建立了TCP连接之后，怎么释放端口？

客户端程序只要和服务端程序连接了，不关闭程序就没办法再次连接。
代码如下，请高手指点

Try
            tlTcpListen = New Net.Sockets.TcpListener(iPort)
            tlTcpListen.Start()
            ToolStripStatusLabel1.Text = "正在监听..."
            tcClient = tlTcpListen.AcceptTcpClient()
             nsStream = tcClient.GetStream()
            srRead = New IO.StreamReader(nsStream)
            ToolStripStatusLabel1.Text = "已经建立TCP连接！"
            While blistener
                Dim sMessage As String = srRead.ReadLine()
                If (sMessage = "STOP") Then
                    tlTcpListen.Stop()
                    nsStream.Close()
                    srRead.Close()
                    ToolStripStatusLabel1.Text = "无连接！"
                    thThreadRead.Abort()
                    Return
                Else
                    Dim sTime As String = DateTime.Now.ToShortTimeString()
                    ListBox1.Items.Add(sTime + " " + sMessage)
                End If
            End While
        Catch ex As System.Security.SecurityException
            MessageBox.Show("侦听失败！", "错误")
        End Try