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Chapter 7
Transmission MediaSignals (that represent data) are transmitted from
one device to another in the form of electromagnetic
energy
Electromagnetic signals travel through transmission
media (metal cables, air/space, fiber-optic, etc).
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Guided Media
cables that provide a conduit from one device
to another.
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Guided Media
Twisted-air !able two conductors each surrounded by an insulator
the most common type of telecommunicationmedium in use.
e.g. telephone system
suitable for voice and
data color-banded for
identification
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Guided Media
Twisted-air !able " effect of noise if on parallel line
the wire closest to the source of noise gets more
interference (high voltage level) " uneven load anddamaged signals
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Guided Media
Twisted-air !able " noise on twisted-pair line
twisted wires at regular intervals (#-$# twists/foot),
the cumulative effect of the interference is e%ual onboth wires
significantly reduce
the impact of noise
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Guided Media
&nshielded Twisted-air (&T) !able cheap, fle'ible, easy to install
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Guided Media
&nshielded Twisted-air (&T) !able E categories of &T !ables
Cat. 1 " used in old telephone system, fine for voice andlow-speed data transmission.
Cat. 2 " suitable for voice, data transmission up to * +bps.
Cat. 3 " now standard cable for most telephone systems,
data transmission up to $ +bps.
Cat. 4 " data transmission up to $ +bps. Cat. 5 " data transmission up to $ +bps.
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Guided Media
&T !able !onnectors snap-in plug lie telephone acs
male (plug), female (receptacle)
popular, 01*2
(* twisted pairs "
3 conductors)
01$$
(# pairs "* conductors)
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Guided Media
Shielded Twisted-air (ST) !able has a metal foil or braided mesh covering each pair of
insulated conductors
prevents penetration of electromagnetic noise and crosstal
(undesired effect of one circuit on another circuit).
more e'pensive
than &T but
less susceptible
to noise
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Guided Media
!oa'ial (!oa') !able has a central core conductor of solid or stranded wire
(copper) enclosed in an insulating sheath, which is in turn,
encased in an outer conductor of metal foil,
braid or combination.
The outer conductor
serves as a shield
against noise and thesecond conductor.
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Guided Media
!oa' !able 0adio 4overnment (04) ratings for coa' cables
04-3, 04-5, 04$$ " used in thic Ethernet 04-23 " used in thin Ethernet
04-25 " used for T6
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Guided Media
!oa' !able !onnectors 78! (bayonet networ connector) " pushes on
and loc into place with a half turn the most popular
T-connectors " allow cables to branch from a main
line used in thin Ethernet
Terminators " re%uired for bus topologies to
absorb the wave at the end and eliminate echo-
bac.
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Guided Media
9iber-optic !able made of glass or plastic and transmits signals in the form of
light.
nformation is encoded onto a beam of light as a series of
on-off flashes that represent $ and bits.
ropagation modes multimode
single mode
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Guided Media
9iber-optic !able " +ultimode Step-nde' multiple beams from a light source move through the core in
different path.
the density of the core remains constant from the center to
the edges.
some beams in the
middle travel in
straight lines through
the core and reach
the destination.
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Guided Media
9iber-optic !able " +ultimode Step-nde' (cont) some beams strie the interface of the core bouncing bac and
forth until they reach destination.
as these different beams are recombined at the receiver, they
result in a signal that is no longer an e'act replica of the signal
that was transmitted.
The distortion limits the
available data rate.
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Guided Media
9iber-optic !able " +ultimode 4raded-nde' multiple beams from a light source move through the core in
different path.
variable core density " density is highest at the center and
decrease gradually to its lowest at the edge.
a series of constantly
changing density
causes each beam
to refract into a curve
the reconstructed
signal allows
greater precision.
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Guided Media
9iber-optic !able " Single +ode a highly focused source of light that limits beams close to
hori:ontal
smaller diameter than multimode fibers
all beams arrive
;together< and can
be recombined
;without< distortion
to the signal
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Guided Media
9iber-optic !able " si:es
= single mode
Fiber Type Core (microns) Cladding (microns)
#.2/$#2
2/$#2
$/$*
3.>/$#2 =
#.2
2.
$.
3.>
$#2
$#2
$*
$#2
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Guided Media
9iber-optic !able " !able !onstruction fiber " made of either glass or plastic of different densities,
ultrapure (material, si:e, shape).
buffer " protects from moisture.
outer acet " teflon coating, plastic coating, fibrous plastic,
etc, choice depends on
where the cable is to be
installed
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Guided Media
9iber-optic !able " ?ight Sources ?E@ (light emitting diode)
cheaper, unfocused light, short distance use
?@ (inection laser diode) focused, preserve signal over considerable distance
9iber-optic !able " !onnectors precise and easy to use
(popular) barrel shape in male and female versions
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Guided Media
dvantages of Aptical 9iber noise resistance
less signal attenuation (loss of energy) " can run miles
without re%uiring regenaration
higher bandwidth (and data rates)
@isadvantages of Aptical 9iber cost
installation/maintenance
fragility " glass fiber is easily broen
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Unguided Media
wireless communication " transport electromagneticwave without using physical conductorB e.g. air.
0adiocommunication
bands
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Unguided Media
Types of ropagation
tmosphereC troposphere " about
> miles from earth
surface, air
ionosphere " above
troposphere
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Unguided Media
Types of ropagation " Surface radio waves travel through the lowest portion of the
atmosphere
signals emanate in all directions follow the curvature of the
planet
6?9 (very low fre%uency) wave " do not suffer
much attenuation in transmission but susceptible
to the high levels of atmospheric noiseB used
mostly for long-range radio and submarinecommunication
?9 (low fre%uency) wave " similar to 6?9B
attenuation is greater during daytime
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Unguided Media
Types of ropagation " Tropospheric signal can be directed in a straight line from antenna to
antenna (line-of-sight) re%uires placement of the receiver and the transmitter within
line of sight distance
also signal can be broadcast at an angle into
the upper layers of troposphere where it is
reflected bac to earth greater distance covered
+9 (middle fre%uency) transmissionB
for + radio, etc.
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Unguided Media
Types of ropagation " onospheric waves radiate upward into ionosphere where there are
reflected bac to the earth
even greater distance than tropospheric propagation with
lower power output
D9 (high fre%uency) transmissionB
for aircraft comm., military comm.,
telephone
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Unguided Media
Types of ropagation " ?ine-of-sight signals are transmitted in straight line directly from antenna
to antenna
6D9 (very high fre%uency)B for 6D9 television, 9+ radio, etc.
&D9 (ultra high fre%uency)B &D9 television,
mobile telephone, paging, etc.
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Unguided Media
Types of ropagation " Space utili:e satellite relays
a broadcast signal is received by an orbiting satellite, which
rebroadcasts the signal to the intended receiver bac on
earth
the satellite is lie super-high-gain antenna and dramatically
increases the distance covered
SD9 (super high fre%uency)
ED9 (e'tremely high fre%uency)B
predominantly for scientific, radar,
satellite, e'perimental comm.
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Satellite Communication
satellite acting acting as a supertall antenna and repeater
+alaysian +EST
http://www.measat.com/http://www.measat.com/
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Satellite Communication
4eosynchronous Satellites it taes a minimum of three satellites e%uidistant to provide
full global transmission
remain fi'ed above a
certain spot
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Satellite Communication
9re%uency bands for satellite communications uplin " transmission from the earth to the satellite
downlin " transmission from the satellite to the earth
+EST Technical Specifications
Band Downlink Uplink
!
u
a
>.F to *.# 4D:
$$.F to $#.# 4D:
$F.F to #$ 4D:
2.5#2 to .*#2 4D:
$* to $*.2 4D:
#F.2 to >$ 4D:
http://www.measat.com/html/system.htmlhttp://www.measat.com/html/system.html
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Cellular Telephony
the service provider must
be able to locate and trac
the caller, assign a channel
to the call, and transfer the
signal from channel to
channel as the caller
moves out of the range of
one channel into the range
of another
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Transmission
ImpairmentThe imperfection of transmission medium cause
impairment in the signal what is sent is not what is received
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Transmission
Impairment ttenuation loss of energy during transmission due to
resistance of the medium.
amplifiers are used to compensate the lost.
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Transmission
Impairment@istortion signal changes its form or shape.
occurs in a composite signal which made ofdifferent fre%uencies.
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Transmission
Impairment8oise thermal noise (random motion of electrons creates an
e'tra signal), induced noise (comes from outside
source), crosstal (effect on one wire on the other )
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Performance
Transmission media performance can be
measured
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Performance
Throughput the time - how fast data can pass through a point
bits per second
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Performance
ropagation Speed the distance " how far a signal (or a bit) can travel
through a medium e.g. light in a vacuum G twisted pair H > ' $3 m/s
coa'ial G fiber optic H # ' $3 m/s
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Performance
ropagation Time time re%uired for a signal (or a bit) to travel from
one point of the transmission medium to another ropagation time H @istance/ropagation speed
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Wavelength
The distance a simple signal can travel in one period wavelength H propagation speed ' period
H propagation speed ' ($ / fre%uency)
H propagation speed / fre%uency
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Media Comparison
+edium !ost Speed ttenuation E+ Security
&T
ST!oa'
Aptical fiber
0adio
+icrowave
Satellite
!ellular
?ow
+oderate+oderate
Digh
+oderate
Digh
Digh
Digh
$-$ +bps
$-$2 +bps$ +bps " $4bps
$ +bps " # 4bps
$-$ +bps
$ +bps " $ 4bps
$ +bps " $ 4bps
5.-$5.# bps
Digh
Digh+oderate
?ow
?ow-Digh
6ariable
6ariable
?ow
Digh
+oderate+oderate
?ow
Digh
Digh
Digh
+oderate
?ow
?ow?ow
Digh
?ow
+oderate
+oderate
?ow