Access Card A coded card, about the size of a credit card, that
grants a user access to a particular area or building—usually by being submitted
to a card reader. It can also be used for photo identification of the cardholder
and for other data collection purposes. Card technologies include magnetic strips,
Wiegand-effect, proximity (active/passive), barium ferrite, and smart/intelligent
Access Code A code that’s entered manually on a keypad to give an
individual access to a particular area through a door or gate in an access controlled
Access Level The door or combination of doors and/or barriers an
individual is authorized to pass through.
Access Relay An electrically operated switch that is activated to
unlock a door.
Access Time The amount of time that an access door is unlocked for
Alarming The ability of CCTV equipment to respond to an input signal,
normally a simple contact closure. The response varies depending on equipment type.
Amplifier Electronic system used to boost, or increase, the gain of
Amplitude Distortion An unwanted change in signal amplitude.
Analog-to-Digital Converter A device that converts incoming analog
signals into digital information.
Angle of View The angular range that can be focused within the image
size. Small focal lengths give a wide angle of view, and large focal lengths give a
narrow field of view.
Annunciator An audible and/or visual signaling device that gives
notice of a door being open.
Aperture The opening of a lens, which controls the amount of light
reaching the surface of the pickup device (CCD). The size of the aperture is
controlled by the iris adjustment. By increasing the f-stop number (f1.4, f1.8, f2.8,
etc.), less light is permitted to pass to the pickup device.
Aspect ratio The ratio of the picture frame width to the picture
frame height in standard TV systems. It is 4 units horizontal over 3 units vertical.
Attenuation The loss of signal strength as it flows through a cable.
Usually expressed in decibels (dB). The loss of signal strength as it flows through a
cable. Usually expressed in decibels (dB).
Audit Trail A listing that may be used to monitor the progress of a
person through protected areas. Can be created in real time.
Authentication Verification of a user’s identity when the user logs
onto a network.
Automatic Frequency Control (AFC) An electronic circuit used in which
the frequency of an oscillator is automatically maintained within specified limits.
Automatic Gain Control (AGC) An electronic circuit in which the gain
of a signal is automatically adjusted as a function of its input or other specified
Automatic Iris Lens A lens in which the aperture opens or closes
automatically to maintain proper light levels on the faceplate of the pickup device
Automatic Level Control (ALC) Assigns the amplifier’s output level
automatically to ensure a consistent paging level. It keeps loud voices from booming
out of the paging system’s speakers and enables people with weak voices to be clearly
heard. It also makes it easier to understand people in noisy environments.
Auto White Balance A feature on color cameras that constantly
monitors the light and adjusts its color to maintain white areas.
AWG (American Wire Gauge) A method of measuring wire-conductor
diameter. The number refers to the number of steps involved in drawing the wire.
The more a wire is drawn or sized, the smaller the diameter is. For example, 24 AWG
wire is smaller than 19 AWG wire.
Back Focal Distance The distance from the rear-most portion of the
lens to the image plane.
Back Light Compensation (BLC) A feature on newer CCD cameras that
compensates electronically for high background lighting to give detail that would
normally be silhouetted.
Badge To use a card key in a reader to gain access to protected areas.
Balun A device used to match or transform an unbalanced coaxial cable
to a balanced twisted-pair cable.
Bandwidth A measure of the carrying capacity of information over a
network. Video, for example, takes more bandwidth to transmit over a network than text does.
Baseband The frequency band occupied by the aggregate of the signals
used to modulate a carrier before they combine with the carrier in the modulation
process. In CCTV, the majority of signals are in the baseband.
Bend Loss Increased attenuation in a fiber that results from the
fiber’s being bent or from minute distortions within the fiber.
Bend Radius A measurement of a cable’s flexibility, it’s the radius
of the smallest circle you can form with the cable without damaging it.
Biometrics Refers to readers that identify human attributes such as
fingerprint, hand geometry, voice recognition, or retinal analysis.
Black Level The level of the video signal that corresponds to the
maximum limits of the black areas of the picture.
BNC (Bayonet-Neill-Concelman) A commonly used connector for coaxial
cable. After insertion, the plug is turned, tightening the pins in the socket.
Boot Sector Viruses Computer viruses that infect the boot sector on a
floppy disk or the Master Boot Record (MBR) on a hard drive by overwriting the
original boot code with its own code. The boot sector, or MBR, generally resides on
the first sectors of a hard disk and controls the boot sequence when a computer is
started up. A virus that infects the these sectors is especially dangerous because,
every time the computer is started up, the virus is loaded into memory from where it
can spread to other parts of the hard disk or to another disk. Boot sector viruses
frequently cause a complete system failure in which a PC can’t start up or find its
Broadband A technique for sending data, voice, and video traffic over
long distances by transmitting high-frequency signals over coaxial or fiber optic
Buffer Capacity Refers to the amount of information the system can
store. This may include the users, time of day, and specific door.
CATV (Community Antenna Television or Cable Television) A
publically or privately owned system that uses coaxial cable to transmit broadcast
television programming received by a central antenna to subscribers.
CCD (Charged Coupled Device) A chip that picks up the image and
converts it to an electrical signal.
CCTV (Closed Circuit Television) A private television system in which
video signals are transmitted over a privately owned cable.
Candela In the International System of Units (SI), the candela is the
base unit of measuring luminous intensity.
Candlepower The unit measure of an incident light.
Channel Balance In a stereo system, the level balances between left
and right channels. Properly balanced, the audio should be centered between the left
and right speakers.
Cladding The plastic or glass sheath that’s fused and surrounding the
core of an optical fiber. It keeps the lightwaves inside the core and adds strength
Clamping Voltages The “sustained” voltage held by a clamp circuit at
a desired level.
Coaxial Cable A type of cable that can pass a range of frequencies
with low loss. It consists of a hollow metallic shield in which one or more center
conductors are put in place and isolated from one another and from the shield.
CODEC (Code/Decode) An encoder plus a decoder. It’s an electronic
device that compresses and decompresses digital signals. CODECs usually perform
analog-to-digital and digital-to-analog conversion.
Composite Video Signal A signal in which the luminance and
chrominance information has been combined using one of the coding standards: NTSC,
PAL, SECAM, etc.
Conditional Refresh A technique used in slow and fast scan
transmission equipment, where only small screen changes are transmitted. Up to a
certain percentage of the on-screen picture can be updated before a full picture
update is required.
Control Panel A set of utilities that change various aspects of the
system’s behavior, such as the color of the background, the port to which printer
data is sent, the speed of the mouse cursor, etc.
Crosstalk Signal interference from one cable pair to another pair
(or other pairs) in the same cable sheath.
Cycles per Second The frequency of an electrical signal or soundwave.
Measured in Hertz (Hz).
Database A collection of data used and produced by a computer program.
The files created at the host of the access control system forms its database.
Data Encryption Standard (DES) An encryption technique that scrambles
data into an unbreakable code for public transmission.
Decibel (dB) A measure of the power ratio of two signals. It is equal
to ten times the logarithm of the ratio of the two signals.
Demilitarized Zone (DMZ) A separate network used to isolate public
services from your private network. Both users from the Internet and users from the
secure network may access servers in the DMZ. Traffic may not travel from the Internet
or the DMZ directly to the secure network without first going through a proxy server
(usually a firewall).
Denial-of-Service Attacks that bombard a Web server with more
requests for connections than it can handle, causing it to become so slow as to be
unusable or even crash entirely.
Depth of Field The front-to-back zone in the field of view that is in
focus in a televised scene. With a greater depth of field, more of the scene is in
Digital Certificates An electronic document, provided by a trusted
third party, made up of a public key, digital signature, owner identity, serial number,
issuer, and expiration date. Used in private and public key encryption.
Digital Disc Recorder A system that enables recording of video images
on a digital disc. .
Digital Signature An electronic code that is unique and virtually
impossible to copy or transfer.
Distortion The unwanted changes in signal or signal shape that occur
during transmission between two points.
Distributed Intelligent Device An access control device that makes
its own access decisions, uploads event messages periodically, and periodically saves
Distribution Amplifier A device that accepts a signal and sends it
out to a number of independent outputs.
Door Open Time The time allowed for a controlled door to remain open
after a valid entry.
Duplex To perform two functions simultaneously. For example, a DVR
can record video while playing back video at the same time.
DVI (Digital Visual Interface) A connector that provides bandwidth
needed for devices as well as plenty of headroom for the future. (See DVI-D and DVI-I.)
DVI-D Digital-only connector.
DVI-I Supports both digital and analog connections.
Dwell Time The length of time a switcher holds on a camera before
moving on to the next camera.
Electronic Access and Control Used to control who is allowed into an
area of a building, the building itself, or even a campus. It can also control when
access is allowed, and it can track when and where each user enters. An electronic
credential—a magnetic card, a PIN, or even a biometric scan—is provided to a user.
The user presents this credential to a reader to gain entry. The door controller,
which contains the programming for who has access, allows entry.
Electronic Shuttering The ability of the camera to compensate for
moderate light changes in indoor applications without the use of auto iris lenses.
Encoding/Decoding The process of organizing information into a format
suitable for transmission and recovery.
Encryption The rearrangement of a previously digitally encoded
signal’s bit stream in a systematic fashion to make the information unrecognizable.
Information is only restored on receipt of the necessary authorization key. This
technique is used for securing information transmitted over a communication channel
with the intent of excluding all other than authorized receivers from interpreting
the message. Can be used for voice, video, and other communications signals.
Encryption Algorithms Mathematical formulas used to scramble information.
Equalization The process of correcting losses of certain components in a signal.
f-number The f-number indicates the brightness of an image formed by
the lens, controlled by the iris. The smaller the f-number, the brighter the image.
f-stop A term used to measure the size of a lens aperture.
Feedback (Acoustic) Unwanted interaction between the output and input
of an acoustical system, for example, between the loudspeaker and the microphone of a
Fiber Loss The amount of signal attenuation in a fiber optic transmission.
Fiber Optics Flexible glass fibers used to conduct energy. Ideal for
secure transmissions. If someone tries to tap fiber, light leaks and transmission
fails, so a tap can be detected instantly.
Field One half of a frame, consisting of either the odd or the even
numbered lines; 60 fields are transmitted every second.
File-Infecting Viruses Common computer viruses that infect executable
files by adding their own code to that of the original file. When a user opens an
infected file, the virus attaches itself to other executable files. When infected
files are transferred to another computer, the virus travels with them and finds more
files to infect. Because they require the transfer of an executable file, which most
people know not to open, common file-infecting viruses tend to spread relatively
slowly and don’t cause the wildfire infections across the Internet that worms do.
Firewall A network node set up as a boundary to prevent traffic from
one segment to cross over to another. Firewalls are used to improve network traffic,
as well as for security purposes. The most common application for a firewall is to
control traffic between a private network and the Internet to intercept outsiders
trying to break into the private network. A firewall exerts this control by applying
rules to information—primarily IP addresses and port numbers—found in
incoming network packets.
Focal Length The distance from the center of the lens to the pickup
device (CCD). The focal length determines the size of the image and the angle of the
field of view seen by the camera through the lens.
Foot-Candle (FC) The light intensity (illumination) of a surface one
foot distant from a source of one candle. It is equal to one lumen per square foot.
(1 FC = 1 lm/sq. ft.). The foot-candle is the unit used to measure incident light.
Frame The total area of the picture that is scanned while the picture
signal is not blanked.
Frequency The measure of the rapidity of alterations of a periodic
signal, expressed in cycles per second or Hz.
Front Porch The portion of the composite video signal that lies
between the leading edge of the horizontal blanking pulse and the leading edge of the
corresponding synchronizing pulse.
Full-Motion Video Video transmission that changes the image 30 frames
per second (fps).
Gain Amount of signal amplification, usually expressed in decibels.
The relative increase in voltage, current, or power from the input signal to the output signal.
GB (Gigabyte) Unit of computer memory consisting of about one
thousand million bytes (one thousand megabytes). Actual value is 1,073,741,824 bytes.
Gen-lock A method used to synchronize one or more cameras by external
means such as Composite video, Composite sync, horizontal sync or vertical sync.
Ghost A shadowy or weak image in the received picture, offset either
to the right or to the left of the primary image. It is the result of transmission
conditions in which secondary signals are created and received earlier or later than
the primary signal.
GHz (GigaHertz) One billion cycles per second.
Ground An electrical connection point that is common to either a
metal chassis, a terminal, or a ground bus.
Ground Fault The temporary current in the ground line, caused by a
failing electrical component or interference from an external electrical source such
as a thunderstorm.
Ground Loop Caused by different earth potentials in a system. Seen on
a video transmission as a black shadow bar across the screen or as tearing in the top
corner of a picture.
Hacker A person who maliciously breaks into networks, breaks the
security on application software, or creates viruses. Hackers often use known
security holes in operating systems to penetrate networks. They find security holes
to exploit by pinging a network to find an open IP address and then probing to find
an open port. Many corporate firewalls are probed thousands of times a day by hackers
looking for a security hole.
Headend The electronic equipment at the start of a cable system;
usually switches, multiplexors, and digital recorder equipment.
Horizontal Resolution The maximum number of individual picture
elements that can be distinguished in a single scanning line.
Image Size The size of an image formed by the lens onto the pickup
device (CCD). The current standards are 1", 2/3", 1/2" and 1/3" measured diagonally.
Impedance The resistance to the flow of current in a circuit.
Incident Light The light that is falling directly over an object.
Insertion Loss The signal strength loss that occurs when a piece of
equipment is inserted into a line.
Interlace A process where every other horizontal line is scanned in
one field while the alternate lines are scanned in the next field to produce a
complete picture frame.
Interleaving A method used in alarms or activity detection, which
allows extra frames of video from alarmed cameras to be added to a time-multiplexed
sequence while a state of alarm exists.
Iris A means of controlling the size of a lens aperture and therefore
the amount of light passing through the lens.
Lag The image retention of an object after the object has been
scanned; can cause a smearing effect.
LCD (Liquid-Crystal Display) A display technology that uses rod-shaped
crystals that flow like liquid and bend light.
Lens An optical device for focusing a desired scene onto the imaging
device in a camera.
Level Control Main iris control. Used to set the auto-iris circuit to
a video level desired by the user. After setup, the circuit adjusts the iris to
maintain this video level in changing lighting conditions. Turning the control
towards High opens the iris and towards Low closes the iris.
Line of Sight An unobstructed view from one location to another that
is used to send a video signal wirelessly between two locations.
Link Lock To lock the field frequencies of multiple cameras to the
same AC power source frequency for the purpose of having the cameras share a common
Looping Occurs when a high impedance device has been permanently
connected in parallel to a video source.
Loudspeaker An electroacoustical transducer that changes electrical
energy to acoustical energy.
Lumen (lm) A unit of measuring light intensity produced by the
luminosity of 1 candela (cd) in one radian of a solid angle.
Lux (lx) A unit of measuring the intensity of light on a surface
(10.764 lx = 1 footcandle [FC]).
Macro Viruses Viruses written in the internal macro language provided
with many applications. Macro viruses are extremely common—especially within
Microsoft® Excel® and Microsoft Word files. They spread easily because they
travel in documents that are often shared and also because many of them, in wormlike
fashion, e-mail themselves to everyone they find in an address book. Because macro
viruses are so easy to write and modify, new ones pop up all the time. Additionally,
because macro viruses spread within an application, they may spread between operating
systems—for instance from a PC to a Mac®.
Mail Bomb A form of denial-of-service attack that shuts down e-mail
servers by swamping them with more e-mail than they can handle.
Manual Iris Lens A lens with a manual adjustment to set the iris
opening (f-stop) in a fixed position. Generally used for fixed lighting applications.
Matrix Switcher A switcher able to route any of its inputs (cameras)
to any of its outputs (monitors); matrix switches often include telemetry control.
Mbps Megabits per second (bps).
Mechanical Focus (Back Focus) The mechanical aligning of the imaging
device with the focal point of the lens; it is most important on zoom lenses to be
sure the image stays in focus throughout the zoom range.
Megahertz (MHz) A unit of frequency equal to 1,000,000 cycles per second.
Modulate To change or vary a parameter, such as the amplitude of a
signal for amplitude modulation or the frequency of a signal for frequency modulation.
Multimode Fiber An optical fiber with a core diameter of 50 to 100
microns. Its core causes some distortion and provides less bandwidth than single-mode
Multipartite Viruses The hybrids of the virus world, most commonly a
combination of boot sector viruses and file infecting viruses. They commonly infect
both system sectors and files. These viruses are fairly rare because they’re difficult
to write but tend to be particularly nasty when they occur.
Multiplexing Transmitting multiple signals over a single
communications line or computer channel.
Network Computers connected together to share information. Two types
of networks are Local Area Networks (LANs) and Wide Area Networks (WANs).
NEXT (Near-End Crosstalk) Signal interference from one cable pair
that adversely affects another pair on the same end.
Noise Random spurts of electrical energy or interference.
NTSC (National Television System Committee) An organization that
formulated the standards for the current United States color television system. This
system is used in most countries of the Americas, as well as other parts of the world.
NTSC uses 525 lines per frame, 29.97 frames per second, and 59.94 fields per second.
Opto-Isolator A small device that converts the input of electrical
signals to light signals and converts them back to electrical signals on the output
Overscan A video-display effect in which the image is enlarged so
that its edges are off the screen.
PAL (Phase Alternation Line) A European color TV system featuring
625 lines per frame, 25 frames per second and 50 fields per second. PAL is used
mainly in Europe, China, Malaysia, Australia, New Zealand, the Middle East, and parts
Passive Device A device that must draw its current from connected
active equipment. A balun, for example, is a passive device.
Peak-to-Peak The amplitude difference between the highest and lowest
parts of a signal.
PIN (Personal Identification Number) A code number used to restrict
access to a service to the person authorized to use it.
Pixel Stands for picture elements. Pixels are the tiny dots of
information that make up a digital image. The more pixels there are on the camera’s
image sensor (CCD or CMOS), the higher the image resolution is. The higher the
resolution, the clearer a video image or an enlarged print is.
Policy Routing Routing method that forwards packets to specific
interfaces based on user-configured policies.
Polymorphic Virus A virus that attempts to defeat virus-scanning
software by using an algorithm to encrypt itself each time it infects a new host.
The encrypted virus escapes detection by the antivirus software and then decrypts
itself to infect the computer. This virus is very difficult to detect because its
signature is different every time it infects a new host. More sophisticated
polymorphic viruses vary their encryption methods, making them even more difficult
Power The rate at which electrical energy is applied to or taken from
a device. It is expressed in terms of watts, milliwatts, or microwatts.
Pre-position Lenses Zoom lenses that use a variable-resistor
(potentiometer) to indicate zoom/focus position to the lens controller. After initial
setup, this enables the operator to view different preset areas quickly without
having to readjust the zoom and focus each time.
Private and Public Keys Mathematical codes used for encryption of
transmitted data. A secret private key and a mathematically related public key are
generated for each party in a transmission. When someone wants to send a secure
message, they use the public key of the recipient to encrypt the message. The
recipient then uses his/her private key to decrypt it. It is virtually impossible
to deduce the private key from the public key.
PTZ Camera Pan, tilt, and zoom camera.
PVC (Polyvinyl Chloride) The type of plastic from which cable jackets
and wire insulation are usually made.
QoS (Quality of Service) Measure of performance for a transmission
system that reflects its transmission quality and service availability.
Radio Frequency (RF) Any of the electromagnetic wave frequencies that
lie in the range extending from below 3 kilohertz to about 300 Gigahertz.
Random Interlace A scanning technique commonly used in CCTV systems
in which there is no external control over the scanning process. There is no fixed
relationship between adjacent lines and successive fields.
Range Finder Used to determine the focal length needed and what the
picture will look like on a monitor. The user looks through the device and adjusts
the range finder to the desired picture. Numbers on the outside of the range finder
indicate the focal length needed.
Reflected Light The scene brightness or the light being reflected
from a scene. Usually it represents 5 to 95 percent of the incident light, and it is
expressed in foot-lamberts.
Resolution A measure of the ability of a camera or television system
to reproduce detail. It is the number of picture elements that can be reproduced with
Retained Image (Image Burn) A change produced in or on the target of
the pickup device (CCD), which remains for a large number of frames after the removal
of a previously stationary light image and that yields a spurious electrical signal
that corresponds to that light image.
RG11 A video coaxial cable with 75 ohms impedance and much thicker
diameter (around 12 mm) than RG59. RG11 provides at least twice the distance of RG59
cable and is most commonly used in large CCTV systems.
RG58 A coaxial cable designed with 50-ohm impedance; not suitable for
RG59 A type of coaxial cable that is most common in small to
medium-size CCTV systems. It is designed with an impedance of 75 ohms, and it has an
outer diameter of around 6 mm.
Roll A loss of vertical sync that causes the picture to move up or
down on the TV screen.
Saturation (Color) The vividness of a color. It is directly related
to the amplitude of the chrominance signal.
Scanning The rapid movement of the electronic beam in a pickup device
of a camera or in the CRT of a television receiver. It is formatted line by line
across the photo-sensitive surface that produces or reproduces the video picture.
When referring to a video surveillance field, it is the panning or the horizontal
Sensitivity The amount of responsiveness to an incident light on the
pickup device (CCD) on a camera, indicating how much the device is affected or changed
Shielding The process of protecting a cable with a grounded metal
surrounding, so electrical signals from outside the cable cannot interfere with
transmission inside the cable.
Signal-to-Noise Ratio The ratio between a useful video signal and
Simplex Multiplexor A multiplexor that enables the user to look at
multiscreen images or perform time-multiplex recording. It cannot record multiplexor
pictures while showing multiscreen pictures.
Single-Mode Fiber An optical glass fiber that consists of a core of
very small diameter. A typical single-mode fiber used in CCTV has a 9-µm core and a
125-µm outer diameter. Single-mode fiber has less attenuation and therefore transmits
signals at longer distances than multimode fiber.
SMPTE (Society of Motion Picture and Television Engineers) A
professional group whose committees set standards in television and motion picture
industries. The RS-422 SMPTE serial interface is used on video equipment.
Sound Pressure Level (SPL) The expression of loudness or volume;
measured in decibels (dB). A 10 dB increase in SPL represents a doubling in volume.
Spam Internet junk e-mail that clogs servers and in-boxes with offers
for dubious products, links to pornographic sites, chain letters, hoaxes, and scams
of all kinds. At best, spam is a nuisance, but if you’re not paying attention, spam
can also be dangerous.
Spot Filter A small insert used in a lens to increase the f-stop
range of the lens.
Stealth Viruses These are computer viruses that actively hide
themselves, often in a PC’s memory. They can fool the operating system by modifying
and forging the results of calls to functions in the infected file, so the system
believes it’s reading the original file. A stealth virus can even hide the fact that
it’s consuming memory. Stealth viruses hide themselves so well, they can sometimes
fool antivirus products into thinking a computer is virus free.
STP (Shielded Twisted Pair) Cabling that is a twisted-pair cable with
a foil and/or braided shield to minimize EMI/RFI.
Surge Protector A device that protects computers from excessive
voltage and current in the power line.
Sync Electronic pulses that are inserted in the video signal for the
purpose of assembling the picture information in the correct position.
TDG (Time and Date Generator) A function that enables the time
and data to be recorded on a tape used in a video surveillance operation.
Telemetry Remote controlling system used to control digital encoded
data. Used for pan, tilt, zoom, focus, preset positions, wash, wipe, etc. Because the
data used to control these functions is digital, it’s usually sent via twisted-pair
or coaxial cable with the video signal.
Terabyte (TB, Tbyte, or Ter) 1,099,511,627,776 bytes.
Time-Lapse Video Recording The intermittent recording of video signals
at intervals to extend the recording time of the recording medium.
Time Multiplexing The technique of recording several cameras onto one
time-lapse VCR by sequentially sending camera pictures with a time interval delay to
match the time-lapse mode selected on the recorder.
Tracking A zoom lens’ ability to remain in focus during the entire
zoom range from wide angle to telephoto position.
Transceiver A hardware device that links a node with a baseband
network backbone, enabling transmitting and receiving capabilities.
Transformer An electromagnetic device that can increase (step up) or
decrease (step down) the voltage of alternating currents.
Trojan Horse A virus program disguised as a legitimate program. A
Trojan horse does not replicate itself but depends on its users to spread. It’s often
a game or utility that seems to do one thing but has incorporated within itself
another, secret function that will cause damage, pass on information about your
computer, or enable its sender to hijack your computer. Trojan horses are often part
of hybrid or multipartite viruses. For instance a Trojan Horse may be “planted” in an
application by a worm or it may incorporate a virus within itself.
Twisted Pair A cable composed of two insulated conductors twisted
together. Because both wires have nearly equal exposure to any interference, the
differential noise is slight.
Unbalanced Signal In CCTV, this refers to a type of video signal
transmission through a coaxial cable. It is called unbalanced because the signal
travels through the center core only, while the cable shield is used for equating
the two voltage potentials between the coaxial cable ends.
Unity Gain In broadband networks, this is the balance between signal
loss and signal gain through amplifiers.
UTP Unshielded twisted pair. A cable with one or more pairs of twisted
insulated copper conductors bound in a single sheath.
Vertical Interval The time it takes for vertical retrace.
Vertical Retrace The return of the electron beam to the top of a
television picture tube screen or a pickup device (CCD) at the completion of the
Video Motion Detection A system that uses the video signal from a
camera to determine if there is any movement in the picture and set off an alarm.
Video Type Lens An auto-iris lens without an internal circuit to
control the iris. All iris control voltages come from a circuit located within the
Virus Software code—usually disguised as something innocent—that
replicates itself in PCs. Some viruses need help to reproduce, some replicate all by
themselves, but all reproduce without your permission or knowledge. Viruses often
have an infection phase where they reproduce and an attack phase where they do damage.
The ability to infect varies from virus to virus, as does the damage they can cause.
Viruses are roughly categorized into subgroups such as common file-infecting viruses,
worms, Trojan horses, macro viruses, and others.
VLAN (Virtual Local Area Network) A network of computers that behave
as if they were connected to the same wire even though they may be physcially located
on different segments of the LAN—or even on a different LAN entirely. VLANs are
configured through software rather than hardware, which makes them extremely flexible.
The advantages of VLANs include increased performance, improved management,
simplification of software configurations, and increased security.
Volt The unit of measurement of electromotive force. One volt is the
force required to produce a current of one ampere through a resistance of one ohm.
VPN (Virtual Private Network) A means of segmenting a network and
prioritizing traffic based on a selected set of users. Tunneling encapsulates the
data on these networks; encryption protects it.
Watt The measurement of electrical power that equates to one watt and
is equal to one ampere of current flowing at one volt.
White Balance An electronic process used in video cameras to retain
true colors. It is performed electronically on the basis of a white object in the
Wide Angle Lens A lens that may be effectively used for a wide angle of view.
Worm Self-replicating computer viruses. Unlike an ordinary virus,
which depends on the transfer of a host file in order to replicate, a worm is an
independent entity that usually spreads itself without needing a computer user to
transfer a file. Most travel primarily by e-mail but some also spread through
nontraditional means through the IRC, peer-to-peer networks, or even Web sites.
Worms tend to spread very rapidly and can cause a lot of damage.
YUV Describes the analog luminance and color-difference signals in
component video systems. Y is for luminance; U and V are the two subcarrier modulation
axes used in the PAL color-coding system.
Zoom Lens A lens system that may be effectively used as a wide angle,
standard, or telephoto lens by varying the focal length of the lens.
Zoom Ratio The ratio of the starting focal length (wide position) to
the ending focal length (telephoto position) of a zoom lens. A lens with a 10X zoom
ratio magnifies the image at the wide-angle end by 10 times.