Unit 11 Networks

1. Kingdom of Saudi Arabia • Prince Norah Bint Abdul Rahman University • College of Computer Since and Information System • NET201 Unit 11Networks

2. Networks • A network is a combination of a number of computers and peripheral devices connected together. • Networks allow: • Communication between computers • Sharing of hardware such as printers • Sharing of software (programs and data) • A network that covers a small area such as an office or a building is called a LAN (local area network)

3. Clients and Servers • The main computers that provide services on the network are called servers such as a file server which provides a central storage area for data files. • The computers that use these services are called clients. • The computers can be connected using various types of cabling, including the ordinary telephone system wiring. • A main data communications cable connecting LANs together is referred to as a backbone.

4. Networks Devices • Various electronic devices are also used to amplify, filter and determine the best path for the signals. These include: • Bridges: for dividing a LAN into separate parts or connecting similar networks together. • Gateways: for connecting different types of networks • Routers: for connecting different networks together and determining the bets path or route for the signals. They are used to connect networks to form the Internet.

5. Network Devices • Modem (modulator/demodulator): used to convert signals from analogue ( having a variety of levels) to digital ( having only two levels, representing on and off) for connection to the ordinary telephone system • Alternatively, an ISDN (integrated services digital network) adapter or a DSL (digital subscriber line) modem can be used to allow digital signals to be used without being converted to analogue signals.

6. Wireless Networks • WiFi • (wireless fidelity) is a set of standards for radio-based wireless networks. • Wireless networks: • Interconnection of computers using signals carried thru the air, usually radio waves, instead of thru connecting cables. • The computers connect to each other and to wired networks using an electronic device known as an AP (access point). • APs enable computers to be connected together to form WLANs (wireless local area network) such as a network that uses radio waves to connect computers in a small area.

7. Wireless Networks • Each computer needs an electronic interface installed, known as a wireless NIC (network interface card). • Some security can be provided on wireless networks by using encryption programs (programs that convert data to coded form to make it more secure). • WEP (wired equivalent privacy) can be used. This is a basic set of standards used to convert data on a wireless network to provide privacy.

8. Data Transmission Modes • When data is transmitted thru a network system, it can be transmitted in different ways: • Asynchronous transmission (or stop-start transmission) sends the data one byte (character) at a time. A start bit (called control bit) is added to indicate the beginning of each byte. Another control bit called the stop bit is added to indicate the end of each byte.

9. Data Transmission Modes • Synchronous transmission sends the data in blocks. Extra bytes of data called synch bytes are added at the beginning and end of each block. They are used to synchronize the sending and receiving devices.

10. Data Transmission • When a message is transmitted thru a network, it is processed in various ways by the software and the hardware: • First, it is processed by the applications program such as an email program, • Then it is processed by the operating system. • Next, it is processed by the hardware such as the network interface card • Finally, it is processed by the network electronics such as a router as it passes thru the network system.

11. Data Transmission • When it arrives at its destination, it is similarly processed in reverse order to display the message on the display screen of the receiving computer.

12. Advantages of Network • HW and SW can be shared • Access to the system can be controlled • Maintenance is easier • Users can communicate easily with each other • Easier to check for viruses • Easier to make backups

13. Disadvantages of Network • More complex to set up • More expensive • More vulnerable to viruses • The whole network depends on the central server • Require more expertise to maintain

14. Unit 11: NetworksStarter 1, 2

15. Unit 11: NetworksReading 3 • Do it orally

16. Unit 11: NetworksLanguage Work (relative clauses with a participle) • Passive participle: • Computers which are equipped with wireless NICs • == Computers equipped with wireless NICs • A network printer which is connected to a wireless print server • == A network printer connectedto a wireless print server

17. Unit 11: NetworksLanguage Work (relative clauses with a participle) • Active participle: • A modem which provides access to the Internet • == A modem providing access to the Internet • A fixed LAN which links computers with cables • == A fixed LAN linking computers with cables

18. Unit 11: NetworksLanguage Work 4 • Enabling • Used • Handling • Directing • Linked • Connecting • Storing, shared • Used • Comprising • Connecting

19. Unit 11: NetworksLanguage Work 5 • The technology needed to set up a home network is here today • You only need one network printer connected to the sever • Here house has a network allowing basic file sharing and multi player gaming • There is a line receiver in the living room delivering home entertainment audio to speakers • Eva has designed a site dedicated to dance

20. Unit 11: NetworksLanguage Work 5 • She has built in links connecting her site to other dance sites • She designed the site using a website creation program called Dreamweaver • At the center of the home of tomorrow is a network accessed thru a control pad • The network can simulate the owner’s presence making sure vital tasks are carried out in her absence • The house has an electronic door keeper programmed to recognize you, giving access to family only

21. Unit 11: NetworksSpeaking 7 • Asynchronous transmission: • Start bit • Error check bit • Stop bit • Start bit • Error check bit • Stop bit

22. Unit 11: NetworksSpeaking 7 • Synchronous transmission: • Start synch bytes • Character • Character • Error check bytes • Stop synch bytes

23. Unit 11: NetworksSpecialist Reading • a)segments b)packets • To determine if the data was scrambled during transmission • Until it receives confirmation from the next point along the route that the packet has arrived undamaged • a) the checksum is calculated and verified for each packet b) the message may be rerouted to avoid congestion on the network

24. Unit 11: NetworksSpecialist Reading • A) presentation layer • Transportation layer • Physical layer • Data-link layer • Application layer • Session layer • Network layer • Transport layer • Data-link layer

25. Unit 11: NetworksAssignment • Writing 8, page 77 • Specialist reading part B, pages 79, 77