TCP小问题，求帮助

 private void btnOpenLister_Click(object sender, EventArgs e)
  {
    socketWatch = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);// 创建负责监听的套接字
     IPAddress address = IPAddress.Parse(tbxIP.Text.Trim()); // 获得文本框中的IP对象
     IPEndPoint endPoint = new IPEndPoint(address, int.Parse(tbxPort.Text.Trim())); // 创建包含ip和端口号的网络节点对象
     if (start == false)
        {
           try
              {
                 socketWatch.Bind(endPoint); // 将负责监听的套接字绑定到唯一的ip和端口上；  
                 socketWatch.Listen(100); // 设置监听队列的长度；  
                 Thread threadWatch = new Thread(WatchConnecting);// 创建负责监听的线程； 
                  threadWatch.IsBackground = true;
                  threadWatch.Start();
                  start = true;
                  btnOpenLister.Text = "停止监听";
                }
                catch (SocketException se)
                {
                    MessageBox.Show("异常：" + se.Message);
                    return;
                }
            }
            else
            {
                try
                {
                    socketWatch.Dispose();  
                    // socketWatch.Close();              
                    start = false;
                    btnOpenLister.Text = "开始监听";                    
                }
                catch
                {
                    MessageBox.Show("停止监听发生错误", "提示");
                }
            }
        }
 private void WatchConnecting()
        {          
            while (start)  // 持续不断的监听客户端的连接请求；  
            {
                // 开始监听客户端连接请求，Accept方法会阻断当前的线程；  
                Socket sokConnection = socketWatch.Accept();                           
                Thread thr1 = new Thread(Thread_data);
                thr1.IsBackground = true;
                thr1.Start(sokConnection);             
            }
        }
private void Thread_data(object sokConnectionparn)
   {
      Socket sokClient = sokConnectionparn as Socket;
        while (start)
          {
             try
              {
                tcpdata1 = new byte[sokClient.ReceiveBufferSize];
                 int k = sokClient.Receive(tcpdata1);
                byte[] tcpdata = new byte[k];
                 Array.Copy(tcpdata1, tcpdata, k);
                 DataReceive(tcpdata);
                 Byte[] data = new Byte[] { 0x01, 0x02, 0x03 };                          
                 sokClient.Send(data); 
                }
                catch
                {
                    sokClient.Close();
                    break;
                }
            }
        }
 private void DataReceive(byte[] tcpdata)
    {
        System.Threading.Thread.Sleep(100); //延时100ms等待接收完数据
         this.Invoke((EventHandler)(delegate
          {
             for (int i = 0; i < tcpdata.Length; i++)
             {
               tbxReceive.Text += tcpdata[i].ToString("X2") + "\t";
               }
          }));
     }   

求问怎么停止监听并释放端口；有三个客户端A、B、C连接此服务端，A发送数据后，B发送数据，如发01（十六进制）；B第一次发数据服务端接收的数据是00，再发一次服务端接收的数据才是01,；C发送数据也如此，第一次发，接收的是00；客户端相互切换发送数据接收数据就有问题。