session_id() does not set PHPSESSID

[happycloud]

Here's code:

<?
php $id = 111111;
session_id($id);  

session_start(); 
echo "session id: ".session_id();    

?> 
<br/>
<a href="session.php?<?echo SID?>">refresh</a> 

Why does the PHPSESSID in url differ from what I set? same with session_name();

Joshua