How Client Pull and Server Push Animation Work

Client Pull

Client pull is executed by the Refresh command. A refresh command is written into an HTML document using the <META> tag. The contents of the <META> tag are added to the header's meta-information that the server sends along with the HTTP response. During a client pull sequence, the browser reads this header information that instructs it to use your PC's internal clock to keep track of the time elapsed between pages retrieved. When the time has elapsed, the browser requests and displays the next page.

Each page in a client pull sequence can be located anywhere on the Web. The URL following the Refresh command might lead the browser to any active server. Page E is located on a different server than pages AD, but is still requested automatically after five seconds.

Note

A client pull sequence might continue for as many or as few pages as the site designer wants. The last page will simply not have a Refresh command in the header. A user can stop the process manually by clicking the browser's Stop button.

Server Push

Server push is more complicated than client pull, but it enables inline animation that does not require an entire web page to load each animation frame.

The HTML source code for a server push animation is deceptively simple. The <IMG> (image) tag references the animation just like a static picture or icon.

Note

The server and client make one connection that is open for as long as the CGI script runs. You can manually end a server push animation by clicking the browser's Stop button.