$ _SESSION无法使用ajax动态调用

Question

Good evening. This is my code:

Page js.js

window.setInterval(function () {
$.ajax({
        async: true,
        cache:false,
        type: 'POST',
        url:'call.php',
        data:{
            request: 'validation_session'
        },
        dataType: "text",
        success: function(item,key){
            console.log(item);
        },
        error: function(e){
                console.log(e);
            }
    });
},3000);

Page Call.php

<?php
    session_start();
    if(isset($_POST['request'])){
         $_SESSION['test']['test1'] = true;
    }
    if(isset($_SESSION['test']['test1'])){
       echo 'okay';
     }

?>

This code is a small representation of my real code but the $_session is't created why? Sorry for my english.