Transmission Media

A transmission medium can be anything that can carry signals or data between the source (transmitter) and destination (receiver).

Transmission can be classified as guided or unguided:

• In guided transmission , there is a physical link made of wire/cable through which data in terms of signals are propagated between the nodes. These are usually metallic cable, fiber-optic cable, etc. They are also known as wired media. 
• In unguided transmission , data travels in air in terms of electromagnetic waves using an antenna . They are also known as wireless media. 

Wired Transmission Media 

Wired communication media use cables or wires to transmit data signals. Some examples are:

Twisted pair cable

This consists of two insulated copper wires twisted around each other to reduce electromagnetic interference. It is commonly used for telephone lines and local area networks (LANs). It is relatively cheap and easy to install, but it has low bandwidth and can be affected by noise.

Co-axial cable

This consists of a single copper wire surrounded by a layer of insulation, a metallic shield and a plastic cover. It is used for cable television, broadband internet and long-distance telephone lines. It has higher bandwidth and less interference than twisted pair cable , but it is more expensive and difficult to install.

Fiber-optic cable

This consists of a thin glass or plastic fiber that carries light signals. It is used for high-speed internet, long-distance communication and optical networks . It has very high bandwidth and immunity to noise , but it is very expensive and requires special devices to convert electrical signals to light signals and vice versa.

Wireless Transmission Media

Wireless media use electromagnetic waves or signals to transmit data without cables or wires . Some examples are:

Radio waves

These are electromagnetic waves that can travel long distances and penetrate through walls. They are used for radio broadcasting, cellular communication, satellite communication and wireless LANs. They have low frequency and high wavelength , which means they can carry less data but cover more area.

Microwaves

These are electromagnetic waves that have higher frequency and lower wavelength than radio waves. They are used for radar, microwave ovens, point-to-point communication and satellite communication. They have higher bandwidth and lower interference than radio waves, but they require line-of-sight transmission and can be affected by weather conditions.

Infrared waves

These are electromagnetic waves that have higher frequency and lower wavelength than microwaves. They are used for remote controls, wireless keyboards, wireless mice and short-range communication. They have low bandwidth and high interference, but they are cheap and easy to use.