c - A small "c" is the symbol for the speed of light in a vacuum.

C - A capital "C" is the designation for Celsius.

Cable - A group of insulated conductors enclosed within a common jacket.

Cable Sheath - A covering over the conductor assembly that may include one or more metallic members, strength members, or jackets.

Campus - The buildings and grounds of a complex, such as a university, college, industrial park or military establishment.

Capacitance - The ability to store electric charge between two conductors separated by a dielectric material. Capacitance is expressed in Farads.

Carrier - An electrical signal of a set frequency that can be modulated in order to carry data.

Carrier Detect - A circuit that detects the presence of a carrier.

Carrier Sense - With Ethernet, a method of detecting the presence of signal activity on a common channel.

Carrier Sense Multiple Access with Collision Detect (CMSA/CD) -A network access method used by Ethernet in which a station listens for traffic before transmitting. If two stations transmit simultaneously, a collision is detected and both stations wait a brief time before attempting to transmit again.

Category 1, Cat 1 - Unshielded twisted pair used for transmission of audio frequencies. Used as speaker wire, door bell wire, etc. Not suitable for networking applications.

Category 2, Cat 2 - Unshielded twisted pair used for transmission at frequencies up to 1.5 MHz. Used in analog telephone applications. Not suitable for networking applications.

Category 3, Cat 3 - Unshielded twisted pair with 100 ohm impedance and electrical characteristics supporting transmission at frequencies up to 16 MHz. Defined by the TIA/EIA 568-A specification.

Category 4, Cat 4 - Unshielded twisted pair with 100 ohm impedance and electrical characteristics supporting transmission at frequencies up to 20 MHz. Defined by the TIA/EIA 568-A specification.

Category 5, Cat 5 - Unshielded twisted pair with 100 ohm impedance and electrical characteristics supporting transmission at frequencies up to 100 MHz. Defined by the TIA/EIA 568-A specification.

Category 5e, Cat 5e, Enhanced Cat 5 - Category 5e is a new standard that will specify transmission performance that exceeds Cat 5. Cat 5e has improved specifications for NEXT, PSELFEXT, and Attenuation. Like Cat 5, it consists of unshielded twisted pair with 100 ohm impedance and electrical characteristics supporting transmission at frequencies up to 100 MHz. To be defined in the TIA 568-A-5 update.

Category 6, Cat 6 - Category 6 is a proposed standard that aims to support transmission at frequencies up to 250 MHz over 100 ohm twisted pair.

Category 7, Cat 7 - Category 7 is a proposed standard that aims to support transmission at frequencies up to 600 MHz over 100 ohm twisted pair.

CATV - Community antenna television, or "Cable TV". CATV is a broadband transmission facility which generally uses a 75 Ohm coaxial cable to carry numerous frequency-divided TV channels simultaneously.

CBX - Computerized Branch Exchange.

Cellular Polyethylene - Expanded or "foam" polyethylene, a material with a reduced dielectric constant consisting of individual closed cells of inert gas suspended in a polyethylene medium.

CDDI - Copper Distributed Data Interface - A version of FDDI that uses copper wire media instead of fiber optic cable.

Channel - The end to end transmission path between two points at which application specific equipment is connected.

Channel Insertion Loss - For fiber optic links, the static loss of a link between a transmitter and receiver. It includes the loss of the fiber, connectors, and splices.

Characteristic Impedance - The impedance that an infinitely long transmission line would have at its input terminal. If a transmission line is terminated in its characteristic impedance, it will appear (electrically) to be infinitely long, thus minimizing signal reflections from the end of the line.

Cheapernet - Another name for thin Ethernet or 10Base2 systems.

Chirping - Refers to the change of optical frequency of laser diodes when the laser diode is pulsed between two different optical power levels. Chirp broadens the laser's spectral width causing chromatic dispersion.

Chromatic Dispersion - Synonym for "material dispersion". Characteristic of long fiber runs�.

Circuit - A system of conducting media designed to pass a signal or voltage between two points or a bi-directional communications path between two pieces of associated equipment.

Cladding - The material surrounding the core of a fiber optic cable. The cladding must have a lower index of refraction than the core in order to contain the light in the core.

Class A - ISO/IEC 11801 designation for twisted pair cabling rated to 100 kHz. Used in voice and low frequency applications. Comparable to Category 1 cabling. Not suitable for networking applications

Class B - ISO/IEC 11801 designation for twisted pair cabling rated to 1 MHz. Used in medium bit rate applications. Comparable to Category 2 cabling. Not suitable for networking applications.

Class C - ISO/IEC 11801 designation for twisted pair cabling rated to 16 MHz. Used in high bit rate applications. Corresponds to TIA/EIA Category 3 cabling.

Class D - ISO/IEC 11801 designation for twisted pair cabling rated to 100 MHz. Used in very high bit rate applications. Corresponds to TIA/EIA Category 5 cabling.

Class E - ISO/IEC proposal for twisted pair cabling rated to 250 MHz. Corresponds to the proposed TIA/EIA Category 6 cabling standard.

Closet - An enclosed space for housing telecommunications and networking equipment, cable terminations, and cross-connect cabling. It contains the horizontal cross connect where the backbone cable cross-connects with the horizontal cable.

Coating - Material surrounding the cladding of the fiber for protection.
Coax, Coaxial Cable - A type of communication transmission cable in which a solid center conductor is surrounded by an insulating spacer which in turn is surrounded by a tubular outer conductor (usually a braid, foil or both). The entire assembly is then covered with an insulating and protective outer layer. Coaxial cables have a wide bandwidth and can carry many data, voice and video conversations simultaneously.

Coherence - Refers to the phase stability of two wavetrains, from the same optical wave, separated in time.

Collision - When electrical signals from two or more devices sharing a common data transfer medium crash into one another. This commonly happens on Ethernet type systems.

Conduit - A rigid or flexible metallic or nonmetallic raceway of circular cross section in which cables are housed for protection and to prevent burning cable from spreading flames or smoke in the event of a fire.

Conductivity - The ability of a material to allow the flow of electrical current. It is the reciprocal of resistivity. Measured in "mhos".

Conductor - A material that offers low resistance to the flow of electrical current.

Continuity - An uninterrupted pathway for electrical signals.

Cord - A very flexible insulated cable.

Core - The central region of an optical fiber through which light is transmitted.

Coupling ratio - The percentage of optical power transferred to the secondary output port of a coupler relative to the total power of the primary and the secondary output ports.

CRC - see Cyclic Redundancy Check

Critical angle - The angle at the interface between core and cladding where a guided ray in the core undergoes total internal reflection.

Cross Connect - A facility enabling the termination of cable elements and their interconnection, and/or cross-connection, primarily by means of a patch cord or jumper.

Cross Connection - A connection scheme between cabling runs, subsystems, and equipment using patch cords or jumpers that attach to connecting hardware at each end.

Crossover - A conductor which connects to a different pin number at each end.

Crossover Cable - A twisted pair patch cable wired in such a way as to route the transmit signals from one piece of equipment to the receive signals of another piece of equipment, and vice versa.

Crosstalk - The coupling of unwanted signals from one pair within a cable to another pair. Crosstalk can be measured at the same (near) end or far end with respect to the signal source.

CSA - Canadian Standards Association

CSMA/CD - see Carrier Sense Multiple Access with Collision Detect.

Current - The flow of charge in a conductor. See "alternating current" and "direct current".

Current Loop - A two wire transmit/receive interface.
Customer Premises - Buildings, offices, and other structures under the control of a telecommunications customer.

Cutoff Wavelength - A distinct boundary, in the wavelength spectrum, which characterizes the mode of operation of a fiber. A fiber operating at wavelengths lower than the cutoff wavelength is multimode while the same fiber operating at wavelengths higher than cutoff wavelength is single mode.

Cut-through Resistance - The ability of a material to withstand mechanical pressure without damage.

Cyclic Redundancy Check (CRC) - An error checking technique used to ensure the accuracy of transmitting digital code over a communications channel. The transmitted messages are divided into predetermined lengths which, used as dividends, are divided by a fixed divisor. The remainder of the calculation is appended onto and sent with the message. At the receiving end, the computer recalculates the remainder. If it does not match the transmitted remainder, and error is detected.