Introduction of proxy server
A proxy server is a kind of gateway that speaks HTTP to the browser but FTP, Gopher, or some other protocol to the server. It accepts HTTP requests and translates them into, say, FTP requests, so the browser does not have to understand any protocol except HTTP. The proxy server can be a program running on the same machine as the browser, but it can also be on a free-standing machine somewhere in the network serving many browsers.
Often users can configure their browsers with proxies for protocols that the browsers do not speak. In this way, the range of information sources to which the browser has access is increased.
In addition to acting as a go-between for unknown protocols, proxy servers have a number of other important functions, such as caching. A caching proxy server collects and keeps all the pages that pass through it. When a user asks for a page, the proxy server checks to see if it has the page. If so, it can check to see if the page is still current. In the event that the page is still current, it is passed to the user. Otherwise, a new copy is fetched.
Finally, an organization can put a proxy server inside its firewall to allow users to access the Web, but without giving them full Internet access. In this configuration, users can talk to the proxy server, but it is the proxy server that contacts remote sites and fetches pages on behalf of its clients.