An SDN architecture can be representing different planes and layers that not necessarily need to be present for every deployment.
The management plane is the set of applications that leverage the functions offered by the Northbound Interface to implement network control and operation logic. This includes applications such as routing, firewalls, load balancers, monitoring, and so forth. Essentially, a management application defines the policies, which are ultimately translated to southbound-specific instructions that program the behavior of the forwarding devices.
Forwarding devices are programmed by control plane elements through well-defined SI embodiments. The control plane can therefore be seen as the “network brain.” All control logic rests in the applications and controllers, which form the control plane.