Fiber Optics Illustrated Dictionary - Part 70 pot

Fiber
Optics
Illustrated
Dictionary
Mellon, and the University
of
Michigan. The
original
NeXT
was
grayscale,
with
color
added
in
later
versions.
The
first
NeXT
was
cube-shaped,
with
later
hardware
resembling
more
conventional
desk-
top
flat

systems,
known
as
NeXT
stations.
The
first
NeXT
was
based
on
the
Motorola
68030
processor
with
a
built-in
68882
math
coprocessor,
and
it
came
standard
with
8
MBytes
of
RAM.

At
the
time,
most
computers
had
1
to
4
MBytes
of
RAM.
The
original
price
was
$6500
and
marketing
efforts
were
aimed
at
higher
education
institutions,
although
busi-
ness
owners

expressed
early
interest
due
to
the
net-
working
capabilities
of
the
system.
The
frrst
edition
of
CRC's
Telecommunications
Il-
lustrated
Dictionary
was
written
on
a
NeXT
com-
puter,
and
even

though
the
basic
technology
is
over
10
years
old,
the
computer
hardware
and
operating
system
have
stood
the
test
of
time
in
essentially
their
original
form.
The
simple,
stunningly
aesthetic

graphical user interface still beats most systems
hands-down;
the
powerful object-oriented
Unix-
based
operating
system
and
shell
connect
seamlessly
with
the
Internet,
and
the
multitasking
operating
sys-
tem
allows
dozens
of
processes
to
run
happily
at
the

same
time.
In
over
3
years
of
24-hour
a
day
opera-
tions running multiple desktop publishing,
Web
browsing,
and
illustration
programs
at
the
same
time,
the
author's
machine
didn't
crash
once.
That's
an
enviable

track
record.
After
using
a
dozen
different
types
of
computers
daily
for
over
20
years,
the
au-
thor
has
seen
few
systems
that
equal
it
(Sun
systems
provide
similar
performance).

The
NeXT
is
an
excellent
networking
computer,
con-
necting
easily
to
the
Internet,
other
NeXT
systems,
and
other
types
of
computers
through
TCP
lIP.
It
is
also
an
excellent
Internet

portal,
with
a
full
comple-
ment
of
Unix
tools,
including
Telnet,
FTP,
and
oth-
ers
easily
downloadable
from
the
Net.
OmniWeb,
by
Lighthouse Design, Ltd.,
is
a powerful Internet
graphical
browser
for
NeXTStep
that

preceded
many
well-known
graphical
browsers.
In
1997,
Apple
Computing,
Inc.
bought
out
NeXT,
Inc.
and
continued
developing
the
operating
system
software
under
the
development
name
of
Rhapsody,
now
better
known

as
Mac
as
X.
See
Jobs,
Steven.
Next
Generation Digital
Loop
Carrier
NGDLC.
Developed
in
the
1980s
as
an
evolution
of
Digital
Loop
Carrier
systems,
NGDLC
is
based
on
very
large

scale
integration
(VLSI)
technology.
ISDN
was
de-
veloped
and
promoted
at
about
the
same
time
that
NGDLCs
were
implemented,
so
many
were
devel-
oped
to
accommodate
ISDN.
Whereas
Digital
Loop

Carriers
were
designed
to
provide
services
over
tra-
ditional
copper
phone
lines,
NGDLC
was
designed
to
work
in
conjunction
with
fiber
optic
cables
or
fi-
ber/copper
hybrid
systems.
See
Digital

Loop
Carrier.
Next
Generation Internet
NGI.
A
U.S.
federal
mul-
tiagency
research
and
development
initiative
estab-
lished in
1997.
NGI works with industry and
academia
to
develop,
test,
and
demonstrate
advanced
networking
technologies
and
applications.
The

fol-
lowing
federal
networks
are
used
as
testbeds
for
the
682
NGI
initiative:
• NSF's
very
high
performance
Backbone
Net-
work
Service
(vBNS)
•
NASA's
Research
and
Education Network
(NREN)
• DoD's
Defense

Research
and
Education
Net-
work
(DREN)
•
DoE's
Energy
Sciences
network
(ESnet)
(pro-
posed
beginning
in
FY
1999)
NGI
is
coordinated
by
the
NGI
Implementation
Team,
coordinated
by
the
Large

Scale
Networking
Work-
ing
Group
of
the
Subcommittee
on
Computing,
In-
formation,
and
Communications
(CIC)
research
and
development
of
the
U.S.
White
House
National
Sci-
ence
and
Technology
Council's
Committee

on
Tech-
nology.
/>Next
Hop
Resolution Protocol
NHRP.
An
internet-
working
architecture,
which
runs
in
addition
to
rout-
ing
protocols
and
provides
the
information
that
en-
ables
the
elimination of
multiple
Internet

Protocol
(IP)
hops
when
traversing a
Next
Hop
Resolution
Protocol
network.
Aims
at
resolving
some
of
the
la-
tency
and
throughput
limitations
of
Classical
IP.
See
Next
Hop
Server,
ROLC,
NBMA.

Next
Hop
Server
NHS.
In
an
NHRP
networking
en-
vironment,
the
Next
Hop
Server
locates
an
egress
point
near
a
given
destination
and
resolves
its
ATM
address,
enabling
the
establishment

ofa
direct
ATM
connection.
See
Next
Hop
Resolution
Protocol.
NGDLC
See
Next
Generation
Digital
Loop
Carrier.
NGI
See
Next
Generation
Internet.
NGSO
nongeostationary
orbit.
NGSO
FSS
nongeostationary orbit
fixed
satellite
service.

NHRP
See
Next
Hop
Resolution
Protocol.
NICI
See
National
Information
and
Communications
Infrastructure
in
Appendix
G.
nickel metal hydride
NiMH.
A
rechargeable
battery
commonly
used
in
portable
devices.
Hydride
is
a
hy-

drogen
compound.
nickel-cadmium
cell
NiCd,
NiCad.
A
very
common,
sealed,
rechargeable
power
cell
that
works
well
in
low
temperatures.
The
positive
electrode
is
nickel
and
oxide,
and
the
negative
electrode

is
cadmium,
with
the
plates
immersed
separately
in
a
potassium-hy-
droxide
electrolyte
solution.
NiCad
batteries
have
been
used
in
many
small,
portable
telecommunica-
tions
devices
but
have
the
disadvantage
ofa

"memory
effect,"
that
is,
they
will
not
fully
recharge
unless
first
fully
discharged,
thus
reducing
the
useful
time
ofthe
battery.
nickname An
easy-to-use,
easy-to-remember
substi-
tute
or
secondary
name.
In
most

cases,
it's a
short
name,
generally
one
easy
to
remember
because
it
is
familiar
or
matches
the
personality
or
properties
of
the
person
or
obj
ect
for
which
it
is
designated.

A
nick-
name
can
also
be
a
name
given
as
a
term
of
intimacy
and
affection
between
two
people
who
are
closely
acquainted.
Nicknames
may
also
be
names
that
are

easy
to
type,
to
save
time,
as
on
public
discussion
areas
of
the
Internet.
See
handle,
NICname.
© 2003 by CRC Press LLC
NICname, Nicname, Nickname
On
Internet
Relay
Chat (IRC), a name that can be set with /nick
<putnamehere>.
Only
one
person
can
have
a

specific
nickname
at
anyone
time
on
IRC.
See
Internet
Re-
lay
Chat,
WhoIs.
Nicol,
William
(ca.
1768-1851) AScottish educator
and
physicist
who
developed
the
Nicol
prism
from
Iceland
spar.
There
are
few

records
about
his
early
life,
but
he
began
publishing
his
research
in
1828
and
spent
the
latter
part
of
his
life
studying
crystals
and
fossils.
He
apparently
developed
his
own

lenses
and
invented
new
methods
for
grinding samples
for
mi-
croscopic
inspection.
Nicol's
sister,
who
was
about
five
years
younger,
married
Edward
Sang,
a promi-
nent
mathematician
and
engineer.
Nicol
prism A refractive component consisting
of

two
blocks ofIceland spar (calcspar) cemented
to-
gether
along
the
diagonal
plane
with
Canada
balsam,
a
material
derived
from
bark
ooze
that
was
a
com-
mon
bonding
agent
in
optics
for
about
200
years.

The
Nicol prism
was
one
of
two
common
birefringent
prisms,
along
with
the
Ahrens
prism.
The
unusually distinct birefringent properties of
Ice-
land spar were described in 1670 by Rasmus
Bartholin,
but
the
mathematics of
its
properties
were
not
worked
out
until almost
150

years
later,
by
Tho-
mas
Young.
William
Nicol
put
two
equally
shaped
calcspar
blocks
together
to
produce
the
Nicol prism, described
in
1828.
The
device
was
used
in
polarimeters
as
early
as

the
1840s.
Historic polarimeters consisted of a
sample
tube
mounted
horizontally
between
an
ana-
lyzing Nicol prism
and
a polarizing Nicol prism.
Monochromatic
light
could
be
shone
through
the
tube
with
the
analyzing
prism
rotated
to
produce
two
light

sources
for
comparison.
Nicol prisms were incorporated
as
substage
polarizers
into
European scientific microscopes, be-
ginning around
the
1850s
or
1860s.
Arotating
Nicol
prism polarization analyzer could
be
mounted
be-
tween
the
microscope nosepiece
and
the
objective
lens
or
over
the

eyepiece,
depending
upon
the
instru-
ment. By selectively rotating the prism and the
sample,
the
polarizing characteristics of
the
sample
could
be
discerned. Nicole prisms continued
to
be
common
in
microscopes
as
recently
as
the
1950s.
In
the
1880s,
William
Thompson
(Lord

Kelvin)
used
a
Nicol
prism
in
his
lectures
and
demonstrations
on
the
polarization of
light.
Edwin
Land
credits
his
in-
vention ofpolarizers
at
the
age
of
19
to
a
demonstra-
tion
he

saw
as
aschoolchild ofa
Nicol
prism.
His
in-
vention
led
to
a patent
and
the
establishment of
the
Polaroid Corporation.
Polarization
is
now
typically
accomplished
with
films
and
coatings. Polarizing beam splitters somewhat
resemble Nicol
prisms,
having
two
blocks

combined
with
a
refractive
coating
layer,
but
the
blocks
are
equi-
lateral triangles
and
the
resulting
component
is
cubi-
cal.
See
Bartholin,
Rasmus;
Iceland
spar;
polariza-
tion,
Wollaston
prism.
NIDS
See

network intrusion detection
system.
NIF
See
network interface
function.
~~~::~~;g~~;~~ir~f:~~~~~:::~
•
ordinate,
and
regulate private sector participation
in
the provision
of
telecommunications services.
/>NIMBUS A satellite program initiated
in
the
early
1960s
by
the
National
Aeronautics
and
Space
Admin-
istration
(NASA),
and

now
operatedjointly
with
the
Oceanic Atmospheric Administration (NOAA).
Nicol Birefringent Polarizing Prism
Icelandsparis a doubly-refractive (birefringent) mineralwith interestingprismaticproperties.
TWo
calcspar blocks
can be bonded along the diagonal with a material
of
slightly lower refraction index
(b)
toform
a Nicol prism which
makes itpossible to more widely separate the two courses
of
light through the material and thus isolate the one
of
interest. In constructing the prism, the natural rhombus angle
of
-72
0
can be ground down to 68
0
(a)
for
more
effective results.
In this example, incident light

(I)
enters the material and is split into two beams, one slightly stronger than the
other.
The
ordinary beam
(0)
is reflected
off
the seam due to its angle and the fact that it has a slightly lower
refractive index than the bonding material (much as light reflects
off
the cladding in fiber optic filaments). The
"extra-ordinary" beam
(E)
hits the seam almost straight
on
andpasses essentially unimpeded across the bonded
seam.
Thus,
the planepolarized light
(E)
exits in the same general direction as the incident light.
683
© 2003 by CRC Press LLC
Fiber
Optics
Illustrated
Dictionary
NIMBUS
is

used
for
research
and
development
by
atmospheric
and
Earth
scientists.
NiMH
See
nickel
metal
hydride.
Nimrod Routing Architecture A
scalable
network
routing architecture intended
to
support
dynamic,
heterogenous
intemetworks
of
arbitrary
size,
Nimrod
was
originally

suggested
by
Noel
Chiappa.
It
was
thereafter refined
by
the
IETF
Nimrod
Working
Group
and
formally
described
in
the
mid-1990s.
Nimrod
achieves
scalability
by
representing
and
ma-
nipulating
routing
information
at

multiple
levels
of
abstraction
to
accommodate
expanding,
diversifying
networks.
Nimrod
is
characterized
by
maps
that
rep-
resent
internetwork
connectivity
and
services,
user
route
generation
and
selection,
and
user
packet
for-

warding
along
established
paths.
It
is
applicable
to
routing
within
single
and
multiple
routing
domains
in
TCP/IP
and
OSI
environments.
See
RFC
1992.
NIOD
Network
Inward/Outward
Dialing.
Nipkow
Disc
- Historic

Image
Scanner
This Nipkow disc shows the spiral series
of
holes
through which the light is beamedas the disc rotates.
This historic example isfrom theAmericanRadio Mu-
seum collection. [Classic Concepts photo.}
Nipkow,
PaulGottlieb A
German
experimenter
who
developed
a
rotating
dial
with
a
spiral
arrangement
of
holes
that
he
patented
in
1884.
It
was

an
early
elec-
tromechanical
television
system.
This
was
later
in-
corporated
into
television
transmitting
and
receiving
units.
See
Nipkow
disc.
Nipkow
disc
A
rotating
disc
with
a
sequential
heli-
cal

pattern
of
holes
used
by
many
early
television
684
experimenters
to
attempt
the
projection of
television
images.
The
perforated
disc
was
rotated
in
front
of
the
image
to
be
transmitted
in

order
to
quantize
the
signal,
in
a primitive
sense,
by
segmenting
the
im-
age
into
lines.
The
photosensitive
material
selenium
was
placed
behind
the
disc
to
register
the
dark
and
light

areas
of
the
image.
Unfortunately,
systems
for
amplifying
the
signal
for
transmission
didn't
exist
at
the
time,
and
didn't
become
practical
until
other
tech-
nological
developments
occurred.
The
disc
is

named
after
its
inventor,
Paul
Nipkow.
Modem
versions
of
the
Nipkow
disc
are
used
in
a
variety
of
applications
and
typically
are
fabricated
from
plastic
or
glass,
with
thousands
of

pinholes
or
microlenses
embossed
into
the
substrate.
They
re-
semble
translucent
CDs
and
are
used
in
optical
scan-
ners
and
confocal
microscopy.
In
a
confocal
micro-
scope
capable
of
resolving

very
tiny
images,
the
per-
forated
disc
rotates
between
a beam-splitter
and
a
lens,
providing
expanded
depth
imaging
through
a
form
of
optical
sectioning.
A
rotation
of
the
disc
en-
ables

an
XY
section
of
the
specimen
to
be
acquired
in
realtime.
Height
can
be
evaluated
through
grab-
bing
a
frame
and
processing
the
image
and
Z
data
combined with it
to
provide a

3D
topographical
"map"
of
the
microscopic
specimen.
See
Baird,
John
Logie;
television
history.
Nippon Advanced Mobile Telephone System
NAMTS.
An
early,
first-generation,
analog
FM-based
mobile
phone
system
with
digital
processing,
first
introduced
in
Japan.

Communication
Services
Lim-
ited
(CSL)
made
the
system
publicly available
in
1984.
Nippon Telephone and Telegraph Corporation
NTT.
The
major
Japanese
telephone
company
and
largest
phone
company
in
the
world.
In
1997,
deregu-
lation
allowed

NTT
to
begin
operating
internation-
ally,
and
its
first
international
subsidiary,
NTT
World-
wide
Telecommunications
Corporation,
began
servic-
ing
overseas
corporate
customers.
See
Arcstar;
Japan
Telecom
Co.
Ltd.;
KDDI
Corp.

NIS
1.
Network
Imaging
Server.
2.
See
Network
In-
formation
Service.
NISDN
1
See
National
ISDN-l
in
Appendix
G.
NIST
See
National
Institute
of
Standards
and
Tech-
nology
in
Appendix

G.
NITF
National
Image
Transfer
Format.
NIUF
See
North
American
ISDN
Users
Forum.
NJE
See
Network
Job
Entry.
NL
port, end
loop
port
In
a
Fibre
Channel
network,
a
port
on

an
endstation
that
enables
it
to
be
connected
to
the
Fibre
Channel
loop.
The
NL
port
is
assigned
the
lowest
addresses
and
thus
has
the
highest
prior-
ity
in
terms

of
obtaining
control
ofa
loop.
See
F
port,
FL
port,
N
port.
NLA
See
Network
Layer
Address.
NLANR
National
Laboratory
for
Applied
Network
Research.
NLC
See
nematic
liquid
crystal.
NLPID

Network
Layer
Protocol
ID.
NMAA
National
Multimedia
Association
of
Ameri-
can.
/>© 2003 by CRC Press LLC
Emily
Noether - Mathematician
EmilyNoetherdevelopedmathematicalgroup theo-
ries that are still widely
used
by
physicists.
NMACS
Network
Monitor
and
Control
System.
NMD
See
nonintrusive
measurement
device.

NMP
1.
See
Network
Management
Processor.
2.
See
Network
Management
Protocol.
NMR
See
nuclear
magnetic
resonance.
NMS
Network
Management
System.
NNI
1.
network node interface.
2.
Nederlands
Normalisatie-Instituut.
A
Netherlands
standards
or-

ganization
established
in
1959,
located
in
Delft.
NNTP
See
Network
News
Transfer
Protocol.
NOAA
See
National
Oceanic
and
Atmospheric
Ad-
ministration.
noble
gas
A
rare
or
inert
gas.
Examples
include

ar-
gon,
krypton,
neon,
and
helium.
These
gases
are
use-
ful
in
illuminated
signs
and
laser
technologies.
See
argon,
krypton,
neon.
nodal clock
In
a
network,
a
reference
clock
source
for

major
timing
functions
associated
with
a
node.
A
valid
clock
reference
may
be
extracted
from
a
vari-
ety
of
sources,
including
a
Primary
Linkage
and
Co-
ordination
Program
(PLCP).
The

best
nodal
clock
in
a
facility
can
be
selected
to
provide
a
unified
timing
source
for
Building-Integrated
Timing
Supply
(BITS)
such
that
a
group
of
network
switches
would
appear
as

a
node
in
the
hierarchical
network
scheme.
node
Junction,
confluence,
meeting
point,
terminal,
intersection.
A
connection
point
in
a
network,
which
may
consist
ofa
router,
switcher,
dialup
modem,
com-
puter,

or
other
interconnecting
device
supporting
the
same
protocol,
or
converting
to
the
needed
protocol.
Together
the
nodes,
equipment,
and
pathways
con-
stitute
the
network
topology.
See
backbone,
leaf
node.
node port

See
N
port.
Noether, Emily "Emmy" (1882-1935) A brilliant
German-born
mathematician,
Emily
Noether
devel-
oped
mathematical
group
theories
which
underlie
many
subsequent
representations
of
modem
physics.
Einstein
praised
her
contributions
and
offered
to
write
her

obituary.
Noetherian
Rings
are
named
after
her
and
grandmaster
chess
player
Emanuel
Lasker
proved
some
Noetherian
algebraic
concepts
(Lasker-No
ether
decomposition
theorem).
noise
Meaningless
or
otherwise
unwanted
sounds
or
signals

interfering
with
the
desired
information
or
transmission
in
electromagnetic
or
acoustic
commu-
nication
systems.
Noise
can
arise
from
bad
shield-
ing,
wires
too
close
together,
overlapping
transmis-
sions,
weather
disturbances,

irregular/reflective
ter-
rain,
incorrect
operation,
deliberate
human
interfer-
ence,
random
varying
velocity,
or
faulty
or
incom-
patible
hardware.
Noise
in
fiber
optic
networks
is
different
from
noise
in
wired
networks.

Electrical
disturbances,
voltage
surges,
and
ground
loops
can
have
a
significant
im-
pact
on
wired
networks
but
may
have
little
or
no
im-
pact
on
fiber
optic
cables,
especially
end-to-end

op-
tical
networks.
:~~:~~:~n!~1~!~=~:~i£~~:~:~~~!
'a
thermal
noise
or
noise
from
back
reflection
and
are
vulnerable
to
noise
anywhere
there
is
ajunction
with
electrical
components.
Thermal
noise
may
be
espe-
cially

problematic
in
systems
using
p-i-n
photodetec-
tors.
Fiber
optic
networks
may
experience
beat
noise
at
the
receiving
end
from
amplification,
depending
upon
the
frequencies
or
from
relative
intensity noise
from
fluctuations

in
the
emissions
from
the
source
illumination.
Another
source
of
noise
in
optical
networks
is
modal
noise,
which
arises
when
the
emitted
light
(e.g.,
la-
ser
light)
travels
through
a

multimode
fiber
in
slightly
different
reflective
paths,
resulting
in
slightly
vary-
ing
distances
for
the
total
path
or
phase
delay.
The
light
reaching
the
output
end
may
exhibit
fluctuat-
ing

interference
patterns
and
may
obscure
whether
the
light
pulse
is
on
or
off.
Microbends
and
pits
may
increase
modal
noise.
Modal
partition
noise
results
from
a
fluctuation
in
intensity
from

the
laser
source
affecting
the
longitudinal
modes
of a
multi
mode
transmission.
Dispersion
of
the
different
modes
can
result
in
varying
speeds
along
the
travel
path,
caus-
ing
fluctations
at
the

destination.
Intersymbol interference noise
may
result
from
un-
even
fluctuations
of
light
pulses
that
overlap
in
the
process
of
traveling
toward
the
destination.
Quantum
noise
resulting
from
the
particle
nature
of
light

can
contribute
to
shot
noise.
There
is
Poisson
variance
in
the
number
of
photons
received
in
any
given
bit
pe-
riod
such
that
the
photonic
energy
fluctuates.
This
may
increase

as
the
optical power increases.
See
crosstalk,
garbage,
interference,
loss
(includes
dia-
grams),
intersymbol
interference.
685
© 2003 by CRC Press LLC
Fiber
Optics
Illustrated Dictionary
noise, modal
See
dispersion,
noise.
noise
canceling
Techniques
and
technology
to
reduce
or

eliminate
noise.
This
may
be
background
noise
or
noise
on
the
transmissions
pathway.
Noise
cancella-
tion
can
be
through
digital
algorithms
which
analyze
the
information
and
screen
out
calculated
noise

(a
feature
now
found
on
digital
cellular
phones),
or
may
be
through
conditioning circuits
in
transmitters
or
receivers.
Noise
cancellation
is
sometimes
achieved
by
adding
noise,
creating a "white"
noise
that
may
be

less
objectionable
than
bursty,
intermittent
noise.
noise filter An electrical circuit
designed
to
detect
or
evaluate
and
exclude
extraneous signals passing
through
a
circuit.
In
digital
circuits,
fairly
sophisti-
cated analysis
may
take
place.
In
analog circuits,
simple

exclusions
ofparticular patterns
or
frequen-
cies
may
be
used.
non-facility-associated signaling
NFAS.
In
ISDN
networks,
a
type
ofsignaling
in
which
the
D
channel
is
at
a
separate
primary
rate
interface
(PRI)
from

an
associated
set
ofB
channels.
Multiple
PRI
lines
can
be
supported
through
a
single
D
channel
using
NF
AS.
In
contrast,
in
facility-associated signaling,
the
D
channel
is
at
the
same

PRI
as
the
associated
B
channels.
nonintrusive measurement device
NMD.
A
device
used
to
measure
various
parameters
in
analog
voice
transmissions
over
communications
networks.
Mea-
sured
parameters
include
noise
level,
speech
level,

echo
path
loss,
and
echo
path
delay.
nonionizing
That
which
does
not
cause
ionization
or
change
the
ion
environment
around
it.
A
number
of
transmissions
media,
including visible
light
rays
and

radio waves,
do
not
cause ionization, but
can
be
propagated
by
ionized
particles
with
which
they
come
in
contact.
nonlinear distortion
In
an
optical waveguide,
the
distortion
that
occurs
over
distance
when
more
than
one

wavelength,
with
different transmission charac-
teristics,
or
more
than
one
pulse,
which
may
reflect
at
different
angles
in
the
waveguide,
travels
at
dif-
ferent
speeds.
Thus,
a signal
sent
together doesn't
always
arrive
at

its
destination
in
synch
with
its
other
components
and
the
effect
is
cumulative
over
dis-
tance.
The
gradual
loss
ofsynchronization
can
have
delete-
rious
effects
not
only
at
the
destination

point,
but
en
route,
as
well,
where
crosstalk
may
result
from
non-
linear
waveform
interaction. Nonlinear distortion
is
influenced
by
the
character of
the
original
pulse,
the
breadth of
the
waveguide,
the
composition of
the

wavelengths
(which
may
be
prone
to
chromatic
dis-
persion),
the
number
of
bends
or
obstacles
(doping)
in
the
lightguide,
and
the
means
of
amplification.
See
chromatic
dispersion,
Raman
scattering.
See

noise.
nonreturn
to
zero
NRZ.
A
simple
binary
encoding
scheme
in
which
ones
and
zeros
are
represented
by
high
and
low
voltages,
and
there
is
no
return
to
a
zero

level
between successive encoded bits,
hence
the
name.
Since
transitions
mayor
may
not
occur
at
each
successive
bit
cell,
the
NRZ
signal
has
spectral
en-
ergy
and,
consequently,
a
direct
current
(DC)
com-

ponent
that
is
a
nonzero
energy
at
DC.
It
is
thus
one
686
type ofbaseband signal.
See
Manchester encoding.
nonvolatile memory Circuits or components that
retain
their
data,
even
if
the
electrical current
is
shut
off.
In
computer
circuitry,

volatile
memory
is
installed
in
greater quantities
than
nonvolatile
memory.
Non-
volatile
memory
is
typically used
for
configuration
settings (e.g.,
video
parameters).
See
EPROM,
read-
only
memory.
Contrast
with
dynamic
random
access
memory.

nonwireline carrier
Also
called
an
ABlock carrier,
for
alternate carrier; that is, a competitive phone
services
carrier
that
is
not
the
established
local
phone
company
(usually a
Bell
carrier,
hence
B Block
car-
rier).
NORC Network Operators Research
Committee.
normal
An
imaginary
line

in
a direction describing
the
perpendicular
to
another
line
or
plane.
In
other
words,
for
any
given
line
or
plane,
there
is
arelation-
ship
that
is
perpendicular
to
that
line
or
plane

for
any
given
point ofreference.
The
term
"normal"
is
unfamiliar
to
many
people
and
the
word
"perpendicular"
is
often
substituted.
The
use
of
the
word
"normal"
appears
to
date
back
to

an
Old
English
term
for
"rectangular"
or
"right." Since a
right
angle
is
90°
perpendicular
to
the
reference
angle
by
definition,
this
may
account
for
the
evolution of
the
term
as
it
is

now
used.
For
simplicity, picture a
very
slender flagpole
an-
chored
squarely
in
a
flat
concrete
slab;
assuming
that
any
point
in
the
center of
the
flagpole
at
a specified
distance
from
the
slab
is

equidistant
from
the
slab
in
any
direction (imagine invisible equal-length guy
wires
all
the
way
around
the
pole),
it
is
considered
normal
to
the
slab,
even
if
the
slab
is
removed
from
the
ground

and
tilted
in
different directions -
as
long
as
the
flagpole
remains
firmly
anchored
in
the
same
position relative
to
the
surface of
the
slab,
it
is
con-
sidered normal
to
the
plane
of
the

slab.
If
you
took
away
the
flagpole
and
substituted
an
imaginary
line,
this
line
expresses
the
slab's normal
geometry,
even
if
the
line
were
extended
out
the
other
side
of
the

slab
(poking
into
the
ground
like
a
pylon
representing
the
negative direction of
the
normal
vector).
While
normal
is
usually visualized
as
a
line,
it
should
be
remembered
that
the
line
could
be

imagined
as
being
anywhere perpendicular
to
the
reference sur-
face,
not
just
in
the middle. For example,
if
you
moved
the
flagpole
from
the
center of
the
concrete
slab
to
the
edge,
while
still
keeping
it

straight (i.e.,
maintaining the even lengths
of
the imaginary
guywires),
the
flagpole
is
still
considered
normal
to
the
plane
of
the
slab.
Thus,jor
some shapes,
normal
can
be
seen
as
aplanar concept expressed
as
a
line
in
the

context of a specific
given
point ofintersection
with
the
reference
plane.
To
understand
the
planar
aspect,
imagine
walls
in
a
house
and
how
they
are
set
at
90°
angles
relative
to
the
plane
of

the
floor.
You
can
pick
any
point of
intersection
with
the
floor
along
the
bottom
of
the
baseboard ofa
wall
and
there
will
be
an
imaginary
line
normal
to
the
floor
concurrent

with
the
plane
of
the
wall.
The
relationship
holds
true
for
other selected points along
the
wall.
The
wall
© 2003 by CRC Press LLC
could
be
pivoted around
one
of
those points, using
it
as
an
anchor, and
any
other point where the wall
touches

the
floor
in
its
new
orientation will still
be
normal
to
the
floor.
However,
the
pivoting relation-
ship
between
the
wall
and
the
floor only holds con-
sistently
for
flat
surfaces.
It
is
fairly straightforward
to
grasp the concept

of
normal
for
straight lines
or
flat
planes, but what
if
the
reference
line
or surface
is
curved? Imagine a tooth-
pick sticking partway into a perfectly round orange.
If
the
line
of
the
toothpick
is
perpendicular
to
the
tan-
gent
plane
of
the

orange relative
to
where
the
tooth-
pick intersects
the
curved surface of
the
orange,
the
toothpick
is
normal
to
the surface
of
the orange,
whether it's
the
outside convex surface
of
the orange
or
the
inside concave surface. In aperfect sphere,
the
relationship
holds
if

the
toothpick passes through
the
center
and
pokes
out
the
other side. However,
if
the
line
of
the
extra long toothpick
is
offcenter, or
the
orange isn't perfectly round, normal cannot
be
as-
sumed
to
be
the
same
on
both sides
of
the orange

through
a
single
line.
Normal
must
be
calculated
rela-
tive
to
one
point
of
intersection
on
asingle reference
surface if
the
calculations
are
to
be
generalizable
to
any
surface.
Ifyou're
having
trouble visualizing

the
angle
at
which
the
toothpick must pierce
the
round orange
to
be
normal, imagine equal-length guywires around
the
toothpick
as
you
did with the flagpole. Now pic-
ture the stakes holding the guywires
as
spinning
around
the
toothpick
to
mark a circle like a compass
and
slicing offa chunk
of
orange through
the
marks.

If
you
place
the
round piece
of
orange
on
your table-
top,
the
toothpick will
now
be
sticking straight
up,
perpendicular
(normal)
to
the
surface
of
the
table.
For
a natural, asymmetric orange (or eggplant),
normal
will
be
related

to
the contours
on
the
fruit's surface
where
the
toothpick pierces the
skin.
Determining
normal
for
a point
on
a bumpy surface
like
the
Earth's terrain or
an
optical diffraction grat-
ing
is
a little
more
complicated, since
it
will change
every
few
inches

or
Jlm,
but here
is
a
way
to
visual-
ize
the
relationship. Imagine flying a small aircraft
(or aflight simulator) a
few
feet
off
the
ground
in
the
desert
and
maintaining that distance
from
the
ground
over
a
series
of
sand

dunes.
As
you
pull
back,
the
nose
of
the
aircraft
pulls
up.
As
you
push
forward,
the
nose
of
the
aircraft pushes
down.
The relationship
of
the
steering stick
may
not
be
perfectly perpendicular

to
the
surface
of
the
sand beneath it
(due
to
lag), but it's
close
and
it
gives
you
away
to
picture approximately
where normal
is
for
a given surface
on
a complex
plane
like
desert terrain.
The
concept ofnormal,
when
applied

to
bumpy
sur-
faces,
has
a fractal nature
in
the sense that bumpy
surfaces often appear
more
complex
as
they
are
more
closely
examined.
Benoit Mandelbrot used
the
ex-
ample
of
a coastline
to
describe
this
relationship
in
fractal geometry
and

he
developed equations based
upon self-similarity leading
to
the
observation that
the
closer
you
look
at
a coastline,
the
longer
it
gets,
due
to
the
fact
that
slight indentations
and
protrusions
can
be
more
readily
seen.
Determining normal

for
a
bumpy
surface
is
somewhat like that.
The
closer a
surface
is
scrutinized
at
the
point where
you
want
to
determine
the
normal
relationship,
the
more
the
quan-
tity
or
shapes
of
the

bumps
and indentations might
influence
the
angle
of
an
imaginary steering stick or
toothpick.
Thus,
normal
is
dependent,
in
part,
upon
the
scale
and
type
of
measuring apparatus (and geometry) used
to
determine
the
relationship
of
the
point
of

intersection
to
the
reference
plane.
Returning
to
the
guywire
anal-
ogy,
imagine atoothpick placed normal
to
the
surface
of
an
irregular eggplant rather than aperfectly round
orange;
the
angle
of
the
toothpick would likely
be
different if
the
guywires were very close
to
the

tooth-
pick
as
opposed
to
some
inches
away
from
the
tooth-
pick.
The
concept
of
normal, which
is
a way
of
conceiv-
ing
perpendicular relationships
in
3D
space
in
any
orientation,
is
essential

in
many aspects
of
geometry,
theoretical physics, robotics, industrial fabrication
(especially telescopes
and
microscopes), mapping,
geology, computer-aided design and drafting,
and
much
more.
It
is
frequently used
to
describe grating
surfaces, layered semiconductorstructures,
and
other
industrial
fabrications.
The
angle
ofincidence
of
a re-
flected wave
is
generally described using surface

normal
as
a reference.
Thus,
normal
is
useful
for
de-
scribing light paths, reflectivity, and diffraction.
Sur-
prisingly, many technical references gloss over or
don't mention the
term
at
all.
See
incidence, normal
wave.
normal
distribution
A theoretical construct based
upon
observations
of
the
distribution
of
certain traits
in

sufficiently large populations. From these obser-
vations,
it
is
possible
to
create a statistical represen-
tation
of
frequency distribution
to
form
abell-shaped
curve
with certain consistent mathematical proper-
ties
across the curve.
It
is
also called a Gaussian
dis-
tribution after
the
observations
of
Karl
Gauss.
Thus,
relationships such
as

the
mode
and
the
mean
fall
in
the
center
of
the
curve
and
are equal
and
frequency
tails off
to
either side through a number
of
symmet-
ric
standard deviations until it becomes
zero.
Once
it
had
been observed that many traits
seem
to

follow
ageneral statistical distribution pattern (many
ofwhich
came
out
of
studies or assumptions about
human
intelligence),
the
normal distribution
or
nor-
mal
curve
was
then assumed
to
apply
to
many
other
frequency distributions, with this assumption then
being built into tools designed
to
measure traits
in
a
population (which
has

some
self-fulfilling
and
circu-
lar aspects that may interfere with the development
ofobjective measuring instruments).
Thus,
it
is
used
as
a basis
for
describing probabilities (though
some
might
say
possibilities). Many students
ask
profes-
sors
ifa class
is
being graded
on
a "bell curve." In
fact,
with small class sizes, there aren't sufficient
numbers
in

the population set
to
justify
the
assump-
tion
of
a normal curve but many instructors apply
normal
curve concepts
to
assigning grades anyway
(or
get
nervous
if
exam
results don't naturally
fol-
low
characteristics
of
a normal curve).
687
© 2003 by CRC Press LLC
Fiber
Optics
Illustrated
Dictionary
In

its
most
general
sense,
in
a
sufficiently
large,
natural
population, a
normal
distribution describes a
sample
set
in
which
there
are
many
members
with similar
traits,
then
a
gradually
lessening
number
with
slightly
different

traits
diverging
in
either direction
from
the
mean.
For
example,
there
may
be
a
large
number
of
men
who
are
5'10"
tall
in
the
U.S.,
with
diminish-
ing
numbers
who
are

smaller
or
taller until a
point
is
reached
where
there
are
no
more
people outside
the
sample
set.
When
plotted
in
Cartesian coordinates,
this
trait
maybe
geometrically illustrated
as
a statis-
tical
curve
resembling
a
symmetric

bell
shape,
with
the
mean
(average)
and
mode
(most
frequent)
cen-
tered
around
those
who
are
5'10',.
In
communications,
the
concept
may
be
useful
for
some
aspects
of
assessing,
estimating,

or
predicting
network
demographics,
peak
time
use,
etc.
normal
wave Energy in wave form (e.g., radio
waves)
that
travels
normal
(perpendicular)
to
a
ref-
erence
plane
or
line.
Since
normal
is
atheoretical
re-
lationship
(an
imaginary

line),
the
concept
ofa
nor-
mal
wave
is
not
dependent
upon
whether
the
wave
impacts
the
reference
surface
which
may,
in
fact,
be
imaginary.
In
practical applications, a
normal
wave
may
fail

to
impact,
reflect
from,
or
travel
through
a
reference
surface
(e.g.,
a
receiving
antenna).
If
the
reference
surface
is
reflective,
and
the
wave
reaches
the
surface,
the
wave
would
be

reflected
back
in
the
direction
from
which
it
came,
a situation called a
Littrow
condition.
See
normal.
Norman, RobertAresearcher
who
published a
clear
statement
of
the
laws
governing
magnetic
attraction
and
repulsion
in
1581.
See

magnet.
Normes Europeenne de Telecommunications
NET.
An
organization providing compliance testing
for
commercial telecommunications products
for
sale
throughout
the
European
Union
to
determine
whether
they
conform
to
mandatory
standards.
Nortel
Northern
Telecom
Limited.
A
leading
global
digital
network

provider providing
commercial
data,
voice,
and
video
services.
Nortel
is
a
dominant
pub-
lic switching equipment supplier in Canada
de-
scended
from
Northern
Electric.
It
is
also
known
for
manufacturing
and
distributing radar
sets
based
on
magnetron

tube
technology,
particularly
during
the
second
world
war.
Nortel technology
is
leased
by
other
companies.
See
Qwest.
NorthAmerican
area
codes
See
the
Appendix
for
a
chart
of
area
codes
for
Canada,

the
U.S.,
and
U.S.
ter-
ritories.
North
American
Basic Teletext Specification
NABTS.
An
Electronic
Industry
Association
(EIA)
and
lTU
standard
that
describes
a
means
to
modu-
late
data
onto
a vertical
blanking
interval

(VBI),
the
transition
time
when
the
electron
beam
in
a
video
dis-
play
travels
from
bottom
right
to
top
left
with
the
elec-
tron
beam
turned
off
so
as
not

to
interfere
with
the
image
that
is
currently
displayed.
This
is
usually
as-
sociated
with
an
NTSC
signal,
as
is
standard
in
North
American
television
broadcasting.
NABTS
can
be
adapted

to
transmit Internet
Protocol
(IP)
data
so
that
broadcast
companies
can
send
vari-
688
ous
data
services
along
with
atelevision
signal.
RFC
2078
describes a
one-way
36-byte packet structure
that
can
be
encoded
into

a single horizontal
scanline
of a television
signal.
Synchronization
packets
are
located
at
the
beginning,
followed
by
address,
index,
and
parameter information,
followed
by
26
bytes of
user
data,
finally
ending
with
forward
error correc-
tion
(FEC)

data.
The
full
NABTS
specification
is
described
in
EIA-
516.
The
entire
NABTS
specification
is
not
always
implemented.
See
NTSC,
RFC
2728.
NorthAmerican CellularNetwork
NACN.
A
com-
mercial provider of international cellular roaming
services through their network backbone, serving
over
7500

cities
worldwide.
Supported protocols
are
System
Signaling 7
(SS7),
X.24,
GSM
and
IS41.
North American Digital Cellular
NADC.
A
com-
mercial digital mobile phone service launched
in
1991,
NADC
was
introduced
as
asecond-generation
system.
IS-54
supports
data
rates
of
48

kbps
at
a
band-
width
of
30
kHz
using digital phase shift keying
(DPSK)
modulation.
IS-136
is
based
upon
time
di-
vision
multiple
access
(TDMA).
See
DAMPS,
time
division multiple
access.
NorthAmericanDirectoryPlan
NADP.
An
X.500-

based
client/server Directory
System
for
providing
global
electronic directory
and
address
book
capabil-
ity,
distributed
by
ISOCOR.
North American ISDN Users
Forum
NIUF.
See
ISDN
associations.
North
American
Network
Operators
Group
NANOG.
An
association oflntemet
Service

Provid-
ers
which
meets
several
times
ayear
to
discuss
tech-
nical
issues
regarding
the
administration
and
opera-
tion
ofInternet-connected
services.
North American Numbering Council
NANC.
A
Federal
Advisory
Committee
established
and
char-
tered

with
the
U.S.
Congress
in
1995
by
the
Federal
Communications Commission (FCC)
to
assist
in
adopting
a
model
for
administering
the
North
Ameri-
can
Numbering Plan
(NANP).
This
identification
scheme
is
used
for

many
telecommunications
net-
works
around
the
world.
NANC
advises
the
FCC
and
other
NANP
member
governments
on
general
num-
ber
issues
and
on
issues
of
number
portability (e.g.,
for
mobile
telephones).

See
North
American
Num-
bering
Plan.
/>NorthAmerican NumberingPlan
NANP.
A
system
of
assigned
codes
and
conventions
introduced
in
1947
for
routing North
American
(World
Number
Zone
1)
calls
through
the
various
telephone

trunks
of
the
pub-
lic
telephone
network.
In
1995,
significant
changes
were
made
to
the
NANP,
mainly
due
to
increased
demand
for
area
codes,
including
changing
the
middle
digits
from

1
and
0
to
2
through
9.
See
Area
Codes
chart
in
the
Appendix.
NorthAmerican NumberingPlanAdministration
NANPA.
A
working
group
that
develops
and
advises
the
North
American
Numbering
Council
(NANC)
on

processes
for
selecting a neutral
NANP
Administra-
tor.
It
oversees a
number
of
task
forces
and
coordi-
nates
with
them
on
issues
related
to
cost
recovery
for
© 2003 by CRC Press LLC
the
NANP
administration.
North
American Telephone Association

NATA.
Now
known
as
the
MultiMedia
Telecommunications
Association,
this
is
an
open
public
policy,
market
development,
and
educational
forum
for
telecommu-
nications
products
and
services
developers
and
resell-
ers.
/>north geographic pole

The
point
at
which
the
imagi-
nary
lines
of
latitude
converge
at
the
north
pole
rela-
tive
to
the
shape
of
the
Earth
and
its
alignment
in
its
orbit
around

the
Sun.
The
general
direction
in
which
north-seeking
compass
needles
point
is
near
"geo-
graphic
north"
in
northern
Canada.
See
north
mag-
netic
pole.
north
magnetic pole A point
in
northern
Canada,
near

the
north
geographic
pole,
to
which
the
north-
seeking
tip
ofa
compass
points.
What
is
called
mag-
netic
north
could
be
seen
as
Earth's
south
pole,
if
the
"north"
end

of a magnet
were
used
to
determine
"north"
on
a
compass
or
alternately
as
the
north
pole
ifa
north-seeking
(south)
pole
ofa
compass
is
used
to
determine
the
direction.
If
that
sounds

confusing,
consider
that
the
designation
of
north
or
south
on
a
magnet
is
not
an
absolute
measure
but
one
assigned
relative
to
the
polarity
of
the
Earth,
for
which
we

have
already
designated
north
and
south
geographic
poles.
Thus,
"magnetic
north"
is
the
direction
toward
which
a
north-seeking
(south)
pole
ofa
compass
points.
The
north
magnetic
pole
is
not
the

same
as
the
Earth's
north
geographic
pole,
despite
its
proximity,
because
the
planet
is
a
dynamic
ecosystem
whose
magnetic
properties
change
over
time,
whereas
geographic
north
is
a
cartographically
fixed

point.
See
north
geo-
graphic
pole.
NOTIFY,
DNS
NOTIFY
A mechanism for
the
prompt
notification
of
network
zone
changes
that
was
proposed
as
a
Standards
Track
Comment
in
1996.
NOTIFY
is
a

DNS
opcode that enables a master
server
to
advise
slave
servers
ofa
change
in
data
so
that
they
may
initiate
a
query
to
discover
the
new
data.
Traditionally
many
networks
were
configured
to
poll

the
server
in
order
to
discover
any
changes
within
the
zone.
This
was
atrade-off
in
terms
of
load
on
the
sys-
tem
vs.
the
currentness
of
information.
A
NOTIFY
transaction,

on
the
other
hand,
establishes
a
means
to
initiate
and
expedite
the
update
process
when
SOA
RR
changes occur (and, theoretically, other
RR
changes),
thus
reducing
delay
without
imposing
ex-
cess
load
on
the

system.
NOTIFY
uses
a
subset
of
the
fields
in
the
DNS
Message
Format.
See
RFC
1035,
RFC
1996.
NOTIFY Set
In
distributed
networks
using
DNS
NOTIFY,
the
NOTIFY
Set
encompasses
servers

to
be
notified
if
changes
to
a
zone
have
occurred
that
should
be
queried
to
enact
updates.
The
set
defaults
to
those
listed
in
the
NS
RRset
but,
in
some

cases,
additions
or
overrides
may
be
possible
to
accommo-
date
special
circumstances
or
stealth
servers
that
are
not
listed
in
the
NS
RRset.
See
NOTIFY.
NOV
News
Overview.
Novell
One

of
the
significant
companies
providing
networking
software
(Novell
Netware)
to
the
busi-
ness
market.
Novell
is
a
public
company
established
by
a
buyout
ofNDSI
by
Ray
Noorda
in
1983.
In

1998,
Novell
began
promoting
Novell
Directory
Service
(NDS)
as
a
means
to
tie
different
networking
plat-
forms
together.
In
the
2000s,
Novell
acquired
Cam-
bridge
Technology
Partners
and
SilverStream
Software.

NOWT Netherlands Observatory
for
Science
and
Technology (Nederlands Observatorium van
Wetenschap
en
Technologie).
Noyce,
Robert
N.
(1927-1990) An
American
elec-
tronics
engineer
and
significant pioneer of
semicon-
ductor
technology,
Noyce
received
the
first
Ameri-
can
semiconductor
patent
(#2,981,877)

and
more
than
a
dozen
other
patents.
Early
in
his
career,
Noyce
did
research
at
the
Philco
Corporation.
In
1956,
he
joined
the
Shockley
Semiconductor
Laboratory
where
he
worked
with

transistors
and
soon
met
Gordon
Moore,
his
longtime
associate
and
business
partner.
Together
they
founded
Fairchild
Semiconductor
and
later,
in
1968,
Intel
Corporation.
Noyce
was
president
of
Intel
until
1975

and
then
served
as
chairman
of
the
board
until
1979
. I
Noyce
narrowly
missed
winning
the
Nobel
Prize
in
physics. Although
his
patent
was
the first
to
be
awarded
for
a pioneer integrated
circuit

(IC)
inven-
tion,
a
patent
application
and
verifiable
invention
by
Jack
Kilby
at
Texas
Instruments
was
determined
to
predate
Noyce's
by
just a
few
months.
Kilby
was
awarded
the
Nobel Prize
in

2000,
a
decade
after
Noyce's
death.
Nevertheless,
Noyce
made
a
mean-
ingful
contribution
with
his
version
of
the
new
con-
cept,
as
his
design
was
commercially
practical
and
his
company,

Intel,
grew
to
be
one
of
the
foremost
chip
design
and
manufacturing
firms
in
the
world.
The
Robert
N.
Noyce
award
is
presented
annually
to
outstanding
contributors
by
the
IEEE

society.
See
in-
tegrated circuit; Intel Corporation; Kilby, Jack;
Moore,
Gordon.
NPA
1.
National
Pricing
Agreement.
AT&T
agree-
ment.
2.
See
Numbering
Plan
Area.
A
three-digit
area
code.
NP
As
include
special,
reserved,
and
unassigned

numbers.
NPR
See
National
Public
Radio.
NPSTC
See
National
Public
Safety
Telecommuni-
cations
Council.
NRC
1.
See
National
Research
Council.
2.
See
Net-
work
Reliability
and
Interoperability
Council.
3.
non-

recurring
charge.
NREN
See
National
Research
and
Education
Network.
NRIC
See
Network
Reliability
and
Interoperability
Council.
NRSC
National
Radio
Systems
Committee.
NRZ
See
nonreturn
to
zero.
NSAI
National Standards Authority of
Ireland.
A

standards body
for
Ireland established
in
1961,
lo-
cated
in
Dublin.
NSAP
network
service
access
point.
NSF
See
National
Science
Foundation.
NSFNET
National
Science
Foundation
Network.
A
network
established
by
the
Office

of
Advanced
Sci-
entific Computing through
the
National Science
Foundation,
which
is
used
for
the
civilian
computing
689
© 2003 by CRC Press LLC
Fiber
Optics
Illustrated
Dictionary
operations
of
the
U.S.
Department
of
Defense.
See
National
Science

Foundation.
NSIE
See
Network
Security
Infonnation
Exchange.
NSlnet
NASA
Science
Internet, a
network
of
the
National
Aeronautics
and
Space
Administration.
NSP
1.
See
National Internet Services Provider.
2.
Native
Signal
Processing.
NSSN National Standards Systems Network.
/>NSTAC
National

Security
Telecommunications
Ad-
visory
Committee.
NT
Northern
Telecom,
Inc.
NTSC
National
Television
System
Committee.
An
organization
fonned
by
the
Federal
Communications
Commission
(FCC)
which
set
black
and
white
stan-
dards

for
the
emerging
television
broadcast
industry
in
1941.
By
1953,
after
the
proposal
and
consider-
ation
of
several
television
systems,
the
FCC
adopted
a
525-line
color
standard
developed
by
Radio

Cor-
poration
of
America
(RCA),
which
was
downwardly
compatible
with
previous
black
and
white
technolo-
gies.
This
is,
in
part,
why
luminance
and
chrominance
infonnation
are
carried
separately.
This
system

was
accepted
by
the
FCC
and
is
widely
used
in
North
America
and
parts
of
South
America.
In
NTSC
broadcasts,
color,
intensity,
and
synchroni-
zation
infonnation
are
combined
into
a

signal
and
broadcast
as
525
scan
lines,
in
two
fields
of
262.5
lines
each
(Europe
typically
uses
625
lines).
Only
480
lines
are
visible;
the
rest
occur
during
the
vertical

re-
trace
periods
at
the
end
of
each
field.
NTSC
is
con-
sidered
to
run
at
30
frames
per
second,
although,
in
color
television
broadcasts,
the
actual
playing
rate
is

approximately
29.97
frames
per
second.
See
High
Definition
TV,
PAL,
SECAM.
NuBus
NuBus
is
a
simple
Apple
Computer
32-bit
backplane
card
slot
standard
(ANSI/IEEE
P
1196)
for
the
connection
of peripherals

to
Apple
Macintosh
computers.
The
clock
is
derived
from
a
10-MHz
ref-
erence. NuBus backplane space
is
limited
to
74.55
x
11.90
mm
(even
though
some
models
have
larger
slots).
NuBus
slots
can

support
up
to
13.9W
of
power
per
card,
although
more
can
be
used
if
other
slots
are
not
filled.
nuclear magnetic resonance
NMR.
A
technology
used
to
reveal
the
inside
of
structures

or
biological
organisms
through
a
series
of
magnetic
scanners
or
a
magnetic
field
enveloping
the
body.
It
is
used
in
addition
to,
and
as
an
alternative
to,
X-rays
in
medi-

cal
research
and
diagnostic
imaging.
null
Empty,
having
no
value.
A
dummy
value,
char-
acter,
symbol,
or
marker.
Null
values
are
sometimes
used
as
delimiters
to
indicate
the
beginning
and/or

end
ofa
value
or
data
stream.
Null
characters
some-
times
are
used
as
padding,
to
even
out
the
size
of
blocks
or
to
provide
extra
time
for
synchronization.
Null
is

a
very
useful
concept,
regularly
used
in
pro-
gramming
and
network
transmissions
protocols.
null attachmentconcentrator
NAC.
In
a
Fiber
Dis-
tributed
Data
Interface
(FDDI)
network,
there
are
a
number
of
types

of
node
configurations,
including
single,
dual,
and
null
attachment
concentrators.
A
null
690
attachment
concentrator
does
not
contain
any
A,
B,
or
S
ports
but
is
configured
with
multiple
M

ports.
The
NAC
may
be
used
in
a
simple
tree
configura-
tion.
It
does
not
support
a
secondary
path
for
redun-
dancy
and
thus
cannot
be
inserted
into
a
dual

ring
network.
See
Fiber Distributed
Data
Interface.
null modem A
serial
transmissions
medium
which
functions
in
many
ways
as
a
modem,
as
it
uses
the
same
software,
protocols,
and
serial transmissions
media,
except
that

there
is
no
modem.
In
other
words,
instead
of
the
signal
going
from
a
computer
to
a
mo-
dem
through
a
phone
line
to
another
modem
and
to
the
destination

computer,
the
signal
goes
from
the
fIrst
computer
through
a
serial
cable
with
no
modem
con-
nected
to
the
second
computer,
and
back
again.
The
transmit
(Tx)
and
receive (Rx) lines
are

swapped
(usually
lines
2
and
3).
This
provides
fast
local
file
transfer capabilities
between
machines.
null modem cable
There
are
many
ways
to
config-
ure
a
modem
cable,
as
long
as
the
two

computers
talk-
ing
to
each
other
are
talking
the
same
language
(trans-
missions
protocol),
but
the
most
common
configu-
ration
for
a
null
modem
cable
is
to
take
a standard
RS-232c

cable
and
cross
(swap)
the
transmit
and
re-
ceive
lines
on
one
end,
that
is,
lines
2
and
3.
Or,
rather
than
taking
apart a
cable,
it
is
usually
easier
to

get a
null
modem
connector
that
swaps
the
lines.
It
looks
very
similar
to
an
extender
or
other
small
coupler.
See
null
modem.
number
portability
NP.
A service
which
enables
subscribers
to

retain
a
geographic
or
nongeographic
telephone
number
when
they
change
their
location,
their
services
provider,
or
their
type
of
service.
This
is
defined
with
regard
to
switching
services
in
the

Telecommunications
Act
of
1996,
and
published
by
the
Federal
Communications
Commission
(FCC),
as:
"

the
ability of
users
of
telecommunications
ser-
vices
to
retain,
at
the
same
location,
existing
tele-

communications
numbers
without
impainnent of
quality,
reliability,
or
convenience
when
switch-
ing
from
one
telecommunications carrier
to
an-
other."
See
Federal
Communications
Commission,
Telecom-
munications
Act
of
1996.
NumberingAdvisoryCommittee
NAC.
This
name

is
used
by
a
number
of
telecommunications
advisory
bodies
worldwide
including
Australia,
Hong
Kong,
Zaire,
and
others.
In
general,
these
committees
pro-
vide
forums
for
the
exchange
of
views
on

number-
ing
issues,
including
assignment,
reassignment,
stor-
age,
access,
and
the
dissemination
of
public
and
gov-
ernmental
infonnation
for
developing
Number
Plans.
Recently,
these
committees
have
given
increased
at-
tention

to
the
allocation
and
availability of
numbers
for
mobile
telecommunications
services.
Numbering
Plan
Area
NPA.
A three-digit geo-
graphic
telephony
area
code.
NP
As
include
special,
reserved,
and
unassigned
numbers.
Within
each
NPA,

there
are
800
possible
NXX
Codes
(also
known
as
central
office
codes).
NPAs
are divided into two
general
categories:
© 2003 by CRC Press LLC
Category Description
Geographic
NPA
The
Numbering
Plan
Area
code
associated
with
a
specific
region.

Service
Access
Code
Nongeographic
NPAs
associated
with
specialized
services
that
may
be
offered
over
multiple
area
codes,
such
as
toll
free
numbers,
900
numbers,
etc.
numeric keypad
Any
compact
block
of

functionally
related
touchtone
telephone,
typewriter,
calculator,
or
computer
input
keys.
The
most
common
type
ofnu-
meric
keypad
is
a
group
of
about
10
to
18
numerical
or
function
keys
arranged

in
a
block.
These
are
usu-
ally
physically
organized
to
facilitate
touch-typing
or,
in
some
cases,
physically
organized
to
slow
down
typ-
ing!
On
early
touchtone
phone
systems,
there
was

no
point
in
entering
numbers
quickly
as
the
switching
on
the
network
could
not
be
accomplished
as
quickly
as
the
numbers
could
be
typed,
so
the
digits
were
re-
versed

to
slow
down
digit
entry.
The
numeric
keypad
on
a
computer
keyboard
typi-
cally consists of
18
keys,
with
the
numerals
zero
through
nine,
and
symbols,
usually
consisting
of
pe-
riod,
plus,

minus,
asterisk
(star),
and
enter
keys.
The
remaining
three
keys
differ
widely
on
various
com-
puter
platfonns,
but
usually
include
symbols
such
as
the
tilde,
slash,
or
pipe
(vertical
bar).

See
keymap,
keypad.
numerical
aperture
NA.
In
a
fiber
lightguide, a
quantitative
description
of
the
lightguiding
capabili-
ties
of
the
"light pipe." If
fibers
were
made
ofjust
one
pure
light-propagating
material
and
were

always
straight
and
perfectly
aligned
with
the
incoming
light
source
(also
assuming
there
is
no
back
reflection
from
the
endface),
the
numerical
aperture
would
probably
be
expressed
in
terms
of

the
diameter
of
the
fiber
fila-
ment.
However,
fiber
optic
cables
may
be
made
from
a
number
of
materials
(e.g.,
glass
or
plastic)
with
dif-
ferent
refractive
indexes
and
are

not
perfectly
straight
nor
necessarily
perfectly
aligned
with
the
source
light.
Cladding
is
laminated
around
the
conducting
core
to
reflect
the
light
back
into
the
filament
and
has
a
dif-

ferent
refractive index
from
the
conducting
core.
Mathematically
expressing
these
different
factors
in
relation
to
one
another
provides
a
numerical
aperture
rating
that
gives
an
idea
of
the
light-guiding
capac-
ity

ofa
fiber
cable
assembly.
See
acceptance
angle.
Numeris, Numeris
The
name
given
to
their
line
of
data telecommunications services by France
Telecom.
Numeris
is
based
upon
Reseau
Numerique
al'integration
de
Service
(RNIS)
standards
to
pro-

vide
its
customers
"
service
that
opens
doors
the
world
over
for
intelligent
telephony,
fast
Internet
ac-
cess,
and
the
efficient
transfer of
information."
Data
rates
on
analog
lines
are
33

Kbps
(56
Kbps
in
some
circumstances).
Access
to
Numeris
can
be
established
through
D
ISDN
(16
Kbps)
or
B
ISDN
(dual
64
Kbps)
channels.
Numeris
Duet
offers
dual
lines
for

simul-
taneous
phoning
and
data
communications
(e.g.,
fac-
simile
or
Internet). Numeris
Commerce
offers D
channel
services
for
ecommerce
applications
such
as
bank
card
transactions.
nutating field
In
radar
tracking,
an
oscillating
feed

from
an
antenna
that
produces
an
oscillating
deflec-
tion
of
the
radar
beam.
Nutt,Emma
N.
Credited
as
the
first
female
telephone
operator.
See
operator,
telephone,
for
additional
in-
formation
and

history.
nuvistor A
type
of
electron
tube
in
a
ceramic
enve-
lope
with
cylindrical,
closely
spaced
electrodes.
nVabbrev.
nanovolt.
NV
See
Network
Video.
nW
abbrev.
nanowatt.
N
x64
A
digital
network

channelized
data
transmis-
sions
system.
As
an
example,
a Tl
line
can
be
split
into
multiple
Nx64k
circuits
for
transmission
across
different
ATM-based
virtual circuits (Ves).
When
implemented through High-bit-rate Digital
Sub-
scriber
Line
(HOSL),
it

enables
a
network
access
pro-
vider
to
provide
data
services
via
two
pairs
of
local
~:~~~::~E~fr~~~ri~!~~iA~:~~£;~~;~~
:.
Nx64 interface A
hardware
network
interface
that
enables
Nx64-compliant
connections
at
speeds
be-
tween
64

and
up
to
about
2048
Kbps,
in
multiples
of
64
Kbps.
This
type
of
interface,
in
conjunction
with
Nx64
data
formats,
is
commercially
promoted
to
pro-
vide
high
bandwidth
access

to
packet-switched
back-
bone
networks
such
as
Frame
Relay,
X.21,
and
X.25.
Thus,
it
is
of
interest,
for
example,
to
businesses
with
Frame
Relay
access
to
the
Internet.
A
number

ofITU-
T V
Series
Recommendations
relate
to
Nx64
stan-
dards
(e.g.,
V.35).
See
Nx64.
NXX
NXX
is
also
known
as
Central
Office
Code,
or
CO
Code.
It
is
an
industry
abbreviation

designating
the
three
digits
ofa
phone
number
preceding
the
last
four
(EXTN).
A
ten-digit
number
is
expressed
with
symbolic
characters
as:
NPA-NXX-EXTN.
NXX
is
a
reference
to
the
exchange
that

services
that
specific
area.
N
refers
to
any
integer
between
2
and
9
and
X
refers
to
any
integer between 0
and
9.
Each
NXX
Code
contains
10,000
station
numbers.
See
North

American
Numbering
Plan,
RNX.
NYNEX
Corporation
One
of
the
Regional Bell
Operating
Companies
(RBOCs)
formed
as
a
result
of
the
mid-1980s
AT&T
divestiture,
Nynex
comprised
several
related
companies,
including
the
New

York
Telephone
company
(NY),
the
New
England
Tele-
phone company (NE), and others
(X)
such
as
NYNEX
Information Resources,
NYNEX
Mobile
Communications,
NYNEX
Business Information
Systems,
and
more.
In
the
early
1990s,
NYNEX
was
developing
interac-

tive
video
network
technology
in
cooperation
with
other vendors. In
1994,
NYNEX
representatives
691
© 2003 by CRC Press LLC