Chapter 7 Computer Networks the Internet and the

Chapter 7: Computer Networks, the Internet, and the World Wide Web Invitation to Computer Science, C++ Version, Third Edition

Objectives In this chapter, you will learn about: n Basic networking concepts n Communication protocols n Network services and benefits n A brief history of the Internet and the World Wide Web Invitation to Computer Science, C++ Version, Third Edition 2

Introduction n Computer network q Computers connected together q Purpose: exchanging resources and information q Just about any kind of information can be sent n Examples: television and radio signals, voice, graphics, handwriting, photographs, movies Invitation to Computer Science, C++ Version, Third Edition 3

Basic Networking Concepts n Computer network q q n Set of independent computer systems connected by telecommunication links Purpose: sharing information and resources Nodes, hosts, or end systems q Individual computers on a network Invitation to Computer Science, C++ Version, Third Edition 4

Communication Links n Switched, dial-up telephone line q q q A circuit is temporarily established between the caller and callee Analog medium Requires modem at both ends to transmit information produced by a computer n Computer produces digital information Invitation to Computer Science, C++ Version, Third Edition 5

Figure 7. 1 Two Forms of Information Representation Invitation to Computer Science, C++ Version, Third Edition 6

Figure 7. 2 Modulation of a Carrier to Encode Binary Information Invitation to Computer Science, C++ Version, Third Edition 7

Communication Links (continued) n Dial-up phone links q n Transmission rate: 56, 000 bps (56 Kbps) Broadband q Transmission rate: exceeding 128, 000 bps (128 Kbps) Invitation to Computer Science, C++ Version, Third Edition 8

Communication Links (continued) n Options for broadband communications q q Home use n Digital subscriber line (DSL) n Cable modem Commercial and office environment n Ethernet n Fast Ethernet n Gigabit Ethernet Invitation to Computer Science, C++ Version, Third Edition 9

Figure 7. 3 Transmission Time of an Image at Different Transmission Speeds Invitation to Computer Science, C++ Version, Third Edition 10

Communication Links (continued) n Wireless data communication q Uses radio, microwave, and infrared signals q Enables “mobile computing” q Types of wireless data communication n Wireless local access network n Wireless wide-area access network Invitation to Computer Science, C++ Version, Third Edition 11

Local Area Networks n Local area network (LAN) q q q Connects hardware devices that are in close proximity The owner of the devices is also the owner of the means of communications Common wired LAN topologies n Bus n Ring n Star Invitation to Computer Science, C++ Version, Third Edition 12

Figure 7. 4 Some Common LAN Topologies Invitation to Computer Science, C++ Version, Third Edition 13

Local Area Networks (continued) n Ethernet q Most widely used LAN technology q Uses the bus topology q Two ways to construct an Ethernet LAN n Shared cable n Hubs: the most widely used technology Invitation to Computer Science, C++ Version, Third Edition 14

Figure 7. 5: An Ethernet LAN Implemented Using Shared Cables Invitation to Computer Science, C++ Version, Third Edition 15

Figure 7. 6 An Ethernet LAN Implemented Using a Hub Invitation to Computer Science, C++ Version, Third Edition 16

Wide Area Networks n Wide area networks (WANs) q q Connect devices that 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, C++ Version, Third Edition 17

Figure 7. 7 Typical Structure of a Wide Area Network Invitation to Computer Science, C++ Version, Third Edition 18

Overall Structure of the Internet n All real-world networks, including the Internet, are a mix of LANs and WANs q Example: a company or a college n One or more LANs connecting its local computers n Individual LANs interconnected into a wide-area “company network” Invitation to Computer Science, C++ Version, Third Edition 19

Figure 7. 8(a) Structure of a Typical Company Network Invitation to Computer Science, C++ Version, Third Edition 20

Overall Structure of the Internet (continued) n Internet Service Provider (ISP) q q n A wide-area network Provides a pathway from a specific network to other networks, or from an individual to other networks ISPs are hierarchical q Interconnect to each other in multiple layers to provide greater geographical coverage Invitation to Computer Science, C++ Version, Third Edition 21

Figure 7. 8(b) Structure of a Network Using an ISP Invitation to Computer Science, C++ Version, Third Edition 22

Figure 7. 8(c) Hierarchy of Internet Service Providers Invitation to Computer Science, C++ Version, Third Edition 23

Overall Structure of the Internet (continued) n Internet q q q A huge interconnected “network of networks” Includes nodes, LANs, WANs, bridges, routers, and multiple levels of ISPs Early 2003 n 170 million nodes (hosts) n Hundreds of thousands of separate networks located in over 225 countries Invitation to Computer Science, C++ Version, Third Edition 24

Communication Protocols n A protocol q n A mutually agreed upon set of rules, conventions, and agreements for the efficient and orderly exchange of information TCP/IP q The Internet protocol hierarchy q Governs the operation of the Internet q Five layers Invitation to Computer Science, C++ Version, Third Edition 25

Figure 7. 10 The Five-Layer TCP/IP Internet Protocol Hierarchy Invitation to Computer Science, C++ Version, Third Edition 26

Physical Layer n Protocols govern the exchange of binary digits across a physical communication channel n Goal: create a “bit pipe” between two computers Invitation to Computer Science, C++ Version, Third Edition 27

Data Link Layer n Protocols carry out q Error handling q Framing n Creates an error-free “message pipe” n Composed of two services q Layer 2 a: medium access control q Layer 2 b: logical link control Invitation to Computer Science, C++ Version, Third Edition 28

Data Link Layer (continued) n Medium access control protocols q n Determine how to arbitrate ownership of a shared line when multiple nodes want to send at the same time Logical link control protocols q Ensure that a message traveling across a channel from source to destination arrives correctly Invitation to Computer Science, C++ Version, Third Edition 29

Network Layer n Delivers a message from the site where it was created to its ultimate destination n Critical responsibilities q q Creating a universal addressing scheme for all network nodes Delivering messages between any two nodes in the network Invitation to Computer Science, C++ Version, Third Edition 30

Network Layer (continued) n Provides a true “network delivery service” q n Messages are delivered between any two nodes in the network, regardless of where they are located IP (Internet Protocol) layer q Network layer in the Internet Invitation to Computer Science, C++ Version, Third Edition 31

Transport Layer n Provides a high-quality, error-free, order preserving end-to-end delivery service n TCP (Transport Control Protocol) q q Primary transport protocol on the Internet Requires the source and destination programs to initially establish a connection Invitation to Computer Science, C++ Version, Third Edition 32

Figure 7. 15 Logical View of a TCP Connection Invitation to Computer Science, C++ Version, Third Edition 33

Application Layer n Implements the end-user services provided by a network n There are many application protocols, including: q HTTP q SMTP q POP 3 q IMAP q FTP Invitation to Computer Science, C++ Version, Third Edition 34

Figure 7. 16 Some Popular Application Protocols on the Internet Invitation to Computer Science, C++ Version, Third Edition 35

Application Layer (continued) n Uniform Resource Locator (URL) q A symbolic string that identifies a Web page q Form protocol: //host address/page q The most common Web page format is hypertext information n Accessed using the HTTP protocol Invitation to Computer Science, C++ Version, Third Edition 36

Network Services and Benefits n Services offered by computer networks q Electronic mail (email) q Bulletin boards q News groups q Chat rooms q Resource sharing n Physical resources n Logical resources Invitation to Computer Science, C++ Version, Third Edition 37

Network Services and Benefits (continued) n Services offered by computer networks q Client-server computing q Information sharing q Information utility q Electronic commerce (e-commerce) Invitation to Computer Science, C++ Version, Third Edition 38

A Brief History of the Internet and the World Wide Web: The Internet n August 1962: first proposal for building a computer network q n Made by J. C. R. Licklider of MIT ARPANET q q Built by the Advanced Research Projects Agency (ARPA) in the 1960 s Grew quickly during the early 1970 s Invitation to Computer Science, C++ Version, Third Edition 39

The Internet (continued) n NSFNet: A national network built by the National Science Foundation (NSF) n October 24, 1995: Formal acceptance of the term “Internet” n Internet service providers start offering Internet access once provided by the ARPANET and NSFNet Invitation to Computer Science, C++ Version, Third Edition 40

Figure 7. 20 State of Networking in the Late 1980 s Invitation to Computer Science, C++ Version, Third Edition 41

The World Wide Web n Development completed in May 1991 n Designed and built by Tim Berners-Lee n Components q Hypertext n q A collection of documents interconnected by pointers called links URL (Uniform Resource Locator) n The worldwide identification of a Web page located on a specific host computer Invitation to Computer Science, C++ Version, Third Edition 42

Figure 7. 21 Hypertext Documents Invitation to Computer Science, C++ Version, Third Edition 43

Summary of Level 3 n Virtual environment q q q Created by system software Easy to use and easy to understand Provides services such as: n n n Resource management Security Access control Efficient resource use Operating systems continue to evolve Invitation to Computer Science, C++ Version, Third Edition 44

Summary n Computer network: a set of independent computer systems connected by telecommunication links n Options for transmitting data on a network: dialup telephone lines, DSL, cable modem, Ethernet, Fast Ethernet n Types of networks: local area network (LAN) and wide area network (WAN) Invitation to Computer Science, C++ Version, Third Edition 45

Summary n The Internet is a huge interconnected "network of networks" n TCP/IP is the Internet protocol hierarchy, composed of five layers: physical, data link, network, transport, and application n The World Wide Web is an information system based on the concept of hypertext Invitation to Computer Science, C++ Version, Third Edition 46