Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As _
   System.EventArgs) Handles Button3.Click
        Dim user = "[" + ComboBox2.Text + "]    "
        Try
            ListBoxCommand(String.Empty)
            If SimpleClient.Connected Then
            rem unwichtig
            Else
                ListBoxCommand(user + "Verbinden...")
                SimpleClient.Connect(ComboBox2.Text, TextBox5.Text)
                ListBoxCommand(user + "Port-" + TextBox5.Text)
                Stream = SimpleClient.GetStream
                Timer1.Start()
                ListBoxCommand(user + "Connected...")
                Button3.Text = "Verbindung trennen (" + ComboBox2.Text + "-" + _
                  TextBox5.Text + ")"
                Button1.Enabled = True
            End If
        Catch ex As Exception
            ListBoxCommand(user + ex.Message)
            ListBoxCommand(user + "Verbindung abgebrochen...")
            MsgBox(ex.Message)
        End Try
    End Sub
 
 
 
 Function SendCommand(ByRef message) As Integer
        Try
            Dim sendBytes As [Byte]() = Encoding.ASCII.GetBytes(message)
            Stream.Write(sendBytes, 0, sendBytes.Length)
        Catch ex As Exception
            ListBoxCommand(ex.Message)
            MsgBox(ex.Message)
        End Try
        Return 0
    End Function

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles MyBase.Load
Das war der Client, und jetzt der Server:
  SimpleServer = New TcpListener(System.Net.IPAddress.Parse(0), 25)
        SimpleServer.Start()
        SimpleServer.BeginAcceptTcpClient(AddressOf OnConnect, New Object)
end sub
 
 
 
 Private Sub OnConnect(ByVal ar As System.IAsyncResult)
        Client = SimpleServer.EndAcceptTcpClient(ar)
        Stream = Client.GetStream
        ReDim bytes(Client.ReceiveBufferSize)
        Stream.BeginRead(bytes, 0, CInt(Client.ReceiveBufferSize), AddressOf _
          onGetData, New Object)
    End Sub
 
    Private Sub onGetData(ByVal ar As System.IAsyncResult)
        Try
            Dim clientdata As String = Encoding.ASCII.GetString(bytes)
            Dim sendBytes As [Byte]() = Encoding.ASCII.GetBytes(clientdata)
            Stream.BeginRead(bytes, 0, CInt(Client.ReceiveBufferSize), _
              AddressOf onGetData, New Object)
            Dim Array As Array = clientdata.Split("[", "]", String.Empty, _
            String.Empty)
rem und so weiter
end sub