Dense wavelength-division multiplexing (DWDM), the technology that has revolutionized long-distance carrier networks, hasn't made it big in the metro space -- yet.

But Metro DWDM, the latest report in Light Reading's series on metro networking, describes a promising future for DWDM in city networks, perhaps not too long from now.

Interest in metro DWDM is being driven by economics that hinge on the technology's potential to do more than just extend the capacity of fiber. According to the report, written by free-lance technical analyst Tim Hills, carriers are attracted by the chance to offer big corporate customers new high-value, high-bandwidth services using wavelengths while saving operational costs.

DWDM makes this possible because it doesn't rely on the Sonet infrastructure, which has limitations in terms of changing and configuring bandwidth. With Sonet, for instance, upgrades to faster services call for reconfiguring multiple nodes on rings running at fixed rates. With wave services, one fiber filled with many channels can be deployed to upgrade data rates on the same service -- and speeds aren't written in stone.

Fulfilling the potential of DWDM (and its little brother, CWDM, or coarse WDM) in metro networks is a matter of ongoing development, even though today's products have come a long way. Metro wavelength capabilities have moved to more than 64 wavelengths in the past three years, for instance, with 32 wavelengths standard; wavelength speeds have increased to 10 Gbit/s; and systems can support rings, meshed rings, and fully meshed architectures.

But DWDM gear needs to feature an optical layer that can be controlled, monitored, switched, routed, and manipulated for the rollout and maintainance of new services.

The DWDM vendors are finding they can't do it all, so most are focusing on specific aspects of metro DWDM. Some are concentrating on DWDM purely for transparent, protocol-independent transport over clear wavelengths. Many of the traditional Sonet vendors are promoting DWDM as a basis for multiservice provisioning platforms (MSPPs) that feature the use of a managed optical wavelength layer, support of an ever-wider range of services and technologies, and a migration path to an all-optical architecture (something that continues to intrigue most carriers).

Other vendors are focused on the integration of DWDM and Ethernet in metro services. Still others have adopted the use of digital wrappers to facilitate the management of DWDM channels.

Each of these approaches has its own issues, pro and con. The report breaks these out, featuring a dynamic table that lets readers compare nine vendors according to 14 features and functions.

Bottom line? DWDM and CWDM products are evolving to reflect carriers' metro requirements. Gone are the days of the "dumb" DWDM box. Emerging is gear that uses DWDM to make metro optical networks dynamic and intelligent.

To read the full report, see Metro DWDM.— Mary Jander, Senior Editor, Light Reading
www.lightreading.com