Telecommunications Terms

This glossary of telecom terms provides standard definitions for words and phrases used by the telecommunications industry. Terms are listed alphabetically.

ACTA (America's Carriers Telecommunication Association)—National trade association dedicated to the needs of the small, non-dominant long distance carrier.

ALT (Alternative Local Transport) An alternative to the established local telephone company for carrying local traffic. Usually these companies construct a fiber ring in an urban area to attract businesses to use their services in addition to or in place of the services of the local telephone company.

BLSR (Bidirectional Line Switched Ring) SONET transport network configuration in which network nodes are connected in a ring, and traffic can be instantly re-routed in the other direction around the ring in the event of a cable cut or degradation of optical signal, thereby routing around the point of failure.

CCS7 (Common Channel Signaling No. 7) Signaling protocol adopted for intelligent networking, in which signaling information for a number of trunks is transmitted on a separate link. Often referred to as SS7, the basis for 800- number database translations, calling card validation, and other advanced services.

CDR (Call Detail Recording) Raw data on long distance use, which is generated by the long distance network and generally passed to the local exchange carrier to be included on the subscriber's combined local/long distance monthly bill.

CIC (Carrier Identification Code) Five- to seven-digit number that identifies which interexchange carrier a call will use. Subscribers can dial these digits with each long distance call, or can pre-subscribe to a particular carrier and let the digital switch software add the CIC.

CompTel (Competitive Telecommunications Association) National trade association dedicated to the survival and prosperity of fully competitive marketplace composed of many participants.

DAL (Dedicated Access Line) Network connection, often leased from a local exchange carrier or competitive access provider, that provides a direct link from a customer to the long distance network. Typical DALs include outbound WATS lines, PBX tie trunks, and foreign exchange lines.

DS-1, DS-3 (Digital Signal) Digital transmission rates for time division multiplexing. DS-1 transmits voice, data, and signaling at 1.544 Mbps. With the same data rate as T-1, DS-1 is equivalent to 24 DS-0 channels. DS-3 operates at 45 Mbps, equivalent to 28 DS-1 facilities. SONET equivalents are VT and STS-1.

DWS (Dialable Wideband Service) An alternative name for multi-rate ISDN. Provides dialed data connectivity at desired bandwidth on a per-call basis (from 128 kbps through 1.536 Mbps in 64 kbps increments).

IDDD (International Direct Distance Dialing) Sometimes known as "international 15-digit dialing," feature that allows subscriber to directly dial international numbers.

IEC (Interexchange Carrier) See IXC IN (Intelligent Network)-The generic term for the Advanced Intelligent Network.

IOC (Independent Operating Company) A local exchange carrier that is not one of the Bell Operating Companies, largely operating in rural and small town areas.

ISDN (Integrated Services Digital Network) In its simplest form (Basic Rate Interface), ISDN provides a means of transmitting two voice channels (each operating at 64 kbps) and one data channel (operating at 16 kbps) over a single pair of twisted copper conductors. Long distance providers, however, would use the Primary Rate Interface ISDN, in which there are 23 "B" bearer channels operating at 64 kbps and one "D" data channel operating at 64 kbps. This interface is commonly used to connect customer PBX systems directly to the long distance network, thereby bypassing the local exchange carrier and the access fees it would charge for long-distance calls.

ITU-TSS (International Telecommunications Union Telecommunications Standards Sector) An international group charged with establishing telecommunications standards (formerly CCITT, Comité Consultatif Internationale de Telegraphique et Telephonique).

MTS (Message Telecommunications Service) Ordinary long distance phone call that originates with switched access through a local exchange carrier, is passed to a long distance carrier for interLATA transport, then terminated to the called party through a local exchange carrier on the other end.

NXX Often referred to as the "prefix," the second three numbers in telephone number, after area code, which identify the central office.

OC-n (Optical Carrier) The hierarchy of optical SONET signals at multiples of 51.840 Mbps. Typical line rates are OC-1 (51.84 Mbps), OC-3 (155.520 Mbps), OC-12 (622.08 Mbps), OC-48 (2,488.32 Mbps), and OC-192 (10Êgigabits per second). A direct counterpart to the electrical STS-N.

TRA (Telecommunications Resellers Association) National trade association that represents resellers' interests through government relations on the state and federal levels.

TRS (Telecommunications Relay Service) Special service for the hearing impaired, required of all local and long distance carriers that provide voice transmission.

Telephony Terms -

ACD (Automatic Call Distribution) A specialized telephone answering method that handles large volumes of incoming calls by distributing them equally among a group of answering positions on standard telephone lines. Calls to airline reservation departments, for instance, are served by ACDs.

ACTA (Americas Carriers Telecommunication Association) National trade association dedicated to the needs of the small, non-dominant long distance carrier.

ADPCM (Adaptive Differential Pulse Code Modulation) A coding scheme standardized by CCITT (see CCITT) that allows an analog voice to be carried on a 32-kbps digital channel instead of the standard 64-kbps PCM channel.

ADSI (Analog Display Services Interface) A protocol that simplifies use of advanced features by displaying text messages generated by a remote computer or central office switch on a display on a users telephone or television set.

ADSL (Asymmetric Digital Subscriber Line) A standard allowing digital broad-band (over 6 Mbps) signals and plain old telephone service to be transmitted up to 12,000 feet over a twisted copper pair.

AIN (Advanced Intelligent Network) Bellcores switching concept that centralizes a significant amount of intelligence rather than constantly placing more and more information in the central office switch.

ALI (Automatic Location Identification) Works hand-in-hand with automatic number identification (see ANI), and uses a computer database to associate a physical location with a telephone number.

AMA (Automated Message Accounting) Format in which a digital switch usually creates the usage data used for billing.

AMPS (Advanced Mobile Phone Service) The name applied to the original analog cellular system. Still the predominant cellular transmission scheme.

ANI (Automatic Number Identification) A feature that sends a calling partys telephone number over the network to the called party. Particularly useful in enhanced 911 systems.

ANSI (American National Standards Institute) A U.S. standards-setting organization, not an arm of the government. Accredits various other standards setting committees.lephony1

AOS (Alternative Operator Services) Name applied to those non-telephone company businesses that provide operator services (e.g., to private pay phone operators).

APS (Automatic Protection Switching) A method of allowing transmission equipment to automatically recover from failures such as a cable cut.

AT (Access Tandem ) A switching system that provides traffic concentration and distribution functions for interLATA traffic.

ATM (Asynchronous Transfer Mode) A transmission/switching scheme that is used for very high speed transmission. ATM will be the technology of choice for multimedia transmission.

BER (Bit Error Rate) A measure of transmission accuracy. It is the ratio of bits received in error to bits sent. A BER of 10-9 (or one error in a billion bits) is common in voice and data transmission systems.

BETRS (Basic Exchange Telecommunications Radio Service) In its simplest form, it is "fixed cellular," a form of wireless local exchange service. In such an application, handoff is not required.

BHCC (Busy Hour Call Completion) A term used in traffic measurement. Normally there is one hour of one day that is considered the "busy hour." Equipment is provisioned based on this measurement.

BISDN (Broadband Integrated Services Digital Network) A very high speed ISDN service intended to support full motion video and image applications, as well as data. Has a base rate of approximately 150 Mbps.

BOC (Bell Operating Company) Any of the 22 regulated telephone companies that are organized into seven Regional Bell holding companies. See RBOC and RHC.

BRI(Basic Rate Interface) This ISDN scheme is identified as 2B1D, and permits two "bearer" channels, each operating at 64 kbps, and one "data" channel, operating at 16 kbps, to be carried over a single twisted pair.

CAC (Carrier Access Code) Five- to seven-digit number that identifies which interexchange carrier a call will use. Subscribers can dial these digits with each long distance call, or can pre-subscribe to a particular carrier and let the digital switch software add the CAC.

CAP (Competitive Access Provider) Alternative carrier (e.g., Teleport and Metropolitan Fiber Systems) that competes with telephone companies in carrying traffic. Usually these companies construct a fiber ring in an urban area to attract businesses to use their services in addition to or in place of the services of the local telephone company.

CCF (Custom Calling Features) The basic custom calling features now available to subscribers include Call Waiting, Call Forwarding, Abbreviated Dialing, Three-Way Calling, etc. These revenue-generating features are available from the central office, and do not require any special customer premises equipment.

CCITT (Comité Consultatif Internationale de Telegraphique et Telephonique) An international group operating under the auspices of the International Telecommunications Union (ITU) and charged with establishing telecommunications standards. Name recently changed to ITU-TSS (International Telecommunications Union-Telecommunications Standards Sector).

ccs (Hundred Call Seconds) A measure of traffic used to determine the capacity of telephone systems.

CCS7 (Common Channel Signaling No. 7) Signaling protocol adopted for intelligent networking, in which signaling information for a number of trunks is transmitted on a separate link. Often referred to as SS7, the basis for 800-number database translations, calling card validation, and other advanced services.

CDMA (Code Division Multiple Access) A digital transmission scheme claimed to be more efficient than other systems and to offer up to 20 times more call handling capacity than analog cellular systems.

CEV (Controlled Environmental Vault) A below-ground enclosure used by the telephone companies for which virtually anything an above-ground hut would be used. These units generally house batteries, electronic equipment, terminating and cross-connect frames, etc.

CLASS (Custom Local Area Signaling Services) A set of more powerful custom calling services now provided by telephone companies; sometimes referred to as advanced custom calling features. Examples are Automatic Callback, Automatic Recall, Calling Number Delivery, Customer Originated Trace, Distinctive Ringing, Selective Call Forwarding, and Selective Call Rejection.

CLID (Calling Line Identification) A relatively new offering that permits subscribers to see the telephone number and/or name of the calling party. Frequently, "calling number blocking" is offered as well. In this case, calling parties can block the display of their telephone numbers.

CO (Central Office) The building in which telephone companies, etc., locate their switching equipment and terminate their circuits. Sometimes used inter-changeably with "exchange."

COCOT (Customer Owned Coin Operated Telephones) In as much as pay phones are no longer the sole province of the telephone company, any entrepreneur can buy, place, and collect from a set of privately-owned pay phones.

CODEC (Coder/Decoder) The electronic circuit converts analog voice signals into digital signals for transmission and switching, and digital signals to analog voice signals so that they can be used by the telephone.

CompTel (Competitive Telecommunications Association) National trade association dedicated to the survival and prosperity of fully competitive marketplace composed of many participants.

COT (Customer Originated Trace) An advanced subscriber feature that allows a telephone user to initiate a trace of the last incoming call. The number is then automatically reported to the service provider, a law enforcement agency, or other designated agency.

CPE (Customer Premises Equipment) The telecommunications equipment located on a customers premises. Usually refers to key systems, private branch exchanges (PBXs), telephones, etc.

CRC (Cyclic Redundancy Check) A form of error detection. Accomplished by reading a block of incoming data, operating on the binary number equivalent of this block (e.g., dividing by another binary number) and noting the remainder. If this remainder is the same as a character transmitted in the message, it is assumed that the transmission was error free.

CSA (Canadian Standards Association) One of several bodiesthis one based in Canadathat develops telecommunications standards.

CSU (Channel Service Unit) A device that is located on the customers premises. It terminates and tests digital data and voice circuits.

CT1, CT2, CT3 (first, second, and third generation of cordless telephones) The first generation is the cordless phone found today in 60 percent of American homes. CT2 is typically used in low-power applications such as "cordless pay phone" or wireless PBX. CT3 is a vague term often applied to new PCS telephones.

dB (Decibel) A logarithmic unit describing the ratio of two powers.

dBm (Decibel Referenced to a Milliwatt) The ratio of two power levels, in which the second is one milliwatt.

DCS (Digital Cross-Connect) A cross-connect system, totally electronic, that routes DS-1, DS-3, and DS-0 lines among multiple paths. The DCS makes de-multiplexing unnecessary. Although it operates very rapidly, it in no way replaces a central office switch. It can, however, re-route traffic should a major system fault occur.

DDS (Digital Data Service) A 56- or 64-kbps digital private line channel.

DECT (Digital European Cordless Telephone) The European standard for wireless transmission. Generally associated with office communications.

DID (Direct Inward Dialing) The feature of Centrex systems and large PBXs that allows a caller outside a company to call an internal extension without going through the switchboard.

DLC (Digital Loop Carrier) A digital transmission system designed for sub-scriber loop plant. Multiplexes many circuits onto very few wires or onto a single fiber pair.

DMS (Digital Multiplex Systems) A system that combines, on a digital basis, a number of circuits. Also the prefix for the Northern Telecom family of digital central office switches (DMS-10, DMS-100/200, DMS-250, DMS-300, and DMS-500).Telephony 1013

DMT (Discrete Multitone) A frequency-agile modulation scheme in which available bandwidth is divided into many sub-channels. Each sub-channel is then analyzed for its ability to carry digital data. Noisy sub-channels carry few or zero bits, while clear channels carry a maximum number of bits. Advanced DSP techniques allow these bits-to-sub-channel assignments to occur in real time.

DPN (Data Packet Network)A packet network is one in which "bundles" of information are transmitted, one after another. This differs from a circuit network, in which an entire circuit is dedicated to a particular user. Also the prefix for Northern Telecoms DPN data networking switches.

DRAM (Digital Recorded Announcement Machine) Device associated with a switching system that provides recorded announcements, such as "Please deposit 50 cents for the first three minutes."

DSCWID (Call Waiting Display with Disposition) An advanced subscriber feature that not only identifies the incoming caller on a telephones display window, but also provides options for handling the waiting call.

DSU (Data Service Unit) A device located on the customers premises that converts a digital data signal to a digital transmission signal.

DTC (Decoder Time Clock) Used in decoding a compressed video signal. A clock distinct from the distant-end encoding clock, but kept in time and phase with the incoming signal by bits inserted in this incoming bit stream.

DTE (Data Terminal Equipment)The name applied to a piece of terminal equipment.

DTMF (Dual Tone Multifrequency) The tones sent out by a touch tone dialing unit.

DWS (Dialable Wideband Service)An alternative name for Multi-Rate ISDN. Provides dialed data connectivity at desired bandwidth on a per call basis (from 128 kbps through 1.536 Mbps in 64 kbps increments).

E-TDMA (Enhanced Time Division Multiple Access) One of many digital transmission schemes proposed as "standard" for cellular radio. Primary proponent is Hughes Network Systems. Fundamentally it is a time division multiple access system.

EAS (Extended Area Service)A service provided by many telephone companies in which towns with a common community of interest are considered "local." Hence subscribers calling these towns do not incur a long distance charge.

ECSA (Exchange Carrier Standard Association) A standards body sponsored by the exchange carriers, and accredited by American National Standards Institute (ANSI). Recently the name of this organization has been changed to Alliance for Telecommunications Industry Solutions (ATIS).

EMI (Electro-Magnetic Interference) Electromagnetic waves emitted by some electrical devices. Distorts or overwhelms communications signals being transmitted over the air.

EPROM (Erasable Programmable Read Only Memory) An integrated circuit read-only memory device that can be electrically programmed and erased either electrically or with ultraviolet light.

ESA (Emergency Stand Alone) The ability of a switch remote to continue handling local calls when links to the host switch are lost. Especially critical for Centrex applications such as hospitals.

ESP (Enhanced Service Provider) The FCC defines enhanced services as "services offered over common carriers transmission facilities...which employ computer processing applications that act on the format, content, code, protocol..." Therefore an enhanced service provider operates, in one way or another, on the information being transmitted.

ETSI (European Telecommunications Standards Institute) One of several Europe-based standards bodies.

FCOT (Fiber Central Office Terminal) Electronic equipment designed to terminate multiple fiber feeders from next generation digital loop carrier systems.

FDDI (Fiber Distributed Data Interface) A standard designed to allow traffic of up to 100 Mbps to be transmitted in a local area network.

FDMA (Frequency Division Multiple Access) The original U.S. transmission scheme for cellular radio. Analog in nature, it is used in every Metropolitan Service Area and Remote Service Area in the country.

FEC (Forward Error Correction) Frequently used in data transmission systems. Redundant bits are transmitted along with the payload, and the location and value of these bits in the message allows the receiving station to not only detect errors but also to correct them.

FITL (Fiber In The Loop) Used generally to refer to the deployment of fiber between the central office and the subscriber.

FM (Frequency Modulation) One of many modulation schemes. The message signal modulates a carrier signal in such a way that the frequency (as opposed to the amplitude or phase) of the carrier is varied.

FOTS (Fiber Optic Transmission System) A generic term applied to any fiber optic transmission system.

FSK (Frequency Shift Keying) A means used to transmit binary data. A "1" is represented by one frequency, and a "0" by a second.

FTTC (Fiber-To-The-Curb) Fiber has been placed first in the long distance network, then in the feeder plant, then the distribution plant. In this case the fiber then proceeds to the curb, with copper going from the curb to the home itself.

FTTH (Fiber-To-The-Home) Extending fiber past the curb, all the way to the wall of the subscribers home.

FX (Foreign Exchange)Provided local exchange telephone service from a central office that serves a different exchange area. Thus a subscriber in one city will receive dial tone from, and have a telephone number of, a distant city.

Gbps (Gigabits per second) Giga is the prefix representing 109, or one billion. For example, 8 Gbps means 8 billion data bits per second.

GPS (Global Positioning System) Atomic clocks control radio signals from orbiting satellites with almost perfect accuracy. A signal sent by three (four in actual practice) synchronous satellites can be received by a vehicle-mounted global positioning system, and through triangulation techniques the vehicle can determine its position to within a few meters.

GSM (Global System for Mobile Communications) A comprehensive network specification that includes transmission scheme, network architecture, network services etc.proposed as "standard" for cellular radio. This system is the standard in Europe and many countries in Asia, and a proposed standard for personal communications services in North America. It is a time division-type system.

HDBH (High Day Busy Hour) The busiest hour of the busiest day of the year for a piece of telecommunications system. A central concept for network planning.

HDSL (High bit rate Digital Subscriber Line) By using sophisticated coding techniques, a large amount of information may be transmitted over copper. The HDSL scheme uses such coding over four copper wires and is primarily intended for high capacity bidirectional business services.

HDTV (High Definition TV) Television with very high resolution and a wide aspect ratio. Requires significantly greater bandwidth than conventional television.

ICN (Integrated Community Network) A shared public network for services such as distance learning, remote arraignment, and medical imaging.

IDDD (International Direct Distance Dialing) Feature that allows subscriber to directly dial international numbers.Telephony 101

IDLC (Integrated Digital Loop Carrier) A digital loop carrier system that connects directly to a digital central office switch.

IEC (Interexchange Carrier) See IXC.

IMTS (Improved Mobile Telephone Service) The precursor to cellular. Utilized a single transmitting station that was able to cover a great piece of geography. Was very channel-limited, and its shortcomings led to the invention of cellular.

IN (Intelligent Network) The generic term for the Advanced Intelligent Network.

IOC (Independent Operating Company) A local exchange carrier that is not one of the Bell Operating Companies, largely operating in rural and small town areas.

IP (Intelligent Peripheral )An Advanced Intelligent Networking network element that, for instance, only controls a specialized set of features (voice recognition services, for instance) or provides a specialized set of functions to support features (IPs, for instance, may supply the voice prompts for some operator services features).

ISDN (Integrated Services Digital Network) In its simplest form, called Basic Rate ISDN, it provides a means of transmitting two voice channels (each operating at 64 kbps) and one data channel (operating at 16 kbps) over a single pair of twisted copper conductors. The two voice channels are called bearer, or "b" channels; the single data channel is the "d" channel. A more complex form of ISDN is called Primary Rate ISDN; in this system there are 23 "B" channels operating at 64 kbps and one "D" channel operating at 64 kbps. Thus the transmission capability of Basic Rate ISDN is 144 kbps, and that of Primary Rate ISDN nearly 1.5 Mbps.

ITU-TSS (International Telecommunications UnionTelecommunications Standards Sector) An international group charged with establishing telecommunications standards (formerly CCITT, Comité Consultatif Internationale de Telegraphique et Telephonique).

IXC (Interexchange Carrier) Quite literally, these carriers transmit information between exchanges; frequently simply called long distance carriers. Major examples are AT&T, MCI, and Sprint.

kbps (kilobits per second) Kilo is the prefix representing 103, or one thousand. For example, 64 kbps means 64,000 data bits per second.

LAN (Local Area Network) A local network connecting a defined set of terminals. Could connect work stations in an office, offices in a building, buildings on a campus, etc.

LATA (Local Access and Transport Area) The geographic area that is the domain of the local exchange carrier. Bell Operating Companies are generally precluded from carrying traffic across LATA boundaries; this traffic must be handed off to an interexchange carrier.

LEC (Local Exchange Carrier) The local telephone company. Generally subdivided into Bell Operating Companies and Independents.

LEO (Low Earth Orbit) Low earth orbit satellites are being proposed for worldwide wireless communications systems. These satellites (every proposal is different, but constellations of many dozen are usually specified) operate at an altitude of 300 to 600 miles, rather than the 22,300 miles of a synchronous orbit satellite. Therefore, they travel across the sky rather than remaining stationary over a single point. Communications with earth stations, or with earth-bound subscribers, requires some kind of hand off.

LMDS (Local Multipoint Distribution Service) A proposed radio-based distribution system. It is anticipated that initial deployment would be for video distribution. Ultimate use would involve two-way voice, video, and data.

LSSGR (LATA Switching System Generic Requirements) Multi-volume set of Bellcore technical references dealing with basic switching requirements used by switch manufacturers, procurement staffs, planners, and switch technicians.

MAN (Metropolitan Area Network) A network linking multiple, geographically separate LANs together usually confined to a metropolitan area.

MBG (Multlocation Business Group) Networking scheme that allows private business to tie sites together through the use of public SS7 trunks.Telephony 101

Mbps (Megabits per second or millions of bits per second) A measure of digital transmission speed used in computer and telephone networks.

MDC (Meridian Digital Centrex) Northern Telecoms name for a package of business communication services provided by a DMS-10, DMS-100, or DMS-500 central office switch.

MDF (Main Distribution Frame) The point of termination inside the central office for outside plant cable and central office equipment lines. A crossconnect between vertical and horizontal components associates the two.

MF (Multi-Frequency) An older signaling protocol used in network trunking. Uses combinations of pulses as specified frequencies to signal across the network.

MFJ (Modification of Final Judgement) Official name for the 1982 Federal court ruling resulting in divestiture of the Bell Operating Companies from AT&T.

MSA (Metropolitan Service Area) FCC designated market areas which are the basis for cellular service boundaries. In addition, there are Rural Service Area (RSA) markets.

MSA (Metropolitan Statistical Area, formerly Standard Metropolitan Statistical Area) A federal government defined geographic area consisting of a large population nucleus and surrounding communities with economic and social association with the nucleus.

MTBF (Mean Time Between Failures) Average period of time a piece of equipment or component remains working before failure.

MTSO (Mobile Telephone Switching Office) Location of the switch controlling operation of a cellular system.

NAMPS (Narrowband AMPS) An enhanced AMPS analog cellular radio standard for increased capacity.

NANP (North American Numbering Plan) The system or method by which calls are routed in the public network of North America. The plan divides phone numbers into three partsan area code, central office code, and subscriber code.

NE (Network Element) An individual piece of telecommunications equipment providing a component function in the overall network. Channel banks, multi-plexers, and SONET transmission gear are all network elements.

NII (National Information Infrastructure) In the words of Vice President Al Gore, "a seamless web of communications networks, computers, databases and consumer electronics that will put vast amounts of information at users finger-tips."

NIU (Network Interface Unit) The demarcation point between service providers-owned and customer-owned wiring and equipment. Also called Network Interface Device.

NNI (Network-Network Interface) The interface connecting one network node to another.

NPA (Numbering Plan Area) Another name for area code. The three digit NPA makes up the first part of every phone number in the North American Numbering Plan.

NVOD (Near Video-On-Demand) Unlike video-on-demand, the customer does not control a virtual channel. Popular movies are placed on multiple channels with staggered start times. Customer tunes to appropriate channel for nearest start time. VCR-like controls (e.g., pause, stop) are not available.

NXX Often referred to as the "prefix," the second three numbers in telephone number, after area code, which identify the central office.

OC-N (Optical Carrier - Level N) The hierarchy of optical SONET signals at multiples of 51.840 Mbps. A direct counterpart to the electrical STS-N. The value of N ranges from 1 to 48.

OCC (Other Common Carrier) Carriers other than AT&T providing long distance service. These companies, plus AT&T, are now referred to as IXCs or interexchange carriers.

ONA (Open Network Architecture) A network architecture arrangement where outside providers can interconnect to the Regional Bell Operating Companies networks and offer enhanced services on an equal footing.

OS (Operations System) A system that furnishes tools to provide network control, monitoring, and business functions from a centralized location. Nearly all pieces of network equipment or major network functions have an OS.

OSI (Open Systems Interconnection) A seven-layer framework of standards for network communication. OSI creates an open systems networking environment where different systems can share data regardless of vendor or platform.

OSS (Operations Support System) A system that furnishes tools to provide network control, monitoring, and business functions from a centralized location. Nearly all pieces of network equipment or major network functions have an OSS.

OTDR (Optical Time Domain Reflectometer) A device used to measure parameters of optical fiber. A light pulse is sent down the fiber and ratio and timing of incident and reflected light power is measured. The device can be used to deter-mine if and where a fiber might be broken.

PAD (Packet Assembler and Disassembler) A device performing the interface between an X.25 data network and an asynchronous device such as a personal computer. The PAD assembles user data into packets with identifying information used to control routing.

PBX (Private Branch Exchange) Customer premises version of a central office switch.

PCM (Pulse Code Modulation) A coding scheme for converting analog voice signals into a digital bit stream. A digitizing technique, PCM is the basis for digital communications in North America.

PCN (Personal Communications Network) A wireless telephone network concept similar to cellular, operating in the 1800-2000 MHz range. Smaller, low-power cells reduce range in comparison to cellular, but keep handset cost low.

PCS (Personal Communications Services) Any service offered on the personal communications network. These include basic telephone, voice mail, paging, and others.

PIN (Personal Identification Number) Authorization number (usually composed of the callers telephone number plus a four-digit code) that allows subscribers to access their long distance carriers when away from home.

PM (Phase Modulation)A form of modulation where the phase of the transmitted signal is changed as the value (content) of the information changes.

POP (Point of Presence) The physical location where a long distance carrier terminates lines before connecting to the local exchange company, another carrier, or directly to a customer.

POTS (Plain Old Telephone Service) Basic telephone servicedial tone without special features.

PRI (Primary Rate Interface) An ISDN interface providing 23 "B" channels, each operating at 64 kbps, and a single "D" channel also operating at 64 kbps to a customers premises.

PSC (Public Service Commission) Also know as Public Utilities Commission. The State agency regulating telephone operations.

PSTN (Public Switched Telephone Network) The worldwide switched voice network.

PTT (Post Telephone & Telegraph) Government controlled agencies providing telephone and telecommunications services in many foreign countries.

PUC (Public Utilities Commission) See PSC.

QAM (Quadrature Amplitude Modulation) Modulation technique combining phase and amplitude modulation to increase the number of bits per second.

RAD/RASP (Remote Antenna Device/Remote Antenna Signal Processing) A technique to separate radio antennas for personal communications services from their associated electronic equipment.

RAM (Random Access Memory) A computers direct access memory. It can be accessed very quickly, can be overwritten with new information, and loses its content when power is turned off.

RAO (Revenue Accounting Office) Generic name for the billing center that computes and creates subscriber bills for telephone companies.

RBOC (Regional Bell Operating Company) A term for the seven Regional Holding Companies created when AT&T divested the Bell Operatin g Companies.

RCC (Radio Common Carrier) A company furnishing services to the public using radio frequencies. The original non-wireline cellular franchise in each market was reserved for an RCC.

REA (Rural Electrification Administration) A government agency and program that makes loans to companies providing telephone service in rural areas.

RF (Radio Frequency) An electromagnetic signal between the audio and infrared frequency range of 500 kHz to 300 GHz.

RFI (Radio Frequency Interference) Disruption of signal reception by radio waves at the same frequency as the desired signal.

RHC (Regional Holding Company) See RBOC. Another name for one of the seven companies formed when AT&T divested the Bell Operating Companies.

RISC (Reduced Instruction Set Computing) A high speed computer processing technology using a simple set of operating commands that allow it to process each command faster.

RSA (Rural Service Area) An FCC designated rural market area for cellular service. These areas were designated in addition to the Metropolitan Service Areas. See MSA.

SCAI (Switch-to-Computer Applications Interface) Protocol that allows a subscribers computer to interact with a digital switch. Makes it possible to coordinate information in a database with incoming and outgoing phone calls to allow a company representative, for instance, to receive a customer call and simultaneously receive the customers file for viewing on a desktop work station.

SCE (Service Creation Environment)T he set of tools and activities required to create new services for subscribers in the AIN arena.

SCP (Service Control Point) The centralized network element in the Advanced Intelligent Network architecture that individual switches call on to obtain information and commands necessary for completing an AIN call.

SDH (Synchronous Digital Hierarchy) Similar to SONET, it is a standard for synchronous digital transmission rates used outside North America.

SMDR (Station Message Detail Recording) A feature of telephone systems that permits information on outgoing telephone calls to be collected and recorded.

SMDS (Switched Multimegabit Data Service) A public, wide-area packet-switched data service developed by Bellcore that provides DS-1 to DS-3 switched access.

SMS (Service Management System) The operations support system for Advanced Intelligent Networking. Provides the mechanism for downloading new features and monitoring the AIN network.

SNA (Systems Network Architecture) IBMs standard network architecture describing logical structure, formats, protocols and operational sequences for transmitting information between software and hardware devices.

SNMP (Simple Network Management Protocol) Network management architecture initially designed for the Internet, but easily applied or extended to any network type. 101

SONET (Synchronous Optical Network) Family of optical transmission rates and interface standards allowing interworking of products from different vendors. Base optical line rate is 51.840 Mbps. Higher rates are direct multiples.

SS7 (Signaling System No. 7) An out-of-band signaling system used to provide basic routing information, call set-up, and other call termination functions. Signaling is removed from the voice channel itself and put on a separate data network. Also known as Common Channel Signaling No. 7 (CCS7).

SSP (Service Switching Point) That node of the Intelligent Network normally associated with an end office. The entrance to the Intelligent Network.

STP (Signal Transfer Point) A packet switch in the SS7 network that enables cost-effective routing of SS7 signals between other network elements.

STS (Synchronous Transport Signal) The electrical equivalent of the SONET-defined optical signal with a base rate of 51.840 Mbps.

TA (Technical Advisory) A document describing Bellcores preliminary view of proposed requirements for products, interfaces, technologies, or services.

TCP/IP (Transmission Control Protocol/Internet Protocol) A communications protocol linking different computer platforms across networks. TCP/IP functions at the 3rd and 4th layers of the open system integration model.

TDD (Telecommunications Device for the Deaf) The teletypewriter device normally associated with telephonesincluding payphonesthat permits hearing-impaired people to communicate over the public switched network.

TDM (Time Division Multiplexing) A digital multiplexing technique for combining a number of signals into a single transmission facility by interleaving pieces from each source into separate time slots.

TDMA (Time Division Multiple Access) A digital cellular transmission standard that increases cellular capacity by dividing frequencies into time slots.

TOPS (Traffic Operator Position System) A Northern Telecom operator services system.

TR (Technical Reference) Bellcore-created technical document with proposed generic requirements for products, interfaces, technologies, or services.

TRA (Telecommunications Resellers Association) National trade association that represents resellers interests through government relations on the state and federal levels.

TRS (Telecommunications Relay Service) Special service for the hearing impaired, required of all local and long distance carriers that provide voice transmission.

TSI (Time Slot Interchange) A high-speed technique for switching time division multiplexed signals so they can be sent out in a different order or on a different signal than they were received.

UNI (User-Network Interface) Interface connecting users to the network.

UPS (Uninterruptible Power Supply) An auxiliary power unit providing continuous power to a telephone system in case commercial power is lost.

VANC (Voice Activated Network Control) Feature that allows subscriber to access advanced services such as call forwarding through voice commands.

VAPN (Virtual Access to Private Networks) A networking scheme that uses public network facilities to extend private network calling to remote sites.

VBR (Variable Bit Rate) A service where the transmission rate varies over time incorporating the concept of bandwidth-on-demand.

VDT (Video Dial Tone) An FCC concept where telephone companies act as a common carrier serving video programmers to deliver video-based services to customers.

VLSI (Very Large Scale Integration) The technique of putting hundreds of thousands of transistors onto a single integrated circuit.

VOD (Video-On-Demand) Customers request video programming from their home and receive it immediately. They control the video stream transmitted from within the network and have full VCR functionality over it (e.g., pause, fast forward, rewind).

VSAT (Very Small Aperture Terminal) A small antenna used for transmitting and receiving data communications.Telephony 101

VT (Virtual Tributary) A SONET structure designed for transporting sub-base rate payloads.

WAN (Wide Area Network) An integrated data network linking metropolitan or local networks over common carrier facilities.

WATS (Wide Area Telephone Service) Discounted toll service offered on an inward or outward basis. Inward WATS is better known as 800 Service.

WDM (Wavelength Division Multiplexing) A method for transmitting two or more separate signals on the same fiber path by carrying each signal at a different wavelength.