Glossary C-D

CD-ROM: Compact Disc Read-Only Memory. An optical disc that looks just like an audio CD, but serves a different need. It stores approximately 680 megabytes of computer data. The data is written to and read from the disk via the light of a laser. Some people also refer to the computer drive that reads these discs as a CD-ROM.

CDMA (Code Division Multiple Access): A form of multiplexing that permits simultaneous use of a single channel by a number of users. CDMA employs digital spread spectrum technology to send the signal in a precise sequence (code) along multiple channels. The code is varied constantly, making it difficult to intercept or clone CDMA signals.

CLASS (Custom Local Area Signaling Service): A service provided by the phone company that sends an electrical signal to a receiving device when other phone company services (voice mail, for example) have been activated. The CLASS signal notifies the subscriber that a message is waiting to be retrieved.

CLEC (Competitive Local Exchange Carrier): CLECs compete with Incumbent Local Exchange Carriers (ILECs) and provide their own switching and networks, though they usually lease the lines and capacity from an ILEC. The Telecommunications Act of 1996 made this competition possible by regulating the prices that ILECs could charge CLECs for use of the ILEC’s network.

CO (Central Office): The phone company facility where subscribers’ lines are linked to switching equipment and connected to other subscribers. A CO will handle a local area, but can connect to a CO in any other locale or to a mobile phone.

CTI (Computer Telephony Integration): A series of applications and peripherals that enables the use of a computer for voice communications and call control. Implemented initially for streamlining call routing and call logs in call centers, CTI now describes any calls made from a computer, whether over the Public Switched Telephone Network (PSTN) or via IP telephony.

Cable Modem: A device that allows users to connect a PC to a local cable TV line for data transmission. Cable modems provide high-speed connections at about 1.5 Mbps (megabits per second), comparable to a Digital Subscriber Line (DSL) and significantly faster than dial-up modems. This type of service is often referred to as broadband service.

Call Appearance: Any phone call that is received on a system-based telephone. Many phone systems allow for multiple call appearances on a single extension, particularly on receptionist telephones that allow one or more callers to be put on hold while other calls are answered.

Call Forwarding: A service provided by the Phone Company that forwards a call received on one phone number to an alternate number that has been designated by the user.

Call Waiting: A service provided by the phone company that allows a subscriber to answer a second call when already on another call on the same phone line. The recipient of the call is generally notified of the second call by a tone provided by the Phone Company’s Central Office (CO).

Caller ID (CID): A service provided by the phone company that sends the telephone number, date, time of the call, and in some cases the name of the calling party to the recipient of the phone call. Associated services include Caller ID Block, which prevents the call information from being sent from the caller's Central Office (CO) and Call Waiting/Caller ID which allows the call recipient to see the number of a second caller when already on another call.

Carbon Microphone: A microphone common to older telephones. Carbon microphones require no power source other than line power in order to operate. Cascade 1) Successive stages, processes, or functions that are directly caused by input from a preceding stage, process, or function. 2) A series of virtually identical interconnected electronic devices such as small telephone systems or stackable network hubs. Cell In wireless telephone applications, a cell refers to the geographical area within range of the transmitter/receiver antenna (or cell site) covered by a service provider’s cell site.

Cell Site: The physical location of the antenna or wireless telephony transmitter/receiver.

Cellular Telephone: A telephone that connects by wireless (radio) signal to a cell site. Originally, the terms "cellular" and "cell phone" referred only to analog service but the term has become a catchall reference to any mobile telephone.

Central Office Line (CO Line): A single analog telephone line sent directly from the phone company.

Centrex (Central Office Exchange Service) : A service package offered by the phone company. It gives standard phone users the ability to access key system or PBX features without having to purchase an expensive system. In essence, the PBX/key systems are maintained and operated by the Phone Company.

Channel: In telecommunications contexts, channel refers to any path between 2 devices. A channel can be anything from a wire linking 2 computers in a network to a specific radio frequency in a wireless application (radio or television, for instance). Client In a standard client/server relationship, the client is the user application that requests information. A common use of client/server is web browsing. The user’s browser acts as the client and the computer delivering the requested information is the server.

Clustering: The act of combining several smaller phone systems in concert to achieve larger-system functions. This method also minimizes downtime in the event of a system malfunction—only a portion of the clustered system is affected rather than the entire network.

Conductor: On a registered jack (RJ), the conductors are the copper pins in the plug of a handset cord and in the telephone jack that connect the telephone to the wall jack. For example, a RJ-14 jack, the standard jack for 2-line telephones, has 4 active conductors, 2 per phone line.

Cookie: A small text message that is placed in your web browser by the web server for a site that you've visited. The message is sent back to the server each time your browser requests a page from that server, so you are identified as a return visitor. This saves you from having to enter the same information about yourself each time you visit. It also provides the opportunity for the server to present you with a customized welcome page and other content.

Cordless Headset: A cordless headset allows you to talk hands free and cord free. However, a cordless headset does require a connection between the cordless headset base unit and the telephone.

Cordless Telephone: A telephone that does not require a wired connection between the base of the phone and the handset (or receiver). Cordless phones may use digital or analog signals between the base and receiver of the telephone. Cordless telephones are designed to work directly from Central Office (CO) lines as opposed to wireless phones, which employ cell sites for operation.

Cramming: The practice of some telecommunications service providers of adding services and charges to a customer’s bill without notifying the customer.

Crosstalk: Crosstalk occurs when an undesired signal from one channel interferes with the signals of a separate channel. Analog cordless phones generate crosstalk when they are tuned to adjacent or identical radio frequencies.

DID (Direct Inward Dial) : A feature offered by key and PBX systems that allows callers to connect directly with PBX users without having to navigate menus or speak with a receptionist

. DIP Switch (Dual In-Line Package Switch) : A small switch usually attached to a circuit board. This switch is used to activate or deactivate the pathways of the circuit board at a specific junction.

DND (Do Not Disturb) : A user-activated function within some telephone systems that makes an extension unavailable to receive internal or external phone calls.

DSL (Digital Subscriber Line) : A network service that provides high-speed data transmission over standard twisted-pair copper wires. DSL service is up to 30 times faster than standard telephone dial-up lines.

DTMF (Dual Tone Multi Frequency): The frequency tone pairs produced by the dial pad on a touch-tone phone. This signal sends instructions to the switching device to which it is connected. DTMF has all but replaced loop disconnects, or pulse, dialing.

Data compression: A technique for storing and transmitting data in a format that requires less space than usual.

Database: A collection of organized, retrievable data. The most common types are the relational database and the hypertext database. A relational database stores information in 3 levels: field (any single referenceable item), record (a collection of related fields), and file (a collection of related records). The conventional phone book is an example of a relational database: individual telephone numbers names and addresses are fields, a line listing is a record, and the complete phone book is a file. Relational databases on computers simplify record retrieval; a user is able to locate a complete record by searching for any of the fields contained in it. The hypertext database is used mainly on the Internet. Hypertext links allow you to point and click on selected words on a web page to link to other locations or pages on the Internet. A hypertext database is not organized in any specific relational format.

Dedicated Line: A phone line maintained for a specific purpose or function. For instance, a company that performs most of its sales by faxed orders will often have a phone line dedicated to receiving fax transmissions.

Demarcation Point (also Point of Demarcation): The point at which the lines from the phone company’s Central Office (CO) physically passes into a building.

Dial-up: A means of establishing an Internet connection through the analog Public Switched Telephone Network (PSTN). Dial-up connections require the use of a modem to convert the digital signal from the computer to an analog signal that can be routed by the PSTN.

Dialpad: The numbered keys on the telephone. Pressing the number on a dialpad sends instructions to the Central Office (CO) for routing a telephone call.

Digital: 1) In telecommunications contexts, digital refers to the method of storing, retrieving, and transmitting data in a sequence of discrete symbols, usually binary. 2) In common usage, digital may refer to a readout that uses numbers rather than scale positions (i.e., digital display, digital clock, etc.).

Digital Adapter: A device used to convert a digital phone line to a format compatible with an analog product. Typical uses of a digital adapter include teleconferencing and data transmission through a PBX.

Directory: In general, any list that provides access to retrievable contents. On a telephone, a built-in directory is a saved phone list accessible through one or a set of function keys. On a computer, a directory stores retrievable information in an "inverted tree" system. Directories on PCs are also commonly referred to as folders. Duplex Adapter An accessory that connects to a 1- or 2-line jack that splits the signal and allows more than 1 phone to be connected to the jack. A duplex adapter does not provide an additional connection to the Central Office (CO), but it does permit connection to a second device.

dB (Decibel) : 1) A logarithmic expression that provides a relative measure (or ratio) of 2 or more electrical states. The decibel is used to describe differences in signal power and voltage in electronics. 2) Absolutes measure for the relative intensity of acoustic sound per unit of area.

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