Subsystem Control allows to gain access to the services implemented by the components in the subsystem.
Operator Control (the client) sends Request Subsystem Control message with its authority code and certificate. The Subsystem Control service replies Confirm Subsystem Control message with response code Granted, and Session Key if control is granted.
The Subsystem Control service notifies all the Access Control services in the subsystem with Session UUID. Operator Control (the client) needs to present the matching Session UUID in order to be granted access to the services.
When not being controlled, the Subsystem Control service broadcasts the default Session UUID to all the Access Control services within the subsystem.
Figure 9 Subsystem Control Message Interaction
In the case that other Operator Control (client) needs to access the subsystem, Subsystem Control service also implements control handover to ask the controlling Operator Control (client) to release control. Below shows the message interactions between two Operator Controls (clients) and the Subsystem Control service during control handover.
Figure 10 Subsystem Control Handover Message Interaction