Telecom Dictionary

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CAB
Carrier Access Business

Cable
A cable is a group of metallic conductors or optical fibers that are bound together, usually with a 
protective sheath, a strength member, and insulation between individual conductors/fibers and 
for the entire group.

CABS
Carrier Access Billing System - We fully explain what a Carrier Access Billing System is on this website. See the main page of this website for more information.

CALC 
customer access line charges

CAP 
competitive access provider

Carrier
A carrier is a local (intra-LATA) or long distance (inter-LATA) telecommunications service 
providing organization. A waveform, pulsed or continuous, that is modulated by another 
information bearing waveform.

Carrier System
A carrier system is a transmission system for transmitting one or more channels of information by 
processing and converting to a form suitable for the transmission medium used. Carrier systems 
are classified as either analog carrier systems or digital carrier systems.

CBR 
continuous bit rate

CCIS 
common-channel interoffice signaling

CCITT
CCITT is the International Consultative Committee for Telephone and Telegraph, a consultative 
committee to the International Telecommunications Union (ITU) which recommend international 
standards for telephone and telegraph services and facilities to aid international connectivity and 
interoperability.

CCSA 
common-control switching arrangement

CCS 
centi-call seconds or common-channel signaling

CDMA 
code division multiple access

Cell Relay
Call relay is the process of transferring data in the form of fixed length packets called cells. Cell 
relay is used in high-bandwidth, low-delay, packet-like switching and multiplexing techniques. 
The objective is to develop a single multiplexing/switching mechanism for dividing up usable 
capacity (bandwidth) in a l-manner that supports its allocation to both isochronous (e.g., voice 
and video traffic) as well as packet data communications services. Standards groups have 
debated the optimum cell size. Small cells favor low delay for isochronous applications but involve 
a higher header to user information overhead penalty than would be needed for most data 
applications. The current CCITT specification for BISDN is for a 53-byte cell which includes a 5-
byte header and a 48-byte payload.

Centi Call Seconds (CCS)
CCS is a unit of the average traffic intensity of a facility during a period of time, a CCS is 100 call 
seconds of traffic during one hour. Therefore a single traffic source, e.g., one call that generates 
traffic 100% of the time produces 36 CCS of traffic per hour, i.e., 3600 seconds of traffic every 
3600 seconds. An equivalent amount of traffic could also be generated by 10 sources that only 
generate traffic 10% of the time. That is, 10 sources of traffic generating 3.6 CCS each, 
contributes the same total traffic as a single 36 CCS traffic source. An alternative measure for 
traffic is erlangs where 1 erlang equals 36 CCS.

CENTRal EXchange (Centrex)
Centrex is a LEC-provided switching service for business customers that permits station-to-station 
dialing, listed directory number service, direct inward dialing and station number identification on 
outgoing calls. The switching functions are usually performed in a central office. Digital Centrex 
offers the advanced features of fourth generation PBXs, without the need to purchase or lease 
equipment and, in most cases, eliminates the need for floor space, electrical prime power and 
heating, ventilation and air conditioning.

Central Offices (CO)
A central office is a telephone company building in which network equipment such as switches 
are installed.

Channel
A channel is a single communications path in a transmission medium connecting two or more 
points in a network, each path being separated by some means; e.g., spatial or multiplex 
separation, such as frequency or time division multiplexing. "Channel" and "circuit" are often 
used interchangeably, however circuit can also describe a physical configuration of equipment 
that provides a network transmission capability for multiple channels. The characteristics of 
channels and circuits are determined by the network equipment and media used to support 
them.

Channel Service Unit (CSU)
Channel Service Units (CSUs) and Data Service Units (DSUs) are required to connect digital 
customer premises equipment (CPE) to carrier networks. A CSU is network channel terminating 
equipment (NCTE) attaching as CPE to telephone company's digital circuits, and protecting the 
network from harm. Other CSU functions include line conditioning and equalization, error control 
(e.g., bipolar signal violations), and the logical ability to respond to local and network loop back 
circuit testing commands. See Data Service Units (DSU).

Circuit Associated Signaling
Circuit Associated Signaling is a technique that uses the same facility path for voice and signaling 
traffic. Historically this approach was selected to avoid the costs of separate channels for 
signaling and because the amount of traffic generated by signaling is small compared to voice, 
minimizing the chance for mutual interference. Circuit associated signaling can be contrasted with 
some common-channel signaling systems that use completely separate packet switched networks 
for signaling traffic.

Circuit Switching
Circuit switching is a process that establishes connections on demand and permits the exclusive 
use of those connections until released. Packet and message switching, primarily used in data 
communications networks are alternative switching techniques.

City Wide Digital Centrex
A city wide digital centrex is a capability to serve multiple business locations within a single NXX 
(exchange code), using multiple LEC central office Centrex switches. Outside callers are unaware 
that multiple business locations are involved.

CLEC
Competitive Local Exchange Carrier, most commonly referred to as Competitive Local Exchange Carrier.

CLLI
Common Language Location Identifier

CMIP 
common management information protocol

Coaxial Cable
Coaxial Cable (also called coax cable or coax) consists of an insulated central conductor 
surrounded by a second cylindrical conductor that is clad with an insulating sheath. The outer 
conductor usually consists of copper tubing or copper braid.

COC 
central office connections

Codec
Codec is a contraction of coder and decoder; a device that encodes analog signals into digital 
signals, for transmission through a network in digital format, and decodes received digital signals 
back into analog signals.

Common Channel Signaling (CCS)
CCS is a signaling system developed for use between stored program control digital switching 
systems, in which all of the signaling information for one or more trunk groups is transmitted 
over a dedicated signaling channel, usually, but not always completely separate from the user 
traffic bearing facilities.

Common Management Information Protocol (CMIP)
CMIP is the OSI protocol for network management. A structure for formatting messages and 
transmitting information between reporting devices (agents) and data collection programs, 
developed by the International Standards Organization and designated ISO/IEC 9596.

Communications
Communications is the process of representing, transferring, interpreting or processing 
information (data) among persons, places, or machines. Communications implies a sender, a 
receiver, and a transmission medium over which the information travels. The meaning assigned 
to the data must be recoverable without degradation.

Conditioning
Conditioning is an adjustment made to the electrical characteristics of a cable pair to improve its 
performance for a specific use.

Conductor
In electrical circuits, a conductor is any material that readily permits a flow of electrons (electrical 
current) through itself. Analogously, optical fibers are sometimes said to conduct light waves and 
are also referred to as conductors.

Corporation for Open Systems (COS)
COS is a nonprofit organization composed of manufacturing, service, and user organizations in 
the computer communications area. Seeks to facilitate the development of the international, 
multi-vendor marketplace through the development, introduction, and verification of OSI and 
ISDN standards and by ensuring vendor equipment interoperability.

CO 
central office

CPU 
central processing unit

Cross Connect
1.in a premises distribution system, equipment used to terminate and administer communications 
circuits. In a wire cross connect, jumper wires or patch cords are used to make circuit 
connections, between horizontal and backbone wiring segments. 2. in transmission systems a 
patch panel for connecting circuits.

CSDC 
circuit-switched digital capability

CSMA/CD
Carrier sense multiple access with collision detection; a local area network contention based 
access control protocol technique by which all devices attached to the network "listen" for 
transmissions in progress before attempting to transmit themselves and, if two or more begin 
transmission simultaneously, are able to detect the "collision". In that case each backs off 
(defers) for a variable period of time (determined by a preset algorithm) before again attempting 
to transmit. (Defined by the IEEE 802.3 standard).

CSR 
Centrex station rearrangement

CSU 
channel service unit

Customer Premises Equipment
Customer Premises Equipment is all telecommunications terminal equipment located on the 
customer premises. except coin operated telephones.