AT&T has deployed Open ROADM technology in its network and says all future reconfigurable optical add-drop multiplexer (ROADM) deployments will be based on the standard.
“At this point, it is in a single metro and we are working on a second large metro area,” says John Paggi, assistant vice president member of technical staff, network infrastructure and services at AT&T.
Shown are the various elements included in the disaggregated Open ROADM MSA. Also shown is the hierarchical SDN controller architecture with the federated controllers overseeing the optical layer and the multi-layer controller overseeing the path creation across the layer, from IP to optical. Source: Open ROADM MSA
Meanwhile, the Open ROADM multi-source agreement (MSA) continues to progress, with members working on Release 6.0 of the standard.
Motivation
AT&T is a founding member of the Open ROADM MSA along with system vendors Ciena, Fujitsu and Nokia. The organisation has since grown to 23 members, 13 of which operate networks. Besides AT&T, the communications service providers include Deutsche Telekom, Orange, KDDI, SK Telecom and Telecom Italia.
The initiative was created to promote a disaggregated ROADM standard that enables interoperability between vendors’ ROADMs.
The specification work includes the development of open interfaces to control the ROADMs using software-defined networking (SDN) technology. The scope of the disaggregated design has also been expanded beyond ROADMs to include optical transceivers, OTN switching to handle sub-wavelength traffic, and optical amplifiers.
AT&T viewed the MSA as a way to change the traditional model of assigning two ROADM system vendors for each of its metro regions.
“We had two suppliers to keep each other honest,” says Paggi. “But once we had committed a region to a supplier, we were more or less beholden to that supplier for additional ROADM and transponder purchases.”
AT&T wanted ‘true hyper-competition’ among ROADM and transponder suppliers and the Open ROADM MSA was the result.
The operator saw the MSA as a way to reduce costs and speed up innovation by using an open networking model. Opening up and standardising the design would also allow innovative start-up vendors to participate. With the traditional supply model, an operator would favour larger firms knowing it would be dependent on the suppliers for 5-10 years.
“Because you can mix and match different suppliers, Open ROADM allows us to introduce disrupters to our environment,” says Paggi.
Evolution
The first Open ROADM revision used 100-gigabit wavelengths and a 50GHz fixed grid. A flexible grid and in-line amplification that extended the reach of 100-gigabit wavelengths to 1,000km were then added with Revision 2.
“In Revision 3 we made Open ROADM applicable to more use cases,” says Martin Birk, director member of technical staff, network infrastructure and services, AT&T. “We started introducing things like OTUCn and FlexO in preparation for 400 gigabits.” The OTN ‘Beyond 100 gigabit’ OTUCn format comprises ‘n’ multiples of 100-gigabit OTUC frames, while FlexO refers to the Flexible OTN format.
Adopting OTN technologies is part of enabling Open ROADM to support 200-, 300- and 400-gigabit wavelengths.
Revision 4 then added ODUFlex, 400-gigabit clients, and support for low-noise amplifiers to further extend reach, while the latest fifth revision adds streaming telemetry for network monitoring using work from the OpenConfig industry group.
“A lot of features that widen considerably the application of Open ROADM,” says Birk.
Revision 6.0
The frequency of each Open ROADM release was initially once a year but now the scope of each revision has been curtailed to enable two releases a year. Members are polled as to what new features are required at the start of each standardisation process.
Now, the MSA members are working on revision 6.0 that covers ‘all directions’ of the standard.
“We are improving the control plane interoperability with more features,” says Birk. “Right now you have a single network view; in future, you could have an idealised network plan and a network view with actual failures, and you could provision services across these network views.”
And with the advent of 600-gigabit, 800-gigabit and even 1.2-terabit coherent wavelengths, OpenROADM members may add support for faster speeds than 400 gigabits.
“Just as our suppliers continue to evolve their roadmaps, so does the Open ROADM MSA to stay relevant,” says Birk.
AT&T’s Open ROADM deployments support 100-gigabit wavelengths while the 400-gigabit technology is still in development.
“The ROADMs will not change; the only thing that will change is the software,” says Birk. “And in a disaggregated design, you can leave the ROADMs on version 2.0 and upgrade the transponders to 400 gigabits and version 5.0.”
This, says Birk, is why it is much easier to introduce new technology with an open design compared to monolithic platforms where an upgrade involves all the element management systems, ROADMs and transponders.
Status
The Open ROADM MSA says it is up to individual network operator members to declare the status of their Open ROADM network deployments. Accordingly, the status of overall Open ROADM deployments is unclear.
What AT&T will say is that it is being approached by vendors that want to demonstrate their Open ROADM technology to the operator.
“When we ask them why they have done this without any agreement that AT&T would purchase their solutions, they respond that they are seeing Open ROADM listed as a requirement in RFPs (Request For Proposals) from many other service providers,” says Paggi. “They have taken it upon themselves to develop Open ROADM-compliant products.”
At the OFC show earlier this year, an Open ROADM MSA showcased an SDN controller turning up a wavelength to send virtual machines between two data centres. The SDN controller then terminated the optical connection on completion of the transfer.
Operators AT&T and Orange were part of the demonstration as was the University of Texas, Dallas. “They [the University of Texas] are a supercomputing centre and they can create some nice applications on top of Open ROADM,” says Birk.
The system vendors involved in the OFC demonstration included Ciena, Fujitsu, ECI Telecom, Infinera and Juniper Networks.