[jQuery] how jquery handle the redirect quest from server(php)?

[Loy]

Hi everyone:
I just started to learn jquery and met this problem:
I would like to use .ajax to send a http request.
For example:
I got the code like the following
$.ajax(
{
 type:"GET",
 url:"./include/coor_generator.php",
 complete:function (xhr,statusText)
   {
    alert(xhr.status);
   }
}
);

However, in 'coor_generator.php', I would like to verify if that user
session is already verified or not, so that the content of
'coor_generator.php' is like:
<?php
 require_once("session.php");
 require_once("DB.php"); //DB class declartion
 $status_code = 1;
 header("Content-type: text/xml");
 header("Cache-Control: no-cache");

 echo "<?xml version=\"1.0\"?>\n";
 echo "<response>\n";
 echo "\t<status>$status_code</status>\n";
......
?>

in 'session.php', the content is:
<?php
    session_start();
    setcookie(session_name(), session_id(), time() + 1*60, "/");
    if(!(isset($_SESSION["username"]))||!(isset($_SESSION
["password"])))
    {
      header("Refresh:0;url=./login.php");
      exit(0);
    }
?>

However, as I tested the script in Firebug, the returned xhr.status
(in .ajax complete option) is always 200. Isn't it supposed to be 301
for redirection?
My objective is very simple: if the user is verified,
coor_generator.php generate some x,y coordinates in a valid XML
format; however, if the user is not verified, redirect the user to the
login page. How to achieve this using Jquery AJAX? Thanks a lot!!!