AJAX Source table displays all records not 10

I use AJAX to load a json array into my table, the json does validate

I initialize my table with this

$(function () {
    if(jQuery().dataTable) {
      var oTable =  $('#thetable').dataTable({
			"oLanguage": {
				"sEmptyTable": "No data"
			},
            "bProcessing": true,
			"bServerSide": true,
            "sAjaxSource":'http://example.com/json.php',
			"fnServerParams": function ( aoData ) {
				aoData.push({ "name": "post_id", "value":'<?php echo $pageID; ?>'  } );
			},
            "aoColumns": [
        { "mDataProp": "post_id","bSortable": false },
        { "mDataProp": "url" },
		{ "mDataProp": "page_type" },
        { "mDataProp": "cat" },
		{ "mDataProp": "tags" },
		{ "mDataProp": "country_code" },
        { "mDataProp": "action_buttons","bSortable": false } 
		]
	});

    }
});

I have compared the XHR from my website to the demo at http://datatables.net/release-datatables/examples/server_side/server_side.html

The query string parameters below are the same on my server and the demo, these are being sent to the server with datatables that I know.

sEcho:1
iDisplayStart:0
iDisplayLength:10

My response from the server in the beginning of the json file is

iTotalDisplayRecords: "54"
iTotalRecords: "54"
sEcho: 1

In the json array are all 54 rows of data.

I think what I need is deferred loading? http://datatables.net/release-datatables/examples/server_side/defer_loading.html

But there is no code example. Or is that not what I need? I've read over what I should be sending to the server, and what I should send back but can't figure out how to get 10 rows to display in my table with the json response.

Thanks in advance.