CWDM On the Move

Coarse wavelength-division multiplexing (CWDM) is at a crossroads, and some key decisions about its future are in the works.

A flurry of recent announcements demonstrates growing interest in CWDM among component and system suppliers, as well as their carrier customers (see Luminent Intros CWDM, SFP Transceivers, Molex Transceivers Go the Distance, and Finisar Launches CWDM Transceivers for three of the latest). Since CWDM is cheaper to implement than dense Wavelength Division Multiplexing (WDM) – albeit more limited – it presents a welcome alternative for use in metro and access networking gear, particularly as the telecom downturn lengthens. (For more on these matters, see the recent Light Reading report: Metro DWDM.)

But proponents say CWDM needs work to fulfill its potential. They're calling for technical changes that will help overcome its limits of distance and capacity. They're planning new standards. And perhaps most importantly, they're asking for an industry change of attitude. These are the elements they say will make the technology more than merely a stop along the way to DWDM.

Change won't come easily. Standards are part of the problem. Although CWDM products have been available for at least two years, the International Telecommunication Union, Standardization Sector (ITU-T) only finished blessing the wavelength grid used by CWDM gear this past June (see ITU Sets Global CWDM Standard). The group has approved the use of 18 wavelengths from 1270 to 1610 nanometers in CWDM products. Channels are spaced 20 nm apart in order to work with cheaper lasers that don't require expensive cooling mechanisms.

But the job's only half done. The part of the standard that will specify exactly how CWDM wavelengths are to be amplified to extend specific distances over different types of fiber remains to be hammered out by the ITU. Until this is done, products aren't going to interoperate -- a drawback for prospective customers.

The work of completing the CWDM specs is being done by the ITU's Study Group 15, the part of the ITU that's charged with setting standards for "transport networks, systems, and equipment." The specific CWDM project is cryptically known as "Question 16," or G.capp (shorthand for CWDM applications). The group devoted to the G.capp is set to meet October 8–10 in Santa Rosa, Calif.

Sources say it could take a year to finalize specs, especially since several proposals are up for consideration, and opinions seem to vary. "With regard to applications, CWDM is best suited for applications that have lower data capacity requirements and for fiber spans that are 50 km or less," writes Peter Wery, chairman of Study Group 15, in an email today. Wery also works at Nortel Networks Corp. (NYSE/Toronto: NT).

Some vendors already have made inroads on blasting the 50km limit. In an announcement earlier this month, for instance, CWDM system vendor Transmode Systems AB and component maker Genoa Corp. announced a field trial in the U.K. that amplified four CWDM channels of Gigabit Ethernet over 125 km of fiber (see Transmode, Vtesse Trial CWDM).

Distance is just one technical issue that's intriguing vendors right now. There's also talk of systems that blend CWDM and DWDM. Also on the rise are "zero water peak" fibers that reduce the attenuation that can wreak havoc on CWDM setups.

All the discussion points to burgeoning interest in CWDM, which could help accelerate its standardization. At last week's NFOEC tradeshow, a group called the Full Spectrum CWDM Alliance (no Website) reportedly met to discuss ways of speeding up the standards process by reaching consensus before ITU meetings convene. So far, the group hasn't made a public announcement.

Another factor key to CWDM's future is carriers' interest in it. And that, fans say, is helping to shape the technology's future as well. One service provider, Looking Glass Networks, says makers of metro gear need to rethink their position on CWDM.

"We would like to use CWDM, as a number of our fiber rings could take advantage of the fiber gain and cheap optics," emails Steve Plote, director of technology at Looking Glass, "but we need to have the CWDM optics installed on our currently deployed equipment." That means, in this case, that ONS 15454 platforms from Cisco Systems Inc. (Nasdaq: CSCO) would need to be outfitted with CWDM interfaces. Also, Plote would like to see his Sonet grooming gear similarly enhanced.

So far, it hasn't happened. Plote says Looking Glass has asked Cisco to add the interfaces "like they have done for their 12400 router and their Catalyst Ethernet switches."

There's no sign of changes for the higher-end gear. "Cisco is currently examining CWDM integration with the Cisco ONS 15454," writes a spokesperson.

For Plote, a change of attitude on CWDM seems as important as technical and standardization issues to the technology's future. "CWDM is a great technology that has been around longer than DWDM; but until it is available on multiple platforms that a carrier can buy today, it will have limited deployments," he writes. "The Ethernet vendors have done a good job of picking up on this; now it is up to the metro transport vendors to do the same."

— Mary Jander, Senior Editor, Light Reading
joestudz 12/4/2012 | 9:40:30 PM
re: CWDM On the Move how you can be running a banner advertisement for Luminent's SFP CWDM transceivers and not mention them in this article on CWDM.
Believe Luminent has supplied more CWDM compnents than any other component supplier and you fail to mention them. How come?
To make up (as penance for your ommission) I think you should set your software up to run their banner advertisement (free) any time someone opens the CWDM article.
nextgen_guy 12/4/2012 | 9:40:29 PM
re: CWDM On the Move It's either a lack of understanding, a lack of research, or a bias. I'm not sure which.

Luminent has been working with CWDM for 5 years now, longer than anyone else in the industry, and they are they real leader in CWDM.

They are the only vendor capable of doing 16-channel CWDM. No one else can do more than 8 channels. Lastly, several of the companies mentioned in the article are actually using Luminent CWDM components.

dishwasher 12/4/2012 | 9:40:27 PM
re: CWDM On the Move Looks like Luminent or its parent only make their way to the LR Analysis pages when there is some interesting small talk to be reported. The Margalit & son story, or CEO Noam Lotan stating that he believed in Marconis FTTH 2 years ago or whatever.

This at a time when MRV is one of the rare components and systems makers that has actually no significant decline in revenue and is reducing its cost of operations on a day to day basis while still developing new marketable products... Which is quite an accomplishment nowadays.
BobbyMax 12/4/2012 | 9:40:21 PM
re: CWDM On the Move There are are some indications that CWDM would be deployed bt the carriers in the MAn Environment. Even in a MAN evironment, coexistebce of DWMS and CWDMs will be needed. CWDM is certainly a safe technology in the access network.

Unfortunately the CDM standards hsve not been made public by ITU-T. It is my understading that the standard would be issued in another 6-8 months.

The basic difference between DWDM and CWDM is one of channe spacing. The channel spacing in DWDM is very narrow requiring more complex circuits. Depending on the size of the MAN, CWDM may not be best alternatine.

The metro market is not growing as fast as it was anticipated once. There are now a lot of CWDM vendors, but it was not quite certain that they are ITU-T compliant.
Mary Jander 12/4/2012 | 9:39:59 PM
re: CWDM On the Move Folk: I merely meant to list some recent announcements, not create a comprehensive list. That said, there was a recent Luminent announcement that I've added to the list.
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