At the beginning of IEC61850 communication, in MMS.InitiateRequest and MMS.InitiateResponce the client and server are exchanging information also about maximal number of outstanding MMS requests (typically it affects number of outstanding responses for MMS.Read requests).
During association the iec850 driver proposes 10 and then acts on this, whatever the server informs in the response.
At the beginning of IEC61850 communication, in MMS.InitiateRequest and MMS.InitiateResponce the client and server are exchanging information also about maximal number of outstanding MMS requests (typically it affects number of outstanding responses for MMS.Read requests).
During association the iec850 driver proposes 10 and then acts on this, whatever the server informs in the response.
Now value received as "Negotiated Max Outstanding Calling" is taken into account. The driver limits the number of simultaneously sent MMS requests to this value and then sends a next request only after server responded to some outstanding one.
There are servers on the market supporting only 1 outstanding requests - then they cannot queue more as one MMS.Read request.