(Above: Dan Pitt marvels at the mention of SDN in an airplane-magazine ad.)

The Open Networking Foundation has decided to research the northbound interface for software-defined networking (SDN), a step that might or might not lead to eventual standardization.

It's a big step, because there's been a cry from some quarters to standardize the northbound interface, which connects management software and applications with the SDN controller. Until now, the ONF has resisted.

The ONF board approved the new NBI Working Group on Wednesday, along with a new working group for wireless operators (which is really nice, but we're not going to talk about that right now). ONF Chairman Dan Pitt announced the new working groups Wednesday morning at the SDN & OpenFlow World Congress in Bad Homburg, Germany.

Note the subtle language change: It's now a northbound interface, whereas the ONF had been calling it a northbound API. “Too many syllables,” Pitt said.

The NBI group will be writing code and coming up with prototypes, Pitt said. But when it comes to an actual standardization, the ONF still isn't ready to commit. The NBI group will decide next year whether the ONF should try to shepherd such a standard.

One complication, and the reason why the ONF has been hesitant to christen a northbound standard, is that there's a variety of possible interfaces. They differ widely, as Pitt showed in one slide that diagramed some northbound interfaces in terms of latitude — how far up the stack they exist — and longitude — the variety of vertical functions the interfaces can serve.