MCI hits 40 Gbits in OC-192 trial

March 1, 1997

MCI hits 40 Gbits in OC-192 trial

paul palumbo

Deploying 2 ¥ 2 bidirectional optical line amplifier equipment from Pirelli Telecom Systems Group and OC-192 Synchronous Optical Network equipment from Hitachi Telecom, MCI Corp. is field-trialing an aggregate transmission of 40 Gbits/sec over existing singlemode fiber facilities connected between St. Louis and Chicago.

Pirelli`s wavelength-division multiplexing (WDM) equipment has been combined with Hitachi`s time-division multiplexing (TDM) equipment to establish a record-setting, high-capacity network that paves the way for MCI to deliver high-bandwidth voice, video, data, and imaging services. Pirelli Cable Corp. is based in Lexington, SC, and Hitachi Telecom (USA) Inc. is based in Norcross, GA.

The 275-mile route will initially carry voice and data traffic, according to Fred Briggs, MCI`s chief engineering officer. Briggs notes that the transmission technologies and equipment not only add speed and capacity to MCI`s network, but also save an estimated 300% compared to installing new fiber and equipment. "From the growth of the Internet to developing multimedia applications, MCI is seeing tremendous demand for bandwidth," remarks Briggs.

In the view of Larry Schwartz, the company`s manager of network engineering, "If this trial is successful, MCI may make this electronics configuration a standard part of its network upgrade plans and begin full-scale deployment later in 1997." He sees the first step in this process as the selection of a number of upgrade routes with actual deployment to follow in 1998.

Additionally, MCI has agreed to purchase $200 million of equipment from Northern Telecom for deployment throughout 1997. Northern Telecom is supplying 10-Gbit/sec OC-192, 2.5-Gbit/sec OC-48 and 622-Mbit/sec OC-12 systems; video transport codecs; and network management software.

MCI`s network backbone currently operates at 10 Gbits/sec. In the trial, the 40-Gbit/sec speed is achieved by stacking OC-48 wavelengths at speeds to 2.5 Gbits/sec bidirectionally. Schwartz explains that previously MCI could get a full-duplex system on a single fiber, but only at an aggregate capacity of 5 Gbits/sec per channel.

Before this OC-192 deployment, the maximum speed achieved was eight wavelengths at 2.5 Gbits/sec each--20 Gbits/sec of bandwidth. Forty-gigabit-per-second capacity allows for the simultaneous transmission of 6400 channels of premium- quality video or 129,000 simultaneous voice conversations.

What the trial means

Traver Kennedy, director, wide area network services and research worldwide for the Aberdeen Group in Boston, observes, "The significance of the St. Louis-to-Chicago trial is that MCI has solidified its position as the world`s leader in high-speed, fully-integrated ATM [Asynchronous Transfer Mode] networking. MCI has the most experience and the widest network in place for supporting the Internet backbone. On the strength of this OC-192 trial, MCI is leading the charge in testing and deploying new ATM systems," Kennedy says.

Schwartz of MCI agrees. "With MCI`s Internet growing at 15% to 20% per month, using the highest-bit-rate gear available gives the company greater flexibility in handling future bandwidth requirements. The ability to implement multiple channels of OC-192 positions the company well," he says.

Yankee Group analyst Randy Carlson, also in Boston, recalls that he has been recommending WDM and OC-48 technologies. "On specific backbone routes, OC-192 makes sense," Carlson points out.

MCI`s total communications infrastructure covers some 36,000 route-miles and nearly 5 billion capacity-circuit-miles, including 500,000 miles of fiber-optic strands. Most of its existing fiber plant is singlemode.

Two duplex channels

At 40 Gbits/sec, the St. Louis-to-Chicago route contains two full-duplex channels of 10-Gbit/sec terminal transmission equipment supplied by Hitachi, with Pirelli`s bidirectional line amplifiers (bdlas) placed at four intermediate sites, and OC-192 regenerator equipment in the middle.

Hitachi is supplying AMN-5192 line- terminating equipment and the OC-192 regenerator. Schwartz says Hitachi was selected because the vendor`s equipment provides more-efficient line protection. That capability means MCI can operate a number of working channels with only one common protection channel shared between channels. Other systems have one protection channel for each working channel, which is more expensive to install and maintain.

The AMN-5192 nodes are equipped with laser transmitters and receivers operating at wavelengths of 1533, 1557, 1541, and 1549 nm. MCI chose Pirelli as the amplifier vendor because its T-31 2 ¥ 2 bdlas are a next-generation product. Previously, MCI had been using Pirelli`s 1 ¥ 1 bdlas. "It`s a breakthrough in technology to deliver bandwidth at 10-Gbit/sec rates," says T.C. Nie, Pirelli`s vice president of product market and engineering. "It is many times more complicated when compared to 1 ¥ 1 bdla," he says.

Pirelli`s T-31 system is designed in modules that enable channel expansion to be handled more cost-effectively. Transmit power amplifiers are equipped with erbium-doped fiber, which is pumped counter-directionally by 980-nm semiconductor lasers.

The line amplifiers extend the distance between fiber-transmission systems for electronic regeneration. In this trial, the distance between regenerators is effectively increased from 140 km (87.5 miles) to 400 km (250 miles). That is why MCI had to install just four Pirelli bdlas between Chicago and St. Louis.

At 10-Gbit/sec rates per channel, any light-signal dispersion is a problem. MCI and Pirelli claim that bdlas work well with both non-zero-dispersion-shifted fiber and dispersion-shifted fiber.

Dispersion-compensating fiber and dispersion-compensating gratings are the two most popular solutions the market is focusing on to address the problem of light dispersion. MCI uses both solutions in its network.

Nie of Pirelli says that the grating approach is much more precise in stabilizing wavelengths. It involves a length of specially produced fiber that has a holographic image written onto it to overcome the fiber plant`s dispersion effects. The advantage of grating is that it might be just one meter long, so long strands of fiber do not have to be wrapped around existing plant, as is the case with dispersion-compensating fiber. q

Paul Palumbo writes from Seaside, CA.

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