Section V: Application Layer Protocols

Providing Internet and World Wide Web Services

Getting connected isn't as difficult as you might think.

The growth of the Internet has been an interesting reflection of the growth of networking in general. The first networks to be deployed in most companies were workgroup networksislands of connectivity. They were of various types, and they weren't connected to each other.

As networking technologies matured, and networking took on greater importance in many organizations, the workgroup networks grew and often became interconnected . The next step was enterprise-wide networking, and it wasn't long before companies began to deploy e-mail across those enterprise networks.

Today, many companies have full internal networks in place, and the growth of the Internet signals a continuance of the networking trend. Companies are now connecting via the Internet to their trading partners and prospective customers, much as the early workgroup networks interconnected to form a larger corporate network where different departments could collaborate on projects.

The Internet is also mirroring another trend: Just as we've seen microcomputers and workstations move from text-oriented, command-driven operating systems to graphical user interfaces, so too have services on the Internet shifted from the terse command-line types to the graphical World Wide Web.

A consequence of this shift toward the Internet is that network managers are often being asked to set up Internet connections and World Wide Web sites. This Tutorial is the first in a series designed to introduce network managers to the Internet and Web technologies.

Internet Services

The World Wide Web steals the lion's share of attention lately, but there is actually a wide variety of services available on the Internet. "Internet Services," gives a brief description of some of the key services available on the Internet.

In the early years, the Internet was mostly used for electronic mail and for exchanging files between computer systems. These applications tended to be textual and command-line oriented, which means that the Internet was, at that time, mostly used by the "initiates." The Internet didn't really open up to the masses until just a few years ago, when the World Wide Weban application with a graphical interfacewas deployed.

The World Wide Web

What is the Web? It has many aspects, which makes it difficult to describe in just a sentence or two. I'll give you a sentence , but then I'll need several paragraphs to elaborate: The World Wide Web is a client-server system for delivering information in hypermedia form.

The medium of the Web is the Hypertext Markup Language (HTML). HTML is essentially a page description language, similar to Adobe Systems' Postscript or Hewlett-Packard's PCL (Printer Control Language). HTML tells the Web browser on the user's PC how to display the text and graphics that represent the content of a particular Web site. A Web browser is an HTML interpreter that requests and receives HTML-coded documents from a Web server and displays the information according to HTML commands embedded in the code.

The server component of this client-server system is a computer running software that operates according to the hypertext transport protocol (http). The Web server responds to users' Web browsers by sending the files the browsers request.

In most cases, a Web server delivers a document one page at a time. (Of course, that page can be much longer than the height of your display screenyou may have to scroll through several screens to see the entire page). These documents are hypertext , much like the Windows Help system. Certain key words are hyperlinks . Usually, the browser will indicate hyperlink text by underlining it and displaying it in a different color than the rest of the text. (Images can also be hyperlinks.) When you click on a hyperlink, it causes the browser to issue a request for the HTML document associated with that link. The Web server will then service that request. In Web lingo, each request for a file (text document or graphic image) is called a hit .

One difference between hyperlinks in HTML and those in other hypertext systems, such as Windows Help, is that HTML hyperlinks can take you to an entirely different server. These hyperlinks, in effect, make the Web one giant document management system, which explains how the World Wide Web got its name . Published on a Web server, other Web sites or Web documents referenced within this article could be made into hyperlinks; a reader could jump to each reference with just a click of the mouse.

Web servers are attractive electronic publishing systems. In the past, the only way to publish something on the Internetand ensure that everyone could read itwas to present it in plain ASCII text. Richer formats, such as text displayed in a particular font, size , or style (italics, for example) were word processor-specific. Graphics, too, require specific viewer programs, which the reader may or may not have had. These factors hindered the presentation and effectiveness of electronic publishing. Enter the World Wide Web.

The Web has given us a level of platform independence. It's somewhat similar to having a videocassette that can be played on a wide variety of videocassette recorders , regardless of the vendor. Standardization in http and HTML means that any Web browser can read any Web document (at least, in theory). As HTML develops, vendors tend to add extensions that add new features to HTML or make life easier for its coders. Not every Web browser can read every proprietary extension, so certain features might not work with all browsers. It's still true, though, that if you stick with base-level HTML and avoid proprietary extensions, almost any browser will be able to read and display your documents. Of course, you need a Web browser running on your computer, and it's safe to say that there are now browsers for almost every type of computer.

Web servers were developed to reside on the Internet, but there's no reason you can't use one on any other TCP/IP network, large or small. This has given rise to the idea of corporate intranets networks that are completely contained within the organizations they serve. Figure 1 shows an example of an intranet, as well as a connection to the Internet. Everything behind the firewall (that is, everything within the dashed lines) is the corporate intranet.

Figure 1: A typical corporate Internet connection. Everything behind the firewall is part of the corporate intranet which is the organization's private network. The dashed line encompasses this particular intranet.

The concept of the Web as a platform-independent, client-server system is tantalizing to developers. Not only is platform independence a nice feature to have on the Internet, it's effective for the intranet as well. Companies such as IBM's Lotus Development are bringing out Internet interfaces for their client-server systems (Lotus Notes, in this case).

Typically, whenever you revise (rev) a client-server system, you have to develop both a new client piece and a new server piece. The amount of work needed on the client side is multiplied several times if you're trying to provide clients for several different operating systems. However, if you use a Web browser as the client, there's no work to be done on the client side whatsoeveryou can simply let companies such as Netscape Communications (Mountain View, CA) or Spyglass (Naperville, IL) provide the browsers.

WAN linksat least those that most companies can affordare typically very restrictive in terms of data throughput when compared with LAN links. Most people consider a T1 line (1.544Mbps) a high-speed link, but it crawls in comparison to 10Mbps Ethernet. For this reason, you must carefully plan the graphic design of your Web pages. Keep graphics small, and never put more than a few on each page, or else your readers will be staring at the Windows hourglass icon for minutes at a time.

As bad as this problem can be in the wide area, it disappears for intranets due to the tremendous throughput of local area networks. If you're going to strictly dedicate a Web site as an intranet server, you can afford to go hog wild with graphics. Ironically, Web servers, which were born on the Internet, seem to be realizing their full potential on the intranet.

If there's a fly in this soup, it's HTML, which is essentially a document publishing system. HTML is read-only and as such, it is not interactive, although you can request new pages by clicking on hyperlinks. There are ways around this, as we'll explore later in the series, but Web designers must really bend over backward to compensate for the one-way nature of HTML.