Proxy servers have two main purposes. They can improve performance and filter requests. By filtering requests, we mean an organization might use a proxy server to prevent its employees from accessing a specific set of Web sites. We are more concerned, for this experiment, in the first purpose of a proxy server, improving performance.

Proxy servers can dramatically improve performance for users of an organization. This is because the proxy server saves the results of all requests for a certain amount of time.

For example, consider the situation where both User A and User B access the Web through the same proxy server. First, User A requests a certain Web page, which we will refer to as Web Page 1.

The proxy sever will forward, based on the Uniform Resource Locator (URL), the request to the Web server where Web Page 1 resides. Depending on the network’s Web connection, the number of graphics in the Web page, etc., this can be a time consuming operation. Now, later, User B requests the same Web page.

Instead of forwarding the request to the Web server where Page 1 resides, the proxy server simply returns the Web Page 1 that it already fetched for User A. Since the proxy server is usually on the same network as the user, this is a much faster operation.

If this series of actions is repeated over several to hundreds of users, the performance increase via reduced access time can a real benefit to the users on a network.

The major online services such as CompuServe and America Online, for example, employ an array of proxy servers to service thousands of users [7]. If User B had requested a Web page that had not been previously requested, the proxy server forwards the request to the real Web server designated in the URL. .

The storing of server requests by proxy servers is referred to as caching. As stated, it was this aspect of the proxy server that we were primarily interested in studying.

Web pages are modified, deleted, renamed continuously, so the proxy server must have a means of checking to see if the page that it has in cache is the most current version. Briefly, a Web caching proxy server “cruises” the Web and examines pages that are currently cached on the server.

If a page has been modified, the proxy server stores the new version on a local drive. Some proxy servers can also use certain guidelines to hit links on that page to pull down related pages.

Most proxy servers are extremely efficient. They can examine and store thousands of Web pages, and when any local user on the LAN asks for a specific stored page, the page flies out of a local drive or cache without Internet transmission delays.

To ensure that the proxy server can do it job, the network must be set up so that users needing access to the Web must use the proxy server as their Internet gateway. One can accomplish this access control through proper router setup, which places all users “behind” the firewall.