Access Line: A communications circuit or channel connecting end-user equipment to a carrier's central office, wire center or other access port. (see also Frame-Relay Access Line)

ADSL: see Digital Subscriber Line.

Amplifier: An electrical device that receives low-level analog signals, including any noise and distortions, and sends them out at a higher level.

Amplitude: The extreme range of a fluctuating quantity, such as voltage; loudness; strength.

Analog Circuit Switch: A switch used to interconnect circuits for real-time transmission of analog signals.

Analog Signal: A nominally continuous signal that varies in amplitude/frequency in response to changes of sound, light, heat, position or pressure.

Analog Value: A value that is continuously variable, such as alternating electrical voltage/current, sound or light.

ANI: (pronounced "annie"), Automatic Number Identification, see Caller ID.

ANSI: American National Standards Institute devises and recommends standards for international telecommunications.

Asynchronous: Refers to digital facilities wherein each network terminal runs on its own clock, which results in significant variations in the actual bit-rate. Multiplexed asynchronous signals must be demultiplexed in order to access individual channels. (also see Clocking)

ATM: Asynchronous Transfer Mode is a high-bandwidth packet-like switching and multiplexing technique for transmission of 53-byte fixed-sized cells.

Attenuation: Reduction in signal strength; fading.

Auto Attendant: Automated voice response (AVR) function usually associated with voice-mail system that allows in-bound callers to desired extension, department, or service without the aid of a live operator.

Automatic Number Identification: see Caller ID.

Auto Redial: A feature that provides for repetitive dialing of a busy number and, when it is no longer busy, to ring back the caller's line.

Bandwidth: Refers to the capacity of a communications circuit or channel. With analog facilities, greater bandwidth means the facility will carry a broader frequency range without significant distortion (hence, the term "broadband" for such facilities). With digital facilities, greater bandwidth translates to greater throughput of digital transmission (e.g., 56 kbps vs 128 kbps). Whether analog or digital, greater bandwidth indicates that the facility will carry more communications in a given time period.

Basic-Rate Interface: Refers to 2B+D ISDN service, which includes two 64-kbps bearer channels and one 16-kbps data channel on a two-wire local-loop circuit.

Baud: The number of state-changes/second that can be handled by various elements in a data system. Bauds are often equivalent to bps in newer system components, but are often less than bps in older apparatus.

Bearer Channel: A 64-kbps ISDN channel for carrying digitized voice, data or video communications.

BECN: Backward Explicit Congestion Notification is a bit set by a frame-relay network to alert an interface device (DTE) that congestion-avoidance procedures should be initiated by the sending device.

B-Channel: see Bearer Channel.

Billing Increment: The minimum amount of billing for communications time. For instance, if billing is in one-minute increments, any usage from 1-60 seconds will be charged for one full minute, any usage from 61-120 seconds will be charged for two full minutes, and so on. As a rule of thumb, for each call you will pay for average unused time equal to about half the billing increment. The amount of billable unused time declines as the billing increment declines (e.g., from one minute to six seconds).

Bit: One digital pulse or "non-pulse" (pulse of different voltage). BLC: see Broadband Loop Carrier.

BlueTooth: A technology for low-cost short-range wireless connectivity between mobile and fixed data devices such as computers, cordless phones, electronic organizers, printers, etc. BlueTooth-chip equipped devices operate in the 2.5 GHz range.

Bonding: An acronym for Bandwidth ON Demand Interoperability Group. Bonding uses inverse multiplexing to combine separate digital channels into a single channel with bandwidth equal to the sum of the separate channel bandwidths. ISDN bonded channels are called 'H' channels. (e.g., HO is 384 kbps; equals six B channels.)

BRI: see Basic-Rate Interface.

Bridge: A physical connection between two telecommunications elements. May be a simple clip on a 66 block connecting two cables. A data bridge is a device that connects two LANs or other data facilities by means of the Logical Link Control, a sub-layer of the OSI Data Link layer.

Bridged Tap: Any section of a cable pair that is not on the direct electric path between the CO and the user's premises.

Broadband: A transmission facility with bandwidth that is greater than one voice-grade channel (4 kHz for analog; 56/64 kbps for digital).

Broadband Loop Carrier: A local-loop system that delivers a variety of services (POTS, ADSL, Ethernet, etc.) from a converged voice and data access network.

Browser: A software program that interfaces with the World Wide Web. It interprets hypertext links and facilitates searching the internet, usually integrating various internet applications and services. Popular browsers include Amiga Voyager, Cello, HotJava, IBM Web Explorer, Microsoft Internet Explorer, Netscape Navigator and OrnniWeb.

Buffer: A device or provision for reducing jitter. Buffers hold incoming VoIP data packets long enough to facilitate releasing them at the precise rate of one packet each 80 milliseconds.

Bursty: Refers to data that uses the available bandwidth only sporadically; during pauses the assigned channels are idle.

Bundle: A grouping of different communications services into a single offering, usually with pricing that applies only to the entire bundle of services.

Burstible T1: An arrangement whereby the full T l bandwidth is available when needed, with usage-based billing up to 1.544 mbps, as used.

Call Waiting: A feature that signals a user during a call in progress that another caller is attempting to get through.

Carrier: see Common Carrier.

Carrier Line Charge: see PICC.

CCITT: Former name of the International Telecommunications Union (ITU) the international Consultative Committee for Telegraphy and Telephony (literally, Comite Consultatif International Telegraphique et Telephonique,)

CDMA: see Code Division Multiple Access.

Central Office: Refers to the telephone company facility/equipment for switching and routing telephone calls.

Centrex: Refers to a class of business services that bundles many special capabilities into a single plan, usually by partitioning off a segment of the CO switch to function as the subscriber's PBX. Simple plans may add a package of specialized capabilities onto standard business lines; sophisticated plans provide direct dialing from outside telephones to internal station numbers, intercommunications, and other functions without the need of complex customer-premises equipment.

Channel: Provisioning for transport of a single communications session at any given time.

Channel Bank: A multiplexer that combines up to 24 analog voice and/or synchronous data channels into a DS l format. Channel banks also digitize analog signals using pulse code modulation (PCM).

Channel Service Unit: An ancillary device that connects a DSO or DS l CO circuit to digital customer equipment. The CSU performs conditioning and equalization functions, and responds to loopback commands from the central office.

CIR: see Committed Information Rate.

Circuit: A dedicated facility (electrical wire, optical fiber, radio, etc.) between/among

communications points. Circuits often provide a single communications channel (ordinary

lines and trunks, for instance), or they may carry multiple channels (ISDN and TI circuits, for instance).

Circuit Switching: The process of switching entire end-to-end paths to complete a connection between a caller and the called end. For the duration of the call, the path that is set up is dedicated to that call.

Business Line: A circuit that connects the LEC central office (brings dial-tone) to key telephone equipment or single-line devices (telephones, facsimile machines, modems, etc.) for business-class switched services. Also, a class of service assigned to a channel carried via a circuit between the LEC CO and such equipment.

Busy Hour: The 60-minutes during a defined period (usually a day) during which a telecommunications facility carries the highest level of traffic.

Busy Signal.' A tone that indicates facilities are unavailable to complete the call, either because some portion of the network is blocked/unavailable (fast busy), or because the called-number line/station is in use

Byte: A group of digital bits, usually eight or seven, that describes one information element.

Cable Modem: A device connected between a coaxial cable and a digital data device to transform signals to and from digital/analog. Cable modems can handle the multi-megabit bandwidths available with internet access via cable-TV facilities.

CALEA: see Communications Assistance for Law Enforcement Act.

Call Block: A feature that enables a user to prevent the calls from specific numbers from seizing a specific line.

Call Collision: The phenomenon whereby an incoming call is already on the line when the user picks up the handset to make an outgoing call.

Caller ID: Feature shows the called party the telephone number/address of an incoming call.

Caller ID Blocking: A feature that enables a caller to prevent the transmission of the originating telephone number to anyone having caller ID.

Call Forwarding: A feature that allows the user to route incoming calls to a different telephone number.

Calling Card: A form of credit card that enables a user to place and charge calls from telephones other than the home service.

Call Return: A feature that enables a user to place a call to the last number from which a call came in, whether or not it was answered.

Call Trace: Enables a user, by dialing a code after hanging up and waiting a short time, to ensure that the time of call and the calling number are recorded by the telephone company.

Call Transfer: A feature that enables a user, after answering an incoming call, to forward it to a different network number.

Circular Hunting: An arrangement such that a call to any number in the hunt group will search all numbers, in sequence, for an available channel before returning a busy signal if no channel is available.

Class Of Service: Refers to the specific capabilities, features, authorizations, limitations, etc. assigned to a particular telephone station or telephone service.

CLEC: Competitive Local Exchange Carrier; a "new" local telephone company. CLECs may be resellers of ILEC services, or they may have their own facilities (facilities-based).

CLLI: see Common Language Location Identifier.

Clocking: The use of repetitive pulses to keep the digital bit rate constant and to indicate where the ones and zeros are located in the data stream.

CO: see Central Office.

CODEC: A COder-DECoder functions like a modem, in that it changes digital video signals into analog and vice-versa. At the same time, it compresses outgoing raw video by eliminating overhead and control information, and it decompresses incoming data by inserting overhead and control information.

Code Division Multiple Access: A cellular/PCS spread-spectrum technology whereby each call is multiplexed and spread across all available channels in a cellular/PCS band.

Co-Location: Refers to separate competitive telecommunications switching facilities (such as ILEC and CLEC) that are physically located on the same premises and interconnected.

Combination Trunk: A two-way trunk in hunting within a main-number group.

Committed Information Rate: The minimum rate (in bits or kilobits per second) at which the rated frame-relay component transfers information under normal conditions.

Common Carrier: An entity that rents the availability of its facilities to the general public.

Communications common carriers include local and long-distance telephone, cellular, paging, PCS, maritime, radio and satellite companies.

Common Channel Signaling System 7: see Signaling System 7.

Common Language Location Identifier: An all-character alphanumeric code that identifies telecom wire centers and other buildings.

Common Assistance for Law Enforcement Act: 1994 law further defines statutory obligation of telecommunications carriers to assist law enforcement in executing electronic surveillance pursuant to court order or other lawful authorization.

Conditioning: Central-office provisions that enhance the performance of full-period or switched lines by reducing distortion, echo, phase-shift:, attenuation, etc.

Cramming: The practice of adding unauthorized services to your bill. Such may include toll-

free numbers, internet access, voice-mail, etc.

CRC: see Cyclic Redundancy Check CSU: see Channel Service Unit.

Cyclic Redundancy Check: A process of determining degree to which frames are transmitted and received accurately. Process involves applying mathematical number to the total frame content of a frame as transmitted and received, and then comparing whether the numbers are identical.

D-Channel: see Data Channel.

Data Channel: An ISDN channel that carries data packets used for out-of-band signaling. The D-channel on basic-rate ISDN (BRI) is 16 kbps; the D-Channel on primary-rate ISDN (PRI) is 64 kbps. A single D channel can be used for multiple groups of BRl or PRl services.

Database Type: As commonly used in telephony, refers to collections of telephone numbers maintained by long-distance service providers to determine routing and billing of long-distance calls. A given long-distance service provider may have several different types of databases for routing calls and for billing calls involving numbers associated with different services and programs.

Data Communications Equipment: As relates to frame-relay and X.25 packet networks, applies to network switching equipment.

Data Encryption Standard: A data encryption algorithm that uses 56-bit symmetric keys to encrypt data in 64-bit blocks. The 56-bit key provides 72,057,594,037,927,900 possible combinations.

Data Link Connection: A virtual-channel end point (frame-relay port, etc.).

Data Link Connection Identifier: A unique number assigned to a frame-relay end point (port).

Data Service Unit: An ancillary device that interfaces data terminal equipment with a DSO or

DS1 CO circuit to allow digital communications without a modem. Used with a CSU when the DTE lacks complete digital line interface capability.

Data Terminal Equipment: Ultimate source or destination of data flowing through a frame-relay network, also called end device.

DCE: see Data Communications Equipment. DE: see Discard Eligible.

Dedicated Access: A full-period private circuit between the service provider and the user. (compare to switched access.)

Dedicated Service: A class of long-distance service that is provided via dedicated access circuit(s) between the user and the long-distance service provider.

Demarc: That point on user premises that separates telephone-company facilities from customer facilities.

DES: see Data Encryption Standard.

Dialing: initiating signals in accordance with the digits dialed - d-c pulses separated by spaces for rotary-dial, DTMF signals for touch-tone.

Dial Tone: Indicates that automatic switching equipment is ready to receive dial signals. Dial

Tone Line: A circuit that connects the LEC central office (brings dial-tone) to user equipment for business or residential-class switched services.

DID: Direct-Inward-Dialing refers to a class of business service that enables direct dialing from outside telephones to internal station numbers via special trunks and customer-premises equipment.

Digital Circuit Switch: A switch used to interconnect circuits for real-time transmission of digital signals.

Digital Loop Carrier System: Time-division multiplexer and fiber CO link for carrying voice grade services to a local copper-wire distribution node. Traditional voice DLCs block most DSL services, but can be upgraded to enable ADSL service.

Digital Signals: Discontinuous (on-off) pulses whose information is contained in their durations, periods and/or combinations.

Digital Subscriber Line: A technology that transmits simultaneous voice and data, at up to multi-megabit speeds, over standard twisted-pair copper telephone wires. The more common variations of this service are:

• Asymmetric DSL (ADSL) provides for slower-speed upstream flow and high-speed downstream flow, as well as regular telephone service. Full-rate ADSL can deliver up to 6.0 mbps downstream (ITU G.992.1). G.1ite ADSL can deliver up to 1.5 mbps downstream and up to 500 kbps upstream (ITU G.992.2).
• Symmetric DSL (SDSL) provides for the same flow both upstream and downstream; the rate is generally greater than the ADSL upstream rate and less than the ADSL downstream rate.
• ISDN DSL (IDSL) is a symmetric data-only service at a guaranteed rate of 1281144 kbps.
• Very-high-speed DSL (VDSL) provides for 50 mbps transmission speed.
• Generic DSL (xDSL) refers to the general family of DSL services.
• Digitizing: The process of converting an analog signal into a digital signal. Direct-Connect: see Hot Line/W arm line.
• Directory Listing: Appearance in the alphabetical/white-pages telephone directory. There are several types of listing, including:
• Standard listing
• Additional listing or cross-reference listing in the subscriber's home directory
• Foreign listing in a directory other than the subscriber's home directory.
• Extra line
• Bold listings and the like (part of directory advertising)

Discard Eligible: A bit indicating that, if congestion occurs, a frame may be discarded to maintain the committed information rate.

Distinctive Ringing: A feature that provides different ringing signals for specific categories of calls, e.g., regular ring for calls to the main number, and two short rings for calls to a secondary number on the same line.

Distortion: An undesirable change in an analog signal caused by non-linear attenuation,

echoing, phase-shift, etc.

DLC: see Digital Loop Carrier System. DLCI: see Data Link Connection Identifier.

Domain: That part of an internet web site address that follows the www, or that part of an email address that follows the "@." Domain names are issued by the National Science Foundation (NSF). Most come with an extension that indicates the domain belongs to a commercial enterprise/business (.com, .biz), educational establishment (.edu), government body (.gov), the military (.mil), a network (.net) or a nonprofit organization (.org).

Downstream: Transmission of signals from a main computer/node to a remote point.

DSO: Digital Standard 0 (zero) defines the characteristics for circuits and associated equipment that provide two-way digital transmission at 64 kilobits per second.

DS1: Digital Standard l defines the characteristics for circuits and associated equipment that provide two-way digital transmission at 1.544 megabits per second, often time-division multiplexed into 24 voice-grade channels of 64 kilobits per second.

DS3: Digital Standard 3 defines the characteristics for circuits and associated equipment that provide two-way digital transmission at 44.736 megabits per second, often time-division multiplexed into 672 voice-grade channels of 64 kilobits per second.

DSL: see Digital Subscriber Line. DSLAM: see DSL Access Multiplexor.

DSL Access Multiplexer: CO device that aggregates local-loop traffic, routing it to and from the switched network private-line services. (Also called xDSL Terminating Unit-Central -XTU-C.)

DSU: see Data Service Unit.

DTE: see Data Terminal Equipment.

DTMF: Dual-tone, multi-frequency signaling. Usually called touch-tone or touch-call.

E L: A term for a carrier system that transfers digital signals at 2.048 megabits per second, providing 32 64-kbps channels. Used in Europe instead ofT1.

E & M: Ear and Mouth (recEive and transMmit) signaling used on private lines, tie lines and

one-way outdial trunks.

EDGE: see Enhanced Data-rate for Global Evolution. EDI: see Electronic Data Interchange.

802.LL: Refers to a family of specifications developed by the IEEE for wireless LAN technology. 802.11 b (WiFi) provides Il-mbps transmission (with fallback to 5.5-, 2- and l-mbps) in the 2.4 GHz band within a range of about 300 feet. 802.11 g provides up to 108¬mbps throughput and is backward compatible with 802.11 b.

Electronic Data Interchange: Electronic transfer of business documents in a structured, computer-compatible data format, often through a value-added network (V AN).

Electronic Numbering: ENUM enables a user to store contact information (phone, fax, e-mail, 1M, cellular, postal address, etc.) that can be accessed by another person through the use of one phone number.

Electronic Serial Number: Unique identification programmed into each wireless phone by the manufacturer. The ESN is transmitted with each call for validation by the carrier.

End Device: see Data Terminal Equipment.

Enhanced Data-rate for Global Evolution: A faster version of GSM wireless service enabling data to be delivered at up-to 384-kbps throughput.

ENUM: see Electronic Numbering.

Erlang: The basic unit used in traffic analysis; equals the measurement interval during the busiest period of measurement - usually, one hour of traffic during the busiest hour of the analysis period.

ESF: see Extended Superframe Format. ESN: see Electronic Serial Number.

Extended-Area Calling: Provision calling to numbers beyond the standard local-calling range.

Extended Superframe Format: In Tl transmission, a sample of one eight-bit byte is taken for

each channel, one timing bit is added, and the entire 193-bit frame is packaged as one frame.

ESF strings 12 such frames together as a 'superframe,' which allows most of the timing bits to be used for other signaling information.

Facilities-based: Refers to a local service provider that offers services via its own central switches and outside telephone lines; it does not simply resell services from the incumbent local exchange company.

FCO: see Foreign Central Office.

FDMA: see Frequency Division Multiple Access.

FECN: Forward Explicit Congestion Notification is a bit set by a frame-relay network to alert an interface device (DTE) that congestion-avoidance procedures should be initiated by the receiving device.

Fiber optics: Transmission technology that transforms digital electrical pulses to light pulses for transmission through glass-fiber cables at speeds defined as OC-l and up. (OC-l is equivalent to 672 64-kbps channels; OC-2 = 1,344 channels ... up to OC-96.)

Fictitious Trunk/Number: A telephone number assigned to a group of outdial-only trunks to provide automatic number identification on outgoing calls. When fictitious numbers are dialed a recorded message will announce that the number is not in service.

Firewall: Provision for protecting a networked server from unauthorized access, usually using software-based protection such as defensive coding.

Fixed Wireless Access: A fixed-location local subscriber connection to the LEC central office via radio. (Also known as Wireless Local Loop.)

Flat-rate service: A local-calling plan that allows unlimited local calling at no additional charges.

Foreign Central Office: A LEC switching facility in the same local exchange area, but outside a user's 'home' service area.

Foreign Directory: A telephone directory for an exchange area other than the one in which a subscriber is located.

Foreign Exchange: A LEC local calling area other than a user's local-calling area.

Fractional T1: A service bandwidth that is less than T1DS l but greater than voice grade.

Fractional T1 usually comes in multiples of 64 kbps from 128 kbps to 768 kbps.

FRAD: see Frame Relay Access Device.

Frame Relay: A system of multiplexed data communications among widely-dispersed sites using specified virtual circuits based on the CCITT Q.922A standard for frame format. Such data frames are variable-length and do not include call-control and data-control overhead. Frames are assembled into complete communications after arrival at the end destination.

Frame Relay Access Device: A device that frames data with control information prior to presentation of the frame to the initial frame-relay switch (DCE). On the receiving end, the FRAD strips away control information so that data is presented in its original form.

Frame-Relay Access Line: A communications channel connecting a frame-relay-compatible device (DTE) to a frame-relay switch (DCE).

Franchise Fees/Surcharges: Fees paid by the LEC to municipalities for the right to provide telephone service within the municipality. Most regulations allow LECs to pass such fees along to their customers.

Frequency Division Multiple Access: A cellular technology that divides each cellular channel into three sub-channels. Each FDMA cell phone is assigned the frequency of one of the sub channels. FDMA is used with analog cellular systems.

FWA: see Fixed Wireless Access or Wireless Local Loop. FX: see Foreign Exchange.

FX Line: A line or trunk that connects customer equipment with a LEC central office in a foreign exchange, thereby providing direct access to the foreign local calling area. (Also may refer to a line or trunk connecting to a foreign central office.)

Glare: see Call Collision.

Global System for Mobile Communications: A cellular/PCS communications that uses an encrypted form of TDMA. GSM is the cellular/PCS standard in Australia, Europe, and much of Africa and Asia. It is also used by many providers in North America.

Grade Of Service: The proportion of initial call attempts, during the busy period, that may experience a block or busy condition. GOS is normally expressed as a decimal (e.g., one blocked or busy call out of 100 initial attempts = P.Ol).

Ground Start: A signaling method that uses each of the loop circuit conductors plus ground to seize the circuit and start dial tone. Because ground start simultaneously transmits near-end conditions and receives far-end conditions, the window for possible call collision ("glare") is reduced to less than O.l second.

GSM: see Global System for Mobile Communications.

H.322: ITU-T recommendation describing visual telephone systems and equipment for local area networks that provide a guaranteed quality of service (guaranteed bandwidth). This standard describes low latency LANs suitable for videoconferencing.

H.323: ITU-T recommendation describing packet-based visual telephone systems and equipment for local area networks that provide a non-guaranteed quality of service (guaranteed bandwidth).

H.324m: ITU-T recommendation describing packet-based multi-media telephone systems and equipment for local area networks that provide a non-guaranteed quality of service (guaranteed bandwidth).

H Channel: An aggregation of ISDN B channels. HO is 384 kbps (six B channels), HIO is 1,472 kbps (23 B channels), Hll is 1,536 kbps (24 B channels), etc.

Held Traffic: Calls/traffic that, when offered to a busy line/trunk group, are re-dialed on the same line/trunk group during the same busy hour.

Hertz: A measure of frequency especially relevant to descriptions of analog propagation. One

Hertz (Hz) = one cycle per second (cps).

Hook Switch: see Switch Hook.

Hot Line: A switched line that is provisioned at the central office such that when the telephone goes offhook a predetermined number is instantly dialed (see also Warm Line).

Hot Spot: A radio coverage area that enables wireless connection to the internet.

Hunt Group: A group of lines or trunks arranged such that an incoming call will be routed to any sequential un-seized facility; provides multiple channels for calls to a single number.

Hunting: Allows calls directed to a busy trunk or line to be automatically routed to the next available sequential channel. Hunting is set at the LEC central office and cannot be readily changed by the user.

ILEC: Incumbent Local Exchange Carrier; the company franchised as the provider of local telephone services in a defined territory in 1996 (or earlier). This term includes Ameritech, Bell Atlantic, BellSouth, Pacific Bell, Southwestern Bell, U S WEST, GTE, Sprint, SNET and a thousand smaller companies.

IMAP: Internet Message Access Protocol; a means of managing email messages on a remote server, similar to the POP protocol. But IMAP offers more options than POP, including the ability to download only message headers, create multi-user mailboxes, and build server based storage folders. (see POP)

Inbound Calls: see incoming calls.

Incoming calls: Calls to your number/location/business that originate elsewhere.

Interexchange: Refers to calls, facilities and services that involve more than one telephone

exchange area; communications between points in different exchanges.

Interlata: Refers to calls between points in different LA TAs. Such calling may be either interstate or intrastate.

International Telecommunications Union: Formerly known as CCITT, the ITU devises and recommends standards for international telecommunications.

Internet Access: Generally refers to the facility used for connecting to the internet. Such may be regular telephone lines (called "dial-up" access), ISDN circuits, DSL services, T1s, etc.

Internet Protocol: A standard for routing within interconnected packet-switched computer networks. Provides for transmitting blocks of data from source to destination hosts identified by fixed-length addresses.

Internet Service Provider: An entity that provides specialized access to the Internet. ISP services may include email service/addresses, domain names, web hosting and wideband connections.

Internet Telephone Service Provider: An entity that provides voice and related IP telephone services to end users, usually via wideband local loops.

Interstate: Refers to calls between points in different states. Such calling is usually interlata, but may be intralata where LA TAs cross state lines.

Intralata (Also called "local toll" or "regional long distance"): Refers to calls between two points that are within the same LATA. Most, but not all, LATAs are entirely within a single state.

Intrastate: Refers to calls between two points that are within the same state. Note, however, that many long-distance service providers exclude intralata calling when they refer to intrastate rates and charges.

Inverse Multiplexer: Combines separate network channels into a single channel with bandwidth

equal to the sum of the separate channel bandwidths.

IOC: see ISDN Ordering Code. IP: see Internet Protocol.

IPSec: IP Security is the internet standard protocol for tunneling, encryption and authentication.

ISDN: Integrated Services Digital Network is a voice/data standard that provides either two

voice channels (BRI, Basic Rate Interface) or 23 voice channels (PRI, Primary Rate Interface) via a single four-wire circuit. Channels can be merged to provide fewer channels of greater capacity.

ISDN Centrex: LEC Centrex offering whereby each station line includes all the characteristics and capabilities of ISDN BRI (2B+D), plus all the features and capabilities of the Centrex system.

ISDN Ordering Code: One of a specific combination of National ISDN services and features.

Each IOC specifies provisioning for an ISDN BRI service including features, directory numbers, call appea4rances, number of terminal identifiers, and number of SPIDs. Not all IOCs are available in all service areas.

ISDN Terminal Equipment: User telephones and other terminals that provide direct digital

connectivity to ISDN channels.

ISP: see Internet Service Provider.

ITSP: see Internet Telephone Service Provider. ITU: see International Telecommunications Union.

Jack: A receptacle into which telephone equipment can be plugged (connected). Also, see network interface.

Jitter: The degree to which data packets fail to arrive at a precise interval. VoIP packets are generated at the rate of one every 80 milliseconds. Because of network and transmission characteristics they do not arrive at the same rate; the resulting distortion in audio/video quality is called jitter.

Kbps: Kilobits per second; a measure of data transmission throughput ("speed"). Each kbps is 1,000 bits per second.

Key System: A telephone system providing access to multiple lines wherein each line appears at a separate button on the telephone. Calls are received or made by selecting the button for the appropriate line.

LAN: see Local Area Network.

LATA: Local Access Transport Area is that area within which long-distance calls may be handled by LECs. These areas are often called "local-toll" or "regional" calling areas." The United States is divided into 198 LATAs.

Latency: The time it takes for information to get through a network, sometimes called delay.

Layer-2 Tunneling Protocol: An alternative to IPSec that encloses non-internet protocols such as IPX, SNA and AppleTalk inside an IP envelope. L2TP relies on other protocols for encryption.

LEC: Local Exchange Carrier; the "telephone company." (see also CLEC and ILEC) Level: Ratio of signal magnitude to base magnitude. (also see amplitude)

Line: A channel or circuit between/among communications points. E.g., Business Line, Dial-T one Line, POTS Line, Residential Line, etc.

Line Supervision: Signaling that communicates the on-hook/off-hook state of each end of the line or trunk to the other; essential for direct call timing.

Local Area Network: A network of interconnected data communications devices generally located within the confines of a single user premises or campus.

Local Exchange Area: That area within which calls are treated as local calls.

Loading Coil: High-inductance devices placed in long subscriber loops to improve voice quality by offsetting cable capacitance. Because they tune the circuit to the voice frequency range (500-2500 Hz), they effectively short-out high-speed data.

Local access: Local telephone services and long-distance services within your Local Access Transport Area (LATA).

Local Loop: A circuit between the telephone service provider's central office and the user premises. This circuit provides access to whatever services the subscriber is using, from POTS to high-speed data access.

Local Reseller: A service provider that buys services from the incumbent local exchange company (Ameritech, Bell Atlantic, BellSouth, Pacific Bell, Southwestern Bell,

US WEST, GTE, Sprint United, SNET, etc.) and then resells them at a discount.

Local Service: Telephone service within your local calling area; includes connections to the local service provider (LEC/CLEC), features and calling plans that may be provided with such connections.

Local Serving Office: LEC central office that provides service to a designated group of subscribers.

Logical Channel: Hypothetical (straight-line) channel defined by its two end points. (also see virtual circuit)

Logical Circuit or Call Path: see Logical Channel, Virtual Circuit.

Login: The process of identifying and authenticating oneself to a computer system. Also, the specific alpha/numeric characters that identify a unique person.

Long Distance: Refers to electronic transmission of intelligence via common-carrier facilities between points in different local-calling areas.

Long-Distance Reseller: A service provider that buys services from one or more long-distance carriers (AT&T, MCI WorldCom, Sprint, etc.) and then resells them at a discount.

Loop Start: A signaling method that uses the electrical circuit (loop) formed by the two circuit conductors and terminating equipment to start the dial tone. With loop start, the window for possible call collision (glare) is the time between ring signals (about five seconds).

LPIC: Lata Primary Intraexchange Carrier is a designation applied to each telephone number that determines which long-distance company will handle intralata l + calls dialed on that line. (LPI Cs can be overridden in a number of ways, such as dialing' l 0 1 0+++' ahead of a long-distance call.)

LSO: see Local Serving Office.

L2TP: see Layer-2 Tunneling Protocol.

Main Distribution Frame: The point at which telco outside-plant circuits are cross connected to network interface devices located at the customer demarc. The MDF contains protection devices to limit surges, and it affords easy access for tests and measurements by telco personnel. At most commercial installations the MDF is located inside the building near the telco cable entrance. However, it may also be located in a pedestal or other external location to serve multiple small premises.

MAN: see Metropolitan Area Network.

Mbps: Megabits per second; a measure of data transmission throughput ("speed"). Each mbps is 1,000,000 bits per second.

MDF: see Main Distribution Frame.

Measured-rate service: A local-calling plan that bills for each completed outgoing local call. A charge is made based on call duration and distance between calling points.

Message-rate service: A local-calling plan that bills for each completed outgoing local call. An allowance of local calls at no additional charge may be included. After any monthly allowance is used, a charge is made for each additional local call, regardless of duration.

Metropolitan Area Network: A network of interconnected data communications devices generally located at separate user premises within the confines of a single metropolitan or local-calling area.

MIN: see Mobile Identification Number.

Mobile Identification Number: The mobile telephone address (telephone number).

Mobile Virtual Network Operator: A re-seller/secondary brand of pre-paid or post-paid cellular services that targets a very specific market demographic segment.

Modem: A device connected between an analog telephone line and a digital data device to transform signals to and from digital/analog. ("Modem" derives from "modulator-demodulator.")

MPLS: see Multi-Protocol Label Switching.

MTS: Message toll service refers to a pricing structure whereby each call is separately billed based on time, duration and/or distance.

MVNO: see Mobile Virtual Network Operator.

Multicast Virtual Connection: A frame-relay capability used to broadcast the same data to a group of up to 64 users.

Multiline Hunt Group: A group of switched channels that do not require a separate telephone number for each channel; all are designated as terminations of a single number.

Multiplexer: Combines individual digital channels into a single data stream for transmission over a single network circuit. Time division multiplexing (TDM) is used for DS+ standards.

Multi-Protocol Label Switching: A network management protocol that overlays data packets/frames with a set of priority header information that routes the packet/frame via pre-assigned paths. The MPLS overlay is stripped off the packet/frame when it reaches the far edge of the MPLS-defined network.

MVC: see Multicast Virtual Connection. NAT: see Network Address Translation. National Access Fee: see PICe.

Network Address Translation: A method of connecting multiple computers/IP devices to the internet or other IP network using a single IP address.

Network Interface: A wiring device/apparatus at the demarc that is used to connect telephone-company facilities to user facilities.

Network Terminator 1: A device at the user premises that performs the four-wire to two-wire conversion between user devices and the ISDN BRllocalloop. The NT1 is used by the CO for line maintenance and performance monitoring.

Network Terminator 2: A device at the user premises that includes all the functions ofNT1 plus protocol handling, multiplexing and switching. The NT1 is often integrated into PBX or key-system ISDN PRl circuit cards.

Night Numbers: Unique telephone numbers assigned to each channel in a multiline hunt group.

Such features enable calls to go through to specified telephones when the user's telephone system is set to night mode.

911 Fee: A tax-like charge authorized by local governments to pay the costs for 911 services.

Noise: Any unwanted addition to or loss from a communication signal- static, hissing, buzzing, crackling, distortion, cross talk, etc.

Non-Published number: A telephone number that is neither printed in the directory nor available from directory assistance. (compare to unlisted number)

NPA: see Numbering Plan Area.

NT1: see Network Terminator 1. NT2: see Network Terminator 2.

Numbering Plan Area: The geographical area within which telephone numbers are preceded by

a common area code. Often used interchangeably with "area code."

NXX: The three-digit exchange portion of a telephone number. OCN: see Operating Company Number.

Off-Hook: The condition that results when a telephone is lifted from its cradle, causing a signal to be sent to the central office (loop closed, current flowing).

Off-peak: Refers to calling that takes place during times that the carrier facilities are underutilized, usually evenings, nights and weekends. Most carriers charge lower rates for off-peak calling.

Off-Premises Extension: A telephone, terminal or PBX station located on property that is not contiguous with that on which the main station or switch is located.

One-Way Service: A line or trunk that is engineered such that only incoming or outgoing calls may utilize the facility.

On-Hook: The condition that results when a telephone is placed on its cradle, causing a signal to be sent to the central office (loop open, no current flowing).

Operating Company Number: Each telecommunications operating company is assigned a unique 4-digit identifying number. A list of these assignments is included in the NECA Tariff number 4.

Operating System: A software program that manages the basic operations of a computer system, such as allocating memory, scheduling tasks, accessing disk drives, and supplying a user interface. With an operating system, such as DOS, Linux, Mac OS 8, Unix, Windows NT, etc. developers can write application software to a common set of programming interfaces called APIs.

OPX: see Off-Premises Extension.

OPX Line: A circuit or channel that connects a user's main-location system with an off-premises extension.

OSI Model: The Open Systems Interconnection Model defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in a transmitting station, proceeding to the bottom layer, over the channel to the receiving station and back up the hierarchy. Each layer is defined by services provided, protocols and formats. Each layer provides services to the layer above and uses services from the layer below.

Layer 7, Application - supports end-user processes. Deals with identification/consideration of communication partners, quality of service, authentication, privacy, syntax constraints, etc.

Layer 6, Presentation/Syntax - formats and encrypts data. Provides freedom from compatibility problems by translating between network and application formats.

Layer 5, Session - sets up, connects, coordinates and terminates exchanges between applications at each end.

Layer 4, Transport - provides transparent transfer of data between end users/hosts, with end-to-end error recovery and flow control.

Layer 3, Network - creates logical paths by switching and routing packets across the network. Routing, forwarding, addressing, internetworking, error handling, congestion control and packet sequencing are functions of this layer.

Layer 2, Data Link - encodes and decodes data packets into bits, furnishing transmission protocol management and handles errors in the physical layer, flow control and frame synchronization. This layer is divided into two sub-layers - Media Access Control (MAC) and Logical Link Control (LLC).

Layer l, Physical - conveys the bit stream through the network at the electrical and mechanical level; defines all physical aspects.

Outbound Calls: see outgoing calls.

Outgoing calls: Calls originating from your location/business.

Out-Of-Band Signaling: Transmission of call setup, ringing, status and identification information through the network via data packets, rather than on the same circuit that carries the call.

Overflow Traffic: Calls/traffic that, when offered to a busy line/trunk group, are not re-dialed during the same busy hour. Generally refers to traffic that is automatically routed to a different line/trunk group. Also, in some LEC busy studies, "overflow" refers to the number of calls that received a busy signal.

Packet: A specified number of digital bits packaged with call-control, data-control and address information to allow it to travel throughout the telecom network and be assembled with related packets, which are then transmitted to the end destination.

Packet Switching: Refers to the process of guiding small bundles of information bytes ("packets") through a network so that all information intended for a given transmission eventually arrives at the intended destination for reassembly into the original message.

Pay Phone Surcharge: Long-distance companies are required to reimburse payphone operators $.24 for each toll-free and card call originated at a payphone. Long-distance companies may elect, in turn, to charge their customers for each such call (at any rate they choose).

PBX: Private Branch Exchange is a system of telephones that gives station users access to many internal and external lines from a single telephone set. Incoming calls are normally routed to the user telephone, and outgoing lines are normally access by dialing a number such as '9'.

PCM: see Pulse Code Modulation.

PCS: see Personal Communications Services. PDA: see Personal Digital Assistant.

Permanent Virtual Connection: A frame relay or X.25 logical link whose originating and terminating endpoints and class of service are defined by network management.

Personal Communications Services: A two-way digital voice/messaging services that operates in the 1900 MHz band.

Personal Digital Assistant: A portable computing device capable of accessing a wireless network for paging, data messaging, e-mail, computing, faxes, etc.

PICC: Primary Interexchange Carrier Charge refers to a monthly fee that may apply for each local telephone line designated to route calls to a long-distance company. Different long-distance companies may give various names to this charge, such as "Carrier Line Charge," "National Access Fee," "Pre subscribed Line Charge," etc. Such charges are not mandated; they are imposed or foregone at the discretion of each carrier.

PIC: Primary Interexchange Carrier is a designation applied to each telephone number that determines which long-distance company will handle interlata 1 + calls dialed on that line. (PICs can be overridden in a number of ways, such as dialing' 101O+++' ahead of a long-distance call.)

PIC Freeze: An anti-slamming mechanism whereby no change of your long-distance company can be made by anyone but you.

PIC Lock: see PIC Freeze.

Point Of Presence: Physical place within a LATA where a long-distance carrier interfaces with

the LEC; may be an IXC central office (CO) or wire center (WC).

Point-to-Point Tunneling Protocol: Microsoft's proprietary alternative to IPSec. POP: see Point of Presence or POP Email.

POP Email: Post Office Protocol; the most widely-used internet email mailbox access standard whereby you connect to a server and download all your messages, which are then deleted from the server. (see IMAP)

POTS: "Plain Old Telephone Service" usually refers to a single dial-tone line. PPTP: see Point-to-Point Tunneling Protocol.

Prepaid Calling Card: A debit card that enables a user to place and charge calls from telephones other than the home service by paying for the card in advance.

Presence: The on-line network status of IP devices such as computers, PDAs, telephones, cellular/PC phones, fax machines, etc. An IP presence-aware application can detect the status of such devices and display it to authorized parties, indicating which are available for communicating with the user of the device(s).

Presubscribed Line Charge: see PICe.

PRI: see Primary-Rate Interface.

Primary-Rate Interface: Refers to 23B+D ISDN service, which includes 23 64-kbps bearer channels and one 64-kbps data channel on a DSI local-loop circuit. (In Europe, PRI consists of30B + D.)

Private Line: A full-period circuit between two or more points for the exclusive (and constant, if desired) use of the subscriber. (compare to switched services)

PSTN: Public Switched Telephone Network.

PTT: Post Telephone & Telegraph administration; refers to the government-owned or controlled telephone companies in many foreign countries.

Pulse Code Modulation: Used to digitize analog signals. PCM samples the analog signal 8,000 times/second and assigns one (of 128) 7-bit digital value to each sample.

Push-Button Dialing: see Touch-Tone.

PVC: see Permanent Virtual Connection.

Local Exchange Carrier: A LEC that provides local loops to fixed subscribers via radio (wireless local loops).

RBHC: Regional Bell Holding Company - Ameritech, Bell Atlantic, BellSouth, NYNEX, Pacific Telesis, Southwestern Bell and U S WEST; the companies divested by AT&T in 1984. Through mergers there are now four such entities - Bell South, Qwest, SBC and Verizon.

RBOC: Regional Bell Operating Company - the local exchange companies owned by the original RBHCs. Today, these LECs go by names such as Ameritech, Bell Atlantic/Verizon, Bell South, Pacific Bell, Nevada Bell, Southwestern Bell and Qwest/U S WEST.

Re-biller: see Local Reseller, Long Distance Reseller.

Regulators: Governmental agencies that administer rates, rules and regulations governing telecommunications services. Regulatory agencies include:

FCC - Federal Communications Commission has jurisdiction over interstate services. PUC -

Public Utility Commissions in each state have jurisdiction over intrastate services.

(May have other names in various states, e.g., Public Service Commission, State Corporation Commission, etc.)

CRTC - Canadian Radio-Television and Telecommunications Commission has jurisdiction over services in Canada.

Remote Call Forwarding: A local telephone number in the LEC central office that forwards all calls to a subscriber-predetermined number.

Repeater: An electrical device that receives low-level/distorted digital signals, regenerates and transmits new digital signals that duplicate the original signals without distortions, and sends them out at a higher level.

Reseller: see Local Reseller, Long Distance Reseller.

Residential Line: A circuit that connects the LEC central office (brings dial-tone) to telephones for residential-class services.

Restrictions: Service Provider provisions that are designed to prevent undesired or unauthorized calling and charges. Among the restrictions available from most LECs are blocking of:

• Specific incoming calls
• Collect calls
• Charges for 3rd_party calls
• Calls to 900/976/9661700 numbers
• Pay-per-use features
• Toll calls

Ringing: Ring signals that recur, usually every six seconds.

Ring Signal: The 50-volt, 20-Hz electrical impulses that activate telephone ringers (bell) or other indicators. Also refers to the artificial sound of ringing to let a caller know that ring signals are being applied to the called line.

Rollover: see Hunting.

RLEC: see Radio Local Exchange Carrier. Rotary: see Hunting.

Rotary Dial: Signaling that utilizes pulses to indicate numbers being dialed.

Router: Equipment that routes data to and from a local area network on the Level-3 LAN protocol (OSI Layer 3, e.g., the IP address). Routers also act as traffic cops, allowing only authorized machines to transmit data into the local network so that private information can remain secure. In addition to supporting dial-in and leased connections, routers also handle errors, keep network usage statistics, and handle security issues.

SCP: see Service Control Point.

Secure VPN: A data VPN that maintains security by encrypting and decrypting data at the edges of the network.

Series Completion Hunt Group: A group of switched channels, each having a separate telephone number, arranged in a fixed sequence for hunting purposes; a call to any number in the group will hunt to the end of the sequence before receiving a busy signal.

Service Control Point: The 'brains' ofSS7, network processor that controls how calls are routed based on out-of-band signaling, call-destination and network status information.

Service Profile Identifier: Identifies the ISDN BRI services and features provided by the CO switch to as many as eight user terminal devices/B-Channel in accordance with ITU Q.932. The SPID is usually the ten-digit phone number assigned to the ISDN channel, plus a prefix and suffix that define the device profile and device address.

Service Switching Point: An SS7 CO switch.

Service Transfer Point: An SS7 network packet router for out-of-band signaling.

Session Initiation Protocol: A signaling protocol for internet conferencing, telephony, presence, events notification and instant messaging developed within the Internet Engineering Task Force (IETF).

Signaling: Refers to the sending of information that tells other network/customer switches how a particular call is to be routed/handled/billed, etc.

Signaling System 7: The out-of-band signaling protocol used by public switched telephone networks.

Signal- To-Noise Ratio: Comparison of the usable/desirable transmitted signal to the noise or undesired transmitted elements. One measure of transmission quality.

SIP: see Session Initiation Protocol.

Six-second billing: Refers to timing of calls for billing purposes whereby the billed time of each call is rounded up to the next whole O.l minute (six seconds).

Slamming: The practice of changing the long-distance service to which your calls are routed, without your authorization.

SLC: see Subscriber Loop Carrier.

SONET: Acronym for Synchronous Optical NETwork, the North American standard for interface parameters; rates, formats, multiplexing methods; and administration, maintenance, and provisioning for high-speed transmission of bits information in laser-light streams.

Speed Calling/Dialing: Allows a user to store frequently-called numbers, which can then be called by dialing or toughing just one or two digits.

SP ID: see Service Profile Identifier.

Splitter: A device used in DSL services that enables use of an analog telephone for dial-up services while accessing a data server (e.g., ISP or frame-relay port) on a full-period basis.

SS7: see Signaling System 7.

SSP: see Service Switching Point.

Start Signal: An electrical pulse or connection that initiates action by "seizing" a line or trunk. STP: see Service Transfer Point.

Subscriber Loop Carrier: A multiplexed facility that carries subscriber loops from the central office to hub facilities nearer user locations. NOTE: "SLC" is a Lucent trademark for SLC¬96 (pronounced "slick 96", this analog version carries 96 local loops to a distribution hub over three pairs of wires) and digital loop carriers SLC Series 5 and SLC 2000.

Supervision: see Line Supervision. SVC: see Switched Virtual Circuit.

Switched Service: A class of long-distance service that is provided via local switched-access circuit(s).

Switched Virtual Circuit: A virtual circuit connection established across a network on an as-needed basis and lasting only for the duration of the data session (call).

Switched Access: A circuit between the user and LEC that enables calling to and from all telephone subscribers. (compare to dedicated access.)

Switch Hook: The telephone mechanism that opens the circuit when the telephone handset is placed on its hook, and closed the circuit when the handset goes off hook.

Synchronous: Refers to digital facilities wherein all network terminals run on clocks that trace back to a highly-stable common reference signal, which results in a constant actual bit-rate. Individual synchronous channels can be accessed at higher bit-rates without need for demultiplexing. (also see Clocking)

T1: A term for a carrier system that transfers digital signals at 1.544 megabits per second in accordance with digital standard l (see DS1).

T3: A term for a carrier system that transfers digital signals at 44.736 megabits per second in

accordance with digital standard 3 (see DS3).

TA: see Terminal Adapter.

TCP: see Transmission Control Protocol. TDM: see Time Division Multiplexing. TDMA: see Time Division Multiple Access.

Terminal Adapter: Interface between ISDN circuit and non-ISDN terminal device at the user premises. (Compare to modem.)

Terminal Multiplexer: Combines electrical digital streams into an optical-carrier format and transforms them into laser-generated light-wave pulses. Performs the reverse functions for received signals.

Three-Way Calling: Allows a user with a plain telephone on a single line to put a caller on hold, dial another number and then, if desired, put all three parties together in a conference.

Tie Line: A trunk that directly connects two PBXs. More precisely called "tie trunk."

Time Division Multiple Access: A cellular/PCS technology whereby each frequency channel is subdivided to enable three simultaneous calls.

Time Division Multiplexing: A method of transmitting multiple channels over a single circuit by dividing the data stream into time slots and assigning each channel an intermittently-repeated time slot. At the receiving end, each time-separated channel is reassembled.

Tip and Ring: Refers to the two wires that comprise a single-station pair or single line. "Tip" is the positive connection, which usually goes to ground through central-office equipment. "Ring" is negative (-50 volts d-c).

Toll-Free Service: Refers to calls via '800', '888', '877' numbers, etc. Touch-Call: see Touch-Tone.

Touch-Tone: Dual-tone multi-frequency signaling that uses standard tone combinations to indicate numbers being entered.

Traffic: Electronic information transmitted via telecommunications channels. Includes usage plus ringing, set-up and other signaling.

Transceiver: Transmitting and receiving equipment in a common housing. Term is typically used with mobile radio and fiber-optic services.

Transmission Control Protocol: A connection-oriented, full-duplex, host-to-host protocol breaks data into packets for routing over packet-switched computer networks; corresponds to OSI Layer 4 (transport layer).

Transmission Format: A line-coding technique that prevents too many consecutive zeros from being transmitted, which would cancel timing. B3ZS and B8ZS are common formats.

3DES: see Triple Data Encryption Standard.

Triple Data Encryption Standard: An encryption algorithm that uses 168-bit keys to encrypt, decrypt and then re-encrypt data. This process improves internet security by providing 374, 144,419,156, 711,000,000,000,000,000,000,000,000,000,000,000,000 possible combinations.

Trunk: A circuit engineered to connect the LEC central office (bring dial-tone) to a PBX telephone system for business-class switched services. Also, a class of service assigned to a channel carried via a circuit between the LEC co and such equipment.

Trusted VPN: A data VPN that depends upon the VAN or other service provider to maintain data security.

Tunneling: A packet/frame/cell encapsulation technique used to transport multiple protocols and/or encrypted data over a single connection. Tunneling prevents unauthorized entities from 'seeing' what's inside the encapsulated data.

Two-way service: A line or trunk engineered to handle both incoming and outgoing calls.

Uniform Resource Locator: Website address, consists of access protocol specification (www, for instance) and site location (abc.com, for instance). Also called IP address.

Unlisted Number: A telephone number that is not printed in the telephone directory, but is

available from directory assistance.

Upstream: Transmission of signals from a remote point to the main computer/node. URL: see

Uniform Resource Locator.

Username: see login.

USF: Universal Service Fund refers to a tax imposed for the purpose of funding internet access for rural schools, libraries and healthcare organizations.

Value Added Network: A voice/data service provider that offers added functions such as email, EDI, electronic funds transfer, X.4OO global messaging, LAN interconnection, VPN across a variety of transmission services (X.25, frame relay, TCP/IP, etc.)

VAN: see Value Added Network.

VDSL: see Digital Subscriber Line.

Virtual Circuit: A voice or data communications link that appears to the user to be a dedicated point-to-point circuit but is not a fixed physical circuit. A virtual circuit is referred to as a logical, rather than physical, call path. Also called virtual connection.

Virtual Private Network: A voice or data service that uses public network facilities to emulate a private-line network. Voice VPNs are provided by AT&T (SDN), WorldCom (V-Net) and Sprint (VPN) for very large customers. Data VPNs use VANs and the internet for very small to very large users, often maintaining security through tunneling protocols.

Virtual Tributary: A signal/channel of less-than-DS3 capacity transported via SONET. Virtual tributaries can be accessed without de-multiplexing the entire SONET signal.

VON: see Voice on the network.

Voice On the Network: Refers to the overall concept of packetized voice over proprietary carrier networks or the internet.

VPN: see Virtual Private Network. WAN: see Wide Area Network.

Warm Line: A switched line that is provisioned at the central office such that when the telephone goes off hook a predetermined number is dialed, after a pause to allow dialing of any number from the telephone, if desired (see also Hot Line).

WATS: Wide Area Telephone Service refers to a pricing structure whereby the duration of all calls is accumulated, and the appropriate rate(s) is applied to total time.

Web Hosting: Providing and managing the hardware and software that make up a company's Web site.

Wide Area Network: A network of interconnected data communications devices located at user premises in different local-calling areas.

WiFi: A wireless LAN that provides access to the internet for portable devices within its coverage area ("hot spot") in accordance with the 802.11 b standard.

Wink Start: A signal returned by one switch when it learns that the other end of an indial-only trunk has been seized. The "wink" indicates that digit detector is active; direct station number digits may now be transmitted.

Wire Center: The location where an IXC or LEC operates testing facilities to maintain subscribers' local lines/trunks/circuits. Wire centers are often in class-5 central offices, but not always.

Wireless Local Loop: A fixed-location local subscriber connection to the LEC central office via radio. (Also known as Fixed Wireless Access.)

WLL: see Wireless Local Loop or Fixed Wireless Access.

World Zones: For purposes of assigning numbers and routing calls, the world is divided into nine calling zones.

1. United States, Canada and most Caribbean nations

2. Africa

3. Western Europe (France, Ireland, Italy, Portugal, Spain, et al

4. Western Europe (Denmark, Germany, Scandinavia, UK et al

5. Central and South America

6. Oceania (Pacific rim)

7. Eastern Europe

8. Asia

9. Middle and near east

Whole-minute billing: Refers to timing of calls for billing purposes whereby the billed time of each call is rounded up to the next whole minute.

XDSL: see Digital Subscriber Line. XTU-C: See DSL Access Multiplexer.

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