TCP proxy program with c sharp - tcp

Question

This is TCP proxy with c#, I want multi clients to my proxy (as below code), and then to server just use one TCP connection (because the server is old PLC device, it's just support one connection).
My problem is how to use single TCP connection from proxy to server.
My English is poor, thanks very much for help.
class Program
{
// proxy listenning
static TcpListener listener = new TcpListener(IPAddress.Any, 9600);
const int BUFFER_SIZE = 4096;
static void Main(string[] args)
{
listener.Start();
// Accept clients.
while (true)
{
var client = listener.AcceptTcpClient();
var clientStream = client.GetStream();
//problem was here: how to use just single connection
TcpClient server = new TcpClient("10.110.59.1", 9600);
var serverStream = server.GetStream();
new Task(() => {
new Task(() => {
byte[] message = new byte[BUFFER_SIZE];
int clientBytes;
while (true)
{
clientBytes = clientStream.Read(message, 0, BUFFER_SIZE);
serverStream.Write(message, 0, clientBytes);
}).Start();
new Task(() => {
byte[] message = new byte[BUFFER_SIZE];
int serverBytes;
while (true)
{
serverBytes = serverStream.Read(message, 0, BUFFER_SIZE);
clientStream.Write(message, 0, serverBytes);
}
client.Close();
}).Start();
}).Start();
}
}//end main
}//end class