virusA virus is computer code that is designed to be functionally similar to a biological virus in the sense that it uses its host to spread itself through a system.. One major category
Trang 1Fiber Optics Illustrated Dictionary
diameter of about 27 lan This type of antenna array
was popularized in the movieContactbased 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 ofthe 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.Itwill enable
more accurate spectroscopic assessments ofthe
cos-mos at different wavelengths The distance ofthe new
stations being added to the current array may be as
far away as 250kIn.The communications links
be-tween existing and new antenna dishes are being
up-dated 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
of circuitry revolutionized the cost and manufacture
of computers 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
transmis-sions in the United States, and one-way
communica-tions in countries with restriccommunica-tions VSATs are
gen-erally organized in a star topology, with the Earth
sta-tion acting as a central node in the network This Earth
station operates with a large satellite dish and a
com-mercial quality transceiver
Insome VSAT implementations, the signal from the
transmitting Earth station to the satellite is amplified
and redirected to a hub Earth station Since all
trans-missions 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 amplifi-cation systems are included onboard the satellite, so that an interim hop to a hub is not required
VSAT systems are appropriate for centralized busi-ness and institutional networks Commercial VSATs typically communicate in C- and Ku-band frequencies very short reach 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 in-dustry 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 for-mat 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 a single fiber or with mul-tiple fibers (or both)
Cisco Systems has been a leading 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 Standards Association
VF access voice frequency access
VFast See V.Fast, V Series Recommendations VFC See Version Fast Class
VGASee Video Graphics Array
vgrep visual grep A variant of a very powerful, useful Unix command See grep
Very Short Reach Interfaces
YSR-l 1.25 ca 300 Similar to Gigabit Ethernet multimode fiber(MMF)
technology.A fullduplex 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 lTVG.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 Afullduplex bidirectional link based upon twelve 850-nm
YCSELs and multimode 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 fullduplex serial link over two multimode fibers based upon
850-nm VCSELs
Trang 2Passive AudioNideo Switcher
This simple consumer switcher provides switching for composite video and audio inputs and outputs through standard RCA receptacles It can switch be-tween four different devices.
puters See super video graphics array, VESA VL video floppyA2-in digital image storage floppy re-leased 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 ArrayVGA 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 graph-ics array (SVGA) See super video graphgraph-ics array video switcherA 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 ofconnectors, slid-ers, and settings and may also provide other functions such as frame synchronization and amplification
video tapeAmagnetic 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 com-mercial broadcast quality tapes Many tapes can store audio in two places, intermixed with the images or
on a separate track along the side ofthe 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 ofthose who watched them Then, in the mid-1950s, taped broad-casts became practical and the live aspect of televi-sion 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) Awhole
dard Astandardized computer interface specification
-See P connector
VHF See very high frequency
VHFantennasA category of antennas designed to
take advantage ofthe particular characteristics ofvery
high frequency (VHF) waves Because of the
wave-length differences between VHF and ultra high
fre-quency(UHF)waves, and the relationship ofthe rods
on the antenna to the length ofthe wave, VHF
anten-nas 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
an-tenna, UHF antenna
VHS Video Home Systems Awidely used video
for-mat developed byNCthat is compatible with
mil-lions 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
for-mats, 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
VibroplexTrade name of a type of semi-automatic
telegraph key introduced in the later 1800s, more
commonly called abug 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 boardSee 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 ToneVDT On-demand consumer video
programming services provided through the existing
public phone copper wire infrastructure This includes
services such as movies-on-demand,
videoconferenc-ing, interactive programmvideoconferenc-ing, financial services, and
interactive shopping Until recently, the concept was
feasible, but the communications rates through
tele-phone 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 AssociationVESA
Anindustry 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
Trang 3Fiber 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 project
VHS-taped entertainment has been widely available
through video rental stores since the early 1990s
In the 1980s, less expensive camcorders
(camera/re-cording combinations) were utilized by consumers to
tape special events, weddings, birthdays, graduations,
and amateur movies By the mid-1990s digital
cam-corders began to appear and, by the late 1990s, the
price dropped to the point where they became
con-sumer 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 ofthe earliest VTR patent applications was
sub-mitted in 1927 One ofthe 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 of programming on standard 8" reels
VCRs are much smaller now, and use convenient
cas-settes rather than reels They have been improved to
supporthighfidelity sound andhighresolution images
video-on-demandVoD A commercial interactive
video system in which the user can request a specific
video to be played at a particular time, unlike
tradi-tional TV programming where the station determines
which programs are to be broadcast, and when A
number ofthese 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 homo-tels 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
videoconferencingThe transmission ofcoordinated
motion images and sound through computer
net-works This is an exciting area with many systems
vying for the front row seat Technologies to
trans-mit 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
then, they were mostly of interest to educational in-stitutions and corporations By 1997, however,
con-· sumer systems were beginning to be practical, espe-cially with the proliferation oftiny monochrome and color video cameras similar to those found in secu-rity systems See audiographics
vidiconA television with a photoconducting pickup sensor
VidModemApatented 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 sig-nals and compression to transmit a 24MHzFM sig-nal through the 20MHzbandwidth that is supported
on phone lines
VinesAcommercial virtual network based upon Unix system V, from Banyan Systems
VIP See virtual IP
Virtual Interface ArchitectureVIA.Anassociation
of vendors who seek to describe and promote a ge-neric systems-area network in order to facilitate the development ofsoftware 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 ProtocolVIP A func-tion that enables the creafunc-tion of logically separated switched IP workgroups across the switch ports of a Cisco switch running Virtual Networking Services (VNS) software
virtual LANvirtual local area network Alocal 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 a correspondence between the virtual LAN and the physical LAN Newer versions of software will even allow configuration and connections to be established through software with graphical user in-terfaces that display the equipment itself as graphic images, with lines to indicate the various intercon-nections See local area network
Virtual LAN Link State ProtocolVLSP A proto-col submitted as an RFC by Cabletron in 1999 It is based upon the OSPF link-state routing protocol de-scribed 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-con-nected mesh topology map ofthe network switch fab-ric 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 rout-ing and provides fast updates oftopological changes See InterSwitch Message Protocol, link switch ad-vertisement See RFC 2642
Trang 4switch characteristic oftelephony networks that sepa-rate 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
Virtual TributaryVT 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 multiplex-ing, and a group may contain only one type of VT
VTs operate in two modes: locked and floating The
VT types are as follows:
Virtual Trunking ProtocolVTP A virtual local area network (VLAN) autoconfiguration protocol from Cisco Systems VTP is a Layer 2 messaging proto-col that enables centralized VLAN switch configu-ration changes (additions, deletions, name changes, etc.), with the changes communicated automatically
to all other switches in the network
virusA virus is computer code that is designed to be functionally similar to a biological virus in the sense that it uses its host to spread itself through a system
Just as a biological virus exploits the characteristics
of its host to survive and replicate, a computer virus
is designed to exploit the characteristics of a com-puter 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
A virus insidiously takes advantage of nonnal com-puter functions to spread itself, just as biological vi-ruses take advantage ofnonnal biological functions
A virus may be associated with or attached to a pro-cess, file, or pattern ofuser activities (e.g., file man-agement functions)
John von Neumann was one of the first theoreticians
to delve at depth into the analogies between comput-ing and self-reproduccomput-ing biological systems, formu-lating a basis for biological analogies for computer viruses Fred Cohen carried on this theoretical
Digital Signal Rate
nected physically, but is communications-linked
through various business telecommunications options
such as cellular phones, videoconferencing systems,
satellite modems, the Internet, etc Some of the
par-ticipants may be working at home or traveling Some
corporations mistakenly consider the 'virtual office'
to be a new concept, but publishers and their
associ-ated writers have successfully employed this business
model for decades See telecommuting, telework
virtual path connectionVPC A path connection
established on ATM networks along with an
associ-ated quality of service (QoS) category that defines
traffic performance parameters
virtual private networkVPN A secure encrypted
connection across a public network that enables
or-ganizations to utilize a public network as a virtual,
private communications tool Through a process
called tunneling, the packet is encapsulated and
trans-mitted AVPN 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 VPNs over
pub-lic networks is the response time
virtual realityVR A phrase to describe
electroni-cally generated environments that interact with
hu-man senses to provide the illusion ofthe "real world"
or to provide a fantasy 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 LanguageVRML(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
multime-dia and shareable virtual environments Its inventors
describe it as a 3D Web browser.Itcan 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
speci-fied 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 3.152Mbps 6.312 Mbps
•
Trang 5Fiber Optics Illustrated Dictionary
tradition in the early-1980s with research and a
num-ber 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 ofa 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 surreptitiously introduced into a system, 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 ofboth 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
Adore Worm A network worm exploiting vulnerabilities in Linux machines, the Adore Worm uses
random Class B subnet hosts as a pathway for downloading a portion of itself from an Asian Web server The worm is stored on the local infected machine and executed throughstart.sh.Itthen moves and replaces/bin/psand/sbin/klogdwith 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 of Linux software
APost Anexample of a typical email attachment virus targeted at the Microsoft Windows OS,
detected September 2001 APost is an uncompressed executable file which, when run, displays anUrgent! Opendialog box When the user clicks the dialog button, an error message is displayed, APost checks for aREADME.EXE file, creates one if absent (on
drive root directories, including network drives), then adds a subkey to the user's autostartup key with a path for the APost file.Itthus 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.Itis 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.)
AutoStart9805 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 QuickTimeCD-ROMAutoPlay 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
Trang 6downloads, which may include email with file
attach-ments, but which most often is through downloads
of public domain and shareware programs from
bul-letin board systems and the Internet Reputable
down-load sites will usually check updown-loads for viruses
be-fore 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 and receive email but
otherwise have little knowledge of computer
tech-nology
In keeping with the general tone ofhumor in the
com-puter community, many viruses have names In fact,
sometimes the name itself is the inspiration for the
posed 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't room to list all ofthem, but here are a few examples of viruses and specialized viruses called 'worms,' to give a basic understanding oftheir scope and common means by which they are spread
Virus attacks deserve serious attention In an infor-mation-based culture, economic and social damage from a virus can be as significant as theft or destruc-tion ofimportant documents in a file cabinet In fact, they have a greater potential for harm since the In-ternet doesn't just reach into one file cabinet, but into
Name
A Sampling of Representative Computer Viruses, 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 itself once to any people listedinthe 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
:.
Trang 7Fiber 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
vi-ruses 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
process-ing times, and deleted or filled up storage
Because oftheir potential to disrupt work and
finan-cial transactions, many organizations have been
es-tablished to deal with the issue of viruses (in
addi-tion 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
pre-vent the spread of viruses in Japan and
initi-ated 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
re-sources ofuniversities, industry, security
pro-fessionals, government, and the media to unite
against efforts at writing and distributing
ma-licious computer software
http://www.eicar.org/
• The u.S Department of Energy (DOE)
sup-ports the Computer Incident Advisory
Capa-bility (CIAC) and an information site for
re-ports of virus-related hoaxes
http:hoaxbusters.ciac.org/
There are about two dozen significant virus-specific
discussion groups on the Internet Of particular
in-terest 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, hoaxAreport ofa computer virus that doesn't
actually exist Virus hoaxes are unfortunately
some-what 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 Avirus that is extant in the general
com-puter community Awild virus is one that has the
po-tential to do harm and infect systems because it has
been "let loose" to replicate indiscriminately or
ac-cording to a pattern established by the person
pro-gramming 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 BulletinA commercial, international
U.K.-based publication providing information and
assis-tance with virus prevention, recognition, and
han-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 ofplatforms, published
by the Virus Test Center in Hamburg, Germany virus checker, antivirus software Acomputer pro-gram that searches and, in some cases, disables vi-ruses on a computer system or network Virus check-ers are a means to detect the undesired contamina-tion or spread ofcomputer viruses before they reduce productivity orharma system Computer viruses have been around almost as long as cost-effective comput-ers, 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 if a po-tential virus is detected They may provide options enabling the user to deal with the virus in a number ofways It should be remembered that a virus checker
is only one aspect of computer security and that se-curity 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 pat-terns or disk access activities They also typically in-clude a database of viruses with known characteris-tics that are explicitly sought and identified A com-puter 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 mainte-nance, 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 vi-rus checkers as a matter ofpolicy These have become quite sophisticated and can detect and sometimes dis-able many different types of viruses However, each time a new application, a new processor, or a new mode ofoperations is introduced into a computer sys-tem, it has the potential to host a new type of virus that exploits the evolving technology Like biologi-cal 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
Trang 8tive 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
pre-vent the infection and spread ofviruses, back up your
data, investigate the available virus checkers,
down-load only from reputable sites, and never open email
or execute email attachments from questionable
sources See virus
visible spectrum The region oflight 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
vis-ible spectrum, but humans cannot always distinguish
between very closely related colors either For
prac-tical 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
per-sonal and commercial needs Outside the visible
spec-trumare the infrared and ultraviolet wavelengths
VisiCalc Visible Calculator Ahistoric 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 Anextra
transmissions line is needed for audio See Cameo
Personal Video System, Connect 918, MacMICA,
IRIS, ShareView 3000
Visual BASIC Abasic Microsoft Windows
program-ming application development product with a
graphi-cal user programming interface from Microsoft
Cor-poration Suitable for prototyping, although extensive
use ofdynamic linked libraries (DLL) may be needed
for extensive applications development
visual ringer Asmall lamp on a phone console,
usu-ally 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 ofelectrostatic charge produced on glass
when rubbed with silk Benjamin Franklin later
pro-posedpositive, 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 ofthe
switch fabric Within the switches are identical
data-bases describing the topology maintained Switches
to determine a routing path over which a call can be connected VLSP supports equal-cost multipath rout-ing 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 Astandard software front end and software layer that provides an entry and exit point to modem functions implemented through a variety ofmodem standards, for DSP Soft-ware Engineering modem products
VNS virtual network system, virtual network service vocodervoice coder Alate 1930s invention that
pro-vided a means for analyzing the pitch and energy con-tent of speech waves This technology led to the de-velopment of a device designed to transmit speech over distance without the waveform The transmis-sion was expressed at the receiving end with a syn-thetic speaking machine This general concept has evolved into linear predictive encoders
VoFR voice over frame relay See Frame Relay, voice over
voice activity detection VAD A capability of digi-tal voice communications systems to distinguish be-tween information, such as speech, and the silences
in between the speech elements Typically, voice con-versations consist ofonly 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 sup-pression
voice-activated system Asystem 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~~.tTech-~~~~~~fd •
not be confused with a speech-recognition system that recognizes actual words, not just a general or particu-lar 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 record-ing rate, and the encodrecord-ing 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 suit-able for transmitting clear voice conversations within frequencies between 300 and 3300 Hz It is not
Trang 9Fiber Optics Illustrated Dictionary
typically suitable for other faster, higher bandwidth
uses Voice is a relatively 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
se-ries of standardized increments.See jumbogroup for
a diagram
voice over ATM VoATM A growing area of
inter-est, voice over ATM involves the digital transmission
ofvoice conversations (which traditionally have been
carried over analog phone lines) over asynchronous
transfer mode (ATM) networks Typically this
in-volves 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
af-fect the transmission ofthe 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
or-der to prevent echo on the line ATM networks make
use ofecho 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
net-work, 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 overIPVoIP Voice over IP involves
digitiz-ing conversations and other human vocalizations so
they can be transmitted over data networks This
usu-ally involves compression of the sound, as voice
ap-plications 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 overIPForum VoIPF A group 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 ofways
in which wide bandwidth data networks can be used
to send telephone voice calls The call can be initi-ated through a regular phone line that connects to a private or public network, or through a computer voice system hooked directly to a network 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 encod-ing 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 de-vices 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,
ver-sion 1, it was based upon the Audio Message
Inter-change Specification (AMIS), which facilitates mes-sage interchange among voice mail messaging on systems from different vendors VPIM differs from AMIS in that it is a digital specification based on com-mon internetworking protocols The VPIM took into consideration common limitations of voice messag-ing 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 pro-tocols for digital voice messaging services.It speci-fies a restricted set of Internet multimedia messag-ing protocols for the provision of a minimum com-mon set of features for internetworking acom-mong dif-ferent voice processing servers See Audio Messag-ing Interchange Specification, Network Voice Proto-col, Voice File Interchange ProtoProto-col, 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 voicemail 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 at-tachment 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,
Trang 10a 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
sys-tems, technical support syssys-tems, and for providing
product information and purchase options to callers
Because electronic voice mail applications are
digi-tal, they can be programmed to provide a wide
vari-ety of services, according to the needs and
imagina-tion of the programmer and user
volt (Symbol v orefor voltage) A SI unit of
electri-cal potential When a difference of electrielectri-cal
poten-tial occurs between materials or portions of
materi-als where there is a pathway between them, electrons
seek a direction of flow which balances that
poten-tial 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) Aphysicist who pursued many
of the ideas proposed by Luigi Galvani by studying
the varying electrical properties of different
materi-als He questioned Galvani's explanation of 'animal
electricity' and proposed that the reaction of the
muscle to stimulation of a 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 asgalvanic 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, aunit
ofelectromo-tive 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 acrown ofcups.The metal plates were
placed in separate cups containing liquid, some
dis-Each cup is now known as avoltaic cell and a pair is
known as avoltaic battery See capacitor, thin film.
Voltaic Piles - Historic Capacitors
Two historic voltaic piles show the alternating lay-ers ofmaterials 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 poten-tial 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, some-times also called a coulomb-meter or coulometer See volt
von Bunsen, Robert Wilhelm AGerman 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)Anearly experimenter who devised a machine that amplified and demon-strated 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 ofthe Earth He noted also that holding certain substances
up to the sphere would produce a spark He discov-ered basic principles of air pumps and demonstrated characteristics ofvacuums with his Magdeburg hemi-spheres in 1663 A university in Magdeburg, Ger-many is named after him
von Kleist, Ewald Christian (1715-1759) AGerman 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