“Open” is the new software-defined networking (SDN) marketing buzzword. Migration to SDN has led to development of a large number of different controllers, each with its own northbound application programming interface (API).
The northbound API connects applications and management software with the SDN controller. Everyone says their APIs are open, but that doesn’t mean they comply with a standard, it doesn’t necessarily mean they are open source, it certainly doesn’t mean they are interoperable among vendors, and it doesn’t prevent vendor lock-in.
Service providers want a northbound API that enables a network to be dynamic, manageable, and application-aware. Vendor-supported APIs can fill the bill, but service providers are starting to making a push for standard SDN APIs to avoid being locked in to one or more vendor-supported ecosystems. We expect the industry to reach a consensus on interoperable northbound APIs within a few years.
Current SDN solutions are not open enough for developers
Vendors, service providers, industry consortia, and academic and research groups have all developed SDN controllers with different northbound APIs. These APIs are all being labeled as “open” because they are made available for third-party development or based on software released under an open source license.
While these different APIs typically offer a common Representational State Transfer (RESTful) architectural style, software applications can’t be moved between different vendors’ SDN solutions, and application developers are forced to code for a specific API.
This has led to a marketing blitz by the developers of different controllers to show support by the largest ecosystem of third-party vendors and create the impression of a de facto standard, whereas in reality service providers are currently limited to multiple incompatible ecosystems.