Data Communications
Taught by
Mr. Kim No, Lecturer @RUPP
M.Sc. In Telecommunications Engineering
Chapter 4:
Transmission Media
1
Transmission Media
 Introduction
2
Transmission Media
 Introduction
 Transmission medium: the physical path between transmitter and
receiver.
 Transmission media operates at Physical Layer of the OSI Model.
 The physical layer is responsible for movements of individual bits
from one device to the another.
 Computers and other telecommunication devices use signal to
represent data.
 Repeaters or amplifiers may be used to extend the length of the
medium.
 For the purpose of telecoms, transmission media can be divided into
two categories: Guided (twisted-pair cable, coaxial cable and fiberoptic cable) and Unguided (usually air- electromagnetic waves ).
3
Transmission Media
 Introduction
 Transmission Media Categories
4
Transmission Media
4.1 Guided Media
For guided media, the medium itself is more important in determining
the limitations of transmission.
 Twisted-Pair Cable
 Twisted-pair cable uses metallic (copper) conductors that accept and
transport signals in the form of electric current.
 Twisted pair cables consist of one or more pairs of insulated copper
wires that are twisted together and housed in a protective jacket.
5
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
 Twisted pair cables have connectors at the end, known as RJ
connectors (RJ-45, RJ-11)
6
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
 Twisting:
- Twisting wires reduces the effect of electromagnetic interference (the EM
energy the cable emits) or crosstalk .
 When the wires are twisted, the waves from different twists cancel out, so
the wire radiates (produce heat) less effectively
- More twists = better quality
 It is important to install cable away from sources of interference such as
high-voltage cables and fluorescent lighting. Televisions, computer monitors
and microwaves are other possible sources of interference.
 Crosstalk: Is the leakage of signals between pairs. Crosstalk degrade
network performance and are often caused by untwisting too much cable
when terminating. If high crosstalk values are detected, the best thing to
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do is check the cable terminations and re-terminate as necessary
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
 Application:
 Twisted pairs can be used for transmitting either analog or digital
signals.
- Telephone network (between house and local exchange)
- LAN (10 Mbps or 100 Mbps)
Advantages:
- Easy to work with (Install)
- Less expensive
Disadvantages:
- Low data rate
8
- Short range
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
 Characteristics:
 Analog transmission
- Amplifiers every 5km to 6km
 Digital transmission
- Repeater every 2km or 3km
 TP is Limited
- Distance
- Data rate
 Susceptible to interference and noise
9
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
 Types:
-
Shielded twisted pair (STP): a metallic shield around the wire pairs minimizes the
impact of the penetration of noise or crosstalk.
Unshielded twisted pair (UTP)
Our discussion focuses
primarily on UTP
because STP is seldom
used outside of IBM
10
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
o Shielded Twisted Pair:
Shielded Twisted Pair cables are used almost exclusively (not
including) in European countries-IBM Production.
Note: Foil is a very thin sheet of metal Preventing the penetration of
noise or crosstalk.
11
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
o Shielded Twisted Pair:
Cost:
- STP cable costs more than thin coaxial or unshielded twisted-pair
cable. STP is less costly, however, than thick coax or fiber-optic
cable.
Capacity:
- The most common data rate for STP cable is 16 Mbps, which is the
top data rate for Token Ring networks.
Attenuation:
- All varieties of twisted-pair cable have attenuation characteristics that
limit the length of cable runs to a few hundred meters, although a 100meter limit is most common.
12
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
o Unshielded Twisted Pair:
The Electronic Industries Association-EIA has developed standards to
classify UST cable to 7 categories. Categories are determined by
cable quality, with 1 as the lowest and 7 as the highest. Each EIA
category
suitable forData
specific
Category isBandwidth
Rate uses.Digital/Analog
Use
1
2
very low
<2
MHz
< 100 kbps
Analog
Telephone
2 Mbps
Analog/digital
T-1 lines
3
16 MHz
10 Mbps
Digital
LANs
4
20 MHz
20 Mbps
Digital
LANs
5
100 MHz
100 Mbps
Digital
LANs
6
200 MHz
200 Mbps
Digital
LANs
7
600 MHz
600 Mbps
Digital
LANs
13
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
o Unshielded Twisted Pair:
14
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
o Unshielded Twisted Pair:
15
Transmission Media
4.1 Guided Media
 Twisted-Pair Cable
o Unshielded Twisted Pair:
UTP connector :
The most common UTP connector is RJ45 (RJ=Registered Jack)
16
Transmission Media
4.1 Guided Media
UTP connector :
Color code for 4 cable pairs
Pair #
1
2
3
4
Primary color Secondary color (stripe)
Blue
White
Orange
White
Green
White
Brown
White
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Transmission Media
4.1 Guided Media
UTP connector :
Color code for 4 cable pairs
 EIA organization defines two different patterns, or wiring scheme,
called T568A and T568B.
 The two schemes are similar except two of the four pairs are reversed
in the termination order. The graphic shows this color-coding and how
the two pairs are reversed.
 On a network installation, one of the two wiring schemes (T568A or
T568B) should be chosen and followed.
18
Transmission Media
4.1 Guided Media
UTP connector :
Color code for 4 cable pairs
 Using the T568A and T568B wiring standards, two types of cables
can be created: a straight-through cable and a crossover cable
A straight-through cable:
is the most common cable type. It maps a wire to the same pins on
both ends of the cable. In other words, if T568A is on one end of the
cable, T568A is also on the other. If T568B is on one end of the cable,
T568B is on the other. This means that the order of connections for
each color is the exact same on both ends.
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Transmission Media
4.1 Guided Media
UTP connector :
Color code for 4 cable pairs
Crossover Cable:
A crossover cable uses both wiring schemes. T568A on one end of the
cable and T568B on the other end of the same cable. This means that
the order of connection on one end of the cable does not match the
order of connections on the other.
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Transmission Media
4.1 Guided Media
UTP connector :
Color code for 4 cable pairs
A straight-through cable:
- Connecting between unlike devices
 Unlike Device:
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Transmission Media
4.1 Guided Media
UTP connector :
Color code for 4 cable pairs
A straight-through cable:
- Connecting between unlike devices
 Unlike Device:
The pins on the RJ-45 data connector of a PC have pins1 and 2 as
transmit and pins 3 and 6 as receive. The pins on the data connector of
a switch have pins 1 and 2 as receive and pins 3 and 6 as transmit
Examples of unlike devices that require a straight-through cable
include:
- Switch port to Router port
- Switch port to PC
- Hub port to PC
22
Transmission Media
4.1 Guided Media
UTP connector :
Color code for 4 cable pairs
Crossover Cable:
- Connecting between like devices
 Like Device:
23
Transmission Media
4.1 Guided Media
UTP connector :
Color code for 4 cable pairs
Crossover Cable:
- Connecting between like devices
 Like Device:
24
Transmission Media
4.1 Guided Media
Example of using Straight-through and Crossover Cable
25
Transmission Media
4.1 Guided Media
Application of UTP:
- Used in telephone lines to provide voice and data channels.
- The DSL lines that are used by the telephone companies to provide
high-data-rate connections also use the high-bandwidth capability of
unshielded twisted-pair cables.
- Local-area networks, such as l0Base-T and l00Base-T, also use
twisted-pair cables.
26
Transmission Media
4.1 Guided Media
UTP VS STP
Unshielded Twisted Pair
(UTP)
Used for telephone wire
Cheapest type of cable
Easiest type to be installed
Suffers from external
Electromagnetic (EM)
interference
Shielded Twisted Pair (STP)
Metal braid or covering that
reduces interference
More expensive
Harder to handle (thick,
heavy)
Provide better performance
than UTP
27
Transmission Media
4.1 Guided Media
 Coaxial Cable
 Like twisted pair, coaxial cable (or coax) also carries data in the form
of electrical signals.
 It provides improved shielding compared to UTP, so has a lower
signal-to-noise ratio and can therefore carry more data
 Although coax has improved data carrying characteristics, most local
area networking uses twisted pair because coax is physically harder to
install and is more expensive.
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Transmission Media
4.1 Guided Media
 Coaxial Cable
Categories of coaxial cables
Divided into two basic categories:
 50-ohm cable [baseband]
 75-ohm cable [broadband or single channel baseband]
Radio
Government
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Transmission Media
4.1 Guided Media
 Coaxial Cable
Categories of coaxial cables
 Baseband Coax:
- 50-ohm cable is used exclusively (only for) for digital transmissions
- 10Base5 Thick Ethernet : thick (10 mm) coax
10 Mbps, 500m max segment length, 100 devices/segment, awkward
(difficult) to handle and install.
- 10Base2 Thin Ethernet : thin (5 mm) coax
10 Mbps, 185m max segment length, 30 devices/segment, easier to
handle.
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Transmission Media
4.1 Guided Media
 Coaxial Cable
Categories of coaxial cables
 Baseband Coax:
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Transmission Media
4.1 Guided Media
 Coaxial Cable
Categories of coaxial cables
 Broadband Coax:
- 75-ohm cable (Cable TV system standard).
- Used for both analog and digital signaling.
- For long-distance transmission of analog signals, amplifiers are
needed every few kilometers.
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Transmission Media
4.1 Guided Media
 Coaxial Cable
Coaxial Cable Connectors:
-
To connect coaxial cable to devices, we need coaxial connectors. The most common
type of connector used today is the Bayone-Neill-Concelman (BNC), connector.
Three popular types of these connectors: the BNC connector, the BNC T connector,
and the BNC terminator.
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Chapter 7: Transmission Media
4.1 Guided Media
 Coaxial Cable
Coaxial Cable Connectors:
-
The BNC connector is used to connect the end of the cable to a device, such as
TV set.
The BNC T connector is used in Ethernet networks to branch out to a connection to
a computer or other device.
The BNC terminator is used at the end of the cable to prevent the reflection of the
signal.
34
Transmission Media
4.1 Guided Media

 Coaxial Cable
Coaxial Cable Connectors:
35
Transmission Media
4.1 Guided Media
 Coaxial Cable
Coaxial Performance:
 Higher bandwidth than twisted-pair
 However, attenuation is higher and requires frequent use of repeaters
Coaxial Cable Applications:
-- Television distribution
 Cable TV
-- Long distance telephone transmission
 Can carry 10,000 voice calls simultaneously
 Being replaced by fiber optic
-- Short distance computer systems links
 Local area networks
36
Transmission Media
4.1 Guided Media
 Coaxial Cable
Characteristics:
 Analog
- Amplifier every few Km
 Digital
- Repeater every 1 Km
 Problem
- Thermal noise
(Thermal noise occurs in almost transmission systems due to the
thermal agitation (movement) of electrons in a conductor. This
noise can affect the quality of a system.)
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Transmission Media
4.1 Guided Media
 Fiber Optic Cable
 A fiber-optic cable is made of glass or plastic and transmits signals in
the form of light.
 Light travels in a straight line as long as it is moving through a single
uniform substance.
 If a ray of light traveling through one substance suddenly enters
another substance (of a different density), the ray changes direction.
38
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
 A fiber-optic cable is made of glass or plastic and transmits signals in
the form of light.
 Light travels in a straight line as long as it is moving through a single
uniform substance.
 If a ray of light traveling through one substance suddenly enters
another substance (of a different density), the ray changes direction.
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Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Bending of light ray
- As the figure shows, if the angle of incidence I is less than the critical
angle, the ray refracts and moves closer to the surface.
- If the angle of incidence is equal to the critical angle, the light bends along the
interface.
- If the angle I is greater than the critical angle, the ray reflects (makes a turn)
and travels again in the denser substance.
40
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Bending of light ray
Ex1:
A ray of light passes through from air into the water at a 27 degree
angle. The refractive index for water is: 1.333. The refractive index
for air is: 1.000293. What is the critical angle?
Solution:
θ = arcsin(n2/n1)
θ = arcsin (1.000293/1.333)
θ = arcsin (0.750407352)
θ = 48.625675
θ = 48.6 degrees
In this example, the angle of incidence (27 degrees) is less than the
critical angle (48.6 degrees)  the ray refracts and moves closer 41
to
the surface.
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Optical Fiber  Architecture:
 Core
• Glass or plastic with a higher index of
refraction than the cladding
• Carries the signal
 Cladding
• Glass or plastic with a lower index of
refraction than the core
 Buffer (one type of component made from
plastic)
• Protects the fiber from damage and moisture
 Jacket
• Holds one or more fibers in a cable
42
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Repeaters:
 For long links, repeaters are needed to compensate for signal loss
43
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Propagation Modes:
There are two forms of fiber optic cable: multimode and single mode.
44
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Propagation Modes:
 Multi Mode
 It is referred to as multimode because there are multiple rays of light,
each carrying data, being transmitted through the cable
simultaneously.
 Each ray of light takes a separate path through the multimode core.
Multimode fiber optical cables are generally suitable for links of up to
2000 meters. However, improvements in technology are continually
improving this distance.
Lecturer: Kim45No
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Propagation Modes:
 Multi Mode
 Multimode step-index fiber
 The density of the core remains constant from the center to the edges.
 Light moves through this constant density in a straight line until it reaches
the interface of the core and the cladding.
 Some beams penetrate the cladding and are lost, while others are reflected
down the channel to the destination
 As a result, beams reach the destination at different times and the signal may
not be the same as that which was transmitted
 Step index multimode was developed first, but rare today because it has a
low bandwidth, It has been replaced by graded-index multimode with a
46
higher bandwidth
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Propagation Modes:
 Multi Mode
 Multimode step-index fiber
47
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Propagation Modes:
 Multi Mode
 Multimode graded-index fiber
- Graded-index refers to varying densities of the fiber; highest at
center and decreases at edge
- May be used to decreases this distortion of the signal through the
cable and to allow for more precise (exact) transmissions
- Eliminates problem with some of the signals penetrating the
cladding
- Since the core density decreases with distance from the center,
the light beams refract into a curve
48
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Propagation Modes:
 Multi Mode
 Multimode graded-index fiber
49
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Propagation Modes:
 Single Mode
 Only one beam from a light source is transmitted through the fiber
 The single mode fiber itself is manufactured with a much smaller
diameter than that of multimode fiber, and with lower density (index
of refraction).
 The decrease in density results in a critical angle that is close enough
to 90° to make the propagation of beams almost horizontal.
- Delays are negligible (to slight or small)
 All the beams arrive at the destination "together" and can be
recombined with little distortion to the signal
 Single mode fibers can transmit data for approximately 3000 meters
and improvements in technology are continually improving this
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distance.
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Propagation Modes:
 Single Mode
51
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Propagation Modes:
52
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Light Sources:
Light source is light-emitting diode (LED) or a laser
Single Mode:
- Uses laser as the light source, suitable for long distance applications
Multimode:
- Uses Light Emitting Diode-LED as the light source
-- LEDs are cheaper than lasers
-- Suitable for long distance applications, but shorter than single
mode.
53
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Fiber Sizes:
Optical fibers are defined by the ratio of the diameter of their core to
the diameter of their cladding, both expressed in micrometers
54
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Fiber-Optic Cable Connectors :
There are three types of connectors for fiber-optic cables:
55
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Fiber-Optic Cable Connectors :
There are three types of connectors for fiber-optic cables:
 The subscriber channel (SC) connector is used for cable TV.
 The straight-tip (ST) connector is used for connecting cable to
networking devices.
 Mechanical Transfer Registered Jack (MT-RJ) is a connector
that is the same size as RJ45. MTRJ connectors are designed to
snap into the Ethernet port of a computer, modem, or wireless
router and provide that computer or network with extremely fast
data transfer rates.
56
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Performance:
 Attenuation is lower than in the case of twisted-pair cable and coaxial
cable.
 Need Repeater
Applications:
 Fiber-optic cable is often found in backbone (SONET) networks
because its wide bandwidth is cost-effective. Today, with wavelengthdivision multiplexing (WDM), we can transfer data at a rate of 1600
Gbps.
 Cable TV companies also use optical fiber and
 Local-area networks such as 100Base-FX network (Fast Ethernet) and
1000Base-X also use fiber-optic cable
57
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Advantages and Disadvantages of Optical Fiber:
 Advantages
Fiber-optic cable has several advantages over metallic cable (twistedpair or coaxial).
 Higher bandwidth. Fiber-optic cable can support dramatically higher
bandwidths (and hence data rates) than either twisted-pair or coaxial
cable (Data rates of hundreds of Gbps)
 Less signal attenuation. Fiber-optic transmission distance is significantly
greater than that of other guided media. A signal can run for 50 km
without requiring regeneration. We need repeaters every 5 km for coaxial
or twisted-pair cable.
 Immunity to electromagnetic interference. Electromagnetic noise cannot
58
affect fiber-optic cables.
Transmission Media
4.1 Guided Media
 Fiber Optic Cable
Advantages and Disadvantages of Optical Fiber:
 Disadvantages
There are some disadvantages in the use of optical fiber.
 Installation and maintenance. Fiber-optic cable is a relatively new
technology. Its installation and maintenance require expertise that is
not yet available every where.
 Unidirectional light propagation. Propagation of light is
unidirectional. If we need bidirectional communication, two fibers are
needed.
 Cost is relatively more expensive than those of other guided media.
59
Transmission Media
4.2 Unguided Media
 Unguided media transport electromagnetic waves without using a
physical conductor.
 This type of communication is often referred to as wireless
communication. Signals are normally broadcast through free space
and thus are available to anyone who has a device capable of
receiving them.
Electromagnetic spectrum for wireless communication
The electromagnetic spectrum, ranging from 3 kHz to 900 THz, used
for wireless communication.
60
Transmission Media
4.2 Unguided Media
 Propagation methods
Unguided signals can travel from the source to destination in several
ways: ground propagation, sky propagation, and line-of-sight
propagation.
The ionosphere is a part of the upper
atmosphere, from about 85 km to 600 km
altitude
61
Transmission Media
4.2 Unguided Media
 Propagation methods
In ground propagation:
 Radio waves travel through the lowest portion of the atmosphere,
hugging the earth.
 These low-frequency signals emanate (propagate) in all directions
from the transmitting antenna and follow the curvature of the planet
 Distance depends on the amount of power in the signal: The greater
the power, the greater the distance.
62
Transmission Media
4.2 Unguided Media
 Propagation methods
In sky propagation:
 Higher-frequency radio waves radiate upward into the ionosphere
(the layer of atmosphere where particles exist as ions) and then reflect
back to Earth
 This type of transmission allows for greater distances with lower
output power.
63
Transmission Media
4.2 Unguided Media
 Propagation methods
In line-of- sight propagation:
 Very high-frequency signals are transmitted in straight lines directly from
antenna to antenna. Antennas must be directional, facing each other, and
either tall enough or close enough together not to be affected by the
curvature of the earth.
 The section of the electromagnetic spectrum defined as radio waves and
microwaves is divided into eight ranges (as table below), called bands, each
regulated by government authorities.
 These bands are rated from very low frequency (VLF) to extremely high
frequency (EHF).
64
Transmission Media
4.2 Unguided Media
 Propagation methods
In line-of- sight propagation:
65
Transmission Media
4.2 Unguided Media
 Wireless transmission waves
We can divide wireless transmission into three broad groups: radio
waves, microwaves, and infrared waves.
66
Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Radio wave:
 Electromagnetic waves ranging in frequencies between 3
kHz and 1 GHz are normally called radio waves; waves
ranging in frequencies between 1 and 300 GHz are called
microwaves.
 Radio waves, for the most part, are omni directional. When
an antenna transmits radio waves, they are propagated in all
directions. This means that the sending and receiving
antennas do not have to be aligned (straight line).
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Radio wave:
 Radio waves, particularly those waves that propagate in the sky
mode, can travel long distances. This makes radio waves a good
candidate for long-distance broadcasting such as AM radio.
 Radio waves, particularly those of low and medium frequencies, can
penetrate walls.
 Omni directional Antenna
68
Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Radio wave:
Application:
- Broadcast radio (AM,FM)
- TV
- Cellular phones
Micro waves:
 Electromagnetic waves having frequencies between 1 and 300 GHz
are called microwaves.
 Microwaves are unidirectional. When an antenna transmits
microwave waves, they can be narrowly focused. This means that the
sending and receiving antennas need to be aligned.
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Transmission Media
4.2 Unguided Media
Wireless transmission waves
Micro waves:
 Microwave propagation is line-of-sight the both antennas
that are far apart need to be very tall.
 Very high-frequency microwaves cannot penetrate walls.
This characteristic can be a disadvantage if receivers are
inside buildings.
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Micro waves:
Unidirectional Antenna
Microwaves need unidirectional antennas that send out signals in one
direction. Two types of antennas are used for microwave
communications: the parabolic dish and the horn antennas.
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Micro waves:
72
Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Micro waves:
Microwave Applications
Microwaves, due to their unidirectional properties, are very useful
when unicast (one-to-one) communication is needed between the
sender and the receiver.
-- Cellular phones
-- Satellite networks
-- Wireless LANs
73
Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Infrared:
 Infrared waves, with frequencies from 300 GHz to 400 THz, can be
used for short-range communication in a closed area using line-ofsight propagation.
 Infrared waves, having high frequencies, cannot penetrate walls.
 This advantageous characteristic prevents interference between one
system and another; a short-range communication system in one room
cannot be affected by another system in the next room.

In
 Addition, we cannot use infrared waves outside a building because the
sun's rays contain infrared waves that can interfere with the
communication.
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Infrared:
Applications
 The infrared band, almost 400 THz, has an excellent potential for data
transmission.
 The Infrared Data Association (IrDA), an association for sponsoring
the use of infrared waves, has established standards for using these
signals for communication between devices such as keyboards, mice,
PCs, and printers.
 For example, some manufacturers provide a special port called the IrDA
port that allows a wireless keyboard to communicate with a PC.
 The standard originally defined a data rate of 75 kbps for a distance up to
8 m. The recent standard defines a data rate of 4 Mbps.
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
(Bluetooth:)
 A technology that makes use of the 2.4 GHz band. It is limited to
low-speed, short-range communications.
 It allows one-to-many communications has made Bluetooth
technology the preferred method over IR.
 Bluetooth can transmit through solid, non-metal objects
 Its typical link range is from 10 cm to 10 m, but can be extended to
100 m by increasing the power.
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
What is Satellite?
 The word "satellite" refers to a machine that is launched into space
and moves around Earth or another body in space which play role as a
“relay station”
 Satellite Microwave, Similar to terrestrial microwave except the
signal travels from a ground station on earth to a satellite (Uplink) and
back to another ground station (Downlink).
 Satellite receives on one frequency, amplifies or repeats signal and
transmits on another frequency
 A communication satellite can be thought of as a big microwave
repeater in the sky.
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
How do Satellites Work?
 Two Stations on Earth want to communicate through radio broadcast
but are too far away to use conventional (simple) means.
 The two stations can use a satellite as a relay station for their
communication
 One Earth Station sends a transmission to the satellite. This is called
a Uplink.
 The satellite Transponder converts the signal and sends it down to the
second earth station. This is called a Downlink.
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
Orbits:
The period of Satellite moves round the earth is calculated by Kepler’s
law:
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
Ex2:
Calculate the period of the moon moves around the earth?
Solution:
 The position of the moon above the earth is 384 000Km
 The earth radius is 6 378km

Period=2439090.99s=28.23 days
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Chapter 7: Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
Ex3:
By using Kepler’s law, calculate the period of the satellite which has
height about 35 786Km from the earth ?
Solution:
 The position of the satellite above the earth is 35 786Km
 The earth radius is 6 378km

Period=86579s=24 hours
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
How does Satellite orbit the earth without fall back to Earth ?
 Most satellites are launched into space on rockets. A satellite orbits
Earth when its speed is balanced by the pull of Earth's gravity.
 Without this balance, the satellite would fly in a straight line off into
space or fall back to Earth.
 Satellites orbit Earth at different heights, different speeds and along
different paths.
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
Frequency band of satellite Communication
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
What Are the Parts of a Satellite?
 Satellites come in many shapes and sizes. But most have at least two
parts in common -- an antenna and a power source.
 The antenna sends and receives information, often to and from Earth.
 The power source can be a solar panel, battery. Solar panels make
power by turning sunlight into electricity.
Three Categories of Satellite
Geostationary Orbit Satellites (GEO)
Medium-Earth Orbit Satellites (MEO)
Low-Earth Orbit Satellites (LEO)
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
Three Categories of Satellite
Geostationary Orbit Satellites (GEO):
 Height of 35,786km above the earth
 Propagation is line-of-sight  need sending and receiving antennas
must face to face forever
 The satellites is placed in orbit such that they remain stationary
relative to a fixed spot on earth.
 If a satellite is placed at 35,786 km above the earth, its angular
velocity is equal to that of the earth, thereby causing it to appear to be
over the same point on earth. This allows for them to provide constant
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coverage of the area
Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
Three Categories of Satellite
Geostationary Orbit Satellites (GEO):
 Number of satellites needed for global coverage are three, separate
120 degree from each other.
Lecturer: Kim87No
Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
Three Categories of Satellite
Medium-Earth Orbit Satellites (MEO):
 Height of 5 000km to 15 000Km above the earth, higher than low
earth orbit (LEO) satellites, but lower than geostationary satellites
(GEO).
 Number of satellites needed for global coverage are 10
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
Three Categories of Satellite
Low-Earth Orbit Satellites (LEO):
 Height of 500km to 2 000Km above the earth
 This type of an orbit reduces transmission times as compared to GEO
 A LEO orbit can also be used to cover a polar region
 Number of satellites needed for global coverage are 50
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
The advantages of satellite communication over terrestrial
communication are:
 The coverage area of a satellite greatly exceeds that of a terrestrial
system.
 Higher Bandwidths are available for use
The disadvantages of satellite communication:
 Launching satellites into orbit is costly.
 There is a larger propagation delay (round-trip delay time) in satellite
communication than in terrestrial communication.
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Transmission Media
4.2 Unguided Media
 Wireless transmission waves
Satellite Communication:
Application:
 Television
 Long distance telephone
 Private business networks
Satellites versus fiber cables:
 More suitable for mobile communication
 Better suited for connecting remote areas.
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Transmission Media
4.3 Summary
 A guided medium provides a physical conduit from one device to
another. Twisted-pair cable, coaxial cable, and optical fiber are the
most popular types of guided media.
 Twisted-pair cable is used for voice and data communications.
 Coaxial cable can carry signals of higher frequency ranges than
twisted-pair cable. Coaxial cable is used in cable TV networks and
traditional Ethernet LANs.
 Fiber optic transmission is becoming increasingly popular due to its
noise resistance, low attenuation, and high-bandwidth capabilities.
Fiber-optic cable is used in backbone networks, cable TV networks,
and Fast Ethernet networks.
 Unguided media (free space) transport electromagnetic waves without
the use of a physical conductor.
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Transmission Media
4.3 Summary
 Wireless data are transmitted through ground propagation, sky
propagation, and line of-sight propagation.
 Wireless waves can be classified as radio waves, microwaves, or
infrared waves.
 Radio waves are Omni-directional; microwaves are unidirectional.
 Microwaves are used for cellular phone, satellite, and wireless LAN
communications.
 Infrared waves are used for short-range communications such as
those between a PC and a peripheral device (Keyboard with PC,
mouse with PC).
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