Glossary U-Z

Glossary U-Z
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U.L.: Underwriters' Laboratories, Inc.
UHF: Ultrahigh frequency. The spectrum extending from 300 to 3000 MHz as designated by the Federal Communications Commission.
Unbalanced Line: A transmission line in which voltages on the two conductors are unequal with respect to ground. In most cases, one of the conductors will be connected to a signal ground.
Unilay: A conductor with more than one layer of helically laid wires with the direction of lay & length of lay the same for all layers.
Unity Gain: Refers to the balance between signal loss on a broadband network & signal gain through amplifiers.
Universal Connectivity: A term used to indicate that all hosts or other nodes in a network support at least one communications protocol family (for example, TCP/IP) in common. Since each node can theoretically be connected to any other node on the network.
Unreliable: In the internet protocol suite, unreliable or best effort protocols do not guarantee delivery of data. Any retransmission that is needed is left to upper layers.
Unshielded: Wiring not protected from electromagnetic & radio frequency interference, but covered with plastic & or PVC.
Unshielded Twisted Pairs: (UTP) General term for all cabling systems used for transmission of data which are not shielded.
Utility Software: Programs that make operation of a PC or a LAN more convenient, including programs to move disk files more easily, diagnostic programs, etc.
UTP: See Unshielded Twisted Pairs
V: See Volt
V.10: A CCITT interface recommendation; electrically similar to RS423.
V.11: A CCITT interface recommendation; electrically similar to RS422.
V.21: A CCITT 300 Bps dial modem recommendation; similar to Bell 103.
V.22: A CCITT 1200 Bps dial modem recommendation; similar to Bell 202.
V.22 bis: A CCITT 2400 bps dial or 2-wire leased line modem recommendation.
V.35: CCITT (ITU) standard governing data transmission at 48 Kbps over 60- to 108-KHz group band circuits.
VA: (Volt-ampere) A designation of power in terms of voltage & current.
Value Added Process: (VAP) An application designed to load & run automatically on a NetWare server in order to help manage resources.
VAP: See Value Added Process
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.
Very High Frequency: (VHF) The spectrum extending from 30 to 300 MHz as designated by the Federal Communications Commission. TV channels 2-13 and FM radio are part of this range.
Very Low Frequency: (VLF) The spectrum extending from 10 to 30 KHz, as designated by the Federal Communications Commission.
VG: See Voice Grade
VHF: See Very High Frequency
Video: Pertaining to picture information in a television system or monitor system.
Video Teleconferencing: The real time, & usually two way, transmission of digitized video images between two or more locations; requires a wideband transmission facility, for which satellite communications has become a popular choice; transmitted images may be freeze frame (where a television screen is repainted) every few seconds or full motion; bandwidth requirements for 2 way video conferencing ranges from 56 Kbits/s (freeze frame) to T1 rated (1.544 Mbits/s)
VINES: See Virtual Network Software
Virtual Circuit: A communications link that appears to be a dedicated circuit & passes sequential packets between devices usually in a packet switching network.
Virtual Memory: Technique for using disk storage space to emulate random access memory.
Virtual Network: Separates the logical topology of a LAN from the physical topology, allowing stations distrusted throughout a campus to interact as if they were on a common network segment.
Virtual Network Software: (Virtual Network Software) Banyan’s network operating system based on Unix & its protocols.
Virtual Reality Modeling Language: (VRML) Used to create 3 dimensional constructs. Mainly used on the Internet
Virtual Routing: A form of routing in which a single high speed interface supports an arbitrary number of logical networks.
Virtual Storage: Storage space that may be viewed as addressable main storage, but is actually auxiliary storage (usually peripheral mass storage) mapped into real addresses; amount of visual storage is limited by the addressing scheme of the computer.
Virtual Telecommunications Access Method: (VTAM) On an SNA (Systems Network Architecture) network, this application provides access to shared information.
Virtualization: The ability to separate the physical layout of a network & its devices from how uses are organized into workgroups (knows a logical configuration).
VLF: See Very Low Frequency
Voice Grade: (VG) A channel that is capable of carrying voice-frequency signals.
Volatile Memory: Memory that requires power to hold data, when power is removed, volatile memory loses its data.
Volt: A unit of electrical pressure. One volt is the electrical pressure that will cause one ampere of current to flow through one ohm of resistance.
Voltage: Electrical potential or electromotive force expressed in volts.
Voltage Drop: The voltage developed across a component or conductor by the current flow through the resistance or impedance of the component or conductor.
VRML: See Virtual Reality Modeling Language
VTAM: See Virtual Telecommunications Access Method
W3: See World Wide Web
WAN: See Wide Area Network
Watt: A unit of electrical power. One watt is equivalent to the power represented by one ampere of current with a pressure of one volt in a dc circuit.
Wave Form: A graphical representation of a varying quantity. Usually, time is represented on the horizontal axis, & the current or voltage value is represented on the vertical axis.
Wavelength: The distance an electromagnetic wave travels in the time it takes to oscillate through one cycle. Measured in nanometers (nm) or micrometers (um).
White Noise: A combination of random noises in the transmission media caused by various electrical & magnetic sources. A certain amount of White noise is inevitable in any transmission media.
Wide Area Network: (WAN) A network that includes nodes distributed over a larger geographic area than a LAN.
Wideband: A system in which multiple channels access a medium (usually coaxial cables) that has a large bandwidth, greater than a voice-grade channel; typically offers higher-speed data transmission capability.
Window: In TCP, a receiving node signals the amount of additional data it has space to receive by indicating a certain window value in the window field of the TCP header. The window is a number which indicates how many bytes of data, beyond the last byte it has acknowledged, the receiver can accept. The field in the packet from receiver to sender which indicates the size of the window is referred to as the window advertisement.
Wiring Closet: The central location for routing & terminating of premise wiring systems.
Work Group: A small group of computer, typically person computers & associated file servers, connected via a LAN for departmental level computing & communications.
Workstation: A building space where the occupants interact with telecommunications equipment (corresponds to the “work area” as used in EIA/TIA-568).
World Wide Web: (WWW or W3) The largest type of Network found on the Internet. Conveys information Via a Home Page.
WORM: See Write Once Read Many
Write Once Read Many: (WORM) Optical disk to which data may be written one & not altered, but from which data can be retrieved as often as necessary.
WWW: See World Wide Web
X-On/X-Off: Transmitter On/Transmitter Off. Control characters used for flow control, instructing a terminal to start transmission (X-On) & to end transmission (X-Off).
X.21: A technical specification recommended by the ITU-T that describes the interface used in the ITU-T packet-switching protocol & in some types of circuit switched data transmission.
X.25 CCITT: protocol governing packet-switched networks using virtual circuits.
X.3: Packet Assembler/Disassembler (PAD) facility in a PDN.
X.400 CCITT: protocol governing international electronic mail transmissions.
Xenix: Microsoft trade name for a 16-bit microcomputer operating system derived from Bell Laboratories' UNIX.
Xerox Network Systems: (XNS) Xerox's data communication protocols.
XNS: See Xerox Network Systems
Zero Insertion Force Socket: (ZIF Socket) Created for Easier replacement of the CPU.
ZIF Socket: See Zero Insertion Force Socket
Zone: One or more connected AppleTalk networks grouped according to network usage.

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