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CAT Cable A twisted-pair wire that has been categorized to indicate maximum data rate and applications. CAT 1 cable is typically used for plain old telephone service (POTS) and has a maximum data transfer rate of under 1 Mbps; whereas CAT 5 cable is used for high-speed applications and can transmit over 100 Mbps on the twisted-pair cable. While superficially appearing similar, CAT cables are very different in capacity and it is important to determine planned use before selecting cabling.
CD-ROM Compact Disc Read-Only Memory. An optical disc that is 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, an 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.
 
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