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Chapter 6

Chapter 6. Computer Networks. O BJECTIVES. Distinguish between the three types of networks: LANs , MANs , and WANs. List different connecting devices and the OSI layers in which each device operates. Understand client-server models. Understand the OSI model and TCP/IP.

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Chapter 6

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  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 information is 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. 6.3 CATEGORIES OF NETWORKS

  12. Categories of networks Figure 6-3

  13. 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

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

  15. MAN Figure 6-5

  16. 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.

  17. WAN Figure 6-6

  18. 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

  19. 6.4 CONNECTING DEVICES

  20. Figure 6-7 Connecting devices

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

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

  23. 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.

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

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

  26. Figure 6-10 Switch

  27. 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.

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

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

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

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

  32. 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。

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