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<HTML><HEAD><TITLE>Chapter 6 -- How Intranet Web Servers and Browsers Work </TITLE><META></HEAD><BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000EE" VLINK="#551A8B" ALINK="#CE2910"><H1><FONT SIZE=6 COLOR=#FF0000>Chapter 6</FONT></H1><H1><FONT SIZE=6 COLOR=#FF0000>How Intranet Web Servers and BrowsersWork </FONT></H1><HR><P><CENTER><B><FONT SIZE=5><A NAME="CONTENTS">CONTENTS</A></FONT></B></CENTER><UL><LI><A HREF="#HowIntranetWebsWork">How Intranet Webs Work</A></UL><HR><P>Without the World Wide Web, there would probably be very few intranets.There are many forces driving corporations to set up an intranet,but the main one is the dominating presence of the World WideWeb. The Web has made it possible for companies to better communicatevital information among employees, departments, and divisions;to better communicate with customers; and to make it easy forthose within a company to get at the vast resources often lockedup in corporate databases and information centers.<P>The Web makes it easy to publish information because each Webpage allows people to incorporate text, graphics, sound, animation,and other multimedia elements. In essence, each page is an interactivemultimedia publication. This means that a company can easily publishsimple documents such as personnel handbooks or expense reports.They can also create sophisticated pages that let people do morethan just read a corporate annual report, and also let them seevideos of the company in action or listen to speeches by corporateofficers. The page at the top (or entrance to a site) is calleda home page.<P>The Web is also a powerful intranet tool because of the way itcan link corporate home pages to one another. <I>Hypertext</I>links any home page to any other home page, and to graphics, binaryfiles, multimedia files, and any Internet or intranet resource.To jump to one home page from another, you merely click on a linkon a home page, and you'll automatically be sent there. It iseasy to create documents that allow employees to find specificcompany information and related material quickly.<P>The Web uses client/server architecture to work. To access theWeb, a client uses a Web browser program. Clients are availablefor all common types of computers, including PCs, Macintoshes,and UNIX workstations. Popular browsers include Netscape and Microsoft'sInternet Explorer. The client/server model works well for an intranet,since it allows many different kinds of clients on different computersto be run, and yet the same corporate resources can be made availableto all clients from the same servers. The operating system ofa server need not be the same as the operating system of a browser.Popular operating systems for servers include UNIX and WindowsNT.<P>Corporations often standardize on a particular browser such asNetscape or Internet Explorer, so that everyone on an intranetwill use the same kind of browser. This is done because the languageof the Web-the Hypertext Markup Language-has not been truly standardized.Additionally, each browser has slightly different capabilities,so pages designed for one browser may not display very well inanother browser.<P>Home pages on an intranet (and the Internet) are built using apage markup language called HTML (Hypertext Markup Language).This specialized language contains commands that tell browsershow to display text, graphics, and multimedia files. It also containscommands for linking the home page to other home pages, and toother Internet resources. HTML is a constantly evolving language,and with each new generation it gets additional capabilities.While there are HTML standards, there are also variations on thelanguage, so those who build intranets have to be careful to useHTML commands that their company's standard intranet browser willeasily understand.<P>It's the browser's job to contact Web servers, receive HTML pages,and then interpret and display those pages. Web locations on anintranet are specified by URLs-uniform resource locators. Youtype in the URL in your browser, or click on a link in order tonavigate to a particular Web page. The packets making up the requestare sent to an intranet router, which checks the destination address,and then routes the request to the proper server. <P>When you type in the URL, the Web browser looks at the URL andthen determines which server to contact, which directory to askfor, and what specific document in that directory is the one thatyou want. It then uses HTTP (Hypertext Transfer Protocol) to contactthe Web server and request the document that you're interestedin. HTTP is an application level protocol.<P>The Web server receives requests from browsers using HTTP. Itsjob is simple: to deliver the page or other object to the browser,using HTTP. It receives the request and sends the requested informationback to the Web browser. After it sends the information, the connectionis closed. In this way, the intranet's resources can be used mostefficiently, since whenever the server isn't sending or receivingdata, it's available.<P>Increasingly, the Web is becoming a true multimedia environment.It allows for animation, video, and other forms of interactivity.It does this in a variety of ways. One way is by using a programminglanguage called Java, which allows intranet programmers to createinteractive applications delivered over the Web. Java appletsrequire that Web browsers be able to read the language. Popularbrowsers like Netscape Navigator are able to do that.<P>Another way that the Web is becoming a multimedia environmentis by the use of an increased amount of sound files. Web browsersby themselves often won't be able to play these kinds of files.Sometimes, home pages contain links to files that the Web browsercan't play or display, such as sound and animation files. In thatcase, you'll need a <I>helper application</I>. You configure yourWeb browser to use the helper application whenever it comes acrossa sound or animation file that the browser itself can't run orplay. A special kind of helper application is known as a <I>plug-in</I>.Plug-ins allow the sound, animation, or video to play right insidethe Web browser. You don't need the browser to run a separateprogram, as you need to with helper applications.<P>The Web is important for intranets because, increasingly, it isa way to allow people within corporations to be able to mine therich amounts of data found in corporate databases. Before intranetsand the Web, it was often difficult to give many people accessto this information. The relative ease of publishing and creatingforms with HTML makes it easier to give people access to thisinformation. Often, some kind of link needs to be forged betweenthe Web and a corporate database that allows someone on the intranetWeb to query a database that doesn't understand HTML. One wayto do this is to use the Common Gateway Interface (CGI). WithCGI programs or scripts, an intranet programmer can allow someonefrom the Web to search a database, and then have the informationsent back to that person in an HTML page that's easy to read andunderstand. The data can be sent back with new HTML links thatwould lead the user to other data, allowing for expanded interactivitywith the information.<P>In some ways, intranet Web servers work the same as their Internetcounterparts. Both receive requests specified by the HTTP requestfrom Web browsers, and both send back the resulting pages usingthe TCP/IP protocol as the actual delivery mechanism. But thereare some major differences as well. Inside an intranet, Web pagescan be delivered at higher speeds than pages delivered over theInternet. That's because corporations can build high-speed intranetsthat aren't bedeviled by the traffic problems, bad connections,and low-bandwidth connections common on the Internet. So whensomeone inside an intranet requests a Web page, that page canbe delivered from the server to the browser at a much higher speed-whichis significant, considering that many pages are rich with graphics,sounds, and other multimedia files, which can take a long timeto deliver over the Internet.<P>Intranet Web servers can also find ways to deliver informationfrom the Internet to intranet users at high speeds. An intranetWeb server can <I>cache</I> pages in memory that intranet userscommonly request. It is important to realize, however, that pagesfrom the cache are not updated, so technically, the data containedin them may have changed-with serious consequences if the itembeing retrieved is a stock quote or an inventory figure.<P>A company with an intranet may want to publish some of its informationon the intranet, or allow people on the intranet to buy goodsand services through it. In this case, the company will not onlyhave their normal private intranet servers-they'll also have publicInternet servers as well. Public information that anyone can seewill be on the Internet servers. However, the company will stillhave intranet servers behind a corporate firewall, protectingvital corporate data from Internet access. <H2><A NAME="HowIntranetWebsWork"><FONT SIZE=5 COLOR=#FF0000>How Intranet Webs Work</FONT></A></H2><P>The heart of any intranet is the World Wide Web. In many instancesa large part of the reason that an intranet was created in thefirst place is that the Web makes it easy to publish company-wideinformation and forms by using the Hyptertext Markup Language(HTML). The Web allows for the creation of multimedia home pages,which are composed of text, graphics, and multimedia contentssuch as sound and video. <I>Hypertext links</I> let you jump fromany place on the Web to any other place on the Web, which meansthat you can jump either to places inside an intranet or outsideon the greater Internet from a home page.<OL><LI>Intranet Webs are based on client/server architecture. Clientsoftware-a Web browser-runs on a local computer, and server softwareruns on a Web intranet host. Client software is available forPCs, Macintoshes, and UNIX workstations. Server software runson UNIX, Windows NT, and a variety of other operating systems.The client software and server software need not run on the sameoperating system. To use an intranet Web, first launch your Webbrowser. If you're directly connected to your intranet, the TCP/IPsoftware you need to run the browser will already be installedon your computer.<LI>When browsers are launched, they will visit a certain locationby default. On an intranet, that location may be a departmentalWeb page or a company-wide Web page. To visit a different location,type in the intranet location you want to visit, or click on alink to the location. The name for any Web location is the URL(uniform resource locator). Your Web browser sends the URL requestusing HTTP (Hypertext Transfer Protocol), which defines the wayin which the Web browser and the Web server communicate with oneanother.<LI>If the request is for a page found on the intranet, routerssend the request to that intranet Web page. A very high-speedconnection may be available, since intranets can be built usinghigh-speed wires, and all traffic inside the intranet can be conductedover those wires. Internet connection can be much slower becauseof the amount of traffic on the Internet, and because there maybe a variety of low-speed connections that the request from theintranet will have to traverse. The packets that make up the requestare individually routed at the network level of the OSI modelto an intranet router, which in turn sends the request to theWeb server.<LI>The Web server receives the request using HTTP. The requestis for a specific document. It sends the home page, document,or object back to the Web browser client. The information nowis displayed on the computer screen in the Web browser. Afterthe object is sent to the Web browser, the HTTP connection isclosed to make more efficient use of network resources.<LI>URLs contain several parts. The first part-the "http://"-details what Internet protocol to use. The "www.zdnet.com"segment varies in length and identifies the Web server to be contacted.The final part identifies a specific directory on the server,and a home page, document, or other Internet or intranet object.</OL><HR><CENTER><P><A HREF="ch5.htm"><IMG SRC="PC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="#CONTENTS"><IMG SRC="CC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="contents.htm"><IMG SRC="HB.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="ch7.htm"><IMG SRC="NC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><HR WIDTH="100%"></P></CENTER></BODY></HTML>⌨️ 快捷键说明
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