function btnStart_click() {
    $.ajax({
        url:ajaxUrl,
        type:"GET",
        dataType:"json",
        data:{
            "action":"session@renew"
        },
        success:function(data, status, xhr) {
            $("#pSid").text("Session ID: " + data.sid);
        },
        error:function(xhr, status, error) {
            alert(error + "\n" + status + "\n" + JSON.stringify(xhr));
        }
    });
}