UDP-Listener reagieren client

Fand ich diesen tollen code auf der MSDN-Website für ein UDP-Client/Server-Verbindung, allerdings kann der client nur an den server senden, kann es nicht wieder Antworten. Wie kann ich diese, so kann der server antwortet dem client, der die Nachricht zu senden.
Der Server

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.IO;
using System.Security.Cryptography;


namespace UDP_Server
{
    class Program
    {
        private const int listenPort = 11000;

        private static void StartListener()
        {
            bool done = false;

            UdpClient listener = new UdpClient(listenPort);
            IPEndPoint groupEP = new IPEndPoint(IPAddress.Any, listenPort);
            try
            {
                while (!done)
                {
                    Console.WriteLine("Waiting for broadcast");
                    byte[] bytes = listener.Receive(ref groupEP);
                    Console.WriteLine("Received broadcast from {0} :\n {1}\n",groupEP.ToString(), Encoding.ASCII.GetString(bytes, 0, bytes.Length));
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }
            finally
            {
                listener.Close();
            }
        }

        public static int Main()
        {
            StartListener();

            return 0;
        }
    }

}

Und der client

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.IO;
using System.Security.Cryptography;

namespace UDP_Client
{
    class Program
    {
        static void Main(string[] args)
        {
            Send("TEST STRING");
            Console.Read();
        }
        static void Send(string Message)
        {
            Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            IPAddress broadcast = IPAddress.Parse("10.1.10.117");
            byte[] sendbuf = Encoding.ASCII.GetBytes(Message);
            IPEndPoint ep = new IPEndPoint(broadcast, 11000);
            s.SendTo(sendbuf, ep);
        }
    }
}