Transmission Media

Transmission media is a communication channel that carries the information from the sender to the receiver. Data is transmitted through the electromagnetic signals.

​

The main functionality of the transmission media is to carry the information in the form of bits through LAN(Local Area Network).

​

It is a physical path between transmitter and receiver in data communication.

Transmission Media Types

Transmission Media is broadly classified into two groups:

1.Guided Media/Wired

2.Unguided Media/Wireless

1.Guided Media

It is also referred to as Wired or Bounded transmission media. Signals being transmitted are directed and confined in a narrow pathway by using physical links.

Features:

High Speed

Secure

Used for comparatively shorter distances

Guided Media Types

Guided Media is three types :

1) Twisted Pair

2) Coaxial Cable

3) Optical Fiber

1) Twisted pair

It consists of 2 separately insulated conductor wires wound about each other. Generally, several such pairs are bundled together in a protective sheath. They are the most widely used Transmission Media.

Twisted pair Types

The twisted pair has two types:

​

1]Unshielded Twisted pair

2] Shielded Twisted pair

1] Unshielded Twisted pair

UTP consists of two insulated copper wires twisted around one another. This type of cable has the ability to block interference and does not depend on a physical shield for this purpose. It is used for telephonic applications.

Unshielded Twisted pair Advantages and Disadvantages

Advantages:

⇢ Easy to install

⇢ High-speed capacity

​

Disadvantages:

⇢ Susceptible to external interference

⇢ Lower capacity and performance in comparison to STP

⇢ Short distance transmission due to attenuation

2]Shielded Twisted pair

​

This type of cable consists of a special jacket (a copper braid covering or a foil shield) to block external interference. It is used in fast-data-rate Ethernet and in voice and data channels of telephone lines.

​

Shielded Twisted pair Advantages

​

• Better performance at a higher data rate in comparison to UTP
• Eliminates crosstalk
• Comparatively faster

Shielded Twisted pair Disadvantages

​

•Comparatively difficult to install and manufacture

•More expensive

• Bulky

2) Coaxial Cable

Coaxial cable is very commonly used transmission media, for example, TV wire is usually a coaxial cable.

The name of the cable is coaxial as it contains two conductors parallel to each other.

It has a higher frequency as compared to Twisted pair cable.

Coaxial Cable Advantages and Disadvantages

Advantages :

​

• It has better shielding as compared to twisted pair cable.
• It provides higher bandwidth.

​

• Disadvantages:

​

• It is more expensive as compared to twisted pair cable.
• If any fault occurs in the cable causes the failure in the entire network.

Coaxial cable Types:

• Baseband transmission: It is defined as the process of transmitting a single signal at high speed.

​

• Broadband transmission: It is defined as the process of transmitting multiple signals simultaneously.

3) Optical Fiber

An Optical Fiber is a cylindrical fiber of glass which is hair thin size or any transparent dielectric medium. The fiber which is used for optical communication is waveguides made of transparent dielectrics.

Optical Fiber Types:

• Generally optical fiber is classified into two categories based on: the number of modes, and the refractive index. These are explained as following below.
• 1)On the basis of the Number of Modes:
• It is classified into 2 types:
• a) Single Mode
• b) Multimode

a) Single Mode

• In single-mode fiber, only one type of ray of light can propagate through the fiber. This type of fiber has a small core diameter (5um) and high cladding diameter (70um) and the difference between the refractive index of core and cladding is very small.

b) Multimode Fiber

Multimode fiber allows a large number of modes for the light ray traveling through it. The core diameter is generally (40um) and that of cladding is (70um).

The relative refractive index difference is also greater than single mode fiber.

There is signal degradation due to multimode dispersion. It is not suitable for long-distance communication due to large dispersion and attenuation of the signal.

​

2. On the basis of Refractive Index:

​

(a) Step-index optical fiber

(b) Graded index optical fiber

(a) Step-index optical Fiber

​

• The refractive index of core is constant. The refractive index of the cladding is also constant. The rays of light propagate through it in the form of meridional rays which cross the fiber axis during every reflection at the core-cladding boundary

(b) Graded index optical fiber

​

• In this type of fiber, the core has a non-uniform refractive index that gradually decreases from the center towards the core-cladding interface. The cladding has a uniform refractive index. The light rays propagate through it in the form of skew rays or helical rays. it is not cross the fiber axis at any time.

2) Unguided Transmission Media

• An unguided transmission transmits the electromagnetic waves without using any physical medium. Therefore it is also known as wireless transmission.
• In unguided media, air is the media through which the electromagnetic energy can flow easily.

Unguided Transmission Media

• Unguided transmission is broadly classified into three categories:
• 1.Radiowaves
• 2.Microwaves
• 3.Infrared

1.Radiowaves

• Radio waves are the electromagnetic waves that are transmitted in all the directions of free space.
• Radio waves are omnidirectional, i.e., the signals are propagated in all the directions.
• The range in frequencies of radio waves is from 3Khz to 1 khz.

Radiowaves Advantages

• Radio transmission is mainly used for wide area networks and mobile cellular phones.
• Radio waves cover a large area, and they can penetrate the walls.
• Radio transmission provides a higher transmission rate.

2.Microwaves

Microwaves are electromagnetic waves having frequencies between 1GHz and 300GHz.

Microwave radio, a form of radio transmission that use. Ultra-high frequencies developed out of experiments with radar (radio detecting and ranging) during the period preceding World War II.

1) Terrestial Microwave

• Terrestrial Microwave transmission is a technology that transmits the focused beam of a radio signal from one ground-based microwave transmission antenna to another.
• Microwaves are the electromagnetic waves having the frequency in the range from 1GHz to 1000 GHz.

2) Satellite Microwave

•A Satellite is a physical object that revolves around the earth at a known height.

• Satellite communication is more reliable nowadays as it offers more flexibility than cable and fibre optic systems.
• We can communicate with any point on the globe by using satellite communication.
• Satellite transmission consists of a line-of-sight propagation path from a ground station to a communications satellite (up link) and back to an earth station (down link).
• The satellite is usually placed in a geosynchronous orbit about 22,300 miles above the earth so that it appears stationary from any point from which it is visible and acts like a repeater in the sky.
• The ground station includes the antennas, buildings, and electronics necessary to transmit, receive, multiplex, and demultiplex signals

Satellite Microwave Advantages

• The coverage area of a satellite microwave is more than the terrestrial microwave.
• The transmission cost of the satellite is independent of the distance from the centre of the coverage area.
• It is easy to install.

Satellite Microwave Disadvantages

• Satellite designing and development requires more time and higher cost.
• The Satellite needs to be monitored and controlled on regular periods so that it remains in orbit.

3.Infrared

• An infrared transmission is a wireless technology used for communication over short ranges.
• The frequency of the infrared in the range from 300 GHz to 400 THz.
• It is used for short-range communication such as data transfer between two cell phones, TV remote operation, data transfer between a computer and cell phone resides in the same closed area.

Characteristics Of Infrared

• It supports high bandwidth, and hence the data rate will be very high.
• Infrared waves cannot penetrate the walls. Therefore, the infrared communication in one room cannot be interrupted by the nearby rooms.
• An infrared communication provides better security with minimum interference.

Conclusion:

In conclusion, transmission media in computer networks plays a crucial role in performance and reliability. The choice of transmission media depends on various factors such as data transfer speed, distance, reliability, cost, and security. The transmission media in computer networks offer greater mobility and flexibility but may be susceptible to interference and signal loss. The selection of transmission

Satellite Transmission

•A satellite is a body that revolves around the earth just in same way earth revolves around the sun.

•A satellite can be natural such as moon or it can be artificial /manmade(created by human).

​

•Man made satellites are widely being used for communication purposes as they cover maximum area on the earth for a particular transmission.

•The paths in which satellites move are called orbits. The orbit can be equatorial, inclined or polar.

•The period of a satellite i.e, the time required for a satellite to make a complete trip around the earth, is determined by Kepler's law.

​

Categories of Satellites

Based on the location of the orbit, satellites can be divided into three categories:

1.Geo-stationary Earth Orbit(GEO)

2.Low-Earth Orbit(LEO)

3.Middle -Earth -Orbit(MEO)

​

Show the figure of the satellites:

1.GEO satellites

• GEO satellites move around the earth at same speed as earth moves around the sun. Such a satellite is called geo stationary.

1.GEO Satellite

• This ensures constant communication and the satellite seems to remain fixed above a certain spot.
• As the orbital speed depends on the distance from the planet, only one orbit can bro geo-stationary.
• Because of the curvature of the earth one geo-stationary satellite cannot cover the whole earth.

2.MEO Satellites

• Medium -Earth Orbit (MEO) satellite lines at lower altitudes between the two Van Allen bells.
• MEO satellites takes approximately 6-8hours to circle the earth.
• As they are at lower attitudes than GEOs they have smaller footprint on the ground and requires less powerful transmitters to reach them. Example of
• MEO satellites is Global Positioning System (GPS).

3.LEO Satellites

• Low-Earth Orbit satellites lie at an altitudes between 500and 2000km and have polar orbits.
• The speed of LEO satellite is 20,000to 25000km/h.
• The footprint has a diameter of 8000kms.
• A LEO system consists of number of satellite that work together as a network. Each satellite acts as a switch.

LEO satellites categories

1.Little LEOs:operates under 1GHz.They are used for low-data-sate messaging.

2.Big LEOs :operates between 1 and 3GHz.Examples of big LEOs are Globalstar and Iridium system.

3.Broadband LEOs:provide communication similar to fiber optic networks. Example is Teledesic.