Hi Mark, Very kind of you for all this information. i will dig into these links ASAP.... thanks a lot, thierry MW> Do a web search for the OSI network model - here's a quick sample: MW> http://www.webopedia.com/quick_ref/OSI_Layers.asp MW> All you need to know about datagrams: MW> http://www.faqs.org/rfcs/rfc768.html