UDP 数据报套接字和组播 IP

我在客户端上接收消息时遇到了一些问题：

本质上，我可以向侦听器发送消息"Hello world"，但是当侦听器尝试发送"回复"时，客户端没有收到消息？

你认为我在这里缺少什么？

客户：

        var socket = new DatagramSocket();
        socket.MessageReceived += HandleMessageReceive;
        await socket.ConnectAsync(new Windows.Networking.HostName("224.192.12.12"), "9991");
        socket.JoinMulticastGroup(_multicastGroupIp);
        DataWriter writer = new DataWriter(_socket.OutputStream);
        writer.WriteString("Hello world");
        await writer.StoreAsync();

听者：

            var stateObject = new StateObject();
            stateObject.LocalEndPoint = new IPEndPoint(IPAddress.Any, 9991);
            stateObject.SocketClient = new UdpClient();
            stateObject.SocketClient.Client.Bind(stateObject.LocalEndPoint);
            stateObject.SocketClient.JoinMulticastGroup(IPAddress.Parse("224.192.12.12"));
            stateObject.SocketClient.BeginReceive(new AsyncCallback(HandleDiscoveryServiceReceive), stateObject);
private static void HandleDiscoveryServiceReceive(IAsyncResult ar)
        {
            var stateObject = (StateObject)ar.AsyncState;
            IPEndPoint localEndPoint = stateObject.LocalEndPoint;
            byte[] data = stateObject.SocketClient.EndReceive(ar, ref localEndPoint);
            string decodedData = Encoding.UTF8.GetString(data);
            System.Console.WriteLine("Got something back: {0}", decodedData);
            UdpClient client = stateObject.SocketClient;
            client.MulticastLoopback = false;
            byte[] msg = Encoding.UTF8.GetBytes("REPLY");
            IPEndPoint remoteEndPoint = new IPEndPoint(IPAddress.Parse("224.192.12.12"), 9991);
            client.Send(msg, msg.Length, remoteEndPoint);
            client.BeginReceive(HandleDiscoveryServiceReceive, stateObject);
        }