Communication medium refers to the physical channel through which data is sent and received. Data is sent in the form of voltage levels which make up the digital signal. A digital signal consists of 0s and 1s; essentially, a 1 corresponds to a high voltage, while a 0 corresponds to a low voltage.
The speed of data transmission or data rate depends upon the type of medium being used in the network. There are basically two types of networks:
- Wired network
- Wireless network
In a wired network, data is transmitted over a physical medium. There are three types of physical cables used in a wired network.
1. Twisted Pair
It consists of a pair of copper wires twisted around each other; the wires are around 1 to 2 mm thick and they are twisted to reduce the interference from the surrounding wires. Remember that a current carrying wire has a magnetic field around it that can interfere with that of another wire when in close proximity.
Invented by Alexander Graham Bell, this form of wire has been in use since the 19th century and is currently the cheapest mediums available. Twisted pairs are also used in telephone wires, but they only consist of four wires or two pairs. In computer networks, eight wires or four pairs are utilized. This is also known as the Ethernet cable or RJ-45 cable. The pairs of wires are bundled together and covered by a protective shield.
2. Coaxial Cable
Offering better data rates and less signal attenuation, a coaxial cable consist of a central copper conductor that is surrounded by a foil shield. The foil is covered by yet another shield known as a braided shield. Unlike twisted pairs, coaxial cables only have a single copper conductor. The conductor and the foil shield are separated by a dielectric.
3. Fiber Optic
It is the most expensive of wired mediums and offers the highest rates of data transmission. They are often used in long distance communications and are never affected by any electromagnetic fields. This is because it involves light.
A fiber optic cable is a thin, flexible, transparent medium made of very fine glass or plastic fibers. It utilizes the principle of total internal reflection. Unlike twisted pairs or coaxial cables, a fiber optic uses light pulses generated by laser or an injection diode to transmit data. Each pulse of light represents a single bit of data.
A wireless network uses radio waves as the sole medium for transmitting and receiving data. There are no wires involved. An example is the wireless router in your home. Radio waves are electromagnetic waves which are transverse in nature and they have the longest wavelength on the electromagnetic spectrum.
They travel at the speed of light and have frequencies ranging from 3 kHz to 3 GHz. Radio waves can easily be absorbed by most materials and can bend around objects as well. However, they are susceptible to nearby electromagnetic fields which can cause losses in the data rate.