Ciao Christian
PCAP file would be easier to read. But let's see..
1st Leg:
Linode Client1 IP: 93.189.137.22 => Kamailio Server: 44.3.44.40 (73 from HB9EUE :-) )
That Linode Client has RTP on: 192.168.1.21
2nd Leg:
Kamailio (44.3.44.40) => Client2 (88.116.10.134) Grandstream
RTP Side 1: 192.168.1.21
Grandstream => Kamaililio 200 OK + SDP
Grandstream tells: RTP on: 188.116.10.134
So, the question is: Can 188.116.10.134 <=> 192.168.1.21 communicate with each other?
I fear not! 192.168.1.21 is obviously behind NAT.
93.189.137.22 probably is a NAT router. Maybe it has a SIP ALG setting which would take care to open ports and rewrite the RTP IP address? If not, you loose!
Kamailio does nothing with the RTP audio stream. So both connected clients would need to be able to directly send UDP packets to each other.
OR: You need to 'backhaul' the rtp audio stream via some RTP proxy like rtpengine which could detect NAT and try to send the RTP stream back to the IP it received it from, instead of the one advertised in the SDP.
Mit freundlichen Grüssen
-Benoît Panizzon-