Standards smooth upgrade to DWDM

The International Telecommunication Union created a standard for Dense Wave Division Multiplexing (DWDM) technology called the ITU grid.

It determines the frequency and spacing of wavelengths, or colors, on fiber-optic cable. All of the long-haul networks that use DWDM are compliant with the ITU grid standard, as are many of the products that enterprise customers might buy to add DWDM capability to their networks.

However, not all of the metropolitan- and campus-area networks that use the older Wave Division Multiplexing (WDM) technology comply with the ITU grid, said Bob Azzi, Sprint's vice president of engineering.

The ITU also created the Optical Carrier (OC) speed levels that distinguish performance on Synchronous Optical Network (SONET) long-haul voice networks. The higher OC numbers represent more advanced capabilities, with current services ranging from OC-3 (155.5 megabits/sec) to OC-192 (9.95 gigabits/sec). OC-768 (40 gigabits/sec) service is expected to be available soon.

SONETprotocol equipment lets carriers move traffic from multiple sources across a backbone of fiber-optic cabling. Some optical experts believe DWDM capabilitie swill slowly replace SONET.

What might help facilitate that transition is a widely used architecture called the Open System Interconnection (OSI) model, developed by the International Standards Organization to enable network devices from multiple vendors to communicate with one another. DWDM, like SONET, works within the OSI model,so it can easily be switched in to work with or replace SONET.

"The larger the metro network, the more cost advantage to deploying integrated DWDM because you can scale the capacity to handle [IP] data, voice and video traffic growth," said Rob Koslowsky, Cisco Systems Inc.'s director of marketing for optical transport.

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