Glossary of Network/LAN Terminology

Attenuation - Decrease in magnitude of voltage, or of a signal in transmission between points. Typically expressed in Decibels (dB), attenuation in data transmissions is most greatly affected by cable length and the frequency of transmission.

Autotest - A pre-programmed series of tests and pass/fail criteria used by a hand-held cable test device to determine the level of performance of data cabling.

Bandwidth - The range of frequencies available for signaling. The difference expressed in cycles per second (hertz) between the highest and lowest frequencies of a band. Category 5 cabling, for example, is rated for a signaling bandwidth of 0-100 MHz.

Baud - A unit of signaling speed. The speed in baud is the number of line changes (in frequency, amplitude, etc) or events per second. Baud rate does not equal bits per second, although in common usage, "baud rate" and "bps" are often used interchangeably.

BER - Bit Error Rate. The degree to which a network experiences errors in data transmissions. Usually expressed fractionally or as an exponential relationship between good data and data errors.

Bit - A contraction of the term binary digit. A bit can be either 0 or 1 and is the smallest possible unit of information in digital code.

BPS (Bits per Second) - The basic unit of measure for serial data transmission capacity. Kbps for kilo (thousands). Mbps for mega (millions). Gbps for giga (billions).

Break-Out Box - A testing device that permits the user to switch, cross, and tie interface leads, and often contains LED's for monitoring leads. Used for the monitoring and diagnosis of serial communications such as RS-232.

Cable Tester - A handheld electronic device that is used to measure the electrical and physical properties of network cabling. Used commonly to certify cabling to known standards, or as a troubleshooting tool.

Coaxial Cable - A popular transmission medium usually consisting of one central wire conductor (two for twinaxial cable) surrounded by a dielectric insulator and encased in either a wire mesh or an extruded metal sheathing. Commonly used for Cable TV (CATV) or older computer networks.

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Crosstalk - The unwanted transfer of energy (signal) from one circuit to another circuit. Crosstalk interferes with the desired data signal. Handheld cable testers can be used to determine the level of unwanted crosstalk in network cabling.

Data Compression - Any of several techniques that reduce the number of bits required to represent information in data transmission or storage (thus conserving bandwidth or memory). Data compression is used to increase the information carrying capacity when bandwidth is not sufficient.

Decibel - (dB) A logarithmic unit of measure for the power or strength of a signal expressed as the ratio of two values. A 3 dB increase in signal strength is twice the original signal. A 3 dB decrease is half the original signal.

Delay - In data communications, the time between transmission and reception of a signal. Usually expressed in nanoseconds. Also see Propagation Delay.

Delay Skew - The difference in time between the arrival (reception) of a data signal and subsequent related data signals. Usually expressed in nanoseconds.

EIA (Electronic Industries Association) - A consultative group of manufacturers recognized as the standards writing group in the United States for electronic equipment.

EIA/TIA 568 - Approved in 1991, this document specifies the standards for commercial building telecommunications wiring. The standard specifically addresses the type of wiring to use, wiring practices, terminations and connections, and cable performance standards. The LANcat; System certifies network cable to this standard.

ELFEXT (Equal Level Far End Crosstalk) - The comparative measurement of FEXT and Attenuation is called Equal Level Far End Crosstalk or ELFEXT. Characterizing ELFEXT is important for cabling links intended to support 4 pair, full-duplex network transmissions.

EMI/RFI (Electromagnetic Interference/Radio Frequency Interference) - Unwanted electromagnetic emissions, generated by lightning or by electronic or electrical devices, that degrades the performance of other electronic devices. Interference may be reduced by shielding.

EPROM (Electrically Programmable Read Only Memory) - Read only, non-volatile semiconductor memory that is erasable under ultra-violet light and re-programmable. EPROMs are used to store operating instructions for electronic equipment.

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Ethernet - A popular local area network design and the product of Xerox Corp., characterized by 10Mbps baseband transmission over shielded coaxial cable and employing CSMA/CD as the access control mechanism. Standardized by the IEEE as specification IEEE 802.3 The newest fully developed Ethernet Networks transmit at 100 Mbps. Future developments of Ethernet will include 1000 Mbps data rates. Also known as 1000Base-T or Gigabit Ethernet.

FEXT (Far End Crosstalk) - Far End Crosstalk or FEXT is similar in nature to NEXT, but crosstalk is measured at the opposite end from the transmitted signal. FEXT tests are affected by signal Attenuation to a much greater degree than NEXT since FEXT is measured at the far end of the cabling link where signal Attenuation is greatest.

Fiber Loss (Optical Loss) - The attenuation (decrease) of the light signal in optical fiber transmission. Optical loss is directly related to the length of fiber and the quality of connections and splices in a fiber segment.

Fiber Optics - Transmission technology in which modulated light-wave signals, generated by a laser or LED, are propagated along a glass or plastic medium, and then demodulated to electrical signals by a light sensitive receiver.

Firmware - A computer program or software that contains operating or instruction code for electronic devices. Firmware is also referred to as "embedded software".

Full Duplex - Refers to a communications system or equipment capable of transmission simultaneously in two directions.

Half Duplex - A circuit which provides transmission alternately in either direction.

Hertz (Hz) - A measure of frequency or bandwidth. The same as cycles per second.

IEEE - Institute of Electrical and Electronics Engineers.

Impedance - The resistance to the flow of alternating current in a circuit.

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ISO - International Standards Organization. The body which promotes the development of worldwide standards.

LED (Light Emitting Diode) - A semiconductor light source that emits visible light or invisible infra red light.

Line Driver - A signal converter that increases a digital signal to ensure reliable transmission over an extended distance.

Link - A physical transmission path between two stations, channels, or parts of communications systems. Network links consist of either copper or fiber optic cabling that has been specifically designed for the purpose of transmitting data.

Local Area Network (LAN) - A data communications system confined to a limited geography area (up to about 10km) with moderate to high data rates (100kbps to 100Mbps). The area served may consist of a single building, a cluster of buildings or a campus.

Loss - Reduction in signal strength, expressed in decibels (dB). Opposite of gain.

Modem Eliminator - A device used to connect a local terminal to a computer port, instead of using a pair of modems. Allows DTE to DTE connection, and provides the necessary control signals that would normally be generated by the DCE.

Multimode - Essentially, an optical fiber designed to carry multiple signals, distinguished by frequency or phase, at the same time.

Nanosecond - One billionth of a second.

Network - A series of computers and related devices interconnected by common communications channels.

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NEXT - An abbreviation for Near-End-Crosstalk. A specific method of measuring the level of unwanted crosstalk in network cabling. Crosstalk measurement is made at the end of the cable closest to the transmitter (near end).

Noise - Random electrical signals, introduced by circuit components or natural disturbances, which degrade the performance of a communication channel.

Parallel Transmission - Transmission mode that sends a number of bits simultaneously over separate lines to a device such as a printer. Usually unidirectional.

Physical Layer - Within the OSI Model, the lowest level (Level 1) of network processing, below the link layer, concerned with the electrical, mechanical, and handshaking procedures over the interface that connects a device to a transmission medium.

Propagation Delay - The time necessary for a signal to travel from one point on a circuit to another.

Protocol - A formal set of conventions governing the format and control of inputs and outputs between two communication devices or processes.

PVC (Permanent Virtual Circuit) - A permanent connection between two DTEs (Data Terminal Equipment) using a fixed logical channel. Once established it requires no setup or disconnect operations before and after a data transmission. Also, PolyVinyl Chloride. A type of plastic commonly used for cladding telecommunications cable.

Repeater - In digital transmission, equipment that receives a pulse train, amplifies it, re-times it, and then reconstructs the signal for retransmission.

RF - Radio Frequency. Electromagnetic waves operating between 10 KHz and 3MHz that carry data signals without the use of wires or cables.

Router - A network component that acts as an interface between two networks. Routers read and forward data packets between networks based on routes and network addresses stored in the router's routing table.

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Shielding - A metallic covering that eliminates electromagnetic and radio frequency interference.

Telecommunications - A term encompassing both voice and data communications in the form of coded signals transmitted over media.

Termination - The act of attaching connectors to bare cabling. In the case of data cabling, terminations must be in accordance with standard wiring codes such as those depicted.

Traffic - The volume of data transmitted over a LAN at any given time. Traffic is generated by the devices and associated software applications that are running on the network. Excessive traffic on a network can seriously impair performance of a LAN. The NETcat and NETcat Plus allow network managers to actively monitor 10 Base-T Ethernet network traffic to help them configure their networks for optimal performance.

Transmission - The dispatching of a signal, message, or other form of intelligence, by wire, radio, telegraphy, telephone, facsimile or other means.

Twisted Pair - Two insulated copper conductors that are wound around each other, mainly to cancel the effects of electrical noise. Typical of standard telephone wiring. Network twisted-pair cabling such as Category 5, consists of 4 twisted pairs in the same sheath (insulation). Twisted pair wiring is available in both unshielded twisted pair wire (UTP) and shielded twisted pair wire (STP) versions.

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