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AT&T Embracing SDN at the Optical LayerAT&T Embracing SDN at the Optical Layer

AT&T is hoping to lure other network operators into its effort to drive SDN down to the optical layer and greatly increase network flexibility.

March 29, 2016

4 Min Read
AT&T Embracing SDN at the Optical Layer

AT&T's determination to move SDN down to the optical layer is an effort to finally optimize a part of the network that has been static and create new possibilities for network flexibility across layers to match surging demand, the man leading the charge tells Light Reading.

Andre Fuetsch, SVP, Architecture & Design, for AT&T Inc. (NYSE: T), announced the Open ROADM effort last week at the Optical Fiber Conference in Anaheim to develop specifications for creating software-controlled Reconfigurable Optical Add/Drop Multiplexers (ROADMs) that would run on open hardware.

This week, he says in an interview that response thus far has been positive, even if there aren't yet any other network operators joining AT&T in the open source group, which published its initial specifications with its public launch. Three vendors -- Ciena Corp. (NYSE: CIEN), Fujitsu Ltd. (Tokyo: 6702; London: FUJ; OTC: FJTSY) and Nokia Corp. (NYSE: NOK) (via its Alcatel-Lucent acquisition) -- are part of the initial effort.

"Traditionally this optical layer in our transport networks has been a very static layer," Fuetsch says. With the exception of tunable lasers, introduced about 15 years ago, it's been very hardware-based and vendor specific, with little to no interoperability. That makes this infrastructure expensive, he comments, "not just to support active services but all the sparing required and all the redundancy required" to support single-vendor deployments.

"By opening up these ROADM switches so that one, we can plug in a different vendor's transponders or different pluggable optics into the ROAD switch, and vice-versa, now all of a sudden, we see a lot of good open innovation opening up for us," Fuetsch says. "Having open interfaces to control components at the optical layer will create a more competitive environment as well."

The result can be software-controlled flexibility that optimizes the photonic layer, "positioning every wavelength to take the best possible path, route or spectrum, whatever the latency requirement is," he says.

"The beauty of SDN enablement is we can now link it in and have this multi-layer optimization so if you have an SDN controller, it's not just above [the] optical network but also Layer 3 where the routers and switches are under SDN control, and now you can do a lot of very interesting clever things to get more out of your network," Fuetsch says.

While the optical layer is essentially analog, not the digital bits of data that comprise higher layers, the two can be treated similarly, he comments. "A packet flow or route is not much different than a wavelength route through the optical network," he comments. "So by treating them [similarly] and having the ability to control them real time or near real time, that gives you a lot more flexibility."

Zoom in on carrier SDN strategies in our SDN section here on Light Reading.

One immediate use case for a combined software-controlled multi-layer network is the ability to run "hotter" -- not reserve as much capacity to protect against equipment failures or fiber cuts, according to Fuetsch. Where AT&T typically runs its network at less than 40% utilization, to maintain failover capacity, implementation of SDN control at Layer 3 lets it engineer traffic more efficiently to get greater utilization without sacrificing performance or resilience, the AT&T executive says.

"By reaching down into the photonic layer with these flexible ROADM switches, we can get even more flexibility," he notes. "If we have a fiber cut, we can respond [in] less than 50 milliseconds, and we can route around that wavelength without impacting the routers above."

There would also be the ability to detect large packet flows and turn up wavelengths on the fly to add capacity to a route, without changing things above the optical layer, Fuetsch says. That additional flexibility will let network capacity be used more fully and efficiently.

The greater flexibility Open ROADMs deliver will be particularly important in the metro segments of the network, he notes. AT&T is bringing SDN control into its core backbone at the photonic and packet layer, and then building extensions of that core backbone into its metro areas, "and that is really where the open ROADM plays in, where you can have this plug and play into all these metro networks you are handing off to," Fuetsch says. "This is a really exciting time for optical engineers. They get to participate in this whole SDN revolution."

AT&T definitely wants other network operators to get caught up in this excitement and join the Open ROADM effort, he admits, but is prepared to push ahead with vendors, if that's how things play out.

— Carol Wilson, Editor-at-Large, Light Reading

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