- Количество слайдов: 47
Using the Internet
Objectives • Learn about the many systems that use the Internet for communication. • Examine the organization of the Internet infrastructure. • Investigate Internet service providers, and learn how to select one.
The Internet and Systems That Use It • The Internet is many networks connected together, all of which use the same method of communication. • The beginnings of the Internet occurred in 1969 when the Advanced Research Projects Agency (ARPA), charged with developing an internet work that could withstand nuclear attacks on the United States, connected two university networks to create a network called the Advanced Research Projects Agency Network (ARPANET).
The Internet and Systems That Use It (Continued) • A protocol is a language or a set of rules for communication, and the Internet uses many different protocols in many different situations. • The Internet is a public network made up of hundreds of thousands of private networks that can also communicate using these same protocols. • These private networks that use the same protocols, standards, and equipment as the Internet are called intranets.
The World Wide Web • The World Wide Web (WWW or W 3) is a collection of interconnected information that is stored on computers all around the world. • A Web browser is software designed to display files available on the Web to the user. • Most of the information on the World Wide Web is stored in files that are formatted using Hypertext Markup Language (HTML). • Essentially, HTML is a set of codes that are included in the text describing how the text should be displayed or printed.
The World Wide Web (Continued) • Files that include HTML code are called hypertext, hypertext files, hypertext documents, Web pages, or simply pages. • Web communication and standards of HTML are controlled and monitored by the World Wide Web Consortium (W 3 C), an organization made up of private, educational, and governmental organizations from around the world. • The software that receives the request from the browser is called a Web server, and the computer that is running the Web server is called a server.
The World Wide Web (Continued) • A Web site is a group of Web pages and related text, databases, graphics, audio, and video files that are served up by a Web server to present information. • The first publicly available Web browser that could display graphics was Mosaic, released in 1993 by the National Center for Supercomputing Applications (NCSA) at the University of Illinois. • Today, the most popular Web browser is Microsoft Internet Explorer, distributed by Microsoft.
Using Web Browsers • A URL (Uniform Resource Locator) is an address for a Web page file or other resource on the Internet. • The first part of the URL stands for Hypertext Transfer Protocol. http: // www. csudh. edu/cis 275/first. htm
Using Web Browsers (Continued) • Domain names are easy for humans to remember and use, but the devices on the Internet rely on numeric addresses to identify every host on every network that is connected directly to the Internet. • Such a numeric address is called an IP address (Internet Protocol address). • A group of controlling protocols is called TCP/IP (Transmission Control Protocol/Internet Protocol), and sometimes is called a protocol stack.
Microsoft Internet Explorer • Microsoft Internet Explorer was first introduced in October 1995, and is included in Windows XP and other Windows operating systems. • Some people still use earlier versions of the software because of the overhead associated with the later versions. • Overhead is the amount of system resources required by the software to function, such as space on the hard drive and computing power.
Microsoft Internet Explorer (Continued) • Internet Explorer is holding the Web pages in a temporary Internet folder on your hard drive called a cache, and can display them without having to go back to the Web server to download again.
Auto. Complete Feature • Internet Explorer keeps track of the URLs you enter in the Address bar. • Internet Explorer also keeps track of data you enter in data-entry forms on Web pages, to make it easy for you to reenter the same data at a later time. • To customize Auto. Complete, follow the directions for Windows XP as illustrated on pages 10 and 11 of the text.
Saving Files on the Web to a Floppy Disk or Hard Disk • Sometimes, it’s helpful to save a Web page to a floppy disk or a folder on your hard drive other than the browser cache folder. • To save a Web file on a floppy disk, use the directions on pages 14 and 15 of the text. • Also follow the directions on page 15 when you want to view a page that you previously saved to a floppy disk.
Limiting the Content Available to a Browser • Internet Explorer 5 and higher versions support the World Wide Web Consortium’s specifications for content selection, called the Platform for Internet Content Selection (PICS). • These specifications allow parents and other responsible individuals (such as employers and educators) to limit the content available to a browser. • PICS is a voluntary rating system in which Web developers assign their site a rating based on language, nudity, sex, and violence.
Introducing HTML • HTML is a subset of the Standard Generalized Markup Language (SGML), a standard developed in 1986 to retain formatting and linking information in a document as it is moved from one computer or software application to another. • An HTML file is sometimes called hypertext, a hypertext file, a hypertext document, a Web page, or a page. • A tag is special HTML or SGML code in a text file that controls how certain parts of the text are to be formatted.
Introducing HTML (Continued) • Some possible formatting options include boldface, underlining, and indentations. • A tag is read by, or interpreted by, the browser as it displays an HTML page. • Tags also can be used as links to point to other Web pages.
Web Pages Built with Frames • Frames allow a Web site designer to display different information in two or more separate areas of the screen. • More than one Web page can be displayed on the same screen, each in its own frame.
Hyperlinks • A Web page often contains a text or graphic that you can click to jump to some other place in the same document or to a different Web page. • This text or graphic is called a hyperlink, a hot link, or simply a link.
Search Engine Web Sites • Search engine Web sites are devoted to the purpose of helping users find information anywhere on the Web. • A subject directory gets information from someone manually entering the data into a database. • A spider search engine searches Web sites all over the Web to get information for its database.
Search Engine Web Sites (Continued) • A meta search engine gets information from databases on other search engine sites. • A spider search engine gets data by using automated search engine software called a spider, robot, or a Web crawler. • This software independently searches the entire Web for keywords in Web sites.
Search Engine Web Sites (Continued) • Meta tags are tags that contain information about the Web page content. • Meta tags can include information about the author of the Web page, the software used to build it, the date and time it was built, information used by PICS, and so forth. • A meta tag included on the page specifically for a spider or Web robot to find and use is called a meta robot tag.
Searching an Individual Web Site • The Web site show in Figure 1 -18 includes a Search box. • This Search box might link to another Web site, but many times a search utility searches only the current site. • Several ways to search a site are summarized in the following list. – Find – Static index – Full text index – Site map – Keyword index
Search Engines • A search engine is used as a software application to search for words in documents or in a database. • A search engine like Google at www. google. com is used by hundreds of thousands of people everyday to find useful information on the Web. • Google has quickly become the most popular search engine on the Web.
Using Search Boxes Effectively • When using search utilities on the Web, knowing how to use Search boxes effectively can make your work easier. • The expressions AND, OR, NOT, and NEAR can be used to narrow a search and the keywords lost, link, title, and image can make your searches more powerful. • Table 1 -2 lists explanations and examples of each.
Evaluating Good Design • The following list describes some guidelines to use when evaluating the overall design of a Web site. – The very best Web sites are shortcuts. – The Web site should create the feeling of community. – Web sites should have a user-friendly home page that loads quickly, gets the user’s attention, and clearly presents what is found on the site. – The remainder of this list appears on page 30 of the text.
Web Sites That Help You Evaluate and Design Web Sites • Some Web sites that can help you evaluate other sites and design your own site are: – builder. com by CNET – www. developer. com by Earth Web – www. wpdfd. com by Joe Gillespie – www. colin. mackenzie. org by Colin Mackenzie – The list is continued on page 30 of the text.
Sending and Receiving E-Mail • E-mail is a method for sending a text message or a file to an individual or group of individuals via the Internet. • Internet e-mail addresses have three parts: the user name, the @ symbol, and the name of the mail server that receives and then delivers the message. • E-mail consists of four components: the sending client, sending server, receiving server, and receiving client.
Chat Rooms • A chat room is a data communications link that several people share for text transmissions in real time. • Real-time communication occurs when people type messages to each other and instantly receive a response. • Chat rooms use an application called Internet Relay Chat (IRC), originally written by Jarkko Oikarinen, that, like e-mail and the World Wide Web, uses the client/server method.
Chat Rooms (Continued) • Another real-time communication technology called instant messaging is based upon the chat room concept. • Instant messaging does not use IRC, but instead uses proprietary software that users must install onto their computers.
Newsgroups • A newsgroup is a service on the Internet or on a private network that allows a group of people to post articles and respond to those articles, so information can be shared among the members of the group. • A newsgroup can be private or public. • It might have a subscription fee, such as the newsgroups of Clari. Net, a commercial newsgroup organization whose main contributor is United Press International.
Newsgroups (Continued) • An ISP can subscribe to Clari. Net for a fee, and then can control access to this newsgroup. • Another example of a newsgroup service is Usenet, which consists of thousands of free newsgroups that circulate over the Internet. • Usenet is the most popular newsgroup service.
A Brief History of the Internet • The Internet came into existence in 1969 when Advanced Research Projects Agency (ARPA) connected the computers of four major universities in the United States (UCLA, Stanford, UC Santa Barbara, and the University of Utah). • Until the late 1980 s, it was a loosely organized group of interconnected networks that were used predominantly by major academic institutions in the United States for research and development.
A Brief History of the Internet (Continued) • In 1986, the National Science Foundation (NSF) formed its network called NSFnet to connect five of these major academic institutions, which were spread from the East Coast to the West Coast: New York, New Jersey, Pennsylvania, Illinois, and California. • Because NSFnet connected smaller networks to each other, it was called a backbone network.
Network Access Points (NAPs) • A NAP is a major Internet connection point that is used to connect and route traffic between smaller commercial backbones.
Internet Service Providers (ISPs) • An Internet service provider (ISP) is a business that provides connectivity to the Internet. • ISPs can be a small business that provides connectivity in only one city, or a large company with access points in many cities and countries.
Services Offered by an ISP • The primary purpose of an ISP is to provide access to the Internet. • To connect to the Internet, a computer needs a physical connection to the ISP, software to communicate over the Internet, and an address so others on the Internet can identify the computer. • To connect to an ISP, a computer must be using an operating system that supports the communication protocol of the Internet, which is TCP/IP.
Services Offered by an ISP (Continued) • Windows XP, Windows 2000, Windows 98, Windows 95, Windows Me, Windows NT, Linux, and the Macintosh operating system all support TCP/IP. • The final thing needed to connect to the Internet is an Internet address so the computer can be identified on the Internet.
Ways to Connect to an ISP • Regular telephone lines are the most common way for an individual to connect to an ISP. • In addition, two competing high-speed methods are available. • Both were introduced to the marketplace at about the same time, cost about the same, and attain about the same speeds. • These two methods are DSL lines and cable modems.
How an Internet Service Provider Works • After you connect to an ISP by cable modem, DSL, or telephone line, the ISP connects you to the Internet. • The ISP’s equipment can be very simple or complex, depending on the ISP’s size. • Figure 1 -36 shows an example of how a small ISP might connect to the Internet. • A local area network (LAN) is a group of computers and other devices networked together that is confined to a small area, such as one building.
How an Internet Service Provider Works (Continued) • A router is a device that connects two or more networks and can intelligently make decisions about the best way to route data over these networks. • The two networks in Figure 1 -36 are the ISP’s LAN and the regional ISP’s network. • This regional network is an example of a wide area network (WAN), a network that covers a large geographical area and might use a number of communications technologies.
How an Internet Service Provider Works (Continued) • Before data gets onto a T 1 line, it must be cleaned and formatted by a device called a CSU/DSU, which is really two devices in one. • The Channel Service Unit (CSU) acts as a safe electrical buffer between the LAN and a public network accessed by the T 1 line. • A Digital Service Unit or Data Service Unit (DSU) ensures that the data is formatted correctly before it’s allowed on the T 1 line.
How an Internet Service Provider Works (Continued)
What You Can Expect from an ISP • An ISP is expected to offer access to the World Wide Web, e-mail services, and possibly FTP services. • Some offer chat room and newsgroup services, as well as some space for a personal Web site.
Point of Presence • A small ISP might have only local telephone number that you can dial for access, but some larger ISPs have local telephone numbers in many major cities and other countries. • A POP (point of presence) is a connection point to the Internet, either a telephone number you can call to access your ISP or an IP address provided by your ISP.
Performance, Price, and Service • It goes without saying that performance, price, and service are three important factors to consider when selecting an ISP • An ISP should have a technical support desk available in the evenings, on weekends, and on holidays. • Another important service is the ability to access your e-mail from a Web site in the event you need to check your mail from someone else’s computer.
Summary • The Internet is a group of networks that encircle the entire globe. • The client/server concept works like this: Client software on one computer requests information from server software that is on another computer. • Web pages are written as hypertext documents using HTML, and are transmitted on the Internet using HTTP. • A search engine is software used to search a Web site, a group of sites, or the entire World Wide Web.
Summary (Continued) • A Web search site such as Google gets information by spiders or robots that search Web sites. • Most individuals and small companies use an Internet service provider (ISP) to connect to the Internet by way of regular telephone lines, DSL lines, or cable modems. • An ISP most often provides e-mail, World Wide Web, chat room, newsgroups, and FTP services.