Over recent years, CSPs and standard bodies have converged on a common architecture for deploying SDN automation. This agreed architecture is based on three tiers of control, starting from the top:
Service orchestrators - assurance tools and systems, which are fundamentally part of the next-generation OSS, comprise the first tier. These systems understand the business side of the operations of the service provider but don’t understand the network in depth.
The hierarchical controller is responsible for understanding the entire network and providing a simplified abstract view toward the OSS tools. The hierarchical controller does not talk directly to the network devices but relies on SDN controllers for different domains, be it microwave domains, WDM/OTN optical domains, or packet domains.
The domain controller is responsible for discovering their network data for optimizing paths within their network, configuring services within their own domain, updating the hierarchical controller about changes in the network, and taking their requests from the hierarchical controller to affect change
in the network.