Hello, I'm using kamailio and OpenImsCore HSS module to set up an IMS enviroment(P/I/S-CSCF and HSS). All these four modules are set up in one cloud server in public network with different ports(4060/4061 5060 6060 3869 3870) to commonicate with each other. Now I have two users Alice and Bob, they are in private network. I can register Alice and Bob with ImsDroid on this IMS, however when I use Alice to call Bob, I can see "You must register first with a S-CSCF" error. As I found this was caused by kamailio.cfg in pcscf module, I comment out these lines below. Then I got another error "Server error on LIR select next S-CSCF". And I captured packets on port 5060, I can see several "Request-Line: OPTIONS sip:sbc-2.ng-voice.com SIP/2.0" and "Request-Line: OPTIONS sip:sbc-1.ng-voice.com SIP/2.0". #if (!pcscf_is_registered("location")) { # send_reply("403","Forbidden - You must register first with a S-CSCF"); # break; #} What's wrong with my IMS? Could any body give me some help? Thank you! Here are my IMS configure files. kamailio.zip <http://sip-router.1086192.n5.nabble.com/file/n148131/kamailio.zip> Here are my hss configure files. hss_config.zip <http://sip-router.1086192.n5.nabble.com/file/n148131/hss_config.zip> -- View this message in context: http://sip-router.1086192.n5.nabble.com/You-must-register-first-with-a-S-CS… Sent from the Users mailing list archive at Nabble.com.