1. Computer network @prepared by S.Shrestha (comp 251)

2. introduction Number of computers (and usually terminals (point of connection)) interconnected by one or more transmission paths. Transmission path often is the telephone line due to its convenience and universal presence. @prepared by S.Shrestha (comp 251)

3. network transfer and exchange of data between the computers and terminals. @prepared by S.Shrestha (comp 251)

4. applications day-day transactions at department stores, banks, reservation counters, etc. @prepared by S.Shrestha (comp 251)

5. advantages Sharing of resources. Allows flexible working environment. – Employees can work at home by using terminals tied through networks into the computer at the office. @prepared by S.Shrestha (comp 251)

6. Computer network Collection of autonomous (acting independently) computers interconnected by a single terminology. Two computers are said to be interconnected if they are able to exchange information. Note: Neither the internet nor the world wide web (distributed system) is a computer network. @prepared by S.Shrestha (comp 251)

8. internet Internet is not a single network but a network of networks and the web is a single distributed system that runs on top of the internet. Internet stands for international networks. Largest computer network system in the world. Global network of computers. @prepared by S.Shrestha (comp 251)

11. History of internet????? @prepared by S.Shrestha (comp 251)

12. Client server model @prepared by S.Shrestha (comp 251)

13. Description One can imagine a company’s information system as consisting of one or more databases and some no of employees who need to access them remotely. In this model, the data are stored on powerful computers called servers. Servers: often these are centrally housed and maintained by a system administration. @prepared by S.Shrestha (comp 251)

14. Contd… In contrast, the employees have simpler machines, called clients on their desks with which they access remote data. For example to include in spreadsheets (i.e. computer program allowing manipulation and flexible retrieval of especially tabulated numerical data). @prepared by S.Shrestha (comp 251)

15. Working mechanism 2 processes are involved, one on the client machine and one on the server machine. Communication takes the form of the client process sending a message over the network to the server process. The client process, then waits for a reply meessage. @prepared by S.Shrestha (comp 251)

16. Contd… When the server process gets the request, it performs the requested work or looks up the requested data and sends back a reply. @prepared by S.Shrestha (comp 251)

18. Network hardware 2 types of transmission terminology that are in wide spread use. Broadcast links Point-point links @prepared by S.Shrestha (comp 251)

19. 1. Broadcast networks Single communication channel that is shared by all the machines on the network. Short messages (packets) sent by any machine are received by all the others. An address field within the packet specifies the intended recipient. Upon arriving a packet, a machine checks the address field. @prepared by S.Shrestha (comp 251)

20. Contd… If the packet is intended for the receiving machine, that machine processes the packet. intended for some other machine Packet ignored @prepared by S.Shrestha (comp 251)

21. broadcasting Addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted, it is received and processed by every machine on the network. @prepared by S.Shrestha (comp 251)

22. multicasting Some broadcast systems also support transmission to a subset of the machines. @prepared by S.Shrestha (comp 251)

23. 2. point-to-point Consists of every connections between individual pairs of machines. To go from source-destination a packet on this type of network may have to first visit one or more intermediate machines. @prepared by S.Shrestha (comp 251)

24. unicasting Point-point transmission with one sender and one receiver. @prepared by S.Shrestha (comp 251)

25. internetwork Connection of two or more networks. Example: internet. @prepared by S.Shrestha (comp 251)

26. Wireless networks Divided into 3 main categories: – System interconnection – Wireless LANs – Wireless WANs @prepared by S.Shrestha (comp 251)

27. System interconnection – Short range wireless network. – System connection networks use master- slave. – System unit (master), mouse-keyboard (slave) Master tells slave what address to use, when they can broadcast, how long they can transmit, what frequencies they can use, and so on. @prepared by S.Shrestha (comp 251)

28. Wireless LANs System in which every computer has a radio modem and antenna with which it can communicate with other systems. @prepared by S.Shrestha (comp 251)

29. Wireless WANs Bluetooth – No cables – No driver installation @prepared by S.Shrestha (comp 251)

30. Home networks Computers (desktop PC) TV, DVD, VCR, etc. Most homes already have networks installed like:- electricity, telephone, cable TV, water, gas. @prepared by S.Shrestha (comp 251)