U

UNIX
UNIX is an operating system used in many workstations and mid-range computer systems. It is an alternative to PC and Macintosh computer operating systems.

UNIX-to-UNIX Copy Program (UUCP)
UUCP is a protocol used for communication between consenting UNIX systems.

Unshielded Twisted Pair (UTP)
UTP is the most common type of network cabling, and is used extensively in telephone networks and many data communications applications. UTP can carry a 100 Mbps-digital signal 100 meters using twisted pairs of cable without requiring that the signal to be repeated.

UPS
UPS stands for Unterruptible Power Source (or supply). It is a power supply that includes a battery to maintain power in the event of a power outage.

Unicast
Unicast is a frame addressed to one individual node.

Uninterruptible Power Supply (UPS)
UPS is an emergency backup power source that instantly takes over when the regular electrical power fails.

Unroutable Protocol
An unroutable protocol is a network protocol that does not support routing at OSI Layer 3, such as NetBIOS or DEC-LAT. An unroutable protocol does not create packets, therefore, Layer 3 devices such as routers cannot be used. NetBEUI, an 802.2 protocol, is another example of an unroutable protocol.

Uplink Port
An unroutable protocol is a network protocol that does not support routing at OSI Layer 3, such as NetBIOS DEC-LAT. An unroutable protocol does not create frames, thus Layer 3 devices such as routers cannot be used.

User Datagram Protocol (UDP)
UDP is part of the TCP/IP protocol suite. UDP provides a simple, connectionless datagram delivery service, without error checking, for certain specialized application services that do not require the full services of TCP.

User-Network Interface (UNI)
UNI is the interface between an ATM user and ATM network. A private UNI defines the interface between an ATM user device and private ATM switch. A public UNI defines the interface between an ATM user device or private ATM switch, and an ATM switch deployed in a public ser­vice provider's network.

Utlilization
Utilization refers to the amount of bandwidth being used at a given point in time or over a period of time. For instance, if a 10Mbps Ethernet LAN is running at 40% utilization, it is using 4 of the 10Mbps available bandwidth.

V

Version control
An application that tracks changes made to a document (or programming source code), and can retrieve a particular version of a document when necessary, is referred to as version control.

Very High-Speed Backbone Network Service (vBNS)
vBNS is an experimental high-speed WAN backbone jointly created in 1995 by the NSF and MCI.

Virtual Channel
A virtual circuit is a communication path that appears to be a single circuit, even though the data may take varying routes between the source and destination nodes.

Virtual Channel Identifier (VCI)
VCI is a value in an ATM cell header that uniquely identifies one ATM virtual channel. Each virtual channel is one data transmission from a source node to a destination node.

Virtual Channel (VC)
All ATM cells that form a single transmission from a source to a destination are referred to as a VC.

Virtual Circuit
A virtual circuit is a communication path that appears to be a single circuit, even though the data may take varying routes between the source and destination nodes.

Virtual Local Area Network (VLAN)
A VLAN is a group of computers in a large LAN that behave as if they are connected to their own small private LAN. VLANs are created using special switches and software, so computers can be assigned to different VLANs without changing their physical configuration.

Virtual Path
A virtual path is a group of two or more ATM virtual channels traveling from the same source to the same destination.

Virtual Path Identifier (VPI)
VPI is value in an ATM cell header that identifies a group of ATM virtual channels moving from the same source to the same destination.

Virtual Private Network (VPN)
VPNs rely on end-to-end network encryption, enabling a secure connection to be established from machine to machine. Each VPN is an encrypted data stream that travels over the same public network, such as the Internet.

Visual Basic Scripting Edition (VBScript)
Microsoft's VBScript is similar to its VB, but is simpler to use. VBScript is natively supported by Microsoft ASP, and is preferred for writing ASP server-side script blocks. Microsoft Internet Explorer supports client-side VBScripts, but the lack of VBScript support in Netscape Navigator limits this practice. Many ASP developers follow the mantra "JScript on the client, VBScript on the server."

Virus
A self-replicating malicious program that spreads by attaching itself to a file is referred to as a virus. Viruses can spread quickly through a network, with effects that range from mildly irritating to highly destructive.

W

Wide Area Network (WAN)
A WAN is the part of a network that connects users to networks, or networks to networks over long distance.

Wiring Closet
A wiring closet is a centralized (often secure) location where cable segments are attached to Network Design. Cables run from each node to the wiring closet, where the cables are connected to hubs, switches, or routers.

Wire Speed
Wire speed refers to transmission that is not slowed down by the processing of an internetworking device.

Workaround
A workaround is a practical survival technique, in which users eliminate the effect of a programming bug by changing they way they use a system. For example, a user workaround may change the style of data input to achieve a certain type of output. Unfortunately, many workarounds become so widely used that programmers are discouraged from fixing the original bugs (and thereby creating unexpected outputs from the workarounds).

Workstations
Workstations are a type of computer, typically more powerful than a PC, but still used by a single user.

World Wide Web Consortium (W3C)
W3C is an independent industry organization that works to develop technically sound open standards for the Web.

World Wide Web (Web)
The Web is a public domain hypertext application used for finding and retrieving information on the Internet.