Swedes Cut Metro WDM Costs

Swedish startup Transmode says its logical rings can cut the cost of metro DWDM nets by a factor of three

December 11, 2001

4 Min Read
Swedes Cut Metro WDM Costs

A new player in the market for metro transport equipment has emerged in the form of Transmode Systems AB.

The Swedish startup only got started in April 2000, but it’s already nailed its first U.S. customer, Stealth Communications Inc., a service provider offering high-bandwidth connections to big corporations in and around Manhattan.

Stealth picked Transmode to provide the optical backbone that underlies its router network after turning down a couple of other conventional metro DWDM solutions. It got close to buying gear from Sorrento Networks Corp. (Nasdaq: FIBR). But Sorrento couldn’t handle the low-cost 850 nanometer VCSELs (vertical cavity surface emitting lasers) that Stealth wanted to use in its router interfaces, according to Shrihari Pandit, Stealth’s president and CEO, who adds that another proposal, from ONI Systems Inc. (Nasdaq: ONIS), was prohibitively expensive.

Transmode got the order, worth $1.5 million in the first year, because of its innovative approach to metro transport networks -- an approach that slashes costs by a factor of three, according to Dirk Lutz, one of Transmode’s founders.

In order to understand Transmode’s technology, it’s best to start by reviewing the current way that most metro DWDM systems work. The more sophisticated ones are ring-based at the physical layer. In other words, the actual fiber links together a number of nodes in a ring. However, the wavelengths running over the fiber follow a logical star topology. There’s a hub, and each node is linked to it using a different wavelength of light.

This has a couple of consequences. First, any communication between nodes on the same ring requires two wavelengths -- one from the source node to the hub and another from the hub to the destination node. Second, when wavelengths whistle past an intermediate node on their way around a fiber ring, they lose quite a bit of power. As a result, the number of intermediate nodes they can whistle past is limited -- and that limits the reach of most metro DWDM rings.

Transmode reckons it's cracked both of these problems by coming up with a way of creating logical wavelength rings over physical fiber rings. In other words, traffic going from one node to another on the same ring does just that, using a single wavelength rather than two, because it doesn’t have to pass via a central hub. As 80 percent of traffic stays within the same metro rings, according to Lutz, this is a big deal.

Likewise, broadcasting only needs a single wavelength rather than multiple ones, and something like 80 percent of metro network traffic is expected to be broadcast, according to Lutz. In other words, another big deal.

Using a lot fewer wavelengths to achieve the same goals has enabled Transmode to use much lower-cost coarse wavelength-division multiplexing (CWDM) in its equipment. This spaces out wavelengths so that much less expensive lasers can be used -- one of the issues that helped it win the Stealth contract. Right now, Transmode’s equipment only supports four wavelengths per fiber, but it’s aiming to offer 16 wavelengths per fiber next year. Each wavelength carries 2.5 Gbit/s of data.

Transmode’s logical rings also help it offer longer reach networks, up to 150 kilometers, because it doesn’t face the problems of light power being eaten away by filters in intermediate nodes. In Transmode networks, traffic is taken off the ring and retransmitted by electrical equipment -- like Stealth’s routers -- at every node.

"We have a patented ability to detect line rates, coding, and types of signals associated with different protocols," says Lutz. "We provide unified physical layer management. We take away the manual process of assigning wavelengths. We offer a way to [easily] serve a lot of access points on a metro ring."

”As far as we can tell, we’re the first ones to deliver a logical ring,” says Terje Hallan, Transmode’s CEO.

Transmode’s transport system is intrinsically more efficient when carrying ring-based protocols such as resilient packet ring (RPR), the spacial reuse protocol (SRP) promoted by Cisco Systems Inc. (Nasdaq: CSCO), and the dynamic asynchronous transfer mode (DTM) technologies promoted by Scandinavian companies such as Dynarc and Net Insight AB (Stockholm: NETI-B), according to Lutz (see Cisco Clarifies Ring Strategy and Fortunes Swing for Swedish Startups ).

Transmode’s technology can also be used to support logical star topology networks, making it suitable for protocols such as gigabit Ethernet, Lutz adds.

Transmode was born out of an earlier company, also called Transmode, that was founded by a bunch of engineers from Ericsson AB (Nasdaq: ERICY) in 1992/93. It's received US$10 million in funding to date, $2 million at its founding from European Equity Partners (EEP) and $8 million in April 2001 from EEP and Amadeus Capital Partners.

Stefan Lindeberg a former European marketing executive with Cisco Systems Inc. (Nasdaq: CSCO), serves on the board of Transmode. Interestingly, he’s also on the board of Lumentis AB, another Swedish startup making metro DWDM platforms (see Lumentis Faces Metro Challenge).

— Peter Heywood, Founding Editor, and Mary Jander, Senior Editor, Light Reading

Subscribe and receive the latest news from the industry.
Join 62,000+ members. Yes it's completely free.

You May Also Like