Fiber Optics Illustrated Dictionary - Part 100 pptx

Fiber Optics Illustrated Dictionary diameter of about 27 lan. This type of antenna array was popularized in the movie Contact based upon the book by Carl Sagan. See Very Large Array, Expanded. http://www.aoc.nrao.edu/ Very Large Array, Expanded EVLA. Based upon the infrastructure of the Very Large Array (VLA), the EVLA will be an updated virtual telescope of mov- able radio-based telescopes with far greater sensitiv- ity and angular resolution than the VLA, operating at frequencies from about 1- 50 GHz. It will enable more accurate spectroscopic assessments of the cos- mos at different wavelengths. The distance of the new stations being added to the current array may be as far away as 250 kIn. The communications links between existing and new antenna dishes are being updated with fiber optic links as part of the Phase I ex- pansion. See Very Large Array. very large scale integration VLSI. In the semicon- ductor industry, VLSls are integrated circuits (ICs) that combine hundreds of thousands of logic and/or memory elements into one very small chip. This type ofcircuitry revolutionized the cost and manufacture ofcomputers. VLSI has enabled the manufacture of palm-sized computers more powerful than room- sized computers from a few decades ago, which were dependent on vacuum tubes and wires for their circuitry. Very SmaU Aperture Terminal VSAT. Very small commercial tenninals for two-way satellite transmissions in the United States, and one-way communications in countries with restrictions. VSATs are generally organized in astar topology, with the Earth station acting as a central node in the network. This Earth station operates with alarge satellite dish and a commercial quality transceiver. In some VSAT implementations, the signal from the transmitting Earth station to the satellite is amplified and redirected to a hub Earth station. Since all transmissions pass through this hub, two hops are needed for intercommunication between satellites. (This results in a bounce pattern known as an M hop.) Some newer configurations, modulation techniques, and amplification systems are included onboard the satellite, so that an interim hop to a hub is not required VSAT systems are appropriate for centralized business and institutional networks. Commercial VSATs typically communicate in C- and Ku-band frequencies. very shortreach VSR. Connections spanning a short distance with the implication that it has fairly high bandwidth characteristics or needs. Thus, the tenn is being widely used in the fiber optics networking industry to describe short distances that require high- quality, fast connections without overengineering the components or making the cost prohibitive. Due to the demand for this type of technology, the Optical Intemetworking Forum has defined a set of four implementation agreements for very short reach (VSR) intra-office interfaces using the OC-192 format and data rate. Short reaches remove the pressure to transmit data serially; parallel cables are practical for VSR connections. This can be implemented with multiple wavelengths over asingle fiber or with multiple fibers (or both). Cisco Systems has been aleading company working with vendors to create functional, standardized OIF- approved SONET /SDH interfaces optimized for VSR interconnections for routes, switches, and dense wavelength division multiplexing (DWDM). See Very Short Reach Interfaces chart. VESA See Video Electronics StandardsAssociation. VF access voice frequency access. VFast See V.Fast, V Series Recommendations. VFC See Version Fast Class. VGA See Video Graphics Array. vgrep visual grep. A variant of a very powerful, useful Unix command. See grep. Very Short Reach Interfaces Spec. Gbps Meters Notes YSR-l 1.25 ca. 300 Similar to Gigabit Ethernet multimode fiber (MMF) technology. A full duplex link based upon twelve parallel 850- nm bidirectional YCSEL channels running over two 12-fiber ribbons. One fiber carries CRC error correction, one carries parity information, and the remaining 10 are for data. The lasers and photodetectors can be built in arrays. YSR-2 ca. 600 Based upon lTV G.691, a serial 1310-nm single-mode fiber interface. Compatible with existing central office (CO) fiber links. Based upon uncooled Fabry-Perot lasers (rather than YCSELs) or those with similar optical characteristics. YSR-3 2.5 ca. 300 A full duplex bidirectional link based upon twelve 850-nm YCSELs and multi mode ribbon fiber technology. Four fibers transmit and four are unused. The lasers and photodetectors can be built in arrays. YSR-4 10 ca. 85/300 A full duplex serial link over two multimode fibers based upon 850-nm VCSELs. 982 © 2003 by CRC Press LLC Passive AudioNideo Switcher This simple consumer switcherprovides switching for composite video and audio inputs and outputs through standard RCA receptacles. It can switch between four different devices. for peripheral device interfaces with personal computers. See super video graphics array, VESA VL. video floppy A2-in. digital image storage floppy released in the mid-1980s to hold video images of 360 lines of resolution. Various methods are now used to store digitized images, including flash memory, 3.5-in. floppies, and various proprietary cards. Video Graphics Array VGA. A graphics standard common on Intel-based International Business Ma- chines (ffiM) and licensed third party computers, supporting 640 x 480 ( 16 colors) and 320 x 200 (256 colors). It has been superseded by super video graphics array (SVGA). See super video graphics array. video switcher A generic phrase for a wide variety of types of passive routing boxes for video signals. Home systems sometimes have simple switchers to select between a VCR and a laserdisc player. Profes- sional switchers may have banks of connectors, slid- ers, and settings and may also provide other functions such as frame synchronization and amplification. video tapeA magnetic recording medium resembling common audio tape designed to store both images and sound. The most common formats for video tape are VHS, S-VHS, S-VHSc (compact S-VHS), Beta, 8mm, and Hi-8mm. S-VHS and Hi-8mm are suffi- ciently good for many professional applications, al- . though higher quality formats are preferred for commercial broadcast quality tapes. Many tapes can store audio in two places, intermixed with the images or on a separate track along the side of the tape, for high fidelity recordings that come close to the quality of CD. Recording times range from 20 minutes to sev- eral hours depending upon the type of tape and the quality settings. All television programming used to be live. The per- formances were saved only in the minds of those who watched them. Then, in the mid-1950s, taped broadcasts became practical and the live aspect of television changed forever. Broadcasts could now be ar- chived, played as reruns, broadcast during convenient times for a specific timezone, or sent overseas to other markets. Station managers could re-air programs without providing royalties to the actors, thus reduc- ing costs (actors weren't happy about this). A whole VHDCI Very High Density Cable Interconnect Stan- dard. A standardized computer interface specification. - See P connector. VHF See very high frequency. VHF antennas A category of antennas designed to take advantage of the particular characteristics of very high frequency (VHF) waves. Because of the wavelength differences between VHF and ultra high frequency (UHF) waves, and the relationship of the rods on the antenna to the length of the wave, VHF antennas tend to be larger and more varied in their shapes than UHF antennas, and can be installed with less precision and still be relatively effective. They are not as broad, however, as a single UHF antenna can cover the entire UHF band, but a VHF antenna is usually optimized for a particular range or specific stations. See antenna, combination antenna, fan dipole antenna, UHF antenna. VHS Video Home Systems. A widely used video format developed by NC that is compatible with millions of home user systems. VHS and Beta formats were released at about the same time. Beta was ac- knowledged as being superior, but was also a bit more expensive, so VHS won the marketing wars. It is slowly being superseded by S- VHS, 8mm, and Hi- 8mm formats, in addition to a number of digital formats, including DVD. S- VHS systems are down- wardly compatible with VHS tapes, that is, you can play a VHS tape in an S- VHS system (but not the other way around). VIA See Virtual Interface Architecture. Vibroplex Trade name ofa type of semi-automatic telegraph key introduced in the later 1800s, more commonly called a bug key. This particular type of bug key was patented in 1904 by Horace G. Martin. By using a vibrating point for automatically gener- ating dots and dashes, it relieved telegraph operators from physical and mental strain. video capture board See frame grabber. video chipsetA logic circuit in a computing device that handles the processing, and sometimes accelera- tion, for video graphics display. Various means of configuring this circuit, and integrating it with the system, control the speed, resolution, and palette set of the display. Video Dial Tone VDT. On-demand consumer video programming services provided through the existing public phone copper wire infrastructure. This includes services such as movies-on-demand, videoconferencing, interactive programming, financial services, and interactive shopping. Until recently, the concept was feasible, but the communications rates through telephone lines were just too slow. With faster data-rate technologies such as DSL, phone lines are now seen as a viable delivery infrastructure for these types of services and may compete with cable services for the growing market. See Open Video Systems. Video Electronics Standards Association VESA. An industry standards body established in 1990 that develops various peripheral standards for Intel-based microcomputers. This organization is responsible for defining Super VGA (SVGA) and the VESA local bus 983 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary series could be shot in a period of weeks and then aired over a period of months, freeing up the actors and production staff to work on the next proj ect. VHS-taped entertainment has been widely available through video rental stores since the early 1990s. In the 1980s, less expensive camcorders ( camera/recording combinations) were utilized by consumers to tape special events, weddings, birthdays, graduations, and amateur movies. By the mid-1990s digital camcorders began to appear and, by the late 1990s, the price dropped to the point where they became consumer items, with film use declining. video tape recorder, video cassette recorder VTR, VCR. A recording and playback device specifically designed to record simultaneous motion images and sound. The input is usually through video patch cords from microphones and cameras for live recording, or from camcorders and CDs, phonographs, and tapes for re-recording or editing. VCRs have been common consumer items since the mid-1980s; prior to that, they were generally used in the television and video editing industries. One of the earliest VTR patent applications was submitted in 1927. One of the early 'portable' video tape recorders, based upon new transistor technology, looked just like a large reel to reel audio recorder. It was introduced by Ampex in 1963. This desktop model weighed about the same as a fairly large TV set, but was nevertheless only one-twentieth the size of previous floor-standing models. It used a single- head helical scanning mechanism and could record 64 minutes ofprogramming on standard 8" reels. VCRs are much smaller now, and use convenient cas- settes rather than reels. They have been improved to support high fidelity sound and high resolution images. video-on-demand VoD. A commercial interactive video system in which the user can request a specific video to be played at a particular time, unlike traditional TV programming where the station determines which programs are to be broadcast, and when. A number of these programs have been tried in various regions with mixed success. It's difficult to institute a pay service in competition with hundreds of'free' channels on TV, which are primarily financed by ad- vertising sponsors. The most successful video-on- demand systems appear to be those installed in mo- tels and hotels that cater to business people attend- ing professional conferences. Thus, one could say tongue-in-cheek that success depends in part on what the market will bare. See audio-on-demand, services- on-demand. videoconferencing The transmission ofcoordinated motion images and sound through computer networks. This is an exciting area with many systems vying for the front row seat. Technologies to transmit speech and images have been around since AT&T's Picturephone system, which was developed many years before it was introduced to the public in the 1970s. However, full motion video as found in videoconferencing, or still frame video and sound as found in audiographics, didn't reach practical speeds and consumer price ranges until the mid-1990s. Even 984 then, they were mostly of interest to educational in- stitutions and corporations. By 1997, however, con- · sumer systems were beginning to be practical, especially wi th the proliferation of tiny monochrome and color video cameras similar to those found in security systems. See audiographics. vidicon Atelevision with aphotoconducting pickup sensor. VidModem A patented signal-processing technology from Objective Communications Inc. that can accom- modate simultaneous two-way video, voice, and data over standard copper wires. VidModem uses FM signals and compression to transmit a 24 MHz FM signal through the 20 MHz bandwidth that is supported on phone lines. Vines A commercial virtual network based upon Unix system V, from Banyan Systems. VIP See virtual IP. Virtual InterfaceArchitecture VIA. An association of vendors who seek to describe and promote a generic systems-area network in order to facilitate the development of software for various X86- and RISC- based computers and their interconnections. VIA was established in 1996 as a small vendor consortium, and has grown to over 50 companies. See Scheduled Transfer. virtual IP, virtual Internet Protocol VIP. A function that enables the creation oflogically separated switched IP workgroups across the switch ports ofa Cisco switch running Virtual Networking Services (VNS) software. virtual LAN virtual local area network. A local area network in which the internal mapping is organized other than on the geography (physical relationship) of the stations. This allows the system to be seg- mented into manageable groups. Network software is used to administrate bandwidth and load, and to maintain acorrespondence between the virtual LAN and the physical LAN. Newer versions ofsoftware will even allow configuration and connections to be established through software with graphical user interfaces that display the equipment itself as graphic images, with lines to indicate the various interconnections. See local area network. Virtual LAN Link State Protocol VLSP. A protocol submitted as an RFC by Cabletron in 1999. It is based upon the OSPF link-state routing protocol described in RFC 2328. VLSP provides interswitch communication between switches running SecreFast VLAN as part of the InterSwitch Message Protocol (ISMP). Its function is to dynamically determine and maintain a fully-connected mesh topology map of the network switch fabric based upon best path trees. Identical link switch databases are maintained by each switch and call- originating switches use this topology database to determine routing paths for call connections. Switch states are distributed through the switch fabric by flooding. VLSP supports equal-cost multipath routing and provides fast updates of topological changes. See InterSwitch Message Protocol, link switch ad- vertisement. See RFC 2642. © 2003 by CRC Press LLC Virtual Switch Controller VSC. A type of soft switch characteristic oftelephony networks that separate the switching layer from the call control layer, enabling a higher degree of interoperability among various protocols and controller systems. The VSC directs calls across multiservice packet infrastructures when combined with industry-standard protocols and interfaces rather than proprietary systems. VSCs can be implemented over newer signal systems such as SS7. Some implementations are also called Media Gateway Controllers (MGC). See Virtual Switch Controller chart on previous page. VirtualTributary VT. In SONET networking, a sub- STS-l signal designed for switching and transport- ing data. A VT Group (VTG) is defined as 12 col- umns, which can be formed by interleaved multiplexing, and a group may contain only one type of VT. VTs operate in two modes: locked and floating. The VT types are as follows: VirtualTrunkingProtocol VTP. Avirtual local area network (VLAN) autoconfiguration protocol from Cisco Systems. VTP is a Layer 2 messaging protocol that enables centralized VLAN switch configuration changes (additions, deletions, name changes, etc.), with the changes communicated automatically to all other switches in the network. virusAvirus is computer code that is designed to be functionally similar to abiological virus in the sense that it uses its host to spread itselfthrough a system. Just as a biological virus exploits the characteristics ofits host to survive and replicate, a computer virus is designed to exploit the characteristics of a computer system and the activities of its users to survive and replicate. There are a number of subcategories ofviruses, which may be organized according to how they are spread or how they affect a system. One major category is a computer worm, a virus that doesn't specifically require a host file (although it still needs a host) in order to replicate. Avirus insidiously takes advantage of nonnal computer functions to spread itself, just as biological viruses take advantage ofnonnal biological functions. Avirus may be associated with or attached to a process, file, or pattern of user activities (e.g., file management functions). John von Neumann was one of the first theoreticians to delve at depth into the analogies between computing and self-reproducing biological systems, formu- lating a basis for biological analogies for computer viruses. Fred Cohen carried on this theoretical Digital Signal Rate virtual office A company or department loosely connected physically, but is communications-linked through various business telecommunications options such as cellular phones, videoconferencing systems, satellite modems, the Internet, etc. Some of the participants may be working at home or traveling. Some corporations mistakenly consider the 'virtual office' to be a new concept, but publishers and their associated writers have successfully employed this business model for decades. See telecommuting, telework. virtual path connection VPC. A path connection established on ATM networks along with an associated quality of service (QoS) category that defines traffic performance parameters. virtual private network VPN. A secure encrypted connection across a public network that enables organizations to utilize a public network as a virtual, private communications tool. Through a process called tunneling, the packet is encapsulated and transmitted. A VPN is a cost-saving measure for businesses that don't want the expense ofsetting up an internally funded secure network, and yet desire interconnec- tivity between remote branches and departments ac- cessible through the relatively inexpensive services of an ISP. VPNs provide a cost-effective alternative to laying cables, leasing lines, or subscribing to frame relay services. The disadvantage to VPN s over public networks is the response time. virtual reality VR. A phrase to describe electroni- cally generated environments that interact with human senses to provide the illusion of the "real world" or to provide afantasy world experience that cannot be achieved in the real world. Sensory headsets, goggles, helmets, implants, gloves, shoes, body suits, computers, monitors, chambers, and a whole host of visuaVtactile/auditory two- and three-dimensional inputs are used to create virtual reality worlds. See Virtual Reality Modeling Language. Virtual Reality Modeling Language VRML (pron. ver-mul). VRML was originally released in 1994 by Tony Parisi and Mark Pesce. Initially dubbed Virtual Reality markup language by Dave Raggett, VRML is a file-format standard, built in part from the Open Inventor File Format, which was made freely distrib- utable later in 1994 by Silicon Graphics, Inc. VRML provides a means for creating 3D multimedia and shareable virtual environments. Its inventors describe it as a 3D Web browser. It can be used in geographical, architectural, and industrial modeling; simulations; education; and games. In August 1996, when the version 2.0 specification ofVRML was released, JPEG and PNG were specified as the two image fonnats required for conform- ance with the specification. VRML plug-ins are available for a number of brow- sers. The files tend to be very large, but there are unique opportunities, too, like taking a virtual ride on Mars Pathfinder, for example, an experience that's worth the download time. VRML 97 was approved in January 1997 as International Standard ISO/IEC 14772-1. See Joint Photographics Group Experts, Portable Network Graphics, virtual reality, VRML. VT Signal Rate VT-1.5 1.728 Mbps VT-2 2.304 Mbps VT-3 3.456 Mbps VT-6 6.912 Mbps OS-I CEPT-I OS-IC OS-2 1.544 Mbps 2.048 Mbps 3.152 Mbps 6.312 Mbps • 985 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary tradition in the early-1980s with research and a number of academic publications specifically related to computer viruses. Cohen is credited with the coin- ing of the term in relation to computer algorithms. Cohen's fonnal definition of a virus has been disputed at length, as it specifically refers to a program that modifies other programs "by modifying them to include a (possibly evolved) copy of itself." While this definition describes some aspects of viruses, it is somewhat more narrow and noninclusive than more recent definitions of computer viruses. The creation and spread of viruses have some legiti- mate research and testing applications. Unfortunately, there are malicious uses as well and these are the ones that make the news. Since a virus is often intrusively or surreptitiouslyintroduced into asystem, the spread occurs without operator knowledge and consent and may not be immediately detected by users. Although the person inserting a virus mayor may not intend explicit harm to the infected system, the recipient is almost always inconvenienced and suffers from a sense of invasion of both security and privacy. Users may also incur losses of time and money unantici- pated by the person introducing the virus, especially now that systems are interconnected through the In- ternet and viruses can quickly spread to large seg- ments of the population. Sometimes a virus contains bugs (programming errors) that cause damage unan- ticipated by the programmer. On personal computers in the 1970s and early 1980s, viruses were frequently spread through the sharing of files on floppy disks. Now viruses are most often A Sampling of Representative Computer Viruses Name Description Adore Worm Anetwork worm exploiting vulnerabilities in Linux machines, the Adore Worm uses random Class B subnet hosts as a pathway for downloading a portion ofitself from an Asian Web server. The worm is stored on the local infected machine and executed through start.sh. It then moves and replaces /bin/ps and /sbin/klogd with files that allow entrance to the system and begins transmitting sensitive data to a number of email addresses, subsequently removing itself from the system (and restoring original files) through a cron daemon (timer program) in order to reduce the chance of detection. Linux vendors became aware of the worm and took steps to reduce the vulnerability ofLinux software. APost An example ofa typical email attachment virus targeted at the Microsoft Windows OS, detected September 2001. APost is an uncompressed executable file which, when run, displays an Urgent! Open dialog box. When the user clicks the dialog button, an error message is displayed, APost checks for a README.EXE file, creates one if absent (on drive root directories, including network drives), then adds a subkey to the user's auto startup key with a path for the APost file. It thus starts each time Windows is loaded and then connects to Microsoft Outlook, grabs the mail server login/password information and replicates itself to the email addresses listed in the address book. Once APost has invaded another machine, the original email host is deleted to obscure its origin. Windows-host email viruses are not uncommon; the Sircam, Mawanella, Magistr, and VBSWG.X all spread through the execution of email-attached files. It is best never to run email executables from questionable sources. (There are even a small number of email viruses that don't require an executable to be run in order to invade a host machine, so beware of unsolicited email.) AutoStart 9805 The first widespread, significant malicious worm to infect Macintosh computers, detected in 1998, AutoStart 9805 caused unexplained disk activity at regular intervals. This worm is limited to PowerPCs/compatibles running MacOS with active QuickTime applications (with QuickTime CD-ROM AutoPlay enabled). The worm "eats" its way through data, with different variants of the worm targeting different types of files, replacing the data with garbage so that it is not recoverable. Fortunately, the specificity of the worm prevents widespread damage, but the nonrecoverability of data may be disastrous for those infected. ExcelMacrol Considered to be the first real Microsoft Excel macro widely distributed as a virus, Laroux Laroux was discovered in 1996. Once a system is infected with this Visual Basic for Applications (VBA) program, Laroux becomes active when Excel is run and it will infect workbooks as they are accessed or newly created. While not as malicious as some viruses, this one is common and causes mischief and inconvenience by replicating itself. 986 © 2003 by CRC Press LLC picked up by uninformed users through network file downloads, which may include email with file attachments, but which most often is through downloads of public domain and shareware programs from bulletin board systems and the Internet. Reputable download sites will usually check uploads for viruses before making them publicly available, but not all site administrators have the time or in-depth knowledge to check every file. More recently, viruses have been spread through bulk mailings of email attachments to users who know how to send andreceive email but otherwise have little knowledge of computer technology. In keeping with the general tone of humor in the computer community, many viruses have names. In fact, sometimes the name itself is the inspiration for the development of a virus or simply ajoke about a proposed virus, e.g., the Paul Revere virus, for example, warns you of an impending attack to your system, once ifby LAN, twice ifby C/:, etc. There are thousands of viruses and dozens that are particularly virulent or significant in various ways. There isn'troom to list all of them, but here are a few examples of viruses and specialized viruses called 'worms,' to give abasic understanding of their scope and common means by which they are spread. Virus attacks deserve serious attention. In an information-based culture, economic and social damage from a virus can be as significant as theft or destruc- tion of important documents in a file cabinet. In fact, they have a greater potential for harm since the In- ternet doesn'tjust reach into one file cabinet, but into Name A Sampling of Representative ComputerViruses, cont. Description Internet Worm A self-reproducing program released onto the Internet in 1988, the Internet Worm affected about 10% of the hosts on the Internet by exploiting a Sendmail weakness. This is one of the more famous worms for a number of reasons. It spread very rapidly, caused more harm than was anticipated by the programmer, R.T. Morris, Jr., and was one of the first to gain broad media attention. The law and network administrators are not tolerant of potentially destructive activities on the Net, and this instance and its originator were not treated lightly. ILOVEYOU A"love letter" Visual BASIC script (VBScript) worm that spreads through email in the manner of a chain letter. The worm uses Microsoft Outlook to spread itself through email; it further overwrites VBScript and may spread using a mIRC client. When executed, the program copies itself to a Windows OS system directory and to the Windows directory, adding itself to the system registry so that it becomes active if the system is restarted. It adds keys to the registry and replaces the Internet Explorer home page with a link to an executable file. If downloaded, the file is added to the registry as well. The executable portion of the code is downloaded from the Internet and functions as a Trojan Horse to attempt to steal a password and modifies the system so that it becomes active each time Windows is started. The Trojan registers a new window class, creates a hidden window and quietly remains resident. After a startup and a certain timer status, it emails them to a specified address, presumably the author's. The program sets itself up to replicate over an IRC channel if the user joins IRC and uses Microsoft Outlook to mass mail itselfonce to any people listed in the address book with the subject ofILOVEYOU. Melissa A rapidly spreading virus that became global within a short time and was discovered in spring 1999. Melissa proliferates through email. When infected, Melissa inserts comments into user documents based upon the television series "The Simpsons." Melissa is also capable of sending out information from a user's computer, information that might be sensitive in nature. The virus was apparently initially propagated through the alt.sex discussion group in Trojan Horse manner, that is, it was contained in a file that was purported to have the passwords for X-rated Web sites. Users who downloaded the document and opened it in Microsoft Word made it possible for a macro to execute, sending the file called LIST.DOC to people listed in the user's email address book. Other Word-fonnat documents can be infected as well, contributing to the quick spread of the virus, and may slow down a system if large email attachments are mailed through a Word email client without the direct knowledge of the sender with the infected system. There has been at least one variant of Melissa discovered. :. 987 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary millions, spread throughout the globe and further can disrupt not just the files but the information exchange mechanisms themselves. Viruses can have life or death consequences if inserted into transportation or health service computer systems. Damage from viruses varies, depending upon the nature of the virus and how it is spread. Common problems include cor- rupted files, interruptions by messages or questions requiring an answer, slowed transmission or processing times, and deleted or filled up storage. Because of their potential to disrupt work and financial transactions, many organizations have been established to deal with the issue of viruses (in addition to those focused on general computer security). Here is a small sampling. • In 1990, the Japanese Ministry of Interna- tional Trade and Industry took steps to prevent the spread of viruses in Japan and initiated the management of Computer Virus In- cident Reports through the Information- Tech- nology Promotion Agency Security Center (IPA/ISEC). • The European Institute for Computer AntiVirus Research brings together the resources of universities, industry, security pro- fessionals, government, and the media to unite against efforts at writing and distributing malicious computer software. http://www.eicar.org/ • The u.S. Department of Energy (DOE) supports the Computer Incident Advisory Capa- bility (CIAC) and an information site for reports of virus-related hoaxes. http:hoaxbusters.ciac.org/ There are about two dozen significant virus-specific discussion groups on the Internet. Of particular interest are the moderated USENET group comp.virus and email discussion list Virus- L. See back door, back porch, logic bomb, Trojan horse, worm, WildList Or- ganization International, and entries prepended by virus. virus, hoax A report ofa computer virus that doesn't actually exist. Virus hoaxes are unfortunately somewhat common. They can cause mental anguish, work stoppage, and loss of productivity without the per- petrator actually writing and distributing a virus. The Good Times virus warning, initiated in 1994, is an example ofa virus hoax that was still circulating sev- eral years later. virus, wild A virus that is extant in the general computer community. A wild virus is one that has the potential to do harm and infect systems because it has been "let loose" to replicate indiscriminately or according to a pattern established by the person programming the virus. Many viruses are developed for academic research or testing purposes and are not distributed into the computing community outside the laboratory or research environment. See virus. Virus Bulletin A commercial, international U.K based publication providing information and assis- tance with virus prevention, recognition, and han- 988 dling. The Bulletin provides news information on security-related conferences as well as hosting an annual conference. Virus Catalog,Computer (CVC) This is considered one of the better technical sources of information on computer viruses for a variety of platforms, published by the Virus Test Center in Hamburg, Germany. virus checker, antivirus software A computer program that searches and, in some cases, disables viruses on a computer system or network. Virus checkers are a means to detect the undesired contamina- tion or spread of computer viruses before they reduce productivity or harm a system. Computer viruses have been around almost as long as cost-effective computers, but it was the late-1980s before virus checkers became widely available and it took a few years of experimentation for them to become really effective. The virus checker itself should be obtained from a reputable source, since a virus checking program is a good place to hide a virus. Most virus checkers will bring up a dialog box or other alarm warning ifa potential virus is detected. They may provide options enabling the user to deal with the virus in a number of ways. It should be remembered that a virus checker is only one aspect of computer security and that security from a network standpoint requires many more sophisticated tools and techniques than a standalone computer to remain secure and optimally functional. In general, virus checkers seek out anomalous patterns or disk access activities. They also typically include a database of viruses with known characteristics that are explicitly sought and identified. A computer running a virus checker is sometimes said to be 'inoculated' against viruses. Since inoculations are generally effective, but not perfect, it's a reasonable analogy. Checkers can be initiated at computer startup and, now that most computers are multitasking, will often run as background tasks. It is usually a good idea to disable virus checkers when system maintenance, new installations, and reconfiguration options are run so that the virus checker doesn't interfere with the process or display an alarm when the maintenance is being carried out. It's also important to remember to restart the virus checker. Many institutional computers are installed with virus checkers as a matter of policy. These have become quite sophisticated and can detect and sometimes disable many different types of viruses. However, each time a new application, a new processor, or a new mode of operations is introduced into a computer system, it has the potential to host a new type of virus that exploits the evolving technology. Like biological viruses, there will never be a 'perfect' virus checker that can anticipate or detect every type of virus. Virus checkers also have disadvantages. They can slow the system or interfere with system extensions, and it takes diligence and time on the part of the user to install, configure, and manage the virus checker itself. In most cases, the management involved in using virus checkers is considered good insurance against the massive damage that can occur from a © 2003 by CRC Press LLC virus that wipes out or corrupts important or sensitive information. In the absence of virus checkers, file backups and redundancy of live files are two strategies for reduc- ing loss from virus attacks. Self-contained systems also help but are almost impractical in the trend to- ward a global computing environment. To help prevent the infection and spread of viruses, back up your data, investigate the available virus checkers, download only from reputable sites, and never open email or execute email attachments from questionable sources. See virus. visible spectrum The region of light waves perceived by humans as color, ranging from approximately 380 to 700 nanometers, or 3800 to 7000 angstroms. Tech- nology cannot reproduce all of the colors of the visible spectrum, but humans cannot always distinguish between very closely related colors either. For practical purposes, the approximately 17 million colors displayed on better quality computer monitors and the approximately 10 million colors that can be printed with pigments on a press are sufficient for most personal and commercial needs. Outside the visible spectrum are the infrared and ultraviolet wavelengths. VisiCalc Visible Calculator. A historic early computer spreadsheet program, introduced in 1979, which was developed by Dan Bricklin and Bob Frankston for the Apple computer. VISIT Video A Macintosh- and IBM-licensed PC- based videoconferencing system from Northern Telecom Inc. that supports video, whiteboarding, and file transfers over Switched 56 or ISDN. An extra transmissions line is needed for audio. See Cameo Personal Video System, Connect 918, MacMICA, IRIS, ShareView 3000. Visual BASIC A basic Microsoft Windows programming application development product with a graphical user programming interface from Microsoft Cor- poration. Suitable for prototyping, although extensive use of dynamic linked libraries (DLL) may be needed for extensive applications development. visual ringer A small lamp on a phone console, usually a light-emitting diode (LED), which lights up when the phone rings. This is convenient in a noisy environment or for those who are hearing impaired. It is also common on multiline phones, to indicate which of the multiple lines are currently ringing. vitreous electricity A term coined by Dufay to de- note the type of electrostatic charge produced on glass when rubbed with silk. Benjamin Franklin later proposed positive, a term that superseded vitreous. See electrostatic, resinous electricity. VLAN See virtual LAN. VLS Protocol The Virtual LAN Link State protocol developed by Cabletron Systems, Inc. is part of the InterSwitch Message Protocol (ISMP) providing interswitch communication between network switches running Cabletron's SecureFast Virtual LAN (SFVLAN). VLSP is used to determine and maintain a fully connected mesh topology map of the switch fabric. Within the switches are identical databases describing the topology maintained. Switches from which calls originate use this topology database to determine a routing path over which a call can be connected. VLSP supports equal-cost multipath routing and recalculates routes quickly with a minimum of routing protocol traffic. See RFC 2642. VLSI See very large scale integration. VLSP See Virtual LAN Link State Protocol. VMI V Series Modem Interface. A standard software front end and software layer that provides an entry and exit point to modem functions implemented through a variety of modem standards, for DSP Soft- ware Engineering modem products. VNS virtual network system, virtual network service. vocoder voice coder. A late 1930s invention that provided a means for analyzing the pitch and energy con- tent of speech waves. This technology led to the development of a device designed to transmit speech over distance without the waveform. The transmission was expressed at the receiving end with a syn- thetic speaking machine. This general concept has evolved into linear predictive encoders. VoATM See Voice over ATM. J VoFR voice over frame relay. See Frame Relay, voice over. voice activity detection VAD. A capability of digital voice communications systems to distinguish between information, such as speech, and the silences in between the speech elements. Typically, voice conversations consist of only about 40% talking, with the rest being pauses, silence, or low-level background noise. By transmitting information only when it is meaningful and filtering out the silent moments, it is possible to create a significant savings in the amount of data that needs to be transmitted. See silence suppression. voice-activated systemA system such as a computer, phone, door, etc. that responds to the sound ofa voice, which might be any voice or a specific voice. Voice- activated systems are calibrated to separate out the patterns and frequencies common to human voices from general background noise or other sounds. Tech- ~~~~ ~e;;~~:[::~~~: i~~~u~~.t ~~ ~~~~fd • not be confused with a speech-recognition system that recognizes actual words, not just a general or particular voice. Sometimes the two are combined. Voice File Interchange Protocol VFIP. A voice file interchange format proposed in 1986 when the ARPANET was still predominant. VFIP was designed to facilitate the interchange of speech files among different computer systems. The specification defined a header for describing voice data that includes a DTMF mask, information about duration and recording rate, and the encoding format. There was no re- quirement for the header to be explicitly attached to the file containing the speech data. See Network Voice Protocol, Voice Profile for Internet Mail, RFC 978. voice grade channel A transmission circuit suffi- ciently fast (usually up to about 56 Kbps) and suitable for transmitting clear voice conversations within frequencies between 300 and 3300 Hz. It is not 989 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary typically suitable for other faster, higher bandwidth uses. Voice is arelatively low bandwidth application and does fine over copper wires, but others such as data transfer and video images require more. voice group In analog voice phone systems, a hier- archy for multiplexing has been established as a series ofstandardized increments.See jumbogroup for a diagram. voice over ATM VoATM. A growing area of interest, voice over ATM involves the digital transmission of voice conversations (which traditionally have been carried over analog phone lines) over asynchronous transfer mode (ATM) networks. Typically this involves taking a synchronous voice signal, segment- ing it into cells, each with its own header, and inter- leaving the cells into the network with cells from other sources, eventually delivering the cell packets to their destination where they are converted back into a synchronous data stream. Since various queuing delays on the network will affect the transmission of the cells, the receiving buffer must have timing capabilities to organize the arriv- ing cells so as to not leave gaps in the synchronous output signal. Delays ofgreater than 50 milliseconds of the conversation roundtrip must be avoided in order to prevent echo on the line. ATM networks make use of echo cancellers to reduce echo delay problems. Delays of greater than 250 milliseconds must also be avoided, as they result in perceptual discomfort on the part of the participants in the conversation. In order to maximize bandwidth over a public network, in which thousands of phone conversations coexist, compression techniques are commonly used to reduce transmission time and resources. See echo canceller, jitter, silence suppression, voice activity detection. voice over frame relay VOFR. See frame relay, voice over. voice over IP VoIP. Voice over IP involves digitiz- ing conversations and other human vocalizations so they can be transmitted over data networks. This usually involves compression of the sound, as voice applications tend to be somewhat bandwidth intensive (though not as much as music and other types of sounds). Commercial VoIP offerings usually include familiar phone services like Caller ill, and newer ones like follow-me services that allow forwarding to cell phones or pagers. Some systems are designed to use the public switched telephone network as a fallback ifthere are problems with transmission over the data network. Group Name group supergroup mastergroup jumbogroup Composition I group 5 groups 10 supergroups 6 mastergroups Number of Voice Channels 12 voice channels 60 voice channels 600 voice channels 3600 voice channels Voice over IP Forum VoIPF. Agroup within the In- ternational Multimedia Teleconferencing Consortium (IMTC) that promotes and recommends voice over Internet Protocol (IP) technologies. See voice over IP. voice over networks There are now a variety of ways in which wide bandwidth data networks can be used to send telephone voice calls. The call can be initiated through a regular phone line that connects to a private or public network, or through a computer voice system hooked directly to anetwork. Thus, In- ternet Service Providers (ISPs) are emerging as col- laborators and competitors with traditional copper line phone service carriers. voice over packet VoP. Devices capable of encoding voice signals for transmission over digital packet data networks. These devices typically support ITU- T G Series Recommendations (e.g., G.729a) and may also have echo cancellers, fax and modem support, and voice-band signaling support features. VoP devices are useful for packetized cable telephone, Voice over IP (VoIP), and DSL access. Voice Profile for Internet Mail VPIM. An experi- mental profile submitted by G. Vaudreuil in Febru- ary 1996 to define a digital computer-based voice messaging mechanism. Now known as VPIM, version 1, it was based upon the Audio Message Inter- change Specification (AMIS), which facilitates message interchange among voice mail messaging on systems from different vendors. VPIM differs from AMIS in that it is a digital specification based on common internetworking protocols. The VPIM took into consideration common limitations of voice messaging platforms as they were implemented at the time. In September 1998, VPIM, version 2 was submitted as a Standards Track protocol by G. Vaudreuil and G. Parsons. It represents contributions by the VPIM Work Group of the Electronic Messaging Associa- tion (EMA). Significant changes to the original ex- perimental specification were made based upon dem- onstrations at two EMA conferences in the mid- 1990s. VPIM is a profile for using MIME and ESMTP protocols for digital voice messaging services. It speci- fies a restricted set of Internet multimedia messaging protocols for the provision ofa minimum common set offeatures for internetworking among different voice processing servers. See Audio Messag- ing Interchange Specification, Network Voice Proto- col, Voice File Interchange Protocol, RFC 1911 (VPIM, version I), RFC 2421 (vpIM, version 2). Voice with the Smile One of the many colloquial names given to the early female telephone operators. Others include Hello Girls, Central, and Call Girls. voice mail A type of data communication in which a voice message is digitally recorded, usually through a small microphone interfaced with a computer, and sent through an email or voicemail client as an attachment or message. In order to hear the message, the receiver must have the capability to replay the message on the destination system. This is usually done either directly through the voicemail client or, 990 © 2003 by CRC Press LLC if sent as an email attachment, it can be played with a separate player utility that is compatible with the type of sound file in which the message is stored. voicemail, electronic A system for intercepting an incoming phone call, playing a prerecorded digital message, and recording a message left by the caller. Many voice mail systems support multiple messages, multiple mailboxes, and menu hierarchies accessed through touchtones entered from the caller's phone keypad, and may also allow a facsimile message to be transmitted manually, since many voice modems and voicemail systems support data and facsimile communications as well. Voice mail systems are not used just as fancy answer- ing machines; they are also employed in faxback systems, technical support systems, and for providing product information and purchase options to callers. Because electronic voice mail applications are digital, they can be programmed to provide a wide variety of services, according to the needs and imagina- tion of the programmer and user. volt (Symbol v or e for voltage) A SI unit of electrical potential. When a difference of electrical potential occurs between materials or portions of materials where there is a pathway between them, electrons seek a direction of flow which balances that potential. A volt is a unit of electromotive force (EMF) equal to that needed to produce a one ampere current through a one ohm resistance. In any given circuit, voltage, current, and resistance are related, so anyone of those values can be computed if the other two are known. The unit is named after Alessandro Volta. See ampere, ohm, Ohm's law, resistance. Volta, Conte Alessandro Giuseppe Antonio Anastasi (1745-1827) A physicist who pursued many of the ideas proposed by Luigi Galvani by studying the varying electrical properties of different materials. He questioned Galvani's explanation of'animal electricity' and proposed that the reaction of the muscle to stimulation ofa nerve was due to unequal temperatures, and set up more rigorous experiments to determine what was happening. He showed how electricity could be generated by chemical action, which became known as galvanic electricity. This was the forerunner of the electrolytic cell. In 1800 he described his invention of the voltaic pile. Volta devised a condensing electroscope to respond to very sensitive charges and, with it, was able to dem- onstrate contact charges (though some were actually chemical interactions). The volt, a unit of electromotive force, is named after him. See Faraday, Michael; volt; voltaic pile. voltaic pile Alessandro Volta developed a system of layers of metal plates and paper or briny cloth that exhibited a difference in potential between the top and bottom, which could be varied with the materials used and the number and organization of the layers. Volta attributed this difference to 'contact' electricity, though we now know that chemical factors play a role. Volta later modified the pile design to create what he called a crown of cups. The metal plates were placed in separate cups containing liquid, some distance apart. The plates were the poles or electrodes. Each cup is now known as a voltaic cell and apair is known as a voltaic battery. See capacitor, thin film. Voltaic Piles - Historic Capacitors Two historic voltaic piles show the alternating layers of materials piled within supporting rods. voltmeter, voltameter A galvanometer or other in- strument such as an ammeter, connected in series with a resistor, calibrated to indicate electric pressure from electromotive force, or voltage differences in potential at different points of an electrical circuit. The voltmeter is connected in parallel across the circuit being tested and must have a higher resistance than that of the circuit being measured. In the past, sometimes also called a coulomb-meter or coulometer. See volt. von Bunsen, RobertWilhelm A German chemist in the 1800s who did numerous experiments with wet cells and made improvements on the early inventions leading to modem batteries. von Guericke, Otto (1600s) An early experimenter who devised a machine that amplified and demonstrated the properties of negative and positive elec- tromagnetic forces. Von Guericke used a spinning large sphere, molded out of sulphur, to investigate theories related to the spinning and magnetism of the Earth. He noted also that holding certain substances up to the sphere would produce a spark. He discovered basic principles of air pumps and demonstrated characteristics of vacuums with his Magdeburg hemi- spheres in 1663. A university in Magdeburg, Ger- many is named after him. von Kleist, Ewald Christian (1715-1759) A German physicist who discovered in 1745 that an electrical charge could be held in a glass vial with a nail or piece of brass wire inserted. A similar jar was developed independently by P. van Musschenbroek, known as the Leyden jar. See Leyden jar. 991 © 2003 by CRC Press LLC . tapeA magnetic recording medium resembling common audio tape designed to store both images and sound. The most common formats for video tape are VHS, S-VHS, S-VHSc (compact S-VHS), Beta, 8mm, and Hi-8mm. S-VHS and Hi-8mm are suffi- ciently good for many professional applications, al- . though higher quality formats are preferred for commercial broadcast quality tapes. Many tapes can store audio in two places, intermixed with the images or on a separate track along the side of the tape, for high fidelity recordings that come close to the quality of CD. Recording times range from 20 minutes to sev- eral hours depending upon the type of tape and the quality settings. All television programming used to be live. The per- formances were saved only in the minds of those who watched them. Then, in the mid-1950s, taped broadcasts became practical and the live aspect of television changed forever. Broadcasts could now be ar- chived, played as reruns, broadcast during convenient times for a specific timezone, or sent overseas to other markets Standard ISO/IEC 1477 2-1 . See Joint Photographics Group Experts, Portable Network Graphics, virtual reality, VRML. VT Signal Rate VT-1.5 1.728 Mbps VT-2 2.304 Mbps VT-3 3.456 Mbps VT-6 6.912 Mbps OS-I CEPT-I OS-IC OS-2 1.544. video-on- demand systems appear to be those installed in mo- tels and hotels that cater to business people attend- ing professional conferences. Thus, one could say tongue-in-cheek that success depends in part on what the market will bare. See audio-on-demand, services- on-demand. videoconferencing The transmission ofcoordinated motion images and sound

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