The thought of software-defined networking (SDN) reaching down to the optical network is nice, but BT Group has "hit a kind of roadblock" when it comes to finding open standards to accomplish the task, said Andrew Lord, BT's head of optical research.

He and a Telefónica representative expressed similar views during a panel Monday morning at the Optical Society of America (OSA) Executive Forum. It's a day-long conference that precedes the annual OFC/NFOEC, an optical-networking conference being held in San Francisco this year.

BT is keen on using SDN to manage packet and optical networks simultaneously, a use case that many optical-transport vendors are pursuing. But BT wants an open, multivendor option, and the open-source options it's investigated — including OpenFlow, OpenStack, OpenDaylight, and Floodlight — all miss the mark.

That's partly because these projects have roots in the data center, not the carrier network, as Lord acknowledged.

"They don't control an optical layer in the way we want," he said. "Once you get out of the data center, they just don't understand optical requirements."

BT will probably have to soldier forward with proprietary options, but Lord was wary about interoperability. One vendor's orchestration capability would have to work with another vendor's gear.

He ended his initial presentation on a less-than-optimistic note: "SDN for transport: quite a good idea, but we don't see how we're going to do it."

BT isn't just stewing in bitterness, though. Lord sympathetically noted that the next couple of years to be a feeling-out period, "where everybody's having a go." (Every standards body is vying for an SDN angle, for instance.) BT doesn't have an "SDN" plan set in stone yet anyway, so the carrier is happy to try "everything" in its labs during this period, he said.

Telefónica feels a similar frustration. It's disappointing that the "signaling and coordination" between the packet and optical layers hasn't emerged more strongly in products after years of discussion, said Pedro Florez, head of IP and transport for Telefónica's global CTO office.

Florez would like to see vendors open their products to support data-plane interoperability between packet and optical layers. Quite a few vendors do this with their own packet and optical products, but vendor-to-vendor interoperability is far from a reality, he said.

To him, it's a matter of vendors' self-interest "stopping the wonderful flow of products that we used to enjoy in the past."

(While the criticisms are valid, some might also characterize them as carrier whining, as someone pointed out to me at lunch. After all, how anxious are the carriers to open their software up to competitors?)

Glenn Wellbrock, director of optical transport network architecture and design at Verizon, shared an interesting take on this topic in a brief chat after the panel session.

He had a good point: The optical network is a messier place than the packet network. Optical transmission involves parameters such as the type of fiber involved or the signal-to-noise ratio of a particular span.

The element management system (EMS) inside optical-transport equipment knows about these factors. So when it comes to a particular zone of the network — an area that's built from the gear of one vendor, such as Alcatel-Lucent or Ciena — the EMS is the place to rely on for this information.

Wellbrock thinks that's going to be important, because that information isn't easily shared with other vendors. "They don't want to open that up, and if they did, it changes with each engineering release," he said.

His answer is to let the EMS provide an abstracted view of the optical network. "So, the SDN controller can still do the dynamic optical layer," creating optical-transport connections on the fly, "but doesn't have to know the characteristics," such as which links are carrying 100 Gb/s or are using dispersion-compensating fiber, Wellbrock said. The optical layer becomes "more like a gray box," he said.

Generalized MPLS (GMPLS) was supposed to do exactly that kind of abstraction, but that dream hasn't been fully realized. "I think it's more doable with EMS," Wellbrock said.

Photo, from left: Aref Chowdhury (Alcatel-Lucent), Andrew Lord (BT), Pedro Florez (Telefónica).