What is the difference between DDE and NetDDE?
DDE and NetDDE are quite different technologies. DDE is the first crack at IPC offered by Microsoft when they decided that their OS was “multi-tasking”. The intent was simple transmission of (name,value) pairs, and it was implemented in as simple a manner as they thought possible. It is well established and robust, once you figure out how to implement it correctly. NetDDE is an extension created by Wonderware, the makers of InTouch. It is an attempt to extend the DDE semantics to the network. It does indeed show real problems with more than a few nodes, and everybody who has tried to use it is aware of this. We don’t use NetDDE (the Wonderware mechanism). It is not reliable. We use local DDE (the Microsoft mechanism), which is reliable. The networking portion of our Cascade Connect connection is done using TCP/IP. We carefully handle timeouts, breaks, re-connections, multiple connections, multiple QNX hosts, etc. at the TCP level. Once the message is on the Windows box, it is converted
