An index of all the common telecoms terms, jargon and acronyms.

Telecommunications Glossary > C

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Cable Entrance Facility

The entrance area in a central office for all types of outside plant cables that carry subscriber lines and interoffice transmission facilities.

CDR – Call Detail Record

A billing feature of a telephone setup, which allows the system to collect and record information on outgoing and incoming phone calls, such as who made and received the call, what time it happened and how long it lasted for.

CPN – Called Party Number

When a call is set up over an ISDN network, SS7 send an initial address message, which contains the CPN as part of the ISUP protocol.

CCV – Calling Card Validation

The process of verifying that a calling card is valid and then processing a call to be billed to that account.

CAC – Carrier Access Code

The sequence that an end-user dials in order to access the carrier’s switch service. The codes are composed of 7 digits, in the form of 101xxxx, where xxxx is the CAC.

CCS – Centi Call Seconds

In telecommunications traffic engineering terminology, CCS represents one hundred call seconds or one hundred seconds of the telephone conversation. One hour of telephone traffic is equal to 36 CCS [60 x 60 = 3600, divided by 100 = 36].

CO – Central Office

The facility of a telecommunications common carrier, where subscribers’ lines are joined to switching equipment for connecting other subscribers to each other, locally and long distance.


A type of phone service offered by local exchange carriers, which provides PBX-like functions to a group of users without the need for an actual PBX. Despite having individual phones connected to the central office, users are able to dial each other by extension, transfer calls and all the other features you might expect with a PBX system.

CIC – Circuit Identification Code

An SS7 term used to identify a particular circuit within a trunk group.

Circuit Switch

A switching system that establishes a dedicated physical connection between end points in a network, for the duration of the communication sessions.


Links that interconnect mated STPS. They’re used to enhance the reliability of the signalling network in cases where one of multiple links are unavailable.


Reducing the size of the data, image, voice or video file sent over a telephone line, lessening the bandwidth needed to transmit the file.

CTI – Computer Telephony Integration

The combining of data with voice systems in order to enhance telephone service. Examples include the delivery of Caller ID information and the ability to access mail, all via a PC.

CLASS – Customer Local Area Signalling Services

A grouping of optional features to basic local exchange or enhanced telephony services that utilise the signalling system 7 (SS7) channel to carry data about a call. CLASS provides subscribers with the ability to screen and selectively reject, forward, trace and redial incoming calls. Caller ID is one example.

CPE – Customer Premise Equipment

The equipment that resides on the customer’s premises, such as a PBX or IAD.

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