Execute Multiple AJAX Requests Simultaneously in ASP.Net

my friends program had an error..not able to load multiple $.ajax calls simultaneously..ajax function are loading one after another using success call backs...but not able to load simultaneously..as a result parial page refresh not working...error occured when ajax calls loaded together..how can we solve this...

$(document).ready(function () {
        $.ajax({
            type: 'POST',
          url: "webservice.asmx/bbb",
            dataType: 'json',
            traditional: true,
            async: false,
            success: function (data) {
                //fill content in div 1
            }
        });

        $.ajax({
          ----------
	-----------------
	----------
        });

        $.ajax({
            ------------
	-----------------
	-------------------
        });
});