Internet 101
- What is the Internet?
- What do I need to access the Internet?
- Internet Services
- The World Wide Web
- Client/Server Computing
- The World Wide Web is a perfect example of client/server computing. The primary function of a
web server is to deliver files to the client on request. The client (called a browser) processes,
displays or executes the files received.
- Requests for files are entered into a web browser in the form of Uniform Resource Locators, or URLs.
- A URL consists of a prefix that indicates the application-level protocol to be used to transmit
the file (such as FTP or HTTP), the host name (or IP address)
of the server on which the file is located, an (optional) port
number of the application process on the server, and (also optionally)
a directory path and the name of the file to be accessed.
- A fully qualified URL might appear as
http://www.thecompany.com:80/index.html.
However, the web browser will assume the use of the HTTP protocol
and the standard web server port number of 80. In addition, the
web server has a default file name (usually index.html or default.htm)
that is sent to a client when no file name is specified in the
URL. Thus, you can enter an abbreviated URL of
www.thecompany.com into the browser to achieve the same result.
- When you specify a directory name on a particular web site without including the name of a file
in that directory, the server will automatically search for the default file name. If no file exists
by that name, the server may send to the browser a
listing of links to each of the files in that directory. The user can then select the file to be
displayed in the browser. (Some web servers allow the administrator to control this feature, usually
called "directory browsing." If directory browsing is disabled, the browser may display an error
message instead of a file listing.
- The web is based on two fundamental concepts, a protocol and a mark-up language:
- HTTP, the HyperText Transfer Protocol, is an application layer protocol that is responsible
for carrying files from the web server to the client browser. HTTP is carried
by the TCP transport protocol, which is in turn carried by IP.
- The term Web Server usually refers to the software that provides HTTP services, rather
than to the machine on which the software is running. The same computer can be a web server,
an FTP server, a DNS server, a mail server, etc., all at the same time (as long as it has the
resources to handle all of the processes).
- Web servers are now being deployed on lower-end workstation computers. Windows NT
4.0 includes an Internet services package with the operating system. The web server
functions themselves are quite simple; the hardware needed to host a web site is dependent
more on the volume of traffic it must support than the requirements of the web server software.
You can very easily run a web server on your desktop machine for light intranet traffic while
you continue to use it for your everyday tasks.
- HTML, the HyperText Mark-up Language,
is the code used to format the text files displayed by a web browser.
HTML files are plain ASCII files containing the text that will
appear in your browser window and codes that define how the text
is to be displayed, and how other files are to be accessed from
(or with) that page. HTML codes, also called tags, are always
enclosed in angle brackets ("<>"). Any text within
the brackets is interpreted by the browser as being an instruction,
and is not displayed on screen. You can view the HTML source code
of the web page that is currently displayed in your browser by
selecting Source from the View menu.
- Most HTML tags come in pairs.
The opening tag (e.g.: <P>) and the closing tag (e.g.: </P>)
encapsulate the text that is to be affected by the code. For example,
the text enclosed between <B> and </B> tags will be
displayed in boldface type. There are many HTML codes, but they
all can be said to perform one of a few basic functions:
- Some codes define the way in which
the enclosed text is to be displayed by adjusting the font size,
and applying effects like bold and italic,
- Some codes define the way that text
is to be laid out in the browser. Paragraph breaks, bulleted lists,
tables and
frames all affect the organization and appearance of web pages.
- Some codes point to graphic files that are to be displayed as part of a web page.
- Graphics are always separate files
on the web, saved as GIF or JPG files and stored somwehere on
the web server. The <IMG> tag is used to specify the path
to the graphic file that is to be displayed.
- Whenever a graphic file is displayed
as part of a web page, an entirely separate TCP session must be
used to download the graphic file to the browser. The more graphics
there are on a single page, the more TCP sessions are needed, and
the longer the page will take to draw.
- Some codes link parts of a web page to another Internet resource
- Links are the primary means of navigation
on the web. They are created by surrounding text or graphics with
<A>, or anchor, tags.
- Links can jump to different locations
in the same HTML file, to another HTML file, to a graphic file,
to an FTP site, or to any other properly defined file type,
including video, audio or other multimedia files.
- Any object on a web page, even a graphic, can be a link. One of the most common
techniques for speeding up a web site is to combine several image links into a single
graphic file, and turn it into an image map. An image map uses specific coordinates
of the graphic file to define multiple links. For example, the
The Company home page uses image maps
for the buttons at the top of the screen. As you run your cursor over the buttons
(without clicking), notice how the links displayed in the status bar at the bottom of the
browser screen change, even though all of the buttons are included in a single graphic
file.
- Some codes link to or embed external programs in a web page. Sometimes called applets,
these are mini-applications that are delivered by the web server to the browser, for execution
on the client computer.
- Using the Web Browser
- Web Trends
- Web Resources
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