Nortel Networks http://www.nortelnetworks.com today responded to comments that it was buying a "fat, dumb" switch with its planned $3.25 billion acquisition of Xros Inc. http://www.xros.com, announced earlier this week (see Nortel Buys a Monster Crossconnect).

In essence, it acknowledged that Xros's X-1000 was fat and dumb compared to its home-grown optical cross-connect, the Optera HDX. It's fatter because it's higher capacity, and it's dumber because it doesn't come with sophisticated network management software.

However, Nortel went on to say that both devices would be needed by many carriers. They could use the X-1000 to cut costs while using the Optera HDX for management control, according to Greg Penz, brand manager in Nortel's optical application and architecture department. "They aren't mutually exclusive," Penz said. "There's a balance point between them."

Confused? Here's what's going on:

Optical cross connects link together wavelengths in carrier backbones, and right now, vendors are tackling this issue with different goals in mind.

One bunch is focusing on developing management software that automates the setting up and tearing down of wavelengths. The software manages this process from the perspective of complete backbone - to speed up provisioning and ensure that traffic is automatically re-routed around failures and that capacity is used efficiently.

As these switches sit in the heart of carrier backbones, this is a very challenging task according to Desh Deshpandi, chairman of Sycamore Networks Inc. http://www.sycamorenetworks.com, one of the vendors developing such a switch. The software might have to handle millions of wavelengths, and the slightest glitch could cause widespread service blackouts, he says. In other words, the software isn't something that could be dashed off quickly by a relatively small startup such as Xros.

Right now, the only management systems that work in carrier networks are electrically based, so all of the vendors in this camp have switches with electrical cores. Vendors in this camp include Nortel with its HDX as well as Sycamore, Tellium Inc. http://www.tellium.com, Cisco Systems Inc. http://www.cisco.com (through its acquisition of Monterey ) and Ciena Corp. http://www.ciena.com (through its acquisition of Lightera).

Another bunch of vendors is developing "all-optical" cross connects that switch light from one port to the other without converting it into electrical signals and then back again into light. Some vendors, including Xros, Lucent Technologies http://www.lucent.com and Siemens AG http://www.siemens.com, are using micro-electro-mechanical systems (MEMS) - arrays of microscopic mirrors - to bounce the light from input to output port. Others are testing liquid crystals, ink-jet printer bubbles and variety of other technologies.

Xros appears to be leading the charge in this camp - by having by far the largest number of ports and by having software that automates the provisioning process (see Xros Launches First 1000-Port All Optical Cross Connect). All the same, it can't respond to electrical management signals to reroute traffic onto alternative wavelengths in the event of failures, according to Greg Reznick, Xros's president and CEO. And it doesn't come with the heavy-duty systems for managing the whole network offered by the likes of Sycamore and Tellium.

In the long run, the vendors in the first camp are aiming to replace their electrical cores with light based ones. However, it'll take six to nine months before it becomes clear which optical switching technology to use, and it'll take another six to nine months to incorporate it in products, according to Nick De Vito, Tellium's vice president of product management and business development.

In buying Xros, Nortel is charging ahead with a two prong solution right now. It expects carriers to use its Optera HDX to automate the setting up and tearing down of bandwidths, and then use Xros's X-1000 in locations where cost saving is the big priority. The X-1000's ability to eliminate electrical interfaces will result in "dramatic" cost reductions, according to Penz.

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