how to schedule ajax calls every N seconds?

You could use setTimeout or setInterval (the latter is probably best suited to what you want to do).

setInterval(makeRequest, (10 * 1000));

...where makeRequest is a function that reloads some content via AJAX.

function proxy()
{
  /* implement call to your Ajax method */
}

setInterval( proxy, 1000 ); // last arg is in milliseconds

You can use serInterval method of javascript:
Just write down the lines at the bottom of your page:

<script>
window.setInterval(function(){
  ajaxCallFunction();  //calling every 5 seconds
}, 5000);

function ajaxCallFunction(){
    //this function uses ajax to interact with the server
}
<script>