2. Thaksalawa Web Site Group Project

4. Transmission of data from one place to another place is called Data Communication.

5. Three components are essential in Data Communication. They are, I.Source / Sender II.Data Communication Medium III.Receiver / Sink Sender/Source Receiver/Sink

6. Sender or source is the data producer or the place where the data is produced for data transmission. EX :- Imagine that you call a friend of yours. Then you become the Sender or Source.

7. The medium (Channel) which is used to transmit data to the receiver is considered here. EX :- According to previous example, the telephone line becomes the data communication medium.

8. The receiver is the person who gets data at the end. EX :- Same as previous example, Your friend is the receiver.

9. Various media are used for data communication. It is possible to group all these media into two main types. 1.Guided Media – If a particular physical medium is used for data communication, it is called guided media. 2.Unguided Media (Radiated Media) – communicating data using media which are not physical is simple and common today. Those media are called unguided/radiated media.

10. Wires are used here for data communication and some most popular media are given below. Twisted wire pair The normal wires used for daily activities can also be used for data communication. Ex:- Normal telephone wires. Twisted pair cable

11. Co-axial Cables Co-axial cables, which consist of a copper net woven around a copper wire, are also used for data communication. This is used in antenna wires for Television Sets. Co-axial Cables

12. Fiber Optics Fiber Optics is a very popular guided media used today for data communication. This is used in modern telephone lines. Fiber Optics Cables

13. No physical medium is used here to build the relationship and the communication media given below are widely used. Radio waves Radio waves, which are very familiar to our normal lives, can be used for data communication very easily. Radio waves

14. Infrared This possesses very low frequency light beams, can also be used for data communication. These are largely used for data communication when cable less keyboards, Mice and television remote controls are used. Infrared remote

15. Microwaves Microwaves are used to communicate data to a longer distance and short signals which contain higher frequencies are used here. Microwave transmission

17. Data is transmitted here one after the other (in a serial way). Such data transmission is done in bits in a computer network. One wire is enough here for data transmission. Sender Receiver

18. Several bits are transmitted at a time in parallel data transmission and several wires are used for this. In most of the instances, the use of at least eight wires for this is the normal way. Sender Receiver

19. To measure the speed of data transmission which is done using bits, bits per second (bps) is considered and units such as kbps (kilobits per second), Mbps (Megabits per second) and Gbps (Gigabits per second) are used to measure the data transmission speed.

21. In simplex data transmission, data is directed one way.There is no any space for data transmission to be directed the other way. The best examples which can be mentioned here are television and radio transmission. All time for one Direction

22. In Half-Duplex data transmission, data can be directed one way at a time.Though data can be transmitted both ways here, until the data transmission to one direction is over, data cannot be transmitted in the other direction. The best example which can be cited here is the Walkie-talkie. Two times at both Directions

23. In full duplex data transmission, data can be transmitted both ways at the same time. The best example which can be shown here is the telephone. Same time at both Directions

25. Speed Since the computers and other devices are well connected to one another in a computer network, it is possible to transmit data and information very easily and fast. Sharing of resources In computer networks, expensive special devices can be commonly used. For instance, only one printer is sufficient for many computers in a computer network. Speed Since the computers and other devices are well connected to one another in a computer network, it is possible to transmit data and information very easily and fast. Sharing of resources In computer networks, expensive special devices can be commonly used. For instance, only one printer is sufficient for many computers in a computer network.

26. Cost The high cost for computer programs and devices can be easily reduced when a computer network is built. Because we can reduce cost by sharing software and hardware resources in a network. E-mail / Electronic mail Email can be used to exchange information very easily among computers.

27. In certain networks (e.g. Star), breakdown of the main computer can adversely affect the process of the entire computer system. There is a possibility to lose resources due to the errors of the network system. Outsiders may access the network and rob data and information there. Controlling the network is not an easy task. It demands special computer software and specially trained officers.

28. The way computers are physically connected is very important in computer networking. How the computers are physically connected to one another is called Network Topology. Computer 1 Computer 2 Computer 3

30. It is very easy to install a star network and it is relatively easy to identify and correct errors there. The main disadvantages of this topology are, using more wires and the breakdown of hub / switch will turn down the whole system. The computers are connected here in the shape of a star as shown in the Figure. A computer or a hub or switch is used here in the middle to connect all the computers to one another. Diagram of a Star topology

31. This network is arranged connecting Computers to one another in the form of a ring or loop. Even though the need of a few wires to connect computers can be mentioned as an advantage. The main disadvantage in a ring network is that if one computer does not operate, the whole network will collapse. Diagram of a Ring topology

32. This computer network is built centering on a main wire and connecting all the computers and other devices to it. The advantages of this are the need of a few wires and ease of connecting computers and other devices. A main disadvantage of this is the fact that the whole network depends on the main wire. Further, closing the main wire at both ends using terminators is a difficult task. Diagram of a Bus topology Terminator Main Wire

33. Tree topology takes the shape of separated branches of a tree. One advantage of this kind of a network is the possibility to control each branch separately. However, building and controlling this network can be a bit complicating task. Diagram of a Tree topology Further, a main wire as in bus topology is used here to connect the branches of this network and the function of the network depends on it. This can be problematic

34. There are three main types of computer networks, 1.Local Area Networks (LAN) 2.Metropolitan Area Networks (MAN) 3.Wide Area Networks (WAN)

35. A computer network which is spread in a small area is called a Local Area Network. In most of the instances, this kind of network is limited to one building or else the network is built connecting a few places which are situated very close to each other. For instance, a computer network built in a school or a university can be called a Local Area Network. LAN technology used in Computer labs

36. Networks which are spread in a larger area than a Local Area Network but smaller than Wide Area Network are called Metropolitan Area Networks. A computer network which is maintained in a government institute can be cited as an example here. For instance, a computer network which connects Divisional Secretariats can be called a Metropolitan Area Network. Braches of an institution connected using WAN

37. A computer network which is spread in a large area is called a Wide Area Network. The best example which can be given for this is the Internet. No geographical restriction can be shown in such a network. Spread of WAN thorough large area

38. It can be noticed that many devices are used in computer networks. Following are some of them. MODEM The MODEM is a device that has to be used here to build the necessary relationship to connect the computer to Internet through telephone lines.

39. Network Hub Network Hub is used in a computer network to connect several computers with one another. Network Switch This device is also used to connect several computers with one another in a network. In a switch the data are routed only to the relevant device while a hub broadcasts data to all devices in the network at once. Network HUB Network Switch

40. Network Interface Card (NIC) Network Interface Card is the card which contains the circuits which are necessary to connect your computer to a network. Nowadays this device is built in the motherboard. Network Interface Card

41. Server Computer The computers which provide necessary services for a computer network are called server computers. Server computers possess a higher configuration than the normal computers. Facebook’s Server computers

42. Client Computer The computers which receive the services in a computer network are called Client Computers. For instance, when you use the Internet, your computer functions as the client computer and the computer which provides you with the service functions as the server computer.