The telephone line that leaves your house or business; it consists of either four or eight wires.
Central office (CO)
Contains the equipment that generates a dial tone, interprets the telephone number dialed, checks for special services, and connects the incoming call to the next point.
Local access transport area (LATA)
A geographic area, such as a large metropolitan area or part of a large state. Telephone calls that remain within one of these are usually considered local telephone calls, while telephone calls that travel from one of these to another are considered long distance telephone calls.
A telephone connection used by telephone companies that carries multiple telephone signals, is usually digital and high speed, and is not associated with a particular telephone number.
Modified Final Judgment
A court ruling in 1984 that required the divestiture, or breakup, of AT&T.
Local exchange carrier (LEC)
The name given to local telephone companies after the divestiture of AT&T in 1984.
Interexchange carrier (IEC or IXC)
The name given to long distance telephone companies after the divestiture of AT&T in 1984.
Central office exchange service (Centrex)
A service from local telephone companies through which up-to-date telephone facilities at the telephone company’s central (local) office are offered to business users so that they do not need to purchase their own facilities.
Private Branch Exchange (PBX)
A large computerized telephone switch that sits in a telephone room on the company property.
Private or tie lines
A leased telephone line that requires no dialing.
Telecommunications Act of 1996
A major event in the history of the telecommunications industry that, among other things, opened the door for businesses other than local telephone companies to offer a local telephone service.
Competitive local exchange carrier (CLEC)
New providers of local telephone services (their creation was initiated by the Telecommunications Act of 1996).
Incumbent local exchange carrier (ILEC)
A local telephone company that existed before the Telecommunications Act of 1996.
A 56,000-bps dial-up modem standard approved by a standards-making organization rather than a signal company it is slightly incompatible with both x2 and K56flex.
An improvement of the V.90 standard that provides a higher upstream data transfer rate and also provides a call waiting service, in which a user’s data connection is put on hold when someone calls the user’s telephone number.
Digital Subscriber Line (DSL)
A technology that allows existing twisted pair telephone lines to transmit multimedia materials and high-speed data.
A type of connection in which the transfer speeds in both directions are equivalent.
A connection in which data flows in one direction at a faster transmission rate than the data flowing in the opposite direction; for example, there are numerous systems that have a faster downstream connection (such as from the Internet) and a slower upstream connection.
A form of digital subscriber line in which there is no POTS signal accompanying the DSL signal, thus there is no need for a splitter.
The generic name for the many forms of digital subscriber line (DSL).
Asymmetric digital subscriber line (ADSL)
A popular form of digital subscriber line that transmits the downstream data at a faster rate than the upstream data. Typical downstream data rates range from 600 kbps to 1500 kbps, while upstream data rates range from 300 kbps to 600 kbps.
A form of consumer DSL that has lower transmission speeds and thus lower consumer costs. Also known as Universal DSL, G.Lite, and splitterless DSL. Typical transmission speeds are in the 200 kbps range.
Very high data rate DSL2 (VDSL2)
A form of digital subscriber line that is a very fast format (between 51 and 55 Mbps) over very short distances (less than 300 meters).
Rate-adaptive DSL (RADSL)
A form of digital subscriber line in which the transfer rate can vary, depending on noise levels within the telephone line’s local loop.
A communications device that allows high-speed access to wide area networks, such as the Internet, via a cable television connection.
A commercially available packet-switched network that was designed for transmitting data over fixed lines (as opposed to dial-up lines).
Permanent virtual circuit (PVC)
A fixed connection between two endpoints in a frame relay network. Unlike a telephone circuit, which is a physical circuit, this circuit is created with software routing tables, thus making it a virtual circuit.
Layer 2 protocol
A protocol that operates at the second layer, or data link layer, of the OSI seven layer model.
Committed information rate (CIR)
The data transfer rate that is agreed on by both customer and carrier in a frame relay network. In general, this is called a service level agreement (SLA).
An agreed-upon rate between a customer and a frame relay provider; this agreement allows the customer to exceed the committed information rate by a fixed amount for brief moments of time.
Asynchronous Transfer Mode (ATM)
A high-speed, packet-switched service, similar to frame relay, that supports various classes of service.
Virtual channel connection (VCC)
Used in Asynchronous Transfer Mode, a logical connection that is created over a virtual path connection.
Virtual path connection (VPC)
Used in Asynchronous Transfer Mode to support a bundle of virtual channel connections (VCCs) that have the same endpoints.
The connection between a user and the network in Asynchronous Transfer Mode (ATM).
One of the types of connections in Asynchronous Transfer Mode (ATM); one of these is created by a network and used to transfer management and routing signals.
Class of service
A definition of a type of traffic and the underlying technology that will support that type of traffic. Commonly found in Asynchronous Transfer Mode (ATM) systems.
Constant bit rate (CBR)
Used in Asynchronous Transfer Mode (ATM), a most expensive type of service that is similar to a current telephone system leased line. Acts very much like a time division multiplexed telephone service, but it is not a dedicated circuit like a leased telephone line. Delivers a high-speed, continuous data stream that can be used with transmission-intensive applications.
Variable bit rate (VBR)
A class of service offered by ATM that is similar to frame relay service. Used for real-time (or time-dependent) applications, such as sending compressed interactive video, and non-realtime (non-time dependent) applications, such as sending e-mail with large, multimedia attachments. Applications often send bursts of data, and the ATM network guarantees that the traffic is delivered on time.
Available bit rate (ABR)
A class of service supported by Asynchronous Transfer Mode (ATM) that is used for traffic that may experience bursts of data (called “bursty” traffic) and whose bandwidth range is roughly known, such as the traffic found in a corporation’s collection of leased lines. You may get a chance to transmit your data, or you may have to wait. But once your data is in the network, it will be delivered. Good for traffic that does not have to arrive in a certain amount of time, and also provides feedback that indicates if part of the ATM network is experiencing congestion.
Unspecified bit rate (UBR)
A class of service offered by ATM that is capable of transmitting traffic that may experience bursts of data, but does not make any promise about when the data may be sent. Plus, unlike available bit rate (ABR), it does not provide congestion feedback when there are congestion problems. Unlike data transmitted in the other classes of service, data transmitted may not make it to the final destination. If the bandwidth necessary to transmit your data is required by data using a higher class of service, your data may be discarded partway through the network connection. Usually the least expensive service.
Computer-Telephony Integration (CTI)
New telephone services and systems that combine more traditional voice networks with modern computer networks.
A telecommunication service that allows users to utilize a single desktop application to send and receive e-mail, voice mail, and fax.
Interactive voice response
A system that enables a company to use a customer’s telephone number to extract the customer’s records from a corporate database when that customer calls the company. The customer records are displayed on a service representative’s workstation as the representative answers the telephone.
Integrated voice recognition and response
A system in which a user calling into a company telephone system provides some form of data by speaking in to the telephone and a database query is performed using this spoken information.
A computer-telephony integration (CTI) application in which a fax image that is stored on a LAN server’s hard disk can be downloaded over a local area network, converted by a fax card, and sent out to a customer over a trunk line. An incoming fax can be converted to a file format and stored on the local area network server.
A computer-telephony integration (CTI) application in which a user can dial into a fax server, retrieve a fax by keying in a number, and send that fax anywhere.
Text-to-speech and speech-to-text conversion
Telephone systems that can digitize human speech and store it as a text file, and take a text file and convert it to human speech.
Third-party call control
A telephone feature which allows users to control a call (for example, set up a conference call) without being a part of the call.
PBX graphic user interface
An interface in which different icons on a computer screen represent common PBX functions such as call hold, call transfer, and call conferencing, making the system easier for operators to use.
A technology in which users can specify which telephone numbers are allowed to get through. All other calls will be routed to an attendant or voice mailbox.
Customized menuing system
A menu system that can be created and/or changed dynamically according to a user’s profile or needs.