IntroductionTo The Internet and The World Wide Web New Perspectives on THE INTERNET
Objectives In this tutorial you will: • Obtain an overview of the tools and information that are available on the Internet • Learn what computer networks are and how they work • Find out how the Internet and World Wide Web began and grew • Compare and evaluate different methods for connecting to the Internet
Internet and World Wide Web:Amazing Developments • The Internet is a large collection of computers all over the world that are connected to one another in various ways. • It is one of the most amazing technological developments of the 20th century.
Communication Tools and Information Resources on the Internet Figure 1-1
Computer Networks • A network interface card is used to connect a computer to a network of other computers. • A server is any computer that accepts requests from other computers that are connected to it and shares some or all of its resources, such as printers, files, or programs, with those computers.
Client/Server Local Area Networks • The server runs software that coordinates the information flow among other computers called clients. • The software that runs on the server is called a network operating system. • Connecting computers this way is called a client/server network.
Local Area Network A network that works over a relatively short distance (no more than a few thousand feet) is called a local area network (LAN). Figure 1-2
Connecting Computers to a Network • Not all LANs use the same kind of cables to connect their computers. • Twisted-pair cable – oldest cable type used by telephone companies, usually Category 1 • Coaxial cable – 20 times faster than twisted-pair but more expensive • Category 5 twisted-pair – carries signals between 10 and 100 times faster than coaxial cable and easy to install • Fiber-optic cable – transmits pulsing beams of light through very thin strands of glass, very expensive, fastest transmission rate
Connecting Computers to a Network Twisted-Pair, Coaxial, and Fiber-Optic Cables Figure1-3
Wide Area Networks • A wide area network (WAN) is a network of networks or an internet (lowercase “i”). • The word internet is short for interconnected network. • The Internet (capital “I”) is a specific worldwide collection of interconnected networks whose owners have voluntarily agreed to share resources and network connections with one another.
How the Internet Began • The first computer networks were created in the 1950s. • Telephone companies were the models for those early networks because most early WANs used leased telephone company lines to connect computers to each other using circuit switching.
Circuit Switching vs. Packet Switching • Circuit switching – centrally controlled, single-connection method where all data travels along a single path between sender and receiver. Most local telephone traffic today is still handled using circuit switching technologies. • Packet switching – files and messages are broken down into packets that are labeled electronically with codes for their origin and destination. Packets travel from computer to computer along the network until they reach their destination.
Packet Switching • Routers are computers that an individual packet encounters on its trip through the network that determine the best way to move the packet forward to its destination. • Routing algorithms are programs that routers use to determine the best path for the packet. • Packet switching networks are more reliable since they rely on multiple routers instead of central point of control and because each router can send individual packets along the best path.
How the Internet Began • In the early 1960s, the U.S. Department of Defense (DOD) began a research project authorized as a part of national security. • The Defense Advanced Research Projects Agency (DARPA) began examining ways to connect all large mainframe computers to each other and to weapons installations that were distributed all over the world.
How the Internet Began • In 1969, DARPA connected the first computer switches at the University of California at Los Angeles, SRI International, the University of California at Santa Barbara and the University of Utah. This experimental WAN, called the ARPANET, grew over the next three years to include over 20 computers. • ARPANET uses the Network Control Protocol (NCP). A protocol is a collection of rules for formatting, ordering and error-checking data sent across a network.
Open Architecture Philosophy • ARPANET grew steadily over the next several years. • ARPANET adhered to an open architecture philosophy. Each network could continue to use its own protocols and data transmission methods internally but converted to NCP when the data moved out of the local network and onto the ARPANET.
Open Architecture Philosophy Open architecture philosophy includes four key points: • Independent networks should not require any internal changes to be connected to the Internet. • Packets that do not arrive at their destinations must be retransmitted from their source network. • The router computers do not retain information about the packets they handle. • No global control will exist over the network.
Open Architecture Philosophy • New protocols were developed by Vincent Cerf and Robert Kahn. These new protocols were the Transmission Control Protocol and the Internet Protocol (TCP/IP). • TCP includes rules that computers on a network use to establish and break connections. • IP includes rules for routing of individual data packets. • The new protocols were technically superior and replaced NCP protocol. • TCP/IP continues to be used today in LANS and on the Internet. • The term Internet was first used in a 1974 article about the TCP protocol written by Cerf and Kahn.
Birth of E-Mail:A New Use for Networks • In 1972, Ray Tomlinson wrote a program that could send and receive messages over the network. • E-mail became widely used in 1976. • By 1981, the ARPANET included over 200 networks.
More New Uses for Networks Emerge • File Transfer Protocol (FTP) enables users to transfer files between computers. • Telnet lets users log in to their computer accounts from remote sites. • Usenet (User’s News Network) allows anyone that connects with the network to read and post articles on a variety of subjects.
Interconnecting the Networks Networks That Became The Internet Figure 1-4
Commercial Interest Increases • The National Science Foundation originally prohibited commercial traffic on the networks it funded. Businesses turned to commercial e-mail services. • Larger firms build their own TCP/IP-based WANs. • The term intranet describes LANs or WANs that use the TCP/IP protocol but do not connect to sites outside the firm. An intranet that allows selected outside parties to connect is called an extranet.
Commercial Interest Increases • In 1989, the NSF permitted two commercial e-mail services, MCI Mail and CompuServe, to establish limited connections to the Internet. • The ARPANET had grown from 4 computers in 1969 to over 300,000 computers on many interconnected networks by 1990. • The greatest growth in the Internet was yet to come.
Growth of the Internet The FNC’s October 1995 Resolution to Define the Term Internet Figure1-5
From Research Project to Information Infrastructure Growth In The Number Of Internet Hosts Figure 1-6
New Structure for the Internet • The Internet is organized around four network access points (NAPs). • A different company operates each of these NAPs. • These companies sell access to the Internet through their NAPs to organizations and businesses.
New Structure for the Internet Network Access Points On The Internet Backbone Figure 1-7
World Wide Web • Hypertext Markup Language (HTML) is a language that includes a set of codes (or tags) attached to text. These codes describe the relationships among text elements. • A hypertext link, or hyperlink, points to another location in the same or another HTML document. • A Web browser is software that lets users read HTML documents and move one HTML document to another. • HTML documents differ from word-processing documents because they don’t specify how a particular text element will appear.
Hypertext and Graphical User Interfaces Come to the Internet • A Web browser presents an HTML document in an easy-to-read format in its graphical user interface. • A graphical user interface (GUI) is a way of presenting program output using pictures, icons, and other graphical elements instead of just displaying text. • The GUI interface presented in Web browsers has been an important element in the rapid growth of the Web.
The Web and Commercialization of the Internet • Businesses recognized the profit-making potential offered by a worldwide network of easy-to-use computers. • The Netscape Navigator Web browser program, the first Web browser, was an instant success. • Microsoft created its Internet Explorer Web browser shortly thereafter.
The Web and Commercialization of the Internet Growth Of The World Wide Web Figure 1-8
Connection Options • Internet service providers (ISPs) offer connections to large organizations and businesses that, in turn, provide Internet access to other businesses and individuals. • ISPs provide their customers with software needed to connect to the ISP, browse the Web, send and receive e-mail messages, and perform other Internet-related functions.
Connection Options The Hierarchy Of Internet Service Options Figure 1-9
Connection Bandwidth • Bandwidth is the amount of data that can travel through a communications circuit in one second. • The bandwidth that an ISP can offer depends on the type of connection it has to the Internet and the kind of connection you have to the ISP. • The bandwidth for a network connection between two points is always limited to the narrowest bandwidth that exists in any part of the network.
Connection Bandwidth • POTS or plain old telephone service is one way to connect computers by using regular telephone service. POTS provides a maximum bandwidth of between 28.8 Kbps and 56 Kbps. • Digital Subscriber Line (DSL) is a higher grade of service offered by some telephone companies that uses a series of protocols. • Integrated Services Digital Network (ISDN) was the first technology that was developed using a DSL protocol. It offers bandwidths up to 256 Kbps.
Connection Bandwidth • Another new technology using the DSL protocol is Asymmetric Digital Subscriber Line (ADSL). It offers transmission speeds ranging from 16Kbps to 9 Mbps. • T1 and T3 are higher-bandwidth telephone company connections used by businesses and large organizations. These connections are much more expensive than POTS or ISDN connections. Smaller firms can share space on a T1 or T3 line.
Connection Bandwidth • The NAPs currently operate the Internet backbone using a variety of connections. • In addition to T1 and T3 lines, newer connections that have bandwidths of more than 1 Gbps are used. These include connection options numbered OC3 and OC12. OC is short for optical carrier. • NAPs also uses high-bandwidth satellite and radio communications links to transfer data over long distances.
Connection Bandwidth • Connection to the Internet through a cable television company is available in parts of the United States. Data is transmitted over the same cables used to provide television service. Cable can deliver up to 10 Mbps to an individual user. • Another option appealing to users in remote areas is connecting via satellite. Using a satellite-dish receiver, bandwidths of approximately 400 Kbps can be downloaded.
Connection Bandwidth Bandwidths For Various Types Of Internet Connections Figure 1-10
Connecting Through Your School or Employer • Some schools and businesses provide telephone numbers that students or employees can use to connect their computers to the Internet through a modem. • Modem is short for modulator-demodulator. • A modem converts your computer’s digital signals into analog signals that can travel on the telephone system’s wires. A modem at your school or employer converts the analog signal back into a digital signal and sends it through a LAN and a router to the Internet for you.
Connecting Through Your School or Employer • Most schools and employers have an acceptable use policy (AUP) that specifies the conditions under which you can use their Internet connections. • Although accessing the Internet through your school or employer might be the least expensive option, you should carefully consider whether the limitations placed on your use of the Internet are greater than the benefits of the low cost.
Connecting Through an Internet Service Provider When shopping for an ISP, you will want to find information such as: • The monthly base fee and number of hours it provides • The hourly rate for time used over the monthly base amount • Whether the telephone access number is local or long distance • Which specific Internet services are included • What software is included • What user-support services are available
Connecting Through an Internet Service Provider • ISPs provide reliable connectivity at a reasonable price. • The terms of their AUPs are often less restrictive than those imposed by schools or employers. • Some ISPs limit the number of customers they serve. Others guarantee that you will not receive a busy signal when you dial in. • The quality of service might deteriorate over time if the ISP adds many new customers without expanding its bandwidth.
Connecting ThroughYour Cable Television Company • One of the fastest growing means of Internet access is the cable modem. Instead of converting the digital signals into telephone-line analog signals, it converts them into radio-frequency analog signals that are similar to television transmission signals. • The signals travel over the same lines that carry your cable television service. • A line-splitter is used to install a cable modem. This device divides the combined cable signals into their television and data components.
Connecting ThroughYour Cable Television Company • An advantage of cable television connection is its high bandwidth. The downloads may be as much as 170 times faster than a telephone line connection. • The cost is usually higher, sometimes more than double. It may, however, save you the cost of a second telephone line. • Cable connection is not available in all areas. • The shared bandwidth can slow down access speeds significantly.
Connecting Through a DSL Provider • Today, ADSL and other types of DSL connections are referred to as simply DSL. DSL connections are increasingly available in the United States. • Telephone companies and in some locations other companies sell these services. Other companies are called third-party DSL providers, and they lease lines from the local telephone company and resell Internet connection services through those lines.
Connecting Through a DSL Provider • DSL’s speeds are similar to cable modems and the subscription rates are similar. • A drawback for most users is that they are buying the service from their local telephone company or third-party provider. Long delays in installation and repairs have been the experience of many users. • A number of large DSL providers have gone out of business recently because they were unable to deliver the services and make a profit. Many subscribers were left without an Internet connection for months.
Connecting Via Satellite • People in rural areas that do not have cable television service often buy satellite receivers to obtain television signals. • Recently, Internet connections via satellite became available. • Some services provide satellite connection for downlinks only, so another connection through an ISP that uses telephone lines to handle the uplink was necessary. • Two companies have recently started offering satellite connections that are two-way.
Connecting Via Satellite • These services offer speeds and charge monthly fees similar to those of cable and DSL providers. • The installation fee is usually considerably higher. The dish must be installed and aimed at a satellite, tasks that often require the skills of a professional installer.