XR Optics Puts Spotlight on Optical Networking

Article By : John Walko

Infinera is trialing a point-to-multipoint coherent transmission technology it expects will prove significantly more efficient than the existing point-to-point approach.

Infinera is trialing a point-to-multipoint coherent transmission technology it calls XR Optics that the company expects will prove a significantly more efficient way to support hub-and-network networking architectures than the existing point-to-point approach.

Even if XR Optics works as well as Infinera hopes, the company will still have to prevail over rivals who are developing competitive innovations.

Optical fiber communications for the past few years has taken a back seat while mobile technologies,  in particular 5G, have enjoyed all the hype. Fiber communications suffer from being considered legacy networks, yet network operators continue to invest heavily in optical as the importance and value of architectures such as long-haul, metro, fixed access and packet transport continue to grow. Many have reassessed their plans as fixed broadband has been a vital lifeline for both businesses and even more importantly, to those working from home.

Moreover, the profile of much of the traffic borne by fiber networks has had to change, not least because of the huge and increasing demand for videoconferencing and streaming.

And all that is augmented by the need for more fiber to help consumers make the most of 5G, for at the end of the day, it becomes vital to backhaul all those small cells.

Traditional point-to-point fiber will just not cut it for the hugely increasing demand. Point-to-multipoint is thus the new mantra.

Add in the fact that carriers also need to invest in fiber and IP transport to support the fast-growing cloud, data-center (to and between the huge sites) as well as 5G traffic, it is not surprising there are also really exciting developments in optical networking.

Neither is it surprising, therefore, that there is healthy competition in the sector, and not just from the giant network infrastructure players such as Nokia, Ericsson and Huawei. Specialist companies such as Ciena, Adva, Adtran, Calix, Cisco, Corning , Juniper and others are all involved in different segments for fixed, IP routing and optical networking solutions.

For instance Infinera, one of the biggest players in the sector, is busy readying the roll-out of a technology it first announced at the ECOC (European Conference on Optical Communications) in September 2019, which was held in Dublin, Ireland.

Dubbed XR Optics, the point-to-multipoint coherent transmission technology leverages the company’s Infinite Capacity Engine (ICE) and photonic IC know-how to distribute coherent Nyquist subcarriers from a single transmission PIC to multiple destinations.

The company suggests XR Optics represents a significantly more efficient way to support hub-and-network networking architectures than the existing point-to-point approach.

Unlike traditional point-to-point approaches that mandate the exact same size transceiver at each end of the fibre, XR optics is designed such that it will allow a single high-speed transceiver to optically aggregate traffic from multiple lower-speed transceivers.

The company says the concept has the potential to transform optical networks, especially in the access and aggregation where the dominant traffic type is point-to-multipoint.

In operation, over typically a fiber pair, an XR Optics coherent pluggable at the hub site generates 400 Gbps capacity, comprised of 16x 25Gbps subcarriers. A passive splitter sends these to each remote site.

Through the management system, each XR coherent pluggable at the remote site, for example the cell tower, tunes into the one or multiple subcarriers it has been assigned to. Once locked in to the assigned digital subcarriers, the XR pluggable at the remote site sends back to the hub, on the second fiber, digital subcarriers that match the same line-up as the received subcarriers.

“The drivers for our development of this technology and philosophy are the increasing demand for higher and higher baud rates and lower power needs to achieve improved $/Gbit capabilities,” Dave Welch, founder and now chief innovation officer of the company told EE Times.

The concept for XR Optics is a system that would behave more like a radio at a cell tower, where just one radio is able to communicate with hundreds of thousands of end points and handle them individually,  said Welch.

Dave Welch

“All I want to do in the network is to get from the radio unit on the tower to a local or regional data center. As of today, that signal, typically, has to pass through 52 transceivers, 18 switches/routers, and 8 transport boxes. When you transition to point-to-multipoint, that reduces to just seven transceivers, four switches/routers and the need for transport boxes goes away.”

“Clearly, that is not going to happen right away, but that is the vision,” said Welch.

He adds the development is very much related to an evolutionary path the company has been following for a while. “And the shift to point-to-multipoint will allow us to pick up the ever increasing edge traffic in a much more efficient way. The XR Optics project is a major driver for us in that area, and our ICE technology plays a very important role here.”

The Nyquist subcarriers—which Infinera dubs ‘coherent subcarrier aggregation’ (CSA)—allow the 25Gbit/s subcarriers or subcarrier bundles to be distributed to multiple end points. The technology will be housed in pluggable optical transceivers installed in routers at both ends, and both ends would need to have the XR optics interfaces.

The set-up will use the same amount of optical spectrum that one carrier would use, so Infinera says the technique allows an operator to increase network capacity without sacrificing undue transmission distance.

Infinera has been collaborating with BT in the UK on parts of the project, and last year, the network operator modeled the performance of the technology and also carried out lab exercises using prototypes.

A point-to-multipoint architecture. Click on the image for a larger view.

“Their work suggests that in a metro setup, XR Optics could produce an amazing 70% in savings in capex over a five-year timescale, compared with a reference architecture that relies on point-to-point optics,” Welch proclaimed.

He added the trials did not attempt to estimate the likely opex savings, and said “dozens of other customers are doing tests and trials with the technology, but to date have not published results.”

“Our XR architecture will radically change the infrastructure scene, reducing power and space requirements and thus costs,” Welch claimed. All that will lead to efficiencies and network simplification beyond access by enabling a single transceiver to aggregate traffic from multiple lower speed transceivers anywhere in the network.

He added, “it is also important to consider that XR will work with existing network architectures.”

In the trials, BT connected metro nodes in chains, with 5 to 10 nodes per chain. The chains link into hubs at both ends (for redundancy) allowing aggregated traffic to pass towards the core. Such a hub-and-spoke architecture is expected to offer the best benefits from the optics technology.

BT also worked on some lab exercises with prototypes of the XR optics, the focus being on broadband service scenarios, with a model metro network with PON overlays and straight PON amongst the applications considered.

For full details of the trials and more technical details see CAPEX Savings Enabled by Point-to-Multipoint Coherent Pluggable Optics Using Digital Subcarrier Multiplexing in Metro Aggregation Networks (PDF).

Since those trials, at least another dozen others have taken place, for example in collaboration with another UK carrier Virgin Media and tower company American Tower.

XR optics over existing PON.

That proof-of-concept was done in collaboration with an operator in Colombia, and focused on how the technology can coexist with PON architectures.

Asked when the company expects to start commercializing XR Optics, Welch suggested prototype versions could be shipping next year, “but full scale deployment could happen in about three to four years’ time.”

He adds “a lot depends on the pace at which carriers drive the technology forward.”  That hints at one of the major obstacles in all this: carriers’ traditional cautious approach and instinct to stick with the status quo.

But Sterling Perrin, principal analyst at Heavy Reading, told EE Times: “Yes, the concept is new. But as trials show, XR Optics is being positioned as an alternative to NG PON in several cases.  It will also compete against 400ZR pluggables on routers.”

He added that while 400ZR is point-to-point, “Cisco is promoting a novel ‘routed optical architecture’ concept that emphasizes switching at every router. I see some competition amongst these two new architectures.

“The good news for Infinera here is that operators are very interested in exploring new architectures right now. There is a general consensus that the status quo no longer works for them,” he told EE Times.

Sterling also cautioned that “XR Optics will not fly as a ‘go it alone’ model, which is part of the reason the company is pushing so hard on the operator trials.

“If operators want it, that is a big incentive for component and other suppliers to get on board. As a new concept, Infinera needs to prove its usefulness with operators.”

The competitive landscape

The analyst also suggests that for Infinera to succeed here, it will have to achieve a certain level of standardization for the technology, which clearly means a broad ecosystem of suppliers, “including major router vendors that will integrate these pluggables.”

Welch said moves are already under way to form and build a coalition around the technology, including equipment manufacturers and maybe even standardization bodies, but would not elaborate.

“We have talked to dozens of carriers about the technology and our plans for rolling it out, and they are comfortable with our approach and assurances regarding multi-sourcing of all the elements of the product such as subsystems and components. We will have an amazing line-up of partners, and we should be in a position to name some of these over the coming months, but for now we have NDA arrangements over when these can be announced,” Welch told EE Times

The two companies definitely to feature the earliest here are Lumentum and II-VI, long-term partners of Infinera for photonic components, integrated lasers and, in the case of Lumentum, high-speed coherent pluggable modules.

Last year, Matthias Berger, VP, Coherent Optics Unit at II-VI commented: “We are looking forward to leveraging our highly integrated laser technology platform together with Infinera’s coherent subcarrier aggregation DSP and transmission expertise to achieve next generation coherent transmission solutions.”

On the router front, Arista Networks is very likely to be involved; indeed it is mentioned in the official release of the XR Optics technology.

Meanwhile, Infinera’s latest iteration of the ICE engine, ICE-6, is targeting the other end of the spectrum from XR Optics developments.

Here, the focus is on the highest performance networks with the longest distances and capacity needs—including long-haul and subsea networks.

Again, it has done numerous trials and is expecting to start earning revenues from commercial deployments at the back end of this year.

At 800G, right now, “it is a two-horse race between Infinera and Ciena,” suggests Heavy Reading’s Perrin.

“But Ciena is out in the lead as they have over 70 customers using their WaveLogic 5e modems already. This is Ciena’s 800G capable technology that is on par with ICE6.”

Perrin suggests the demand will be there “but Infinera will be playing catch up on Ciena’s roughly one year lead in the segment.”

The good news for Infinera, he asserts is that beyond Ciena, “there may not be much competition here for a while.”

Infinera has also published impressive distance specs from its trials that well exceed what we have seen from Ciena, Perrin told EE Times.

As already noted, there are other significant developments in the optical networking segment, and, not surprisingly, some of these focus on open networking solutions.

The aim is devise systems that would allow operators to leverage their current optical infrastructure and combine the best available transponder with the most appropriate optical engine, from any vendor, which would meet the specific needs of their application, be it for their metro, long haul or submarine network.

So, industry watchers will need to keep their eyes on such optical communications  developments.

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