Commonly referred to as Ethernet. It is a local area network protocol that operates at 10Mbps.
Commonly referred to as Token Ring. Operates at either 4 or 16Mbps.


(American National Standard Institute). Voluntary U.S. industry association organized to develop standards.
Commonly referred to as FDDI. A local area network protocol that operates at 100Mbps.
Having a variable time interval between successive data or information in the form of characters, operations, events. Transmission in which the data or information is individually synchronized or timed usually by start and stop bits (S/S).
Acronym for Asynchronous Transfer Mode, a high performance networking technology based on the switching of fixed length, 53 byte cells. ATM switching supports the switching of voice, video, and data; also supports isochronous communication.
A general term describing the loss of power between two points, measured in decibels per kilometer (dB/km) at a specified wavelength (nm).


Backbone Network
A main or high speed transmission facility or medium usually designed to connect lower speed channels or clusters of terminals. May describe common carrier main transmission path.
A range of frequencies available for signaling; the differences between the highest and lowest frequencies of a band are expressed in (Hz).
Acronym for Bi-Polar Violation.
A device used to connect two separate LANs or used to divide a large LAN into smaller LANs. Each LAN acts as its own LAN, but uses a bridge device to communicate from one LAN to another.
B-ISDN (Broadband ISDN)
A network standard from the CCITT and ANSI committee. It supports voice, data and video in the same network.
Path or channel, usually electrical, with one or more conductors, where all devices are able to receive all transmissions at the same time.


Acronym for Consultative Committee, International Telephone and Telegraph. An international standards body responsible for setting international communications standards that allow interoperability among telephony and data communications equipment.
Acronym for Carrier Detect (Detect Carrier Detect).
The use of unshielded or shielded twisted pair cable to transmit the FDDI signal.
CO (Central Office)
The local telephone company switch that terminates subscribers’ lines for switching and connecting to the public network.
CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
Access protocol for Ethernet.
Counter-Rotating Ring
Aka. Self-Healing Ring; has two physical transmission lines or rings with transmitting and receiving signals in each ring traveling in opposite directions. If the line or a device along the ring fails, the ring re-anneals by bypassing the device and or line and forms with the other ring to form a new single ring.
The unwanted transfer of energy from the disturbing circuit to another called the disturbed circuit. Usually from an adjacent analog channel.
Acronym for Channel Service Unit, a device furnished as an integral part of a digital access line where a user wishes to supply the bipolar signals. It provides the network with protection against user side electrical anomalies such as surges, and provides the user with network clocking.
Acronym for Clear To Send.


Acronym for Data Communication Equipment, aka. Data Circuit-Terminating Equipment.
Acronym for Data Communication Ready.
The spreading of light pulses that takes place in multimode fiber optic transmission. Dispersion limits the potential transmission distance because the spread out light pulses reach the destination at different times making the signal unreadable.
Digital Signal, Level 1 is the North American data rate used for T1 carriers. It operates at 1.544Mbps and supports 24 phone lines.
Digital Signal, Level 2 is the North American data rate used for T2 carriers. It operates at 6.312 Mbps and supports four T1 lines or 96 phone calls
Digital signal, Level 3 is the North American data rate used for T3 carriers. It operates at 44.736 Mbps and supports 28 T1 lines.
Acronym for Data Service Unit, a DCE used with digital communications circuits to provide digital data services interface. Located on the users premises, the DSU interfaces directly with the DTE, and provides loop equalization, remote and local test capabilities, and the logic and timing necessary to provide a standard EIA/TIA or CCITT interface. Converts signals between those used at the DTE's serial interface and bipolar signals used on the digital network. Also Network Terminal Unit (NTU).
Acronym for Data Terminating or Data Terminal Equipment.
Acronym for Data Terminal Ready.


The European standard for high speed, point to point transmission operating at 2.048 Mbps and defines 64 Kbps sub-channels.
Acronym for Electronic Industries Association. EIA, a standards body, has a set of standards which includes data communications and interface standards among others.
Acronym for Electro-Magnetic Interference.
Product name for one of the first popular LAN technologies, later standardized as IEEE 802.3.


Stands for Front End Processor. It is an IBM communication controller that routes traffic to and from cluster controllers.
Fiber Optic Cable
Thin filaments of glass or other transparent material sheathed in an insulator through which a light beam may be transmitted for long distances by means of multiple internal reflections. A waveguide used to transmit digital information.
Acronym for Fiber Distributed Data Interface, is a shared medium, ring topology LAN that operates at 100 Mbps. It is ANSI standard X3T9.5, using fiber optic cable as the medium.
Flow Control
A method for a receiver to control the information flow from a transmitter. It eliminates data overflow at the receiver.
Acronym for Field Programmable Gate Array.
Full Duplex
A communication method where both ends can transmit and receive simultaneously.


Half Duplex
A communication method where one end transmits while the other end receives, then reverses the process.
A device for local area networks (LANs) that is used to interconnect multiple devices over an internal bus.


Aka. phase jitter, caused by power line harmonics and perceived in the form of minor phase changes.


A local area network is a group of PCs connected over a common medium within a building.


(Medium Access Control)A designated hardware address for each device on a LAN or MAN. This address is burnt into The network interface card (NIC) by its manufacturer.
A metropolitan area network is a group of PCs connected over a common medium within a campus environment or the same city.
Multi-Drop Line
Aka. Multipoint Line, a data link supporting multiple DTE connections, usually with one DTE controlling the link by polling the other DTEs for input and addressing output to the other DTEs. Utilizing frequency division or statistical MUX, a multipoint line can support multiple independent point-to-point channels.
Multimode fiber
An optical fiber that supports more than one propagating mode of light propagation.
Aka. or Multiplexor or Mux,. A device using several communications channels at the same time, transmits and receives messages and controls communications lines, may be a microprocessor.


Acronym for Numerical Aperture.
A network-connected device, such as a server or PC.


Optical Carrier Signal Level 1 refers to SONET data transmission at 51.840Mbps.
Acronym for Optical Carrier 3, a transmission rate standard for fiber optic telephony or data communications circuits. OC3 operates at 155 Mbps speed and is part of the SONET hierarchy.
Optical Carrier Signal Level 12 refers to SONET data transmission at 622.080Mbps.
Order Wire
Voice channel used to communicate between two locations.
(Open Data Interconnection Reference Model) This is the International Standards Organization (ISO) model of how data communications systems can be interconnected. Communication is partitioned into seven function layers. Each layer builds on the services provided by those under it.


A grouping of data, usually consisting of data and an address header prior to being sent over a network.
Acronym for Private Branch Exchange, is a small private version of a phone company's larger central switching office.
Acronym for Pulse-Coded Modulation, a means of converting analog to digital form.
Point-of Presence (POP)
The physical access location within a specific location of the long distance or common carrier.
The method used for terminal to controller communications. The controller systematically asks for each terminal if it needs to transmit to the controller.
A set of rules for data communication. All devices communicating together must adhere to the same rules.


Path or channel; usually electrical, where devices along the path receive transmissions sequentially from one device to the next along the ring.
Similar to a bridge but provides more complex and flexible networking support. It usually also supports WANs.
An interface used between DTE and DCE employing serial binary data interchange, defined by EIA, aka. EIA-232. Similar to standard V.24 of CCITT.
Standard defined by EIA, aka. EIA-422. Deals with the electrical characteristics of balanced voltage digital interface circuits. Similar to standard V.11 of CCITT.
Standard defined by EIA, aka. EIA 423. Deals with electrical characteristics of unbalanced voltage digital interface circuits. Similar to standard V.10 of CCITT.
Standard defined by EIA, aka. EIA-449. Deals with general-purpose 37- and 9-position interface for data terminal equipment and data circuit-terminating equipment employing serial binary data interchange.
Standard defined by EIA, aka. EIA-485. Standard for electrical characteristics of generators and receivers for use in balanced multipoint systems.
Acronym for Request To Send.


Acronym for Supervisory Control and Data Acquisition.
SNMP (Simple Network Management Protocol)
A standard management protocol used to provide a common means of managing network devices.
Single mode fiber
An optical fiber that supports only one mode of light propagation above the cutoff wavelength.
Synchronous Transmission
Having a constant time interval between successive bits of data or information.
Acronym for Synchronous Optical NETwork, is a hierarchical standard for a high speed (45 Mbps to 2.4 Gbps) transport network.
Network in which all terminals are connected through a single point or node, such as a star coupler.


Transmission rate standard for telephony or data communications circuits. T1 operates at 1.544 Mbps speed. Usually this circuit is subdivided into many 64 Kb channels.
Acronym for Transmission Control Protocol/Internet Protocol.
Time Division Multiplexing
A type of multiplexer that allocates a defined amount of backbone bandwidth for each connected device.
Time Slot
Unit of backbone bandwidth allocated for each port.
Token Ring
A LAN topology where a control packet or token is passed from station to station in sequential order. The stations wishing to access must wait for the token before transmitting data, in the token ring the next logical station is also the next physical station.


Virtual Path
A software-controlled point-to-point connection between two devices or segments.


Wide Area Network (WAN)
A computer network interconnected over distances beyond a city or metropolitan area.