...
Orchestration processes interact with other platform components or external systems via standard and well-defined APIs.
Controllers (Infrastructure, Network and Application) participate in service instantiation and are the primary players in ongoing service management; for example, control loop actions, service migration and scaling, service configuration, and service management activities. Each controller instance supports some form of orchestration to manage operations within its scope.
...
See the attached presentation for an explanation of the system architecture of MSO, and it's its interaction with other OpenECOMP components: MSO High-level Design.