GLOSSARY

100 Base-TX�100 Mbps 802.3/Ethernet over standard UTP cable. Also called Fast Ethernet, it used RJ-45 connectors and EIA/TIA T568B pinning. Maximum cable length from hub to node is 100 meters without a repeater.

Active Terminator�A terminator that can compensate for variations in the terminator power supplied by the host adapter through means of a built-in voltage regulator. See also Forced Perfect and Passive Terminators.

Attenuation�Loss of signal strength as a function of distance. In optical fibre, it is the �dimming� of the light as it travels through the fibre expressed in decibels per unit (dB/km).

AUI�Attachment User Interface. Most commonly used with reference to the 15 pin D type connector and the cables used to connect single and multiple channel equipment to an Ethernet transceiver.

Backbone�The part of the network that carries the heaviest traffic. It is the main trunk cable from which all connections to the network are made.

Balun�(Balanced/Unbalanced) An impedance matching device to connect balanced twisted pair cabling with unbalanced coaxial cable.

Bandwidth�The data-carrying capacity of a transmission medium, usually measured in hertz (Hz) which equals cycles per second.

BPS�Bits per second. Often preceded by K (kilo/thousand) or M (mega/million).

Buffer�The material that surrounds the fibre cladding in a fibre optic cable construction.

Bus�A collection of wires in a cable (or copper traces on a circuit board) used to transmit data, status, and control signals. ISA, EISA, VL-Bus and PCI are examples of PC buses. SCSI is also a bus, as is a Local Area Network topology in which all workstations are connected to a single cable. On a bus network all workstations hear all transmissions on the cable. Each workstation then selects those transmissions addressed to it based upon address information contained in the transmission.

Bus Mastering�A method of transferring data through a bus in which the device takes over the bus and directly control the transfer of data to the computer�s memory. Bus mastering is a method of Direct Memory Access (DMA) transfer.

Cladding�The transparent material, usually glass, that surrounds the core of the optical fibre. Cladding glass has a lower refractive index than core glass.

Core�The centre of an optical fibre. The core of communications grade fibre is made of glass that has a higher refractive index than the surrounding cladding glass.

Cross Connect�The physical connection between patch panels or punch down blocks that facilitates connection from the workstation to the host or network.

Crosstalk�The unwanted introduction of signals from one channel to another.

Crossover Cable- An RJ-45 cable that allows you to connect two network cards without the use of a hub or two hubs without using a uplink (crossover) port.

D-sub Connector�A widely used family of connectors probably deriving its name from its 'D� shape. Specific connectors are denoted by a letter for its size and a number for its pin configuration. For example, a DB-15 connector is a D-sub connector of size B, with pin configuration number 15.

Differential�A SCSI bus configuration in which each signal is sent on two wires. The signal is derived by taking the difference in voltage between the two wires, effectively eliminating unwanted noise in the wire.

DTE�(Data Terminal Equipment) The RS232-C standard referring to equipment that transmits data on pin 2 and receives data on pin 3. This standard typically applies to terminals, PCs and printers.

EIA 568�(Electronic Industries Association) A commercial building wiring standard for voice and data communications developed in 1989 by the EIA.

EMI�Energy generated by outside sources, such as lighting systems and electric motors, which is received by copper data/voice cable and interferes with transmission.

Fast SCSI�The common nomenclature associated with SCSI-2, the second generation of SCSI offering mandatory parity checking improvements over SCSI-1.

Forced Perfect Terminator�A type of terminator containing a sophisticated circuit that can compensate for variations in the power supplied by the host adapter, as well as variations in bus impedance of complex SCSI systems. See also Active and Passive Terminators.

Home Run�A cable usually consisting of two, three or four pair cable run from a wall plate in a fixed wall office to a termination point at the distribution frame.

IEEE�Institute of Electrical and Electronic Engineers. An international professional society that issues its own standard and is a member of ANSI (American National Standards Institute) and ISO.
IEEE 802.3�is a physical layer standard for 10 Base T, 100 Base T, Ethernet and Starlan.
IEEE 802.5�is a physical layer standard for Token Ring.
IEEE 802.11� is a physical layer standard for Wireless LAN/WAN compatibility.
IEEE 802.12� is a physical layer standard for 100VG AnyLAN.

Impedance�A measure of a material�s resistance to the transfer of electricity.

ISDN (integrated Services Digital Networking)�A CCITT defined standard for a public-switched service that allows the digital transmission of voice, data and video over one network.

LAN�(Local Area Network) A data communications network spanning a limited area. It allows communication between three or more computers and peripherals, in most cases using a high-speed media as its backbone.

Mbps�Megabits per second.

P-cable�A 68-wire cable used for 16-bit SCSI-3 buses. P-cables can be used with Q-cables for 32-bit SCSI-3 buses.

Passive Terminator�A terminator that provides a fixed-value impedance match between the end of the SCSI bus and the cable. Passive terminators are comprised only of resistors and are susceptible to variations in the power supplied by the host adapter. Also see Active Terminators.

Patch Cord�The connecting cord between the terminal device and the drop.

PCI (Peripheral Component Interconnect)�A motherboard connection slot that supports 32-bit bus transfer rates.

Ring�A Local Area Network topology in which data is sent from workstations via a loop or ring. One conductor or a pair (versus tip).

SCSI (Small Computer System Interface)�An intelligent bus for transmitting data and commands between a variety of devices. There are many implementations of SCSI, including Fast SCSI, Wide SCSI, Fast Wide SCSI, Fast-20 and Fast-40.

SCSI-2�The second generation of SCSI. Includes many improvements to SCSI-1, including Fast SCSI, Wide SCSI and mandatory parity checking.

SCSI-3�The third generation of SCSI. Introduces Fast-20 and Fast-40 as improvements to the parallel bus. The standard also includes a number of specifications for high-speed serial bus architectures such as SSA, Fibre channel and IEEE 1394. Also known as Ultra SCSI.

SEQUENCE OPTIONS � The way that a twisted pair cable is connected to an RJ-45 connector is called a sequence option, the two most common are shown below:

EIA 568B�This has become the most widely specified sequence worldwide for new data installations. It is also a subset specified by the IEEE 802.3 10 Base�T Ethernet over twisted pair standards.

10 Base�T�This is a modification of the EIA 568B sequence, leaving pair #1 open and starting with pair #2. This provides an additional level of protection from interconnection of voice and data equipment. If voice equipment is always wired on pins 4 and 5 (pair #1) and data equipment never has pins 3 and 4 active, no interconnection is possible.

ST®�A registered trademark of AT&T for their fibre optic connector. Originally an acronym for �straight tip�.

Terminator�An electrical circuit attached to each end of a SCSI bus to minimise signal reflections and extraneous noise. SCSI defines passive, active and forced-perfect termination schemes.

Topology�The architecture of a network, or the way circuits are connected to link the network nodes together.

Transceiver�A device used in contention networks for sending data over the network and receiving data from the network.

Twisted Pair�Two wires twisted together to reduce susceptibility to RF crosstalk.

Ultra SCSI�Also known as SCSI-3. Is a third generation SCSI standard that introduced parallel bus speed improvements (Fast-20 and Fast-30) and the miniaturised 68-pin micro connector.

USB�(Universal Serial Bus) consolidates serial, parallel, keyboard, mouse and game ports into one a synchronous and isochronous communications port with bandwidth for data transfer speeds up to 12 Mbs/sec without termination. By daisy-chaining USB hubs, up to 127 I/O devices can be connected to one USB port on the PC. USB is completely plug n� play, meaning peripherals can be correctly detected and configured automatically as soon as they are connected.

UTP�Unshielded Twisted Pair. Twisted pair cable with neither individual nor overall shielding.

Wavelength�The distance an electromagnetic wave travels during the time it takes to oscillate through one complete cycle. The wave-lengths of light used in fibre communications are usually measured in nanometres (NM). The common wavelengths or �windows� are 850 nm, 1300 nm and 1550 nm.