[SR-Users] Internet RTP filters

Hi everybody, First to say sorry if this is not the right list to send this post, anyway we hope somebody can help us. We have Kamalio 3.1.3 working since many time ago. We use an RTP Proxy for NAT issues in the server side and STUN for NAT issues in the internet client side. Calls in Spain are working fine. This month one of our users has gone to Rwanda (our University has created a Hospital and a School in a region called Nemba). They are using an internet connection by satellite, with a low bandwith (128kb down, 16 up). In some countries we have trouble with internet calls. SIP signaling works fine, the call rings and is stablished, but there is a problem with RTP streams: - RTP streams sent by RTP proxy to client in internet never arrives to the client in the internet (although they RTP is sent to the right IP and port) - RTP streams sent by client in the internet never arrives to RTP proxy (although RTP is sent to the right IP and port) As I said this happens sometimes, and it's happening in Rwanda. We usually solve this problem making a VPN connection to the University, then the RTP stream works fine. However when our Rwanda's users connect to VPN, the Bandwith goes down (45 kbps down and 8kbps up), so they can hear as perfectly, but we can't hear them. Does anyone know if T companies are filtering RTP traffic? I've tried to change ports in RPT Proxy with no result. How could we solve this? Thanks in advance and best regards, Ricardo Dominguez Universidad Miguel Hernández de Elche