title: Web Page update without polling
body: <p>I'm developing a web app where a user can request a service and a provider will be available to respond to him. So, When a user requests for some sort of service, our application will send a notification to the provider (asking him to respond to the user).
  What I'm trying to do is: when a user requests a service, the provider gets the notification instantly (something like facebook does).</p>
  
  <p>One way to get this is using AJAX to send requests to the server every 5-10 secs; what we call is polling (so far i know). But, this method has some defects, i see:-</p>
  
  <ul>
  <li>Since, the request will be sent every 5-10 secs, it will be a load to the server to manipulate requests and return empty data(very frequently).</li>
  <li>Also its useless to send requests to the server even when there are not any updates.</li>
  <li>Imagine someone request a service just after the server has responded to a request. So, providers must have to wait another 5-10 secs to get a notification that someone has requested something.</li>
  </ul>
  
  <p>So, I wanted to know if there is some technique where we can update our web page instantly when a change occurs in our system without polling requests using AJAX.</p>