Facebook Connect: Authentication and login issue

Question

I am trying to integrate Facebook Connect as the only means of logging in to our community site. I am having a problem with session persistence as my application seems to regularly loses it's Facebook login session.

First, I'd like to know if I have to execute this code for each page on my site:

$fb_params = array(
   'appId'  => $id,
   'secret' => $secret,
   'cookie' => $cookie,
);

$facebook = new Facebook($fb_params);

Next, I have this tag to render the user login:

<fb:login-button perms="offline_access, email, user_location, user_online_presence, user_photos, user_status, read_friendlists, user_about_me"></fb:login-button>

As you can see I already have the "offline_access" attribute set but still, my application seems to lose the login session as getSession() regularly returns NULL value after a few minutes.

Help would be very much appreciated.