All Categories :
Intranets
Chapter 6
How Intranet Web Servers and Browsers
Work
CONTENTS
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 Wide
Web. The Web has made it possible for companies to better communicate
vital information among employees, departments, and divisions;
to better communicate with customers; and to make it easy for
those within a company to get at the vast resources often locked
up in corporate databases and information centers.
The Web makes it easy to publish information because each Web
page allows people to incorporate text, graphics, sound, animation,
and other multimedia elements. In essence, each page is an interactive
multimedia publication. This means that a company can easily publish
simple documents such as personnel handbooks or expense reports.
They can also create sophisticated pages that let people do more
than just read a corporate annual report, and also let them see
videos of the company in action or listen to speeches by corporate
officers. The page at the top (or entrance to a site) is called
a home page.
The Web is also a powerful intranet tool because of the way it
can link corporate home pages to one another. Hypertext
links any home page to any other home page, and to graphics, binary
files, multimedia files, and any Internet or intranet resource.
To jump to one home page from another, you merely click on a link
on a home page, and you'll automatically be sent there. It is
easy to create documents that allow employees to find specific
company information and related material quickly.
The Web uses client/server architecture to work. To access the
Web, a client uses a Web browser program. Clients are available
for all common types of computers, including PCs, Macintoshes,
and UNIX workstations. Popular browsers include Netscape and Microsoft's
Internet Explorer. The client/server model works well for an intranet,
since it allows many different kinds of clients on different computers
to be run, and yet the same corporate resources can be made available
to all clients from the same servers. The operating system of
a server need not be the same as the operating system of a browser.
Popular operating systems for servers include UNIX and Windows
NT.
Corporations often standardize on a particular browser such as
Netscape or Internet Explorer, so that everyone on an intranet
will use the same kind of browser. This is done because the language
of 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 in
another browser.
Home pages on an intranet (and the Internet) are built using a
page markup language called HTML (Hypertext Markup Language).
This specialized language contains commands that tell browsers
how to display text, graphics, and multimedia files. It also contains
commands for linking the home page to other home pages, and to
other 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 the
language, so those who build intranets have to be careful to use
HTML commands that their company's standard intranet browser will
easily understand.
It's the browser's job to contact Web servers, receive HTML pages,
and then interpret and display those pages. Web locations on an
intranet are specified by URLs-uniform resource locators. You
type in the URL in your browser, or click on a link in order to
navigate to a particular Web page. The packets making up the request
are sent to an intranet router, which checks the destination address,
and then routes the request to the proper server.
When you type in the URL, the Web browser looks at the URL and
then determines which server to contact, which directory to ask
for, and what specific document in that directory is the one that
you want. It then uses HTTP (Hypertext Transfer Protocol) to contact
the Web server and request the document that you're interested
in. HTTP is an application level protocol.
The Web server receives requests from browsers using HTTP. Its
job is simple: to deliver the page or other object to the browser,
using HTTP. It receives the request and sends the requested information
back to the Web browser. After it sends the information, the connection
is closed. In this way, the intranet's resources can be used most
efficiently, since whenever the server isn't sending or receiving
data, it's available.
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 programming
language called Java, which allows intranet programmers to create
interactive applications delivered over the Web. Java applets
require that Web browsers be able to read the language. Popular
browsers like Netscape Navigator are able to do that.
Another way that the Web is becoming a multimedia environment
is by the use of an increased amount of sound files. Web browsers
by themselves often won't be able to play these kinds of files.
Sometimes, home pages contain links to files that the Web browser
can't play or display, such as sound and animation files. In that
case, you'll need a helper application. You configure your
Web browser to use the helper application whenever it comes across
a sound or animation file that the browser itself can't run or
play. A special kind of helper application is known as a plug-in.
Plug-ins allow the sound, animation, or video to play right inside
the Web browser. You don't need the browser to run a separate
program, as you need to with helper applications.
The Web is important for intranets because, increasingly, it is
a way to allow people within corporations to be able to mine the
rich amounts of data found in corporate databases. Before intranets
and the Web, it was often difficult to give many people access
to this information. The relative ease of publishing and creating
forms with HTML makes it easier to give people access to this
information. Often, some kind of link needs to be forged between
the Web and a corporate database that allows someone on the intranet
Web to query a database that doesn't understand HTML. One way
to do this is to use the Common Gateway Interface (CGI). With
CGI programs or scripts, an intranet programmer can allow someone
from the Web to search a database, and then have the information
sent back to that person in an HTML page that's easy to read and
understand. The data can be sent back with new HTML links that
would lead the user to other data, allowing for expanded interactivity
with the information.
In some ways, intranet Web servers work the same as their Internet
counterparts. Both receive requests specified by the HTTP request
from Web browsers, and both send back the resulting pages using
the TCP/IP protocol as the actual delivery mechanism. But there
are some major differences as well. Inside an intranet, Web pages
can be delivered at higher speeds than pages delivered over the
Internet. That's because corporations can build high-speed intranets
that aren't bedeviled by the traffic problems, bad connections,
and low-bandwidth connections common on the Internet. So when
someone inside an intranet requests a Web page, that page can
be delivered from the server to the browser at a much higher speed-which
is significant, considering that many pages are rich with graphics,
sounds, and other multimedia files, which can take a long time
to deliver over the Internet.
Intranet Web servers can also find ways to deliver information
from the Internet to intranet users at high speeds. An intranet
Web server can cache pages in memory that intranet users
commonly request. It is important to realize, however, that pages
from the cache are not updated, so technically, the data contained
in them may have changed-with serious consequences if the item
being retrieved is a stock quote or an inventory figure.
A company with an intranet may want to publish some of its information
on the intranet, or allow people on the intranet to buy goods
and services through it. In this case, the company will not only
have their normal private intranet servers-they'll also have public
Internet servers as well. Public information that anyone can see
will be on the Internet servers. However, the company will still
have intranet servers behind a corporate firewall, protecting
vital corporate data from Internet access.
The heart of any intranet is the World Wide Web. In many instances
a large part of the reason that an intranet was created in the
first place is that the Web makes it easy to publish company-wide
information 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 contents
such as sound and video. Hypertext links let you jump from
any place on the Web to any other place on the Web, which means
that you can jump either to places inside an intranet or outside
on the greater Internet from a home page.
- Intranet Webs are based on client/server architecture. Client
software-a Web browser-runs on a local computer, and server software
runs on a Web intranet host. Client software is available for
PCs, Macintoshes, and UNIX workstations. Server software runs
on UNIX, Windows NT, and a variety of other operating systems.
The client software and server software need not run on the same
operating system. To use an intranet Web, first launch your Web
browser. If you're directly connected to your intranet, the TCP/IP
software you need to run the browser will already be installed
on your computer.
- When browsers are launched, they will visit a certain location
by default. On an intranet, that location may be a departmental
Web page or a company-wide Web page. To visit a different location,
type in the intranet location you want to visit, or click on a
link to the location. The name for any Web location is the URL
(uniform resource locator). Your Web browser sends the URL request
using HTTP (Hypertext Transfer Protocol), which defines the way
in which the Web browser and the Web server communicate with one
another.
- If the request is for a page found on the intranet, routers
send the request to that intranet Web page. A very high-speed
connection may be available, since intranets can be built using
high-speed wires, and all traffic inside the intranet can be conducted
over those wires. Internet connection can be much slower because
of the amount of traffic on the Internet, and because there may
be a variety of low-speed connections that the request from the
intranet will have to traverse. The packets that make up the request
are individually routed at the network level of the OSI model
to an intranet router, which in turn sends the request to the
Web server.
- The Web server receives the request using HTTP. The request
is for a specific document. It sends the home page, document,
or object back to the Web browser client. The information now
is displayed on the computer screen in the Web browser. After
the object is sent to the Web browser, the HTTP connection is
closed to make more efficient use of network resources.
- 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.
Contact
reference@developer.com with questions or comments.
Copyright 1998
EarthWeb Inc., All rights reserved.
PLEASE READ THE ACCEPTABLE USAGE STATEMENT.
Copyright 1998 Macmillan Computer Publishing. All rights reserved.
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