The control hierarchy for SDN networks is converging toward a three-tier structure. This paper describes this three-tier control hierarchy, which includes a service orchestrator, a network controller, and multiple domain controllers. It also describes the benefits of using a three-tier structure, which include faster innovation, a stable ecosystem of collaborating parties, and flexibility to replace building blocks with minimal effort and without vendor lock-in.
Selecting the right IP/optical network controller is critical for end-to-end service delivery in a multilayer, multivendor, multidomain network. This paper lists a set of questions that we suggest service providers ask suppliers when determining whether the solution can truly deliver comprehensive, accurate visibility and control.