SIP in higher education

Hi
  I have one question about the applicacion rtpproxy, I am trying to 
establish an RTP comunication  throught  your proxy, but it seems that it 
cuts the data from the other user, so the comunication is only 
unidirectional, I tried it with symmetric clients but this did not solved the 
problem, Have you got any idea??

  thanks for your time

David.