SymmetricRTPSession & quality of transmitted file

Hei list,

I am using the audiotx.cpp as a base class to transfer a file to a destination.
As i realized that audiotx was opening a random socket to send the source,
i decided to use the SymmetricRTPSessions instead.  This is just because that 
two communication partners should know only one port of the other.

So far so good:
Now to my surprise, the quality of the transmitted file on the receivers' side is unbelievable worse if i use the SymmtericRTPSession to create the socket object.  Why is that? Do i have to do sthing more, like block receiving until send finishes? 

The code is almost the same with audiotx.cpp,  except that i use "SymmetricRTPSession socket" and do a busy waiting in the execution procedure(main()) like:  while(!transmitter->getTStateFinished() ); 

Thanx in advance