MCI said today it successfully transmitted 40 Gigabits per second signals over 3,040 kilometers of fiber optic cable in its Dallas metro area network, marking the first field demonstration of technology from Xtera Communications, Mintera and Juniper Networks to support high-bandwidth traffic over Ultra Long Haul distances.

The significance of the test is that it showed an ability to transmit 40 Gbps signals over long distances without repeaters, meaning that network operators would be able to layer the newer 40 Gbps signals onto their existing 10 Gbps networks, without major re-engineering, said Glenn Wellbrock, director fo network technology development at MCI.

"This is a much more cost-effective way to deploy 40 Gig systems," he said. "The real enabler here was the new modulation format. Everything we’ve done so far has usually involved standard on-off keying. This trial involved phase shift keying."

Traditional modulation turns a laser on and off in bursts of 25 picoseconds to designation the one or the zero of a digital signal, Wellbrock explained. Over long distances, the ability to distinguish between an on or off signal in such a short burst of time is significantly diminished, which sets the distance limits on higher speed systems such as 40 Gbps. Using the phase shift keying, the light is always on and the information is contained in theamplitude of the signal, he said.

"The inherent difference between the one and the zero is quick a big bigger, so the effective extension range is quite a bit larger," he said.

In addition, both the 'one' and 'zero' bits are strong signals, so there is less chance of a stronger signal bleeding over into the weaker one, Wellbrock added.

Realistically speaking, the earliest 40 Gig deployments will not involve the gear that MCI tested in Dallas but will use more mature 40G sytems over shorter distances, he said. But the ease and greater cost efficiencies of the new technologies will speed their use in the network.

The tests are significant as service providers continue to add capacity to existing fiber networks to handle increased demand for data services, and the convergence of all services on an IP backbone. MCI used Xtera’s all-Raman DWDM system, Mintera’s advanced modulation format long-read OC-768 transponders and Juniper’s T640 IP routers with OC-786 short reach interfaces.

MCI said the tests were conducted in October and November and carried 74 channels of 10 Gigabits per second traffic and two channels of 40 Gbps traffic over 38 individual 80 km spans of standard single mode fiber

"MCI continues to lead the industry in technology innovation and the delivery of next generation IP services," said Jack Wimmer, MCI vice president of Network Architecture and Advanced Technology, in a prepared statement. "As we execute on our IP convergence strategy, and as customer applications drive bandwidth onto our network, 40 Gbps transmission becomes an increasingly important technology to enable efficient scaling of our network."