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ONF launches SDN northbound interface working group

The Open Networking Foundation forms a northbound interface working group to model and prototype technology, but not to necessarily pursue a standard.

The Open Networking Foundation launched a working group focused on defining northbound interfaces for software-defined networks, and it will explore whether standards are necessary -- an issue experts are still split on.

Initially, the Northbound Interface Working Group will develop information models for these interfaces, gather feedback from end users and develop prototypes.

Some people and vendors in the SDN community have pushed for standardization of northbound application programming interfaces (APIs) so that customers can take SDN applications with them if they switch controllers. A standard would also, in theory, make it easier for developers to write applications for a broad number for SDN stacks.

"Ultimately you're going to need something flexible," said Teren Bryson, IT director for a global industrial equipment manufacturer. "If the industry actually does go for wholesale adoption of OpenFlow and controller-based SDN, I think open standards are going to be the key for that -- and interoperability."

However, one of the chief arguments for standardization of northbound APIs -- avoidance of vendor lock-in -- isn't necessarily compelling, he said. "Everyone uses Microsoft Active Directory. They run OSPF [Open Shortest Path First] on their Cisco gear because they don't want to be locked into EIGRP [Enhanced Interior Gateway Routing Protocol]. But OSPF, as implemented by Cisco, is not going to be completely based on standards. Everyone wants standardization, but then vendors are going to differentiate from there."

The Open Networking Foundation (ONF) has steadfastly opposed any standardization of northbound interfaces in the past, claiming such a move would stifle innovation by narrowing the scope of applications that could be developed.

However, in announcing the formation of the Northbound Interface Working Group, the ONF acknowledged that the proliferation of different approaches to northbound APIs has created confusion in the market and impeded the progress of SDN. The working group, while exploring the different approaches to northbound interfaces, will determine whether standards are necessary.

Why northbound API standards may be pointless

Standardization of northbound APIs are difficult because the problems they try to solve are so varied, said Eric Hanselman, research director with New York-based 451 Research.

"Any effort to come up with a [standard approach] is going to constrain what the problems are that you are trying to solve," Hanselman said. "The question is, how much visibility do you want to have through the stack? If you want to create capacity for storage transactions, you probably have a slightly different set of capabilities [in the northbound interface] than you would if you want to be able to make sense of a control environment for path management. If you have compliance issues and want to make sure network paths have certain physical characteristics, you're going to need all sorts of primitives in there to be able to control those paths -- like I want it to go through these localities and not these. If you are just trying to get a path for storage with [specific] performance characteristics and capacity for a given amount of time, that's a very different approach for how you expose capabilities in the network."

Beyond the different problems applications try to solve through northbound interfaces, there are also the questions of the different industries that would use such interfaces. Enterprises and service providers are each looking for extremely different technologies to solve very different problems, Hanselman said. Moreover, service providers are even divided among themselves over how to approach certain aspects of SDN in their networks, he said.

"I think the conversation itself [that the ONF working group will start] is valuable at this point. Simply being a vehicle for deeper exploration for what [is] going to be a multiplicity of APIs is very valuable," Hanselman said.

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