Transmission Media

Contents:

1. Introduction
2. Types of Transmission Media
3. Twisted Pair Cable
4. Coaxial Cable
5. Fibre Optic Cable
6. Microwaves
7. Radio Waves
8. Satellite Link
9. Infrared

Introduction:

Transmission media also known as Communication media is a medium through which data or signal is transferred between two communicating devices(nodes) through wires or without wires. If the data is sent across network through wires, it is called guided media and if the data is sent without wires, it is called unguided media.

Types of Transmission Media/Communication Media:

Guided Media (Wired Media):

Guided media are also known as physical or conducted media. These media use wires for transmitting data. Various wired connections are twisted pair wire, coaxial cable and fibre optic cable.

Unguided Media (Wireless Media):

A transmission media that does not require the use of cables for transmission of data is known as unguided media. Wireless transmission is also known as unguided media or non-physical media as the transmission takes place through various types of electromagnetic waves, such as radio waves, terrestrial microwave transmissions, satellite transmissions, cellular radio systems, infrared transmissions, etc.

Twsited Pair Cable:

It is made of two plastic insulated copper wires which are twisted together to form a single wire. The wires so twisted are helpful in avoiding interference from the nearby similar pairs, which is known as crosstalk. Twisted pair can be specified as Category 1–5 and is abbreviated as Cat 1–5. Category 6 twisted pair can support data transmission as high as 200 mbps for 100 metres

Types of Twisted

• Shielded twisted pair (STP): STP cables are covered in metal foil. This makes them indifferent to noise and crosstalk.
• Unshielded twisted pair (UTP): UTP has seven categories, each suitable for a specific use. In computer networks, mostly Cat-5, Cat-5E and Cat-6 cables are used. UTP cables are connected by RJ-45 connectors

Advantages:

• It is simple to use.
• It is inexpensive and does not require skilled personnel
• It is less susceptible to electrical interference caused by nearby equipment or wires
• These media can be used for both analog and digital data transmission.
• Fault tolerent

Disadvantage:

• STP wire is physically larger and more expensive than twisted pair wire
• STP is more difficult to connect to a terminating block.

Coaxial Cable

A coaxial cable is generally called a coax wire. It consists of insulated copper wires surrounded by a braided metal shield and covered in a plastic jacket. Coax cables are capable of carrying higher frequency signals than twisted pair cables. Coaxial cable also comes in two primary physical types: thin coaxial cable and thick coaxial cable.

Advantages:

• Coaxial cable can support greater cable lengths between network devices than twisted pair cable
• It is useful for transmitting analog as well as digital data across the network
• Coax are used for transmitting several channels simultaneously
• Coaxial cable has excellent noise immunity because of thick covering outside the insulated wires.
• It is relatively inexpensive as compared to fibre optic cable

Disadvantages:

• A thick coaxial cable does not bend easily and thus is difficult to install.
• It is expensive as compared to twisted pair cable.

Fibre Optic Cable:

Fibre optic transmits light signals rather than electrical signals. In it Light is used to transmit data.It is the newest form of guided media. Several glass fibres are bundled together and are encased in an insulated covering. Light signals travel into the fibre optic cable at one end and are received at the other end.

Optical fibres may be single mode or multimode. Single mode optic fibre transmits only single light width but multimode fibre uses multiple light paths.

Advantages:

• Fibre optic typically offers better bandwidth and can carry more information at once.
• As the signal travels in the form of light, there is less attenuation and signal degradation
• Fibre optic cables are much thinner and lighter than metal wires.
• A signal can run for 50 km without requiring regeneration.
• The data is more secure

Disadvantages:

• A highly skilled labour is required for its installation and maintenance.
• It is relatively expensive as compared to other guided media.
• As light travels in a straight line, two fibres are needed if we need bidirectional communication.

Unguided Media(Wireless Media):

Some of the features of wireless Media are Listed below:

1. Transmission and reception are achieved by means of an antenna.
2. Transmission can be either directional or omnidirectional.
3. Directional:  Transmitting antenna puts out focused beam, both the transmitter and receiver must be alligned
4. Omnidirectional: The signal spreads out in all directions and can ebe received by many antennas.

Microwave:

Microwave signals are used to transmit data. It is a line-of-sight transmission as signal travels in a straight line. In microwave communication, two directional parabolic antennas are mounted on towers, buildings or hills to send and receive signals through air.

Advantages:

• It is a cheaper source of communication as it avoids using cables and maintaining repeaters.
• Communication through microwave is much easier over difficult terrain.
• Microwave system permits data transmission rate of about 16 gigabits per second.

Disadvantages:

• It is an insecure mode of communication.
• The cost of implementing towers, antennas is relatively high.
• Microwave propagation is affected by weather conditions such as rain, thunderstorm, etc.

Radio Waves:

Radio waves use radio frequencies which are allocated to private businesses for direct voice communication. A radio set-up uses transmitter and receiver. A transmitter sends radio waves and encodes them into sine waves which, when received by a receiver, are decoded and the message is received.They are not line-of-sight transmission and, hence, can penetrate buildings easily

Advantages

• They can be used indoors or outdoors.
• They are omnidirectional and can travel in any direction.
• Radio wave transmission offers mobility.
• It is cheaper than laying cables and fibres.
• It offers ease of communication over difficult terrain.

Disadvantages

• Radio wave communication is an insecure mode of communication
• Radio wave propagation is susceptible to weather effects like rain, thunderstorm, etc.

Satellite Link:

Data is transmitted with the help of Satellite and Towers. Data is transmitted from an earth station to a satellite, it is known as uplink and when transmission takes place from a satellite to an earth station, it is known as downlink. In satellite, there are transponders that send and receive signals from/to the earth station. It provides various types of services such as transmitting fax, voice data, video, email and other internet applications.

Advantages:

• The area covered is quite large.
• Earth station which receives the signals can be at a fixed position or can be relatively mobile
• No line-of-sight restrictions

Disadvantages:

• It is very expensive as compared to other transmission mediums.
• Installation is extremely complex
• Signals sent to the stations can be interrupted by external interference

Infrared:

The type of transmission that uses infrared light to send data is known as infrared transmission. The data is transmitted through air and can propagate in the open space; however, it cannot penetrate the walls of the room.

Advantages

• It is a secure medium of transmitting data.
• It is a cheap mode of transmission.

Disadvantages

• It can work only for short distances.
• It cannot penetrate walls and is affected by distance, noise and heat.

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