AT&T’s Tse: We could not wait for open optical standards

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As part of its ongoing movement to virtual networking, AT&T is keen on implementing a more open network construct for its optical segment. But the service provider wanted to get the benefits of such a system before the broader industry developed a new standard.

Two key elements in the evolving open optical network are new advances around reconfigurable add-drop multiplexers (ROADMs) and SDN-based controllers.

Kathy Tse, director, Photonic Technology Planning for AT&T told attendees at an OFC panel earlier this week called “Transport SDN – What is Ready, What is Missing?” that it began implementing its open optical elements ahead of standards being developed.

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“I’ll be the first to admit we started a lot of what we’re doing while the standards were not ready and we had to do things the way we did things,” Tse said. “The standards aren’t where we need them to be and we weren’t willing to wait for standards development to start.”

The service provider is also using SDN to provision and control optical bandwidth in its core network.

Earlier this week, AT&T tested a 400 Gbps Ethernet (400GbE) connection using live traffic on the carrier’s network between New York and Washington, D.C.

For this demonstration, AT&T used an SDN controller to create a service along the direct path between the two cities. By using software control, the telco rerouted the service to a second path to simulate a response to a network failure.

“We’re already well into deploying this stuff and getting our feet wet with SDN in our network,” Tse said. “It is not an OpenROADM network, which we’re starting with in our metro network, but is an SDN-controlled network.”

CDC ROADMs enable flexibility, efficiency

While the industry still has a long way to go in reaching a consensus on open optical networks, AT&T and other telcos like Verizon are seeing benefits from the vendor community’s development of colorless, directionless, and contentionless (CDC) ROADMs.

Residing in a service provider’s central office (CO), a CDC ROADM allows any wavelength (carrying 100G traffic) from any direction be dropped to any switch/router port, or any switch/router port can send its 100G traffic to any wavelength heading for any direction.

The advent of CDC ROADMs is enabling AT&T to be more efficient with optical wavelength planning.

“Just a year or two ago all the wavelength planning for Layer 0 was being done on offline systems,” Tse said. “You can now buy systems where can go and ask for a wavelength and it will automatically find one for you and the best path through the network.”

However, Tse said the industry still needs to improve the open nature of ROADM node controllers (RNCs) and maintenance elements.

“We need RNCs that work across vendor equipment without special development,” Tse said. “The customized and special development that has to be done when we add new features to the network drives us crazy.”

Vying for industry consensus

Helping to guide service providers on how to take advantage of open network concepts in their optical networks are industry groups like OpenROADM and the Facebook-led Telecom Infrastructure Project (TIP).

Led by AT&T and other vendors, OpenROADM defines interoperability specifications for Reconfigurable Optical Add/Drop Multiplexers (ROADM).

AT&T said in implementing OpenROADM in its metro network, the service provider designed an architecture that allows it to use various transponders and other optical elements in its network.

“The one thing about OpenROADM is way to deconstruct ROADMs, but the way we did is construct a box around the modem so we’re not trying to deconstruct the ROADM,” Tse said. “You’re able to mix and match different ROADMs and transponders, and it’s very critical to have the transponders interoperate because you’re talking about a flexible network.”

Tse added while these efforts to drive open optical platforms are positive, the telecom service provider industry still lacks consensus.   

“The hard part is coming together as a user community on a common set of user interfaces and models,” Tse said. “Everybody has their own ways of doing things and we’re trying to drive it with OpenROADM, but there’s still a lot of work there where everyone gets what they want.”