RTPDuplex & RTPSessions

Hello,

i just tried to use the RTPDuplex Class for my implementation as i am merging a sender and a receiver.
Mainly it looks like:

   // first send stream 
    if(this->anno_fstream != NULL){
        while(!this->anno_fstream->eof()){

            this->anno_fstream->read(reinterpret_cast<char *>(buffer), PACKET_SIZE) ;
            rtp_socket->putData(PACKET_SIZE*i, buffer, PACKET_SIZE) ;

            Thread::sleep(TimerPort::getTimer()) ;
            TimerPort::incTimer(PERIOD) ;
            i++ ;
        }
    }

 // then receive stream  
for(i=0 ; true ; i++){
        const AppDataUnit* adu;
        do{
            adu = rtp_socket->getData(rtp_socket->getFirstTimestamp()) ;
            if(adu == NULL){
                Thread::sleep(5) ;
            }
            else cout << "." ;

        } while( (adu == NULL) || (adu->getSize() <=0)) ;

        dump_file->write((char *)adu->getData(), adu->getSize()) ;   
        Thread::sleep(TimerPort::getTimer()) ;
        TimerPort::incTimer(PERIOD);
}

To my surprise RTPDuplex doesn't send and receive any rtp packets even if the connect method doesn't
deliver any errors.. I've read in couple of previous threads which are telling the RTPDuplex is not supported/maintained  anymore.

What i wonder is, what is the difference of RTPDuplex from RTPSession? Does it mean that normal 
RTPSession classes are one-directional sockets?  Isn't it possible to use a normal RTPSession object to
send and receive rtp packets at the same time? What does RTPDuplex offers that other not do?

Thanx in advance,