Whenever you request a web page, you send a message to a server, and the server responds. As far as I know, most interaction occurs this way: the client says one thing to the server, and the server says one thing back. The server can’t “speak until spoken to”.
Are there any technologies that let the server initiate a conversation? For instance, if you had a page that you wanted to always keep up to date, the way I’d do it now is periodically make an AJAX request to get updated info from the server. However, it would be nicer if the server could just let the client know at the moment when new info was available. Is there anything around that can do this?
The concept you are looking for is push technology.