At the CeBIT trade fair in Hannover, Germany, today, Siemens AG http://www.siemens.com unveiled another example of an optical networking product that isn’t quite what it’s cracked up to be.

At first glance, the TransXpress Optical Service Node (OSN) looks like a big breakthrough. It’s an optical cross connect “solution”, says Siemens, that’s all-optical and can be configured to connect as many as 2,160 wavelengths.

A genuine optical cross connect of that sort of capacity would have carriers wooping for joy. Many of them are facing a crisis right now: The roll-out of DWDM (dense wave division multiplexing) is multiplying the number of wavelengths in their backbones by orders of magnitude – and they can’t find optical cross-connects big enough to interconnect them.

Lucent Technologies http://www.lucent.com has come closest to addressing this demand with its 256 port LambdaRouter, but that’s less than the minimum 1,000 ports most carriers say they need. And while the LambdaRouter itself is all-optical, carriers can't use it to build all-optical networks (see Optical Illusions).

Unfortunately, Siemens’ OSN is another of example of vendors promising more than they can really deliver. It’s actually a combination of a 2,160 port patch panel, a 512 port optical cross-connect and some management software. (In fact, the OSN on show at CeBIT only incorporates a 32 port optical cross-connect; the 512-port version won't be ready until the end of the year.)

The combination enables carriers to automate provisoning of a small proportion of their wavelengths, using the optical cross connect. The remainder of ports will have to be connected together manually. In this case, the OSN’s management system will turn on lights next to the ports to be connected together, making the task almost idiot proof.

Siemens says that its solution is a good half-way house on the road towards very high capacity, all-optical networks. It enables carriers to connect large numbers of wavelengths today, albeit mainly manually. And it paves the way for automating a larger proportion of the provisioning process in the future by installing bigger optical cross connects in the OSN as they become available.

It’s worth taking a closer look at the optical cross-connect used in Siemens’ OSN. Like Lucent’s LambdaRouter, its based on MEM (micro-electro-mechanical) technology – an array of microscopic mirrors that can be tilted to deflect wavelengths to different output ports.

Siemens is using MEM devices from Optical Micro-Machines Inc. (OMM) http://www.omminc.com. These tilt mirrors in a single plane, which limits their capacity to 32 by 32 ports, according to Patrick Leisching, an engineer in Siemens’ advanced optical networks division. Nine devices have to be linked together in a matrix to deliver the 512 by 512 port capacity planned, he adds.

Leisching says other MEM devices, notably ones from Lucent and Xros Inc.http://www.xros.com , can tilt mirrors in any direction and thus have more capacity. However, mirror-positioning takes up a lot more power – so much that they can’t be used in current day systems, according to Leisching. “The technology of Lucent and Xros is good for 2002. OMM’s is ready now,” he adds.

Leisching also notes that some mirrors stop tilting after they’ve been flapped up and down 60 times. He declines to name the vendor concerned. OMM’s mirrors have gone through millions of tilting cycles in Siemens’ tests, he says.

Lucent refutes Leisching's comments, pointing out that its LambdaRouter is already being used by MCI Worldcom Inc. http://www.wcom.com in a live network.

--by Peter Heywood, international editor of Light Reading http://www.lightreading.com