Glossary Terms - "C"

Call Forwarding
A feature permitting the user to program a phone to ring at an alternate location; call forwarding may be in effect at all times or just when a particular phone is busy or doesn't answer.

Call Forwarding - Busy
A feature causing an inbound call to ring on an alternate pre-determined number when the called number is busy. The number to be forwarded to is managed by the service provider and selected by the customer. The customer cannot change it without activity by the service provider.

Call Forwarding – No Answer
A feature causing an inbound call to ring on an alternate pre-determined number when the called number is not answered after a pre-determined number of rings. The number to be forwarded to is managed by the service provider and selected by the customer. The customer cannot change it without activity by the service provider.

Call Hold
A feature allowing the user to put one caller on hold while other calls are made or answered.

Call Park
A feature allowing a call for a busy extension to be put into a hold-like state until someone at that extension or another extension becomes free to answer it. The call is brought out of "park" by dialing a special code.

Call Transfer
A feature allowing a call to be transferred to another phone.

Call Waiting
A feature that provides audible or visual indicators to let a single-line-phone user know that she has another call waiting for her.

Caller ID
A telephone company service allowing the subscriber to view the phone number and/or name of the calling party on a display device before answering the phone. Caller ID usually requires some kind of hardware phone interface to provide the displayed information.

Camp-On
A PBX feature where a subscriber calling a busy number is placed into a waiting condition; and both phones ring automatically when the called party hangs up from the first call.

Carrier
1. A continuous frequency capable of being modulated with a second (information carrying) signal.
2. A communications company or authority providing circuits to carry private traffic (also known as common carrier.)

CATV (Community Antenna Television)
A broadband 75-ohm coaxial cable based Radio Frequency transmission system which is gaining popularity as a data transmission system.

CDMA
Short for Code-Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques. Unlike competing systems, such as GSM, that use time-division multiplexing (TDM), CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence. CDMA was developed by Qualcomm, Inc.

Cellular
Refers to communications systems, especially the Advance Mobile Phone Service (AMPS), that divide a geographic region into sections, called cells. The purpose of this division is to make the most use out of a limited number of transmission frequencies.

Each connection, or conversation, requires its own dedicated frequency, and the total number of available frequencies is about 1,000. To support more than 1,000 simultaneous conversations, cellular systems allocate a set number of frequencies for each cell. Two cells can use the same frequency for different conversations so long as the cells are not adjacent to each other.

For digital communications, several competing cellular systems exist, including GSM and CDMA.

Central Office
The site that contains the local telephone company's equipment that routes calls to and from customers. This site also contains equipment that connects customers to long distance services and internet service providers.

Centrex
A PBX-like service provided by a local telephone company in which incoming calls can be dialed direct to any station without an operator’s assistance (DID.) The Centrex switch is not located on-site.

Channel
A path for electrical transmission between two or more points without common carrier provided terminal equipment (also called a link, line, circuit, or facility.)

Channel Bank
Equipment that performs TDM-type multiplexing of lower speed (generally voice converted to 64 Kbps digital) channels into a higher speed composite (generally in 24 channel digroups of 1.544 Mbps each.)

Circuit Switching
Temporary connection of two or more channels to create a through circuit.

Class of Service
The categorizing of telephone subscribers according to specific type of telephone use requirements (your class of service governs your access rights to selected circuit types or switch features.)

Clear Channel
1.The characteristic of a transmission path where the full bandwidth is available to the user.
2.In T1, 64 Kbps channels that do not require some portion of the channel (typically 8 Kbps) being reserved for carrier framing or control bits.

CLEC
A Competitive Local Exchange Company (also know as an Alternative company – ALEC). A company offering and providing local exchange service in direct competition to any other local exchange service provider (RBOC, ILEC, CLEC, ALEC, etc).

Client/Server Model
In most cases, the “client” is a desk-top computing device or program “served” by another networked computing device. The server can be a minicomputer, workstation, or microcomputer with attached storage devices. A client can be served by multiple servers.

CLIR
Caller Line ID Restriction. The ability to block someone who you're calling from seeing your number.

CO (Central Office)
A center (normally a Class 5 office) where communications carriers terminate customer lines (subscriber local loops) where calls are switched. In local area exchanges, central offices switch calls within and between the 10,000-line exchange groups that can be addressed uniquely by the area code and first three digits of a phone number.

Coaxial Cable
Cable consisting of an outer conductor surrounding an inner conductor, with a layer of insulating material in between (generally provides a much higher bandwidth than twisted pair wire.)

Codec (Coder/Decoder)
a device that transforms analog input into a digitally coded output and transforms digital signals into analog output. They are most commonly found in videoconferencing systems because of videoconferencing's intensive ISDN usage.

Collocation
The placement of competitors' equipment on or near telco premises so that they may interconnect directly (and cheaply) with the local telephone exchange.

Common Carrier
A government-regulated private company offering telecommunications services or communications facilities to the general public on a non-discriminatory basis under operating rules mandated by the appropriate state and/or federal regulatory authority.

Conditioning
A procedure used to make circuit transmission impairments lie within certain acceptable limits which are specified in a tariff (typically used on telephone lines leased for data transmission to improve transmission speed and quality.) Usually done with special equipment or routing.

Conference Call
A telephone call among three or more parties. The sound quality of conference calls is typically degraded by a loss of sound over the telephone lines unless bridged and amplified before re-transmission.

Convergence.
The merging of different technologies such as telephony, computers and cable.

CP/CPE (Customer Premises/Customer Premises Equipm
In telephony, refers to the user’s location and the equipment at that location that interfaces to the telephone network (also referred to as NCTE or Network Channel Terminating Equipment.)

CSU (Channel Service Unit )
User owned equipment installed on customer premises at the interface between customer premises and the operating phone company to terminate a DDS or T1 circuit. CSUs provide network protection and diagnostic capabilities.

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