The issue is, this is a SIP Registration message, it certainly does NOT contain SDP, in fact there are other SIP messages that does NOT contain SDP message but still need nathelper to recognize it behind a NAT so that OPENSER can send response back to the client correctly. In summary, nathelper should be able to base on the SIP message to handle it correctly. Best Regards, Bill Zhang -----Original Message----- From: Marc Haisenko [mailto:haisenko@comdasys.com] Sent: Thursday, August 03, 2006 12:09 AM To: users(a)openser.org Cc: Bill Zhang Subject: Re: [Users] Can not register to OPENSER On Thursday 03 August 2006 00:46, Bill Zhang wrote: body The message says it, and your SIP message proves it: the SIP message has no body. nathelper operates on the SDP body, it mangles them (together with rtpproxy) so that the SDP body sent to the receiver contains the address of your machine running OpenSER instead of the real phone. This is so that the machine can act as RTP proxy on network edges. Since your SIP message has no SDP body there is nothing nathelper can do :-) C'ya, Marc -- Marc Haisenko Comdasys AG Rüdesheimer Straße 7 D-80686 München Tel:   +49 (0)89 - 548 43 33 0 Fax:   +49 (0)89 - 548 43 33 29 e-mail: haisenko(a)comdasys.com http://www.comdasys.com