[Serusers] Checking user credentials on INVITE method

I know Jan won't be happy for this question because it may look simple. But I have tried everything I can and after failing I decided to ask it here. I have realized that SER checks the username and password when a UA sends a REGISTER command but it doesn't check the password when a user sends a INVITE command. This makes SER accept calls from people who did not even register. This is true because my GATEWAY doesn't register with SER but I can make calls from PSTN to my IP network. So, my question is: HOW do I instruct SER to check the username and password of the CALLER? Thanks, __________________________________ NZEYIMANA Emery Fabrice NEFA Computing Services, Inc. P.O. Box 5078 Kigali Office Phone: +250-51 11 06 Office Fax: +250-50 15 19 Mobile: +250-08517768 Email: dg(a)nefacomp.net http://www.nefacomp.net/