The standard model of interaction between a web user agent such as a browser and a web server such as Apache is that the user agent makes HTTP requests and the server makes a single reply to each one. In the case of a browser, the request is made by clicking on a link, entering a URL into the address bar, clicking on the forward or back buttons, etc. The response is treated as a new page and is loaded into a browser window.
This traditional model has many drawbacks. The first is that each request opens and closes a new TCP connection. HTTP 1.1 solved this by allowing persistent connections, so ...
