AT&T, XO decline CRS-1 IP/optical integration

In recent years, Cisco has been turning up the volume on its promotion of the benefits of optical and IP integration in its CRS-1 carrier core routing platform. But it’s unknown to what extent carriers are buying that pitch. Two big U.S. carriers who recently announced major deployments of the CRS-1--AT&T and XO Communications--opted not to take Cisco’s suggestion of integrating the gear’s optical and IP functions.

Cisco began trumpeting what it called “IP over dense wavelength division multiplexing” (IPoDWDM) on its CRS-1 core routing platform in late 2005, naming Comcast as a customer. The drumbeat has increased since then, becoming fairly full-throated at the OFC/NFOEC optical trade show earlier this year. The pitch goes something like this: Most core routers include only short-reach optical components interface with adjacent optical switches and multiplexers for long-haul transport. Transponders on the optical gear convert the router’s traffic into wavelengths that are standardized for the long haul (converting, say, a 1310 nanometer wavelength from the router into a 1550 nanometer wavelength for the long haul). But if the long-haul optics were instead on the routers in the first place, it would eliminate some of the components involved and thus save money.

“They’re pushing it every chance they get,” said Randy Nicklas, chief technology officer for XO Communications. “They push it with XO. They push it probably to anybody that buys their equipment. And it sounds appealing.”

So why didn’t XO or AT&T do it? For XO, the question is to some extent made moot by a compatibility issue between IPoDWDM and the long-haul optical switching platform it had already installed from Infinera. The IPoDWDM approach sends transmissions across the long-haul network as “alien” or “foreign” wavelengths—wavelengths entering the standard long-haul format without doing it in the standard process, through a transponder card. Infinera’s gear doesn’t admit alien wavelengths, so IPoDWDM isn’t currently an option for XO.

AT&T, which hasn’t deployed Infinera gear as far as we know, declined to elaborate on why it chose to deploy native 40 Gb/s links across the country on CRS-1s without using IPoDWDM. But a spokesman for the carrier said AT&T Labs is evaluating the approach.

Why might AT&T have made that choice? “It’s got to come down to total system cost,” Nicklas conjectured. “Is it really going to be cheaper overall to put up a channel between two routers…by using ITU-grid optics natively on the router?”

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