If you look at your trace the call is sending a re-invite over and over and over again with no reply
you need to examine your network topology and find out why the packets FS is sending to your phone never make it.
also try disabling session-timers on the snom
are you talking about our problem, that we get a hangup after 120 seconds? i just ask to avoid, that we are talking about different things. if we connect without stun and call the 5900, we can hear the music, so i assume, that we are receiving packets from fs!? but after about 120 seconds, we receive the hangup. before everything was fine and as expected. we also tried disabling session-timers in the snom - same problem. thant's the problem, we tried soooooo many things, but simply nothing changes the problem or makes something different (like sending the hangup later or earlier).