Verizon Communications. The company created on June 30, 2000, by the merger of Bell Atlantic and GTE. According to Verizon Communications, Verizon (pronounced Vurr-EYE-zon) comes from the Latin words "veritas," and "horizon." "Veritas" means truth, and also connotes certainty and reliability. "Horizon" refers to the apparent junction between earth and sky, and signifies the endless possibilities ahead. See also Bell Atlantic and GTE.


Very Easy Rodent Oriented Netwide Index to Computerized Archives. An Internet service that allows users to search Gopher systems for documents.


Versit is a loose association between Apple, AT&T, IBM and Siemens Rolm. Its "vision"? To "enable diverse communication and computing devices, applications and services from competing vendors to interoperate in all environments. Communicate and collaborate with anyone , any time, anywhere .." The products include PDAs, notebooks , phones, servers and "collaboration products." One early thrust : standardize on call control within Novell/AT&T's Telephony Services. Background: Call control among PBXs "conforming" to Telephony Services is not standard. PBXs often do the same things differently. Example: Conference a call on one PBX, the PBX may put one call automatically on hold as the other is dialed . Another PBX may expect it to be done manually. The good news: IBM has agreed to pass all its CallPath call control standards over to Versit. Versit's members (including Novell coopted for this task) are now working on making Telephony Services call control more standard. Upshot: Developers won't have to test their "standard" telephony services software on each and every PBX. What works on one will work on the others. That's the goal. In late July 1995, Versit effectively merged all its activities into another association, called ECTF. ( See ECTF and PBX Driver Profiles.


A vCard. See vCard.

Vertex Shader

A graphics term . A graphics function, much like a pixel shader, that runs on the GPU and operates on vertices (interesting lines or curves) and hence polygons. It lets programmers add complex special effects to objects in a 3-D world. Game developers can design custom animation effects using programmable vertex shaders.


Descriptive of the "vertical side" of a North American wire distributing frame, on which terminal blocks for cables are mounted vertically, as opposed to the horizontally- mounted blocks on the equipment side of the frame. Frames of vertical-only blocks are not uncommon at intermediate cable connection points between main frames , hence the term Vertical Intermediate Distributing Frame, or VIDF.

Vertical And Horizontal Coordinates

V & H Coordinates. For purposes of determining airline mileage between locations, vertical and horizontal coordinates have been established across the United States. These V&H coordinates are derived from geographic latitude and longitude coordinates. See V & H.

Vertical Beamwidth

See Elevation Beamwidth.

Vertical Blanking Interval

The interval between television frames in which the picture is blanked to enable the trace (which " paints " the screen) to return to the upper left hand corner of the screen, from where the trace starts, once again, to paint a new screen. Several companies are eyeing the vertical blanking interval as a place to send digital data, including news and weather information. The vertical blanking interval was the basis of teletext, a 1970s technology that, with the help of a decoder, displays printed information on the TV screen. Teletext has never caught on in the U.S. in part because the amount of data that could be transmitted comfortably was small. Currently the vertical blanking interval is used to transmit closed-captioned text in television broadcasts. See Closed Captioning.

Vertical Cavity Surface Emitting Laser

See VCSEL (pronounced "VIX-els").

Vertical Integration

A firm is vertically-integrated when it owns or controls a firm in an upstream or downstream market. For example, a coal- fired power station which owns a coal mine is vertically-integrated.

Vertical Interval

The portion of the video signal that occurs between the end of one field and the beginning of the next . During this time, the electron beams in the cameras and monitors are turned off (invisible) so that they can return from the bottom of the screen to the top to begin another scan.

Vertical Linearity

A video term. A control that allows you to set spacing consistently across the monitor. Thus a shape intended to have a 1-inch diameter will have a 1- inch diameter wherever it appears.

Vertical Market Application

An application that is industry-specific and typically very task-specific .

Vertical Portal

A website that caters to one industry and purports to have everything that someone interested in that industry would want in their daily life.

Vertical Redundancy Check

VRC. A relatively poor method of error control used in asynchronous transmission in support of the ASCII coding scheme. A check bit, or parity bit added to each ASCII character in a message such that the number of bits in each character, including the parity bit, is odd (odd parity), or even (even parity). The term comes from the fact that the bits representing each character of data conceptually is viewed in a vertical fashion. For instance, the word "CONTEXT" consists of 7 letters , each of which consists of 7 bits, viewed as follows :



1 [*]

1 1 0 0 1 0 0

2 [*]

1 1 1 0 0 0 0

3 [*]

0 1 1 1 1 0 1

4 [*]

0 1 1 0 0 1 0

5 [*]

0 0 0 1 0 1 1

6 [*]

0 0 0 0 0 0 0

7 [*]

1 1 1 1 1 1 1

8 [**]

0 0 1 0 0 0 0



Vertical Scanning Frequency

An imaging term. The rate at which the electron beam traces across vertical phosphor dots on the CRT.

Vertical Service

Options that the customer can add to his basic service such as touchtone, conference calling, speed dialing, etc. No one can explain why it's called "vertical" service.

Vertical Service Code

VSC. Customer-dialed codes that provide access to certain features and services provided by Local Exchange Carriers (LECs), Interexchange Carriers (IXCs), Commercial Mobile Radio Service (CMRS) providers, and others. Such services include call forwarding, automatic callback, and customer-originated call trace. The VSC format is *XX or *2XX for touchtone access, and 11XX or 112XX for rotary dial access. For example, call forwarding is invoked by dialing *72 for touchtone, or 1172 for rotary dial. Vertical service code assignments are available at:

Very High Data Rate Digital Subscriber Line


Very High Frequency

VHF. Frequencies from 30 MHz to 300 MHz.

Very Large Scale Integration

VLSI. Semiconductor chip with several thousand active elements or logic gates ” the equivalent of several thousand transistors on a single chip. VLSI is the technique for making the micro chip, the so-called "computer on a chip."

Very Long Event

A local area network term. A very long event is the condition that occurs when the repeater is forced to go into a jabber protection mode because of the excessive number of times a port receives a packet.

Very Low Frequency

VLF. Frequencies from 3 KHz to 300 KHz.

Very Short Reach

See VSR.

Vertical Refresh Rate

The number of times the monitor redraws its screen every second. A too-low refresh rate can result in flicker, causing eyestrain.


Video Electronics Standards Association, San Jose, CA. Along with eight leading video board manufacturers, NEC Home Electronics founded VESA in the late 1980s. The association's main goal is to standardize the electrical, timing, and programming issues surrounding 800 x 600 pixel resolution video displays, commonly known as Super VGA. VESA has also issued a standard called "local bus," a new high-speed bus for the PC designed to move video between the CPU and the screen a lot faster than the conventional AT bus.


Very Early Smoke Detection System Alarm. Used in data colocation centers to alert the Network Operation Center's technical staff of a possible fire before the sprinklers go off and destroy all the equipment.

Vestal Virgin

A celibate woman who tended the sacred fire in the temple of Vesta in ancient Rome. There were originally four, and eventually six vestal virgins. They stayed on the job for 30 years by which time they'd probably lost all interest in having sex. It's hard to imagine why you need six people to tend one little fire.

Vestigial Sideband

A partially suppressed sideband.

Vestigial Sideband Transmission

VSB. A modified sideband transmission technique in which one sideband and the carrier are suppressed, and only a portion of the remaining sideband is transmitted. Reduced power requirements is an advantage. See also Amplitude Modulation, DSBSC, DSBTC, and SSB.


  1. Voice Frequency.

  2. Variance Factor. An ATM term. VF is a relative measure of cell rate margin normalized by the variance of the aggregate cell rate on the link.


An earlier name for the 56Kbps modem spec. See 56 Kbps Modem.


Virtual File Allocation Table. A fat file system is a file system based on a file allocation table, maintained by the operating system, to keep track of the status of various segments of disk space used for file storage. The 32-bit implementation in Windows 95 is called the Virtual File Allocation Table (VFAT). An extension of the FAT file system in DOS and Windows 3.xx, VFAT supports long filenames while retaining some compatibility with FAT volumes . See also FAT.


Voice Frequency Directory Number. A Northern Tom term.


Virtual Facilities Group. A way of limiting inbound calls to a specific number on a PRI. See Virtual Facilities Group .


Variable Frequency Oscillator.


Voice Frequency TeleGraph.


Voice Frame Relay Access Device. A CPE (Customer Premises Equipment) device used in Voice over Frame Relay (VoFR), a VFRAD is used for access to a Frame Relay network in support of voice communications. There must be matching FRADs at all locations on the network, as there must be matching logic in place for compression and decompression . See also FRAD, Frame Relay and VoFR.


Voice Grade. A term commonly applied to describe a circuit or channel of sufficient bandwidth to support voice communications. An analog voice grade circuit or channel provides bandwidth of 4 KHz. A digital voice grade circuit or channel provides bandwidth of 64 Kbps under traditional PCM encoding, but can be less using IP telephony.


Video Graphics Array. A graphics standard developed by IBM for the IBM PC. VGA allows the PC's screen to generate any of four levels of resolution ” with one of the sharpest being 640 horizontal picture elements, known as pels or pixels, by 480 pels vertically with 16 colors. VGA is superior to earlier graphics standards, such as CGA and EGA. VGA is barely adequate for CAD-CAE. See Monitor for all the numbers on pixels in various screens. VGA was the graphics standard introduced for IBM PS/2 line and quickly adopted by PC compatibles; supports analog monitors with a 31.5 Hz horizontal scan rate. Today VGA is about the lowest graphics resolution most computers support.


Voice Grade Equivalent. A term commonly applied to a level of digital bandwidth sufficient to support a voice conversation using standard encoding techniques-i.e., 56/64 Kbps using PCM (Pulse Code Modulation). Voice Grade (VG) generally refers to an analog local loop circuit which provides 4 KHz bandwidth. See also VG.


Voice Grade Facility.


Voice Grade Private Line.


Very High Density. Techniques of recording 20 megabytes and more on a 3 1/2" magnetic disk.


Very High Frequency. Portion of the electromagnetic spectrum with frequencies between about 30 MHz and 300 MHz. Operating band for radio and television channels. See VHF Drop-Ins.

VHF Drop-Ins

Full power VHF TV stations that may be squeezed into locations that do not comply with the FCC's spacing requirements.


Virtual Host Interface.


Video Home System using half-inch tape introduced by Matsushita/JVC in 1975 and now the most popular form of video tape. There is also a VHS at 3/4". It's often used inside ad agencies for previewing work in progress. Industrial video tape ” the stuff the TV stations use ” is one inch. And it shows a much better quality picture than half-inch VHS.

VI Architecture

See Virtual Interface Architecture


See Vendors Industry Association.

Via Net Loss

VNL. A planning factor used in allocating the attenuation losses of trunks in a transmission network. A specified value for this loss is selected to obtain a satisfactory balance between loss and talker echo performance. The lowest loss in dB at which it is desirable to operate a trunk facility considering limitations of echo, crosstalk, noise and signing.

Vibratory Plow

A plow that rips open the ground by vibrating a plow share.

Vibration Isolation

High precision technique for the alignment of tiny objects. Allows micropositioning to reliably occur.


Voice Interface Card. Connects a system to either the PSTN or to a PBX.


From Latin, translated as "I see," video adds the element of sight to communications. While some of us are visually-oriented, and others of us are more oriented kinesthetically-oriented (learn by doing, as in with muscles and tendons and energy and sweat), we all find a communication to be enhanced through pictures... especially motion pictures. Motion pictures are the essence of video, and video is the essence of true and full communications. Visual communications, by the way, are also extremely bandwidth- intensive . See Multimedia.

Video Capture

Video Capture means converting an analog video signal into a digital format that can be saved onto a hard disk or optical storage device and manipulated with graphics software. This is accomplished with a device internal in a computer called a "frame grabber" or video capture board. Images thus captured are digitized, and can be dropped into a document or database record and may be transmitted locally on a LAN or long distance over a WAN. See Video Capture Board.

Video Capture Board

To capture a single frame of motion video successfully, you need a board inside your PC that can capture the two fields comprising a single video frame. The best source of single frame video images is a laser disk player which can pause and display a perfect frame of video without noise or jitter. Video cameras or camcorders aimed at a static, non-moving image also work well. VCR, which produces a jittery image when the tape is paused , are the poorest source. See also Frame Grabber.

Video Codec

The device that converts an analog video signal into digital code.

Video Compression

A method of transmitting analog television signals over a narrow digital channel by processing the signal digitally. You can compress an analog TV signal into one T-1 signal of 1.544 megabits per second. More advanced compression techniques will enable video signals to be compressed into fewer bits per second. One increasingly common method allows a full- color reasonably full-motion video to be compressed into two 56 Kbps channels.

Video Conference

See Videoconference.

Video Dial Tone

Video dial tone in telco-speak means the phone company, in competition with the cable TV business, provides video to houses and offices. It does not affect the content of that video signal in any way. Thus the term video dial tone, which is like voice dial tone, whose content the phone company also does not affect or change in any way, shape or form. Video Dial Tone was named by the FCC, for a service in which subscribers can dial up any video program they wish across a network. The FCC proposed rules for telephone companies to provide Video Dial Tone in 1992, and finalized them in 1994. Included were the rules for common-carrier transport (level two Video Dial Tone). Telephone companies must apply (with "section 214" applications) to the FCC for approval to provide the Video Dial Tone service. The FCC reviews these applications on a case-by- case basis.

Video Driver

A piece of software which translate instructions from the software you are running into thousands of colored dots, or pixels, that appear on your video monitor. A video driver is also called a display Driver. Symptoms of a video driver giving trouble can range from colors that don't look right, to horizontal flashing lines to simply a black screen. In the Macintosh world, Apple rigidly defined video drivers. Windows, in contrast, is a free- for-all. Windows 3.1 defined the lowest common denominator of displays ” namely 16 colors at 640 x 480 pixels. But most multimedia programs and many games won't run with only 16 colors. They require at least 256 colors.

Video Electronics Standards Association


Video Mail

Electronic mail that includes moving or still images.

Video Memory

See Shared Video Memory.

Video Modulator

A device used to place video information on higher frequency signals for transmission.

Video Monitor

A high quality television set (without RF circuits) that accepts video baseband inputs directly from a TV camera, videotape recorder, etc.

Video Networking

I first saw the term video networking in a white paper written by L. David Passmore of Decisys, Inc. The white paper was in a press kit from Madge Networks, announcing new video hardware architecture. David wrote "When people typically think of video networking, they think of it as an application, namely video confer- encing. However, video networking is really an architecture that supports a range of business applications featuring video communications. These applications can be deployed over the video network to span the LAN and WAN environments. Furthermore, if the video network is deployed properly, it can provide a consolidated (data, voice and video) WAN access solution across the enterprise."

Video On Demand

VOD. Punch some buttons . Order up Gone With the Wind to start playing at your house at 8:26 P.M. on Channel 35. Bingo, you have video on demand. It's a great concept with two major problems: The equipment to provide the service is complex and expensive. Second, there's little consumer research on whether consumers are prepared to pay the high price that will be necessary. Still, it's a neat idea. In short, video on demand is a service that allows many users to request the same videos at the same time or anytime . Video on demand requires a high-end video server with hundreds of gigabytes of storage. See NVOD, Video Dial Tone and Video Server.

Video On Demand

The virtual VCR" service, where a subscriber can watch any video program at any time, with pause, resume, forward and possibly re-wind control. Compare to Near-Video-on-Demand.

Video Path

The electronic path within the device that routes and processes the video signals. Video path length refers to the amount of time required for a signal to travel from input to output.

Video Pill

A camera about the size of a vitamin pill that, when ingested, transmits images from a person's stomach and intestinal tract . Gives new meaning to the term "The Last Mile."

Video Processing Amplifier

A device that stabilizes the composite video signal, regenerates the synchronizing signals, and allows other adjustments to the video signal parameters.

Video Scaler

Video scalers are used to convert television-video signals to computer- video signals. Until recently, devices called line doublers were used for this, but they cause images processed through projectors to become distorted , and are limited to a 4:3 aspect ratio and a refresh rate of 60Hz. A video scaler's processing algorithms can manipulate the signal to best fit the display or projector, and allow you to choose the refresh rate and aspect ratio.

Video Server

A device that could store hundreds, if not thousands of movies, ready for watching by subscribers at their individual whim. A video server could be jukebox like device that would stack several hundred movies. Or it could be a powerful, large computer with several large hard disks and/or optical disk drives . The device would be used in conjunction with the local telephone companies' service called video dial tone ” providing movies over normal phone lines to their subscribers or it could be used with the CATV industry's Video On Demand service. A video server could also simply sit on a home local area network and feed movies to various TVs in various parts of your suburban mansion.

Video Signal

Transmission of moving frames or pictures of information requiring frequencies of 1 to 6 Megahertz. A commercial quality full-color, full-motion TV signal requires 6 MHz.

Video Switcher

Device that accepts inputs from a variety of video sources and allows the operator to select a particular source to be sent to the switcher's output(s). May also include circuits for video mixing, wiping, keying, and other special effects.

Video Teleconferencing

Also called Videoconferencing. The real-time, and usually two-way, transmission of digitized video images between two or more locations. Transmitted images may be freeze-frame (where television screen is repainted every few seconds to every 20 seconds) or full motion. Bandwidth requirements for two-way video- conferencing range from 6 MHz for analog, full-motion, full-color, commercial grade TV to two 56 Kbps lines for digitally-encoded reasonably full motion, full color, to 384 Kbps for even better video transmission to 1,544 Mbit/s for very good quality, full-color, full motion TV. See also Videoconferencing.

Video Telephony

Real time video call similar to a voice call.

Video Wall

Multi-screen video system where a large number of video monitors (typically 16 monitors arrayed in a 4 x 4 matrix) or back projection modules together produce one very large image or combinations of images. Video walls come with their own software, which lets you program the video effects you want. Typically, you can feed a video wall everything from VGA computer output to moving TV (NTSC) signals. Video walls are used for exhibitions and trade shows. They're not cheap. But, when programmed properly, they ARE spectacular.

Video Windows

A Bellcore invention which is basically a large, high capacity video conferencing device. Bellcore's Video Windows are connected by two optical links, each carrying 45 million bits of information per second. Though impressive, Bellcore's Video Windows is not considered "high definition" TV. For that to happen, you'd probably need 100 to 150 million bits being transmitted in both directions each second.

VideoCipher II

VC. An encryption system belonging to M/A COM.


Videoconference is to communicate with others using video and audio software and hardware to see and hear each other. Audio can be provided through specialized videoconferencing equipment, through the telephone, or through the computer. Videoconferencing has traditionally been done with dedicated video equipment. But, increasingly personal computers communicating over switched digital lines are being used for videoconferencing. See also Videoconferencing.


Video and audio communication between two or more people via a videocodec ( coder /decoder) at either end and linked by digital circuits. Formerly needing at least T-1 speeds (1.54 megabits per second), systems are now available offering acceptable quality for general use at 128 Kbit/s and reasonable 7 KHz audio. Factors influencing the growth of videoconferencing are improved compression technology, reduced cost through VLSI chip technology, lower-cost switched digital networks ” particularly T- 1, fractional T-1, and ISDN ” and the emergence of standards. See Videoconferencing Standards.

Videoconferencing Standards

ITU-T H.261 was the standards watershed . Announced in November 1990, it relates to the decoding process used when decompressing videoconferencing pictures, providing a uniform process for codecs to read the incoming signals. Originally defined by Compression Labs Inc. Other important standards are H.221: communications framing; H.230 control and indication signals and H.242d: call setup and disconnect. Encryption, still-frame graphics coding and data transmission standards are still being developed.


A French encryption system created by the Thomson Company.

Videophone 2500

In January, 1992, AT&T introduced a product called Videophone 2500, which transmitted moving (albeit slowly-moving) color pictures over normal analog phone lines. The phone carried a price tag $1,500 a piece. It was not compatible with one MCI later introduced, made for it by GEC-Marconi of England and costing only $750 retail. Videophone 2500 relies on video compression from Compression Labs, Inc. of San Jose, CA. According to the New York Times, the phone took two years, about $10 million and 30 full-time people at AT&T to develop. The January 3, 1993 New York Times carried a quote from John F. Hanley, group VP for AT&T consumer products division, "We could make an AT&T phone talk to an MCI phone. It would be in both of our interests." The AT&T phone and the MCI phone are now effectively dead. See H.323.

Videotape Formats

Videotape formats are, in general, classified by the width of magnetic tape used.

  • 1": Used for professional or "broadcast quality" video recording and editing. Comes in large, open reels.

  • 3/4": U-matic (Sony). Most industrial video uses this format, stored in inch-thick cassettes.

  • 1/2":Cassette based, primarily consumer format. VHS - the most popular home videotape format - is 1/2", as is Sony's Beta format. Their higher-quality counterparts (Super-VHS and Super Beta, respectively) are also in the 1/2" format.

  • 8mm: New consumer format that provides high-quality recording in tiny tape format. Popularly used in hand-held camera- recorders (camcorders).

Videotape recorder

A device which permits audio and video signals to be recorded on magnetic tape.


Two-way interactive electronic data transmission or home information retrieval system using the telephone network. Videotex has not been successful because of its (erstwhile) need for expensive, proprietary (i.e. dedicated) equipment and lack of variety in information offered . There are various forms of videotex. The "classic" European version of interactive videotex typically works at 75 baud going out from the terminal and 1200 baud coming in from the central office. Some American versions ape the European system. Some have 1200 baud both ways. In interactive videotex, you can do everything from sending serious electronic mail to your business suppliers to holding raunchy conversations with perverts in distant cities. As long as you pay your bills, no European PTT seems to care about what you transmit or receive. In France, videotex is called Minitel. And it's a success because the French phone company funds it. It has also retarded the development of the Internet in France.


Interactive version of teletext, with a return channel using variable forms of low-speed data. English "Prestel" typifies one realization of videotex.


Vertical Intermediate Distributing Frame. Distributing Frame in which cables terminate in vertically mounted blocks. Compare with Horizontal.

Vidicon Camera

An image sensing device that uses an electron gun to scan a photosensitive target on which a scene is imaged .


  1. In satellite communications, the ability of a satellite to "see" a satellite earth- station, aimed sufficiently above the horizon and clear of other obstructions so that it is within a free line of sight. A pair of satellite earthstations has a satellite in "mutual" view when both enjoy unobstructed line-of-sight contact with the satellite simultaneously .

  2. An alternative way of looking at the data in one or more database tables. A view is usually created as a subset of columns from one or more tables.

Viewable Area

An imaging term. The actual size of the live area of a CRT. For example, a 17" CRT size monitor can have a viewable area ranging from 15.8" to 16.1".


An information retrieval system that uses a remote database accessible through the public telephone network. Video display of the data is on a monitor or television receiver. Another name for Videotex, the original English (UK) name for it. See Videotex.


Vikings were not the dirty, smelly, lice-ridden lot they are depicted as having been. An English chronicler, at the height of the Viking raids on the British Isles, bitterly complained that "British womenfolk rather go with the Vikings, because they are always washing their hands and faces, combing hair and beard, changing their shirts, and, oh shame! every Saturday they are taking a full bath and washing all their clothes," which British men did not do because Christians of the time considered washing vanity and therefore something to avoid for the good of their souls at the expense of their bodies. In fact, the ancient Nordic word for Saturday, "Laugrdag," means "washing day."


Vendor Independent Messaging. A new E-mail protocol developed by Lotus, Apple, Novell and Borland to provide a common layer where dissimilar messaging programs can share data and back-end services. A group called the Vendor Independent Messaging Group will is intent on developing an open, industry-standard interface that will allow e-mail features to be built into a variety of software products. See also MAPI, which is the E-mail protocol developed by Microsoft.

Violent Agreement

We are definitely in agreement.


Virtual Image Phase Array .


A deadly computer virus.


  1. Virtual IP Routing extends private route tables and address spaces from the enterprise into the service provider's routing/switching infrastructure. VIPR is essentially a logical partitioning of a physical IP router owned and operated by the service provider.

  2. Voice over IP Router. See IP.


A video term. Abbreviation of vertical interval reference. Reference signal inserted into the vertical interval of source video. This signal is used further down the video chain to verify parameters and to automatically adjust gains and phase.

Viral Marketing

Your customers are your marketing tool. They show how your product or service makes them. Thus they become your greatest selling tool. For example, you sell a product called call screener. You call Harry's number. Your call screener goes out to find Harry. In the meantime, it's telling you about this product and asking if you'd like to learn more. Rick Bennett of Salt Lake City, Utah, is the world's leading expert on viral marketing. I know this because he told me so.


A guide to the Internet. Someone who's been there before.


See Backslash.


Something that has the essence of, or creates the effect or has the appearance of, something else. In the context of communications, there are Virtual Channels (VCs), Virtual Circuits (VCs), and Virtual Private Networks (VPNs), to name just a few. A Virtual Circuit, for example, is a pre-defined path through the network across which all the data flow, from edge-to-edge, in a connection-oriented environment. It is not a dedicated private- line circuit, dedicated to one user organization. Rather, it is shared amongst perhaps a large number of user organizations. Therefore, it is not guaranteed to be immediately available to support packet data transfer for any individual user organization, as it might be suffering some level of congestion if others are using it at that particular moment. However, the Virtual Circuit behaves something like a circuit in that the path is defined through the network, and all data packets travel that same path during the course of any given data call. Therefore and within limits, the Virtual Circuit has something of the essence of, or creates the effect or has the appearance of, a true circuit, but without being one. The advantage of a Virtual Circuit lies in its shared nature. While the Virtual Circuit is not always immediately available and while, therefore, individual data packets comprising a data stream associated with a given data call will suffer variable and unpredictable levels of latency (i.e., delay), it is much less expensive than a dedicated circuit. See also Transparent, Virtual Channel, Virtual Circuit, and Virtual Private Network.

Virtual 8086 Mode

Virtual 8086 mode allows the Intel 80386 and beyond microprocessors to emulate multiple real mode processors and still switch to and from protected mode. The processor can load and execute real mode applications (in virtual 8086 mode), then switch to protected mode and load and execute another application that requires access to the full extended memory available. The microprocessor, together with a control program like Microsoft Windows or OS/2 assumes the responsibility of protecting applications from one another. See Real Mode and Protected Mode.

Virtual ACD

Virtual Automatic Call Distributor. In simple terms, an ACD directs incoming calls (typically toll-free ones) to an appropriate person who can answer the call and handle the caller's needs. An ACD traditionally has been both hardware and software, in short a switch designed to handle incoming calls. A Virtual ACD is a term that has come to mean a software-only application that performs call routing at an enterprise level through interfaces to carrier networks and legacy ACD equipment. Moreover, the Virtual ACD can perform queuing and agent-management functions in lieu of the traditional ACD platform. The application can reside in a carrier network or on the customer's premises. It's basically designed to switch calls before they get to a site-specific ACD. There are huge advantages to a Virtual ACD. The main one is that the application can instruct the network to adjust which calls end up on which of the customer's nodal ACDs ” we're talking about companies who have many ACDs, often in different parts of the world. The Virtual ACD can be fed constant information on the busy/free status of each site-specific ACD, such as which ones are manned and which are closed (for weather or time, etc.).

Virtual Banding

  1. In WATS services, virtual banding is the ability of trunks to carry traffic to all WATS bands, with billing based on the end points of the call instead of the band over which the traffic went.

  2. MCI's definition: Allows customers of MCI's, PRISM, Hotel WATS, and University WATS to call nationwide while only paying for the distance to the actual area. For example, if a customer calls to a Band 1 area, Band 1 pricing is used. Similarly, if a call is placed to a Band 4 area, Band 4 pricing is used.

Virtual Bypass

Virtual bypass is a way smaller users can fill the unused portion of local T-1 dedicated loops going from a user site to a local office of a long distance company, called a POP (Point of Presence).

Virtual Call Capability

  1. Provides setup and clearing on a per call basis. Each call placed appears to have a dedicated connection for the duration of the call.

  2. A data communications packet network service feature in which a call setup procedure and a call-clearing procedure will determine a period of communication between two DTEs. This service requires end-to-end transfer control of packets within a network. Data may be delivered to the network before the call setup has been completed but it will not be delivered to the destination address if the call setup is not successful. The user's data are delivered from the network in the same order in which they are received by the network. See also Virtual Circuit.

Virtual Call Center

Several Groups of agents , usually in geographically separate locations, that are treated as a single center from a management, scheduling and call-handling perspective.

Virtual Call Service

Virtual Call Service is a packet switching capability that allows a customer to establish a virtual circuit between two data terminals for the duration of a call.

Virtual CD Image

Created by dragging and dropping files into into the main window of many CD authoring programs. Can be used to write directly to CD on-the-fly , or to master a real ISO 9660 image to hard disk.

Virtual CD Player

A virtual CD player which the related device driver fools the operating system into believing is a real one connected to your system. It is used to stimulate CD performance from a real ISO image residing on hard disk.

Virtual Cell

A call, established over a network, that uses the capabilities of either a real or virtual circuit by sharing all or any part of the resources of the circuit for the duration of the call.

Virtual Channel

A single connection across a UNI or NNI allowing the switching of different ATM cells in a virtual path to different destinations.

Virtual Channel Identifier

VCI. A 16-bit field in the ATM cell header identifying the Virtual Circuit which the data will travel from transmitting device to target device. The Virtual Channel is contained within a Virtual Path.

Virtual Channel Switch

An ATM term. A network element that connects VCLs. It terminates VPCs and translates VCI values. It is directed by Control Plane functions and relays the cells of a VC.

Virtual Circuit

A communications link ” voice or data ” that appears to the user to be a dedicated point-to-point circuit. Virtual circuits are generally set up on a per-call basis and disconnected when the call is ended. The concept of a virtual circuit was first used in data communications with packet switching. A packetized data call may send packets over different physical paths through a network to its destination, but is considered to have a single virtual circuit. Virtual circuits have become more common in ultra-high speed applications, like frame relay or SMDS. There the connection might be permanently connected like a LAN. When the user wants to transmit he simply transmits. There's no dialing in the conventional sense, just the addition of an address field on the information being transmitted. A virtual circuit is referred to as a logical, rather than physical path for a call. A virtual voice circuit is anything from as simple as a phone with an auto dialer in it to a high- speed link in which voice calls are digitized and sent on the equivalent of a ultra high-speed, wide-area equivalent of a local area network. There are two basic reasons people buy virtual circuits. They're cheaper and faster. See Permanent Virtual Circuit.

Virtual Circuit Capability

A network service feature providing a user with a virtual circuit. This feature is not necessarily limited to packet mode transmission. e.g., an analog signal may be converted at its network node to a digital form, which may then be routed over the network via any available route. See Virtual Circuit.

Virtual Colocation

First, you can spell it collocation or colocation. I prefer the latter. There are two definitions of this evolving term. Adjacent/Physical and Virtual. First: Imagine that you're a CLEC, a Competitive Local Exchange Carrier. Your idea is to put your switching, transmission and/or Internet equipment in the central office of an ILEC (Incumbent Local Exchange Carrier) and rent some of the ILEC's raw copper circuits out to your customers. You are now able to legally do this. And your idea is to put high-speed data (e.g. DSL) on the raw copper circuits. If you put your equipment inside the ILEC's central office (inside a cage, for example) you have physical/adjacent colocation of your equipment with theirs. Some of the central offices, however, are not large enough to accommodate all the equipment that the various new CLECs are trying to locate in their central office. So the ILECs have figured a new deal. It's called virtual colocation. The CLEC puts his equipment in the ILEC's central office. But the ILEC installs it, configures it, maintains it, fixes it, and does everything necessary to keep it running. The CLEC can remotely monitor and remotely control his equipment as much as possible. But he can't physically go near it. Obviously, the CLEC has to train the ILEC's people and trust them to do the right thing. See also Colocation.

Virtual Computing

A new term for software that shapes computing hardware into hardware that never was. Virtual computing uses FPGAs ” Field Programmable Gate Arrays. See FPGAs.

Virtual Connection

A logical connection that is made to a virtual circuit.

Virtual Container

See VC and SONET.

Virtual Device

A device that software can refer to but that doesn't physically exist.

Virtual Disk

A portion of RAM (Random Access Memory) assigned to simulate a disk drive. Also called a ram disk. See RAM DISK.

Virtual Enterprise Network

Network World of July 31, 2000 wrote IT executives gathered last week at the annual Catalyst Conference put on by consulting firm,

The Burton Group, to share their concerns. They focused on how to integrate directories internally and with partners' corporate systems to help manage e-commerce and online groups of suppliers and partners , a concept The Burton Group refers to as a virtual enterprise network.

Virtual Facilities Group

A European term. A traffic control method where virtual PRIs can be created with fewer than the usual 24 or 30 B channels. This limits the amount of inbound traffic. For example, if a virtual facility were created with 10 channels, and 10 calls were in use, the 11th call would be rejected by the network with a Cause 34 (No circuit/channel available). Multiple virtual facilities can be associated with different numbers on the same PRI. The end result is to limit the number of inbound call setup messages (calls) for specific numbers on a PRI. See PRI.

Virtual Fax

A device consisting of a personal computer and an image scanner that can duplicate the functions of a facsimile machine.

Virtual File Allocation Table

VFAT. A fat file systems is a file system based on a file allocation table, maintained by the operating system, to keep track of the status of various segments of disk space used for file storage. The 32-bit implementation in Windows 95 is called the Virtual File Allocation Table (VFAT). See FAT.

Virtual Hard Drive Memory Factor

The available space on a hard drive partition that Windows can address as physical memory.

Virtual Interface Architecture

April 16, 1997 - Compaq Computer Corp., Intel Corp., Microsoft Corp. and other industry leaders today announced an initiative to define high-speed communication interfaces for clusters of servers and workstations. Called the Virtual Interface (VI) Architecture specification, the initiative will enable a new class of scalable cluster products offering high performance, low total cost of ownership and broad applicability. More than 40 companies will participate in the process to complete the draft technical specification before its public release.

A cluster is a group of computers and storage devices that function as a single system. Businesses use clusters in place of individual computers for higher availability and enterprise-class scalability. It is possible to use standard local area network (LAN) and wide area network (WAN) technology to connect the machines in a cluster. However, large clusters and high-performance applications require lower latency, higher bandwidth and additional features not offered by standard LAN and WAN technology. A system area network (SAN) is a specialized network optimized for the reliability and performance requirements of clusters.

The VI Architecture specification provides standard hardware and software interfaces for cluster communications. This will spur innovation in SAN technology and make the LAN, WAN and SAN differences transparent to the applications. The VI Architecture specification will support reliable, high-performance SANs, helping clusters achieve their full potential as cost-efficient platforms for large-scale, mission-critical applications.

"Information technology industry leaders continue to lower the cost of information processing on all fronts while enabling advanced customer solutions by bringing value-added technology to the mass market," said Britt Mayo, director of information technology at Pennzoil Company. "Their efforts to drive the creation of an industry standard for the VI Architecture will make multisystem solutions widely available at new levels of price/performance."

The VI Architecture specification will be media, processor and operating system independent. The software interface will support a variety of efficient programming models to simplify development and ensure performance. The hardware interface will be compatible with standard networks such as ATM, Ethernet and Fiber Channel as well as specialized SAN products available from a variety of vendors.

Virtual Internet

A virtual Internet is the service of a corporation or other entity that provides private-label dial-up Internet access for its customers by fully outsourcing their dial-up infrastructure and support functions. In other words, the provider is not a provider, but a virtual provider.

Virtual ISDN

This is an alternative way for a customer to get ISDN service. A customer can be serviced out of a nearby central office which has ISDN capabilities but not charged the extra mileage charges as they would with a foreign exchange. The phone company does not add on charges because the costs are recouped from the large volume of customers serviced out of the CO. A customer will usually have to change phone numbers if the CO where they receive their POTS service becomes ISDN capable.

Virtual LAN

A logical grouping of users regardless of their physical locations on the network. Racal-Datacom defines a virtual LAN as "a LAN extended beyond its geographical limit and flexibly configured to add or remove locations." LANs are typically extended beyond their geographical limits (i.e. several thousand feet within a building or campus) by using telephone company facilities, like T-1, T-3, Sonet, etc.

Virtual Machine

A virtual machine is part of a computer's hard disk that thinks it's another computer. The virtual machine thinks it's a complete computer; it doesn't know about the "real" computer except in terms of what the software creating the virtual machine chooses to share with it (like ports or networking).

Virtual Machine Facility

VM/370. An IBM system control program, essentially an operating system that controls the concurrent execution of multiple virtual machines on a single System/370 mainframe.

Virtual Machine

VM. Software that mimics the performance of a hardware device. For Intel 80386 and higher processors, a virtual machine is protected memory space that is created through the processor's hardware capabilities.

Virtual Memory

  1. In computer systems, the memory as it appears to the operating programs running in the CPU. Virtual memory is typically the addition of RAM memory and swapfile memory ” portion of a hard disk devoted solely to swapfile memory.

  2. The term used with Apple Macintoshes to connote the ability to use disk swap files as RAM. This requires the Macintosh to be running System 7 and PMMU.

  3. The space on your hard disk that various versions of Windows (including Windows for Workgroups and NT) use as if it were actually memory. Windows NT does this through the use of swap files. The benefit of using virtual memory is that you can run more applications at one time than your system's physical memory would otherwise allow. The drawbacks are the disk space required for the virtual-memory swap file and the decreased execution speed when swapping to the hard disk is required.

Virtual Memory Manager

Virtual Memory Manager is a software-only approach to Expanded Memory. These work almost identically to the EMS emulators, except that they use your hard disk rather than extended memory as the storage medium for blocks of memory copied out of your program. As you can imagine, this is painfully s-lo-w. Use this approach only as a last resort.

Virtual Network

A network that is programmed, not hard-wired, to meet a customer's specifications. Created on as-needed basis. Also called Software Defined Network by AT&T. See Software Defined Network and Virtual Private Network.

Virtual Network Operator

VNO. A service provider that offers telecom services by piggybacking on the networks of facilities-based operators.

Virtual Office

Employees who are constantly on the move carry their offices with them. Laptops and various telecommunications services allow mobile workers to connect to the central office from virtually any location.

Virtual Path

Contains virtual circuits that are to be switched together to a common destination such as an Interexchange Carrier.

Virtual Path Identifier

VPI. An 8-bit field in the ATM header, identifying the Virtual Path (i.e. Virtual Circuit) over which the transmitted data will flow from the transmitting device to the target device.

Virtual Path Switch

An ATM term. A network element that connects VPLs. It translates VPI (not VCI) values and is directed by Control Plane functions. It relays the cell of the VP.

Virtual Printer Memory

In a PostScript printer, virtual printer memory is a part of memory that stores font information. The memory in PostScript printers is divided into banded memory and virtual memory. Banded memory contains graphics and page-layout information needed to print your documents. Virtual memory contains any font information that is sent to your printer either when you print a document or when you download fonts.

Virtual Printer Technology

VPT. Virtual Printer Technology is the enterprise network printer architecture developed by Dataproducts Corporation that enables a printer to become an intelligent node in a networked computing environment and provide printing services to other network nodes through a Client/Server type relationship.

Virtual Private Network


Virtual Private Office

I found this definition of Virtual Private Office in the September 13, 1997 issue of the Economist, one of my favorite magazines. They had a roundup of telecommunications. Here's how they started their roundup :

In Anderson Consulting's smart new offices in Wellsley, just outside Boston, Mark Greenberg is entitled as a senior partner to three filing-cabinet drawers of storage space. In one, he keeps a bubble-wrapped package, containing the sort of personal mementoes_family photographs, shields and so on_with which businessmen like to decorate their offices, together with a diagram to show how they should be arranged. On the rare days when Mr Greenberg is not visiting a client or jetting around the world, he reserves an office. When he arrives, his treasures are neatly laid out on the desk for him to make him feel at home.

But this is, in effect, a virtual private office, his just for the day. Struck by the waste involved in maintaining expensive permanent offices for people with itinerant lives, the partners in the world's largest management consultancy have created something that feels like a cross between a hotel and a luxurious club. The Wellesley office is staffed by the cream of Boston's hotels: people who understand the business of providing services for important and self-important people. The reception desk looks like a hotel foyer; each floor has lots of little " huddle rooms" with comfortable armchairs, as well as brainstorming rooms with less comfortable ones; and there are open spaces for coffee and conversation with colleagues.

Virtual Reality

VR. The publisher of Virtual Reality Report says, "Virtual reality is a way of enabling people to participate directly in real-time, 3-D environments generated by computers." Virtual reality involves the user's immersion in and interaction with a graphic screen/s. Using 3-D goggles and sensor-laden gloves, people "enter" computer-generated environments and interact with the images displayed there. Says Business Week, "Imagine the difference between viewing fish swimming in an aquarium and donning scuba gear to swim around them. That's the sensory leap between regular computer graphics and virtual reality. There are three kinds of VR (Virtual Reality) immersion. First, the toe in the water experience of beginners who stand outside the imaginary world and communicate by computer with characters inside it. next, wading up to the hips, are the "through the window" users, who use a "flying mouse" to project themselves into the virtual, or artificial, world. Then there are the hold-the-nose plungers: "first persona interaction within the computer-generated world via the use of head-mounted stereoscopic display, gloves, body- suits and audio systems providing binaural sound. The trick with virtual reality is not only to simulate another world but to interact with it ” pouring in data affecting its plots, changing its characters and introducing real-world unpredictability into this "mirror world." Once virtual reality was called artificial reality. But artificial means "fake," while virtual means "almost." The father of virtual reality is Joran Lanier. A term close to virtual reality is telepresence. See Telepresence.

Virtual Route

Virtual circuit in IBM's SNA. See Systems Network Architecture.

Virtual Route Pacing Control

A congestion control at the path control level. See Systems Network Architecture.

Virtual Router Redundancy Protocol


Virtual Storage

Storage space that may be viewed as addressable main storage to a computer user, but is actually auxiliary storage (usually peripheral mass storage) mapped into real addresses. The amount of virtual storage is limited by the addressing scheme of the computer.

Virtual Telecommunication Access Method

VTAM (Pronounced "Vee-Tam.") A program component in an IBM computer which handles some of the communications processing tasks for an application program. VTAM also provides resource sharing, a technique for efficiently using a network to reduce transmission costs.

Virtual Terminal

VT. A universal terminal. The ISO virtual terminal (VT) protocol is designed to describe the operation of a so-called universal terminal so any terminal can talk with any host computer.

Virtual Terminal Protocol

VTP. Virtual Terminal Protocol enables computers to communicate with various types of terminals by interpreting and translating the instructions for both the computer and the terminal.

Virtual Tributary

VT. A structure designed for transport and switching of SONET payloads of less than OC-1 (Optical Carrier level 1), which runs at a total signaling rate of 51.84 Mbps. Prior to conversion to an optical format, the SONET frame is defined at the electrical level in a the form of STS (Synchronous Transport Signal). It is at this point that the Synchronous Payload Envelope (SPE) is defined at a total rate of DS-3, or more exactly, T-3. The SPE can be further defined at subrate levels as follows: 1) VT1.5, which equals a T-1 frame running at 1.544 Mbps; 2) VT2, which equals and E-1 frame at 2.048 Mbps; 3) VT3, which equals a T-1c frame at 3 Mbps; and 4) VT6, which equals a T-2 frame at 6 Mbps. In applications requiring that VTs be mixed within the same STS-1 frame, the SPE can be divided into as many as seven VT Groups. A given VT Group most commonly supports four VT1.5 signals, or 3 VT2 signals. See also SONET, SPE, STS, Virtual Tributary Group, VT1.5 and VT2.

Virtual Tributary Group

A SONET/SDH Term. A SONET frame can comprise as many as seven Virtual Tributary Group, each of which contains signals of the same type, such as T-1 or E-1 frames. See also SONET and Virtual Tributary.

Virtual Visit Virtual Wavelength Path

See VWP.


The process of implementing a network based on virtual Network segments.


A software program capable of replicating itself and usually capable of wreaking great harm on a computer. The term was first used by David Gerrold, a science fiction writer who wrote a story about malignant code that spread from one computer to another. The story was entitled "Virus." See also Virus Hoax.

Viscount of Vapor

During the 1980s, Bill Gates, chairman and co-founder of Microsoft, became known as the Viscount of Vapor, because so many of his announced new products failed to materialize, or when they did materialize, appeared much later than he said they would.


Visibility means the ability to be seen. In the Spring and Summer of 2001, many technology companies were telling their shareholders that they had no "visibility." What they meant was that they could not predict future sales and earnings. Their customers were simply not telling them of their plans and were simply not buying until the last moment, or buying sporadically.

Visible Light

Wavelengths between 400 and 700 nanometers and frequencies between 430 and 750 THz comprise the portion of the electromagnetic spectrum that is visible to the human eye. Constituting a mere 1/10,000,000,000,000,000,000,000,000th of the total electromagnetic spectrum, it's a very small part, but very important to us. Visible light is in a shorter wavelength (i.e., higher frequency) range that Infrared (Ir) light, and in a longer wavelength (i.e., lower frequency) range than ultraviolet (UV) light.

The spectrum of visible light can be subdivided by color. Beginning at the longest wavelength and ending at the shortest wavelength, the colors are red, orange, yellow, green, blue, and violet. An easy way to remember their order (as if you would really want to do such a thing) is to make a word, or words, out of it, just like you used to do in elementary school when you studied for a test. How about naming an imaginary person Roy G. Bv? That's not much of a name. It used to make more sense when the area between blue and violet was designated indigo. Then the key was Roy G. Biv, which is still a pretty odd name. Indigo is no longer considered to be a separate color in the visible spectrum. That's your trivia lesson for the day.

Visitors' Location Register

VLR. A wireless telecommunications term. A local database maintained by the cellular provider in whose territory you are roaming. When you place a call in a roaming scenario, the local provider queries the HLR (Home Location Register) over the SS7 network through the use of a REGNOT (REGistration NOTification). The HLR is maintained by your cellular provider of record in order to verify your legitimacy and to secure your profile of features. The HLR responds to the REGNOT with a "regnot" (lower case), and transfers the necessary data. This information is maintained by the local provider as long as you remain an active roamer within that area of coverage. This process of query and download is accomplished via SS7 links between SCPs (Signal Control Points). SCPs typically are associated with MSCs (Mobile services Switching Centers), also known as MTSOs (Mobile Traffic Switching Offices) for registering visiting mobile station users. VLRs and HLRs are employed in a variety of cellular networks, including AMPS, GSM and PCS. See also AMPS, GSM, HLR, MSC and PCS.


A videotext service offered in Canada.

Visual Area Networking

What one manufacturer calls its new collaborative graphics technology, whch allows remote PC users to access and manipulate complex 3-D images stored on a centralized supercomputer.

Visual Basic

A version of the programming language BASIC written by Microsoft Corporation for Windows. The new program promises to make it much easier for businesses to develop customized Windows applications. Some programmers are calling the software a major breakthrough in ease of programming. When I wrote this, Microsoft had sold over one million copies of Visual Basic.

Visual Carrier

The portion of a television signal which carries the video portion of the picture.

Visual Display Unit

VDU. Another term for a computer monitor. VDU is preferred in Europe.

Visual Fault Locator

A device used to locate breaks and discontinuities in optical cabling, using red laser light. Fiber breaks typically show up as a spot of continuous or blinking red light. The device can also be used to locate particular cables in bundles.

Visual Message Waiting Indicator

VMWI. You are talking to someone on the phone, or perhaps you went to lunch , or on a business trip, or got to work late.

Someone else called and left a message on your voice mailbox. You get a Visual Message Waiting Indicator ” a little lamp lights on your display phone says "Message Waiting." That's VMWI. Big fancy name for a very simple concept ” a light or message on your phone that tells you someone called.

Visual Voice Mail

An application displaying and controlling voice messages on a desktop computer. Usually associated with unified messaging.

Visual Voice Messaging

A term created by Microsoft as part of its At Work announcement in June of 1993. There'll be At Work-based visual voice messaging servers sitting on a LAN. Messages for PC users on the LAN will be able to be displayed in a list, much like electronic mail, including the caller's name or number, the time he or she called and the length of the call. This information would let the user browse all messages and select the order for listening to the messages. Administrative options, such as creating a new greeting, will be accessed with a single button. Operations that are difficult today, such as forwarding a voice message to multiple people, will be dramatically simplified, according to Microsoft. One will simply select the recipients from the phone book and broadcast the message. Using visual voice messaging, users will be able to bypass today's inconsistent, time consuming and confusing audio menus and access their voice messages with the push of a button or the click of a mouse on a Windows type icon. Messages will be able to be retrieved in any order and even delivered to a single mailbox along with other messages such as e-mail and faxes. These visual voice messaging servers will, according to Microsoft, provide applications beyond basic voice messaging, such as supporting voice annotation of PC documents or reading electronic mail over the phone to a traveler .


A combination of computerized graphics and imaging technology that provides high-resolution, video-like results on the workstation or personal computer's screen.

Visually Impaired Attendant Service

Visually impaired attendant service capability is achieved by augmenting the normal visual signals provided on a standard attendant position with special tactile devices and/or audible signals which enable a visually impaired person to operate the position.


VME International Trade Association. A widely supported industry trade group in Scottsdale, AZ. VITA is chartered to promote the growth and technical excellence of the VME bus and Futurebus-based microcomputer board market. VITA is chartered to submit standards for ANSI registration. See VME.

Visual Carrier

The portion of a television signal which carries the video portion of the picture.


Vertical Interval Time Code. Contains the same information as the SMPTE time code. It is superimposed onto the vertical blanking interval, so that the correct time code can be read even when a helical scanning VCR is in the pause or slow (DT) mode.

Viterbi Decoder

Algorithm for decoding Trellis encoded signals.

Vitreous Silica

Glass consisting of almost pure silicon dioxide.


A new PC bus from VESA ” the Video Electronics Standards Association. The VL bus is up to 20 times as fast as an ISA bus, the most common PC bus and the one common to the original PC, the PC XT and the PC AT and clones . VL-Bus was popular on 486 PCs. Pentium-based machines now largely use the newer , PCI bus. As a result, VL-Bus is pretty obsolete. See ISA, Microchannel and PCI.


Virtual Local Area Network. A VLAN in a switched network is a collection of devices grouped together to form a virtual network within a larger network. VLANs allow an administrator to create networks based on parameters beyond the network address, hence the name "virtual." The virtual aspect of VLANs refers to the fact that devices in a VLAN behave as though they are on the same wire, even though they may be physically located on different segments of the LAN. In fact, a VLAN can even extend across a WAN, a wide area network. The reason to create a VLAN is to segment a large subnet. This simplifies user mobility and provides broadcast controls. Switches are configured with policies (or rules) that limit which device can access which VLAN. These rules are set on a switch port or range of ports. The most secure rules combine two or more characteristics of the connecting device, such as some combination of port, MAC address, IP address, and/or routing protocol. These rules can be statically configured or dynamically learned. If a rule is violated, that device is not allowed to access the network and alarms and/or trouble logs are generated. This provides an extra level of security for non-mobile devices such as printers and servers, especially when they are deployed in a semi-public space. See VLAN Assigment Methods .

VLAN Assignment Methods

Policy-based VLANs allow various methods for users to be assigned to VLANs independent of their physical attachment to the network, which is important for maintaining user mobility. VLANs can be formed based on a variety of characteristics including: Switch port, MAC address, IP address, Protocol type, Multicast- aware, DHCP aware, 802.1Q tags, User identity (through authentication). These characteristics can be deployed as standalone rules or combined. See VLAN.


Variable length coding.

Newton[ap]s Telecom Dictionary
Newton[ap]s Telecom Dictionary
ISBN: 979387345
Year: 2004
Pages: 133 © 2008-2017.
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