Computer Networking Key Terms: C
Key Data Communications and Networking terms that begin with C are:
CA*net: The Canadian network that forms part of Internet2.
Carrier: An analog signal at some fixed amplitude and frequency that then is combined with an information-bearing signal to produce an intelligent output signal suitable for transmission of meaningful information. Also called carrier wave or carrier frequency.
Carrier frequency: The basic frequency or pulse repetition rate of a signal bearing no intelligence until it is modulated by another signal that does impart intelligence.
CD: 1. Collision detection in the CSMA (Carrier Sense Multiple Access) protocol for LANs. 2. Carrier detect occurs when a modem detects a carrier signal to be received.
Central office: The switching and control facility set up by the local telephone company (common carrier) where the subscriber’s local loop terminates. Central offices handle calls within a specified geographic area, which is identified by the first three digits of the telephone number.
Also called an end office or exchange office.
CENTREX: A widespread telephone company switching service that uses dedicated central office switching equipment. CENTREX CPE is where the user site also
has customer premises equipment (CPE).
Certificate authority (CA): A CA is a trusted organization that can vouch for the authenticity of the person or organization using authentication (e.g., VeriSign). A person wanting to use a CA registers with the CA and must provide some proof of
identify. CA issues a digital certificate that is the requestor’s public key encrypted using the CA’s private key as proof of identity that can be attached to the user’s e-mail or Web transactions.
Channel: 1. A path for transmission of electromagnetic signals. Synonym for line or link. Compare with circuit. 2. A data communications path. Circuits may be divided into subcircuits.
Character: A member of a set of elements used for the organization, control, or representation of data. Characters may be letters, digits, punctuation marks, or other symbols. Also called a byte.
Checking, echo: A method of checking the accuracy of transmitted data in which the received data are returned to the sending end for comparison with the original data.
Circuit: The path over which the voice, data, or image transmission travels. Circuits can be twisted-wire pairs, coaxial cables, fiber-optic cables, microwave transmissions, and so forth. Compare with
channel, line, and link.
Circuit switching: A method of communications whereby an electrical connection between calling and called stations is established on demand for exclusive use of the circuit until the connection is terminated.
Cladding: A layer of material (usually glass) that surrounds the glass core of an optical fiber. Prevents loss of signal by reflecting light back into the core.
Client: The input–output hardware device at the user’s end of a communication circuit. There are three major categories of clients: computers, terminals, and special-purpose terminals.
cluster controller: A device that controls the input–output operations of the cluster of devices (computers, terminals, printers, and so forth) attached to it. Also called a terminal controller. For example, the 3274 Control Unit is a cluster
controller that directs all communications between the host computer and remote devices attached to it.
Coaxial cable: An insulated wire that runs through the middle of a cable. A second braided wire surrounds the insulation of the inner wire like a sheath. Used on LANs for transmitting messages between devices.
Code: A transformation or representation of
information in a different form according to some set of preestablished conventions.
Code conversion: A hardware box or software that converts from one code to another, such as from ASCII to EBCDIC.
Codec: A codec translates analog voice data into digital data for transmission over computer networks. Two codecs are needed—one at the sender’s end and one at the receiver’s end.
Collapsed backbone network: In a collapsed BN, the set of routers in a typical BN is replaced by one switch and a set of circuits to each LAN. The collapsed backbone has more cable but fewer devices. There is no backbone cable. The “backbone” exists
only in the switch.
Collision: When two computers or devices transmit at the same time on a shared multipoint circuit, their signals collide and destroy each other.
Common carrier: An organization in the business of providing regulated telephone, telegraph, telex, and data communications services, such as AT&T, MCI, Bell-South, and NYNEX. This term is applied most
often to U.S. and Canadian commercial organizations, but sometimes it is used to refer to telecommunication entities, such as government-operated suppliers of communication services in other countries.
Common Management Interface Protocol (CMIP): CMIP is a network management system that monitors and tracks network usage and other parameters for user
workstations and other nodes. It is similar to SNMP, but it is more complete and is better in many ways.
communication services: A group of transmission facilities that is available for lease or purchase.
comparison risk ranking: The process by which the members of a Delphi team reach a consensus on which network threats have the highest risk. It produces a ranked list from high risk to low risk.
Component: One of the specific pieces of a network, system, or application. When these components are assembled, they become the network, system, or
application. Components are the individual parts of the network that we want to safeguard or restrict by using controls.
Computer Emergency Response Team
(CERT): The job of CERT, located at Carnegie Mellon University, is to respondto computer security problems on the Internet, raise awareness of computer security issues, and prevent security
breaches. It was established by the U.S. Department of Defense in 1988 after a virus shut down almost 10 percent of the computers on the Internet. Many
organizations are starting their own computer emergency response teams, so the term is beginning to refer to any response team, not just the one at Carnegie Mellon University.
Concentrator: A device that multiplexes several low-speed communication circuits onto a single high-speed trunk. A remote data concentrator (RDC) is similar in function to a multiplexer but differs
because the host computer software usually must be rewritten to accommodate the RDC. RDCs differ from statistical multiplexes because the total capacity of the high-speed outgoing circuit, in characters per second, is equal to the total capacity of the incoming low-speed circuits. On the other hand, output capacity of a statistical multiplexer (stat mux) is less than the total capacity of the incoming
Conditioning: A technique of applying electronic filtering elements to a communication line to improve the capability of that line so it can support higher data transmission rates. See also
Configuration: The actual or practical layout
of a network that takes into account its software, hardware, and cabling. Configurations may be multidrop, point-to-point, LANs, and the like. By
contrast, a topology is the geometric layout (ring, bus, star) of the configuration. Topologies are the building blocks of configurations. Compare with topology.
Connectionless routing: Connectionless routing means each packet is treated separately and makes its own way through the network. It is possible that different packets will take different routes through
the network depending on the type of routing used and the amount of traffic.
Connection-oriented routing: Connection-oriented routing sets up a virtual circuit (one that appears to use point-to-point circuit switching) between
the sender and receiver. The network layer makes one routing decision when the connection is established, and all packets follow the same route. All packets in the same message arrive at the destination
in the same order in which they were sent.
Content caching: Storing content from other Web sites on your network to reduce traffic on your Internet connection. A content engine regularly stores incoming static content such as banners and graphics files so that future requests for those items can be processed internally.
Content delivery: Storing content for your Web sites on the content delivery provider’s servers spread around the Internet to reduce traffic on your Internet connection. The content delivery provider’s
servers contain the static content on your pages such as banners and graphics files. Software on your Web server locates the nearest content delivery server to the user (based on his or her IP address) and changes the references on your Web pages to draw the static content from that server. Content delivery was pioneered by Akamai, which is one of the leading content delivery services on the Internet.
Contention: A method by which devices on the same shared multipoint circuit compete for time on the circuit.
Control: A mechanism to ensure that the threats to a network are mitigated. There are two levels of controls: system-level controls and application-level controls.
Control character: A character whose occurrence in a particular context specifies some network operation or function.
Control spreadsheet: A two-dimensional matrix showing the relationship between the controls in a network, the threats that are being mitigated, and the components that are being protected. The controls listed in each cell represent the specific control enacted to reduce or eliminate the
Core layer: The core layer is the central part of
a network that provides access to the distribution layer. It is often a very fast BN that runs through the center of a campus or office complex.
CRC: Cyclical redundancy check. An error-checking control technique using a specific binary prime divisor that results in a unique remainder. It usually is a 16- to 32-bit character.
CSMA/CA: Carrier Sense Multiple Access (CSMA) with Collision Avoidance (CA). This protocol is similar to the Carrier Sense Multiple Access (CSMA) with
Collision Detection (CD) protocol. Whereas CSMA/CD sends a data packet and then reports back if it collides with another packet, CSMA/CA sends a small
preliminary packet to determine whether the network is busy. If there is a collision, it is with the small packet rather than with the entire message. CA is thought to be more efficient because it reduces the time required to recover from collisions.
CSMA/CD: Carrier Sense Multiple Access (CSMA) with Collision Detection (CD). A system used in contention networks. The network interface unit listens for the presence of a carrier before attempting to send and detects the presence of a collision by monitoring for a distorted pulse.
customer premises equipment (CPE): Equipment that provides the interface between the customer’s CENTREX system and the telephone network. It physically resides at the customer’s site rather than the telephone company’s end office. CPE
generally refers to voice telephone equipment instead of data transmission equipment.
Cut-through switching: A type of switching in which messages are forwarded as they arrive, almost on a bit-by-bit basis.