international telegram or cablegram. CALLBACK TRUNK GROUP A trunk group used to obtain operator assistance for special functions on delayed calls returned from the distant end. A typical application commonly employs a tandem to cord switchboard trunk group. CALLING RATE In traffic engineering, the intensity of calls in a system during the busy hour; usually expressed per traffic path. Also referred to as calling intensity. CAROT A test and maintenance facility associated primarily with electronic toll switching systems like the #4ESS. CAROT enables rapid routine testing of trunks to ensure quick identification of faults. CARRIED TRAFFIC That part of the traffic offered to a group of servers that successfully seizes a server, i.e., carried traffic equals offered traffic minus overflow traffic. CARRIER 1. A method of transmission where multiple channels are carried over a single bearer facility via amplitude, phase or pulse modulation. 2. A company authorized by the appropriate regulatory agency to pro vide communications services. (See COMMON CARRIER). CARRIER ACCESS CODE A set of digits dialed by an end user in addition to, or in lieu of, a destination code to designate the IC to be used for that particular call. Various formats are or will be available for access to Message Telecommunication Service/Wide Area Telecommunications Service (MTS/WATS)-like services. These include a digit number (lOXXX - dialed as a prefix to the destination code) or a 7-digit number (950-lOXX), where XX is used in both cases to identify a particular IC. Feature Group A arrangements will continue to use the BOC locally assigned NPA ~ 7 digits as a carrier access code. CARRIER INTERCONNECTION PLAN A long-term plan for interconnecting ICs and the BOC IntraLATA net works. The carrier interconnection plan provides the features known as Feature Group D. Exchange access plan and equal access are two other names that have been used to refer to the features provided by this plan. CARRIER SYSTEM A transmission system wherein two or more channels are derived from a single path. Individual channels are modulated on different "carrier" frequencies at the sending point and demodulated at the receiving point. (See CARRIER.) CARTERFONE (DECISION) A 1968 ruling by the Federal Communications Commission (FCC) that telephone company customers should be permitted to connect their own equipment (e.g., telephone instruments, data modems, etc.) to the public telephone network, provided that such interconnection did not adversely affect the public network or its use by others. (Prior to this decision, only telephone company-provided equipment could be connected to the network.) CATHODE RAY TUBE (CRT) An electronic vacuum tube, such as a television picture tube, that can be used to display images. CCITT An international telecommunications advisory committee - "Committee Consultant International Telegraphique et Telephonique" - established by the United Nations (as a subgroup within the International Telecommunications Union) to recommend worldwide standards for communications common carrier services. CELLULAR RADIO SYSTEM A technique for mobile radio telephone wherein a service area is subdivided into a grid of small units (cells). Each cell has its own transmitter/receiver to serve only that area. As the mobile user moves from cell to cell, the control of the land-line portion of the call is automatically passed to the next cell's facilities. CENTRAL OFFICE (CO) A general term usually referring to a telephone company building in which telephone equipment is installed. Also used to refer to an end office switching system. CENTRAL OFFICE CODE (also called NXX CODE) A 3-digit identification number under which up to 10,000 station codes are associated. Exchange area boundaries are associated with the central office code that accordingly has billing significance. Note that multiple central office codes may be served by a single central office or switch. Sometimes called a switch prefix. CENTRALIZED AUTOMATIC MESSAGE ACCOUNTING (CAMA) An arrangement that provides for the recording of detailed billing information at a centralized location other than an end office, usually a tandem. CAMA equipment also may be associated with position systems, desks, and so on. CENTRALIZED AUTOMATIC MESSAGE ACCOUNTING OPERATOR NUMBER IDENTIFICATION (CAMA-ONI) OPERATOR An operator located at a position that is connected temporarily on a customer dialed station-to-station call. The operator secures the calling number from the customer and keys the number into the CAMA equipment. CENTREX A PBX-like service in which incoming calls can be dialed direct to any station without an operator's assistance. Outgoing and intercom calls can be dialed directly by the station user. CENTREX CO refers to a CENTREX service where the switching equipment is located at the telephone company's Central Office. CHANNEL The smallest subdivision of a circuit in which a single type of communication service is provided (i.e., voice channel, data channel). CHANNEL BANK Transmission facility terminating equipment used to multiplex/ demultiplex several different channels on a frequency division or time division basis. CHANNEL BUSY TONE An audible signal indicating a call cannot be completed because all switching paths or toll trunks are busy, or that equipment is blocked. The tone is applied 120 times per minute. CHANNEL TERMINAL That portion of multiplexing equipment required to derive a desired subscriber channel from the bearer facility. CHANNEL GROUP (See GROUPCHANNEL.) CHANNELS 1. An alternate term for the paths through a switching machine that can be used to connect input to output. 2. The individual voice signal facilities that are multiplexed together in a carrier system. CIRCUIT Circuit has the following definitions: 1. A communication path between two or more points. 2. A network of circuit elements, such as resistors, inductors, capacitors, semiconductors, etc., that perform a specific function. 3. A closed path through which current can flow. CIRCUIT NOISE LEVEL The ratio of the circuit noise to a nominal reference point; this ratio is either expressed in decibels (above the reference noise, dbrn) or in adjusted decibels (dba, which reflects a specified adjustment due to external interference). CIRCUIT SWITCHING A switching system that completes a dedicated transmission path from sender to receiver at the time of transmission. The connecting of two or more channels to create a through circuit between two points. CLADDING The material, usually glass, that surrounds the core of the optical fiber. Light bounces off the interface between the cladding and fiber and returns to the fiber. CLASS OF SERVICE One of several categories of main stations provided in the tariff for the purpose of charging customers for the particular service selected. Different routing treatments may be required for individual categories. The following are some common examples of services that are frequently offered: o Coin o Flat Rate o 800-Service o Message Rate o PBX o WATS Further modification, such as individual, 2-party, 4-party, public, or semipublic, may be required. CLIPPING A distortion of voice signals in which the beginnings of final sounds are cut off. CLOCK A device or signaling element used to develop timing within a system. CLOSED USER GROUP (CUG) This is an optional facility (feature) for systems using virtual call service. If subscribed to, CUG enables the data terminal equipment to be long to one or more closed user groups. A closed user group permits the data terminal equipment belonging to the group to communicate with each other, but precludes communication with all other data terminal equipment. COAXIAL CABLE (See CABLE, COAXIAL.) COAXIAL CARRIER A wideband carrier system using coaxial cables to minimize phase delays, noise, and echo effects inherent over conventional cable systems. A pair of coaxial cables incorporate multiple coaxial conductors. COAXIAL LINES Transmission lines in which one conductor is contained within an outer circular conductor separated by an insulating material. This line is more suitable for high frequency transmission than is the more common paired cable. CODE A predetermined set of information elements representing an alphabet or set of informational characters. CODE BLOCK A control application that limits a percentage of traffic to a specific destination code or station address. CODEC An apparatus which samples analog speech and converts it into a digital bit stream, and vice versa. (An analog/digital-digital/analog converter.) CODEC is the acronym for COder/DECoder. COHERENT LIGHT Light of which all parameters are predictable and correlated at any point in time or space (see LASER). COIN SUPERVISORY TRUNK GROUP A trunk group that provides the capability for a cord switchboard operator to collect coin local overtime and check for stuck coin. Typical applications employ the following types of trunk groups: o End Office to Cord o Switchboard o End Office to Trunk o Concentrator o Trunk Concentrator to Cord Switchboard COMBINED OVERFLOW FINAL TRUNK GROUP A final trunk group that receives route-advanced overflow traffic, COMMAND In switching parlance, an instruction to a switch causing it to operate or release. COMMAND PULSES Pulses transmitted from a control device (such as a dial) to either a direct control switch or to an intermediate device (e.g., a pulse register). COMMON BATTERY A system of current supply where all DC energy for stations connected to an exchange or PBX are supplied by one source. COMMON CARRIER A government-regulated private company that furnishes the general public with telecommunications service and facilities; e.g., a telephone or telegraph company. COMMON CHANNEL INTEROFFICE SIGNALING (CCIS) A type of signaling between processor equipped switching systems in which the voice and signaling portions of a call are separated. The signaling portion employs a separate data link(s) as a signaling path that carries information for error and network control, as well as information to control the connection, monitoring, and disconnection of calls. The voice portion is carried on a trunk from one or more CCIS trunk groups. COMMON CONTROL An automatic arrangement in which items of control equipment in a switching system are shared; they are associated with a given call only during the periods required to accomplish the control functions. All crossbar and electronic switching systems have common control. COMMON LANGUAGE LOCATION IDENTIFIER (CLLI) Codes used to ensure uniform abbreviation of facility names, place names, etc. COMMON-CONTROL SWITCHING ARRANGEMENT (CCSA) An arrangement in which switching for a private network is provided by one or more common-control switching systems. The switching systems may be shared by several private networks and also may be shared with the public telephone networks. COMMUNICATION The conveyance of data, voice, or other information through a medium between two points without alteration of the structure or content of a message. COMMUNICATIONS The field, industry, or study of communication through a medium. The collective services offered by common carriers. COMMUNICATIONS SATELLITE CORPORATION (COMSAT) Created by authorization of Congress in the Communications Satellite Act of 1962. This private corporation (not an agency of the United States Government, although subject to governmental regulation) was created primarily to provide for the establishment, operation, and management of a commercial communications satellite system. COMSAT presently acts as manager for INTELSAT and also represents the United States in INTELSAT. COMMUNITY DIAL OFFICE (CDO) A small automatic switching system that serves an exchange area having its own numbering plan and ordinarily having no operating and maintenance force located in its own building; operation is handled and maintenance is directed from a conveniently located point referred to as an operator office. COMPLETED CALL SECONDS (CCS) A unit of traffic quantity used in traffic engineering. One CCS is the equivalent of a 100-second call or an aggregate of 100 call-seconds. COMPLETING MARKER In a Number 5 Crossbar Office, the common control equipment used to control call-completion operations. COMPONENT BUSY SEASON The busy season during which the highest levels of traffic generally occur for which components of network facilities should be engineered. COMPRESSION (MORE OFTEN CONCENTRATION) The switching function of making a large number of inputs all accessible to a smaller number of outputs. The inverse is EXPANSION. COMPRESSOR Electrical device which compresses the volume range of a signal. CONCENTRATION 1. Applies to a switching network (or portion of one) that has more in puts than outputs. 2. In a traffic network, combining calls arriving on many lines or trunks to transmit them more efficiently in a trunk group. 3. Locating as much equipment as possible at a given place to achieve economies in such things as building costs, power arrangements, and maintenance. CONCENTRATOR Equipment designed to improve the efficiency of data or voice transmission, allowing access lines to bid for a share of transmission channels; the ratio of access lines to transmission channels is determined from the probability of any given access line requiring service. Concentrator is a term which has been applied to several types of devices. To the telecommunications industry, it usually means a de vice which is a switching system arranged to connect a large number of inputs to a smaller number of outputs. To the computer industry, it is now a stored program unit for remote multiplexing and data manipulation in a communications network. CONDITIONING The addition of equipment to a leased voice-grade channel in order to provide the appropriate line characteristics required for data transmission. CONNECTING ARRANGEMENT Interface equipment required by the telephone company when connecting privately owned data and voice equipment into the public network. CONNECTION Connection has the following definitions: 1. A point where a junction of two or more conductors is made. 2. Generally, a telephone connection is a two-way voiceband circuit, completed between two points by means of one or more switching systems. It contains two loops and may contain one or more trunks. CONNECTOR In Step-by-Step switching systems, a two-motion electromechanical switch that operates on the last two digits of the telephone number to connect from a selector to any one of 100 customer numbers. The connector performs the following functions: 1. Tests for busy. 2. If busy, returns busy tone. 3. If idle, rings the called party and returns ringback tone to the calling line. CONNECTOR (CONTINUED) 4. Provides a supervisory signal indicating that answer has occurred, and trips ringing. 5. Provides talking battery to the calling line on INTRAoffice calls and to the called line. 6. Disconnects when the customer hangs up. CONTACT BANK The array of fixed contacts of a gross motion switch. CONTROL In switching systems, the overall control of the switches. This includes: o Monitoring to determine when action is needed. o Logic to determine what action is needed. o Command - to initiate the actions. CONTROLLED ENVIRONMENTAL VAULT (CEV) A below-ground manhole or splicing chamber which is used as a structure to house multiplexers, digital loop carrier equipment, switch equipment, etc. depending upon the need. Because the equipment being housed requires a central office type environment as well as power for lighting and ventilation, CEVs must be specially constructed to prevent the entrance of water and to protect the equipment. CROSS CONNECTIONS Flexible, interchangeable connections usually made on a distribution frame to associate two pieces of equipment, two cable pairs, or one of each. CROSSBAR 1. A line switch having several horizontal and vertical paths which are electromagnetically or electronically interconnected. Any vertical path can be connected with any horizontal path. 2. Switching system using mechanisms called crossbar switches, consisting of rectangular fields of contact springs operated in coordination by horizontal and vertical numbers. CROSSBAR NO. 5 The most recent type was designed primarily to serve the residential sections of large cities and the fringe areas around these cities. CROSSBAR SWITCH The basic element of any Crossbar System. A crossbar switch is a relay mechanism consisting of 10 horizontal paths and 10 or 20 vertical paths. Any horizontal path can be connected to any vertical path by means of electromagnets. A two-stage operation is used to close any crosspoint. First a selecting magnet shifts all selecting fingers on a horizontal bar, then a holding magnet shifts a vertical actuating card to close the selected contacts. CROSSBAR TANDEM A two-wire common control switching system with a space division network used as local tandem, toll tandem, and CAMA switching. The system is Western Electric manufactured. CROSSPOINT ARRAY An arrangement of switching elements used in some switching net works, characterized by incoming and outgoing talking paths arranged at right angles to each other, with switching elements at intersections. CROSSTALK Interference or an unwanted signal from one transmission circuit, detected on another (usually parallel) circuit. CROSSTALK, INTELLIGIBLE (See INTELLIGIBLE CROSSTALK.) CUSTOMER-PROVIDED EQUIPMENT (CPE) Apparatus and associated wiring provided by the customer, not the Telco. The equipment must meet the Telco's specifications. CUSTOMER STATION EQUIPMENT Telephone company equipment located on the customer's premises, such as a telephone instrument or data set. CUSTOMER SWITCHING SYSTEM A switching system that provides service for a customer, typically a business customer. Systems in this category include key telephone systems, private branch exchanges, automatic call distributors, and telephone answering systems. The term is replacing business communications system. CUSTOMER PREMISES EQUIPMENT (CPE) All telecommunications terminal equipment located on the customer's premises, encompasses everything from black telephones to the most advanced data terminals and PBXs. CYCLE DATA 1. The interval of space or time necessary to complete one set of events before they are repeated. 2. The amount of time necessary to complete one waveform. Information which is arranged in a formalized manner suitable for further handling. Usually this implies automatic handling such as communications or processing. DATA COMMUNICATIONS In telephone company terminology, data communications refers to end to-end transmission of any kind of information other than sound (including voice) or video. Data sources may be either digital (such as a computer) or analog (such as an electrocardiogram transmitter). Data transmission should not be confused with digital transmission. Data transmission refers to transmission of information from a data source. Digital transmission refers to a particular kind of transmission facility implementation. DATA COMMUNICATIONS EQUIPMENT (DCE) Devices used for the origination, transmission or reception of data on electromagnetic transmission systems. DATA COMPRESSION The process of reducing the volume of transmitted data while conveying the original information content. DATA LINK The communications path between a pair of data communications de vices. The data link includes all devices and transmission media in the path. DATA SET Equipment for performing the conversion between signals from data processors or terminals (usually digital) and signals suitable for transmission over telephone lines for control of the connection. Data sets can be either transmitters or receivers, or both. That portion of the data set that converts the terminal signals for transmission (modulator) is called a modem, a contraction for modulator/demodulator. In common usage, the terms data set and modem are often used interchangeably, although strictly speaking, a data set has control functions in addition to modulation and demodulation. DATA SINK A device which accepts signals from a data transmission system. DATA SOURCE A device capable of originating data signals for transmission. DATA TERMINAL A device, associated with a computer system for data input and output, that may be at a location remote from the computer system, thus requiring data transmission; e.g., a teletypewriter is a data terminal, as is a magnetic tape reader. The term also applies to devices for terminal-to-terminal communications. DATA TERMINAL EQUIPMENT (DTE) A device which accepts and/or receives data to a data communications system. The DTE to Data Communications Equipment interface is standardized in a number of specifications, the most common of which is EIA's (Electronic Industries Association) RS232C interface. DECIBELS ABOVE ONE MILLIWATT (dBm) The application of decibel terminology to absolute signal strength relative to one milliwatt. OdBm = 1 milliwatt. DECIBELS ABOVE REFERENCE NOISE (dBrnC) The application of decibel terminology to the measurement of noise. The expression is that of the strength of a noise signal relative to 90 dBm as measured by a frequency function (C-message weighting) that expresses the average subjective reaction to interference as a function of frequency. DECODE The process of interpreting previously coded information back into the usable form in which it existed before the coding process. DECODER 1. A device which performs the decoding process. 2. In some telephone switching systems, a decoder is a device for translating dial digits into control signals. DEDICATED LINE or DEDICATED SERVICE A communication line or system provided to a single organization and used exclusively by that organization. DELAY The amount of time lost between the initiation and the completion of a function. DELAY DISTORTION The signal distortion caused by the differing transmission delays of signals of different frequencies to pass through a transmission line. DELAY EQUALIZER A device used to equalize the signal distortion caused by the differing frequency delay characteristics of a transmission line. The delay equalizer operates by adding delay to the faster transmitting frequencies. DELTA MODULATION A technique of converting an analog signal, such as voice, to a digital pulse format. In this format, the existence or absence of a pulse represents a rising or declining analog wave form, respectively. DEMODULATION The process of converting information signals previously modulated into transmission carrier form back into the form in which they existed before the modulation process. DESTINATION CODE A combination of digits that provides a complete address to reach a destination in the message network. Most destination codes are made up of some of the following components: o Area (NPA) Code o End Office Code o Station Number o Service Code o Toll Center Code DIAGNOSTICS A set of processes for identifying or isolating an error or malfunction in a communications device or system. DIAL A device that is part of a customer's telephone set and is used to generate a coded signal to control the central office switching equipment. The action of entering control information through a dial device. DIAL LONG LINE (RANGE EXTENDER) Equipment, usually located in a central office, that extends the dialing, supervision and other signaling range of a loop. DIAL PULSES Regular, momentary interruption of signaling current used to transmit numerical information either into a register or to control a switch directly. DIAL PULSING A means of signaling consisting of regular momentary interruption of a direct or alternating current path at the sending end in which the number of interruptions corresponds to the value of a digit or character. The interruptions are usually produced by a rotary telephone dial, but may be produced by a sender in a switching system. DIAL TELEPHONE, ROTARY (See ROTARY DIAL TELEPHONE.) DIAL TONE An audible tone sent from an automatic switching system to a customer to indicate the equipment is ready to receive dial signals. DIAL TONE DELAY A measure of time required to provide dial tone to customers. This measures one aspect of the performance of a switching system. DIAL TONE MARKER The common control equipment used to control call-operating operations in a Number 5 Crossbar System. DIAL TRAIN The series of pulses or tones that is sent from the originating station and the switching equipment in order to specify the destination of the desired call. DIALUP The technique of initiating and routing a call by means of dial signals from the originating station. DIAPHRAGM A thin, flexible sheet that can be vibrated by sound waves as in a microphone, or by magnetic waves as in a telephone receiver. DIGIT A representation of a quantity with a limited number of states. A decimal digit can represent ten different states. A binary digit can represent two states. A binary digit is also called a bit. DIGITAL 1. Pertaining to the capability of being represented by a digit. The characteristics of a device or system which operates using digits to represent quantities; e.g., digital computer, digital data transmission. DIGITAL FACILITY A switching or transmission facility designed for the handling of digital signals. DIGITAL MICROWAVE A microwave system in which most or all of the modulation of the radio frequency carrier is controlled directly by digital signals. The carrier is still a radio frequency and the modulation may be frequency or phase shift, but the control of that modulation is the digital bit stream. This is in contrast to analog microwave, in which a digital bit stream would be converted to an analog carrier by a voice grade modem and then frequency shifted up to the appropriate carrier frequency. DIGITAL SIGNAL An information signal which has a limited number of states. Any item of information, whether it is in a data format or not, can be converted to a digital signal, e.g., voice and video, which are usually originated in analog (continuous signal) form, can be converted to digital signals. DIGITAL SIGNAL LEVEL One of several transmission rates in the time-division multiplex hierarchy (i.e., DS1 = 1.544 Mb/s, DS3 = 44.736 Mb/s). DIGITAL SPEECH INTERPOLATION (DSI) A technique of sharing voice communication paths among a larger number of users by means of allocating the silent periods inherent in human speech to active uses. An earlier technology was called Time Assignment Speech Interpolation or TASI. The technique is somewhat analogous to that of the statistical multiplexing of data transmission. DIGITAL TRANSMISSION The transmission of a digital signal between two or more points. The usual definition applies to the manner in which the transmission carrier is modified to carry the transmitted information. For example, in digital microwave systems, the radio frequency carrier is an analog signal, but its information modulation is derived from the digital signal. DIGITIZE The process of converting any information from its base states to a digital form; i.e., a form in which only a limited number of states exist. It should be noted that a digital form does not necessarily imply a character encoded form of information. DIODE An electrical device through which current can flow freely in only one direction. DIRECT DISTANCE DIALING (DDD) A method of making long-distance toll telephone calls automatically on the public switched telephone network by entering the final destination code through the originating station's telephone set dial. DIRECT INTERLATA CONNECTING TRUNK GROUPS Those trunk groups used for switched LATA access that interconnect an IC's POP directly with a BOC end office switching systems. (See TANDEM INTERLATA CONNECTING TRUNK.) DIRECT PROGRESSIVE SYSTEM A switching system in which the switches are at least partially under the direct control of a customer's dial and in which the path through the switching office is selected progressively one step at a time. DIRECTIONAL RESERVATION OF EQUIPMENT (DRE) A control application that reserves trunk capacity for incoming traffic. DIRECTORY ASSISTANCE (DA) A service in which a customer will be connected to an operator at a DA bureau by dialing the proper service code or number and shall be told the directory number of the customer whom he/she desired to call, provided that the customer's number is, or will be, published (listed) in the telephone directory. (Formerly called information service.) DIRECTORY ASSISTANCE TRUNK GROUP A trunk group that provides the means for customers or operators to obtain listed directory numbers and newly connected numbers. Applications commonly employ the following types of trunk groups: o End Office to Trunk o Concentrator o End Office to Desk o Tandem to Trunk Concentrator o Tandem to Desk o Cord Switchboard to Trunk Concentrator o End Office to Automatic Call Distributor o Tandem to Automatic Call Distributor DIRECTORY NUMBERS The telephone numbers assigned to subscribers' main stations. DISTORTION The modification of the shape or waveform of a transmitted signal caused by imperfections of the transmission system or by outside interference. Most forms of distortion are the result of the varying response of the transmission system to different frequency components of the transmitted signal. DISTRIBUTED PROCESSING A technique of distributing the information processing functions over a number of devices. The devices may be computers or data terminals with some level of intelligence. The devices may or may not be interconnected with communication facilities. DISTRIBUTED SWITCHING A technique of distributing the switching function of a communications network over a number of switching or routing devices. There may or may not be some central control over the switching process. There will usually be some form of signaling information passed between the switches. DISTRIBUTION 1. The portion of a switching system in which a number of inputs is given access to the same number of outputs. 2. The flexible interconnection of equipment to either cable pairs or other equipment units. (See DISTRIBUTION FRAME.) DISTRIBUTION CABLE A hierarchical level of cable plant usually referring to that cable which is installed between the trunk or feeder cable and the drop cable to a customer's premises. DISTRIBUTION FRAME A framework for supporting terminals to which outside cables and/or cables from equipment units can be connected. The purpose of the frame is to allow flexible interconnection between the cables or the equipment. DIVERSITY The technique of using one, two, or more separate transmission channels. These channels may be along the same paths, in which case the diversity is that of frequency or polarization. The channels may be along separate physical paths, in which case there is space diversity. DMS 10 DIGITAL SWITCHING SYSTEM The DMS-10 digital switching system is a family of time division multiplexed digital switching systems for local, tandem, and toll applications. The Northern Telecom DMS-lOE digital switching system is a small Class 5 digital switch that can satisfy the need as a Community Dial Office (CDO) replacement vehicle. This system can be expanded to 8000 subscriber lines. The DMS-lOE digital switching system offers Custom Calling Features, CAMA, LAMA (Local Automatic Message Accounting), Integrated Business Services (IBS), Equal Access, and Operations Support System (OSS) interfaces. The Northern Telecom DMS-lOM digital switching system has the same feature capability as the DMS-lOE digital switching system for serving up to 1800 subscriber lines. Packaged as a fully self-contained cabinet, the DMS-lOM digital switching system is designed for the small central office market where it can be used for capping existing office growth. DMS-100 DIGITAL SWITCHING SYSTEM The DMS-100 digital switching system is a large local Class 5 digital switching system that can be expanded up to 100,000 subscriber lines. Major features offered include LAMA, Integrated Business Network (IBN), Equal Access and OSS interfaces. The DMS-100 digital switching system is manufactured by Northern Telecom Ltd. DMS-lOOF DIGITAL SWITCHING SYSTEM The DMS-lOOF digital switching system family provides a series of time division multiplexed digital switching systems for local, tandem, and toll and international gateway applications. Major features offered include LAMA, CAMA, IBN, TOPS, CCIS, Equal Access, and OSS interfaces. These systems are manufactured by Northern Telecom Ltd. DMS-200 DIGITAL SWITCHING SYSTEM The DMS-200 digital switching system is a large toll/tandem digital switching system that can be expanded up to 60,000 trunk circuits. Major features offered include CAMA, Traffic Operator Position Service (TOPS), CCIS, Equal Access, and OSS interfaces. The DMS-200 digital switching system is manufactured by Northern Telecom Ltd. DOUBLE SIDEBAND TRANSMISSION The transmission of a modulated carrier signal and its two sidebands. These two sidebands result from the addition and subtraction of the modulation frequency to the carrier. DOWNLINK The transmission link from a satellite to an earth station. DRIFT A slow change in a nominally constant quantity. The term is usually applied to a signal, particularly to the frequency of a signal. DROP A connection between a device and a communications network (synonymous with a station). DROP CABLE A hierarchical level of cable plant usually referring to the final link of outside plant that connects to a subscriber's premises. DRY CONTACT An electrical contact made by a pair of metallic contacts as in an electro-mechanical relay. DUAL TONE MULTIFREQUENCY (DTMF) SIGNALING The generic name for the tone signaling scheme used to signal from telephones to switching equipment. Not to be confused with the Multi frequency (MF) signaling system often used between two switching systems. DUPLEX A channel or a device which can communicate in both directions simultaneously. DX SIGNALING A signaling process used on long metallic circuits. The process uses a bridge circuit to detect the small current signals. The term DX is an old term used to refer to distant transmission. DYNAMIC OVERLOAD CONTROL (DOC) A control application that is automatically activated by switching systems to speed up call processing and limit attempts from connected offices. E&M LEAD SIGNALING A specific form of interface between a switching system and a trunk in which the signaling information is transferred across the interface via two-state voltage conditions on two leads (each with ground return) separate from the leads used for message information. The message and signaling information are combined (and separated) by a signaling sys tem appropriate for application to the transmission facility. The term E&M lead signaling is used also in some special service applications. EARTH STATION The end of a satellite communications link which is located on earth. It may be a transmit/receive station or it may be a receive-only station. ECHO The distortion created when a transmitted signal is reflected back to the originating station. It becomes a serious distraction to a speaker when the echo signal is delayed in time. ECHO CANCELLER A device used in a transmission line to reduce echo; it operates by put ting a signal on the return transmission path which is equal and opposite to the echo signal. ECHO SUPPRESSOR A device used in a transmission line to reduce echo; it operates by attenuating the return signal path from the distant end. ECHO TALKER The echo of a talker's voice that is returned to the talker by a telephone transmission system. Some level of minimal delay echo is desirable to give the telephone some "life." A longer delay is very distracting to the talker. ECONOMIC CCS (ECCS) The engineered objective load in CCS to be carried on the last trunk (or theoretical last trunk) in a non-modularized high-usage trunk group. It is developed from incremental CCS and cost ratio data. EIA INTERFACE A standardized set of signal and connector characteristics for the inter connection of electronic equipment specified by the Electronic Indus tries Association (EIA). This term is often used (incorrectly) to refer to the RS232C interface, which is the primary interface between data terminals and modems and other communications equipment. ELECTRO OPIICAL TRANSDUCER A device used to convert electrical signals into light signals and vice versa. It is used at the ends of fiber optic transmission systems. ELECTRONIC CALL DISTRIBUTION A device used to distribute incoming calls evenly over one or several groups of answering stations. Without such a device, the first line in a group would be continuously busy while the last line would only get calls when all other lines were in use. (See AUTOMATIC CALL DISTRIBUTOR.) ELECTRONIC SWITCHING SYSTEM A switching system in which control of the switched network resides in computer-like electronic equipment. ENCODE The process of converting information into another form (usually digital) to obtain characteristics required by a transmission or storage sys tem. END DISTORTION A form of distortion of asynchronous transmission signals which causes the shift of the end of pulses from their proper position relative to the beginning of the start pulse. END OFFICE The local exchange office at which a subscriber's loop terminates. END OFFICE CODE That part of a destination code consisting of the first three digits of a customer's 7-digit directory number. It is usually expressed as an "NXX code," where N represents Digits 2 through 9 and X represents Digits 0 through 9. It is also commonly called a central office code. END USER ACCESS LINES The facility between the EO and the Network Interface (NI) at the end user's premises. The end user's access line includes certain non-traffic sensitive central office equipment, the outside plant facilities, the Net work Channel Terminating Equipment (NCTE) (when necessary), and the NI located on the end user's premises. END USERS Customers who use (rather than provide) telecommunications services, i.e., those who either originate or terminate telecommunications. ENHANCED 911 A 911 emergency system that speeds response time by providing the dispatcher with the address and number of the telephone used to make the call for help. ENHANCED SERVICES As defined in Computer Inquiry II, an enhanced service is any offering over the telecommunications network that is more than a basic service, e.g., services that use computer processing applications to act on the format, content, code, protocol, or other aspects of the end user's transmitted information. They provide the end user with additional, different, or restructured information and may involve end user's interaction with stored information. (See BASIC SERVICES.) ENVELOPE DELAY (PHASE) DISTORTION Distortion of the transmitted signal which results from the different transmission speed characteristics of different frequency components of the signal. Mathematically, it is the derivative of the phase shift with respect to frequency. EQUAL ACCESS An unbundled BOC tariff offering for LATA access, the first phase of which was offered to all ICs starting no later than September 1, 1984. Such access is equal in type and quality to that provided to AT&T Communications and its affiliates. (See ACCESS CHARGE.) EQUAL ACCESS END OFFICE (EAEO) An EO that provides all of the features of equal access as required by the MFJ. EQUALIZATION The process of compensating for variations in the signal attenuation. Its purpose is to produce a flat frequency response. ERLANG A measure of traffic intensity. One Erlang is one fully occupied traffic path. It is one traffic path continuously occupied or multiple paths carrying an aggregate load of one call-hour per hour. ERLANG B One of the basic traffic models and related formulas used in telecommunications traffic engineering. The assumptions are Poisson input, negative exponential holding time, and blocked calls cleared. It is used for trunk engineering. ERLANG C One of the basic traffic models and related formulas used in telecommunications traffic engineering. This is the queuing model with assumptions of Poisson input, negative exponential holding time, and blocked calls delayed. The queuing discipline may be arbitrary but is usually approximately first come, first served. It is used for common control engineering. ERROR A discrepancy between two different states of information which are intended to be identical. For example, received versus sent, measured versus true. ERROR RATE A measure of the ratio of incorrectly received data to the total amount of data received. It is usually expressed as a probability of error bits to total bits (e.g., l x10 to the sixth power). EXCHANGE OR EXCHANGE AREA (TRADITIONAL DEFINITION) A geographic area established by a BOC for the administration and pricing of telecommunications services in a specified area that usually em braces a city, town, or village and its environs. It consists of one or more central offices and the associated facilities used in furnishing telecommunications service within that area, and does not have the same meaning as the exchanges defined by the MFJ. [See LOCAL ACCESS AND TRANSPORT AREA (LATA).] EXCHANGE SERVICE A communication service permitting the interconnection of any two of a number of customers' telephones through switching equipment. EXPANDOR A device that increases the output voltage range over the range of the input voltage. EXPANSION The switching function of making a small number of inputs accessible to all of a larger number of outputs. The inverse is CONCENTRATION. EXPANSIVE CONTROLS Control applications that reroute traffic from congested portions of the network to trunk routes and switching systems having available capacity. EXTENDED AREA SERVICE A telephone service which provides service beyond the usual boundary to contiguous areas without toll charges. This exists in areas where there is a community of interest. The toll charges are not applied in return for a somewhat higher basic exchange service rate. EXTENSION 1. An extra telephone instrument associated with a main telephone station on the premises but at a different location. 2. Each telephone served by a PBX. 3. The process of passing a call from an attendant position in a PBX to the desired station user. EXTENSION STATION LINE A circuit between an extension service location and the associated main service location or a central connecting point of the main service. EYE PATTERN An oscilloscope display used to determine visually the quality of a line signal being received. It is called an eye pattern because the pattern appearing on the scope resembles the elliptical shape of the human eye. A wide open pattern displays a good line. Reductions in the height demonstrate amplitude degradations. Horizontal reductions show timing degradations. FACILITIES NETWORK The aggregate of transmission systems, switching systems, and station equipment; it supports a large number of traffic networks. FACILITY 1. Any one or all of the elements of a physical plant used to provide communications services. Often used synonymously with a transmission path including all of the physical equipment associated with that path. 2. A component of the operating system of a computer (e.g., sort facility). FACILITY NODE A physical location where a number of inter-building transmission facility routes converge, terminate, and can be cross-connected. As used here, the facility nodes terminate both interLATA facilities and LATA access facilities to one or more BOC wire centers. FACSIMILE Graphic information transmitted over the telephone network. This term is often used to describe the transmission system and station equipment used in such transmission. FAR-END CROSSTALK (FEXT) Signal distortion caused by coupling of an outgoing signal at the distant end of a circuit with the return signal being transmitted from that remote station. FEATURE/FUNCTION ACCESS CODE A code of the form *XX or XX currently used by end users for control of and access to Custom Calling Services (such as activation and deactivation of Call Forwarding and making changes to Speed Calling lists). In addition to BOC usage, future applications of *XX or XX may include access to special features, functions, or services provided by ICs when a carrier access code has been dialed. A BOC may screen and route a call to an IC POP based upon the feature/function access code. (See CARRIER ACCESS CODE and SERVICE ACCESS CODE.) FEATURE GROUP D The trunk side access to exchange carrier end office switching systems and tandems. It provides for the equal-access service that the BOCs must offer per the MFJ. FEDERAL COMMUNICATIONS COMMISSION (FCC) The federal agency empowered by law to regulate all interstate and foreign radio and wire communications services originating in the United States, including radio, television, facsimile, telegraph and telephone systems. The agency was established under the Communications Act of 1934. Current legislation to rewrite the 1934 Act proposes changing the FCC's authority regarding regulation jurisdiction from interstate service to interexchange services which would include both interstate and much of what is, today, intrastate toll services. FEEDBACK The return of part of the power of an output signal to the input side of the device or process. FEEDBACK AMPLIFIER An amplifier in which part of the power of the output signal is returned to the input of the amplifier in order to change the performance characteristics of the amplifier. If the feedback is positive (same phase as the input), the amplification is increased. If the feedback is negative, the amplification is decreased but is stable and controllable. FEEDER CABLE A large pair-size loop cable emanating from a central office and usually placed in an underground conduit system with access available at periodically placed manholes. FEEDER ROUTE A network of loop cable extending from a wire center into a segment of the areas served by the wire center. FEEDER SECTION A segment of a feeder route that is uniform throughout its length with respect to facility requirements and facilities in place. FERREED SWITCH A coordinate switch in which the contact material is magnetic and there fore can be self-latching, depending on the current conditions pulsed into a coordinate array of magnetic coils. FERRITE SHEET MEMORY The temporary call-store memory of the No. 1 ESS. It is so called be cause the basic memory units are sheets of ferrite material drilled to produce toroid-like arrays. FERROD A ferrite rod wound with an induction coil and used as an antenna or other sensitive current detection application. FIBER OPTICS A technology which uses a thin fiber of optical glass to transmit optical energy. It can be used for illumination or, in communications applications, for transmission of information using a modulated optical signal. FILTER A device which transmits a selective range of matter or energy. An electrical filter transmits a selected range of frequencies while attenuating all other frequencies. A filter may be used to reject unwanted frequencies or to select desired frequencies. FINAL TRUNK GROUP A last-choice trunk group that receives overflow traffic may receive first-route traffic for which there is no alternate route. FINE MOTION SWITCH Any switch characterized by small motion (typically less than 1/8 inch) of the moving contact. A relay is an example. (See GROSS MOTION SWITCH.) FIRST-ATTEMPT LOAD An offered load that includes any load resulting from retrials. FLOATING BATTERIES The usual scheme for powering telephone equipment in which batteries are simultaneously charged (from either a generator or a commercial source) and discharged to operate the telephone equipment. FLOW CONTROL PARAMETERS NEGOTIATION - FOR VIRTUAL CALLS This facility is established by service provisioning. It permits negotiation on a per-call basis of the flow control parameters, window size and packet size, for each direction of data transmission at the interface. FOREIGN EXCHANGE SERVICE Exchange service from an exchange other than the one from which service would normally be provided. The use is primarily to reduce cost to the user for traffic to or from a heavily used remote location. FOUR-WIRE (See FULL DUPLEX.) FOUR-WIRE CIRCUIT A two-way circuit using separate one-way paths for transmission and reception. Most long-distance transmission is four wire because it is less subject to interference. FOUR-WIRE REPEATER A telephone repeater with two amplifiers, one for each direction of transmission, for use on a four-wire circuit. FOUR-WIRE TERMINATING SET A hybrid circuit device which interfaces a four-wire circuit with a two wire circuit. FRAME Frame has the following definitions: 1. A segment of a signal, analog or digital, that has repetitive characteristics in that corresponding elements of successive frames represent the same things. Examples are: a television frame, which represents a complete scan of a picture; or a telemetry frame, which represents values of a number of parameters in a specific order. In a time division multiplexed system, a frame is a sequence of time slots, each containing a sample from one of the channels served by the multiplexer system, and each channel occupies the same sequence position in successive frames. 2. An assembly of equipment units. FRAMING The process of establishing a reference so that time slots or elements within the frame can be identified. FREQUENCY The rate of recurrence of some repetitive event such as an electrical signal. It is measured in cycles per second (cps) or Hertz. FREQUENCY DIVISION MULTIPLEXING (FDM) A transmission technique in which the available frequency range of a transmission path is divided into a number of narrower band subchannels, each of which becomes a separate transmission path. FREQUENCY FROGGING The technique of changing the relative positions of channels in a common spectrum periodically, along a transmission path, to reduce intermodulation noise or crosstalk. FREQUENCY MODULATION (FM) A modulation technique in which the carrier frequency is shifted by an amount proportional to the value of the modulating signal. The amplitude of the carrier signal remains constant. FREQUENCY SHIFT KEYING (FSK) A technique for transmitting information by altering the carrier frequency to a discrete set of frequencies corresponding to the discrete levels of the input data stream. FULL DUPLEX TRANSMISSION The process of operating a circuit so that each end can transmit and receive simultaneously. FUNDAMENTAL FREQUENCY The lowest frequency component of a complex signal. GAIN The ratio between the output signal and the input signal of a device. GENERIC PROGRAM A program that is applied to a group or class of devices. Specifically used to refer to the programs that are applied to a class of electronic switching systems. GIGABIT A gigabit is equal to one billion bits. GIGAHERTZ One billion cycles per second. GRADE OF SERVICE Grade of service has the following definitions: 1. An estimate of customer satisfaction with a particular aspect of service vice (such as noise or echo). It combines the distribution of subjective options of a representative group of people with the distribution of performance for the particular aspect being graded. For example, with a specified distribution of noise, 95% of the people may judge the noise performance to be good or better; the noise grade of service is then said to be 95% good or better. 2. The proportion of calls (usually during the busy hour) that cannot be completed due to limits in the call-handling capability of a component in a network. For example, service objectives are defined on a per link (per-trunk group) basis for the last-choice groups in a traffic network. (See SERVICE OBJECTIVE.) GRADE-OF-SERVICE TRUNK GROUP A trunk group engineered to a specific blocking objective, i.e., a final trunk group or an only-route trunk group. GRANDFATHERED The process of continuing an otherwise discontinued service for prior subscribers. GRAY CODE A binary code in which the coded representation of sequential characters differs from the preceding character by only one bit. DECIMAL 0 1 2 3 4 5 6 7 BINARY 000 001 011 010 110 111 101 100 GRAY 000 001 010 011 100 101 110 111 GROSS MOTION SWITCH Any switch in which the moving contact travels a large distance to connect to the desired fixed contact. Travel may vary between 1/8 inch to as much as 20 to 24 inches. An example is a rotary switch. (See FINE MOTION SWITCH.) GROUND START A technique of signaling from a telephone set to an exchange by connecting one side of the line to ground. It is commonly used on coin telephone and PBX lines to the central office. (See SIGNALING.) GROUP BUSY HOUR (GBH) The busy hour for a group of servers. It may be either a bouncing busy hour or a time-consistent busy hour. GROUP CHANNEL Twelve voice grade channels. This is one of the levels of the transmission hierarchy. GUARDBAND The unused frequencies between two frequency divided channels which provides the margin of safety for the prevention of crosstalk. HALF DUPLEX A channel or device which can communicate in both directions but not simultaneously. HALF-DUPLEX TRANSMISSION A technique of operating a communications circuit so that each end can transmit or receive but not simultaneously. Normal operation is alternate, one-way-at-a-time transmission. HANDSET Any of the various forms of manual telephone instruments, usually considered to be the sender-receiver associated with the voice telephone unit. HARDWARE A descriptor for the physical components of a system, as opposed to the programs, procedures and operations of a system. HARDWIRED 1. Equipment which is wired together so that its function is fixed (as compared to equipment in which plug-in components may be varied to change the function). 2. Equipment units which are permanently cabled together (as compared to those which may be flexibly interconnected at a distributing frame). HARMONIC A secondary signal component whose frequency is a whole number multiple of the primary signal frequency. HARMONIC DISTORTION A signal distortion caused by the presence of harmonic frequencies which are, in turn, generated by non-linearities in the transmission path. HEADSET A voice communications sending and receiving device worn on the head. HERTZ (HZ) A unit of frequency. One Hertz is equal to one cycle per second. HIERARCHICAL NETWORK A network that includes two or more different classes of switching systems in a defined homing arrangement. HIGH PASS FILTER A filter which attenuates all frequencies below a given design limit and allows all signals above that limit to be passed through the unit. HIGH-USAGE GROUP A trunk group which is the primary direct route between two switching systems. The group is provided with an alternate route for overflow traffic in order to provide an acceptable level of blocking. HIT A random and momentary disturbance on a transmission path which could result in a transmission error. HOLDING TIME The length of time an attempt, call, or message occupies a component of the network. Holding times are normally expressed in seconds or minutes. HOME TANDEM A tandem of a higher office class to which another tandem or an end office has a final trunk group. Home tandems may exist for all or defined subsets of tandem switched traffic. HOMING ARRANGEMENT The last-choice trunk group(s) between switching systems in a specific routing ladder. HUNDRED CALL SECONDS (CCS) A measure of traffic intensity. It is one traffic path occupied for 100 seconds per hour. Thirty-six hundred call seconds equals one Erlang. HUNT Used to describe the automatic process by which a switch progresses from contact to contact, usually seeking an idle path. HYBRID COIL A transformer-like device which is designed to provide the interface between a two-wire and four-wire circuit. The device has four ports designed such that a signal input to one port will be split evenly to the two adjacent ports with no signal coupled to the opposite port. One port is connected to the two-wire line. The two adjacent ports are connected to the four-wire line. The opposite port is connected to a balanced net work to cancel any stray signals. IMPEDANCE The total opposition offered by an electrical component or circuit to the flow of electrical current. IMPULSE NOISE Line noise characterized by high amplitude, short duration pulses converting the entire bandwidth of the transmission path. Such noise is typically the result of switching transients or electrical storms. IN-BAND SIGNALING A method of transmitting control signals using the same bandwidth as the basic information transmission stream. In the case of voice transmission, the bandwidth is that of the voice frequencies. TOUCHTONE is a form of in-band signaling. IN-WATS A toll telephone service of the long-distance telephone carriers which provides a reduced rate, reverse charge telephone service. It is commonly recognized as 800 service by reason of the area code used. INCOMING PEG COUNT A measurement of the number of attempts, counted at the incoming end of a trunk group, that have seized a trunk in the group. Incoming peg count measurements are generally used where no peg count measurement is available at the originating end of the trunk group. INCOMING REGISTER Equipment used to receive call completion information on an interoffice call in which the completing office uses a crossbar system. INCOMING TRUNK 1. A trunk coming into a central office. 2. A PBX trunk arranged to receive calls from the central office. INCREMENTAL CCS (ICCS) The increase in the calling capacity of a trunk group that results from adding one trunk to the group while maintaining the Objective ECCS or level of blocking. It is not to be confused with the average CCS per trunk or with ECCS. (See ECONOMIC CCS.) INDUCTIVE CONNECTION A connection between a telephone instrument and another device by means of the electromagnetic field generated by the telephone instrument. No direct electrical connection is established between the two devices. INFORMATION Any type of knowledge or data in a usable form. INSIDE WIRE (IW) All wire on the end user's side of the network interface, excluding fully protected premises wire and intra-system wire (described in Part 68 of the FCC rules). INTEGRATED SERVICES DIGITAL NETWORK (ISDN) A switched digital transmission network capable of handling voice and data traffic. Work on the standards for such networks is proceeding in the U.S. and in the rest of the world. INTELLIGIBLE CROSSTALK Crosstalk which is of sufficient level to be able to be understood by a listener. INTERLATA A term used to describe services, revenues, functions, etc. that relate to telecommunications originating in one LATA and terminating in another LATA or outside of a LATA. INTERLATA CARRIER (IC) Any carrier that provides telecommunications services between a point in a LATA and a point in another LATA or outside a LATA. INTERCEPT OPERATOR A person who provides intercept service at an intercept position of a switchboard or at an auxiliary services position of a centralized intercept bureau. INTERCEPT SERVICE A service in which a telephone call directed to an improper telephone number is redirected to an operator or to a recording. The caller is in formed why the call could not be completed and, if possible, is given the correct number. INTERCEPT TRUNK GROUP A trunk group that provides information concerning called numbers that are unassigned, changed, disconnected, or placed on trouble intercept. Typical applications commonly employ the following types of trunk groups: o End Office to Desk o End Office to Trunk Concentrator o End Office to Cord Switchboard o End Office to Announcement System o Tandem to Cord Switchboard o Tandem to Desk o Trunk Concentrator to Announcement System INTERCONNECTION A term generally used to describe the connection, with or without a protective connecting arrangement of customer- or OCC-provided equipment or communications systems to facilities of the BOCs or the independent telephone companies. INTEREND OFFICE TRUNK GROUPS A category of trunk groups that interconnect end offices. INTERFACE The point of interconnection between terminal equipment and telephone company communication facilities. INTERFACE DEVICE A device which meets a standard interface specification on one side and meets some other interface on its other side. The purpose of the device is to allow another device with a nonstandard interface to connect to a standard interface. INTERFERENCE Undesired energy received with a signal which makes the signal more difficult to understand. The interference may be man-made (e.g., electrical noise from other machinery), or it may be from atmospheric disturbances (e.g., lightning), or from any number of other sources. INTERMEDIATE HIGH-USAGE TRUNK GROUP A high-usage trunk group that receives route-advanced overflow traffic and may receive first-route traffic and/or switched-overflow traffic. INTERMODULATION DISTORTION Signal distortion caused by the combining of two frequencies or their harmonics to produce new signal components. INTERNATIONAL TELECOMMUNICATIONS SATELLITE CONSORTIUM (INTELSAT) An international organization established in 1964 to govern a global commercial communications satellite system to provide communications between many countries. Membership is in excess of 80 countries. The Communications Satellite Corporation acts as manager for INTELSAT and also represents the United States. INTEROFFICE CHANNEL A portion of a communications circuit between central offices of a common carrier which serves customers located in different central office areas. When associated with foreign exchange service, the term denotes the channel which interconnects a primary wire center to a different wire center. INTEROFFICE TRUNK A trunk used to interconnect two Central Offices. INTERPOSITIONING An equipment configuration in which carrier-provided terminal equipment accesses exchange carrier facilities through customer-provided terminal equipment. INTERSTATE Between states. Communications services between states are regulated by the Federal Communications Commission. INTERTANDEM TRUNK GROUPS A category of trunk groups that interconnect tandems. INTRALATA A term used to describe services, revenues, functions, etc. that relate to telecommunications originating and terminating within a single LATA. INTRAOFFICE TRUNK The equipment necessary in some switching offices to allow a call originated in one office to complete to a number in the same office. INTRASTATE Within a given state. Communications services within a state are generally regulated by the state utility commission. INWARD OPERATOR TRUNK GROUP A trunk group used to provide distant operators with the means of obtaining an inward operator's assistance for the completion of calls. A typical application commonly employs a tandem to cord switchboard type trunk group. JACK A connecting device into which a plug can be inserted in order to form a temporary electrical connection. JUNCTOR Within a switching system, a connection or circuit between inlets and outlets of the same or different switching networks. An intraoffice trunk. JUNCTOR TRUNK GROUP A special purpose trunk group used to provide a particular feature. It is normally used for such purposes as coin control, billing supervision, etc. JURISDICTION A geographic area presided over by the same regulatory body, within the boundary of a single state and an area in which a common carrier is authorized to provide service. KEY PULSING A method of signaling by depressing keys on a line otherwise arranged for rotary pulse dialing. KEY STATION LINE The circuit which extends from the key set to the key system common equipment. KEY SYSTEM A group of associated key sets and common equipment located on a customer's premises and connected to provide the various features accessible to a key set. KEY TELEPHONE SET A telephone instrument with keys or buttons which are used to select a specific line from several possible incoming lines. The buttons usually have lamps and can provide features such as call holding, line status, signaling, conferencing and intercom. KILO A prefix representing 1000. It is part of a magnitude prefix series which includes mega-, giga-, tera-, and peta-. KILOBIT One thousand bits. It is usually used to designate 2 to the 10th bits, which is actually 1024 bits. One or more characters or words which are used to identify a record, message or file in an information handling system. KILOHERTZ One thousand hertz, or one thousand cycles per second. LASER An acronym for Light Amplification by Stimulated Emission of Radiation. A device which concentrates electromagnetic energy into a narrow band of coherent light. LAST TRUNK BUSY (LTB) A measurement of the number of times the last trunk in a group was busy during measurement period. (See MEASUREMENT.) LAST TRUNK CCS (LTCCS) The load in CCS carried on the last trunk (or theoretical last trunk) in a high-usage trunk group. LAST-CHOICE ROUTE The last-choice group trunk group (or a series of last-choice trunk groups) between two switching systems. LAST-CHOICE TRUNK GROUP A final trunk group or only-route trunk group in a hierarchical network. LATA ACCESS Any activity or function performed by a BOC in connection with the origination or termination of interLATA telecommunications for an IC. This includes, but is not limited to, the provision of network control signaling, answer supervision, automatic calling number identification, carrier access codes, directory services, testing and maintenance of facilities, and the provision of information necessary to bill customers. (See SWITCHED LATA ACCESS.) LATA TANDEM (LT) A BOC switching system that provides an intraLATA traffic concentration/distribution point for EO switching systems or other tandems within a LATA. LINE Line has the following definitions: 1. A pair of wires carrying direct current between a central office and a customer's terminal. A line is the most common type of loop. (See LOOP.) 2. In carrier systems, the portion of a transmission system that extends between two terminal locations. The line includes the transmission media and associated line repeaters. 3. Also used to indicate the side of a piece of central office equipment that connects to or toward the outside plant; the other side of the equipment is called drop side. 4. A family of equipment or apparatus designed to provide a variety of styles, a range of sizes, or a choice of service features. LINE EQUIPMENT Equipment located in a central office and associated with a particular line. This includes a line relay or equivalent that is activated when the customer's telephone is off-hook. LINE FINDER A component of a switch which locates an idle line and connects it to the line requesting service. LINE LINK The input side of the switching network in the Number 5 Crossbar sys tem. LINE LOAD CONTROL A control application that limits the number of customers who can obtain dial tone. LINE NOISE Noise originating in a transmission path. LINE RELAY The relay equipment associated with a customer's line, used to alter the switching machine of a demand for service for that line. It is used also to deny incoming access to a line already in use. LINE SPEED The maximum rate at which signals may be transmitted over a given channel. It is usually measured in baud or bits per second. LINEAR DISTORTION Undesirable changes in the amplitude of a transmitted signal due to imperfections in the transmission path. LINES, TELECOMMUNICATIONS (See TELECOMMUNICATIONS LINES.) LOAD A volume of traffic that equals the sum of the holding times for a number of calls or attempts. Loads are normally expressed in either CCS or ERLANGS. A statement of load is inherently an average of all of the instantaneous loads over a basic time interval such as an hour. LOAD BALANCING The process of assigning customers to line equipment to maintain a proper distribution of traffic in a switching system. Load balancing also is done at other places in switching equipment, such as on incoming selectors in step-by-step systems. LOAD COIL (ALSO LOADING COIL) An inductance coil installed at regular distances along a transmission line to improve the transmission characteristics of the line over the range of voice frequencies. LOADED LINES A transmission line which has had load coils installed in series with each conductor, usually at definite spaced intervals. A common plan used in the U.S. is 88 millihenry coils installed at 6000-foot intervals. ONA - OPEN NETWORK ARCHITECTURE Unbundling of network capabilities to allow third-party providers known as Enhanced Services Providers to economically access some portions of the telephone network in order to sell enhanced services to customers. ONA was part of Computer Inquiry III issued by the FCC in May, 1986. ON HOOK The normal inactive condition of a telephone terminal. In this condition, the switchhook contacts at the telephone instrument are open and a no current signal is sent to the central office. ONE-WAY TRUNK A trunk circuit which can be seized at only one end. ONLY-ROUTE TRUNK GROUP A trunk group that is the one and only route for particular traffic items. It receives only first route traffic, does not receive overflow traffic, and has no alternate route. OPEN WIRE A transmission path consisting of a pair of wires, spaced a parallel distance apart and mounted on insulators, usually on a pole line. OPERATOR NUMBER IDENTIFICATION Operator identification of a calling number is required because there is no ANI equipment in the originating office. The operator obtains the calling station number then keys this number into CAMA equipment. OPTICAL CARRIER LEVEL 1 (OC-l) The optical designation for SONET signals. The OC-1 designation reflects that at that point, the signal is in an optical (as opposed to electrical) format and is transmitting at the level 1 rate of 51.84 Mbps. ORDER WIRE A transmission channel connecting operating personnel employed by the communications service provider. ORIGINATING REGISTER In a Number 5 Crossbar System, the equipment that is connected to a subscriber initiating a call to receive the dial pulses or TOUCHTONE signals from the subscriber's telephone. ORIGINATING REGISTER LINE MEMORY In a Number 5 Crossbar System, short-term memory used to hold call processing data. OTHER COMMON CARRIER (OCC) Specialized common carriers, domestic and international record carriers and domestic satellite carriers engaged in providing communications services. OUT-OF-BAND SIGNALING Any signaling method which uses frequencies that are not in the normal transmission frequency bands of the information transmissions. It includes DC signaling as well as tone signaling which is out of the voice frequencies. OUTGOING CALLS BARRED This facility prevents a packet switch from accepting outgoing virtual calls from the data terminal equipment. OUTGOING SENDER Equipment used to transmit call completion information on an interoffice call. OUTSIDE PLANT The physical facilities of a communications carrier which are located outside of the carrier's buildings. It includes cables, pole lines, conduit, and some equipment such as load coils. Microwave towers and equipment, and cable repeaters are not considered part of outside plant. OVERFLOW A measurement of the number of attempts failing to find an idle server in a group of one or more servers. OVERFLOW LOAD That part of the offered traffic that is not carried, i.e., overflow traffic equals offered traffic minus carried traffic. PACKET A group of bits treated as a unit for communications routing. This unit includes addressing, routing, and customer data. PACKET SWITCHING A switching technique where addressed packets are individually routed to the destination. The routing is a function of the availability of transmission paths. Long messages are broken into multiple packets which are routed individually and then reassembled in the proper order at the destination. PAD 1. A process of filling a transmission block with null data. 2. A device which introduces transmission loss in order to achieve a desired impedance. 3. An abbreviation for Packet Assembly/Disassembly, a function required to interface a packet switched network. PAD SWITCHING A technique of automatically cutting a transmission loss pad into and out of a transmission circuit for different operating conditions. PAIR GAIN The number of customers served by a communication system less the number of wire pairs used by that system. Pair gain can be achieved by multiplexing and by concentration. PAIRED CABLE A cable in which all of the conductors are arranged in the form of twisted pairs. This form of cable is, by far, the most common form of cable used for communications. PANEL SYSTEM An almost obsolete register progressive control switching system. PARITY BIT A bit added to a coded character to provide a predetermined odd or even count of the total number of bits in the character. In ASCII code, for example, the 8th bit is a parity bit added to a seven-bit code. PARTY LINE A circuit assigned to serve two or more subscribers with discriminatory signaling for each station. PASS BAND The range of frequencies which can be satisfactorily provided on a transmission path. PATCH PANEL A device in which temporary connection can be made between incoming lines. It is used for modifying or reconfiguring a communications system or for connecting devices such as test instruments to specific lines. A patch panel differs from a distribution frame in that the interconnections are intended to be more permanent on a distribution frame. PEAK LOAD The traffic volume at the highest level during a given time period. It is usually expressed as the traffic volume during the highest one-hour period of the day. (See BUSY HOUR.) PEG COUNT (PC) A measurement of the number of attempts to seize a server in a group of one or more servers. PERIPHERAL EQUIPMENT Any input/output device connected to a control/processing unit (e.g., tape drives, card readers). PERMANENT SIGNAL A sustained off-hook supervisory signal, originating outside a switching system and not related to a call in progress. Permanent signals can occupy a substantial part of the capacity of a switching system. PHANTOM CIRCUIT A third circuit derived from two physical circuits by means of repeating coils installed at the terminals of the physical (side) circuits. PHASE DISTORTION An unwanted modification of a transmitted signal caused by the nonuniform transmission of the different frequency components of the signal. Same as Delay Distortion. PHASE JITTER An unwanted modification of a transmitted signal caused by the rapid fluctuation of the frequency of the transmitted signal. PHASE MODULATION A transmission technique in which the phase angle of the carrier relative to its original position is varied by the value of the signal to be transmitted. POINT OF PRESENCE (POP) A physical location within a LATA at which an IC establishes itself for the purpose of obtaining LATA access and to which the BOC provides access services. POPs apply to both switched and special access, al though different ones may be used for different services. POINT-TO-POINT A line or a transmission between two points which neither requires nor transmits an intermediate point. POISSON In traffic theory, Poisson refers to a distribution or a process resulting in a distribution of events such that the intervals between adjacent events are independent random variables that are members of identical exponential distributions. Under certain conditions, the arrival of telephone calls to be routed over a trunk group can be approximated by a Poisson distribution. Named after the l9th century French mathematician. POWER LEVEL The measure of signal power at some point. The measure can be referenced to some power level, in which case the measurement is expressed in dB. It may also be referenced to one milliwatt, in which case the measurement is expressed in dBm. PREFIX Any dialed digit input prior to the destination address. Prefixes are used to place an address in proper context, to indicate service options, or both. Examples: Prefix 1, to indicate a toll call; Prefix 0, to request the services of an operator. PREMISES The office or building of the user or a set of buildings on a user's property which is not divided by a public road. PRESUBSCRIPTION A BOC tariffed service that permits each customer served from an equal access EO switching system to automatically route, without the use of access codes, all the customer's interLATA communications to one IC of the customer's choice. The customer may also gain access to other ICs using the appropriate carrier access code, e.g., 10XX. (See PRIMARY INTERLATA CARRIER.) PRIMARY HIGH-USAGE TRUNK GROUP A high-usage trunk group that is offered first-route traffic only. PRIMARY INTERLATA CARRIER (PIC) The IC designated by a customer to provide interLATA services automatically without requiring the customer to dial an access code for that carrier. (See PRESUBSCRIPTION.) PRIMARY RATE INTERFACE (PRI) A T-1 rate interface between the customer and the ISDN. PRI gives customers access to a wide array of channel arrangements to utilize the available bandwidth of 1.54 MBps. PRIVATE BRANCH EXCHANGE (PBX, PABX) A private telephone switching system, usually located on a customer's premises. The abbreviation PBX is a general term applied to all types of PBXs, both manual and automatic. The abbreviation PABX implies an automatic PBX. The system provides intra-premises exchange telephone service, as well as access to the public exchange network and/or private facilities. Although these switches are increasingly being used for data communications, as well as voice, they are primarily designed for voice. PRIVATE LINE A circuit leased by customers for their exclusive use, connecting two or more terminal equipments only to each other and working independently of any central office switched interconnections; it may be used for voice, data, television, etc. PRIVATE LINE MAGAZINE Defunct hardcopy magazine now on the web. The finest self indulgent nonsense about the telephone system. http://www.privateline.com PRIVATE VOICEBAND NETWORK A network that is made up of voiceband circuits, and sometimes switching arrangements, for the exclusive use of one customer. These networks can be nationwide in scope and typically serve large corporations or government agencies. PROCESSOR The intelligent central element of a computer or other information-handling system. PROGRAM A series of predetermined, machine understandable instructions which control the functions of a processor. PROGRAM CIRCUIT A voice circuit which is used for the transmission of radio program materials. It is a telephone circuit that has been equalized to handle a wider range of frequencies than are required for ordinary speech signals. PROGRAM STORE In an electronic switching office, the semipermanent memory used for the controlling stored program. PROPAGATION DELAY The elapsed time for a signal to travel from one point on a transmission path to another point. It is a function of the distance and the speed of the signal through the transmission media which is usually some major fraction of the speed of light. PROTECTOR FRAME A frame, usually part of the MDF, that serves as termination for loop cables. The protector frame contains electrical protection devices that normally provide conducting paths but will break down and electrically isolate a loop from the switching equipment when an abnormally high voltage occurs as may result from lightning or contact between a power line and a telephone line. PROTOCOL A set of rules by which a communication network is operated in order to perform a specified set of communications functions. Binary synchronous communications is a data communications protocol. PUBLIC SERVICE COMMISSION (PSC) The state regulatory authority responsible for communications regulation. Also known as Public Utility Commission, Corporate Commission, and in some states the Railway Commission. PUBLIC SWITCHED NETWORK Any common carrier network that provides circuit switching between public users. The term is usually applied to the public telephone net work, but it could be applied more generally to other switched networks such as Telex, Execunet, etc. PUBLIC SWITCHED TELEPHONE NETWORK (PSTN) The network is an integrated system of transmission and switching systems, signaling processors, and associated operations support systems (OSS) that is shared by the public. Sometimes referred to as PTN, PSN, PN (Public Telephone Network, Public Switched Network, Public Network.) PUBLIC TELEPHONE SERVICE (PTS) Ordinary telephone service in which a customer has a connection to a central office and can be connected to any other customer of the service. Sometimes called plain old telephone service (POTS). PULSE A momentary, sharp change in the current, voltage or other quantity that is normally constant. It has a sharp rise and fall and is of finite duration. Also called an impulse. PULSE AMPLITUDE MODULATION (PAM) A modulation technique in which the amplitude of each pulse is related to the amplitude of an analog signal. Used, for example, in time division multiplex arrangements in which successive pulses represent samples from the individual voiceband channels; PAM is also used in time division switching systems of small and moderate size. PULSE CODE MODULATION (PCM) A technique for converting an analog signal, such as voice, into a digital bit stream for transmission. In this technique, the instantaneous value of the analog signal is converted into a binary code which is transmitted as a serial bit stream. PULSES PER SECOND (PPS) The number of pulses per second. The number of dial pulses per second. PULSING That part of signaling that forwards the destination code required to route a call. PUSH BUTTON DIALING The use of buttons on a telephone rather than a rotary dial to address a telephone message to a terminal point on the network. Push button dialing usually enlists two-tone signaling. In AT&T's terminology, the registered trademark "TouchTone" is used. QUANTIZATION Representation of samples by a discrete or finite numerical value. QUANTIZING NOISE Signal errors which result from the process of digitizing (and therefore ascribing finite quantities to) a continuously variable signal. QUEUE 1. A waiting line generated by the time required to move through a channel or a process. 2. The process of forming queue. RAIN BARREL EFFECT Signal distortion of a voice telephone line caused by the under attenuated echo on the return path. The resultant distortion gives a near singing effect like that of speaking into a rain barrel. RANGE EXTENDER A device that permits a central office to serve a line that has resistance that exceeds the normal limit for signaling. A range extender does not extend transmission range. Range extenders are also used in special service circuits. RANGE EXTENDER WITH GAIN) A unit that provides range extension in a loop for both signaling and transmission. RATE 1. The potential capacity for data transmission channels measured in bits per second (bps). 2. The service charge of a communications common carrier. REAL TIME An operating mode in which the information to be handled is sent, processed and returned in a time interval which is short relative to the perception or the requirement of the person or process requiring the information. RECEIVER That portion of a transmission path which converts the signals as received from the transmission system into the signals required by the destination equipment. RECEIVING The process by which a device accepts information from a transmission system. The device which receives the information is referred to as a receiving or destination station. REDUNDANCY Additional system or information elements used to improve reliability. System components would include back-up devices such as stand-by processors or modems. Information redundancy includes parity bits and the extra bits used in error checking codes. REDUNDANT BITS The extra bits included in a transmission for purposes of detecting and/ or correcting errors. REFERENCE LEVEL The measure of a value used as a starting point for further measurements. In communications applications, this term usually refers to a power level of a signal or a noise. A common reference level is 0 dBm; that is, one milliwatt. REFERENCE NOISE A reference level of noise power. This is usually 0 dBrnc, which is 10-9 milliwatts of noise at 1000 Hz. REGENERATION The technique of reshaping and amplifying received signals to their original form. This technique is usually applied to digital pulses. REGENERATIVE REPEATER A device which regenerates incoming digital signals and retransmits these signals on an outgoing circuit. REGISTER A part of an automatic switching system that receives and stores signals from a calling device or other sources for interpretation and action, some of which is carried out by the register itself. REGISTER PROGRESSIVE CONTROL A generic type of switching system in which the call progresses blindly one step at a time through the network under control of a translator and a register into which the originating subscriber has dialed the desired telephone number. REGULATED PUBLIC UTILITY A firm that supplies an indispensable service under essentially non-competitive conditions with governmental regulation of prices, rate of return, and service quality. REGULATION 1. The governmental process by which communication services, their rates and availabilities are controlled. 2. The process of controlling the signal levels and other variables on a transmission system. RELATIVE TRANSMISSION LEVEL The ratio of the test-tone power at one point to the test-tone power at some other point in the system chosen as a reference point. The ratio is expressed in decibels. The transmission level at the transmitting switch board is frequently taken as zero level reference point. RELAY 1. A device, usually electromechanical, by which the variation in current in one circuit causes the opening or closing of contacts controlling the current flow in one or more other circuits. 2. A process of retransmitting signals or messages through an intermediate point or repeater. RELAY LOGIC Equipment functions in which algorithmic decision-making is performed by relay operations. (The usual contrast is electronic logic in which the algorithm is carried out by two-state devices, such as flip-flops.) RELIABILITY The ability of a system to perform its specified function without failure. The definition of reliability requires a specification of function, variation from function which is unacceptable, time between failures, duration of failures, etc. Many of these definitions can only be expressed in probabilistic terms. REMOTE ACCESS A process of communicating with a computer from a location which is physically removed from that computer. REGENERATIVE REPEATER A device which regenerates incoming digital signals and retransmits these signals on an outgoing circuit. REGISTER A part of an automatic switching system that receives and stores signals from a calling device or other sources for interpretation and action, some of which is carried out by the register itself. REGISTER PROGRESSIVE CONTROL A generic type of switching system in which the call progresses blindly one step at a time through the network under control of a translator and a register into which the originating subscriber has dialed the desired telephone number. REGULATED PUBLIC UTILITY A firm that supplies an indispensable service under essentially non-competitive conditions with governmental regulation of prices, rate of return, and service quality. REGULATION 1. The governmental process by which communication services, their rates and availabilities are controlled. 2. The process of controlling the signal levels and other variables on a transmission system. REMOTE SWITCHING SYSTEM (RSS) An electronic switching system that is remote from its host or control office. All or most of the central control equipment for the RSS is located in the host switching system. REORDER TONE A signal from an exchange to a subscriber instructing the subscriber to replace the call because all circuits are busy, or for other reasons. The tone is repeated 120 times per minute. The tone is also called Channel Busy or Fast Busy Tone. REPEATER In analog circuits, such as telephone and video, this device is basically an amplifier. It amplifies signals which have become too weak and re transmits them along the circuit. REPEATING COIL A transformer which connects one telephone circuit with another with out any DC connection between the circuits. REROUTING A short-term change in the routing of selected traffic items. Rerouting may be planned and recurring or a reaction to a nonrecurring situation. It is generally associated with network management activity. RESISTANCE DESIGN A telephone company design technique for subscriber loop circuits. This technique is designed to employ wire which will have the smallest diameter (least amount of copper) which will ensure a loop resistance less than the signaling limit of the central office equipment serving the loop. RESTRICTIVE CONTROLS Control applications that remove traffic from congested portions of the network. RETRIAL Any subsequent attempt by a customer, operator, or a switching system to complete a call within a measurement period. RETURN LOSS A measure of the dissimilarity of the impedance of a transmission line and the impedance at its termination. It is a ratio, expressed in decibels, of the power of the outgoing signal to the power of the signal reflected back from an impedance discontinuity. If the terminating impedance exactly matches the characteristic impedance of the line, there is no reflection and the return loss is finite. REVERSE BATTERY SUPERVISION A form of call supervision in which the signals are furnished from the terminating end of a loop to the originating office by reversing the direction of current flow. RING 1. An audible signal. 2. The process of generating a signal to a subscriber's telephone set. 3. In a 3-conductor switchboard plug, the ring-shaped contact between the tip and the sleeve. 4. A form of network configuration in which the stations are each connected to a preceding and a following station. The central control station, if any, is one more station on the ring. RING CONDUCTOR One of two wires of a cable pair used in the subscriber loop. Carries the battery from the central office. RING TRIP The process of removing the ringing signal from the line at the central office when the called station is taken off-hook. RINGDOWN A method of signaling which employs a ringing signal to operate a device such as a lamp in order to alert an operator. The term originates from the manual ringdown operation of a magneto telephone set. RINGER A device at a subscriber's telephone set which responds to a ring signal to produce an audible alert. RINGING The process of alerting the called party by the application of an intermittent 20-Hz signal to the appropriate line; this produces a ringing sound at the called telephone set. When the ringing signal is applied to the called line, an intermittent signal called audible ringing is sent to the calling telephone to indicate that ringing is taking place. RINGING TONE The signaling tone sent to the originating caller to indicate that the called line is being alerted. ROTARY DIAL TELEPHONE A telephone set at which the dial signaling is entered from a rotary dial as opposed to a TouchTone dial. ROUTE The particular trunk group or interconnected trunk groups between two reference points used to establish a path for a call. This term is also used as a verb to define the act of selecting a route or routes. ROUTE ADVANCE Within a switching system, the routing to an alternate route trunk group (or trunk subgroup) when all trunks in a prior trunk group (or trunk sub group) are busy. ROUTING The assignment of a communication path through a network with multiple possible paths in order to connect an originating station with the requested destination station. ROUTING CODE The combination of characters or digits required by the switching system to route a transmission to the desired destination. ROUTING INDICATOR The address or routing code in the beginning of a message which specifies to the network the final circuit or destination of the message. ROUTING, ALTERNATE The assignment of an alternate path through a network when the primary route is not available. SAMPLE The value of a signal, such as voltage, selected at a specific point in time. SATELLITE OPERATED PBX A PBX system which is operating at a remote location and is tied into the primary PBX by means of tie lines. The satellite does not have its own unique incoming central office trunks. All incoming calls are ex tended to the stations by means of the tie lines. SATELLITE, COMMUNICATION 1. An earth orbiting system which receives radio signals from ground based antennae (earth stations) and retransmits these signals, at a slightly different frequency, back to other earth stations. 2. A secondary system, operating remotely from, but in conjunction with, a central control system. SCANNER In an electronic switching office, a device that scans various parts of the switching network to determine when some change in operations is occurring. Information about the change is passed from the scanner to temporary memory in the controlling computer. SEIZE, SEIZURE An action of a switching system in selecting an outgoing trunk or other component for a particular call. SELECTOR SWITCH The intermediate distributing switch in a step-by-step system. It is directly controlled by the customer dial in its vertical motion and hunts for an idle path in its angular motion. SENDER Equipment in a switching system used to transmit and/or receive the called number to or from a distant office; a sender is usually arranged to transmit on a multi-frequency or dial pulse basis. Under certain conditions of trouble, a sender may remain connected to a trunk without performing its intended function; this is know as a stuck sender SERIAL TRANSMISSION The data transmission technique in which signal elements follow each other in time on a single transmission channel. SERIALIZE To change from parallel-by-bit to serial-by-bit. SERVER An item of equipment or a call-carrying path that responds to attempts. SERVICE A term defining the overall quality of telephone system performance. For network engineering purposes, service is normally stated in terms of blocking or delay. SERVICE ACCESS CODE (SAC) A code of the form "NO/lX" that takes the place of an NPA in the dialing sequence in order to access a particular service provided by an IC, BOC, or independent company. SACs currently in use include 700 (IC Services), 800 (800 Service), and 900 (National DIAL-IT* network communications service). SACs are associated with supplementary features that may be ordered by an IC as part of the access charge tariff. A BOC may screen calls and route to an IC-specified point of presence based upon a SAC dialed. There is no requirement that SACs be of the Form N00 nor that all N00 codes be SACs. SIDE HOUR Any hour other than a busy hour. It is usually used to describe an hour with a load approaching that of the busy hour. SIDEBAND The frequency bands above and below the carrier frequency which are produced as a result of modulation of the carrier frequency. SIDETONE The portion of the transmitted signal which is passed back to the receiver at the transmitting location. It is this feedback to the speaker which gives a "live" characteristic to the telephone. SIGNAL 1. A physical, time-dependent value which is the basis for conveying information through a transmission channel. 2. The act of transmitting status or control information between stations. 3. A wave used to convey information such as voice, television, data, or information for network control. SIGNAL PROCESSOR (SP) An equipment unit for electronic switching systems for use in larger offices to perform repetitive, time-consuming input-output tasks for central control. SIGNAL-TO-NOISE RATIO A measure of the relative power of the intelligence component on a channel compared to the power of the noise component on that channel. It is usually measured in decibels. SIGNAL TRANSFER POINT (STP) In CCIS, a message switching system that permits signaling messages to be sent from one switching system to another by way of one or more other offices at which STPs are located. It reduces the number of CCIS data links required to serve a network. SIGNALING The process of transmitting status or control information between stations. It includes alerting signals to operators, as well as information signals to automatic equipment. SIMPLEX A communications system or device which is capable of operating in one direction only. SIMPLEX CIRCUIT A transmission path which is capable of transmitting in only one direction. The ITU definition differs from this more common definition. ITU simplex is a path which can operate in either direction, but only one direction at a time. This is commonly called half-duplex. SINGLE FREQUENCY SIGNALING A method of conveying dial-pulse and supervisory signals from one end of a trunk or line to the other, using the presence or absence of a single specified frequency. A 2600-Hz tone is commonly used. SINGING A continuous whistle or howl caused by oscillation in a telephone circuit. It occurs when the sum of the gains in the circuit exceeds the sum of all the circuit losses and includes the losses from input port to output port of the hybrids. Provision of adequate margins in transmission objectives has made this a rare occurrence. SIGNALING SYSTEM 7 (SS7) The most advanced signaling system (replacing CCIS6) being implemented in telco networks. SS7 allows customers to access databases through the Common Channel Signaling network and utilize such services as CLASS, BOC-800, and other future services. SINK The component of a communications system which receives information. SKIP ROUTE A control application that causes traffic to bypass a specific route and advance to the following rate selection. SLEEVE 1. A control lead used in some patch cords, switchboards, and switching systems. 2. The long cylindrical contact member on a switchboard plug. SNEAK CURRENT An unwanted but steady current which seeps into a communication circuit. It is usually too weak to cause immediate damage, but if unchecked could potentially create harmful heating effects. SOFTWARE The programs, procedures, and other non-hardware elements of a computer system. SOURCE The component of a communications system which transmits information. SPACE DIVISION SWITCH A switching array in which several connections exist simultaneously in time and are separated spatially. SPECIAL LATA ACCESS A BOC-tariffed service offering that provides for a non-switched communications path (access link) between an IC Point of Presence (POP) and the premises of its end users, or to a BOC central office for Centrex services. It includes all LATA access services that do not use a BOC switching system SPECIAL SERVICE Any of a variety of switched services, non-switched services, or special rate services that are either separate from public telephone service or contribute to certain aspects of public telephone service. Examples are PBX service, WATS, foreign exchange service, and private line services, such as circuits for burglar alarms, data, teletypewriter, and television. SPECIAL SERVICE CIRCUIT A circuit used to provide a special service to a specific customer. SPEED CALLING An optional feature of a telephone system which allows the placing of calls to frequently called numbers through the use of an abbreviated number of dial digits. It is also called abbreviated dialing. START (ST) SIGNAL In MF pulsing, a signal used to indicate that all digits have been transmitted. STATION CODE The final four digits of a standard seven- or ten-digit address. These digits define a connection to a specific customer's telephone(s) within the larger context of an NPA and central office code. The term "main station code" is an equivalent expression. In the past, a line number and a party letter often were combined to provide station identification. With the discontinuance of party letters, the four numerics have assumed the role of station identification. STATION EQUIPMENT A general term used to describe the customer equipment on the end of a telephone connection. This equipment usually includes a telephone set, a private branch exchange switching system (PBX), a teletype machine, etc. STEP-BY-STEP SWITCH 1. A bidirectional, biselective switch (vertical and angular) in which the moving contact selects from among 100 fixed contacts arranged in a 10 x 10 array. 2. The basic switching unit of the system of the same name, which is presently in more widespread use than any other switching scheme in the world. STEP-BY-STEP (SXS) SWITCHING EQUIPMENT A two-wire or four-wire progressive control switching system with a space division network. The two-wire version is used for local, local tandem, toll tandem, and private line switching. It can have ANI, CAMA, CENTREX, and private line switching features. The four-wire version is used as a local tandem or toll tandem. The system is manufactured by a number of manufacturers. STEPPING MAGNET An electromagnet arranged to operate and release, so that its armature may be used to drive a ratchet (typically used to operate a gross motion switch). STORED PROGRAM A set of instructions in memory which may be executed by a processor. In the case of an Electronic Switching System (ESS), a stored program contains all the rules on how to switch and all the parameters describing that which must be switched. It does not include the short-term requirements associated with setting up an individual call. STORED PROGRAM CONTROL (SPC) Control of a switch network by means of programmable operating instructions, resident in a semipermanent memory. SUB-VOICE GRADE A communications channel with a bandwidth less than that of a voice grade channel. Usually it is derived from a voice grade channel by some form of multiplexing. SUBSCRIBER LOOP A communication channel between a subscriber station and a carrier's central office. Usually this is a pair of wires. SUBGROUP (SG) A group of 60 voice grade channels. This is one of the levels of the standard transmission hierarchy. It has a bandwidth of 240 KHz. SUPERVISION The process of monitoring and controlling the progress of a call. The status signals include off-hook, dial tone, loop seizure, answer tone, ringing tone, etc. d d SUPERVISORY SIGNALS Signals used to indicate or control the states of circuits involved in a particular connection. A supervisory signal indicates to equipment, to an operator, or to a customer that a particular state in a call has been reached and may signify the need for action to be taken. SWITCH A mechanized operations system that inventories and assigns nodal equipment and related facilities. SWITCH is designed to replace COS MOS. SWITCH ACCESS The ratio of the number of input terminals to the number of output terminals of a switch. SWITCH ROOM That part of a switching center or central office building that houses the actual switching equipment. SWITCH TRAIN The sequence of switches which are involved in the completion of a circuit path from an originating station to a destination station. SWITCHED LATA ACCESS A BOC service offering under tariff that provides for a switched communications path between an IC POP and the premises of its end users. It includes all LATA access services that use a BOC switching system (EO or AT) SWITCHHOOK A switch on a telephone set, associated with the structure supporting the receiver or handset. It is operated by the removal or replacement of the receiver or handset on the support. SWITCHHOOK FLASH A signaling technique whereby the signal is originated by momentarily depressing the switchhook. The technique is sensitive to variations in the time of depression. Too short a signal will not be recognized and too long a signal will be interpreted as a disconnect signal. SWITCHING The process of interconnecting circuits to form a communication path between pairs of stations out of a population of a much larger number of potential stations. The process may be implemented using a wide range of technologies and it includes a number of peripheral functions in addition to the connection function such as call supervision, routing, call recording, etc. SWITCHING CENTER A location with a complete set of switching equipment including all of the accessory equipment such as power supplies, test equipment, and transmission equipment. SWITCHING SYSTEM An assembly of equipment arranged for establishing connections between lines, lines to trunks, or trunks to trunks. Switching systems may employ either direct response connections or operate in a store-and forward mode. SWITCHING SYSTEM, TANDEM (See TANDEM SWITCHING SYSTEM.) SYNCHRONOUS DATA TRANSMISSION Data transmission in which the nominal signal element spacing is fixed. This is called "synchronous transmission" because the receiver must be in synchronism with the time pattern of the incoming symbols. Contrasts with asynchronous data transmission. SYNCHRONOUS OPIICAL NETWORK (SONET) A standard format for optical transmission originally proposed by Bellcore but now being standardized on a worldwide basis. The standard, if implemented by manufacturers, would permit end-to-end compatibility of different manufacturers' equipment. SYNCHRONOUS TRANSMISSION A data transmission technique in which the sending and the receiving stations are held in synchronization with each other for the duration of a transmission of a block of data or for the entire transmission. Synchronization is maintained either by high accuracy clocks at both ends of the line or by timing signals included in the transmitted data. The primary alternative to synchronous transmission is asynchronous transmission, which the sending and receiving stations remain in synch only for the duration of a single character. (See ASYNCHRONOUS TRANSMISSION.) T-CARRIER A digital transmission system standardized by AT&T for short and medium distance transmission. T-carrier is a PCM system using 64 Kbps for a voice channel. Multiplex levels are established as follows: Designation T-1 T-2 T-3 T-4 Bit Rate 1.544 Mbps 6.312 Mbps 44.736 Mbps 274.176 Mbps Number of Voice Circuits 24 96 672 4032 TALKING BATTERY Battery supplied from the Central Office to power the transmitter of the subscriber's telephone set. TANDEM The connection of networks or circuits in series; that is, the connection of the output of one circuit to the input of another. TANDEM CONNECTING (TC) TRUNK A one- or two-way trunk between an EO switching system and an AT or LATA tandem switching system. TANDEM INTERLATA CONNECTING (TIC) TRUNK The trunk used for switched LATA access that interconnects an IC POP with a BOC AT switching system. (See DIRECT INTERLATA CONNECTING TRUNK GROUPS.) TANDEM SWITCHING SYSTEM A switching system in the message network that establishes trunk-to trunk connections. TANDEM TIE TRUNK SWITCHING A switched network configuration in which transmission can be routed through two consecutive tie trunks. TANDEM TRUNK A trunk circuit which connects a tandem switch to another tandem switch or to a telephone company central office. TARIFF The schedule of rates and regulations pertaining to the services of a communications common carrier. Tariffs are filed with the appropriate regulatory agency. TELECOMMUNICATIONS 1. The transmission of intelligence through a medium by means of electrical impulses. 2. The collective services of the communications common carrier. TELECOMMUNICATIONS LINES Telephone and other communications lines that are used to transmit messages from one location to another. TELEGRAPH A communications system for the transmission of written messages by manual or machine code. TELEMETER A communications system for the transmission of digital or analog data which represents status information on a remote process, function or device. TELEPHONE 1. A communications system for the transmission of voice messages. 2. The device which acts as the terminal point in a voice telephone net work. TELEPHONE SET The terminal equipment on the customer's premises for voice telephone service. Includes transmitter, receiver, switchhook, dial, ringer, and associated circuits. TELEPHONY A general term encompassing all the technology associated with voice telecommunications. TELETYPEWRITER (TTY) A communication terminal which is capable of receiving coded character signals from a communications network and converting these signals into printed pages. This specific term is a trademark of the Teletype Corporation, an AT&T subsidiary. TERMINAL Terminal has the following definitions: 1. Equipment at the end of a communication circuit. User terminals include telephone sets and teletypewriters. 2. Carrier terminals include the modulation and demodulation equipment and the multiplex equipment used to combine and separate individual channels at the ends of a transmission system. 3. A point at which an electrical connection can be made to a device, circuit, or equipment. It is usually characterized by some means for securely fastening a wire or cable. TERMINAL REPEATER A repeater for use at the end of trunk line. TERMINATED LINE A transmission line with a resistance connected across the conductors at the far end. If this resistance matches the characteristic impedance of the line, no signals will be reflected from the far end to distort information transmissions. TERMINATION Termination has the following definitions: 1. An item that is connected to the terminals of a circuit or equipment. 2. An impedance connected to the end of a circuit being tested. 3. The points on a switching network to which a trunk or a line may be attached. TIP SIDE (TIP WIRE) That conductor of a circuit which is associated with the tip of a plug, or of a telephone circuit. TIE LINE A private line communications channel linking two or more points together. TIE TRUNK A special service circuit connecting two private branch exchanges (PBXs) or equivalent switching systems. TIME CONSISTENT BUSY HOUR Over a number of days, the identical hour each day during which the highest average traffic is measured. TIME DIVISION A method of serving a number of simultaneous channels over a common transmission path by assigning the transmission path sequentially to the various channels, each assignment being for a discrete time interval. TIME DIVISION MULTIPLEXING (TDM) A transmission technique in which a single communications channel is subdivided into a number of time slots, each of which carries the information of a separate data stream. TIP SIDE (TIP WIRE) That conductor of a circuit which is associated with the tip of a plug, or of a telephone circuit. TIE LINE A private line communications channel linking two or more points together. TIE TRUNK A special service circuit connecting two private branch exchanges (PBXs) or equivalent switching systems. TIME CONSISTENT BUSY HOUR Over a number of days, the identical hour each day during which the highest average traffic is measured. TIME DIVISION A method of serving a number of simultaneous channels over a common transmission path by assigning the transmission path sequentially to the various channels, each assignment being for a discrete time interval. TIME DIVISION MULTIPLEXING (TDM) A transmission technique in which a single communications channel is subdivided into a number of time slots, each of which carries the information of a separate data stream. TIME DIVISION SWITCH A switch in which a number of connections exist at the same point in space and are kept separate by existing at different points in time. TIME OUT The process of exceeding a preset time limit within which some specified action is to have taken place. For example, if a station fails to respond to a poll within a set time, it is said to have timed out. TIME SHARING A method allocating the use of a facility, usually a computer, to a number of users by interweaving their use in rapid succession so that each appears to have simultaneous use of the facility. TIME-SHARING The use of a facility or equipment for more than one purpose or function or for repetition of the same function within the same overall time period. This is accomplished by interspersing or interleaving the required actions in time. TIP In a two-conductor switchboard plug, the ball-shaped contact at the end of the plug. TIP AND RING The two conductors associated with a two-wire cable pair. The terms tip and ring derive their names from the physical characteristics of an operator's cordboard plug, in which these two conductors terminated in the days of manual switchboards. Use of the names tip and ring has ex tended throughout the plant. The cordboard plug also had a sleeve, and the name is occasionally used for a third conductor associated with tip and ring. TIP CABLE A small (usually 100-pair) cable connecting terminals on a distributing frame to cable pairs in the cable vault. TIP CONDUCTOR One of two wires of a cable pair used in the subscriber loop. Carries the ground from the central office. TIP, RING, GROUND The conductive paths between a central office and a station. The tip and ring leads constitute the metallic pair of wires that carry a balanced speech or data signal. The ground path, in combination with the conductors, is used occasionally for signaling. TRUNK INVENTORY RECORD KEEPING SYSTEM (TIRKS) A mechanized system which inventories and maintains records for trunks, equipment and carrier systems for the intra-office network of a telco. TOLL 1. The charge for making calls outside the boundaries of an exchange. 2. A general term applied to the facilities and services of carriers used in conjunction with making toll calls. TOLL RESTRICTION - PBX Permits a user to call within the local service area, but prevents toll calls and calls to a toll operator without the assistance of an attendant. Toll restriction is available on an individual basis under either of the following options 1. Battery Reversal: Provides a battery reversal signal from the central office on attempted toll calls which causes the PBX system to route the call to intercept tone. 2. 0/1: Screens calls from restricted lines, and routes calls in which the first or second digit following the access code is a 0 or a 1 to intercept tone. However, station users on 0/1 toll restriction lines can be al lowed to make toll calls to up to ten preselected exchange or area codes. TOLL TRAFFIC Traffic that is classified as "toll" in the tariff on file with the appropriate regulatory body. This term includes all traffic for destination beyond the local service area and extended service area. Trunk forecasting and servicing procedures are independent of the local/toll classification of traffic. TOUCHTONE A technique of telephone dialing. It is a trademark term used by AT&T to describe a dual tone, multifrequency signaling system commonly used in the switched telephone network in the U.S. TOUCHTONE DIAL A pushbutton pad and associated tone-generating circuitry used to transmit dialing signals from a subscriber station to an exchange. TRAFFIC A flow of attempts, calls, and messages. TRAFFIC CAPACITY The total volume of traffic which a communications facility can handle within a specified time period. TRAFFIC ENGINEERING The part of telephone engineering that is concerned with the quantitative load-carrying capacity of the network. TRAFFIC USAGE Total occupancy of a network. This is calculated as the product of holding time and calling rate, and can be expressed as call-hours. Traffic usage may be made up of many short calls or a few long calls - it doesn't matter. TRANSMISSION The process of transferring information from one location to another by means of some form of communications media. Transmission has the following definitions: 1. Designates a field of work, such as equipment development, system design, planning, or engineering, in which electrical communication technology is used to create systems to carry information over a distance. 2. Refers to the process of sending information from one point to an other. 3. Used with a modifier to describe the quality of a telephone connection: good, fair, or poor transmission. 4. Refers to the transfer characteristic of a channel or network in general or, more specifically, to the amplitude transfer characteristic. You may sometimes hear the phrase, "transmission as a function of frequency." TRANSMISSION FACILITY An element of physical telephone plant that performs the function of transmission, e.g., a multipair cable, a coaxial cable system, a micro wave radio system, or a fiber optic cable. TRANSMISSION LINE Any metallic medium on which an electrical signal can be impressed. A very complete mathematical model exists describing the progress of the electrical signal along the medium. This model is the basis for most telephone transmission work. TRANSMISSION OBJECTIVES Electrical performance characteristics for communication circuits, systems, and equipment based on both economic and technical considerations of telephone facilities, and on reasonable estimates of the performance desired. Characteristics for which objectives are stated include loss, noise, echo, crosstalk, frequency shift, attenuation distortion, envelope delay distortion, etc. TRANSMISSION LEVEL The power of a transmission signal at a point on a transmission facility. It may be measured in absolute terms (dbm) or in a ratio to its level at some reference point (db). TRANSMITTER A device which generates the signal to be carried on the transmission media. This usually implies a process of converting the signal from its existing form into a form which is compatible with the media, and also a process of placing that signal on the transmission media at sufficient power to carry it to the intended destination. TRUNK In a network, a communications path connecting two switching systems used in the establishment of an end-to-end connection. In selected applications, it may have both of its terminations in the same switching sys tem. TRUNK CIRCUIT A circuit, part of a switching system, associated with the connection of a trunk to the switching system. It serves to convert between the signal formats used internally in the switching system and those used in the transmission circuit, and it performs logic and sometimes memory functions associated with supervision. TRUNK GROUP The output side of the switching network in the Number 5 Crossbar System. TRUNK OCCUPANCY The percentage of time that trunks are in use. Trunk occupancy may also be expressed as the carried CCS per trunk. TWISTED PAIR A pair of wires used in transmission circuits and twisted about one an other to minimize electrical coupling with other circuits. Paired cable is made up of a few to several thousand twisted pairs. TWISTER MEMORY The semi-permanent program-store memory of the Number 1 ESS office. It takes its name from the interrogate/read portion of the memory which is based on a copper conductor, around which is twisted a helix of magnetic material. TWO-WAY TRUNK A trunk that can be seized at either end. TWO-WIRE CIRCUIT A circuit formed by two conductors insulated from each other. It is possible to use the two conductors as a one-way transmission path, a half duplex path, or a full-duplex path. UNATTENDED OPERATION The features and controls of a station or a subsystem which enable it to perform its function without human operators. Examples include such devices as individual terminals or switching systems or microwave repeaters. UNBALANCED An impairment on a transmission system in which the impedance of different sides of the system, such as conductors in a circuit pair, are not equal. UNIPOLAR A transmission technique in which a current on the line indicates a mark or a one and the absence of current indicates a space or a zero. It is used in low speed transmission systems such as for teletypewriters. UPLINK The transmission link from an earth station to a communications satellite. USAGE A measurement of the load carried by a server or group of servers, usually expressed in CCS. Usage may also be expressed in erlangs. VALIDITY CHECK Any check which is designated to ensure the quality of a transmission. A validity check compares a group of bits with the code being used to ensure that group of bits constitutes a valid character. VIRTUAL CALL SERVICE A packet switching capability that allows a customer to establish a virtual circuit between two data terminal equipments for the duration of a call. VIRTUAL CIRCUIT A logical association of sequential links in each direction of transmission between two data terminal equipments. As each packet is transmitted, the packet switch dynamically establishes a temporary physical path on a link-by-link basis from the sending to the receiving data terminal equipment. No permanent physical circuit is maintained between the two terminations. VOICE FREQUENCY (VF) The frequency range for the average human voice, which, when applied to station carrier, is 300 to 3400 Hz. VOICE GRADE CHANNEL A channel suitable for the transmission of speech, digital or analog data, or facsimile, generally having a frequency range of about 300 to 3400 Hz. WAVEFORM The characteristic shape of a period signal usually shown as a plot of amplitude over a period of time. WIDE AREA NETWORK (WAN) A communications network, serving geographically separate areas. Can be established by linking two or more metropolitan area networks (MANs) together to allow data terminals in one city to access data in another city, county, or state. WIDE AREA TELECOMMUNICATIONS SERVICE (WATS) WATS permits customers to make (OUTWATS) or receive (INWATS) long-distance voice or Dataphone data set calls and to have them billed on a bulk rather than individual call basis. The service is provided within selected service areas, or bands, by means of special private access lines connected to the public telephone network via WATS-equipped central offices. A single access line permits inward or outward service, but not both. WINDOW SIZE Window size specifies the maximum number of data packets that can be transmitted into a packet switch network without receiving additional authorization from the network. WIPER The term commonly used for the moving contact of a gross motion switch. WIRE CENTER The building in which one or more local switching systems are installed and where the outside cable plant is connected to the central office equipment. WIRE CENTER SERVING AREA That area of an exchange served by a single wire center.