Fiber Optics Illustrated Dictionary - Part 11 potx

designed
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
of
user
services
across
mul-
tiple
public
carriers.
2.
An lTU-Tstandard
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
signaling
layer
en-
abling
the
transfer
of
connection
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
of
commercial
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.,
A
Series
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
B·l~

,
1988Y~:;~fW~~~~~li~tl1~lJCJl:~in
;~t~I~Imr-nUIli$.~:··

B.l~
c
1988

·'fEi
anddefi
l1if.jpDS.

B.14·
1988·
.:t'et11'lS
and
~1.s
for
infbrn1J1tion
q~~~~
.••.
~
•.•
~I~~llnj~~.
B.lS
;.J99§NQIil~cl.~~~t'::~~#eq't~~~::1ltl4
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
. .
BSeries StandardsA
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
of
these
documents
is
available
for
purchase
from
the
TIA
online.
See
TIA/EIA

B
Series
chart.
Bsignal
See
Grade
B
signal.
B-911
A
telephone
emergency
response
system
with
a
subset
of
the
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
92
Category
conversation
interactive
Example
activities
telephone,
conferencing,
audio
graphics,
videotelephone,
videoconferencing
distance
education,
services-on-

demand,
Web
browsing,
retrieval
services
such
as
news,
stocks,
etc.
© 2003 by CRC Press LLC
lTU-T
in
1990.
These
developed
into
broader
stan-
dards
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
of
ATM
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
Master
Antenna
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
MPEG
animations,
a picture
intended
to
become
a
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
by
1834.
While
Babbage's
Document
Date
TIAIEIA B Series
Standards
Committee/Description
TIA/EIA-568-B.3
1
Apr
02
TR-42
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).
TIAlEIA-568-B.2-2
1
Dec
01
TR-42
Commercial Building Telecommunications Cabling Standard - Part
2.·
Balanced
Twisted-Pair Cabling Components - Addendum
2 (ANSI/TIA/EIA-568-B.2-2-2001)
Provides
corrections
to
the
568-B.2
Standard.
TIA/EIA-568-B.l-l 1
Aug
01
TR-42
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.
TIAlEIA-568-B.1
1
Apr
01
TR-42
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.
TIA/EIA-568-B.2
1
Apr
01
TR-42
Commercial Building Telecommunications Cabling Standard - Part 2: Balanced
TWisted Pair Cabling Components
This
standard
specifies
cabling

components,
transmission,
system
models,
and
the
measurement
procedures
needed
for
verification
of
balanced
twisted
pair
cabling.
TIA/EIA-568-B.2-3
1
Mar
02
TR-42.7
Commercial Building
Telecommunications CablingStandard - Part
2: Balanced
TWisted-Pair Cabling - Addendum
3 - Additional Considerations
for
Insertion Loss
and
Return Loss Pass/Fail Determination (ANSI/TIA/EIA-568-B.2-3-2002).

This
addendum
adds
clause
1.2.5
to
TIA/EIA-568-B.2.
93
© 2003 by CRC Press LLC
Fiber
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
of
time.
Ada
Love-
lace
collaborated
with
him
in
his
work.
There
is
a
cra-
ter
on
the
moon
named
after
Charles
Babbage.
See

Charles
Babbage
Institute.
babble
Crosstalk
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
of
noise
sources
combined.
babble signal A
deliberate
transmission
consisting
of

composite
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,
j
am
signal.
BABT
See
British
Approvals
Board
for
Telecommu-
nications.
BAC
See
binary
asymmetric
channel.
back bias
1.
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
of
regenerative
circuits
in
electron
tubes,
an
im-
portant
milestone
in

radio
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
called
reverse
bias.
It
refers
to
an
external
voltage
used
to
reduce
the
flow
of
current
across
a
p-njunction,
thus
increasing
the
breadth
of
the
depletion
region.
back doorA

security
hole
that
is
accessible
without
going
through
the
normal
login/password
procedure.
A
back
door
may
be
deliberately
left
by
the
develop-
ers
or
maintainers
ofa
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 EMF An
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 processor In
computing,
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 haul
See
backhaul.
94
back lobe In a
directional
antenna,
there
is
a
main
lobe
and
there
may
be
additional
lobes,
one
of
which
extends
backward
from
the
direction
of
the
channeled

signal,
called
a
back
lobe.
back porch
1.
On
a
computer
system,
a
file
access
point
to
the
system
or
an
application
with
limited
privileges
which
may
not
be
publicly
announced

or
which
may
have
a
group
password.
In
other
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
of
the
system.
A
back
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
apublicly

visible,
lim-
ited
access
area
open
to
anyone.
2.
In
video
broad-
casts,
the
portion ofa
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 projectionA
means
of
presenting
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
projection
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
projectors,
etc.)
that
are
separate
devices

from
the
actual
display
screen.
In
these
environments,
back
projection
screens
are
less
common.
One
of
the
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.
backreflection Ina
fiber
lightguide,
light
that
reflects
back
in
the
originating
direction.
Thus,
it

may
inter-
act
with
the
original
propagating
signal.
In
most
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
© 2003 by CRC Press LLC
that
exists
at
the
coupling
joint. Super polishing a
concave
endface
can
provide
up
to
an
additional-IS
dB
of
back

reflection
for
high-speed,
high-bandwidth,
systems
such
as
broadband
digital
communications
systems.
An
angled
interface
(e.g.,
8°)
is
more
diffi-
cult
to
"machine"
and
connect
due
to
rotational
align-
ment
requirements,

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
of
time.
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.
backscatter
See
backscatter.
backboardA
sturdy
surface
on
which
to
mount
elec-
trical panel boxes, punchdown blocks, or other
threading
or
wiring

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.
backboneA
primary
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.
In
August
2001,
Cogent
Communications,
Inc.
an-
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
of
the
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
circuitA
main
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
of
the
circuit that
customarily
carries
the
heaviest
traffic.
Abackbone
can
connect
a
main-
frame
with
local

area
networks
(LAN
s)
or
individual
terminals
or
individual
systems
with
peripherals
such
as
modems,
printers, video cameras,
etc.
Bridges,
routers,
and
switches
perform
a
variety
of
traffic
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

rout-
ers; collapsed backbones, with a configuration
switching
hub
generally contained within a
single
building
complex;
and
hybrid backbones
which
in-
clude collapsed backbones
in
individual building
complexes
interlinked
with
FOOl distributed
back-
bones,
for
example.
See
campus
backbone.
backbone radio circuit In packet
radio
communi-
cations,

a
packet-radio
bulletin
board
system
(PBBS)
that
provides
automatic
routing
services
for
a
num-
ber
of
users.
background communication Data
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.
Single-tasking
systems
don't
do
this.

Background
communications
are
character-
istic
ofmultitasking
systems
and
some
task-switch-
ing
systems, which will time-splice the processor
between
the
two
activities.
background noise
Ambient
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
95
© 2003 by CRC Press LLC
Fiber
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
of
the
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.
backhaul In
telephone
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
of
reasons,
includ-
ing
cost,

availability,
and
traffic
levels.
Backhauling
may
also
occur
in
companies
with
a
number
of
branch
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
access
ftp
sites,
chat
channels,
or
other
services
by
backhauling,
perhaps
even
to
the
originating
city,
than

to
call
out
from
a
more
limited
local
service.
backhaul broadcasting
In
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
being
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.
Ifa
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 bus
1.
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.
In
phone
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 propagationIn a
net-
work,
the
information that
is
being transferred

is
96
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
if
there
is
congestion
on
the
network,
and
it
may
propagate
upstream
to
form
backpressure.
backscatter Backscatter

is
a
phenomenon
in
which
radiant
energy
is
propagated
in
areverse
direction
to
the
incident
radiation,
sometimes
in
a
diffuse
pattern.
Backscatterusually
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.
In
radar,
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

of
the
target.
In
directional
antenna
assem-
blies,
backscattering of
signals
to
the
rear of
the
an-
tenna
may
cause
interference.
See
zone
of
silence.
backscatter, ionospheric
In
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
of
the
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.
backup An alternate
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 link A

secondary
link
which
may
not
typi-
cally
carry
traffic
or
may
carry
only
overload traffic
unless
there
is
a
failure
in
the
primary link,
in
which
case
it
becomes
available
for
transmission until

the
fault
is
corrected.
See
alternate
routing.
backup ring
On
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 serverA
server
system
expressly
designated
to
automate
the
handling
of
data
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.
A
backup
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.
backwardchannelA

channel
in
which
transmissions
are
flowing
in
the
direction
opposite
to
the
flow
of
the
majority
of
the
data,
usually
the
infonnational
© 2003 by CRC Press LLC
data.
Some
interactive systems
are
designed
so
that

control 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 compatibility
The
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
abit set
to
notify
an
interface
device
that
transmissions flowing
in
the
other direc-
tion

are
congested
and
that
congestion
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 bit
BIB.
1.
In
data networking,

a signal bit
or
sequence
of
bits 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 learning
An
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.
backwave
In
radiotelegraphy,
an
undesirable inter-
ference
heard
between code signals.
Bacon, Roger
(ca.
1220-1292) An English philoso-
pher,
scientist,
and
a member of

the
Franciscan
Or-
der.
In
1265,
he
completed
an
encyclopedic
document
of
the
knowledge
of
the
time
entitled
Opus
majus.
BACP
See
Bandwidth Allocation Control Protocol.
BADC binary 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
of
a
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
Indicator
BFI.
A
means
of
signaling
an
error condition
in
a frame-based communications
medium
such
as
apacket networking error condition
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, heat A 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, lightAdevice
to
selectively control
the
emis-
sion
oflight.

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
common
in
scientific 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
acomponent 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, sound A device
to
direct sound
and
to
pre-
vent sound waves
from
interfering with
one
another.
Abaffle 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.
BAFTA
See
British
Academy
ofFilm
and
Television
Arts.
bag phone slang
See
transportable
phone.
Bain, Alexander (1811-1877 [dates approximate;
reports vary]) A Scottish chemist and clockmaker
97
© 2003 by CRC Press LLC
Fiber
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
with

high
noise
on
the
line,
which
would
create
spu-
rious
marks
on
the
tape.
Bain
received
a
patent
for
his
version
of
the
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 ChemicalTelegraph A

historic
automatic
print-
ing
telegraph
based
on
chemical
methods,
patented
in
1848
and
1849
(U.S.
#5,957
&
6,328).
If
you
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
of
the
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
of
people
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
of
the
principles
of
the
Nipkow
disc
to
develop
his
system.
Alight-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
of
using
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
of
phe-
nol,
formaldehyde,
and
coloring agents.

He
was
awarded
a
patent
for
Bakelite
in
December
1909
(U.S.
#942,809).
This
new
material
was
hard
and
acid-,
heat-,
and
wa-
ter-resistant.
It
was
quickly
put
to
use
in

thousands
of
industrial
products
as
a
noncorrosive
coating
and
chemical
binder
for
composite
materials. Bakelite
Frequency Range Designations
ITU
Designation
Abbrev.
Frequency
Wavelength
Typical
or
Example
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
7
high HF
3-30
MHz
100
m-l0
m

CB 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.
98
© 2003 by CRC Press LLC
also
provided
new
ways
to
create colorful, water-re-
sistant,
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.
Bakelynr
It
looks
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 Museum A
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
of
historical
electrical
machines
was
added
to
the
activities

of
the
museum,
including
several
Oudin
and
D'
Arsonval
coils
and
many
electrostatic generators.
/>balance
To
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 ofbreaks
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 bridgeAbridge 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 abreak
or
anomaly
in
the
wiring.
See
Wheatstone bridge.
balanced circuit A 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 line
An
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 ofcrosstalk
and
interference, resulting
in
cleaner
signals.
balanced modulation
Modulation
is
a
means
of
add-
ing
information
to
acarrier
signal
by
varying
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.
It
was
found
in
amplitude modulation
(AM),
using

electron tubes, that
the
control
grids
of
two
tubes could
be
connected
in
parallel,
and
the
screen
grids connected
for
push-pull operation such
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
of
com-
f~::;
~~~~~:l
:~~~:
~~c~~~~~~e
a':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.
balcony A
small
ledge
or
platform
for
aerial
jobs
used
by
film
crews, antenna technicians, or utility pole
workers.
bale, bonfire Asignal
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
of
Parliament.
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.
In
an
electrical circuit, a device
that
stabi-
lizes a current or provides sufficient voltage
to
start
up
amechanism
(such
as

afluorescent
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.
balun balanced/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 offrequencies between
two
de-
fined limits, usually expressed in hertz
(Hz).
See
bandwidth.
2.
A
group
of
electronic
tracks
or
chan-
nels.
3.
Agroup

of
channels assigned
to
a particular
broadcast spectrum,
e.g.,
UHF
(300
to
3,000
MHz).
See
chart ofregulated band
designations.
4.
The
range
or
scope
of
operations
of
an
instrument.
5.
An
AT
&T-
designated
WATS

Service
Area.
band
allocations Frequency 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
ofFrequencyAllocations

and
the
U.S.
Govern-
ment
Table
of
FrequencyAllocations,
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
99
© 2003 by CRC Press LLC
Fiber
Optics
Illustrated
Dictionary
represented
in
the Frequency Allocations and
Com-
mon
Uses chart
is
avery 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-
trum
ranges 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 BandAllocations chart.
band center
The

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 splitterAmultiplexer that subdivides
an

avail-
able frequency into anumber
of
smaller 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
ofApplications
AM
band
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
10-200
MHz
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
300
MHz +
Approx.
lower
end
ofradar
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
granted to
phone
companies serving
MTAs.
UPCS
1890-1930
MHz
Unlicensed Personal Communications Services
(PCS).
S-band
2310-2360
MHz
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.
L-band
1-2
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.
V-band
40-75
GHz
Radar
band.
W-band
75-110
GHz
Radar
band.
100
© 2003 by CRC Press LLC
band, citizens
See
citizens band
radio.
band-elimination filter
BEF.
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 A resonant
circuit filter
for
locking out a specified range, or
ranges,
of
transmissions
according
to
their frequency
ranges.
banded cable
Two
or
more
cables
physically held
in
proximity
to
one
another (aggregated) with
metal
or
plastic
straps
or
bands.

bandpass
The
range
of
frequencies that will pass
through
a
system
without excessive weakening
(at-
tenuation), expressed
in
hertz.
See
bandpass
filter.
bandpass filter Adevice with aresonant 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
of
available
frequencies.
See
band
splitter.
bandspread tuning A
means
of
spreading aband
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 ofa
range
offrequencies
between
the

minimum
and
maximum
endpoints,
typi-
cally
measured
in
hertz (cycles per second).
Techni-
cally,
the
term
bandwidth
is
associated with analog
systems.
In
recent 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
can
turn
on
and
off.
4.
The
capacity
to
move
information through asocial,

data,
or physi-
cal
system.
5.
Anumerical expression of
the
through-
put
of
a
system
or
network.
bandwidth allocation, bandwidth reservation
In
a
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.
BandwidthAllocation Control Protocol
BACP.
In
ISDN,
aprotocol providing mechanisms
for
control-
ling
the
addition
and
removal
of
channels
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
asystem where
the
data
transmission
is
capable
of
broader bandwidth,
but
the
physical
media
caused abottleneck

due
to
its
inherent limitations (e.g., replacing copper wiring
with
fiber optic).
bandwidth compression
Techniques
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
bidirectional
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
compressions
such
as
JPEG
may
be
used.

bang
colloq.
!Exclamation
point.
1.
A
common
sym-
bol
used
in
many
programming languages. For
ex-
ample,
in
C
it
represents a logical
not.
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 ofa 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 ofhundreds
or thousands of
modems,
connected
to

phone
wires.
See
bank switching.
bank switching A method
of
extending access
to
banks
of
components,
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 alimited
amount
of
memory
at
one
time.
By
paging
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.
banner A clearly visible, often graphic representa-
tion
heralding
an
advertisement or a
new
section
in
a
printout
or
other text or image communication.
Its
purpose
is
to
command attention and often (1)
to
101
© 2003 by CRC Press LLC