Chapter 6

1. Chapter 6 ComputerNetworks

2. OBJECTIVES Distinguish between the three types of networks: LANs, MANs,and WANs. List different connecting devices and the OSI layers in whicheach device operates. Understand client-server models. Understand the OSI model and TCP/IP. Understand the rationale for the existence of networks. After reading this chapter, the reader should be able to:

3. 6.1 NETWORKS, LARGE AND SMALL

4. Network • Computer network–A combination of computers connected through transmission media. • LAN (Local Area Network) • MAN (Metropolitan Area Network) • WAN (Wide Area Network) • Internetwork– (e.g. Internet)Networks can be connected using connecting device.

5. Model and Protocol • Model–the specification set by a standards organization as a guideline for designing networks. • Protocol–a set of rules that controls the interaction of different devices in a network/internetwork.

6. 6.2 OSI MODEL

7. Note: The OSI (Open Systems Interconnection) modelis a theoretical model that shows how any two different systems can communicate with each other. • OSI Model–is a framework of 7 layersthat gives network designers an idea of the functionality of each separate but related layer.

8. Figure 6-1 The OSI model

9. the header or traileris dropped in each layer. • control informationis added to the data in the form of headers or trailers. Flow of data in the OSI model Figure 6-2

10. Functions of the Layers • Physical • transmit a bit stream over a physical medium. • Data-Link • Organizes bits into logical units called frames. • Node-to-node delivery • Network • Source-to-destination delivery of a packet. • Transport • Source-to-destination delivery of the entire message. • Session • Establishes, maintains, and synchronizes the dialog between communicating systems. • Presentation • Deals with the fact that different systems use different coding methods. • Application • Enables the user to access the network.

11. OSI Layers 實例：

12. 6.3 CATEGORIES OF NETWORKS

13. Categories of networks Figure 6-3

14. LAN (Local Area Network) • Allow resource sharing between computers. • Computers • Peripheral devices • Transmission medium (e.g. cable) • 3 types of topology • Bus topology • Star topology • Ring topology

15. LANs Figure 6-4 • Hub – • a device that facilitates connection • LAN acts logically like a bus. • Star –the dominant topology today.

16. MAN Figure 6-5

17. MAN (Metropolitan Area Network) • Uses services provided by a network service provider. (Tel. Company) • Individual users’ computers • Organizations’ LANs • Many Tel. Company provide a popular MAN service called SMDS(Switched Multimegabit Data Services) • Prior to SMDS's arrival in 1995, the only way to connect LANs was through a dedicated private line.

18. WAN Figure 6-6

19. WAN (Wide Area Network) • The connection of individual computers or LANsover a large area (country, world). • User using a telephone line to connect to an ISP (Internet Service Provider) is using a WAN. • Negotiates fee • ISP • Tel. company

20. 6.4 CONNECTING DEVICES

21. Figure 6-7 Connecting devices

22. Repeater (L1) Figure 6-8 • Regenerates the signal. • Extends the physical length of a network.

23. Note: Repeaters operate at the first layer of the OSI model.

24. Bridge/Switch • Bridge • A traffic controller • Divide a long bus into smaller segmentsso that each segment is independent trafficwise. • Regenerate data • Switch • A sophisticated bridge with multiple interfaces. • A station that needs to send a frame sends it directly to the switch.

25. Figure 6-9 Bridge (L1-L2)

26. Note: Bridges operate at the first two layers of the OSI model.

27. Figure 6-10 Switch

28. Router • Connect LANs, MANs, and WANs. • Routes a packet based on the logical address (network layer) of the packet. • Connect two independentnetworks: LAN-WAN, LAN-MAN, WAN-WAN… V.S. • Bridge • filters a frame based on the physical address (data-link layer) of the frame. • Connect two segments of a LAN or two LANs belonging to the same organization.

29. Routers (L1-L3) in an internet Figure 6-11

30. Note: Routers operate at the first three layers of the OSI model.

31. Gateway (L1-L7) • A protocol converter. • Understands the protocols used by each connected network and is able to translate from one to another.

32. Connecting devices and the OSI model Figure 6-12 internetworking IP address packet Mac address networking frame

33. ISP (Internet Service Provider)a company that provides access to the Internet. For a monthly fee, the service provider gives you a software package, username, password and access phone number. Equipped with a modem, you can then log on to the Internet and browse the World Wide Web, and send and receive e-mail. • ICP （Internet Content Provider）網際網路內容提供者。指的是在網際網路上提供各種服務內容的廠商。如Yahoo雅虎、AOL美國線上等，都是屬於ICP的一種。任何人只要有網路的空間放置網頁，都可以成為ICP。而ICP的收入大都來自廣告收入。 • Web portalA Web site or service that offers a broad array of resources and services, such as e-mail, forums, search engines, and on-line shopping malls. • ASP (Application Service Provider)ASP 業者向軟體公司購買應用程式，然後將此程式放在 ASP 業者的機房內，然後供企業或個人以存取網路的方式連接到機房來使用應用程式，並依據使用方式與規定向客戶收取費用。

34. 6.5 THE INTERNET AND TCP/IP

35. Internet • internetwork (internet) • A network of networks • Connect individual LANs, MANs, and WANs. • Internet – the most famous one

36. TCP/IP and OSI model

37. TCP/IP • Transmission Control Protocol/InternetProtocol • A suite of protocols that officially control the Internet. • Physical and data-link layers: Does not define any specific protocol. • Network layer: Supports the Internet Protocol (IP) • Transport layer: Defines Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) • Application layer: Equivalent to the combined session, presentation, and application layers

38. TCP/IP Network layer • Supports the Internet Protocol (IP) • Every computer connected to the Internet is identified by a unique international address – IP address. (32bits) IP addresses in dotted-decimal notation Figure 6-14

39. TCP/IP Transport layer • Defines Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) • TCP is a reliable transport protocol. It divides a message into a sequence of segments that are numbered sequentially. • If one segment is lost, it is sent again. • If a segment is received out of order, it is ordered with the help of the sequence numbering mechanism.

40. TCP/IP Application layer • Equivalent to the combined session, presentation, and application layers of OSI model. • Communication on the Internet uses the client-server model. • Client – an AP running on a local machine. • Server – an AP running on a remote machine.

41. Client-server model

42. FTP • File Transfer Protocol • The standard protocol on the Internet for transferring a file from one machine to another.

43. SMTP(Simple Mail Transfer Protocol) • A user machine that is turned off will not receive email. • POP(Post Office protocol) • UA(user Agent)- a user interface to facilitates these transactions

44. Email address • Local part – user mailbox • Domain name – the computer that serves as the SMTP server

45. TELNET • TErminaL NETwork • A general client-server program on the Internet allows remote login. • Enables the establishment of a connection from a local system to a remote system in such a way that the local terminal appears to be a terminal at the remote system.

46. HTTP • HyperText Transfer Protocol • the underlying protocol used by the World Wide Web. • use a special kind of addressing called URL(Uniform Resource Locator).

47. URL • Method – the client-server program used for transferring the documents. • Host – the computer where the information is located. • Port – the port number of server. • Path – the path of the file where the information is located.

48. WWW • World Wide Web • Hypertext – a document containing special text, words, and phrases that can create a link to other documents. • Page – a document of hypertext available on the web. • Home page

49. Browser Coordinates all activities. Display the document. A client AP that retrieves the document.

50. Categories of Web documents