The photonic layer is of particular interest to network planners. By using more advanced DWDM and Reconfigurable Optical Add/Drop Multiplexer (ROADM) technologies, operators expect the optical layer to make the greatest contribution toward the reduction of transport costs.
"ROADMs are widely deployed in metro and long-haul networks globally," says Sterling Perrin, senior analyst at Heavy Reading. "But what's been deployed so far has limited flexibility."
Add operational overload to limited flexibility. Since they only take fixed wavelengths, traditional ROADMs cannot exploit tunable transponders. If a transponder needs to be re-tuned, a service engineer must first unplug it and insert it into a new ROADM port. None of this helps carriers achieve their operational efficiency goals.
ROADMs are also limited in the number of "directions" to which an added wavelength can be routed -- that is, the number of connected nodes to which that added wavelength can be sent.
"Operators want ROADMs to do more of what they're good at," says Perrin. "They'd like an optical network that is fully flexible, with add/drop nodes operated in an automated fashion."
And it seems that demand for flexible ROADMs might be about to ramp: During the past decade, operators have focused on networking flexibility at the electrical layers, but these are now burdened. "It starts at the IP routers at Layer 3. Operators are now looking at how they can push traffic down the OSI stack to transport bits less expensively," says the Heavy Reading man.
There are several ways this can be done: Traffic can be moved to layer two, utilizing Sonet/SDH and Ethernet; to layer one, where Optical Transport Network (OTN) technology can be deployed; or to layer zero, the optical layer.
The problem with the optical layer is that it's the least flexible in terms of switching traffic rapidly, says the Heavy Reading man. "Innovation is needed to make the optical layer more useful in taking on some of these previous electrical layer functions -– that's all in flux right now."
So operators are looking to the system vendors -- and the component companies that make the Wavelength Selective Switch (WSS) modules at the heart of ROADMs -- to deliver new capabilities. The operators want Colorless and Directionless ROADMs -- designs that are fully automated in wavelength and direction -- as well as WSSs with higher port counts (or degrees).
They also want non-blocking Contentionless ROADMs that allow similar-wavelength lightpaths from different nodes to be dropped without wavelength contention. (See Verizon: Give Us More Flexible ROADMs for 100G.)
Another attribute on the carrier wish list is Gridless to accommodate future lightpaths above 100 Gbit/s. Operators want to ensure that the ROADMs they deploy will be more flexible in terms of bandwidth, allowing them to accommodate 400Gbit/s or 1 Tbit/s transmissions that are too "wide" to fit within today's 50 GHz channels.
"The hold-up has been the technology [progressing] to a point needed to create architectures that are colorless, directionless, contentionless, and gridless," says Perrin. And the delay isn't limited to the WSS elements, but also to Control Plane software and alternative technologies, such as 3D MEMS (microelectromechanical systems). "It even includes coherent technology, which is another way of making the optical layer more flexible," adds Perrin. (See Operators Hang Big Hopes on ROADMs.)
"3D MEMS is a new trend," says the analyst. A decade ago vendors were looking at the technology to create optical cross-connects. Now, lower port-count versions are appearing that could be used at the add/drop while working with WSSs.
"The advantage of 3D MEMs is that it reduces the number of WSSs needed," says Perrin, who cites 3D MEMS firms such as Calient Technologies Inc. and CrossFiber Inc. . (See Calient Gets Ambitious With Optical Switching.)
What's really needed? Cost reduction
The half-dozen leading ROADM vendors interviewed by Light Reading all acknowledged the need for colorless and directionless features. They are less clear about a timescale for contentionless ROADMs as they're unsure about carrier demand, and some question whether gridless ROADMs will ever be deployed.
For all involved -– the operators and the vendors -– cost is the biggest hurdle. Market demand is largely met by existing, lower-degree, modest ROADMs, and while operators generally want greater functionality, high initial costs mean advanced ROADM shipment volumes during the next five years will be limited. That, in turn, makes cost reduction from the supply side a significant challenge.
"I've talked to several operators, and they are gung-ho on making the optical layer more flexible," says Perrin, who reiterates that the carriers want a meshed switching layer that takes on more of the electrical layer's burden. "It will never do all the electrical layer's functions, but the more [bits it can transport] the less expensive it is to transport those bits," he notes. "That’s the fundamental driver."
The current technology hold-ups, and the operator/supplier discussions, mean it will be about two years before next-generation ROADMs are deployed, predicts Perrin.
So what are the vendors doing to meet the major operators' needs and shorten that time to market? Light Reading spoke with the following companies about their ROADM platform offerings and strategies:
- Alcatel-Lucent (NYSE: ALU)
- Ciena Corp. (NYSE: CIEN)
- Cisco Systems Inc. (Nasdaq: CSCO)
- Fujitsu Network Communications Inc.
- Huawei Technologies Co. Ltd.
- Tellabs Inc. (Nasdaq: TLAB; Frankfurt: BTLA)
Here’s a hyperlinked contents list:
- Page 2: Alcatel-Lucent
- Page 3: Ciena
- Page 4: Cisco Systems
- Page 5: Fujitsu Network Communications
- Page 6: Huawei Technologies
- Page 7: Tellabs