Question

So I am currently working on a client application that listens on port 5004 for RTP packets. Since there may be multiple servers sending RTP packets, I can’t use sockets to connect to a specific remote host. Instead, I have tried the following to listen on a local port:

Socket socket = new Socket("127.0.0.1", 5004);
Socket socket = new Socket("localhost", 5004);
Socket socket = new Socket(InetAddress.getByName("localhost"), 5004);
Socket socket = new Socket(InetAddress.getLocalHost(), 5004);

Any of the above will give me this exception:

java.net.ConnectException: Connection refused: connect

I have also tried using a DatagramSocket, but DatagramPackets require that I specify the size of the packet to be read.

To summarize, I need to find a way to listen on local port 5004 for RTP packets of unknown size without connecting to a specific remote host/address. Any help is greatly appreciated!

EDIT:

I now have a ServerSocket set up to listen for connections, but I still can’t manage to read in any packets.

try {   ServerSocket server = new ServerSocket(5004);
        Socket s = server.accept();
        BufferedReader rtpReader = new BufferedReader(new InputStreamReader(s.getInputStream()));
        while (true){
            int k = rtpReader.read();
            if (k == -1) break;
            System.out.println(k);
        }
}

Note: The RTP packets are sent over a Multicast address.

The problem turned out to be the Multicast. Refer to Nikolai’s answer. Thanks alot!

Answer 1

You have to use java.net.MulticastSocket, and join the multicast group. Something like:

// put your multicast address here
InetAddress group = InetAddress.getByName( "244.10.10.10" );
MulticastSocket sock = new MulticastSocket( 5004 );
sock.joinGroup( group );

byte[] buf = new byte[1472];
DatagramPacket pack = new DatagramPacket( buf, buf.length );

while ( whatever ) {
    sock.receive( pack );
    // handle data
}

sock.leaveGroup( group );