El Wednesday 21 May 2008 16:47:38 Pezhman Lali escribió: Buff... that's a terrible question... Well, using OpenSer "nathelper" module in conjuntion with RtpProxy server (or "mediaproxy" module with MediaProxy server) you can solve NAT issues in all cases except those ones: - You use a non-symettric SIP/RTP client (hope nowadays all are symetric). - You are behind a router with SIP ALG enabled. This last case is really dangerous and there is no server side solution for this (you need to dissable ALG in the router). http://www.voip-info.org/wiki/view/Routers+SIP+ALG NAT keepalive is performed by OpenSer "nathelper" module and it works for UDP clients. If you use SIP TCP then you must set the REGISTER "expires" to less than 32 seconds. Also a recent patch for OpenSer SIP TCP stack allows OpenSer keeping hte TCP connection if the user sends CRLF (so OpenSer replies with CRLF CRLF). The very complex draft "outbound" is not implementer in OpenSer (in fact, it's a draft still...). It's mechanism for keeping NAT in SIP TCP: http://tools.ietf.org/html/draft-ietf-sip-outbound Regards. -- Iñaki Baz Castillo ibc(a)in.ilimit.es