Glossary U-Z0-A | B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T | U-Z
B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T |
Underwriters' Laboratories, Inc.
- UHF: Ultrahigh frequency. The
spectrum extending from 300 to 3000 MHz as designated by the Federal
- 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
- Unilay: A conductor with more than one layer of helically
laid wires with the direction of lay & length of lay the same for all
- Unity Gain: Refers to the balance between signal loss on a
broadband network & signal gain through amplifiers.
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.
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
- 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
- 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
- Very Low Frequency: (VLF) The spectrum
extending from 10 to 30 KHz, as designated by the Federal Communications
- VG: See Voice Grade
- VHF: See
Very High Frequency
- Video: Pertaining to picture
information in a television system or monitor system.
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
- VINES: See Virtual Network
- 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
- Virtual Network Software:
(Virtual Network Software) Banyan’s network operating system based on Unix &
- Virtual Reality Modeling Language:
(VRML) Used to create 3 dimensional constructs. Mainly used on the
- Virtual Routing: A form of routing in which a single high
speed interface supports an arbitrary number of logical networks.
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
- Virtual Telecommunications Access
Method: (VTAM) On an SNA (Systems Network Architecture) network, this
application provides access to shared information.
The ability to separate the physical layout of a network & its devices from how
uses are organized into workgroups (knows a logical
- VLF: See Very Low
- 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
- 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
- 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).
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
- 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
- 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.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
- X.3: Packet Assembler/Disassembler (PAD) facility in a
- X.400 CCITT: protocol governing international electronic mail
- Xenix: Microsoft trade name for a 16-bit microcomputer
operating system derived from Bell Laboratories' UNIX.
- Xerox Network Systems: (XNS) Xerox's data communication
- XNS: See Xerox Network Systems
- Zero Insertion Force Socket: (ZIF Socket) Created for Easier
replacement of the CPU.
- ZIF Socket: See Zero Insertion
- Zone: One or more connected AppleTalk networks
grouped according to network usage.