I am trying to create a new Notice Alert using PHP and Javascript. Suppose that a 100 users are currently logged into to the Online Notice Board Application and any One user posts a new notice. I want an immediate alert signal on all the users screen. I know, that the simplest way of doing it is to constantly Ping the server but I don't want to do it as it will slow down the server. Moreover, I am on a shared host. So I don't have access to any Socket Port. That means, I cannot establish any direct Socket Communication Channel from the Server to the User Machine.

Can any one suggest me some other solution to this kind of problems???