fnServerData is not working

var oTable = $('#mytable').dataTable( {
"bProcessing": true,
					"bServerSide": true,
					"sPaginationType": "full_numbers",
					"sAjaxSource": "server_processing.php",
                                            "fnRowCallback": function( nRow, aData, iDisplayIndex, iDisplayIndexFull ) {
                                             //my code 
                                              return nRow;
                                             },
                                            "fnServerData": function ( sSource, aoData, fnCallback ) {
                                               aoData.push(  { "name": "as_strno", "value": $('#strno').val() },
                                                 { "name": "as_temp_ref", "value": $('#as_temp_ref').val() });
                                                aoData.push( { "name": "dateaddedSto", "value": $('#listings_row #dateaddedSto').val() });
                                            $.getJSON( sSource, aoData, function (json) { 
						fnCallback(json)
                                               } );
                                    }
                          } );