refresh session php

1this is a session timeout i use.
2
3when the session is initially created:
4
5session_start();
6$_SESSION['LAST_ACTIVITY'] = time();
7the function that gets called in other pages to update the session timeout when navigating to new pages
8
9function check_timeout($timeout, &$SESSION)
10    {
11        if (isset($_SESSION['LAST_ACTIVITY']))
12        {        
13            if((time() - $_SESSION['LAST_ACTIVITY']) > $timeout)
14            {
15                end_session($SESSION);
16            }
17            $_SESSION['LAST_ACTIVITY'] = time();
18        }
19        else 
20        {
21            end_session($SESSION);
22        }
23    }
24i have a separate function (end_session()) to end a session. the & in the parameter allows the session to be updated by the function.
25
26on each page, i call:
27
28session_start();
29check_timeout($timeout, $SESSION);