Data Transmission Media

Data Transmission Media
Transmission media is a pathway that carries the information from sender to
receiver. We use different types of cables or waves to transmit data. Data is
transmitted normally through electrical or electromagnetic signals.
Types of Transmission Media
Transmission media is broadly classified into two groups.
Wired or Guided Media or Bound Transmission Media : Bound transmission
media are the cables that are tangible or have physical existence and are limited by
the physical geography. Popular bound transmission media in use are twisted pair
cable, co-axial cable and fiber optical cable. Each of them has its own characteristics
like transmission speed, effect of noise, physical appearance, cost etc.
Wireless or Unguided Media or Unbound Transmission Media : Unbound
transmission media are the ways of transmitting data without using any cables. These
media are not bounded by physical geography. This type of transmission is called
Wireless communication. Nowadays wireless communication is becoming popular.
Wireless LANs are being installed in office and college campuses. Radio,
microwave, and satellite transmissions fall into this category.
Transmission Media
Wired/ Guided/ Bound Wireless/ Unguided/ Unbound
Twisted
Pair
Coaxial
Fiber
Optic
Radio
wave
Microwave Satellite
The data transmission capabilities of various Medias vary differently
depending upon the various factors. These factors are:
1. Bandwidth. It refers to the data carrying capacity of a channel or medium. Higher
bandwidth communication channels support higher data rates.
2. Radiation. It refers to the leakage of signal from the medium due to undesirable
electrical characteristics of the medium.
3. Noise Absorption. It refers to the susceptibility of the media to external electrical
noise that can cause distortion of data signal.

4. Attenuation. It refers to loss of energy as signal propagates outwards. The amount
of energy lost depends on frequency.
Now let’s discuss both the guided and the unguided data transmission media.
Twisted Pair
 A twisted pair cable consists of four pairs of copper wires coated with an
insulating material like plastic or Teflon, twisted together.
 Twisted pair cabling is often used in data networks for short and medium
length connections because of its relatively lower costs compared to optical
fiber and coaxial cable.
 Twisted pair is of two kinds—Shielded Twisted Pair (STP), and Unshielded
Twisted Pair (UTP).
 STP cable has an extra layer of metal foil between the twisted pair of copper
wires and the outer covering. The metal foil covering provides additional
protection from external disturbances.
 UTP is the most commonly used medium for transmission over short distances
up to 100m.
Figure 1: Twisted Pair Cable
Figure 2: Cross section of (a) UTP (b) STP

Coaxial Cable
A coaxial cable is a type of shielded and insulated copper cable that is used in
computer networks and to deliver cable TV services to end users. Coaxial cable is
also known as coax.
It consists of four primary components, as follows:
[1] A core copper wire, which serves as the primary channel
[2] A dielectric plastic insulator, which surrounds the copper
[3] A braided copper/aluminum sheath beneath the insulator. This is used to
protect from external electromagnetic interference.
[4] The last layer, which is made of Teflon or plastic coating, is used to protect
the inner layers from physical damage, such as fire and water.
Figure 3: Coaxial cable (A: outer plastic sheath, B: woven copper shield, C: inner
dielectric insulator, D: copper core)
Optical Fiber
 Optical fibers are being used for transmission of information over large
distances more cost effectively than the copper wire connection.
 Optical fiber transmits data as light signals instead of electric signals.
 An optical fiber cable consists of(1) core–optical fiber conductor (glass) that
transmits light, (2) cladding–an optical material that surrounds the core to
prevent any light from escaping the core, and (3) jacket—outer covering made
of plastic to protect the fiber from damage.

Figure 4: (a) Optical fiber (b) Cross section of optical fiber
The Advantages of Optical Fibers over wires are:
 Optical fibers do not cause electrical interference in other cables, since they
use light signals.
 Due to much lower attenuation and interference, optical fiber has large
advantages over existing copper wire in long-distance and high-demand
applications.
 A fiber can carry a pulse of light much farther than a copper wire carrying a
signal.
 Optical fiber can carry more information than a wire (light can encode more
information than electrical signal).
 A single optical fiber is required for light to travel from one computer to
another (two wires are required for electric connection).
 They are highly secure as they cannot be tapped and for lack of signal
radiation.
The Disadvantages of Optical Fiber are:
 Installing an optical fiber requires special equipment.
 If a fiber breaks, finding the broken location is difficult.
 Repairing a broken optical fiber is difficult and requires special equipment.

Radio Transmission
The electromagnetic radio waves that operate at the radio frequency are also used to
transmit computer data. This transmission is also known as Radio Frequency RF)
transmission. The computers using RF transmission do not require a direct physical
connection like wires or cable. Each computer attaches to an antenna that can both
send and receive radio transmission.
Figure 5: Radio transmission
Microwave Transmission
Microwave transmission refers to the technique of transmitting information over a
microwave link. Microwaves have a higher frequency than radio waves. Microwave
transmission can be aimed at a single direction, instead of broadcasting in all
directions (like in radio waves). Microwaves can carry more information than radio
waves but cannot penetrate metals. Microwaves are used where there is a clear path
between the transmitter and the receiver.

Figure 6: Microwave transmission
Satellite Transmission
A satellite is an object that revolves around another object. For example, earth is a
satellite of The Sun, and moon is a satellite of earth.
The communication across longer distances can be provided by combining radio
frequency transmission with satellites. Geosynchronous satellites are placed in an
orbit synchronized with the rotation of the earth at a distance of 36,000 km above
the surface of the earth. Geosynchronous satellites appear to be stationary when
viewed from the earth. The satellite consists of transponder that can receive RF
signals and transmit them back to the ground at a different angle. A ground station
on one side of the ocean transmits signal to the satellite which in turn sends the signal
to the ground station on the other side of the ocean.
Figure 7: Satellite transmission

Transmission Modes
The direction in which data can be transmitted between any two linked devices is of
three types—(1) Simplex, (2) Half-duplex, and (3) Full-duplex, or duplex.
SIMPLEX Mode
In this type of transmission mode, data can be sent only in one direction i.e.
communication is unidirectional. We cannot send a message back to the sender.
Unidirectional communication is done in Simplex Systems where we just need to
send a command/signal, and do not expect any response back.
Examples of simplex Mode are loudspeakers, television broadcasting, television and
remote, keyboard and monitor etc.
HALF DUPLEX Mode
Half-duplex data transmission means that data can be transmitted in both directions
on a signal carrier, but not at the same time.
Example of half duplex is a walkie- talkie in which message is sent one at a time but
messages are sent in both the directions.
FULL DUPLEX Mode
In full duplex system we can send data in both the directions as it is bidirectional at
the same time in other words, data can be sent in both directions simultaneously.
Example of Full Duplex is a Telephone Network in which there is communication
between two persons by a telephone line, using which both can talk and listen at the
same time.

In full duplex system there can be two lines one for sending the data and the other
for receiving data.

Data Transmission Media

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Data Transmission Media