Ethernet Technical Summary

Appendix A: Ethernet Glossary

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A

Access Method

The rules by which a network device gains the rights to transmit a communication on the network. Common methods include carrier sense multiple access with collision detection (CSMA/CD), token passing, and demand priority.

Adapter

Another name for a Network Interface Card (NIC)

Address Resolution Protocol (ARP)

In TCP/IP, a Network layer protocol used by an end station to determine the physical address of another station on the same LAN.

Alignment Error

Alignment errors are caused by frames that do not contain an integral number of bytes. Such a frame does not end on a byte boundary, and is some odd number of bits in length.

ARP

see Address Resolution Protocol

Asynchronous

Transmission where sending and receiving devices are not synchronized. Data must carry signals to indicate data division.

Attachment Unit Interface (AUI)

The IEEE 802.3 standard name for the cable connecting an Ethernet transceiver (MAU) to a networked device. An AUI cable is equipped with a 15-pin connector that mates with a 15-pin connector on the networked device.

Attenuation

The decrease in magnitude of a signal as it travels through any transmission medium such as a cable or optical fiber. Measured in dB per unit of length.

Attenuation Crosstalk Ratio (ACR)

The difference between attenuation and crosstalk, measured in dB, at a given frequency. A quality factor for cabling to assure that signal sent down a twisted pair is stronger at the receiving end of the cable than any interference imposed on the same pair by crosstalk from other pairs.

AUI

see Attachment Unit Interface.

Auto-Negotiation

The algorithm that allows two devices at either end of a link segment to negotiate common data service functions (i.e. transmission rate, half vs. full duplex, etc.)

AWG

American Wire Gage - A wire diameter specification. The smaller the AWG number, the larger the wire diameter.

B

Backbone

A cable connection between telecommunication or wiring closets, floor distribution terminals, entrance facilities, and equipment rooms either within or between buildings. In star networks, the backbone cable interconnects hubs and similar devices, as opposed to cables running between hub and station. In a bus network, the bus cable.

Backoff

The process by which a station then remains silent for a random period of time following a collision before attempting to transmit again. See also Binary Exponential Backoff.

Backoff Delay

The length of time that a station on a CSMA/CD (Ethernet) network must wait before attempting to retransmit a frame after detecting a collision.

Balanced Cable, Balanced Line

A cable having two identical conductors that carry voltages of opposite polarities and equal magnitude with respect to ground. The conductors are twisted to maintain balance over a distance.

Balanced Transmission

A mode of signal transmission in which each conductor carries the signal of equal magnitude, but opposite polarity. A 5 volt signal for example, appears as a +2.5 Volts on one conductor and -2.5 Volts on the other.

Balun

An impedance matching transformer that converts the impedance of one interface to the impedance of another interface. Sometimes used to adapt 150 ohm shielded twisted pair (STP) cabling for use with 100 ohm Ethernet systems. The term is derived from "balanced / unbalanced". May also be called a "media filter".

Baseband

A transmission method in which the entire bandwidth of the transmission medium is used to transmit a single digital signal. The signal is driven directly onto the transmission medium without modulation of any kind. Baseband is simpler, cheaper and less sophisticated than Broadband. All Ethernet media types are baseband except for 10Broad36 which is broadband.

Bandwidth

The range of frequencies required for proper transmission of a signal. Expressed in Hertz (cycles per second). The higher the bandwidth, the more information that can be carried. A continuous range starting from zero is said to be "baseband", while a range starting substantially above zero is "broadband".

Baud

The number of changes in signal per second. A given baud rate does not necessarily transmit an equal number of bits/sec. For example, a signal with four voltage levels may be used to transfer two bits of information for every baud.

BEB

see Binary Exponential Backoff

Bend Loss

A form of increased attenuation in an optical fiber caused by an excessively small bend radius. The attenuation may be permanent if microfractures caused by the bend continue to affect transmission of the light signal.

Bend Radius

Radius of curvature that a fiber optic or metallic cable can bend before the risk of breakage or increased attenuation occurs.

BER

see Bit Error Rate

Binary Exponential Backoff (BEB)

Algorithm used with CSMA/CD (Ethernet) networks to schedule retransmissions after a collision. So called because the backoff delay expands exponentially (becomes longer) with repeated collisions.

Binary Logarithmic Arbitration Method (BLAM)

A proposed enhancement of the Binary Exponential Backoff algorithm designed to eliminate the unfairness caused by the "capture effect". Although implemented by some Ethernet products, BLAM was never approved as part of the Ethernet standard.

Bit

One binary digit.

Bit Error Rate

A measure of data integrity, expressed as the ratio of received bits that are in error, relative to the amount of bits received. Often expressed as a negative power of ten.

Bit Stream

A continuous transfer of bits over some medium.

Bit Time

The length of time required to transmit one bit of information.

BLAM

see Binary Logarithmic Arbitration Method

BNC

A coaxial connector that uses a "bayonet" style turn and lock mating method. Used with RG-58 or smaller coaxial cable. Used with 10Base2 Ethernet thin coaxial cable. BNC is an acronym for Bayonet-Neill-Concelman or Bayonet-Navy-Connector.

BPS

Bits per second.

Braid

Fine wires interwoven to form a tubular flexible structure that may be applied over one or more wires for the purpose of shielding. May also be formed into a flattened conductor to be used as a grounding strap.

Branch Cable

In 10Broad36, the AUI Cable interconnecting the data terminal equipment and transceiver (MAU) system components.

Bridge

A device which connects two or more networks at the data link layer (layer 2). Bridge devices are specified in the IEEE 802.1D standard. Bridges are not form part of the collision domain (i.e. Bridges may be used to split a network into multiple collision domains).

Broadband

A transmission facility having a bandwidth sufficient to carry multiple voice, video or data channels simultaneously. Each channel occupies (is modulated to) a different frequency bandwidth on the transmission medium and is demodulated to its original frequency at the receiving end. Channels are separated by "guardbands" (empty spaces) to ensure that each channel will not interfere with its neighboring channels. This technique is used to provide many CATV channels on one coaxial cable. 10Broad36 is the only broadband Ethernet media type. All other Ethernet media types are "baseband".

Broadcast

The act of sending a frame to all stations. Also describes the class of media for which CSMA/CD Ethernet is designed, in which all stations are capable of receiving a signal transmitted by any other station.

Broadcast Address

A multicast address identifying the group of all stations on a network.

Broadcast Domain

Segments joined together by bridges form a broadcast domain.

Broadcast Storm

A condition that may occur in networks that can cause a large number of broadcast packets to be propagated unnecessarily across an enterprise-wide network, thereby causing network overload.

Bus Topology

A network structure in which each station is directly attached to a common communications channel. The following Ethernet media systems use a bus topology: 10Base5, 10Base2, and 10Broad36.

Byte

A group of 8 bits. Also known as an "octet".

C

c

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

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.

Capture Effect

A condition where the backoff delays selected by different stations following the same collision can become very lopsided, resulting in an unfairness problem. Also called "channel capture".

Carrier

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

Carrier Sense

A method of detecting the presence of signal activity on a common channel. With Ethernet, a method of detecting whether another station is transmitting.

Carrier Sense Multiple Access with Collision Detection

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. So called because it a) allows multiple stations to access the broadcast channel at will, b) avoids contention via carrier sense and deference, and c) resolves contention via collision detection and retransmission.

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.

Channel

A logical medium in a communication system over which data is transmitted.

Channel Capture

same as "Capture Effect".

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.

Circuit

1. A system of conducting media designed to pass a signal or voltage between two points. 2. 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.

Class I Repeater

A Class I Repeater operates by translating the line signal on the incoming port to a digital signal. This allows the translation between different types of Fast Ethernet media systems such as 100Base-TX and 100Base-FX. A Class I repeater introduces delays when performing this conversion such that only one repeater can be put in a single Fast Ethernet LAN segment.

Class II Repeater

A Class II Repeater immediately repeats the signal on the incoming port to all the ports on the repeater. Very little delay is introduced by this quick movement of the data across the repeater, thus two class II repeaters are allowed per Fast Ethernet segment.

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.

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. Coaxial cables are know for low susceptibility to interference.

Coaxial Cable Section

A single length of coaxial cable, terminated at each end with a male BNC connector. Cable sections are joined to other cable sections via BNC plug/receptacle barrel or Type T adapters.

Coaxial Cable Segment

A length of coaxial cable made up from one or more coaxial cable sections and coaxial connectors, and terminated at each end in its characteristic impedance.

Code Rule Violation (CRV)

An analog waveform that is not the result of the valid Manchester encoded output of a single optical transmitter.

Collision

A condition that occurs on a CSMA/CD (Ethernet) transmission medium when two or more stations transmit signals concurrently.

Collision Detect

A method of detecting two or more simultaneous transmissions on a common signal channel.

Collision Domain

A single CSMA/CD network. If two or more Ethernet stations are within the same collision domain and both transmit at the same time, a collision will occur. Ethernet stations that are separated by a repeater are in the same collision domain. Ethernet stations that are separated by a bridge are in different collision domains. The concept of collision domain applies only to half duplex Ethernet. Collisions do not occur in full duplex Ethernet configurations.

Concentrator

LAN equipment that allows multiple network devices to be connected to the LAN cabling system through a central point. Sometimes called a "hub".

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.

Conductor

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

Contention

Interference between colliding transmissions (see collisions). Normal part of Ethernet CSMA/CD protocol.

Continuity

An uninterrupted pathway for electrical signals.

Core

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

CRC

see Cyclic Redundancy Check

Cross Connect

A group of connection points, often wall or rack mounted in a wiring closet, used to mechanically terminate and interconnect twisted-pair building wiring.

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.

CSMA/CD

see Carrier Sense Multiple Access with Collision Detect.

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.

D

D Connector

see Subminiature D Connector

Data Grade

A term used for twisted-pair cable used in networks to carry data signals. Data grade media has a higher frequency rating than voice grade media used in telephone wiring.

Data Link Layer

Layer 2 of the OSI reference model. This layer takes data from the network layer and passes it on to the physical layer (layer 1). The data link layer is responsible for transmission and reception of Ethernet frames, 48-bit addressing, etc. It includes both the media access control (MAC) and logical link control (LLC) layers.

Data Terminal Equipment (DTE)

Any source or destination of data connected to the local area network.

dB

Decibel. A unit for measuring the relative strength of a signal. Usually expressed as the logarithmic ratio of the strength of a transmitted signal to the strength of the original signal. A decibel is one tenth of a "bel".

DB-9

Nine pin D connector.

DB-15

Fifteen pin D connector.

DB-25

Twenty-five pin D connector.

Deference

For CSMA/CD Ethernet, the process by which a station delays its transmission when the channel is busy to avoid contention with ongoing transmission.

Destination MAC Address

Address identifying the station or stations on a LAN to which a frame is being sent.

DGM

Data Grade Media (see Data Grade)

Dielectric

An insulating (non-conducting) material.

Differential Manchester Encoding

see Manchester Encoding

Dispersion

The phenomenon in an optical fiber whereby light photons arrive at a distant point in different phase than they entered the fiber. Dispersion causes receive signal distortion that ultimately limits the bandwidth and usable length of the fiber cable. The two major types of dispersion are 1) mode (or modal) dispersion caused by differential optical path lengths in a multimode fiber, and 2) material dispersion caused by differing transmission times of different wavelengths of light in the fiber optic material.

Distortion

Any undesired change in a wave for or signal.

DIX

Acronym identifying the three companies that released the original Ethernet specification in 1980: Digital, Intel, and Xerox.

Drain Wire

An uninsulated wire in contact with a shield throughout its length. Used to terminate the shield.

Drop Cable

The cable which allows connection and access to and from the trunk cables of a network such as the cables that connect individual PCs to the bus on a bus LAN. In Ethernet, synonymous with "AUI Cable".

DTE

see Data Terminal Equipment.

Duplex

1. (data communications) A circuit used to transmit signals simultaneously in both directions. 2. (general) Two receptacles or jacks in a common housing which accepts two plugs.

E

Earth

A term for zero reference ground.

EIA

Electronic Industry Association (formerly RMA or RETMA). An association of manufacturers and users that establishes standards and publishes test methodologies.

Eight-pin connector, Eight-pin modular

A twisted pair connector that closely resembles the RJ-45 connector, but has better electrical characteristics than typical telephone grade RJ-45 connectors.

Electromagnetic Interference

An interfering electromagnetic signal. Network wiring and equipment may be susceptible to EMI as well as emit EMI.

ELFEXT

Equal Level Far End Crosstalk

EMI

see Electromagnetic Interference.

Ethernet

A local area network (LAN) protocol defined in the IEEE 802.3 standard in which computers access the network through a Carrier Sense Multiple Access / Collision Detect (CSMA/CD) protocol.

Ethernet Cable

Informal name for the 50-ohm, 10 mm coaxial cable specified in the Ethernet 10Base5 standard. Often called "thick Ethernet" cable to distinguish it from the 5 mm coaxial cable specified by the 10Base2 standard.

Ethernet Version 2

The original Ethernet specification produced by Digital, Intel, and Xerox (DIX) that served as the basis for the IEEE 802.3 Ethernet standard.

Excessive Collision Error

If a station receives 16 consecutive collisions when attempting to transmit a single frame, then the frame is dropped due to an excessive collision error.

Extended LAN

A network that consists of two or more separate LAN data links that are interconnected using bridges.

F

f

Frequency

Far End Cross Talk (FEXT)

Crosstalk that is measured on the quiet line at the opposite end as the source of energy on the active line. FEXT is not typically measured in cabling, with Near End Cross Talk (NEXT) being the preferred crosstalk measurement.

Fast Ethernet

Ethernet standard supporting 100 Mb/s operation.

Fast Link Pulse (FLP)

A link pulse which encodes information used in the Auto-Negotiation protocol. Fast link pulses consist of bursts of the normal link pulses originally used in 10Base-T.

FCC

Federal Communications Commission.

FCS

see Frame Check Sequence

FEXT

see Far End Cross Talk

Fiber Optics, Fiber Optic Cable

The technology in which communication signals in the form of modulated light beams are transmitted over a glass or plastic fiber transmission medium. Fiber optic cables offers high bandwidth, small space needs and protection from electromagnetic interference, eavesdropping and radioactivity.

Fiber Optic Medium Attachment Unit (FOMAU)

A MAU for fiber applications.

Fifty-pin Connector

Commonly referred to as a Telco, CHAMP, or blue ribbon connector, this connector is used on Ethernet 10Base-T hubs as an alternate twisted-pair segment connection method. The 50-pin connector connects to 25-pair cables, which are frequently used in telephone wiring systems and which typically meet Category 3 specifications.

Filtering

Bridges and switches can reduce the level of congestion on a LAN through the process of filtering. A filtering bridge or switch forwards a packet from one LAN segment to another only as required. Packets that are not forwarded by a bridge or switch are said to be "filtered".

Filtering Rate

The maximum number of frames per second that a bridge or switch can continuously receive, parse, and make a forwarding decision on.

Flow Control

The process of controlling data transmission at the sender to avoid overfilling buffers and loss of data at the receiver.

FOIRL

Fiber Optic Inter-Repeater Link. An early Ethernet fiber optic connection method intended for connection of repeaters. Defined in the IEEE 802.3c standard.

FOMAU

see Fiber Optic Medium Attachment Unit.

Forwarding

The process of moving frames from one port to another in a bridge or switch.

Forwarding Rate

The maximum number of frames per second that can be forwarded by a bridge or switch, assuming no congestion on the output port.

Frame

The sequence of bits that form the unit of data transmission at the LAN data link layer or medium access control layer. In Ethernet, a frame consists of the sequence of bits transmitted by a station from the "preamble" through the "frame check sequence". Also called "packet".

Frame Bursting

A technique permitted only in half-duplex Gigabit Ethernet networks that optionally allows a station to transmit a series of frames without relinquishing control of the transmission medium. It improves the performance of Gigabit Ethernet when transmitting short frames.

Frame Check Sequence (FCS)

An encoded value appended to each frame by a transmitting station to allow transmission errors to be detected by the receiving station. Implemented as a 32-bit cyclic redundancy check (CRC) code.

Frequency

The number of times a periodic action occurs in a unit of time. Expressed in hertz (abbreviated Hz). One hertz equals one cycle per second.

FTP

see Screened Twisted Pair (ScTP) cable

Full Duplex

Data transmission over a circuit capable of transmitting in both directions simultaneously. For Ethernet, full duplex operation was defined in the IEEE 802.3x standard.

G

Gb/s

Gigabits per second. One Gb/s equal one billion bits per second.

Giants

Giants are frames which are longer than the maximum Ethernet size (1518 or 1522 bytes). Giant packets usually occur when you have a jabbering node on your network; one that is continuously transmitting, or transmitting improperly for short bursts-probably due to a bad transmitter on the NIC. Giants can also be caused by packets being corrupted as they are transmitted, either by the addition of garbage signals, or by the corruption of the bits that indicate frame size.

Giga

A prefix meaning one billion

Gigabit Ethernet

A version of Ethernet that operates at 1 Gb/s (1000 Mb/s).

Gigahertz (GHz)

One billion hertz.

GIPOF

Graded Index Plastic Optical Fiber

Globally Administered MAC Address

A form of LAN station addressing in which MAC addresses are 48-bits in length and whose values are globally unique. Address values are set by the organization that manufactures the Network Interface Card (NIC) or other LAN station. A manufacturer applies to the IEEE for a unique block of addresses and assigns to each device it manufactures a unique MAC address from its assigned block. The address is permanently "burned" into the device through a PROM or other form of non-volatile storage. Sometimes called "universal addressing".

GMII

Gigabit Media Independent Interface

Graded Index Fiber

A multimode fiber optic cable design in which the index of refraction of the core is lower toward the outside of the core and progressively increases toward the center of the core, thereby reducing modal dispersion of the signal.

Group Address

An address specifying a group of logically related stations on a network. Also called a "multicast" address.

Ground

A common point of zero potential such as a metal chassis or ground rod.

H

Half Duplex

Data transmission over a circuit capable of transmitting in either direction, but not simultaneously. For Ethernet, the CSMA/CD method is a half duplex protocol.

Headend

The equipment in a cable system which receives the various program source signals, processes them, and retransmits them to subscribers. In the 10Broad36 Ethernet media system, the location that serves as the root for the branching tree of the physical medium; the point to which all inbound signals converge and the point from which all outbound signals emanate.

Hertz

The unit of frequency, one cycle per second (abbreviated Hz).

Hub

A device at the center of a star topology network. Hubs can be active (where they repeat signals set to them) or passive (where they do not repeat but merely split signals sent through them). Hub may refer to a repeater, bridge, switch, router, or any combination of these.

I

IEEE

Institute of Electrical and Electronics Engineers. A professional organization and standards body. The IEEE Project 802 is the group within IEEE responsible for LAN technology standards.

IEEE 802.1

The IEEE standards committee defining High Level Interfaces, Network Management, Internetworking, and other issues common across LAN technologies.

IEEE 802.2

The IEEE standards committee defining Logical Link Control (LLC).

IEEE 802.3

The IEEE standards committee defining Ethernet networks.

Impedance

A unit of measure, expressed in Ohms, of the total opposition (resistance, capacitance and inductance) offered to the flow of an alternating current.

Impedance Match

A condition where the impedance of a particular circuit cable or component is the same as the impedance of the circuit, cable, or device to which it is connected.

Impedance Matching Transformer

A transformer designed to match the impedance of one circuit to another.

Individual Address

A MAC address that identifies a single station. The low order bit of the first byte (first bit transmitted) of an individual address is always "0".

Insertion Loss

A measure of the attenuation of a device by determining the output of a system before and after the device is inserted into the system. For example, a connector causes insertion loss across the interconnection (in comparison to a continuous cable with no interconnection).

Intelligent Hubs

Wiring concentrators that can be monitored and managed by network operators.

Inter-Frame Gap (IFG)

The delay or time gap between frames. Also called Inter-Packet Gap.

Inter-Packet Gap (IPG)

The delay or time gap between packets. Also called Inter-Frame Gap.

Isochronous

Signals which are dependent on some uniform timing or carry their own timing information imbedded as part of the signal. Voice and video signals are isochronous signals, but data transfer is generally not.

Isochronous Ethernet, Isoethernet

A LAN technology developed by National Semiconductor that adds 6 Mb/s of isochronous services to a cable that also carries normal 10 Mb/s Ethernet traffic. Allows voice and/or video to be carried on the same cable as data traffic.

J

Jabber

Term used with Ethernet to describe the act of continuously sending data. A jabbering station is one whose circuitry or logic has failed, and which has locked up a network channel with its incessant transmission.

Jack

A female connector.

Jacket

The outer protective covering of a cable.

Jam, Jamming Sequence

In CSMA/CD Ethernet, the signal that a station transmits when it detects a collision condition on the transmission medium. The jamming sequence is sent to ensure that all stations know the collision has occurred.

Jitter

The slight movement of a transmission signal in time or phase that can introduce errors and loss of synchronization. More jitter will be encountered with longer cables, cables with higher attenuation, and signals at higher data rates. Also, called phase jitter, timing distortion, or intersymbol interference.

Jumper Cable Assembly

An electrical or optical assembly consisting of a pair of transmission lines terminated at their ends with a plug connectors.

K

L

LAN

see Local Area Network.

LAN Adapter

see Network Interface Card

Laser

Light Amplification by Stimulated Emission of Radiation. A device which produces light with a narrow spectral width. Used in fiber optic communication systems, usually single mode, where high capacity and low attenuation are required.

Late Collision

A late collision is an Ethernet CSMA/CD collision that takes place after 64-bytes of a frame has been transmitted on the network by an originating station. It is considered a failure in the network because the collision arrives too late in the frame transmission to be automatically dealt with by the Ethernet medium access control function. The frame being transmitted will be dropped, requiring that application software detect its loss and initiate a retransmission. Late collisions may be caused by overly long cable lengths that result in excessive delay in propagating collisions through the network. In a normal Ethernet network, collisions should propagate throughout the network before the first 64-bytes of a frame are transmitted.

LED

see Light Emitting Diode.

Light Emitting Diode

A semiconductor diode which emits incoherent light when a current is passed through it. Used as a light source in fiber optic transmission.

Link

A transmission path between two points not including terminal equipment, work area cables, or equipment cables.

Link Aggregation

Link Aggregation provides for increased link availability and bandwidth between two Ethernet stations by allowing multiple "physical" links to be combined to operate as a single "logical" link. Defined by the 802.3ad Working Group. Also called "Trunking".

Link Light

An optional status LED on an Ethernet transceiver that indicates the status of the link integrity test. If this light is lit on the transceivers at both ends of the link, it indicates that the link has passed the integrity test.

Link Pulse

A communication mechanism used in Ethernet link segments to indicate link status and, in auto-negotiation equipped devices, to communicate information about abilities and negotiate communication methods. The original 10Base-T used Normal Link Pulses (NLP) which indicate link status only. Ethernet nodes equipped with auto-negotiation exchange information using a Fast Link Pulse (FLP) mechanism which is compatible with NLP.

Link Segment

In Ethernet, a point to point segment that connects two and only two transceivers at its endpoints.

LLC

see Logical Link Control

Local Area Network (LAN)

A term used to refer to a form of networking technology that implements a high-speed, relatively short distance form of computer communications. Ethernet is one type of LAN.

Locally Administered Address

With locally administered addressing, the organization installing the network is responsible for assigning a unique MAC address to each network station. This could be done using DIP switches on the NIC or using a software function. A locally administered address overrides any globally administered address assigned during manufacture of the NIC.

Logical Link Control (LLC)

A protocol defined in the IEEE 802.2 standard for data-link-level transmission control. It is the upper sublayer of the IEEE Layer 2 (OSI) protocol that complements the MAC protocol. LLC is independent of any specific LAN technology.

M

MAC

see Medium Access Control

MAC Address

The 48-bit address used in Ethernet to identify a station. Generally a unique number that is programmed into a device at time of manufacture.

MAC Frame

Name for the data unit exchanged between peer Medium Access Control sublayer entities. Also called simply a "frame".

Manageable Hubs

Another definition for intelligent hubs. Each of the ports on the managed hub can be configured, monitored, and enabled or disabled by a network operator from a hub management console.

Management Information Base (MIB)

A list of manageable objects (counters, etc.) for a given device. Used by network management applications.

Manchester Encoding

A method of LAN signal encoding in which each bit time that represents a data bit has a transition in the middle of the bit time. Used with 10 Mb/s Ethernet (10Base2, 10Base5, 10Base-F, & 10Base-T), and Token-Ring LANs.

MAU

see Medium Attachment Unit

Mega

A prefix meaning one million

Mbaud

Megabaud. One million baud.

Mb/s

Megabits per second. One Mb/s equals one million bits per second.

MDI

see Medium Dependent Interface

Media

Wire, cable, or conductors used for transmission of signals.

Medium Access Control (MAC)

A mechanism operating at the data link layer of local area networks which manages access to the communications channel (medium). It forms the lower layer of the IEEE data link layer (OSI layer 2) which complements the Logical Link Control (LLC). MAC is a media-specific protocol within the IEEE 802 specifications.

Medium Attachment Unit (MAU)

The transceiver in Ethernet networks. Also a common name for the MSAU (Multi-station Access Unit) in Token-Ring networks.

Medium Dependent Interface (MDI)

The connector used to make the mechanical and electrical interface between a transceiver and a media segment. An 8-pin RJ-45 connector is the MDI for the 10Base-T, 100Base-TX, 100Base-T2, 100Base-T4, and 1000Base-T media systems.

Media Independent Interface (MII)

Used with 100 Mb/s Ethernet systems to attach MAC level hardware to a variety of physical media systems. Similar to the AUI interface used with 10 Mb/s Ethernet systems. An MII provides a 40-pin connection to outboard transceivers (also called PHY devices).

Mega

Prefix meaning one million.

Megahertz (MHz)

One million hertz.

MIB

see Management Information Base

Midsplit Broadband

A broadcast network configuration in which a broadband cable is divided into two channels, each using a different range of frequencies. One channel is used to transmit signals and the other is used to receive. For Ethernet, midsplit broadband is a configuration that can be used only with the 10Broad36 media system.

MII

see Media Independent Interface.

Mixing Segment

Ethernet term used in IEEE 802.3 standards to describe a segment that may have more than two transceivers.

MMF

set Multimode Fiber

Mode

A single electromagnetic wave traveling in an optical fiber.

Modular Hubs

A hub that starts with a chassis, or card cage, with multiple card slots, each of which can accept a communications card, or module. Each module acts like a standalone hub; when the communications modules are placed in the card slots in the chassis, they connect to a high-speed communications backplane that links them together so that a station connected to a port on one module can easily communicate with a station on another module.

Modular Jack

The equipment mounted half of a modular interconnection. Typically a female connector. A modular jack may be keyed or unkeyed and may have six or eight contact positions, but not all the positions need to be equipped with jack contacts.

Modular Plug

The cable mounted half of a modular interconnection. Typically a male connector. A modular plug may be keyed or unkeyed and may have six or eight contact positions, but not all the positions need to be equipped with contacts.

MT-RJ

Proposal for a new duplex fiber optic connector standard from AMP/Siecor.

Multicast

An addressing mode in which a given frame is targeted to a group of logically related stations.

Multicast Address

An address specifying a group of logically related stations on a network. Also called a "group" address.

Multimode Fiber

A fiber optic cable which supports the propagation of multiple modes. Multimode fiber may have a typical core diameter of 50 to 100 µm with a refractive index that is graded or stepped. It allows the use of inexpensive LED light sources and connector alignment and coupling is less critical than single mode fiber. Distances of transmission and transmission bandwidth are less than with single mode fiber due to dispersion.

N

N connector

A coaxial connector used for Ethernet 10Base5 thick coax segments.

Near-End Crosstalk

Crosstalk between two twisted pairs measured at the same end of the cable as the disturbing signal source. NEXT is the measurement of interest for crosstalk specifications.

Network

An interconnection of computer systems, terminals or data communications facilities.

Network Interface Card (NIC)

A circuit board installed in a computing device used to attach the device to a network. A NIC performs the hardware functions that are required to provide a computing device with physical communications capabilities. Also Network Interface Unit (NIU).

NEXT

see Near-End Crosstalk.

Next Page Function

Additional feature of auto-negotiation. Next pages are a means by which devices can transmit additional information beyond their link code.

NIC

see Network Interface Card.

NIR

Near-end Crosstalk-to-Insertion Loss Ratio

Node

End point of a network connection. Nodes include any device connected to a network such as file servers, printers, or workstations.

N-Way

Name originally used for the Ethernet "auto-negotiation" algorithm.

O

Octet

Eight bits (also called "byte")

Ohm

The electrical unit of resistance. The value of resistance through which a potential of one volt will maintain a current of one ampere.

Open

A break in the continuity of a circuit.

Optical Fiber

A thin glass or plastic filament used for the transmission of information via light signals. The signal carrying part of a fiber optic cable.

Optical Fiber Cable

An assembly consisting of one or more optical fibers.

Optical Fiber Duplex Adapter

A mechanical media termination device designed to align and join two duplex connectors.

Optical Fiber Duplex Connection

A mated assembly of two duplex connectors and a duplex adapter.

Optical Fiber Duplex Connector

A mechanical media termination device designed to transfer optical power between two pairs of optical fibers.

Optical Time Domain Reflectometry.

A method for evaluating optical fiber based on detecting and measuring backscattered (reflected) light. Used to measure fiber length and attenuation, evaluate splice and connector joints, locate faults, and certify cabling systems.

Open Systems Interconnect reference model (OSI)

A communications model developed by the International Standards Organization (ISO) to define all of the services a LAN should provide. This model defines seven layers, each of which provides a subset of all of the LAN services. This layered approach allows small groups of related services to be implemented in a modular fashion that makes designing network software much more flexible.

OTDR

Optical Time Domain Reflectometry.

Out of Window Collision, OOW Collision

Same as "late collision".

Outlet

A connecting device in the work area on which a horizontal cable terminates.

Outlet Box

A metallic or non-metallic box mounted within a wall, floor, or ceiling used to hold outlet, connector, or transition devices.

Output

The useful signal or power delivered by a circuit or device.

P

Packet

Bits grouped serially in a defined format, containing a command or data message sent over a network. Same as a "frame".

PAM5x5

Signal encoding scheme used in the Ethernet 100Base-T2 and 1000Base-T media systems.

Parallel Detection

An auto-negotiation device's means to establish links with non-negotiation, fixed speed devices.

Patch Cable, Patch Cord

A flexible piece of cable terminated at both ends with connectors. Used for interconnecting circuits on a patch panel or cross connect.

Patch Panel

A passive device, typically flat plate holding feed through connectors, to allow circuit arrangements and rearrangements by simply plugging and unplugging patch cables.

Pause Frames

A optional flow control technique for full-duplex Ethernet networks. One end station may temporarily stop all traffic from the other end station by sending a pause frame.

PC

Personal Computer

Photodetector

Used on the receiving end of a fiber optic cable to convert light energy into electrical energy.

PHY

Physical Layer device.

Physical Address

The unique address value associated with a given station on the network. An Ethernet physical address is defined to be distinct from all other physical addresses on the network.

Physical Layer

Layer one of the seven layer ISO Reference Model for Open Systems Interconnection. The physical layer is responsible for the transmission of signals, such as electrical signals, optical signals, or radio signals, between computing machines.

Pin-diode

A photodetector used to convert optical signals to electrical signals in a receiver.

Plastic Fiber

An optical fiber made of plastic rather than glass.

Plenum

The air handling space between the walls, under structural floors, and above drop ceilings used to circulate and otherwise handle air in a building. Such spaces are considered plenums only if they are used for air handling. Work spaces are generally not considered plenums.

Plenum Cable

A cable that is rated as having adequate fire resistance and low smoke producing characteristics for use in air handling spaces (plenum).

Plug

A male connector.

PMD

Physical Media Dependent

POF

Plastic Optical Fiber.

POTS

Plain Old Telephone System

Preamble

A sequence of 64 encoded bits which a station transmits before each frame to allow synchronization of clocks and other physical layer circuitry at other stations on the channel.

Promiscuous Mode

A mode of operation where a device receives every frame on the LAN, regardless of destination address.

Propagation Delay

The signal transit time through a cable, network segment, or device.

Protocol

A set of agree-upon rules and message formats for exchanging information among devices on a network.

PSELFEXT

Power Sum Equal Level Far End Crosstalk

PSNEXT

Power Sum Near End Crosstalk

Pulse

A current or voltage which changes abruptly from one value to another and back to the original value in a finite length of time.

Q

R

Receiver

A device whose purpose is to capture transmitted signal energy and convert that energy for useful functions. In fiber optic systems, an electronic component that converts light energy to electrical energy.

Reflection

A return of electromagnetic energy that occurs at an impedance mismatch in a transmission line, such as a LAN cable.

Refractive Index.

The ratio of the speed of light in a vacuum to its velocity in a transmitting medium, such as an optical fiber core.

Repeater

A device that receives, amplifies (and sometimes reshapes), and retransmits a signal. It is used to boost signal levels and extend the distance a signal can be transmitted. It can connect two or more LAN segments and physically extend the distance of a LAN. It immediately copies all bits arriving on each segment to all other segments, whether or not they are part of a valid frame.

Reversed Pair

A wiring error in twisted pair cabling where the conductors of a pair are reversed between connector pins at each end of a cable.

RFI

Radio Frequency Interference. Electromagnetic interference at radio frequencies.

RG/U

Radio Grade/Universal. RG is the common military designation for coaxial cable.

Ring

1. A polarity designation of one wire of a pair indicating that the wire is that of the secondary color of a 5-pair group (e.g. the blue white wire of the blue pair). 2. A wiring contact to which the ring wire is attached. 3. The negative wiring polarity (see Tip).

Ripcord

A cord placed directly under the jacket of a cable in order to facilitate stripping (removal) of the jacket.

RJ

A term from the telephone industry, used for jacks (connectors) that were registered for use with particular types of telephone services. RJ stands for "registered jack".

RJ-45

A USOC code identifying an 8-pin modular plug or jack used with unshielded twisted pair cable. Officially, an RJ-45 connector is a telephone connector designed for voice grade circuits only. RJ-45 type connectors with better signal handling characteristics are called 8-pin connectors in most standards documents, though most people continue to use the RJ-45 name for all 8-pin connectors.

Round-Trip Propagation Time

In bit times, the time required in the worst case for a transmitting station's collision detect signal to be asserted due to normal contention on the channel. This delay is a primary component of the slot time.

Routers

These are more complex internetworking devices that are also typically more expensive than bridges. They use Network Layer Protocol Information within each packet to route it from one LAN to another.

Running Disparity

A binary parameter having a value of "+" or "-", representing the imbalance between the number of ones and zeros in a sequence of 8B/10B code groups.

Runt Frame

An Ethernet frame that is less than the minimum length of 64-bytes. In a half-duplex Ethernet environment, runt frames are almost always caused by collisions. If runt frames occur when collisions are not high or in a full-duplex Ethernet environment, then they are probably the result of underruns or bad software on a network interface card.

Rx

Receive

S

SC Connector

A fiber optic connector having a 2.5mm ferrule, push-pull latching mechanism, and the ability to be snapped together to form duplex and multifiber connectors. SC connectors are the preferred fiber optic cable for premises cabling, and are recommended by the TIA/EIA-568-A Standard for structured cabling. Used with Ethernet 100Base-FX and 1000Base-LX/SX fiber optic media systems.

Screen

see Shield

Screened Twisted Pair (ScTP) cable

Four pair UTP, with a single foil or braided screen surrounding all four pairs in order to minimize EMI radiation or susceptibility. Screened twisted pair is sometimes called Foil Twisted Pair (FTP). ScTP can be thought of as a shielded version of the Category 3, 4, & 5 UTP cables.

Screened/Shielded Twisted Pair (SSTP)

Four pair cabling, with each pair having its own individual Shield, in addition to an overall shield surrounding all four pairs. SSTP offers similar performance to Type 1 STP except with 4 pairs (rather than 2) and in a 100 ohm impedance (rather than 150).

ScTP

see Screened Twisted Pair cable

Segment

On Ethernet, a media segment may be made up of one or more cable sections joined together to produce a continuous cable for carrying Ethernet signals.

Shared Ethernet

Same as "half-duplex" (CSMA/CD) Ethernet.

Sheath

see Jacket

Shield

A metallic foil or multiwire screen mesh that is used to prevent electromagnetic fields from penetrating or exiting a transmission cable. Also referred to as a "screen".

Shield Coverage

The physical area of a cable that is actually covered by shielding material, often expressed as a percentage.

Shield Effectiveness

The relative ability of a shield to screen out undesirable interference. Frequently confused with the term shield coverage.

Shielded Twisted Pair (STP)

A type of twisted pair cable in which the pairs are enclosed in an outer braided shield, although individual pairs may also be shielded. STP most often refers to the 150 ohm IBM Type 1, 2, 6, 8, & 9 cables used with Token Ring networks.

Signal

The information conveyed through a communication system.

Signal to noise ratio

The ratio of received signal level to received noise level, expressed in dB. Abbreviated S/N. A higher S/N ratio indicates better channel performance.

Signal Quality Error (SQE)

Also called "heartbeat", SQE is a signal sent by transceivers over an AUI cable to an Ethernet NIC. It is sent after a frame is transmitted in order to verify the connection, and is also used by the transceiver to notify a station that a collision was detected. The SQE signal is used primarily in 10Base5 environments as a test signal to reassure the station that the transceiver is still operating correctly. The SQE test should be disabled when a transceiver is connected to a repeater.

Silver Satin

The name for the silver-gray voice-grade patch cable used to connect a telephone to a wall jacket. Typical silver satin patch cables do not have twisted pair wires, which makes them unsuitable for use in LAN applications. The lack of twisted pairs will result in high levels of crosstalk.

Simplex Transmission

Data transmission over a circuit capable of transmitting in one preassigned direction only.

Single Mode Fiber

An optical fiber that will allow only one mode to propagate. The fiber has a very small core diameter of approximately 8 µm. It permits signal transmission at extremely high bandwidth and allows very long transmission distances.

Slot Time

A key parameter for half-duplex Ethernet network operation. Defined as 512 bit times for Ethernet networks operating below 1 Gb/s, and 4096 bit times for Gigabit Ethernet. In order for each transmitter to reliably detect collisions, the minimum transmission time for a complete frame must be at least one slot time, whereas the round-trip propagation delay (including both logic delays in all electronic components and the propagation delay in all segments) must be less than a slot time.

SMA Connector

A threaded type fiber optic connector. The 905 version is a straight ferrule design, whereas the 906 is a stepped ferrule design.

SMF

see Single Mode Fiber

S/N

see Signal to noise ratio

SNR

see Signal to noise ratio

Source

In fiber optics, the device which converts the electrical information carrying signal to an optical signal for transmission over an optical fiber. A fiber-optic source may be a light emitting diode or laser diode.

Spanning Tree

A structure that includes all the bridges and stations on an extended LAN in which there is never more than one active path connecting any two stations.

Splice

A joining of conductors generally from separate sheaths.

Splice Closure

A device used to protect a cable or wire splice.

Split Pair

A wiring error in twisted pair cabling where one of a pair's wires is interchanged with one of another pair's wires. Split pair conditions may be determined with a transmission test. Simple DC continuity testing will not reveal the error, because the correct pin-to-pin continuity exists between ends. However, the error may result in impedance mismatch, excessive crosstalk, susceptibility to interference, and signal radiation.

SQE

see Signal Quality Error

SSTP, S/STP

see Screened/Shielded Twisted Pair

ST Connector

Designation for the "straight tip" connector developed by AT&T. This fiber optic connector features a physically contacting non-rotating 2.5mm ferrule design and bayonet connector-to-adapter mating. Used with Ethernet 10Base-FL and FIORL links.

Stackable Hubs

Hubs that look and act like standalone hubs except that several of them can be "stacked" or connected together, usually by short lengths of cable. When they are linked together they can be managed as a single unit. Also allows users to be added without adding repeater hops, i.e. the entire stack counts as a single logical repeater.

StarLAN

Term used by AT&T for their implementation of the 1Base5 standard.

Star Network

A network in which all stations are connected through a single point.

Star Topology

A network configuration in which there is a central point to which a group of systems are directly connected. All transmissions from one system to another pass through this central point. Ethernet 10Base-T is one example of a media system that uses a star topology. All stations are connected through a central device called a "hub".

Station

A unique, addressable device on a network. A station is identified by a destination address (DA).

Station Address

see MAC Address

Step Index Fiber

An optical fiber in which the core is of uniform refractive index with a sharp decrease in the index of refraction at the core-cladding interface. Step index multimode fibers generally have lower bandwidths than graded index multimode fibers.

STP

see Shielded Twisted Pair

STP-A

Refers to the enhanced IBM Cabling System specifications with the Type "A" suffix. The original IBM Type 1, 2, 6, & 9 specifications were designed to support operation of 4 and 16 Mb/s Token-Ring. The enhanced Type 1A, 2A, 6A, & 9A cable specifications were designed to support operation of 100 Mb/s FDDI signals over copper.

Structured Wiring

Telecommunications cabling that is organized into a hierarchy of wiring termination and interconnection structures. The concept of structured wiring is used in the common standards from the TIA and EIA.

Subminiature D Connector

A family of multipin data connectors available in 9, 15, 25 and 37 pin configurations. Sometimes referred to as DB9, DB15, DB25 and DB37 connectors respectively. An Ethernet AUI connector is a 15-pin subminiature D connector.

Surge

A temporary and relatively large increase in the voltage or current in an electric circuit or cable. Also called transient.

Surge Suppression

The process by which transient voltage surges are prevented from reaching sensitive electronic equipment.

Switch

A switch is a multi-port bridge. Each port on the switch is in its own collision domain.

Synchronous

Transmission in which the data character and bits are transmitted at a fixed rate with the transmitter and receiver being synchronized.

T

Tap

On Ethernet 10Base5 thick coaxial cable, a tap is a method of connecting a transceiver to the cable by drilling a hole in the cable, inserting a contact to the center conductor, and clamping the transceiver onto the cable at the tap.

TDR

See Time Domain Reflectometry

Terminator

A device that provides electrical resistance at the end of a transmission line. Its function is to absorb signals on the line, thereby keeping them from bouncing back and being received again by the network.

Thicknet, Thick Ethernet

Ethernet 10Base5 coaxial cable.

Thinnet, Thin Ethernet

Ethernet 10Base2 coaxial cable. Also called "cheapernet".

TIA

Telecommunications Industry Association. Body which authored the TIA/EIA 568-A "Commercial Building Telecommunications Wiring Standard" in conjunction with EIA.

Time Domain Reflectometry

A technique for measuring cable lengths by timing the period between a test pulse and the reflection of the pulse from an impedance discontinuity on the cable. The returned waveform reveals many undesired cable conditions, including shorts, opens, and transmission anomalies due to excessive bends or crushing. The length to any anomaly, including the unterminated cable end, may be computed from the relative time of the wave return and nominal velocity of propagation of the pulse through the cable. See also Optical Time Domain Reflectometry.

Tip

1. A polarity designation of one wire of a pair indicating that the wire is that of the primary (common) color of a 5-pair group (e.g. the white-blue wire of the blue pair). 2. A wiring contact to which the tip wire is connected. 3. The positive wiring polarity (also see "ring").

Topology

The physical or logical interconnection pattern of a network. See "bus topology" and "star topology".

Transceiver

A combination of the words TRANSmitter and reCEIVER. A transceiver is the set of electronics that send and receive signals on the Ethernet media system. Transceivers may be small outboard devices, or may be built into an Ethernet port. Also called Media Attachment Unit, or MAU.

Transceiver Cable

Same as AUI cable.

Transmission Medium

The cable or other physical circuit that is used to interconnect systems in a network.

Transmitter

A device that converts electrical signals for transmission to a distant point. In fiber optic systems, the electronic component that converts electrical energy to light energy.

Transparent Bridge

A bridge that is used to form an extended LAN consisting of a tree structure in which only one active path connects any two stations in the extended LAN. Stations on the interconnected LANs are not aware of the presence of transparent bridges. Transparent bridges learn appropriate routes for messages by observing transmissions that take place on the LANs to which they are connected and forwarding messages that they receive to the opposite network when required.

Truncated Binary Exponential Backoff

See "Binary Exponential Backoff".

Trunking

See "LInk Aggregation".

Twinaxial Cable, Twinax

A type of communication transmission cable consisting of two center conductors 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. It is similar to coaxial cable except that there are two conductors at the center.

Twisted Pair

A multiple conductor cable whose component wires are paired together, twisted, and enclosed in a single jacket. Each pair consists of two insulated copper wires twisted together. When driven as a balanced line, the twisting reduces the susceptibility to external interference and the radiation of signal energy. Most twisted-pair cabling contains either 2, 4, or 25 pairs of wires.

Tx

Transmit

Type N Connector

A threaded barrel constant impedance coaxial connector for large diameter cable such as Ethernet 10Base5 thicknet cable.

U

Unbalanced Line

A transmission line in which voltages on the two conductors are unequal with respect to ground. Generally one of the conductors is connected to a ground point. An example of an unbalanced line is a coaxial cable.

Unicast Address

An address that is assigned to uniquely identify a single station on a network.

Unshielded Twisted Pair (UTP)

Twisted pair cabling that includes no shielding. UTP most often refers to the 100 ohm Category 3, 4, & 5 cables specified in the TIA/EIA 568-A standard.

UTP

see Unshielded Twisted Pair.

V

Vampire Tap

see Tap

Velocity of Propagation

The transmission speed of electrical energy in a length of cable compared to speed in free space. Usually expressed as a percentage. Test devices use velocity of propagation to measure a signal's transit time and thereby calculate the cable's length.

VGM

Voice Grade Media (see Voice Grade)

Virtual LAN

A method in which a port or set of ports in a bridge or switch are grouped together and function as a single "virtual" LAN.

VLAN

see Virtual LAN

Voice Grade

A term used for twisted-pair cable used in telephone systems to carry voice signals.

W

Wavelength

The distance between successive peaks or nodes of a wave.

wire fault

An error condition caused by a break in the wires or a short between the wires (or shield) in a segment of cable.

Wiring Closet

see Closet

Workgroup

A collection of workstations and servers on a LAN that are designated to communicate and exchange data with one another.

Workstation

A computer connected to a network at which users interact with software stored on the network.

X

X

symbol for "crossover"

Y

Z

0-9

1 Gb/s

One gigabit per second. Equivalent to 1 billion bits per second.

1 Mb/s

One megabit per second. Equivalent to 1 million bits per second.

1Base5

IEEE 802.3 shorthand term for StarLAN at 1Mb/s data transfer rate.

10Base2

IEEE 802.3 shorthand term for 10 Mb/s Ethernet based on Manchester signal encoding over thin coaxial cable. Also called "Thinnet" or "Cheapernet".

10Base5

IEEE 802.3 shorthand term for 10 Mb/s Ethernet based on Manchester signal encoding over thick coaxial cable. Also called "Thicknet".

10Base-F

IEEE 802.3 shorthand term for 10 Mb/s Ethernet based on Manchester signal encoding over fiber optic cable.

10Base-T

IEEE 802.3 shorthand term for 10 Mb/s Ethernet based on Manchester signal encoding over category 3 or better twisted pair cable.

10Broad36

IEEE 802.3 shorthand term for 10 Mb/s Ethernet on broadband cable.

100Base-FX

IEEE 802.3 shorthand term for 100 Mb/s Fast Ethernet based on 4B/5B signal encoding over fiber optic cable.

100Base-T

IEEE 802.3 shorthand term for entire 100 Mb/s Fast Ethernet system.

100Base-T2

IEEE 802.3 shorthand term for 100 Mb/s Fast Ethernet based on PAM5x5 signal encoding and using two pairs of category 3 twisted pair cable.

100Base-T4

IEEE 802.3 shorthand term for 100 Mb/s Fast Ethernet based on 8B6T signal encoding and using four pairs of category 3 twisted pair cable.

100Base-TX

IEEE 802.3 shorthand term for 100 Mb/s Fast Ethernet based on 4B/5B signal encoding and using two pairs of category 5 twisted pair cable.

100Base-X

IEEE 802.3 shorthand term for any 100 Mb/s Fast Ethernet system based on 4B/5B signal encoding. Includes 100Base-TX and 100Base-FX.

1000Base-CX

IEEE 802.3 shorthand term for 1000 Mb/s Gigabit Ethernet based on 8B/10B signaling over copper cable.

1000Base-LX

IEEE 802.3 shorthand term for 1000 Mb/s Gigabit Ethernet based on 8B/10B signaling using long wavelength laser transmitters over fiber optic cable.

1000Base-SX

IEEE 802.3 shorthand term for 1000 Mb/s Gigabit Ethernet based on 8B/10B signaling using short wavelength laser transmitters over fiber optic cable.

1000Base-T

IEEE 802.3 shorthand term for 1000 Mb/s Gigabit Ethernet over twisted pair cable.

1000Base-X

IEEE 802.3 shorthand term for any 1000 Mb/s Gigabit Ethernet based on 8B/10B signaling. Includes 1000Base-CX, 1000Base-LX, and 1000Base-SX.

4B/5B Code

Scheme used to encode data for transmission in which 4-bit binary data values are encoded into 5-bit symbols for transmission across the network media. 4B/5B is used with Ethernet 100Base-TX and 100-Base-FX media systems.

8B6T

Signal encoding method used with the 100Base-T4 Ethernet media system.

8B/10B Code

Scheme used to encode data for transmission in which 8-bit binary data values are encoded into 10-bit symbols for transmission across the network media. 8B/10B is used with 1000Base-X Gigabit Ethernet media systems.

802.1

see IEEE 802.1

802.2

see IEEE 802.2

802.3

see IEEE 802.3