Sonet network build deploys dispersion-shifted fiber for OC-192 speeds

BEN HARRISON

Widespread deployment of optical carrier, level 192, synchronous optical networks moving at 10 gigabits per second is expected next year because users are demanding more bandwidth and new services. To anticipate this need, Qwest Communications, Denver, is building a Dallas to Los Angeles $300 million fiber-optic network using two new technologies: dispersion-shifted fiber and OC-192 Sonet transport systems.

According to Douglas H. Hanson, president and chief executive of Qwest Communications, its OC-192 Sonet system is expected to be completed in the next 12 to 18 months. "We selected OC-192 because it will be available in January 1996, during the time frame we are constructing the network, and because it is more cost-effective than using four OC-48 wavelength-division multiplexing systems."

Hanson notes that Qwest is using dispersion-shifted fiber because singlemode fiber won`t run on OC-192 transmission speeds. "Dispersion-shifted fiber gives us lower cost and greater capacities. We want to deploy state-of-the-art technologies to the fullest."

According to Bill Magill, senior analyst at Ryan Hankin Kent in San Francisco, "Analysis of the relative costs of wavelength-division multiplexing and time-division multiplexing OC-192 networks shows that TDM is the lower-cost alternative for most applications, even when accounting for the additional expense of dispersion compensators. Most Sonet vendors will be introducing their OC-192 TDM solutions one to two years before their WDM alternatives. Problems such as polarization dispersion may exclude the use of 10-Gbit/sec systems on some older fiber routes, however."

Magill also notes, "Although some serious engineering problems remain unsolved, especially concerning receiver performance, 10-Gbit/sec laser rates no longer present an obstacle to OC-192 TDM technology, and some vendors are experimenting with lasers at much higher speeds. It is unlikely that TDM-based systems will be capable of supporting 40-Gbit/sec transmission rates, however. Ryan Hankin Kent expects OC-768 solutions to be based almost exclusively on four-wavelength WDM technology. Demand for 40-Gbit/sec transmission systems is expected to emerge about the year 2000."

Commenting on other advantages of dispersion-shifted fiber for the build, C.J. Phillips, president of Alcatel Telecommunications Cable, Claremont, NC, notes that Qwest Communications is looking at lower attenuation for dispersion-shifted fiber. "They are using dispersion-shifted fiber because of the distances involved. Singlemode fiber is certainly the most commonly used."

This deployment will be one of the first major OC-192 Sonet installations. According to Bob Tregemba, executive vice president of operations and engineering at Qwest Communications, the company is negotiating with key vendors that are still responding to requests for proposals on this major build. Among them are Alcatel Network Systems in Richardson, TX, and Northern Telecom, Montreal, Canada.

Joe Bass, senior director of lightwave products for Alcatel, says that formal announcement of the company`s OC-192 product is pending, and that he is delighted Qwest Communications is looking at Alcatel for its fiber networking solution.

Another growth perspective for OC-192 Sonet systems comes from AT&T Network Systems. Kathy Szelag, director of transmission systems, says AT&T plans to offer two products for carriers to get to OC-192, providing both WDM and TDM systems.

"AT&T expects its wavelength-division multiplexing system to be out early in 1996," Szelag says. Its architecture includes four OC-48 systems put onto the same fiber, passively multiplexed together using four colors of light. The time-division multiplexed architecture relies on lasers operating at 9.6 Gbits/sec.

Still another viewpoint about OC-192 Sonet transport systems comes from Heena Patel at Bell Communications Research, in Red Bank, NJ. She cites motivating factors behind the development of OC-192 systems, including demand for more bandwidth, requirements for new services, availability of technology supporting 10-Gbit/sec systems and the possible advantage of using OC-192 systems in Sonet self-healing rings.

Her observations are published in the proceedings of the National Fiber Optics Engineers Conference, held in June, where she presented a paper titled "A Reliability Analysis of OC-192 and OC-48 Sonet Systems."

OC-192 deployment is important to Northern Telecom`s Sonet plans. Although the company has not yet announced a time frame for rollout of OC-192 products, it has been investing in product development and reportedly has work underway on Sonet products that transport information faster than OC-192 rates of 10 Gbits/sec. According to Wilf Cameron, vice president of account marketing transmission, "We may not be the first, but we want to be among the leaders with a deployable OC-192 product."

Cameron also notes that an important aspect of OC-192 is the capability to manipulate bandwidth. Key features of high-end Sonet products are network management and software download capability. These features are also important for the Qwest Communications build.

SP Construction Services, a division of Qwest Communications, is constructing this new fiber-optic network. In addition to providing a fiber link between Dallas and Los Angeles, the system will serve Houston, San Antonio and El Paso, TX; Tucson, Phoenix and Yuma, AZ; as well as San Bernardino, Riverside and the Los Angeles basin areas of California.

The fiber network system, which is being constructed along the Southern Pacific railroad rights-of-way, will also cross the border to Mexico at several locations in Texas, Arizona and California. It will connect with Qwest`s existing fiber system, Cal-Fiber, which links Los Angeles, San Francisco, Sacramento, Roseville and other communities along the California coast.

SP Construction Services is currently building a fiber-optic system between El Paso, TX, and Denver by means of Albuquerque, NM. This link will also connect to the new Dallas to Los Angeles system. Combined with the existing fiber conduit system owned by Qwest, which connects Sacramento, CA, and Denver, the two will ultimately form a Sonet ring.

The company claims its build will be one of the most secure fiber-network systems in the United States. This security results from the company`s protected fiber construction technique, which encases thin fiber cables in conduit tubing buried more than 4 feet deep.

Chief Executive Hanson says fiber-cable security is one of the main advantages of the Qwest Communications build. The company uses railroad rights-of-way to install high-density polyethylene conduit that is 48 to 54 inches deep, thus eliminating almost all backhoe failures. This construction technique employs a rail-car mounted plow that can bury six conduits simultaneously, each of which can hold 144 fibers within a fiber cable, at distances to 18 miles daily.

Additionally, the company`s 24-hour cable protection center--Call Before U Dig--facilitates fiber-cable security. Before any digging takes place, Qwest is contacted and company inspectors monitor construction activity underway so that cables are not cut. The center also ties into the company`s Denver headquarters, which provides 24-hour network surveillance, troubleshooting and customer service.

Hanson explains how the system serves fiber-optic network users. A construction customer was in danger of a system failure on a particular network span. Qwest`s surveillance technicians identified a "dying" laser between normal preventive maintenance routines and notified the system provider before intermittent failures signaled an alarm. A maintenance window was scheduled, the failing laser was replaced and the network was restored without service interruption.

Hanson says the network management center allows Qwest technicians to manage, rather than react to, events. Technicians can see the event and redirect customers to alternate paths on the network. Should a reroute not be available, the center allows expedited restoration and reduced outage time for customers. q

Douglas Hanson, president and chief executive of Qwest Communications, says using the Southern Pacific railroad rights-of-way will eliminate backhoe failures on the Dallas to Los Angeles network.