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Slide 1
CHAPTER 3 TRANSMISSION MEDIA ; SIGNAL POWER
Slide 2
Introduction Communications network cannot exist without a
medium to connect the source and the receiver to provide a path
over which messages can be sent. Medium : 1) Physical wire or cable
2) Wireless transmission medium
Slide 3
Guided Media Twisted Pair Wire Coaxial Cable Fiber Optic
Cable
Slide 4
Twisted Pair Wire: 1) Unshielded Twisted Pair (UTP) The cable
has four pairs of wires inside the jacket. Each pair is twisted
with a different number of twists per inch to help eliminate
interference from adjacent pairs and other electrical devices. The
tighter the twisting, the higher the supported transmission rate
and the greater the cost per foot. The EIA/TIA (Electronic Industry
Association/Telecommunication Industry Association) has established
standards of UTP and rated six categories of wire (additional
categories are emerging).
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The standard connector for unshielded twisted pair cabling is
an RJ-45 connector. This is a plastic connector that looks like a
large telephone-style connector A slot allows the RJ-45 to be
inserted only one way. RJ stands for Registered Jack, implying that
the connector follows a standard borrowed from the telephone
industry. This standard designates which wire goes with each pin
inside the connector
Slide 7
Shielded Twisted Pair (STP) Each pair of wires is placed into a
metallic shield Which is a wrapping made of thin wires to absorb
any interference. The wires then are put into a plastic outer
shell. STP typically is used when many wires need to be packed
together in a small space or in an environment with considerable
electrical equipment. STP wires are reliable for transmitting data
in high-interference area.
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Coaxial Cable Coaxial cabling has a single copper conductor at
its centre. A plastic layer provides insulation between the centre
conductor and a braided metal shield Although coaxial cabling is
difficult to install, it is highly resistant to signal
interference. In addition, it can support greater cable lengths
between network devices than twisted pair cable.
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Fiber Optic Cable Fiber optic cabling consists of a center
glass core surrounded by several layers of protective materials. It
transmits light rather than electronic signals eliminating the
problem of electrical interference. This makes it ideal for certain
environments that contain a large amount of electrical
interference
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Fibre optic cable has the ability to transmit signals over much
longer distances than coaxial and twisted pair. It also has the
capability to carry information at vastly greater speeds. This
capacity broadens communication possibilities to include services
such as video conferencing and interactive services.
Slide 15
There are three common types of fibre cables Multimode step
index is an early form of fiber optic cable that uses a plastic
coating or a mirror- like cladding around the core to reflect the
light from the laser and LED.As the light is reflected off the
sides of the cables, it moves down the cable to its destination.
Multimode graded index- the core of the varies in density, which
bends the light. Single mode can provide more distance, but it is
more expensive.
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Unguided Media Type of unguided Media :Air,Vacuum of space
Forms of transmission that use unguided media : broadcast radio,
terrestrial and satellite microwave transmission, cellular radio,
spread spectrum radio, and infrared transmission.
Slide 18
Wireless (Unguided Media) Transmission transmission and
reception are achieved by means of an antenna directional
transmitting antenna puts out focused beam transmitter and receiver
must be aligned omnidirectional signal spreads out in all
directions can be received by many antennas
Slide 19
Wireless Examples terrestrial microwave satellite microwave
broadcast radio infrared
Slide 20
Terrestrial Microwave A system, method, technology, or service,
such as Multichannel Multipoint Distribution Service, which
utilizes microwave line of sight communications between sending and
receiving units located on the ground or on towers, as opposed to a
sender and/or receiver antenna being located on a communications
satellite. Used, for instance, for telephone, TV, and/or data
services. Also called Terrestrial Microwave radio. uses radio
frequency spectrum, from 2 to 40 Ghz parabolic dish transmitter,
mounted high used by common carriers as well as private networks
requires unobstructed line of sight between source and receiver
curvature of the earth requires stations (repeaters) ~30 miles
apart
Slide 21
Satellite Microwave Transmission Microwave transmission refers
to the technology of transmitting information or energy by the use
of radio waves whose wavelengths are conveniently measured in small
numbers of centimeter; these are called microwaves. a microwave
relay station in space can relay signals over long distances
geostationary satellites remain above the equator at a height of
22,300 miles (geosynchronous orbit) travel around the earth in
exactly the time the earth takes to rotate
Slide 22
Satellite Microwave Applications Television distribution
Long-distance telephone transmission Private business networks
Slide 23
Microwave Transmission Disadvantages line of sight requirement
expensive towers and repeaters subject to interference such as
passing airplanes and rain
Slide 24
Satellite Transmission Links In satellite communication, signal
transferring between the sender and receiver is done with the help
of satellite. In this process, the signal which is basically a beam
of modulated microwaves is sent towards the satellite. Then the
satellite amplifies the signal and sent it back to the receivers
antenna present on the earths surface. So, all the signal
transferring is happening in space. Thus this type of communication
is known as space communication.
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dish uplink stationdownlink station satellite transponder
22,300 miles Satellite Transmission Process
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Satellite Transmission Applications television distribution a
network provides programming from a central location direct
broadcast satellite (DBS) long-distance telephone transmission
high-usage international trunks private business networks
Slide 27
Principal Satellite Transmission Bands C band: 4(downlink) -
6(uplink) GHz the first to be designated Ku band: 12(downlink)
-14(uplink) GHz rain interference is the major problem Ka band:
19(downlink) - 29(uplink) GHz equipment needed to use the band is
still very expensive
Slide 28
Fiber vs Satellite
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Radio radio is omnidirectional and microwave is directional
Radio is a general term often used to encompass frequencies in the
range 3 kHz to 300 GHz. Mobile telephony occupies several frequency
bands just under 1 GHz.
Slide 30
Infrared Infrared (IR) light is electromagnetic radiation with
longer wavelengths than those of visible light, extending from the
nominal red edge of the visible spectrum at 0.74 micrometers (m) to
0.3 mm. Uses transmitters/receivers (transceivers) that modulate
noncoherent infrared light. Transceivers must be within line of
sight of each other (directly or via reflection ). Unlike
microwaves, infrared does not penetrate walls.
Slide 31
Attenuation It is the gradual loss in intensity of any kind of
flux through a medium. For instance, sunlight is attenuated by dark
glasses, X-rays are attenuated by lead, and light and sound are
attenuated by water In electrical engineering and
telecommunications, attenuation affects the propagation of waves
and signals in electrical circuits, in optical fibers, as well as
in air (radio waves)
Slide 32
Attenuation (Cont.) Reduction of signal strength during
transmission. Attenuation is the opposite of amplification, and is
normal when a signal is sent from one point to another. If the
signal attenuates too much, it becomes unintelligible, which is why
most networks require repeaters at regular intervals. Attenuation
is measured in decibels