[support] Why changing the session id?

Hello, I like to make a little shop, on my website. I like to give possibility to anonymous users to add some products to the cart. In the cart I try to store the user id and the session id (what is give the session_id() function). But the problem is, if a user is logged in the session id is changing. Why? And How can I access the anonymous user session? Ámon Tamás Sitefejlesztő és programozó -- 5NET Informatikai Kft. 1062 Budapest, Aradi utca 38. A 3/11 telefon: (1) 461-0205 | fax: (1) 461-0206 e-mail: amont@5net.hu | web: http://www.5net.hu