CAC
Connection Admission Control - ATM 
A set of actions taken at a virtual circuit or virtual path connection setup to determine if the connection can be accepted. The decision is based on the anticipated traffic at the virtual circuit, the quality of service - QoS - requirements, and the current network load. 

CALL
An instruction in a program that calls another section of code, which once executed, resume at the calling point in the program.

CAM
Channel Access Method

CAM
Controlled Attachment Module

Campus Network
A departmental LAN spread over multiple buildings.

CAP
Carrier Amplitude Phase modulation, associated with xDSL technologies

CAR
Committed Access Rate - Cisco ¨

CARP
Cache Array Routing Protocol

CAS
Channel Associated Signaling 
Translate and carry the analogic signaling the signaling bytes. Also called R2 or norm Q421 Ex: Taxation / hang up line / request to hang up. 
See ABCD bit

CAU
Controlled Access Unit 
A 8230 -Basically a MAU with intelligence.
A CAU supports up to 4 LAMs. The Ring In/Ring Out ports of a CAU are copper but can replaced with fiber connectors. 

CBAC
Context Based Access Control - Cisco ¨

CBC
Cipher Block Chaining

CBDS
Connectionless Broadband Data Service 
European high speed, packet switched, datagram-based WAN networking technology. Similar to SMDS. 

CBR
Constant Bit Rate - ATM. A type of telecommunication service characterized by a service bit rate specified by a constant value


CBWFQ
Class Based Weighted Fair Queuing - Cisco ¨

CCBS
Completion of Calls to Busy Subscriber - automatic call back when busy. Usually provided by the PABX.

CCC
Clear Coded Channel

CCE
Configuration Control Elements - Functionality related to management of FDDI paths and stations.

CCIE
Cisco Certified Inter network Expert - Cisco¨

CCIS
Common Channel Interoffice Signaling

CCITT
Consultative Committee on International Telegraphy and Telephones- See International Telecommunication Union-Telecommunications / ITU-T 

CCNA
Cisco Certified Network Associate - Cisco ¨

CCP
Compression Control Protocol

CCS
Common Channel Signaling 

CD
Call Deflection - Redirection of a call received by a third party, during the ringing time.

CD
Carrier Detect - Modem

CD
Collision Detection

CDDI
Copper Distributed Data Interface - . Cisco Systems ¨ version of FDDI that uses UTP wires instead of optical fiber.

CDE
Common Desktop Environment 
A CDMA-based narrowband digital air interface technology that is used in the Americas, Asia-Pacific, and other areas. CDMAOne is implemented in the 800 MHz and 1900 MHz frequency bands.

CDP
Cisco Discovery Protocol - Cisco ¨

CDV
Cell Delay Variation

CDVT
Cell Delay Variation Tolerance - ATM

CDWFQ
Called Distributed Weighted Fair Queuing - Cisco ¨

CEI
Connection Endpoint Identifier

Cell Delineation
The identification of cell boundaries in an ATM cell stream.

Cell Header
An ATM layer, protocol control information. The 5-byte data field at the beginning of an ATM cell. 

Cell Relay
Form of packet transmission using a 53-byte cell, used in B-ISDN networks. Also known as ATM. 

1 - Network technology based on the use of small, fixed size packets, or cells. Cells contain identifiers that specify the data stream to which they belong. Because the cells are fixed length, they can be processed and switched in hardware at very high speeds. Cell relay is the basis for many high-speed network protocols, including IEEE 802.6, DQDB, the SMDS Interface Protocol, and ATM. A 53-byte protocol data unit - PDU - used in ATM technology for transporting information. Its fixed size contains a 5-byte header and a 48-byte body. 

2 - The basic geographical unit of a cellular communications systems. Service coverage of a given area based on an interlocking network of cells, each with a radio base station - transmitter/receiver - at its center. The size of each cell is determined by the terrain and the number of users.

CELP
Code Excited Linear Prediction . A compression algorithm used in a low bit-rate voice encoding. CELP is used in ITU-T recommendations G.728, G.729, G.723.1

CEP
Certificate Enrollment Protocol - Cisco ¨

CEPS
Common Electronic Purse Specifications - Visa Europay ¨

CER
Cell Error Ratio - ATM

CES
Circuit Emulation Service - ATM

CHANNEL
A type of SNAª connection that provides direct channel attachment to a mainframe.

CHAP
Challenge Handshake Authentication Protocol 
A security feature that prevents unauthorized access to devices running the feature. CHAP is only supported on lines using PPP encapsulation.
A method of establishing security on PPP links where the peers must share a plaintext "secret." The caller sends a challenge message to its receiving peer and the receiver responds with a value it calculates based on the secret. The first peer then matches the response with its own calculation of what the response should be. If the values match, the link is established. 

CID
Channel ID - ATM Designates the Frame Relay subchannel ID for Voice over Frame Relay.

CIDR
Classless Inter Domain Routing 
An address aggregation scheme that employs supernet addresses to represent multiple IP destinations. Rather than advertise a separate route for each destination, a router uses a supernet address to advertise a single route - called an aggregate route - representing all destinations. 

CIP
Channel Interface Processor - Cisco ¨

CIR
Committed Information bate 
The committed rate in bits per second. 
The average rate of information transfer a subscriber has stipulated for a Frame Relay PVC.


Circuit Switching
The basis of telephone call handling, with a circuit connection being set up between caller
and called party. This connection is held open for the duration of the call, even when no information- voice, data, images, video - is being transmitted. The alternate is packet switching. A communications model in which a dedicated communication path is established between two hosts and on which all packets travel, open only for the duration of the transmission. Once the connection is closed, other devices can use it. The telephone system is an example of a circuit switched network.

CISCO
San Francisco - 1984 

Proprietary protocols:

CLEC
Competitive Local Exchange Carrier
A telecommunication company utilizing an incumbent carrier's telecom facilities in conjunction with its own localized equipment to provide unregulated, modern services. 

CLI
Caller Line Identification 
The directory number of the caller provided by the telephone company to the party called during call setup. Also referred to as Caller ID. 

CLI
Command Line Interface / Interpreter - Cisco ¨

CLID
Calling Line Identification

Client/Server
A processing model that connects applications on client/user workstations with applications on servers to facilitate distributed processing.

CLNP
Connectionless Network Protocol - OSI 

CLNS
Connectionless Network Service 
Method of data delivery using datagrams with addressing information to route messages on LANs. The OSI equivalent of IP. 

CLP
Cell Loss Priority 
Part of the ATM cell header that indicates the priority of the cell and whether or not the network can discard it under heavy traffic conditions. 

CLTP
Connectionless Transport Protocol - OSI

CLR
Certificate Revocation List - Cisco ¨

CLSI
Cisco Link Services Interface - Cisco ¨

CMIP
Common Management Interface Protocol 
OSI network management protocol created and standardized by ISO for the monitoring and control of heterogeneous networks.

CMIS
Common Management Information Services. The OSI standard functions for network monitoring and control.

CMNS
Connection-Mode Network Service. Extends X.25 to FFDI, Token-Ring ...

CMOL
CMIP Over Link Layer

CMOT
CMIP Over TCP-IP. Use of the OSI CMIP network over an Internet TCP/IP stack. 

CMPT
Common Management Information and Services Protocol over TCP

CMS
Conversational Monitor System - IBM ¨

CMTS
Cable Modem Termination System

CNA
Cisco ¨ Networking Academies

CNID
Calling Party Name Identification - IP Telephony

CNR
Communication Network Riser 

CODEC
Coder Decoder / COmpression / DECompression
A device that typically uses pulse code modulation to transform analog voice into a digital bit stream and vice versa.


COPS
Common Open Policy Service - Protocol used to control the optical source layer.

COS
Class Of Service

COSE
Common Opened System Environment - HP ¨/ IBM ¨ / SCO ¨ 

CP
Control Point - IBM ¨

CPCS
Common Part Convergence Sublayer

CPI-C
Common Programming Interface for Communication - A layer of the IBM¨ SAAª that defines API's for distributed processing applications.

CPL
Control Panel - File extension 
In Windows, files with that extension contain drivers, password

CRC
Cyclic Redundancy Check 
An error-checking technique in which the frame recipient calculates remainder by dividing frame contents by a prime binary divisor and compares the calculated remainder to a value stored in the frame by the sending node.

CR-LDP
Constrain-based Routing Label Distribution Protocol - Reservation resource protocol

CS
Carrier Selection

CS-ACELP
Conjugate Structure Algebraic CELP. Voice compression algorithm specified in ITU-T recommendation G.729, providing 8 kbps, or 8.1 compression.

CSI
Called Subscriber Identification. An identifier whose coding format contains the telephone number from the remote fax terminal.

CSM
Cabling System Manager - Physical Networks ¨ 

CSO
Composite Second Order Beat. The peak of the average level of distortion products due to second-order non-linearities in cable system equipment. 

CSPDN
Circuit-Switched Public Data Network

CS-PDU
Convergence Sublayer Packet Data Unit

CS-SLIP
Compressed Serial Link Internet Protocol 
A protocol that minimizes traffic and speed throughput on SLIP lines.

CSMA-CA
Carrier Sense Multiple Access with Collision Avoidance 

CSMA-CD
Carrier Sense Multiple Access with Collision Detection 
A channel access mechanism wherein devices wishing to transmit first check the channel for a carrier. If no carrier is sensed for some period of time, devices can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices, which subsequently delays their retransmission's for some random length of time. CSMA/CD access is used by Ethernet and IEEE 802.3.

CSMA-CR
Carrier Sense Multiple Access with Collision Resolution

CSRP
Customer Synchronized Resource Planning

CSTA
Computer Supported Telecommunications Applications 
Phone services : Make call, answer call, transfer call, conference call, hold call. Notify alerts : Alerting, connection clearedÉ 

CSU
Channel Service Unit 
A device needed to to adapt the V.35 interface on a frame relay DTE to the T1 or E1 interface on a frame relay switch. 
Channel Server Unit/Digital Server Unit. A device used to terminate telephone company equipment and prepare data for router interface. 

CTD
Cell Transfer Delay - ATM

CUT
Control Unit Terminal - IBM ¨. A mode of 3270 terminal operation that supports only single host session.

CVSD
Continuously Variable Slope Delta modulation

CXML
Commerce Extensible Markup Language