[Serusers] How to configure SER for that kind of use

Hi all, I need to configure two ser servers to do such a thing : SER2 is the registrar proxy, knowing ips ... SER1 is a must go through proxy. Each packet must go through him before being sent to SER2. ________ ________ | | REGISTER | | Phone B ---->| |------------------>| | | SER1 | | SER2 | | | | | | IP .4 | REGISTER | IP .8 | Phone A ---->| |------------------>| | |_______ | |________| CALL from A to B ________ ________ | | CALL | | Phone B <----| |<------------------| | | SER1 | | SER2 | | | | | | IP .4 | CALL | IP .8 | Phone A ---->| |------------------>| | |_______ | |________| When a call is done by A, it must go through ser1 then to ser2 and before coming back to phone B it must go to SER1. I can't find a way to do that with a script. If someone can help me, it would be great. Thanks, Laurent