Session Problem in PHP

Why the session expires in the mid of navigation of a site.
Suggest any efficient way to store the username.
Any example will be greatly appreciated.

Also how to reassign the session value when it expires?
Can we do this using hidden controls? If yes, then how it can be done using hidden control?

do you have session_start on every page?

also, you may want to refer to
http://us2.php.net/manual/en/function.session-cache-expire.php

and change this if need be:
http://us2.php.net/manual/en/ref.session.php#ini.session.cache-expire

Also how to reassign the session value when it expires?

The idea of session cookies is that they don't expire until the end of the session. So, if they are working fully, you shouldn't need to worry about this.

~Phil~