Invitation to Computer Science 6 th Edition

1. Invitation to Computer Science 6thEdition Chapter 7 Computer Networks, the Internet, and the World Wide Web

2. Objectives In this chapter, you will learn about: • Basic networking concepts • Communication links • Computer Networks • Communication protocols • Network services and benefits • The Internet and the World Wide Web Invitation to Computer Science, 6th Edition

3. Introduction • Networking • Might foster growth of democracy and global understanding • Can equalize access to information and eliminate the concept of “information haves” and “information have-nots” Invitation to Computer Science, 6th Edition 3

4. Basic Networking Concepts • Computer network • Set of independent computer systems connected by telecommunication links • Individual computers on the network • Referred to as nodes, hosts, or end systems Invitation to Computer Science, 6th Edition 4

5. Communication Links • In early days of networking: • Most common way to transmit data was via switched, dial-up telephone lines • Transmission rate: 56,000 bps (56 Kbps) • Voice-oriented dial-up telephone network • Originally a totally analog medium • Modem • Modulates, or alters, a standard analog signal called a carrier so that it encodes binary information Invitation to Computer Science, 6th Edition

6. Figure 7.1 Two Forms of Information Representation Invitation to Computer Science, 6th Edition

7. Figure 7.2 Modulation of a Carrier to Encode Binary Information Invitation to Computer Science, 6th Edition

8. Communication Links (continued) • Broadband • Has rapidly been replacing modems and analog phone lines for data communications • Transmission rate: Exceeding 256,000 bps (256 Kbps) • kilobit (kbit) 210 • megabit (Mbit) 220 • gigabit (Gbit) 230 • terabit (Tbit) 240 Invitation to Computer Science, 6th Edition

9. Communication Links (continued) • Options for broadband communications • Home use • Digital subscriber line (DSL), asymmetric, • Cable modem • Commercial and office environment • Ethernet • Fast Ethernet • Gigabit Ethernet Invitation to Computer Science, 6th Edition

10. Communication Links (continued) • Digital subscriber line • Provided by either your local telephone company or someone certified to act as their intermediary • Asymmetric digital subscriber • Does not have the same transmission speed in the download direction as in the upload direction • Cable modem • Makes use of links that deliver cable TV signals into your home • Offered by cable TV providers Invitation to Computer Science, 6th Edition

11. Communication Links (continued) • Ethernet (commercial and office) • Designed to operate at 10 Mbps using coaxial cable • Fast Ethernet • Transmits at 100 Mbps across coaxial cable, fiber-optic cable, or regular twisted-pair copper wire • Gigabit networking • Transmission lines that support speeds in excess of 1 billion bits per second (Gbps) Invitation to Computer Science, 6th Edition

12. Communication Links (continued) • Ten-gigabit Ethernetstandard • Version of Ethernet with data rate of 10 billion bits per second • Adopted by IEEE in 2003 Figure 7.3 Transmission Time of an Image at Different Transmission Speeds Invitation to Computer Science, 6th Edition

13. Communication Links (continued) • Wireless data communication • Uses radio, microwave, and infrared signals • Enables “mobile computing” • Types of wireless data communication • Wireless local access network • Wireless wide-area access network Invitation to Computer Science, 6th Edition

14. Communication Links (continued) • Wireless local access network • User transmits from his or her computer to a local wireless base station • Wi-Fi (Wireless Fidelity) • Used to connect a computer to the Internet when it is within range of a wireless base station • Metropolitan Wireless Local Access Network • Routers provide convenient, low cost wireless Internet access to all residents Invitation to Computer Science, 6th Edition

15. Communication Links (continued) • Bluetooth • Often used to support communication between wireless computer peripherals • Wireless wide area access network • Computer transmits messages to a remote base station provided by a telecommunications company • 3G • Offers voice services as well as data communication at rates of 0.5 to 2.4 Mbps Invitation to Computer Science, 6th Edition

16. Computer Networks • Local area network (LAN) • Connects hardware devices such as computers, printers, and storage devices that are all in close proximity • The owner of the devices is also the owner of the means of communications • Common wired LAN topologies • Bus • Ring • Star Invitation to Computer Science, 6th Edition

17. Computer Networks • Bustopology • All nodes are connected to a single shared communication line • Ringtopology • Connects the network nodes in a circular fashion • Star topology • A single central node that is connected to all other sites Invitation to Computer Science, 6th Edition

18. Figure 7.4 Some Common LAN Topologies Invitation to Computer Science, 6th Edition

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20. Computer Networks (continued) • Ethernet • Most widely used LAN technology • Uses the bus topology • Two ways to construct an Ethernet LAN • Shared cable • Switch: The most widely used technology Invitation to Computer Science, 6th Edition

21. Computer Networks (continued) • Shared cable • A wire is strung around and through a building • Users tap into the cable at its nearest point using a transceiver • Repeater • Device that simply amplifies and forwards a signal • Bridge (switch) • “Smarter” device that has knowledge about the nodes located on each separate network • It examines every message to see if it should be forwarded Invitation to Computer Science, 6th Edition

22. Figure 7.5 An Ethernet LAN Implemented Using Shared Cables Invitation to Computer Science, 6th Edition

23. Local Area Networks (continued) • Switch • Located in a room called a wiring closet • Contains a number of ports, with a wire leading from each port to an Ethernet interface Invitation to Computer Science, 6th Edition

24. Figure 7.6 An Ethernet LAN Implemented Using a Switch Invitation to Computer Science, 6th Edition

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27. Computer Networks • Wide area network (WAN) • Connects devices that are not in close proximity but rather are across town, across the country, or across the ocean • Users must purchase telecommunications services from an external provider • Dedicated point-to-point lines • Most use a store-and-forward, packet-switched technology to deliver messages Invitation to Computer Science, 6th Edition

28. Computer Networks • Packet • Information block with a fixed maximum size that is transmitted through the network as a single unit Figure 7.7 Typical Structure of a Wide Area Network Invitation to Computer Science, 6th Edition

29. Overall Structure of the Internet • All real-world networks, including the Internet, are a mix of LANs and WANs • Example: A company or a college • One or more LANs connecting its local computers • Individual LANs interconnected into a wide-area company network Invitation to Computer Science, 6th Edition

30. Figure 7.8(a) Structure of a Typical Company Network Invitation to Computer Science, 6th Edition

31. Overall Structure of the Internet • Individual networks are interconnected via a device called a router • Internet Service Provider (ISP) • A wide-area network • Provides a pathway from a specific network to other networks, or from an individual’s computer to other networks • ISPs are hierarchical • Interconnect to each other in multiple layers to provide greater geographical coverage Invitation to Computer Science, 6th Edition

32. Figure 7.8(b) Structure of a Network Using an ISP Invitation to Computer Science, 6th Edition

33. Figure 7.8(c) Hierarchy of Internet Service Providers Invitation to Computer Science, 6th Edition

34. Overall Structure of the Internet (continued) • International ISP • Also called tier-1 network or an Internet backbone • Provides global coverage • Internet • Huge interconnected “network of networks” that includes nodes, LANs, WANs, bridges, routers, and multiple levels of ISPs • Early 2011 • 818 million nodes • Hundreds of thousands of separate networks located in over 230 countries Invitation to Computer Science, 6th Edition

35. Communication Protocols • Protocol • Mutually agreed upon set of rules, conventions, and agreements for the efficient and orderly exchange of information • Internet Society • Nonprofit, nongovernmental, professional society composed of more than 100 worldwide organizations • Internet protocol hierarchy • Also called a protocol stack • Has five layers Invitation to Computer Science, 6th Edition

36. Figure 7.10 The Five-Layer TCP/IP Internet Protocol Hierarchy Invitation to Computer Science, 6th Edition

37. Why need layers? • The layered concept of networking was developed to accommodate changes in technology. Each layer of a specific network model may be responsible for a different function of the network. Each layer will pass information up and down to the next subsequent layer as data is processed. Invitation to Computer Science, Java Version, Third Edition

38. Physical Layer • Physical layer protocols • Govern the exchange of binary digits across a physical communication channel • Goal of the physical layer • To create a “bit pipe” between two computers Invitation to Computer Science, 6th Edition

39. Figure 7.11 The Concept of a Bit Pipe Invitation to Computer Science, 6th Edition

40. Data Link Layer • Error detection and correction problem • How do we detect when errors occur, and how do we correct them? • Framing problem • Identifying the start and end of a message • Data link protocols (layer 2a, layer 2b) • Address and solve error handling and framing • Medium access control protocols (layer 2a) • Determine how to arbitrate ownership of a shared line when multiple nodes want to send messages at the same time Invitation to Computer Science, 6th Edition

41. Figure 7.12 The Medium Access Control Protocols in Ethernet Invitation to Computer Science, 6th Edition

42. Data Link Layer (continued) • Collision • Two or more messages transmitted at exactly the same time • Common occurrence in contention-based networks like Ethernet • Layer 2b logical link control protocols • Ensure that message traveling across this channel from source to destination arrives correctly • ARQ algorithm • Basis for all data link control protocols in current use Invitation to Computer Science, 6th Edition

43. Figure 7.13 A Message Packet Sent by the Data Link Protocols Invitation to Computer Science, 6th Edition

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45. Network Layer • Network layerprotocols • Deliver message from the site where it was created to its ultimate destination • Responsibilities of the network layer • Creating a universal addressing scheme for all network nodes • Delivering messages between any two nodes in the network Invitation to Computer Science, 6th Edition

46. Network Layer (continued) • Provides a true network delivery service • Messages are delivered between any two nodes in the network, regardless of where they are located • IP (Internet Protocol) layer • Network layer in the Internet Invitation to Computer Science, Java Version, Third Edition

47. Network Layer (continued) • Nodes identify each other using a 32-bit IP address • Domain Name System (DNS) • Converts from a symbolic host name such as macalester.edu to its 32-bit IP address 141.140.1.5 • Local name server • Checks to see if it has data record containing a specific IP address Invitation to Computer Science, 6th Edition

48. Network Layer (continued) • Routing • Process of selecting one specific path • Shortest path • Path via which message can travel the fastest Invitation to Computer Science, 6th Edition

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