The solution is rather simple, at subclass Reciever add: run { ... if(jg) { obj=channel.receive(0); if(obj instanceof Message) { byte[] buffer = ((Message)obj).getBuffer(); in=new DataInputStream(new ByteArrayInputStream(buffer)); } else { System.out.println("received non-msg: " + obj.getClass()); continue; } } else { sock.receive(packet); in=new DataInputStream(new ByteArrayInputStream(buf)); } number=in.readInt(); matrix [number] [1] =1; if (num_received != number) { System.err.println(" lost packet "+ number); num_received = number; } ... num_received++;