MessageHeader sendMH = new MessageHeader(MessageHeader.MessageHeaderType.BindingRequest);


                ChangeRequest changeRequest = new ChangeRequest();
                sendMH.addMessageAttribute(changeRequest);

                byte[] data = sendMH.getBytes();


                s = new DatagramSocket(4500);
                s.setReuseAddress(true);

                DatagramPacket p = new DatagramPacket(data, data.length, InetAddress.getByName("stun.l.google.com"), 19302);
                s.send(p);

                DatagramPacket rp;
                rp = new DatagramPacket(new byte[32], 32);

                s.receive(rp);
                MessageHeader receiveMH = new MessageHeader(MessageHeader.MessageHeaderType.BindingResponse);

                final MappedAddress ma = (MappedAddress) receiveMH
                        .getMessageAttribute(MessageAttribute.MessageAttributeType.MappedAddress);
                System.out.println(ma.getAddress() + " " + ma.getPort());