Tag engine to opc server communication protocol

[unclebump]

When the tag engine talks direct to a plc with modbus rtu, there is a CRC checksum built into the communication protocol to provide reliable data transfer. When the tag engine talks directly to an opc server program, what protocol is used?? Is there any kind of checksum to verify data integrity??

[Roli]

OPC Client to OPC Server communication protocol is based on Microsofts DCOM architecture, which is an object model oriented communication mechanism based on RPC (TCP/IP). I as know, there is no checksum verification specifically as known in PLC protocols. However, there are some mechanism to support fault tolerance better. (see DCOM Technical Overview, section, Fault Tolerance)

You could find more info from Microsofts MSDN library e.g. Serach from MS MSDN Library on "DCOM", or DCOM Overview.

The OPC specification could be downloaded from the ion.org>OPC Foundation, specifically you could find a white paper on OPC, DCOM and Security as pdf file.


Hope this helps

Roland
PS: If someone needs more info on Modbus specification you might find it on Modbus.org