The PI Connector for IEC 61850 is written to be compliant with the IEC standard. And the communication we use is MMS. We use the software library from SISCO (https://www.sisconet.com/) called MMS Lite which supports this. This is pretty much an industry standard software stack for writing both 61850 clients and servers. The PI Connector is a 61850 client.
Hope this helps you. Please let us know if you have more questions.
Have a great day,