void Main()
{
    Socket socketA = null;
    Socket socketB = null;
    var maxWaitingRequest = 10;
    var localSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    localSocket.SetSocketOption(SocketOptionLevel.Socket,SocketOptionName.ReuseAddress,true);
    localSocket.Bind(new IPEndPoint(IPAddress.Any, 81));
    localSocket.Listen(maxWaitingRequest);
    while (true)
    {
        var remoteSocket = localSocket.Accept();
        if (socketA == null)    //client
            socketA = remoteSocket;
        else if (socketB == null)   //server
        {
            socketB = remoteSocket;
            ThreadPool.QueueUserWorkItem(new WaitCallback(transfer), new Socket[] { socketA, socketB });
            ThreadPool.QueueUserWorkItem(new WaitCallback(transfer), new Socket[] { socketB, socketA });
        }
    }
}

public static void transfer(object obj)
{
    var socketA = ((Socket[])obj)[0];
    var socketB = ((Socket[])obj)[1];
    while (true)
    {
        try
        {
            var data = new byte[10240];
            int read = socketA.Receive(data);
            if(read > 0)
                socketB.Send(data.Take(read).ToArray());
        }
        catch
        {
            socketA.Close();
            socketA.Close();
            break;
        }
    }
}

static Queue<string> msgList = new Queue<string>();
static readonly object msgLocker = new Object();
static int localPort = 20000;
static string msg = "I am A";

void Main()
{
    var localSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    var localEP = new IPEndPoint(IPAddress.Any, localPort);
    localSocket.Bind(localEP);
    localSocket.Connect(new IPEndPoint(IPAddress.Parse("127.0.0.1"), 81));
    ThreadPool.QueueUserWorkItem(recieveHandler, localSocket);
    
    Thread.Sleep(10000);
    localSocket.Send(System.Text.Encoding.Default.GetBytes(msg));
    
    while (true)
    {
        lock (msgLocker)
        {
            if(msgList.Count >0)
                Console.WriteLine(msgList.Dequeue());
        }
        
        Thread.Sleep(1000);
    }
}

public static void recieveHandler(object p)
{
    var localSocket = (Socket)p;
    while (true)
    {
        var data = new byte[1024];
        var read = localSocket.Receive(data);
        if (read > 0)
        {
            Console.WriteLine("recieved " + read.ToString() + " bytes");
            lock (msgLocker)
                msgList.Enqueue(System.Text.Encoding.Default.GetString(data.Take(read).ToArray()));
        }
    }
}
// Define other methods and classes here