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1 8 A B C D E F G H I J L M N O P Q R S T U V W
  • CAM

Short for channel access method, a protocol for how data is transmitted in the bottom two layers of the OSI model. CAMs describe how networking systems put data on the network media, how low-level errors are dealt with, and how the network polices itself. Polling, contention and token passing are three examples of CAMs.

  • Carrier Ethernet

Carrier Ethernet is a ubiquitous service based on standardized equipment and protocols providing seamless connectivity between high speed Ethernet-based LANs and WANs. Carrier Ethernet is characterized by industry-defined attributes for service level agreements, provisioning, system-wide management, and carrier-class OAM. Originally implemented in the core network, Carrier Ethernet is now being extended to the edge and access segment.

  • Cat-5

Short for Category 5, network cabling that consists of four twisted pairs of copper wire terminated by RJ45 connectors. Cat-5 cabling supports frequencies up to 100 MHz and speeds up to 1000 Mbps. It can be used for ATM, token ring, 1000Base-T, 100Base-T, and 10Base-T networking.
Cat-5 is based on the EIA/TIA 568 Commercial Building Telecommunications Wiring Standard developed by the Electronics Industries Association as requested by the Computer Communications Industry Association in 1985.

  • Cat-5e

Short for Category 5 Enhanced, Cat-5e network cabling is used as a cabling infrastructure for 10BASE-T (Ethernet), full duplex 100BASE-TX (Fast Ethernet) and 1000BASE-T (Gigabit Ethernet, or GbE) networks. The Cat 5e standard provides performance of up to 100 MHz and can be used up to a maximum length of 100 meters. As with Category 5 (Cat-5) cables, Cat 5e cables typically consist of four unshielded twisted pairs (UTP) of copper wire terminated by RJ45 connectors. Cat 5e is distinguished from the original Cat 5 standard primarily in its performance requirements. Cat 5e has stricter specifications in a number of areas, including Near-End Crosstalk (NEXT), Power Sum Equal-Level Far-End Crosstalk (PS-ELFEXT), attenuation and return loss. The Cat 5e standard was first released in 1999 as part of the Telecommunications Industry Association’s TIA/EIA-568-5-A document specification. The Cat 5e cable standard is backward compatible with the Cat 3 and Cat 5 cable standards.

  • Cat-6

Short for Category 6, Cat-6 network cabling is used as the cabling infrastructure for 10BASE-T (Ethernet), 100BASE-TX (Fast Ethernet), 1000BASE-T (Gigabit Ethernet, or GbE) and 10GBASE-T (10-Gigabit Ethernet, or 10 GbE) networks. The Cat 6 standard provides performance of up to 250 MHz (500 MHz for the newer Cat 6a standard) and can be used up to a maximum length of 100 meters (55 meters for 10GBASE-T networks). The Cat 6 standard was first released in 2002 as part of the Telecommunications Industry Association’s TIA/EIA-568-B.2-1 document specification. Cat 6 is backward compatible with the Cat 3, Cat 5 and Cat 5e cable standards, and as with Cat 5 and Cat 5e cabling, Cat 6 cables consist of four unshielded twisted pairs (UTP) of copper wire terminated by RJ45 connectors. In addition to its support for higher performance than the Cat 5 specification, the Cat 6 standard also includes more stringent specifications for crosstalk and system noise. While Cat 6 is expected to supersede both Cat 5 and Cat 5e cabling in the future, all three types of cables continue to be popular for use in network installations.

  • Cat-7

Short for Category 7, Cat-7 network cabling is used as a cabling infrastructure for 1000BASE-T (Gigabit Ethernet, or GbE) and 10GBASE-T (10-Gigabit Ethernet, or 10 GbE) networks. The Cat 7 standard provides performance of up to 600 MHz (1000 MHz for the Cat-7a, or Augmented Category 7 standard) and can be used up to a maximum length of 100 meters. Category 7 cable is able to achieve higher performance than preceding Ethernet standards such as Cat 5, Cat 5e and Cat 6 by requiring each of its twisted wire pairs to be fully shielded. This is known as Screen Shielded Twisted Pair (SSTP) or Screened Foiled Twisted Pair (SFTP) wiring, and it almost completely eliminates alien crosstalk while significantly improving noise resistance. The Cat 7 standard was published in 2002 by the International Organization for Standardization (ISO) and is also known as Class F cabling. While more expensive than Cat 5e and Cat 6 cabling, Cat-7 cabling does have a 15-year lifecycle (compared to estimated 10-year lifecycles for Cat 5e and Cat 6), which helps improve its overall return on investment (ROI).

  • CCK

Short for Complementary Code Keying, a set of 64 eight-bit code words used to encode data for 5.5 and 11Mbps data rates in the 2.4GHz band of 802.11b wireless networking. The code words have unique mathematical properties that allow them to be correctly distinguished from one another by a receiver even in the presence of substantial noise and multipath interference.
CCK works only in conjunction with the DSSS technology that is specified in the original 802.11 standard. It does not work with FHSS. CCK applies sophisticated mathematical formulas to the DSSS codes, permitting the codes to represent a greater volume of information per clock cycle. The transmitter can then send multiple bits of information with each DSSS code, enough to make possible the 11Mbps of data rather than the 2Mbps in the original standard.

  • CD

Carrier Detect
A modem interface signal indicating to an attached terminal that the local modem is receiving a signal from the remote modem.

  • CDDI

Abbreviation of Copper Data Distribution Interface, a network technology capable of carrying data at 100 Mbps over unshielded twisted pair (UTP) cable. CDDI is a trade name of Crescendo Communications (acquired by Cisco Systems in 1993) and commonly used instead of the general term Twisted Pair Physical Layer Medium (TP-PMD). TP-PMD is the general ANSI standard name for this FDDI -like service. CDDI cable lengths are limited to 100 meters.

  • central tunneling

In VPN technology, central tunneling is the process of forcing all traffic from a remote VPN through a central site. Central tunneling allows additional security as remote VPN users are protected by a firewall at the central site, and also enables NAT, IDS, IPS and anti-virus and spam filtering. Central tunneling does increase bandwidth at the central site.

  • centralized network

A type of network where all users connect to a central server, which is the acting agent for all communications. This server would store both the communications and the user account information. Most public instant messaging platforms use a centralized network. Also called centralized server-structure.

  • certification authority

Abbreviated as CA, a trusted third party organization or company that issues digital certificates used to create digital signatures andpublic-private key pairs. The role of the CA in this process is to guarantee that the individual granted the unique certificate is, in fact, who he or she claims to be. Usually, this means that the CA has an arrangement with a financial institution, such as a credit card company, which provides it with information to confirm an individual's claimed identity. CAs are a critical component in data security and electronic commerce because they guarantee that the two parties exchanging information are really who they claim to be.

  • challenge-response

0.      A common authentication technique whereby an individual is prompted (the challenge) to provide some private information (the response). Most security systems that rely on smart cards are based on challenge-response. A user is given a code (the challenge) which he or she enters into the smart card. The smart card then displays a new code (the response) that the user can present to log in.

1.      In biometrics, challenge response is the term used to describe the method by which the identification of a person is detected based on voluntary or involuntary responses. Challenge response is a type of biometric system security.

  • Channel

A path for electrical transmission between two or more points. Also called a link, line, circuit or facility.

  • CHAP

Short for Challenge Handshake Authentication Protocol, a type of authentication in which the authentication agent (typically a network server) sends the client program a random value that is used only once and an ID value. Both the sender and peer share a predefined secret. The peer concatenates the random value (or nonce), the ID and the secret and calculates a one-way hash using MD5. The hash value is sent to the authenticator, which in turn builds that same string on its side, calculates the MD5 sum itself and compares the result with the value received from the peer. If the values match, the peer is authenticated.
By transmitting only the hash, the secret can't be reverse-engineered. The ID value is increased with each CHAP dialogue to protect against replay attacks.

  • choke packet

A specialized packet that is used for flow control along a network. A router detects congestion by measuring the percentage of buffers in use, line utilization and average queue lengths. When it detects congestion, it sends choke packets across the network to all the data sources associated with the congestion. The sources respond by reducing the amount of data they are sending.

  • chunk

Also called a data chunk, by RFC2960 SCTP (Stream ControlTransmission Protocol) standards it is the term used to describe a unit of information within an SCTP packet that contains either control information or user data.

  • cipher text

Data that has been encrypted. Cipher text is unreadable until it has been converted into plain text (decrypted) with a key.

  • CLI

Command line Interface.The CLI can typically be accessed using Telnet, SSH, or RS232 (Serial port).

  • Clock

A term for the source(s) of timing signals used in synchronous transmission.

  • CMIP

Short for Common Management Information Protocol, and pronounced see-mip, an OSI standard protocol used with the Common Management Information Services (CMIS). CMIS defines a system of network managementinformation services. CMIP was proposed as a replacement for the less sophisticated Simple Network Management Protocol (SNMP) but has not been widely adopted. CMIP provides improved security and better reporting of unusual network conditions.

  • CNA

Short for Converged Network Adapter, CNA is a technology that supports data networking (TCP/IP) and storage networking (Fibre Channel) traffic on a single I/O adapter. CNAs support both Enhanced Ethernet and Fiber Channel over Ethernet (FCoE).

  • coaxial cable

A type of wire that consists of a center wire surrounded by insulation and then a grounded shield of braided wire. The shield minimizes electrical and radio frequency interference.
Coaxial cabling is the primary type of cabling used by the cable television industry and is also widely used for computer networks, such as Ethernet. Although more expensive than standard telephone wire, it is much less susceptible to interference and can carry much more data.


An audio codec converts analog audio signals to digital signals for transmission over digital circuits, and then converts the digital signals back to analog signals for reproduction.

  • collapsed backbone

A network backbone that consists of the backplane of a single switch, rather than multiple switches connected together. From the ports of the single switch, cables connect to the hubs of individual LAN segments.Collapsed backbones are typically used for mid-sized LAN networks. The architecture is easier to manage, easier to keep secure and less costly as there are fewer networking devices.
However, a collapsed backbone architecture typically uses more cabling over longer distances and a failure in the central switch will cause the whole network to go offline.

  • collision

The situation that occurs when two or more devices attempt to send a signal along the same channel at the same time. The result of a collision is generally a garbled message. All computer networks require some sort of mechanism to either prevent collisions altogether or to recover from collisions when they do occur.

  • collision detection

1.      In networks, the process by which a node determines that a collision has occurred. Collisions occur with most networks, so a protocol is required to recover from such events. Ethernet uses CSMA/CD as its collision detection and recovery system.

2.      In virtual reality environments, collision detection is a program interface that determines how close a user is to a real physical objects and will stop their movement before colliding with the object.

  • collision domain

A group of Ethernet or Fast Ethernet devices in a CSMA/CD LAN that are connected by repeaters and compete for access on the network. Only one device in the collision domain may transmit at any one time, and the other devices in the domain listen to the network in order to avoid data collisions.
A collision domain is sometimes referred to as an Ethernet segment.

  • Compression

Any of several techniques that reduce the number of bits required to represent information in data transmission or storage, thereby conserving bandwidth and/or memory.

  • Concentrator

Device that serves as a wiring hub in star-topology network. Sometimes refers to a device containing multiple modules of network equipment.

  • congestion

A state occurring in part of a network when the message traffic is so heavy that it slows down network response time.

  • congestion notification

A signaling technique used by data transmission systems in order to indicate the status of network congestion. Devices that are communicating data across a network rely on congestion notification to determine when to send or delay the transmission of data packets.
Forward congestion notification indicates to upstream data switching devices that data is being transmitted through congested channels and some of the data or packets may be discarded. Backward congestion notification indicates to downstream devices that data is going through congested channels.

  • connection-oriented service

One of two techniques used in data communications to transfer data at the Transport Layer (Layer 4). A Connection-oriented service requires a session connection be established before any data can be sent with a direct physical connection between the sessions. This often considered to be a more reliable network service than the alternative, connectionless service.

  • connectionless

Refers to network protocols in which a host can send a message without establishing a connection with the recipient. That is, the host simply puts the message onto the network with the destination address and hopes that it arrives. Examples of connectionless protocols include Ethernet, IPX, and UDP.
In contrast, connection-oriented protocols require a channel to be established between the sender and receiver before any messages are transmitted.

  • connectionless service

Abbreviated as COS, connectionless service is one of two techniques used in data communications to transfer data at the Transport Layer (Layer 4). A connectionless service does not require a session connection between sender and receiver; the sender starts sending datagrams to the destination. In contrast with a connection-oriented service, this is less reliable but faster.

  • connectivity

A computer buzzword that refers to a program or device's ability to link with other programs and devices. For example, a program that can import data from a wide variety of other programs and can export data in many different formats is said to have good connectivity. On the other hand, computers that have difficulty linking into a network have poor connectivity.

  • contention

1.      Competition for resources. The term is used especially in networks to describe the situation where two or more nodes attempt to transmit a message across the same wire at the same time.

2.      A type of network protocol that allows nodes to contend for network access. That is, two or more nodes may try to send messages across the network simultaneously. The contention protocol defines what happens when this occurs. The most widely used contention protocol is CSMA/CD, used by Ethernet. Also see polling and token passing.

  • Control Characters

In communications, any extra transmitted characters used to control or facilitate data transmission (for example, characters associated with polling, framing, synchronization, error checking, or message delimiting).

  • Control Signals

Signals passing between one part of a communications system and another (such as RTS, DTR, or DCD), as part of a mechanism for controlling the system.

  • COR

Short for central outdoor router, the central router in a multi-device WLAN. The device is typically placed in a geographic central location and communicates with up 32 remote locations that use an ROR.

  • CPE

Customer Premises Equipment
Generally refers to communications equipment located at the customers' premises for use with communication service providers' services. In some cases, these are customer-owned or leased; in other cases, these are the property of the service provider.

  • CRC

Short for cyclic redundancy check, a common technique for detecting data transmission errors. Transmitted messages are divided into predetermined lengths that are divided by a fixed divisor. According to the calculation, the remainder number is appended onto and sent with the message. When the message is received, the computer recalculates the remainder and compares it to the transmitted remainder. If the numbers do not match, an error is detected.
A number of file transfer protocols, including Zmodem, use CRC in addition to checksum.

  • credential

An object that is verified when presented to the verifier in an authentication transaction. Credentials may be bound in some way to the individual to whom they were issued, or they may be bearer credentials. The former are necessary for identification, while the latter may be acceptable for some forms of authorization.
Electronic credentials can be digital documents used in authentication and access control that bind an identity or an attribute to a claimant's token or some other property, such as a current network address. Credentials are verified when presented to the verifier in an authentication transaction. Anonymous credentials are used to evaluate an attribute when authentication need not be associated with a known personal identity.

  • crosstalk

A disturbance, caused by electromagnetic interference, along a circuit or a cable pair. A telecommunication signal disrupts a signal in an adjacent circuit and can cause the signals to become confused and cross over each other.

  • cryptography

The art of protecting information by transforming it (encrypting it) into an unreadable format, called cipher text. Only those who possess a secret key can decipher (or decrypt) the message into plain text. Encrypted messages can sometimes be broken by cryptanalysis, also called codebreaking, although modern cryptography techniques are virtually unbreakable.
As the Internet and other forms of electronic communication become more prevalent, electronic security is becoming increasingly important. Cryptography is used to protect e-mail messages, credit card information, and corporate data. One of the most popular cryptography systems used on the Internet is Pretty Good Privacy because it's effective and free.
Cryptography systems can be broadly classified into symmetric-key systems that use a single key that both the sender and recipient have, and public-key systems that use two keys, a public key known to everyone and a private key that only the recipient of messages uses.


Short for Carrier Sense Multiple Access/Collision Avoidance, a network contention protocol that listens to a network in order to avoid collisions, unlike CSMA/CD that deals with network transmissions once collisions have been detected. CSMA/CA contributes to network traffic because, before any real data is transmitted, it has to broadcast a signal onto the network in order to listen for collision scenarios and to tell other devices not to broadcast.


Short for Carrier Sense Multiple Access / Collision Detection, a set of rules determining how network devices respond when two devices attempt to use a data channel simultaneously (called acollision). Standard Ethernet networks use CSMA/CD to physically monitor the traffic on the line at participating stations. If no transmission is taking place at the time, the particular station can transmit. If two stations attempt to transmit simultaneously, this causes a collision, which is detected by all participating stations. After a random time interval, the stations that collided attempt to transmit again. If another collision occurs, the time intervals from which the random waiting time is selected are increased step by step. This is known as exponential back off.
CSMA/CD is a type of contention protocol.  Networks using the CSMA/CD procedure are simple to implement but do not have deterministic transmission characteristics. The CSMA/CD method is internationally standardized in IEEE 802.3 and ISO 8802.3.


Channel Service Units / Data Service Units
CSUs and DSUs are usually grouped together. They convert carrier line signals to digital signals.

  • CTS

Clear To Send
A modem interface control signal from the data communications equipment (DCE) indicating to the data terminal equipment (DTE) that it may begin data transmission.

  • Current Loop

Method of data transmission. A mark (binary “1”) is represented by current on the line, and a space (binary “0”) is represented by the absence of current.

  • CVE

Acronym for Common Vulnerabilities and Exposures.
CVE is a dictionary-type list of standardized names for vulnerabilities and other information related to security exposures. CVE aims to standardize the names for all publicly known vulnerabilities and security exposures. The goal of CVE is to make it easier to share data across separate vulnerable databases and security tools.