This is a compression mechanism commonly used for storing large amounts of data on limited-space optical me-dia.. Broadband ISDN is intended for services that require channel rates great
Trang 1designed to provide enhanced broadband phone fea-tures through CDMA technology InterDigital is col-laborating with Siemens AG and Samsung Electron-ics Company, Ltd., in developing the proprietary B-CDMA technology See COMA
B-DC, BDC broadband digital cross-connect See broadband digital cross-connect system
B-DCS, BDCS See broadband digital cross-connect system
B-frame bidirectionally predictive-coded frame.In MPEG animations, a picture that has been encoded into a video frame according to information derived from both past or later frames in the sequence, using predicted motion compensation algorithms This is a compression mechanism commonly used for storing large amounts of data on limited-space optical me-dia See I-frame, P-frame
B-ICI B-ISDN (Broadband-ISDN) InterCarrier In-terface 1 A specification defined by The ATM F 0-rum for the connecting interface between public ATM networks, for the support ofuser services across mul-tiple public carriers 2.AnlTU-T standard for proto-cols and procedures for broadband switched virtual connections (SVCs) between public networks B-ICI SAAL Broadband Inter-Carrier Interface Sig-naling ATM Adaptation Layer A sigSig-naling layer en-abling the transfer ofconnection control signaling and ensuring reliable delivery of the protocol message See asynchronous transfer mode, SAAL, AAL5 B-ISDN Broadband ISDN See ISDN for an intro-duction to ISDN concepts B-ISDN was designed to meet some of the demands for increased speed and enhanced services on primary ISDN lines It was geared to the needs ofcommercial users It has since evolved into a strategy for delivery for many new tele-communications services including teleconferencing, remote banking, videoconferencing, interactive TV, audio, and text transmissions Broadband ISDN is intended for services that require channel rates greater than single primary rate channels (i.e., voice at 64 kbps) and thus are offered over fiber optic-based tele-phone systems B-ISDN services can be broadly or-ganized as follows:
The essential characteristics ofB-ISDN services were approved in the I-series Recommendations by the
messaging, data paging, electronic mail, data
files (images, sound, formatted documents)
Fiber Optics Illustrated Dictionary
station, Fiber Distributed Data Interface, optical
by-pass, port adaptor See Aport for a diagram
B Series Recommendations A series of ITU-T
rec-ommendations providing guidelines for the various
means of expression of information, including
defi-nitions, symbols, and classification These guidelines
are available as publications from the lTU-T for
pur-chase and some are downloadable without charge
from the Net Since lTV-T specifications and
recom-mendations are widely followed by vendors in the
telecommunications industry, those wanting to
maxi-mize interoperability with other systems need to be
aware of the information disseminated by the
ITV-T A full list of general categories is listed in the
Ap-pendix and specific series topics are listed under
in-dividual entries in this dictionary, e.g., ASeries
Rec-ommendations
:.· · r
Rae Date.'PeIPrintinn
BJ ·1988';~~llIi~i~ml~~~ns
B.3 1988 U~oftheinterna.tional systemlofunits
(~I) •• '.' •· • i.
B."lQ 1988 ~1'~caJ$,Ym~~~~angrule§{~tJ1e
~tion Qf«Q~\DIlel1taticil1m'
telecpmmunicatiQDS
B.ll 1988 Le.~Ititne-~~fthe term·UTe
;~t~I~Imr-nUIli$.~:·· .
B.l~ c 1988 ·'fEianddefil1if.jpDS
B.14· 1988· :t'et11'lSand~1.sforinfbrn1J1tion
wa'V~leJ1gth'llJl4~;U$ed ~ '.
tele(:Oll1tnunicltiQJ1S
B.16 1988 q~9fcertain~linked.witb
g~~~i~lJgll~I~~r ·· •.••.•• •.•••.•• •.••••.•• ·i: •
B.l1 1988 AAAptionofme.~fPIrTSp~*~cation
an4descriptiQ1.lJapguage (SDL)
B.18 19~1 Traftjcintensity~t
B.19 1996 J\.ll~~~~lltioIl~~~:initblls· us~m
jel~~mm~~@ti.9gs
B Series Standards A series ofTIA/EIA documents
related to cabling standards, many of which are
di-rectly relevant to fiber optic cable design and
instal-lation, as illustrated in the accompanying chart The
text ofthese documents is available for purchase from
the TIA online See TIA/EIA B Series chart
B signal See Grade B signal
B-911A telephone emergency response system with
a subset ofthe capabilities ofa fu1l911 system Most
notably, it doesn't include Automatic Location
Infor-mation (ALI)
B-CDMA Broadband Code Division Multiple
Ac-cess InterDigital Communication Corporation's
commercial wireless local loop TrueLink product
Category
conversation
interactive
Example activities
telephone, conferencing, audiographics, videotelephone, videoconferencing
distance education, services-on-demand, Web browsing, retrieval services such as news, stocks, etc
Trang 2dards and specific recommendations for
implemen-tation, including network architecture, operations,
and maintenance
Recommendations to use ATM as the switching
in-frastructure for B-ISDN contributed to the formation
of the international ATM Forum which promotes
commercial implementation ofATM and related
tech-nologies
Physical layer transmission for B-ISDN is
accom-plished through the Synchronous Optical Network
(SONET) system See I Series Recommendations
B-LT See broadband line termination
B-MAC, BMAC Broadcast MasterAntenna Control
A device to control a communications antenna (e.g.,
microwave radio antenna) Traditionally it has been
a self-contained unit, but computer software
appli-cations that emulate a controller unit are gaining
popularity (with the traditional switches and dials
being graphically displayed on the screen)
B-NT broadband network termination See
broad-band line termination
B-picture bidirectionally predictive-coded picture.In
frame that is encoded according to infonnation de-rived from both past or later frames in the sequence, using predicted motion compensation algorithms Once encoded, it is considered to be a B-frame See MPEG encoder
B-scope, E-Scope A radar screen displaying infor-mation on range (V-axis) and bearing in rectangular coordinates See A-scope, C-scope
B-TE Broadband Terminal Equipment An equip-ment category for broadband ISDN (B-ISDN) con-necting devices, B-TE encompasses terminal adapt-ers and terminals See ISDN
B8ZS binarylbipolar eight-zero substitution A line-code substitution technique to guarantee density in network transmissions independent of the data stream It is used on T1 and E1 network lines The zeros can be replaced at the receiving end to restore the original signal
Babbage, Charles(1791-1871)An E.nglish re-searcher who contributed a great deal to the theory and practice of computing and conceived his now-famous analytical engine by1834.While Babbage's
TIAIEIA B Series Standards
Committee/Description
Optical Fiber Cabling Components Standard (ANSI/TIA/EIA-568-B.3-2000)
Specifies the component and transmission requirements for an optical fiber cabling system (e.g., cable, connectors)
Provides corrections to the 568-B.2 Standard
Commercial Building Telecommunications Cabling Standard - Part 1: General Requirements - Addendum 1 - Minimum 4-Pair UTP and 4-Pair ScTP Patch Cable Bend Radius
Applies to minimum 4-pair unshielded twisted-pair (UTP) and 4-pair screened twisted-pair (ScTP) patch cable bend radius
Commercial Building Telecommunications Cabling Standard - Part 1: General Requirements
This standard specifies a generic telecommunications cabling system for commercial buildings that will support a multi-product, multi-vendor environment
TWisted Pair Cabling Components
This standard specifies cabling components, transmission, system models, and the measurement procedures needed for verification of balanced twisted pair cabling
and Return Loss Pass/Fail Determination (ANSI/TIA/EIA-568-B.2-3-2002).
This addendum adds clause 1.2.5toTIA/EIA-568-B.2
Trang 3Fiber Optics Illustrated Dictionary
ideas for computers could not be easily built with
technology available in the 1800s, the basic ideas
were sound and have stood the test oftime Ada
Love-lace collaborated with him in his work There is a
cra-ter on the moon named afcra-ter Charles Babbage See
Charles Babbage Institute
babbleCrosstalk from other communications circuits
and the noise resulting from such crosstalk This is
typical of electrical circuits and is not a significant
problem in fiber optic circuits except where
electri-cal switches or loop sections are part of the system
The term generally implies a number ofnoise sources
combined
babble signalA deliberate transmission consisting
ofcomposite or otheJ.Wise confusing signals to obscure
the intended transmission from unwanted listeners
A babble signal may be used as a jamming
mecha-nism to deliberately interfere with other
transmis-sions See frequency hopping, jam signal
BABT See British Approvals Board for
Telecommu-nications
BAC See binary asymmetric channel
back bias1 A technique for restoring the
environ-ment in a vacuum tube which may have been altered
by external forces, by applying a voltage to the
con-trol grid 2 A means of feeding a circuit back on
it-selfbefore its point of origin or contact One
impor-tant application of this technique has been the
cre-ation ofregenerative circuits in electron tubes, an
im-portant milestoneinradio signal amplification
Re-generation was developed independently by E.
Arm-strong and L de Forest and hotly contested in a patent
suit 3 In semiconductors, back bias is sometimes
more commonly calledreverse bias It refers to an
external voltage used to reduce the flow of current
across ap-njunction, thus increasing the breadth of
the depletion region
back doorAsecurity hole that is accessible without
going through the normal login/password procedure
A back door may be deliberately left by the
develop-ers or maintaindevelop-ers of a software application or
oper-ating system in order to gain entry later, sometimes
much later Back doors have legitimate uses for
main-tenance and configuration but are sometimes abused
by disgruntled ex-employees or employees engaged
in embezzlement or other illegal or unauthorized
ac-tivities See back porch
back electromotive force, back EMFAn
electro-motive force opposing the main flow of force in a
circuit
back end 1.A program that sends output to a
par-ticular device or front end See client/server 2 The
final step in a transparent (to the user) task or
pro-cess 3 In networking, the manner in which a lower
layer provides a service to the one above it 4 In
elec-tronics, the final production stages of assembly and
testing
back end processorIncomputing, a chip or set of
chips or separate computing unit that handles 'back
end' tasks such as data storage and retrieval in order
to free up the main CPU for processing tasks
back haulSee backhaul
back lobeIna directional antenna, there is a main lobe and there may be additional lobes, one ofwhich extends backward from the direction ofthe channeled signal, called a back lobe
back porch1 On a computer system, a file access point to the system or an application withlimited
privileges which may not be publicly announced or which may have a group password.Inother words, there may be some files available to certain employ-ees that may not be generally accessible by all em-ployees It's like a meeting place on a friendly neigh-borhood porch in a back yard where invited people are welcome to visit as long as they don't go inside the house and disturb the privacy of the home own-ers This environment is somewhat like an unadver-tised anonymous FTP environment in that users of the 'porch' do not have full privileges or access to all parts ofthe system Aback porch differs from a back door in that it is a circumscribed, known area, with limited privileges A back door, on the other hand, may provide full privileges and is often not known
to anyone but the person who programmed the soft-ware A front porch would be a publicly visible, lim-ited access area open to anyone 2.Invideo broad-casts, the portion of a composite picture signal be-fore the video signal which is between the edge of the horizontal synchronization pulse and the edge of the associated blanking pulse
back projectionAmeans ofpresenting information
on a visual display system by illuminating, or other-wise activating, the display elements from behind In its broadest sense, most TV and computer screens are back projection systems However, a further distinc-tion can be made that a projecdistinc-tion system implies a larger display system, as would be used in a seminar, theater, or lecture hall, environments traditionally equipped with front projection systems (film projec-tors, slide projecprojec-tors, etc.) that are separate devices from the actual display screen In these environments, back projection screens are less common
One ofthe main advantages ofa back projection sys-tem is that the audience and various speakers can stand or sit directly in front of the display without obscuring the image projection with shadows Back projection also tends to show up better in rooms where there is sufficient ambient light for people to take notes The main disadvantage of such a system
is that it usually requires specialized equipment for both the projection and the display screen, whereas films and slides can be shown on many types of sur-faces, including a plain wall
back reflectionIna fiber lightguide, light that reflects back in the originating direction Thus, it may inter-act with the original propagating signal.Inmost cases back reflection is undesirable and occurs where there are excessive bends, foreign particles, poorly fused joints, bad doping characteristics, or bad terminators Fiber optic filament endfaces are commonly polished
to fine tolerances and particular angles to control or eliminate back reflection Sometimes a slightly con-cave endface can reduce back reflection better than
a flat endface by reducing the fiber-to-air interface
Trang 4concave endface can provide up to an additional-IS
dB ofback reflection for high-speed, high-bandwidth,
systems such as broadband digital communications
systems.Anangled interface (e.g.,8°)is more
diffi-cult to "machine" and connect due to rotational
align-ment requirealign-ments, but provides even better contact
and back reflection tolerances of up to -15 dB better
than super polished endfaces (up to about -70 dB)
Once a fiber filament is polished, it is still important
to ensure that the end is thoroughly cleaned without
introducing scratches, otherwise back reflection
can result from particle interference Since a
single-mode fiber core is only about 9 microns in diameter,
even small particles can potentially obscure the core
Hand cleaning with an air blower and isopropyl
al-cohol or machine cleaning should be done just
be-fore coupling, especially if the fibers have been
shipped or stored for any length oftime The endface
should be checked with a magnifier (e.g., a
micro-scope) before coupling, otherwise any stray particles
could mar the surface when subjected to pressure in
the joint See attenuation, fusion splice See
accep-tance angle, Littrow configuration
back scatterSee backscatter
backboard Asturdy surface on which to mount
elec-trical panel boxes, punchdown blocks, or other
threading orwiring equipment that needs a firm
back-ing and wouldn't be secure if mounted on plaster,
wallboard, or some other brittle surface Sometimes
equipment is preinstalled and tested on a backboard,
so it can be assembled lying down in a convenient
position, e.g., off-premises, and then quickly mounted
where desired
backboneAprimary ridge, connection link, or
foun-dation, generally represented as longitudinal with
branches A telecommunications backbone is a
ma-jor supporting transmission link from which smaller
links, nodes, and drops are connected Since the late
1990s, the number and scope of optical fiber-based
communications backbones has been steadily
increas-ing
In 1999, RCN Corporation, a large regional Internet
service provider (ISP), announced that it had selected
a dense wavelength division multiplexing (DWDM)
optical transport system for its east coast fiber
back-bone The system was intended to support up to 40
wavelength paths transmitted over a single strand of
fiber
In spring 2000, Metromedia Fiber Network, Inc
(MFN) announced an acceleration strategy for
de-ploying and extending their optical Internet
infra-structure internationally throughout North America
and Europe The company's intention is to be the
larg-est global provider of fiber-based infrastructure by
2004
In late 2000, China Telecom began building China's
largest capacity broadband network, projected to
ex-tend about 40,000 cable kilometers in a rapidly
grow-ing region that did not previously employ optical
fi-ber The system is being built upon Coming LEAF®
fiber, an advanced non-zero dispersion-shifted fiber
nounced completion of the majority of an 80-Gbps bandwidth expansion to its I2,400-mile long-haul OC-192-based backbone that serves Internet Proto-col communications to reach 45 of the 50 largest metropolitan service areas (MSAs)
Not all optical service providers are expanding, how-ever In late January 2002, it became known that Glo-bal Crossing was filing for the fourth largest corpo-rate bankruptcy ever recorded in the U.S Global Crossing had laid approx 100,000 miles offiber optic cables around the world, including submarine cables in the Atlantic and Pacific Oceans Sale ofthe company as a whole or some of its assets were both put forward as Chapter 11 strategies for continuance
of the company See 6bone, Mbone
backbone data circuitAmain data communications circuit, usually of national distribution, from which there are secondary branches The term was originally used to describe key USENET/email sites but is now used more generally A backbone is sometimes de-fined in terms of the speed of communications and primary nature of the data, and it is sometimes con-sidered the part ofthe circuit that customarily carries the heaviest traffic Abackbone can connect a main-frame with local area networks(LANs) or individual terminals or individual systems with peripherals such
as modems, printers, video cameras, etc Bridges, routers, and switches perform a variety oftraffic con-trol and direction functions within the system More regional, medium-sized installations, as at universi-ties and large corporations, may be called campus backbones
Backbones can generally be categorized into three types:distributed backbones,utilizing multiple
switching hub generally contained within a single building complex; andhybrid backboneswhich in-clude collapsed backbones in individual building complexes interlinked with FOOl distributed back-bones, for example See campus backbone
backbone radio circuitInpacket radio communi-cations, a packet-radio bulletin board system (PBBS) that provides automatic routing services for a num-ber ofusers
background communicationData communication that occurs while other user actions are taking place;
it carries on in the background without intruding on other activities For example, a user may be using a word processor while a file is uploading or download-ing in the background Sdownload-ingle-taskdownload-ing systems don't
do this Background communications are character-istic of multitasking systems and some task-switch-ing systems, which will time-splice the processor between the two activities
background noiseAmbient noise, environmental noise, noise without significant meaning If back-ground noise levels are too high, they can interfere with communications There are now digital systems, such as cellular phones, that can selectively screen out background noise and increase the clarity of
a transmission from a noisy environment This
Trang 5Fiber Optics Illustrated Dictionary
capability has both industrial and social
communi-cation advantages The same types of algorithms are
often used in videoconferencing and audio editing
systems to enable users to condition the sound to
fil-ter out unwanted frequencies or noise
background process, background taskA computer
program operating or waiting in the background, not
in immediate sight or use ofthe user, often at a lower
priority level, becoming active quickly when needed
or brought to the foreground, or when other processes
are idle On data and phone systems, tasks such as
system operations, archiving, cleanup of temporary
files, print spooling, diagnostics, etc., are frequently
run as background tasks and may function primarily
on off-peak hours or when more CPU time is
available
backhaulIntelephone and computer network
com-munications, to send a signal beyond a destination
and then back to the destination For example, a phone
call from Seattle to north San Francisco may be routed
through Palo Alto and back to San Francisco
Backhauling happens for a number ofreasons,
includ-ing cost, availability, and traffic levels Backhaulinclud-ing
may also occur in companies with a number ofbranch
offices A call to one branch may, for various
busi-ness reasons, be backhauled to another, in order to
serve the caller's needs
Backhauling on the Internet is quite common For
ex-ample, in some cases it may be cheaper or easier to
Telnet to an ISP in a distant city with better rates and
services, and then accessftpsites, chat channels, or
other services by backhauling, perhaps even to the
originating city, than to call out from a more limited
local service
backhaul broadcastingIn cable broadcasting, to
bring back a signal (haul) from a remote site (such
as a big sports event or hot news tornado zone) to the
local TV station or network head station for
process-ing before beprocess-ing distributed to viewers
backoffA retransmission delay which may occur
when a transmission cannot get through to its
desti-nation, due to an interruption, collision, a medium
already in use, etc If a transmission fails, rather than
trying again immediately, the sending or interim
sys-tem may wait momentarily before retransmitting The
retransmission interval may be random or may be set
within a certain range by backoff algorithms
incor-porated into the protocols being used Backoff (one
word) is the noun fonn; back off (two words) is the
verb form
backplane, backplane bus1 In desktop computers,
the physical connection between a data bus and power
bus (both of which are usually on the motherboard)
and an interface link or card (which are usually
in-serted into slots) See bus 2.Inphone exchanges, the
high-speed line and power sources that connect
in-dividual components, often through circuit board
slots The speed and quantity of transmissions
through the exchange are in large part determined by
the capacity of the backplane See bus
backpressure, backpressure propagationIna
net-work, the information that is being transferred is
almost always accompanied by metadata describing the infonnation content and, on large networks, about its progress from source to destination In hop-by-hop routing, there is network communication about the location and subsequent routing as well This over-head can sometimes add up ifthere is congestion on the network, anditmay propagate upstream to form backpressure
backscatterBackscatter is a phenomenon in which radiant energy is propagated in a reverse direction to the incident radiation, sometimes in a diffuse pattern Backscatter usually happens when the radiant energy comes in contact with an object, particles, or various projections in an uneven terrain, or when it encoun-ters outer boundaries or particles in a transmissions medium, as in fiber optic cables
Sometimes backscattering is useful, and sometimes
it is undesirable.Inradar, the signals returned when radar waves hit a target and are reflected back to the sensing device are used to track the location and movement ofthe target.Indirectional antenna assem-blies, backscattering of signals to the rear of the an-tenna may cause interference See zone of silence backscatter, ionosphericIn the E and F ionospheric regions (where many radio waves are bounced from the sender to the receiver) at the general angle at which the wave hits the ionized particles, some ofthe waves are propagated back in the direction from which they came Backscatter may cause interference
to the original signal or may result in the transmis-sion being heard by receivers near the transmitting station (although the signal is generally weak) See
E layer, F layer, ionosphere
backupAnalternate resource in case of failure or malfunction of the primary resource The alternate may be identical (or as close as possible) to the origi-nal, as in data archives, or may be a substitute which
is just sufficient for short-term functioning, as in a backup light source or power supply
backup linkA secondary link which may not typi-cally carry traffic or may carry only overload traffic unless there is a failure in the primarylink,in which case it becomes available for transmission until the fault is corrected See alternate routing
backup ringOn Token-Ring networks, a second ring
is often set up to provide a backup in case of failure
of the first ring Depending upon the setup, the sys-tem may switch automatically or may need to be switched manually See Fiber Distributed Data Interface
backup server Aserver system expressly designated
to automate the handling ofdata protection tasks The server can be configured to back up certain machines, directories, or files at predetermined times, or when processing overhead from other tasks is low Abackup server is usually configured with drivers for a num-ber of backup devices, such as tape drives and mag-neto-optical disks, and may be secured against fire
or public access to protect the backed up data backward channelAchannel in which transmissions are flowing in the direction opposite to the flow of the majority of the data, usually the infonnational
Trang 6control signals and queries flow through the back
channel, while the majority of the data flows through
the fOlWard channels, as in video-on-demand Thus,
the system can be optimized to accommodate faster
data flow rates in the forward direction Some
sim-plified Internet access systems are designed this way,
with a modem or other connect line set for faster data
rates for downloading, and slower data rates for
que-rying as, for example, for Web browsing
backward compatibilityThe capability ofa system
to run legacy (older model) programs or to support
older equipment For example, 1.4 megabyte floppy
drives are usually backwardly compatible with 770
kilobyte floppy diskettes; they can read, write, and
format the older, lower capacity floppy diskettes
Similarly, a new version of a word processing
pro-gram may be able to read and write data files created
by an older version of the software
Backward Explicit Congestion Notification
BEeN In Frame Relay networking, a flow control
technique that employs a bit set to notify an interface
device that transmissions flowing in the other
direc-tion are congested and that congesdirec-tion avoidance
pro-cedures should be initiated by the sending device for
traffic moving in the direction opposite to that of the
received frame
backward indicator bitBIB 1 In data networking,
a signal bit or sequence ofbits that is used to request
retransmission when an error condition is detected
2 A flow control status bit used in Signaling System
7 (SS7) In MTP Layer 2, a Message Signal Unit
(MSU) indicator carried in bit 8 of the first octet in
conjunction with the backward sequence number
(BSN)
backward learningAn information routing system
based upon the assumption that network conditions
in one direction will be symmetric with those in the
opposite direction Thus, a transmission moving
ef-ficiently through a path in one direction would
as-sume this to be an available, efficient route in the
other direction as well
backwaveIn radiotelegraphy, an undesirable
inter-ference heard between code signals
Bacon, Roger(ca 1220-1292)AnEnglish
philoso-pher, scientist, and a member of the Franciscan
Or-der In 1265, he completed an encyclopedic document
of the knowledge of the time entitledOpus majus.
BACPSee Bandwidth Allocation Control Protocol
BADCbinary asymmetric dependent channel See
binary asymmetric channel
bad blockInmagnetic storage that is segmented into
blocks, a section with write or read failures Some
operating systems will map out bad block sectors on
a diskette or hard drive during formatting so they will
not be addressed or used and will continue to format
the remaining good parts ofa disk This is one of the
reasons why the amount displayed for the usable
por-tion of a disk can differ from the total storage
capac-ity of the disk
Bad Frame IndicatorBFI A means of signaling an
error condition in a frame-based communications
alert or a cellular radio speech decoder frame error alert In its simplest form, BFI uses binary logic to indicate an error-free frame (usually "1") or a bad
~a;!~:~;~;2}::S~~:~~:~~~~~e~:::.
aged him to get a good education to improve his op-portunities in life He had an agile mind and emigrated
to the United States to pursue his interests and pro-fessional connections He is responsible for the in-vention of Bakelite, the frrst synthetic polymer, and Velox, a new type of photographic paper See Bake-lite, Bakelyzer
barne, heatA corrugated, latticed, or slitted struc-ture that aids in controlling heat In fiber optics a fi-ber routing tray for handling the positioning of mul-tiple fiber cables can also serve as a heat baffle for channeling heated ambient air away from compo-nents or joints that might be adversely affected by heat See heat sink
baffle, lightA device to selectively control the emis-sion of light When the device can be readily opened
or closed or is frequently done so, it is more often called a shutter When it is generally fixed, or is only infrequently opened or closed, it is usually called a baffle
Baffles are commoninscientific instruments that il-luminate specimens or work stages Such devices may have a baffle to prevent light from directly illu-minating a sample and may optionally have a baffle
to prevent stray light from disturbing nearby work areas A baffle may be one of the components of an integrating sphere, which is a component installed in the entrance port of a monochromator By rotating the sphere, the viewing angle can be controlled A baffle may also be used to selectively cast a shadow against which a fiber optic light source can be directed for calibration purposes
Since optical components can be impaired by dust and moisture, it is sometimes advisable to close or cover
a baffle during storage or times of low use Since a baffle has many small surfaces, it may be difficult to clean Removing it and cleaning it in alcohol or wa-ter or vacuuming it, if it is difficult to remove, can help prevent contamination of nearby components
See stray light
baffle, soundA device to direct sound and to pre-vent sound waves from interfering with one another
A baffle consists of a series of carefully spaced cor-rugations that provide a longer path within a limited amount of space It can be constructed of wood, metal, or synthetics and works by lengthening the air path along the diaphragm through which the sound waves travel and by reducing interaction among them
Baffles are commonly used in speaker systems to im-prove the clarity of the sound
BAFTASee British Academy ofFilm and Television Arts
bag phoneslangSee transportable phone
Bain, Alexander ( 1811-1877 [dates approximate;
reports vary]) A Scottish chemist and clockmaker
Trang 7Fiber Optics Illustrated Dictionary
who developed an electrochemical paper tape
record-ing system in the mid-1800s, suitable for telegraphic
signals, at about the same time Samuel Morse was
developing a somewhat similar system The Bain
system worked reasonably well except in situations
withhigh noise on the line, which would create
spu-rious marks on the tape
Bain received apatent for his version ofthe telegraph
in the 1840s which was contested by Morse but was
sufficiently different to hold up in court Morse
sub-sequently bought out the Bain systems and converted
them to his own See Bain Chemical Telegraph
Bain Chemical Telegraph Ahistoric automatic
print-ing telegraph based on chemical methods, patented
in 1848 and 1849 (U.S #5,957 &6,328) Ifyou have
seen the output from a facsimile machine on thermal
paper, you have the general idea of how it worked
Bain's system used paper that was coated with a
chemical that was sensitive to electrical impulses on
the receiving end of the transmission When a
mes-sage was received, the electrical impulses would
ini-tiate a chemical reaction that would change the color
of the paper in the active areas, creating an image to
match the one that had been transmitted, essentially
a historic facsimile machine Later enhancements of
the general principles ofthe Bain machine led to very
fast telegraphic systems Seen Bain, Alexander;
tele-graph, history
Baird, John Logie (1888-1946) Although historical
research makes it clear that a number ofpeople
inde-pendently developed different aspects of television
reception and display, in the late 1800s John Baird, a
Scottish inventor, was one of the earliest successful experimenters He was able to transmit a two-tone image ofa face onto a small television screen in 1926 and by 1932 had developed a practical system for broadcasting images
Baird used some ofthe principles ofthe Nipkow disc
to develop his system A light-sensitive camera was placed behind a perforated rotating disc, just as Nipkow had placed light-sensitive selenium behind
a perforated rotating disc The Baird system could only display a crude 30-line image at a frame rate a little less than halfof that used now, but the 'proofof concept' technology launched an industry that is still going strong
In the 1920s, in collaboration with Clarence W Hansell, Baird patented the concept ofusing conduct-ing rods or pipes to transmit images, a forerunner to fiber optic transmissions However, it was Heinrich Lamm who successfully used optical fibers for im-age transmission See Lamm, Heinrich; Nipkow, Paul
Bakelite The development ofBakelite in 1907 revo-lutionized industrial production and heralded the "age ofplastic." Inventor Leo Baekeland created this first synthetic polymer with a trademarked mixture ofphe-nol, formaldehyde, and coloring agents He was awarded a patent for BakeliteinDecember 1909 (U.S
#942,809)
This new material was hard and acid-, heat-, and wa-ter-resistant.Itwas quickly put to use in thousands
of industrial products as a noncorrosive coating and chemical binder for composite materials Bakelite
Frequency Range Designations
Uses
2 extremely low ELF 30-300 Hz 10 Mm-l Mm
3 ultra low ULF 300-3000 Hz IMm-30 km
4 very low VLF 10-30 kHz 30 km-l0 km
5 low LF 30-300 kHz 10 km-l km Facom distance
measure-ment and navigation
6 medium MF 300 kHz-3 MHz 1 km-l00 m AM radio
8 very high VHF 30-300 MHz 10 m-l m TV channels, FM radio,
land mobile radio (cellular), ISM, LAWN, amateur radio
9 ultra high UHF 300 MHz-3 GHz 1 m-l00 mm TV channels, CB radio,
land mobile radio (cellular), PCS, radar
10 super high SHF 3-30 GHz 100 mm-l0 mm Satellite, amateur satellite,
U-NIl bands, radar
11 extremely high EHF 30-300 GHz 10mm-l mm Satellite
12 tremendously high THF 300-3000 GHz
Note: In the above frequency ranges, the lower limit is exclusive, the upper limit inclusive.
Trang 8sistant, moldable household products, dials, small
ap-pliance casings, and even jewelry Many early
tele-phones and radios used Bakelite in their construction
See Baekeland, Leo
BakelynrItlooks like a B-movie adaptation of a
Jules Vern diving bell on wheels, but it actually is a
floor-standing iron pressure cooker devised by Leo
Baekeland to mix simple organic chemicals into his
versatile Bakelite synthetic resin See Bakelite
Bakken Library and MuseumA museum located
in Minneapolis, Minnesota, that houses a collection
of about 11,000 books, journals, and manuscripts
documenting the history ofelectricity and magnetism
and their applications in life sciences and medicine
The collection focuses on 18th through 20th century
works, including those of Franklin, Galvani, Volta,
and other well-known pioneers In 1969, the
collec-tion ofhistorical electrical machines was added to the
activities ofthe museum, including several Oudin and
D'Arsonval coils and many electrostatic generators
http://bakkenmuseum.org/
balanceTo equalize, to counterbalance, to bring into
harmony or equipoise, to offset in equal proportion,
to arrange such that opposing elements cancel one
another out or are of comparable weight, size,
con-struction, value, strength, or importance Balancing
is commonly done in electrical circuits to equalize
loads or to diagnose the location of breaks or
inter-ruptions in a line Stereo volume is usually balanced
to equalize the volume or perceptual evenness of the
left and right channels
balanced bridgeA bridge circuit in which the
mea-sured output voltage is equal to zero Bridge circuits
are sometimes used diagnostically to seek out and
measure unbalanced circuits in order to detect a break
or anomaly in the wiring See Wheatstone bridge
balanced circuitA circuit in which the electrical
properties are symmetric and equal with respect to
ground See balanced bridge
balanced configurationApoint-to-point High Level
Data Link Control (HDLC) network configuration
with two combined stations
balanced lineAn electrical circuit consisting of two
conductors with matched voltages at any
correspond-ing point along the circuit, and which have opposite
polarities with respect to ground It is not uncommon
to use more than one line to carry related
transmis-sions or a split transmission, especially in newer
mul-timedia applications By matching voltages and
set-ting opposite polarities, it is possible to reduce the
incidence of crosstalk and interference, resulting in
cleaner signals
balanced modulationModulation is a means
ofadd-ing information to a carrier signal by varyofadd-ing its
prop-erties such as amplitude or frequency In the early
days of radio wave broadcasting, experimenters
sought ways to manipulate or reduce the amount of
bandwidth that was needed to carry the desired
in-formation Itwas found in amplitude modulation
(AM), using electron tubes, that the control grids of
two tubes could be connected in parallel, and the
that the sidebands were singled out for transmission without the carrier Double sideband modulation is another name for balanced modulation.Inelectronic music, balanced modulation refers to a way
ofcom-f~::;~~~~~:l:~~~: ~~c~~~~~~ea':J~:::~:~~:.
phase is valid for positive and negative signals As
in radio communications, only the sidebands from the original signal remain See amplitude modulation, modulation, single sideband
balconyAsmall ledge or platform for aerial jobs used
by film crews, antenna technicians, or utility pole workers
bale, bonfireA signal fire, one of the oldest optical networks, and one which could be used at night In the 1400s in Scotland, a simple signal code, using one
to four bales, was established by an act ofParliament
ballast 1 A physical object that improves stability through its mass or can be jettisoned to reduce mass
Ballast is commonly used in boats and hot air bal-loons 2.Inan electrical circuit, a device that stabi-lizes a current or provides sufficient voltage to start
up a mechanism (such as a fluorescent bulb) or trans-mission Apparently about 50% of fluorescent light-ing ballasts produced until the late 1970s contain haz-ardous PCBs of 50 ppm or higher in the potting ma-terial that surrounds the capacitor and should not be disposed of in landfills They can be sent to autho-rized disposal centers
balunbalanced/unbalanced A small, passive trans-forming device used to match impedance on unbal-anced lines that are connected together, such as twisted-pair cable and coaxial cable, so the signal can pass through the differing types of lines As with many interface devices, there may be some signal loss through the balun See bazooka
BAN 1 base area network 2 basement area network
3 Bay Area network 3 See Billing Account Num-ber 4 See body area network
band 1 The range of frequencies between two de-fined limits, usually expressed in hertz (Hz) See bandwidth 2 A group of electronic tracks or chan-nels 3 A group of channels assigned to a particular broadcast spectrum, e.g., UHF (300 to 3,000MHz).
See chart ofregulated band designations 4 The range
or scope ofoperations ofan instrument 5 An AT&T-designated WATS Service Area
band allocationsFrequency ranges for radio wave communications have to be shared, and devices com-municating on similar frequencies can have devas-tating effects on one another For this reason, the fre-quency spectrum is allocated and regulated in order
to maximize use of the available spectrum, and also
to designate waves suitable for different types of ac-tivities In the U.S., this information is contained in the Federal Communications Commission (FCC) Table ofFrequency Allocations and the U.S Govern-ment Table ofFrequency Allocations, which together comprise the National Table of Frequency Alloca-tions Other organizations such as the ITU have tables
as well The values in the tables change, and what is
Trang 9Fiber Optics Illustrated Dictionary
represented in the Frequency Allocations and
Com-mon Uses chart is a very generalized overview to
pro-vide a basic understanding
When new frequencies are available, they may be
allocated to amateur or specialized uses or auctioned
for commercial use When a user stops using an
al-located frequency, it is reassigned The available
spec-trumranges have been established for various types
ofcommunications and some regions are unlicensed
Some of the more interesting unlicensed uses have
been listed in the Frequency Band Allocations chart
band centerThe computed arithmetic mean between the upper and lower frequency limits of a frequency band This measure can be used to adjust modulation,
to constrain it, or to provide the maximum possible amplitude range for an amplitude modulated (AM) signal
band splitterA multiplexer that subdivides an avail-able frequency into a number ofsmaller independent channels, using time division multiplexing (TOM) or frequency division multiplexing (FDM) See band-pass filter
Frequency Band Allocations (Radio Waves) and Common Uses
Name Approx Range Examples of Applications
AMband 535-1605 kHz Amplitude modulation, used commonly for radio broadcasts Videoconf around 24 MHz Certain local videoconferencing systems
Mobile various Frequencies around 48 MHz are used for consumer outdoor mobile
intercom units
Radar 10-200MHz Imaging radar applications
Amateur 50-54 MHz Amateur radio use Frequencies allocated for amateur use are
144-146 MHz frequently changed as the FCC often puts a higher priority on
commercial users This is despite the fact that amateurs have contributed a great deal to radio communications technology FMband 88-108 MHz Frequency modulation, used commonly for radio broadcasts and
some low power FM transmitters (intercoms, bugs)
SAR 141 MHz Synthetic Aperture Radar for environmental sensing and image
processing
Radar 300MHz+ Approx lower end of radar for remote sensing applications
USDC 824-894 MHz U.S Digital Cellular FDMA and TDMA cellular phone services A-F block 1850-1910 MHz Personal Communications Services (peS) A to F block licenses
1930-1975 MHz grantedtophone companies serving MTAs
UPCS 1890-1930MHz Unlicensed Personal Communications Services (PCS)
S-band 2310-2360MHz Frequencies sensitive to terrain, making them unsuitable for some
types of transmissions
U-NII 5150-5350 MHz Unlicensed National Information Infrastructure wireless
communications, including PCS
P-band 22-.39 GHz Experimental radar SAR
C-band 4-8 GHz Microwave frequencies, more specifically 3.40 to 6.425 GHz
Satellite - larger antennas VSATS Incumbent telephony operations (2.0 GHz) Experimental radar SAR
X-band 8-12.5 GHz Dedicated for use by the U.S military for satellite communications
SLAR
Ku-band 10.95-14.5 GHz Now subdivided into fixed satellite service (FSS) at 11.7 to 12.2
GHz, and broadcasting satellite service (BSS) at 12.2 to 12.7 GHz VSATs
K-band 18.5-26.5 GHz Satellite applications with smaller antennas, radar
Ka-band 26-40 GHz Satellite applications with smaller antennas, radar
Q-band 36-46 GHz Satellite, radar
Trang 10band-elimination filterBEF.Aresonant circuit
fil-ter with a single, continuous attenuation band, in
which the lower and higher cutoff frequencies are
neither zero nor infinite
band-stop filter, band-rejection filter Aresonant
circuit filter for locking out a specified range, or
ranges, oftransmissions according to their frequency
ranges
banded cableTwo or more cables physically held
in proximity to one another (aggregated) with metal
or plastic straps or bands
bandpassThe range of frequencies that will pass
through a system without excessive weakening
(at-tenuation), expressed in hertz See bandpass filter
bandpass filterA device with a resonant circuit,
of-ten used in conjunction with frequency division
tech-niques, that recognizes and selectively allows
con-trol offrequencies, letting through those that are
de-sired A band-reject filter is complementary in the
sense that it recognizes and selectively screens out a
range offrequencies in order to fonn a 'blackout' area
within the full spectrum ofavailable frequencies See
band splitter
bandspread tuning Ameans of spreading a band of
frequencies over a wider area in order to adjust the
tuning more precisely This is most commonly found
in shortwave radios and more than one set of dials
may be used, with differently spaced tickmarks on
the tuning gauges to aid in adjusting the settings
bandwidth 1.The extent of a range of frequencies
between the minimum and maximum endpoints,
typi-cally measured in hertz (cycles per second)
Techni-cally, the term bandwidth is associated with analog
systems Inrecent years, it has been more loosely
applied to mean data rates in digital systems and,
hence, is sometimes expressed in bits per second
(bps) 2 The range of the frequency required for the
successful transmission ofa signal It may range from
a few kHz for a slow-scan or sideband signal to 100
kHz for a frequency modulated (FM) signal That is
not to say that the bandwidth of a signal necessarily
takes up the entire range ofthe band that may be
des-ignated for its use See band spectrum table 3 In a
cathode-ray tube (CRT) device, the speed at which
the electron gun canturnon and off.4.The capacity
to move information through a social, data, or
physi-cal system.5.Anumerical expression ofthe
through-put ofa system or network
bandwidth allocation, bandwidth reservationIna
network, the process of assessing and allocating
re-sources according to flow, priorities, type, etc It
en-ables priority administration of the network traffic
when congestion occurs
Bandwidth Allocation Control ProtocolBACP In
ISDN, a protocol providing mechanisms for
control-ling the addition and removal ofchannels from a
mul-tichannellink
bandwidth augmentation 1.Adding additional
fre-quencies or channels to an existing bandwidth range
2 Replacing existing physical transmissions media
with broader bandwidth media in a system where the
but the physical media caused a bottleneck due to its inherent limitations (e.g., replacing copper wiring with fiber optic)
bandwidth compressionTechniques for increasing the amount of data that can be transmitted within a given frequency range The increased demand for broadband applications such as video has motivated technologists to find more efficient ways to use ex-isting transmissions media, resulting in better com-pression schemes and better management of the di-rection of transmission in bididi-rectional systems Compression can be very medium-specific For ex-ample, in sending voice, blanks between words may
be removed; in sending images, white pages may be compressed or eliminated; in sending complex mul-ticolored images, lossy formats such as fractal com-pression or other lossy comcom-pressions such as JPEG may be used
bangcolloq.! Exclamation point.1 Acommon sym-bol used in many programming languages For ex-ample, in C it represents a logicalnot.2 Although its use is diminishing, it was at one time used in email addresses to designate a break between portions of
an address, where an at sign(@)may now be used Here is an example of a bang path:
{uunet,ucbvax} !galileo.berkeley.edu!usemame bankA row or matrix, usually of similarly sized or configured components or data cells Individual units
in a bank are often interrelated, by shape, function,
or electrical contact In its simplest sense,aphysical bank does not necessarily have connections between individual cells but may appear similar and be mounted in rows and columns Banks may also be electrically related, either by induction, physical con-nections between the cells themselves, or by tempo-rary electrical connections that occur when a bar drops down over a bank of cells, or a brush passes over the bank
Many large-scale telecommunications devices and junctions are set up in banks Punchdown blocks at switching centers are set up in banks, often on racks
or panels Memory banks can be physical rows of memory chips in a circuit board Large Internet Ac-cess Providers (lAPs) may have banks of hundreds
or thousands of modems, connected to phone wires See bank switching
bank switching Amethod of extending access to banks ofcomponents, such as memory chips, beyond the extent of any of the individual components, es-pecially in situations where the operating system or microprocessor can address only a limited amount of
memory at one time Bypaging or swapping between
banks, the virtual memory capacity is extended be-yond the default physical memory or operating sys-tem (OS) or central processing unit (CPU) capacity Bank switching is a tradeoff that may slow down memory access
bannerA clearly visible, often graphic representa-tion heralding an advertisement or a new secrepresenta-tion in a printout or other text or image communication Its purpose is to command attention and often (1) to