php session

hi,i am new to php ,

i hv created login page,registere..........

nw i want to give session timeout for login user........and please send me one example.

plzz help....

 

I use iframe pages, so I made the following In main pages I make the following check

   if (!isset($_GET["sessionName"])) Header("Location: index.php");
     session_name($_GET["sessionName"]);
     session_start();
     if (!isset($_SESSION["user_id"])) Header("Location: index.php");

In iframe pages:

     if (!isset($_SESSION[$_SESSION["user"]."_id"])) {
?>
     <script>
     window.parent.location.href = '<?php echo ($_SESSION["user"] == "user" ? "index.php" : "indexa.php") ?>';
     </script>
<?php 
     }

PHP:

 

hi,i am sending my code in below attachments,u please go through the code and send me hw to write session timeout for the login page.