The results of a pair of demonstrations conducted by researchers at Siemens in Munich, Germany, indicate that 40-Gbit/sec transmission systems are approaching commercial availability. However, a source at the company's U.S. offices indicates that more work must be accomplished before the company achieves this goal.
The demonstrations used electronic time-division multiplexing to generate 40-Gbit/sec channels that researchers combined using wavelength-division multiplexing (WDM). In the first experiment, technicians at the company's Transport Systems Laboratories combined 80 such channels to transport 3.2 Tbits/sec over a single fiber, a capacity Siemens touts as a world record. Siemens reports the channels traveled 40 km without error.
The second laboratory demonstration used the company's current TransWave WL WDM equipment to transmit eight channels of 40 Gbits/sec each, for a total capacity of 320 Gbits/sec. The non-return-to-zero signals traveled 120 km over standard singlemode fiber with the aid of a pair of regenerators.
Yet, the demonstrations do not signal the imminent arrival of 40-Gbit/sec products from Siemens, says Mike McLaughlin, vice president and general manager of the Optical Networks Division of the Siemens Information and Communications Networks Group. "There are still a lot of issues as to exactly what the service-level interfaces need to be, what kind of multiplexing structure is best," he explains. "We're somewhat outside the realm of traditional SONET [Synchronous Optical Network] standards for how to implement a system at this rate, both on the line interface side of it as well as the multiplexing standard. There are certain things that you can extrapolate from the existing SONET standard to apply to this product, but there are certain things that are just not known and will require, I think, some sort of industry consensus through the standards bodies to allow us to move forward to productization."
McLaughlin sees progress on the standards front in the current discussions revolving around such issues as digital wrappers and forward error correction. Service providers will play a leadership role in driving this process, he says. If the customer community develops clear requirements, the industry and standards bodies will fall in line.
This evolution should be completed in the relatively short term. "Our customers are going to need this product within the next two to three years, and our expectation is we'll be able to meet that customer need," McLaughlin says.
The pairing of 40-Gbit/sec with WDM in the Siemens lab reflects the company's current philosophy concerning how the greater transmission speeds will be applied in carrier networks. "Initially, our view is clearly that [40-Gbit/sec transmission technology] will be deployed with WDM systems. The primary applications where the economics are most compelling for 40 Gbits/sec is in the ultra-high-capacity long-haul networks," McLaughlin states. "In time, as the cost of the electro-optics in these systems decreases, you may start to see some more metro applications, where you can get this kind of capacity and the flexibility that you get with a TDM [time-division multiplexing] system implemented for metro or regional networks as well."