Slide 1
TRANSMISSION MEDIA &
ITS CLASSIFICATION
TRANSMISSION MEDIA
Means through which data is transmitted from one place to
another .
Transmission medium is the cable or air over which data can
travel from sender to receiver.
In the OSI Model, transmission media are located below the
physical layer.
TRANSMISSION
MEDIA
GUIDED
MEDIA
UNGUIDED
MEDIA
TWISTED-
PAIR CABLE
CO-AXIAL
CABLE
FIBEROPTIC
CABLE
CLASSIFICATION OF TRANSMISSION MEDIA
MICROWAVES
INFRARED
RADIOWAVES
GUIDED TRANSMISSION MEDIA
It is the transmission media in which signals are confined to a
specific path using wire or cable.
Also known as Wired or Bounded media.
Examples of wired media are:
copper pair wires, co-axial cables and fiber optic cables.
UNGUIDED TRANSMISSION MEDIA
It transports electromagnetic waves without using a physical
conductor.
Instead signals are broadcast through air.
Also known as Wireless media.
Examples of wireless media are:
Radio and Infrared light.
S
There are three type of guided media :
Co-axial cable.
Twisted pair cable.
3. Optical fiber cable.
GUIDED TRANSMISSION MEDIA
CO-AXIAL CABLE
trc
It contains two conductors that are parallel to each other.
It provides better shielding than Twisted pairs.
It can span longer distances at higher speeds.
Inner conductor is a solid metal
wire(copper) as the core enclosed
in insulating dielectric medium.
The insulator is encased by a
cylindrical conductor(mesh).
The tough jacket forms the cover of
the cable.
Fig. Co-axial cable
TWISTED PAIR CABLES
The least expensive & most widely used medium is twisted
pair.
It consists of two insulated copper wires.
The wires are twisted together in a helical form , just like a
DNA molecule.
Twisted pair comes in two forms:
Unshielded twisted pair.
Shielded twisted pair.
Twisting helps to reduce the interference(noise) &
crosstalk.
TYPES OF TWISTED PAIR
UTP(Unshielded twisted pair):
UTP is a ordinary telephone wire.
Very cheap & easy to install.
They are badly affected by the
noise interference.
STP(Shielded twisted pair):
It has a metal foil or braided mesh
to cover each pair of insulating
conductors(shield).
It reduces the interference of the
noise but makes the cable bulky &
expensive.
OPTICAL FIBER CABLE
An optical transmission has
three main components:
The light source
The transmission medium
The detector.
It consists of an inner glass core surrounded by a glass
cladding.
Consists of three concentric sections
Fig: Optical fibre cable
LIGHT SOURCES FOR FIBER
For data transmission to take place, the transmitter must be
capable of inducing data 0 to 1 into the light source.
At the receiver, a photodiode is used to translate light back
into data bits.
2 light sources are widely used:
LED(Light Emitting Diode).
Injection Laser Diode(ILD).
FIG: LIGHT SOURCES FOR OPTICAL FIBER
WORKING PRINCIPLE
Light enters into the fiber gets reflected within the fiber.
Most of it propagates along the length of the fiber & comes
out from the far end.
A small portion of it escapes
through the side walls.
The light stays inside the fiber & does not escape through
the walls because of the total internal reflection.
FIG: WORKING PRINCIPLE OF OPTICAL FIBRE CABLE
OBSERVATIONS
Two important observations:
When the angle of incidence is greater than the critical angle,
light will be reflected within core totally.
If the incident light makes an angle less than the critical
angle then it gets refracted. The refracted ray enters into the
cladding & gets lost.
FIG: INTERNAL REFRACTION OF INCIDENT LIGHT
No physical connection (cables or wires) required
Cables are dependent on terrain unlike wireless transmission
PRINCIPLE:
Moving electron produces EM waves and can propagate through free
space
By attaching antenna, EM waves can be broadcast
WIRELESS /UNGUIDED TRANSMISSION
ELECTROMAGNETIC SPECTRUM
Radio , microwave ,visible light portion can
be used for transmission
of information
Radio communication is divided into eight ranges, called
bands,
each regulated by
government authorities.
FIG: ELECTROMAGNETIC SPECTRUM
BANDS
BandRangePropagationApplicationVLF330 KHzGroundLong-range radio
navigationLF30300 KHzGroundRadio beacons andnavigational
locatorsMF300 KHz3 MHzSkyAM radioHF 330 MHzSkyCitizens band
(CB),ship/aircraft communicationVHF 30300 MHzSky
andline-of-sightVHF TV, FM radioUHF 300 MHz3 GHzLine-of-sightUHF
TV, cellular phones, paging, satelliteSHF 330
GHzLine-of-sightSatellite communicationEHF30300
GHzLine-of-sightLong-range radio navigation
Radio Waves :
Easy to generate
Travel long distances
Penetrate buildings easily
Radio waves are omnidirectional so no need to align source and
destination physically
At low frequencies,radio waves penetrate
At high frequencies, radio waves bounce off obstacles
RADIO TRANSMISSION
Before use of fibre optics , microwaves were used for long
distance
telephonic transmission system
Adavantage of microwaves over fibre optics is that they are
realatively inexpensive
Do not penetrate walls
They have another use, namely, Industrial/Scientific/Medical
band
These bands do not require govt. Licensing
These bands are used for cordless telephones, garage door
systems,security gates,etc.
MICROWAVE TRANSMISSION
Used for short range communication
Directional,cheap and easy to build
Do not pass through solid objects that is why used in lans
Remote controls for TVs, VCRs use infrared transmission
INFRARED TRANSMISSION
Unguided optical signalling used for this transmission
LANs in two buildings can be connected via laser mounted On
rooftop
It is unidirectional
Offers high bandwidth and low cost
Easy to install and no licensing is required
Disadvantage is that cannot penetrate through rain or thick
fog
LIGHTWAVE TRANSMISSION
