US West updates Sonet networks

Mar 1st, 1996

US West updates Sonet networks

PAUL PALUMBO

Denver-based US West has selected Northern Telecom to install synchronous optical network, or Sonet, equipment in seven metropolitan areas. This $100-million contract is an extension of US West`s business philosophy that dates back to 1989, when the company first began deploying fiber ring-based redundancy for high-traffic portions of its network to protect major business customers` communications.

Deployment of US West`s Network 21 architecture, which includes the Northern Telecom Sonet hardware, is currently underway in Denver, Phoenix and Seattle. Rich Stohr, director of Technology Selection for US West Communications, says the project began at the end of 1995, and its future depends on competition and capital to fund development.

Today`s competitive business services marketplace demands a high degree of fiber-route diversity and reliability. If a fiber is cut, for example, US West`s Network 21 architecture can calculate bandwidth requirements and reroute traffic within 50 milliseconds.

At the same time, improved bandwidth provisioning is available because Northern Telecom`s electronics provide end-to-end observability, from customer to interexchange carrier, and from customer to customer. The network upgrade allows for almost immediate detection of bandwidth bottlenecks through the network.

Northern Telecom`s Sonet elements were selected because US West wanted a reliable set of electronics to support its service assurance. "The primary emphasis from an architecture perspective is to further leverage fiber already in the ground through the use of electronics," according to Stohr. At the same time, he says, "There are probably going to be some locations where additional fiber is required."

Northern Telecom`s basic infrastructure comprises a Sonet Digital Multiplexing System Transportnode, which encompasses the necessary amplifiers and optics that drive light pulses through both dispersion- and nondispersion-shifted fiber.

In the past, electronics have depreciated over a long time. The average length of depreciation for Sonet electronics is approximately 12 years (ranging from 10 to 15 years) across US West`s 14-state operating region, according to Stohr. Even so, the $100-million investment may not stretch beyond seven years, because rebuilding rates for Sonet continue to be shortened. Since 1980, bit rates have tripled every four years, and Northern Telecom is estimating that Sonet technology is being updated every four years. Northern Telecom has built hardware migration functionality into its components so that software add-ons allow providers to activate different types of services.

Bandwidth management

US West issued a request for proposals to identify an end-to-end network solution for both access and interoffice networks. Northern Telecom`s solution is to connect the transport node to fiber by means of bidirectional line-switched rings, in which each ring has a number of nodes. Each node incorporates bidirectional optics, which allows US West to add significant bandwidth between adjacent nodes.

Wire centers that have the highest incidence of traffic are targeted for US West`s Network 21 architecture. Those areas will require OC-48 rates of 2.5 gigabits per second, possibly leading to OC-192 rates of 10 gigabits per second.

OC-3 and OC-12 rates at 155.52 and 622.08 Mbits/sec, respectively, are in the access part of the network, and higher speeds are required for the interoffice section of the network.

There is also a mix of service interfaces. For example, a considerable amount of interoffice traffic has DS-3 rates of 44.736 Mbits/sec, but a greater capacity at the OC-12 interface is also available at the crossconnects. That interface could be used to dump a DS-3 circuit to a crossconnect and tie in at an OC-12 optical rate. The result is a more-streamlined architecture, because data traffic does not need to be brought down to DS-3 rates, then back up again. It improves reliability and bandwidth management, and US West is able to install an OC-12 connection.

According to Rob Koslowsky, director of transport marketing for Northern Telecom, "That`s especially helpful for US West, because the company uses a lot of Tellabs` crossconnects, which allows Northern Telecom to supply optical connectivity." He says that this type of network design is moving networks toward central office simplification.

US West decided to put in 2-fiber bidirectional line-switched ring technology to maintain its edge in ring deployment, and through its request for proposals process was convinced that Northern Telecom products had a superior bit-error rate, or BER, performance (1䁾-12) over the life of the node. With people surfing the World Wide Web or shipping larger amounts of data for a variety of applications, those improved BER characteristics are important to service providers. They translate into better network performance, which benefits business customers.

Koslowsky says that US West wanted to minimize "stranded" bandwidth and bandwidth bottlenecks. Stranded bandwidth refers to network elements from other competitors that might not be completely compatible with Northern Telecom`s Sonet Digital Multiplexing System Transportnode equipment, which operates at 1557 and 1533 nm.

He notes that "the technology migration path is currently OC-48 bidirectional line-switched rings in the interoffice part of the network, moving to OC-192 by 1997 to 1998, with OC-12 [rings] in the access." This is appropriate for tying in business applications, which use a lot of bandwidth with a mix of services. Presently, OC-12 rings are considered the standard for local access business customers, according to Koslowsky.

Planning tools

With the advent of the Internet and more people working at home, home businesses are on the rise, and customers are demanding more bandwidth. With all of these activities, the predictability of network requirements is more difficult than it was 10 years ago.

According to Koslowsky, "Businesses no longer spend an average of 3 to 5 minutes per call, so engineering and planning models based on how things were 10 years ago are no longer very useful." US West and Northern Telecom are jointly planning cost-effective networks in terms of bandwidth. Northern Telecom supplies the service, and US West builds in network "headroom" for future needs. Software was developed by a Bell Northern research team.

A typical design would be a ring with an OC-12 connection in the central office. Further out in the network would be Northern Telecom`s OC-48 matched nodes. Those nodes connecting US West`s central offices would be coupled to bidirectional line-switched rings in the access part of the network. Any disruption at one central office would immediately alert the network, and traffic would be switched to another office. The rings can accommodate interface speeds for voice, data, frame relay and all other types of DS-0 switched and nonswitched applications.

US West is building a considerable amount of bandwidth into its network, while delivering survivability via matched nodes. Northern Telecom is providing those nodes through an application known as service adaptive access, through which a standard telephone service line, for example, can be converted into an integrated services digital network circuit. q

Paul Palumbo writes from Seaside, CA.

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