So we need to give an abstract model about the forwarding network status, which abstract the information for the control
network and management network to form necessary and dynamic views of the forwarding network. Since there are differences between the information needed by the control network and that needed by the management work, the forwarding network needs to provide two kinds of interfaces for status perception: one for the control network; the other for the management network. And that means we may need to design or use two protocols for status perception: one for the
communication between a controller and a forwarder; the other for the communication between a manager and a forwarder.