In order not to make a new thread, I will write my question here.
Right now I make an offer for the client and I have got some troubles with it.
I need to put together the Control Center for nearly 250 distributed PLC's. 100 of them are SAIA-Burgess ones and will probably communicate via OPC. Other PLC's (150 pcs.)will be S7-1200. Those remote stations are small - 20-30 IOs only. Communication will be done via mobile phone network GPRS. What is the best option for me to make a Control Center on WinCC 7.3? In other words how could I communicate with such number of devices?
Thank you.

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new subject after Splitting from Simatic WinCC 7.2 maximum number of connections to S7-1200 CPU