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Appendix A: Ethernet Glossary
A B C D E F G H I
J K L M N O P Q R
S T U V W X Y Z 0-9
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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.
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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".
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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K
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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
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