Software-Defined Networking or SDN is a relevant new term for an older paradigm of programmable networks. In summary SDN refers to the ability of writing applications to program the behavior of the network and the network devices.

SDN framework

An IP network element is composed of numerous logically separate entities that cooperate to provide a given functionality (such as a routing or IP switching) and yet appear as a normal integrated network element to external entities. Two primary types of network element components exist: control-plane components and forwarding-plane components.