mci trials optical crossconnect system

Oct. 1, 1997

mci trials optical crossconnect system

By GRACE F. MURPHY

After years of research, mci recently moved an optical crossconnect system from Hitachi Telecom Inc. out of the laboratory and into one of its Dallas, TX-based Synchronous Optical Network (Sonet) fiber rings. mci, Hitachi, and market analysts say the field trial could lead to development of a completely optical, high-bandwidth system within the next few years. The trial appears to be the first use of such equipment in a commercial network by a U.S. telecommunications provider.

In fiber-optic networks today, information is converted from light into an electronic signal, routed to the next circuit, then converted back into light. The optical crossconnects remove the electronic element, eliminating the need to convert the signals. mci officials hope the trial will prove that removing electronics from the equation will improve transmission and restoration speeds and save money on costs incurred whenever electronic devices are upgraded to accommodate higher speeds.

Jack Wimmer, mci`s director of transmission network development, says the company`s growing demands for capacity led it to work with several suppliers to develop the optical crossconnect technology. Hitachi was "particularly responsive and supportive in getting us to the point where we can put this technology out the fastest," he says.

The field trial is constructed to duplicate actual network use, according to Wimmer. "It allows us to run real customer-like applications in a real network. For example, we will be running experiments with video, atm [Asynchronous Transfer Mode], frame relay, IP [Internet protocol] for the Internet, and voice, besides the purely technical part of the measurements and analysis that will go on," he says.

George Cagle, vice president of Sonet engineering for Hitachi, says that because the optical crossconnects are transparent, they are wavelength- and data-rate independent.

"Obviously if it`s compatible with the existing transmit elements, whether it be OC-48 [2.5 Gbits/sec], OC-192 [10 Gbits/sec], OC-12 [622 Mbits/sec], or systems that are carrying wdm [wavelength-division multiplexing] traffic, the optical crossconnect system is transparent to those signals and provides a seamless integration into the network, so it has extremely beneficial capabilities," he says.

The Dallas area was selected for its proximity to mci engineering and vendor support, and due to the diversity of existing fiber (see figure on page 1). The trial involves a five-node configuration that encompasses both ring and mesh topologies and OC-48 and OC-192 rates. Hitachi`s system is directly connected to the fiber lines and has 16 ¥ 16 crossconnection capability.

Hitachi`s Cagle says the company developed a switch architecture that minimizes optical loss in large-capacity long-distance transmission lines when switching between them.

The optical switches let service providers reconfigure their fiber networks more quickly and inexpensively than with electronic systems, Cagle says. Traditionally, line protection requires dedicated protection fibers for each optoelectronic system operating at a specific bit rate and wavelength.

According to Cagle, the optical crossconnect technology can accomplish automatic and quick fiber network restoration by switching from failed optical routes to multiple restoration fibers that are shared with other routes.

That`s important for service providers, says Wimmer. Instead of the thousands of switching events that need to take place with restoration at the Sonet ring or electronic crossconnect level, the number of events needed and time taken to restore traffic are significantly reduced.

"When you do this optically, now, instead of switching thousands of DS-3s [44.736 Mbits/sec], we are switching perhaps tens of fibers. So the number of events is smaller; therefore, the cycles can be reduced, and the reliability can be increased," Wimmer says.

A quicker step

mci is not the first carrier or company to experiment with all-optical crossconnect technology. For instance, the Multiwavelength Optical Networking (monet) consortium is working on three all-optical test beds in New Jersey (see Lightwave, April 1997, page 1) and Lucent Technologies of Warren, NJ, displayed a new all-optical crossconnect system at June`s supercomm `97 show (see Lightwave, July 1997, page 1). Pirelli`s Telecom Systems Group of Lexington, NC, and nec America of Herndon, VA, will soon unveil optical crossconnect systems.

According to John Ryan, a partner with the California industry research firm Ryan Hankin Kent, the monet crossconnect system trial and Lucent`s trade show demonstration cannot be compared to mci`s field trial.

"[The others] were always intended to be experiments on the new technology, whereas mci and Hitachi are doing field trials for having a deployable system in the near future," Ryan says.

Scott Clavenna, a senior analyst at Pioneer Consulting in Cambridge, MA, adds that mci`s all-optical crossconnect system is the first to be deployed in a commercial network over an existing fiber-optic network in the field.

"What has been going on previously are all-optical network consortia that are public-private partnerships funded by government agencies and carriers. monet has been using and trialing Lucent`s all-optical crossconnect, but that has really been more of a technology trial in a laboratory setting. It does operate over existing fiber-optics along the East Coast but it`s not really carrying any live traffic. Those folks are just trying to develop monitoring systems, technology, and different types of products," Clavenna says.

Even though mci doesn`t expect to deploy the crossconnects commercially for one or two years, Clavenna says that mci`s network is noteworthy because most experts didn`t expect to see such a step happen until 1998.

One of the largest obstacles mci will encounter before deploying the crossconnects commercially is getting the network management system to work correctly, Clavenna predicts. "The software required to manage this optical system will always be a limiting factor in getting this out quickly. The same thing happened with Sonet," he says.

Clavenna surmises that mci selected an urban corridor for a trial area because there are a number of businesses using high-speed data services.

"The biggest selling point for very high data services has almost always been restoration capability," he says.q

FLOATING PRODUCTION

Smooth-sleeve drilling/production

risers eliminate VIV, drag effects

Riser deflection reduced to zero

William Furlow

Senior Editor

While the basic understanding of vortex induced vibration (VIV) has been around since the beginning of the last century, a recent discovery by researchers at Shell Inter national E&P may change the way that technologists treat this phenomenon. VIV occurs when currents move across cylinders at a rate high enough to make them vibrate. This vibration can cause fatigue prob lems in tubulars and interfere with instal lation and drilling operations.

Shell has re searched how this phenomenon takes place in different size tubulars. Don Allen, Research Engineer with Shell International E&P, claims the company holds about 90% of the relevant VIV data on drilling and production risers. He himself has conducted more that 50 experimental programs on the effects of currents moving across a cylinder. The variables in such experiments include the velocity of the currents and the diameter and length of the cylinder.

Allen performs these tests at the (US) Naval Surface Warfare Center in Carderock, Maryland. At the center's David Taylor Model Basin, a variety of cylinders are examined as they are moving through the water on a rotating arm at speeds high enough to generate critical and super-critical Reynolds numbers (velocity times diameter over kinematic viscosity) in the range of 100,000 to 400,000.

Cylinder test design

To reach such numbers on cylinders of greater diameter, Allen said it was necessary to have the cylinders custom-made from fiberglass composite materials. In previous tests, simple PVC pipe was used. To be flexible enough for the tests, yet rigid enough not to fail, the larger diameter pipes composites became the material of choice.

However, this left a very rough surface that Allen feared would interfere with the quality of the test. It was then decided to have the surfaces of these tubulars ground down smooth, so that they were similar to the surfaces of other pipes tested. It was this polishing process that led to Allen's discovery.

The new pipes were installed on the rotating arm and the experiment conducted. Allen became concerned when the rotating arm reached the velocity calculated to produce the critical Reynolds numbers. At this point, the pipe should have been vibrating violently, but there was no movement at all.

Allen said that if he had not had such a long history of performing VIV experiments, he might not have realized that a breakthrough had been made. His first reaction, he said, was "What did I do wrong?" It was later that night that he hit upon the difference in the experiment.

As part of the experiment protocol, Allen kept a record of the roughness of each piece of pipe tested over the years. The formula (roughness height divided by pipe diameter) gives a measurement of how rough the surface is. Allen had a sample of the composite pipe examined and determined it was slightly less rough than the PVC he had been using all along. It was a combination of the smoother surface and larger diameter that made the critical difference.

Further tests were conducted on pipes with various degrees of surface roughness to validate Allen's findings. Not only did the smooth surface of the pipe eliminate VIV at critical Reynolds numbers, but it also reduced drag substantially.

Testing discovery

Drilling risers are often subjected to VIV and drag problems during periods of high loop currents (A Gulf of Mexico phenomenon, which exists elsewhere). This can interfere with operations and cause drilling to shut down. Allen said the problem has been addressed in the past with strakes, fairings, and other devices installed on the outer surface of the risers and designed to interrupt the cycle that leads to vibration.

The deepwater drilling riser has a variety of non-cylindrical features. Many joints are encased in syntactic foam buoyancy modules. The bare joints have choke and kill lines exposed, and the bolts on flanges and the straps that hold the buoyancy to the riser all work against the smooth sleeve concept.

To overcome this, Shell has designed the smooth sleeve, a near perfect cylinder that encases the riser joints. Each smooth sleeve is about 10-ft long and has a diameter to fit the riser. The sleeves are made of fiberglass with a gel coat. A number of these sleeves can be installed on one riser joint. Allen said Shell has developed a formula for placement of these on risers. Once the riser is installed and placed in tension, these sleeves protect it from

The smooth sleeve closes like a clamshell around riser joints.

Smooth sleeves were installed on the Stena Tay drilling riser for tests offshore Trinidad.

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