Chapter 7 Computer Networks the Internet and the

Chapter 7: Computer Networks, the Internet, and the World Wide Web Invitation to Computer Science, Java 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, Java 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, Java 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, Java 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, Java Version, Third Edition 5

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

Figure 7. 2 Modulation of a Carrier to Encode Binary Information Invitation to Computer Science, Java 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 256, 000 bps (256 Kbps) Invitation to Computer Science, Java 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, Java Version, Third Edition 9

Figure 7. 3 Transmission Time of an Image at Different Transmission Speeds Invitation to Computer Science, Java 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, Java 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, Java Version, Third Edition 12

Figure 7. 4 Some Common LAN Topologies Invitation to Computer Science, Java 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, Java Version, Third Edition 14

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

Figure 7. 6 An Ethernet LAN Implemented Using a Hub Invitation to Computer Science, Java 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, Java Version, Third Edition 17

Figure 7. 7 Typical Structure of a Wide Area Network Invitation to Computer Science, Java 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, Java Version, Third Edition 19

Figure 7. 8(a) Structure of a Typical Company Network Invitation to Computer Science, Java 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’s computer to other networks ISPs are hierarchical q Interconnect to each other in multiple layers to provide greater geographical coverage Invitation to Computer Science, Java Version, Third Edition 21

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

Figure 7. 8(c) Hierarchy of Internet Service Providers Invitation to Computer Science, Java 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 2005 n 317 million nodes (hosts) n Hundreds of thousands of separate networks located in over 225 countries Invitation to Computer Science, Java 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, Java Version, Third Edition 25

Figure 7. 10 The Five-Layer TCP/IP Internet Protocol Hierarchy Invitation to Computer Science, Java 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 network devices Details: voltage levels, wavelengths, radio frequencies Note: different specifications for different machines and different mode of communication Invitation to Computer Science, Java Version, Third Edition 27

Data Link Layer n Protocols carry out q q Error handling (detection and correction) Framing - identify the start and stop of a message 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, Java Version, Third Edition 28

Data Link Layer (continued) n Medium access control protocols q Determine how to arbitrate ownership of a shared line when multiple nodes want to send at the same time - collisions are possible. n Possible techniques: a. taking-turns protocols examples: polling and token-passing b. channel partitioning protocols examples: TDM (time-division multiplexing) FDM (frequency-division multiplexing) c. random access protocols (contention based) example: Carrier sense multiple protocol (ethernet) Invitation to Computer Science, Java Version, Third Edition 29

Data Link Layer (continued) n Logical link control protocols q q Ensure that a message traveling across a channel from source to destination arrives correctly How to handle errors? A M(1) B Packet Seq number M(2) ACK(1) Packet ARQ algorithm (automatic repeat request) ERROR M(3) Packet Invitation to Computer Science, Java Version, Third Edition Packet ACK(3) 30

Network Layer (IP protocol) n Delivers a message from the site where it was created to its ultimate destination n Critical responsibilities q q Create a universal addressing scheme for all network nodes Deliver messages between any two nodes in the network (route the packets between two nodes) Invitation to Computer Science, Java Version, Third Edition 31

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, Java Version, Third Edition 32

Network Layer (continued) Router Key concepts Host names example: gordon. edu IP addresses example: 200. 56. 34. 100 Domain name system (DNS) (def) converts a symbolic host name to 32 -bit IP address Routing store and forward & best path Invitation to Computer Science, Java Version, Third Edition 33

Transport Layer n Provides a high-quality, error-free, orderpreserving, 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, Java Version, Third Edition 34

Transport Layer Port: 23 Port: 78 Port: 80 Router Port: 567 Router Host A: 122. 45. 65. 17 Host B: 100. 44. 5 Key Concepts 1. Port Numbers (def) identifies a specific application on a host 2. Well-known port numbers 3. TCP (transport control protocol) requires a handshake and connection setup 4. UDP (user datagram protocol) Invitation to Computer Science, Java Version, Third Edition 35

Logical View of a TCP Connection Invitation to Computer Science, Java Version, Third Edition 36

Application Layer n Implements the end-user services provided by a network n There are many application protocols q HTTP (hypertext transfer protocol) q SMTP (simple mail transfer protocol) q POP 3 q IMAP q FTP (file transfer protocol) Invitation to Computer Science, Java Version, Third Edition 37

Figure 7. 16 Some Popular Application Protocols on the Internet Invitation to Computer Science, Java Version, Third Edition 38

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, Java Version, Third Edition 39

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, Java Version, Third Edition 40

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, Java Version, Third Edition 41

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, Java Version, Third Edition 42

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, Java Version, Third Edition 43

Figure 7. 20 State of Networking in the Late 1980 s Invitation to Computer Science, Java Version, Third Edition 44

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, Java Version, Third Edition 45

Figure 7. 21 Hypertext Documents Invitation to Computer Science, Java Version, Third Edition 46

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, Java Version, Third Edition 47

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, Java Version, Third Edition 48

Summary (continued) 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, Java Version, Third Edition 49