In data communication, the transmission medium plays an important role. A transmission medium is nothing but it is a pathway that carries the information from sender to receiver. Data is transmitted normally through electrical or electromagnetic signals.
Types of Transmission Media
Transmission media is broadly classified into two groups.

1.Wired or Guided Media or Bound Transmission Media
Guided Media are the cables that are tangible or have physical existence and are limited by physical geography. Signals being transmitted are directed and confined in a narrow pathway by using physical links.

Its features are:-
  • High Speed
  • It is mostly used for comparatively shorter distances
  • It is secure
3 major types of Guided Media:
(I)Twisted Pair Cable
It is made of two plastic insulated copper wires twisted together to form a single media. Generally, several such pairs are bundled together in a protective sheath. The twists between wires are helpful in reducing noise(electromagnetic interference) & crosstalk.
  • Data rate (speed):-up to 10 Gbps (depending upon category)
  • Bandwidth:-up to 4700 MHz
  • Distance:-up to 100m
Two types of twisted-pair cables:
1.Shielded Twisted Pair (STP):
This type of cable consists of a special jacket to block external interference. It is used in fast-data-rate Ethernet and in voice and data channels of telephone lines.

Advantages:
  • It eliminates crosstalk
  • Comparatively faster
  • Better performance at a higher data rate in comparison to UTP
Disadvantages:
  • Much thicker diameter and not as flexible
  • More expensive than UTP
  • The shield of STP cables must be grounded properly otherwise it acts as an antenna and picks up unwanted signals.
2.Unshielded Twisted Pair (UTP):
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.

Advantages:
  • Least expensive
  • High-speed capacity
  • Easy to install
Disadvantages:
  • It can be used up to cable segment lengths of about 100 meters only.
  • It is more susceptible to interference compared to most of the other cable types.
  • Lower capacity and performance in comparison to STP

(II)Coaxial cable
It has an outer plastic covering containing 2 parallel conductors each having a separate insulated protection cover. The core wire lies in the center and is made of a solid conductor. Coaxial cables are widely used for cable TV connections and LANs.
  • Data rate (speed):-10 Mbps
  • Bandwidth:-750 MHz (default)
  • Distance:-up to 500m
The coaxial cable transmits information in two modes:
  • Baseband mode:-It is defined as the process of transmitting a single signal at high speed.
  • Broadband mode:-It is defined as the process of transmitting multiple signals simultaneously.
It is of three types    (RG stands for Radio Government.)
  • RG-59(Cable TV)
  • RG-58(Thin Ethernet)
  • RG-11(Thick Ethernet)
Advantages:
  • High Bandwidth
  • Better noise Immunity
  • Easy to install and expand
  • Inexpensive
Disadvantages:
  • It is more expensive as compared to a twisted pair cable.
  • If any fault occurs in the cable causes the failure in the entire network
(III)Optical Fibre Cable
It uses the concept of the reflection of light through a core made up of glass or plastic. The core is surrounded by a less dense glass or plastic covering called cladding. It provides faster data transmission than copper wires. And it is used for the transmission of large volumes of data. The optical fiber cable can be unidirectional or bidirectional.
  • Data rate (speed):-up to 10 Gbps
  • Bandwidth:-up to 4700 MHz
  • Distance:-up to 80 Km
Advantages:
  • High capacity and bandwidth
  • Lightweight
  • Less signal attenuation
  • Immunity to electromagnetic interference
  • Resistance to corrosive materials
Disadvantages:
  • Optical fiber cables are expensive
  • Difficult to install and maintain
  • Light waves are unidirectional, so two frequencies are required for full-duplex transmission
2.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.

Its features are:-
  • It is used for larger distances
  • The signal is broadcasted through air
  • less Secure
3 major types of Unguided media:
(I)Radiowaves
These are easy to generate and can penetrate through buildings. The sending and receiving antennas need not be aligned i.e. the wave sent by the sending antenna can be received by any receiving antenna. Radio waves are electromagnetic waves that are transmitted in all directions of free space. And radio waves are omnidirectional i.e. the signals are propagated in all directions. An example of the radio wave is FM radio, television, cordless phones.

The range in frequencies of radio waves is from 3KHz to 300 GHz.

Advantages:
  • Radio transmission provides a higher transmission rate.
  • Radio waves cover a large area, and they can penetrate the walls. Hence used for radio and television transmission and for cellular mobile phone service.
  • It is used in various medical applications. it is used in Diathermy instrument for surgery.
Disadvantages:
  • Uncontrolled radiation of radio frequency affects small birds, flora and fauna, elderly humans, pregnant women, etc.
  • Areas near radio frequency cellular towers have been observed with more lightning compare to other areas.
  • Radiofrequency waves are available both in LOS and non-LOS regions of the transmitter, they can be easily intruded by hackers and crucial data can be decoded for malicious motives.
(II)Microwaves
It is a line of sight transmission i.e the sending and receiving antennas need to be properly aligned with each other. The distance covered by the signal is directly proportional to the height of the antenna. And microwaves are unidirectional as the sending and receiving antennas are to be aligned i.e. the waves sent by the sending antenna are narrowly focussed.

Microwaves are electromagnetic waves having a frequency in the range of 1GHz to 1000GHz.

Advantages:
  • Microwave transmission is cheaper than using cables.
  • Communication over oceans can be achieved by using microwave transmission.
  • It is free from the land acquisition as it does not require any land for the installation of cables.
  • Microwave spectrum has larger bandwidth and hence a large amount of information can be transmitted using it.
Disadvantages:
  • Microwave transmission is susceptible to weather conditions. This means that any environmental change such as rain, wind can distort the signal.
  • Eavesdropping creates insecure communication. Any malicious user can catch the signal in the air by using its own antenna.
  • A signal can be moved out of phase by using a microwave transmission.
(III)Infrared
Infrared waves are used for very short-distance communication. They cannot penetrate through obstacles. This prevents interference between systems. 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 a closed area.

Frequency range:-300GHz-400THz.

Advantages:
  • Infrared transmission requires a minimum power to operate and can be set up at a low cost.
  • It has a response time faster than thermocouples.
  • It provides secured communication due to line of site are point to point to the mode of communication.
Disadvantages:
  • Infrared waves at high power can damage the eyes.
  • It is supposed to lower the rate of data transmission compared to wired transmission.
  • Infrared signals are interpreted by objects and people.
Some other types of Unguided Media 
(I)Satellite Transmission
Satellite communication is more reliable nowadays as it offers more flexibility than cable and fiber optic systems. We can communicate at any point on the globe by using satellite communication. The satellite accepts the signal that is transmitted from the earth station, and it amplifies the signal. The amplified signal is retransmitted to another earth station.

Advantages:
  • It is used in a wide variety of applications such as weather forecasting, radio/TV signal broadcasting, mobile communication, etc.
  • The transmission cost of the satellite is independent of the distance from the center of the coverage area.
  • It has a small fading margin on the order of about 3dB.
  • It is easy to obtain service from one single provider and uniform service is available.
  • It covers a wide area of the earth hence entire country or region can be covered with just one satellite.
Disadvantages:
  • Satellite manufacturing requires more time. And satellite design and development requires higher cost.
  • Satellite once launched, requires to be monitored and controlled on regular periods so that it remains in the orbit.
  • The satellite has limited life which is about 12-14 years. Due to this fact, another launch has to be planned before it becomes un-operational.
(II)Bluetooth
Bluetooth wireless technology is short-range communication technology. It is intended to replace the cables connecting portable units and maintaining high levels of security. It is based on Ad-hoc technology which is a local area network with very limited coverage. Bluetooth based on IEEE 802.15.1 standard for wireless Personal Area Networks. Bluetooth employs Radio Frequency for communication.

Data rates:-It depends on Versions
  • 1Mbps (for version 1.2)
  • 3Mbps (for version 2.0)
Range:-It depends on the device 
  • Class 3 radios:-1m or 3 feet
  • class 2 radios:-10m or 30 feet (commonly found in mobile devices)
  • class 1 radios:-100m or 300 feet (primarily used in industries)
Advantages:
  • It avoids interference from other wireless devices.
  • It has lower power consumption.
  • It is easily upgradeable.
  • It has a range better than infrared communication.
  • Bluetooth devices are available at a very cheap cost.
Disadvantages:
  • It has low bandwidth as compared to Wi-Fi.
  • security is a very key aspect as it can be hacked.
  • It can lose connection in certain conditions.
  • It allows only short-range communication between devices.
(III)Wi-Fi
Wi-Fi stands for wireless fidelity. It commonly uses the 802.11 b protocol. It is a local area wireless technology that allows an electronic device to participate in computer networking using 2.4 GHz UHF and 5 GHz SHF ISM radio bands. WiFi network is established by installing wifi AP(Access point) or wifi router. And the wifi router or Access Point is connected with the internet using a physical or wired ethernet cable or fiber optic cable.

Advantages:
  • Installation is very quick and easy. it does not require technical knowledge of wifi or WLAN system and its protocols.
  • It is easy to add or move wifi clients or wifi stations to the wifi network created by Access Point.
  • It is easy to integrate wifi functionality in mobile and computing devices.
  • Latest wifi standard versions such as 11n and 11ac deliver fast data connection rates e.g 300Mbps and higher
Disadvantages:
  • Full security is difficult to achieve due to the wifi connection being wireless in nature. It requires proper security authentication protocols and configuration.
  • Data transfer rate decreases when the number of clients or computers connected with the wifi network increases.
  • Wifi devices operate in full functionality and without any interruption when they are within the range of access point and receiving good signal strength.

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