Java Reference
In-Depth Information
information. The Internet is not some specific network; rather, the Internet is comprised of those communications
that follow an Internet protocol over any network. In other words, the network hardware used to transmit information
does not define the Internet.
Is this hurting your brain? Maybe an alternative look at the Internet is needed.
Internet 101
The majority of Internet users don't clearly understand what the Internet is. For example, it is a common
misconception that the World Wide Web (WWW, or the Web) and the Internet are the same thing. The Internet
actually encompasses many methods of communicating over a network, and the WWW is only one of these
communication methods. In other words, the WWW is just one piece of the Internet.
For instance, using a telephone to call someone is not communicating over the Internet. But, if you hook the
phone line into a computer and send an e-mail message, you are communicating over the Internet. The same is true if
you have a cable or satellite television connection. Hook the cable to your TV and you are receiving communications
over the TV network. However, if you order Internet access from a cable or satellite company and connect the cable to
a PC, you will be able to access Web pages. Notice that the network hardware (phone lines, coaxial cable, or satellite
dish) does not determine whether the network is part of the Internet. Rather, it is the
type of communication
that
determines if it is an Internet communication.
Of course, communicating over the Internet is not quite as easy as attaching a phone line or cable to the
computer. You actually need software to communicate over the Internet, and there are separate software applications
to support the different types of communication. For instance, communications over the WWW follow the rules called
HTTP (Hypertext Transfer Protocol). Or, said another way, HTTP dictates how information in the form of Web pages
is transferred over the Internet. Some other examples of Internet protocols are POP (Post Office Protocol) and SMTP
(Simple Mail Transfer Protocol), both of which define the rules for transferring information as e-mail; and FTP (File
Transfer Protocol), which defines the rules for transferring files between computers. If you use the Internet frequently,
you may be bewildered because you have never heard these terms before (even though you can probably send e-mail
and look at Web pages with the best of them!). This is because people use software applications that format the
information according to the various protocol rules. In other words, the software does all the heavy lifting.
To communicate over the WWW, there are two primary pieces of software involved: the browser and the server
software. The browser (such as Microsoft Explorer, Firefox, Chrome, etc.) is on the client computer. The server
software (such as IBM's WebSphere Application Server, Apache Tomcat, and Microsoft's Internet Information
Services) resides on the server (the computer that manages the Web pages).
One of the “rules” of HTTP is that every Web page is identified with a unique “address.” Also, every server is assigned
a unique address called an IP (Internet Protocol) address. IP addresses consist of a very long number broken up into four
parts, with each part separated by a period (e.g., 123.218.76.4). This is not a very user-friendly way to locate information
on the WWW. Therefore, URL (Uniform Resource Locator) addresses were created.” URLs consist of at least a server
(host) address—a series of words separated by periods such as
www.spam.com
. Sometimes the server address is followed
by a directory path and the file name of a specific Web page (
web.fccj.org/~rjanson/cgs1062/JIorderpage.html
).
When you specify a WWW address (either IP or URL) and press Enter, the browser builds a Web page
request
and
formats the request so that it is routed (sent) to the correct server. You can compare this to writing a letter (building
the Web page request) and then addressing an envelope to send the letter in (formatting the request). In the case of a
Web page request, the address follows the rules of HTTP.
The server receives the request, retrieves the appropriate Web page, packages the Web page (again, think of it as
addressing an envelope), and sends the page to the browser. The browser receives and displays the Web page.
Wow, there's a lot going on! Just like the telephone system, communications over the WWW are very complex and
do not happen by magic. It is the browser and server software that makes the WWW seem simple.
E-mail works very similarly. The user has client e-mail software (Microsoft's Outlook) that requests mail from
the e-mail server software. When you send an e-mail, Outlook formats the note according to the rules of SMTP and,
through the magic of the Internet; the e-mail is routed to the correct mail server. FTP, the other protocol listed earlier,
also requires client and server software.
Fortunately, there is server software that supports many protocols. Therefore, instead of installing many different
server software applications, companies purchase a single application (like WebSphere) that supports all of these protocols.
