Hello, well I got it solved now .... to configure my upstream provider I had to put freeswitch IP address into this sofia conf fields <param name="rtp-ip" value="212.6.123.118"/> <param name="sip-ip" value="212.6.123.118"/> This solved my "Invalid Session Description" resp. "invalid transport IP address" due to DNS issues on my provider side. Then I had to configure <registration name="EWE TEL"> ... <param name="register-from" value="sip:032223930016@sip01.voice.ewetel.de"/> This is freeswitch's address in my providers voip domain <param name="register-to" value="sip:032223930016@212.6.123.118"/> Dunno what exactly this does, but it tells my provider at least on which IP address the number 032223930016 can be found. ... </registration> I can do establish now a ring from uac, through freeswitch, through provider, through PSTN to my old classic phone at office... quite long way to get from pc mouse to phone on the desk ... ;) Tomorrow I will test a real call when I'm back in office ... regards helmut ------------------------------------------------------------------------ Hello, after fixing my sofia configuration cause of my "invalid transport IP address" problem I got a new problem :( Freeswitch tries to set up a call to my upstream provider on behalf of originating uac. My provider replies with a 407 "Proxy Authentication Required". Freeswitch acknowledges to my provider and sends a 603 "Decline" message back to uac and terminates the call. Looks all quite clean. But ... Shouldn't freeswitch send authentication data to my provider as a response to 407 message? If so, is this data the same as for registration? And further where can I tell freeswitch to do so? regards helmut -------------------------------------------------------------------------