Communication Media And Communication Devices:-
Guided Communication Media:-
It is also called physical or bounded communication media. In this type of media signals pass through a physical path. It uses cables that guide the data signals along a specific path. The following are some important guided media.
• Telephone Cable
• Twisted Pair Cable
• Coaxial Cable
• Fibre Optic Cable
Standard telephone cable is widely used Communication lines. Telephone lines a particularly useful to the user of data communication because the complex network lines that has already been established allows data to be transmitted to any location in the world The disadvantage of telephone line is that transmission speed is very slow. Therefore, its u for data communication is slowly declining.
It is mainly used for long distance transmission. It can transmit data at much higher range of 10 to 100 megabits per second. They are also used by telephone companies to transmit data over long distance. Coaxial cables are packed into a very large Cable that can handle hundreds of thousands telephone calls at the same time. Coaxial cab provides high quality data transmission without distortion or loss of signal. Coaxial cables ha been laid under the ocean.Both telephone line and coaxial cables are made up of Copper.
Twisted Pair Cables:-
Twisted pair cables are twisted together pairs. It provides shielding from outside interference. Cables with a shield are Call Shielded Twisted Pair (STP) cables. Cable Without shields are Called Unshielded Twisted Pa (UTP) cables.
Fibre Optic Cable:-
It is new technology that is replacing the Conventional cable in communication system Fibre optic cable is smooth hair-thin strands of transparent material that transmits light waves high speed.
The main advantage of fibre optic cable over wire cables includes weight and size reduction and increased speed of transmission. Fibre optic cable is not affected by electromagnetic interference. Therefore, noise and distortion a reduced. Fibre optic cable can transmit both voice and digital data.
It is also called unbound media. In this type of communication media transmission takes place through open air. They are not guided through any specific path. The following are important unguided media.
Microwave transmission signals travel through open space much like radio signal. Microwave systems transmit information with transmitters which are normally installed on high buildings, mountains tops or high towers. Long distance microwave channels consist of a series of relay stations (boosters) spaced approximately 30 miles apart. Two stations must be within sight of one another. For transmitting information long distances, signals are amplified and retransmitted from station to station.
Satellite is a relay station positioned approximately 22,000 miles above the earth. It orbits around the earth with exactly the same speed as the rotation speed of earth. Earth stations beam signals to the satellite. The satellite amplifies and retransmits the signals to another earth station which can be located thousands of miles away.
Satellite communication is ideal for long distance communication. Transmission by satellite allows large amount of data to be sent long distance at rapid speeds. Its use has increased dramatically in recent years. However, a major drawback of satellite communication has been the high cost of placing the satellite into its orbits. These satellites are launched either by rockets or by space shuttles
A device that is used in telecommunication systems for transmitting data from one location to another is known as Communication device.
Commonly used communication devices can be classified into switches, routers and gateways.
A Switch or network switch (also known as hub) is a small hardware like a box that connects multiple computers together in a local area network (LAN). A switch inspects data packets as they are received, determines the source and destination device of each packet and forwards them appropriately. A packet a basic unit of Communication over a computer network. When data is transmitted, it is broken down into packets which are reassembled to the original form once they reach the destination Switches allow computers to communicate directly with one another in the smooth and efficient manners.
A router is a communication device which is used to Conn two or more networks. Today, most of the networks are Connected Internet. When the computer is sending data to another Computer the Internet, router receives the data packets, looks for the remote computer address and forwards it to a computer that is closer to the remote Computer. It forwards the data packets by Selecting the be path-way based on network traffic. Many routers take part transmitting the data packets from one location to another.
It is a device that is used to Connect a network to another network that uses different protocols. If we have to link different kinds networks, such as a network of IBM mainframe Computers and network of PCS, We might have to use a gateway, Gateways changes the format of the data packets but not the Contents of the message, to make it conform to the application program of the remote Computer.