In server push, however, the connection is kept open until all the data is received by the client. That is the main difference between the two mechanisms. Client pull requires a special directive either in the HTML document header or as a part of the CGI program's HTTP response. This directive instructs the client to retrieve a specified document after a certain amount of time. The HTTP connection between the client and the server is kept open indefinitely.
Browsers provide a way to update their windows called refreshing .
In the example shown above, we trick the browser into issuing its refresh command every five seconds, so that it retrieves the document. The document simply uses server side includes to display the current time. The META tag is part of the HTML 3.0 specification used to simulate HTTP response headers in HTML documents. So, the date command is used to output the current date and time. This example loads the file specified by the URL after five seconds.