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.The rapidgrowth in popularity of the Web is due to the flexible way people can navigatethrough worldwide resources in the Internet and retrieve them.The number of Web servers is also increasing rapidly and the traffic over port 80,which is the well-known port for HTTP Web servers, on the NSF backbone has hada phenomenal rate of growth too.The NSFNET, however, was converted back to aprivate research network in 1995; therefore comprehensive statistics of backbonetraffic are not as easily available anymore, if they are at all.8.1.1 Web BrowsersGenerally, a browser is referred to as an application that provides access to a Webserver.Depending on the implementation, browser capabilities and hencestructures may vary.A Web browser, at a minimum, consists of an HTMLinterpreter and HTTP client which is used to access HTML Web pages.Besidesthis basic requirement, many browsers also support FTP, NNTP, e-mail (POP andSMTP clients), among other features, with an easy-to-manage graphical interface.Figure 251 on page 438 illustrates a basic Web browser structure.© Copyright IBM Corp.1989, 1998 437 GraphicalUserInterfaceDriverHTML OptionalInterpreter InterpreterControllerHTTPTorClientrDispatcheranspoFTPrClienttLayeMailrClient3376E\3376F8O7Figure 251.Structure of a Web BrowserAs with many other Internet facilities, the Web uses a client/server processingmodel.The Web browser is the client component.Examples of Web browsersinclude Mosaic, Netscape Navigator, Microsoft Internet Explorer, or Sun HotJavabrowser.Web browsers are responsible for formatting and displaying information,interacting with the user, and invoking external functions, such as telnet, or externalviewers for data types that Web browsers do not directly support.Web browsershave become the "universal client" for the GUI workstation environment, in muchthe same way that the ability to emulate popular terminals such as the DEC VT100or IBM 3270 allows connectivity and access to character-based applications on awide variety of computers.Web browsers are widely available for all popular GUIworkstation platforms and are inexpensive.438 TCP/IP Tutorial and Technical Overview 8.1.2 Web ServersWeb servers are responsible for servicing requests for information from Webbrowsers.The information can be a file retrieved from the server's local disk, or itcan be generated by a program called by the server to perform a specificapplication function.There are a number of public-domain Web servers available for a variety ofplatforms including most UNIX variants, as well as personal computer environmentssuch as OS/2 Warp and Windows NT.Some well-known public domain servers areCERN, NCSA httpd, and Apache servers.IBM has released the Domino Go Webserver, a scalable, high-performance Webserver that is available on OS/390 as Version 5 (including WebSphere ApplicationServer as described in 8.6.4.2,  IBM Web Application Servers on page 458).Domino Go Webserver V4.6.2.5 is available on many workstation platforms (AIX,Solaris, HP-UX, OS/2 Warp, Windows NT, and Windows 95).Both versionsprovide state-of-the-art security, site indexing capabilities, advanced server statisticsreporting, PICS support, and relational database connectivity with Net.Data (see8.6.4.1,  IBM Web Connectors on page 457).Domino Go Webserver is thesuccessor to IBM's well-known Internet Connection Secure Server (ICSS), and it isa Java-enabled Web server that supports the development and running of servlets(see 8.5,  Java on page 449).8.1.3 Web Server Application TechnologiesAs mentioned earlier, Web server can serve static (mere HTML pages) or dynamic(generated by a program upon invocation) content.This section discusses somecommonly used technologies used to provide dynamic content and to facilitateinteraction between a Web server and an application server that is not directlyaccessible to a client (Web browser).8.1.3.1 Common Gateway Interface (CGI)The Common Gateway Interface (CGI) is a means of allowing a Web server toexecute a program that is provided by the Web server administrator, rather thanretrieving a file.CGI programs allow a Web server to generate a dynamicresponse, usually based on the client's input.A number of popular Web serverssupport the CGI, and a variety of programming languages can be used to developprograms that interface with CGI [ Pobierz caÅ‚ość w formacie PDF ]

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