Preparing your system
=====================

This section describes which tools you 'll want to get. They should allow you
to follow along nicely. These are:

 + A PC running windows or linux. OPyCua is developped on debian Squeeze. It
   *should* run on any platform with support for Python.

 + A fairly recent version of 
   `Python <http://python.org/download/releases/2.7.3/>`_ . 
   We're using Python 2.6.6. Python 3 is untested, but might work just fine.

 + The python `Construct module <http://pypi.python.org/pypi/construct>`_ .
   Construct is a parser for binary data. It has some advantages over 
   `struct <http://docs.python.org/library/struct.html>`_.

 + `Wireshark <http://www.wireshark.org/>`_ with the 
   `OPC ua dissector <http://anonsvn.wireshark.org/viewvc/releases/wireshark-1.6.7/plugins/opcua/>`_
 
 .. note:: 
 
     * The OPC ua dissector is included with wireshark as from version 1.6.x
     * Debian squeeze uses wireshark 1.2.11.  A possible workaround is running
       wireshark in a chroot as described on the old wiki:
       `schroot <http://sourceforge.net/p/opycua/wiki/Schroot/>`_ .
 
 + An OPC ua client and server.



Talking OPC ua
--------------

To test the communication with a *real world* server, 
we use the following setup:: 

    +-------------+             +-------------+
    | Windows Box |             | Debian Box  |
    | with OPC UA |<--network-->| with OPC UA |
    |   Server    |             |    Client   |
    +-------------+             +-------------+
    
There are some (alot of) free OPC UA servers and clients available. 
Pick one from this `list of OPC UA products <http://www.opcfoundation.org/Default.aspx/OPCUAProducts.asp>`_ 
at the OPC Foundation website. 
    
We'll be using the *free* client and server from Unified Automation GmbH. 
To download, you'll have to register. The client is available for both 
windows and linux. The server is only available for windows.
    
 * `UaExpert for Linux V1.2.1 <http://www.unified-automation.com/uaexpert.htm>`_
 * `OPC UA Demo Server for Windows <http://www.unified-automation.com/opc-ua-servers/>`_
    
    
To configure the client to talk to our experimental server. 
Go to menu **Server > Add** and switch to the **advanced** tab. 
There you can enter the Endpoint URL. 
If you are running server and client on the same machine, 
you can find the endpoint url in the uaExpert server window. 
If the server runs on a different PC, you should use an endpoint URL like::
    
    opc.tcp://192.168.0.1:4840    
    
where 192.168.0.1 is the IP address of the pc running the server and 4840 
the port used by the server.
    
.. note:: 

    + Make sure you use SecurityPolicy None. Otherwise wireshark can't 
      decode your packets.
    + By default, the server uses port 4841, not the *standard* 4840. 
      Because of this, wireshark won't decode the packets correctly. 
      You can either change the port of your server, or (easier) change the 
      port in Wireshark (go to **edit > preferences** and find the opc ua 
      protocol)
    
.. 
   Add some screenshots !!