General question about connector

Dear experts,

We are preparing for a project which involves multiple different MES/SCADA/PCL systems. Some systems have OPC servers connected to them, according to the Menu, xMII could connect to them via UDS. Others have "I/O server" or "I/O device" (quote from customer) connected to them. I am pretty new to this field, could anyone tell me what is the I/O server, and xMII be albe to connect to them? Or do we have to replace these I/O servers with OPC servers?

Many thanks

Yiming.