Keeping ahead of the bandwidth curve

Keeping ahead of the bandwidth curve

Information superhighways of the future will require innovative solutions for delivering optimum bandwidth mileage

wilf cameron, rob koslowsky

northern telecom Inc.

Many service provid ers are looking for innovative ways to increase the traffic-handling capacity of existing fiber routes without incurring the expense of laying additional fiber cable. This trend will accelerate as new and emerging services dramatically increase the demand for additional network bandwidth and for enabling such technologies as asynchronous transfer mode. The network infrastructure to address these emerging needs is synchronous optical networks configured to protect against electronic, cable and node failure, and to support new services. Ramping up for the information superhighways of the future will require innovative solutions to maximize resources and deliver optimum bandwidth mileage.

Moving maximum traffic from point A to point B is not a new challenge: Telecommunications managers have been addressing this issue for years and have usually responded by packing transport pipelines to capacity or by increasing the size of the pipeline, itself. During the 1980s, this was accomplished by replacing the copper bottleneck with digital microwave radio technology and optical fiber systems. By the close of the decade, fiber transport was the delivery vehicle of choice for high-bandwidth transport.

Asynchronous technologies that contained vendor-specific protocols were developed during the 1980s. This experience revealed that fiber technology reduces burst-errors--an important requirement for data transmission. Field operation of fiber electronics confirmed the reliability of laser device technology and the reduction in maintenance routines, which is important to operations personnel.

Available bandwidth attracts use, resulting in the development of higher speed optics. Fiber cables require no upgrades. Capacity and reach were extended through the deployment of new fiber electronics. Cable-cut survivability became a definite requirement. Outages were not acceptable for fiber cables that simultaneously carry 8064 voice circuits.

At the same time, Sonet and synchronous digital hierarchy signaling standards were being developed. Service providers and manufacturers realized that the expansion of the communications infrastructure and the shrinking globe required common terms and standards to readily enable messaging to change routes and travel on other highways. Product compatibility among vendors would allow efficient packing of circuits and access with add/drop multiplexing and virtual tributary bandwidth management.

From 1990 to 1995, thousands of Sonet network elements have been shipped. This translates into an additional field capacity of more than 8 million digital signal fiber systems, level 1, that support Sonet routes in Canada and the United States. Service providers now deliver advanced telecommunications capabilities throughout the world, with product reliability that exceeds industry standards. Outages have been reduced to a few minutes per year per DS-3. Furthermore, network survivability within rings and between rings is now available, allowing a damaged central office to be bypassed by uninterrupted traffic.

The industry has pushed network performance from a bit-error rate of 1䁾-9 to 1䁾-12, an improvement of three orders of magnitude. To ensure quality processes, procurement and production, today`s manufacturing environments subscribe to an International Standards Organization 9001 level. And the traffic on the highways continues to increase as quickly as the highways are constructed: Available bandwidth continues to attract use.

Manufacturers have managed the complexity of the electronics for the fiber-optic networks so providers can deliver high-end services. To facilitate service demand, fiber-optic terminal evolution has seen the industry triple or quadruple fiber bit-rate capacity every four years.

Another perspective to consider is that from 1980 to 1994, during which time the number of DS-1s being transported on a fiber system increased from four to 2688, the following occurred with fiber electronics technology:

Capacity is 772 times greater on the same two fibers.

Flexibility is five times greater with point-to-point, regenerators, rings, add/drop multiplexing and hubbing.

Size is the same--approximately one-half of a 7-foot, 23-inch wide rack.

Power consumption is the same--a few hundred watts.

Functionality has significantly increased through the introduction of software (versus firmware)-based architecture.

Craft interface is integrated and no longer "outboard" and features graphical displays and supports control of a total network.

Enabled by the laying of fiber networks, service providers are seeking a share of the growing access market by delivering voice, information and entertainment to businesses and residences. Cable Television Laboratories Inc., Louisville, CO, is considering gigabit Sonet rings for digital video distribution; Bell Communications Research is examining Sonet rings for new service deliveries by telephone companies; competitive access providers are looking at gigabit Sonet rings for service delivery for ATM and corporate America is eyeing gigabit Sonet rings for high-speed data transfer.

A solid Sonet infrastructure allows significant growth and service flexibility. Sonet technology ensures service providers can rapidly deploy services.

The requirements for a service-ready Sonet infrastructure are:

Ensure high capacity optical carrier-48 and OC-192 solutions are available.

Deliver cable-cut ring and node-failure ring (matched nodes) survivability.

Provide bandwidth management across the OC-48 or OC-192 pipeline.

Ensure traditional and emerging (concatenated OC/synchronous transport signal, level 3c or OC/STS-12c video for trunking) services are supported among multiple ring structures.

Simplify network upgrades with software-based evolution.

Operate in today`s operating-system environment and the upcoming common management-information service element.

The fiber-optic network infrastructure is weaving a web of high-capacity traffic pipes across the country, and a mix of services to those who wish to connect to communities. But what does the roadmap of the future look like from a service provider`s perspective?

As more traffic is added to the infrastructure with larger chunks of bandwidth, the service providers should review fiber and related electronics bit rates. They will need to examine the long-haul or interoffice equation. Such route analysis and subsequent planning is driven by dollars-per-bit economics. "How far and how fast can this traffic be propelled?" will be the question for network managers.

Capacity continues to increase with optical wavelength-division multiplexing and higher bit-rate time-division multiplexing technologies. For example, one of the nation`s largest interexchange carriers, Wiltel Inc. in Tulsa, has applied narrowband wavelength-division multiplexing to increase the traffic handling capacity of its existing fiber network. Optical amplifiers and signal modulating technologies also increase the network`s capacity. Service providers` right-of-way fiber investments are secure in terms of Sonet capacity, reach and performance--well into the 21st century.

Building the passing lane

During the past four years, the overbuilding of existing asynchronous systems that have Sonet OC-48 capacity has lowered the cost of Sonet deployment. Re-use of existing fibers has been critical. Wavelength-division multiplexing increases the capacity of Sonet systems and more than doubles the traffic-carrying capacity of a given fiber. Deployment costs are lowered. Optical amplifiers extend the reach of Sonet systems by boosting the gain and compensating for fiber-induced pulse-spreading. Deployment costs are lowered, because fewer sites that house electronic regenerators are needed. OC-192 increases the capacity of Sonet systems by quadrupling the traffic-carrying capacity of a given fiber. Again, deployment costs are lowered. Network operators also gain flexibility here, because bandwidth management across an entire 192 STS-1 (or 5375 DS-1s) is possible.

In fact, OC-192 technology will be able to overbuild existing OC-48 routes, operating over the same optical amplifiers that are being installed today. Also, this pipeline will be able to carry OC-48 broadband payloads, OC-12c tributaries connecting super computers, concatenated OC-3c channels linking ATM routers and plain old STS-1s for voice and data applications. The future will be plain old STS-1s--not plain old telephone service--and progressive service providers are putting their stake in the ground today.

Fiber is driving the prove-in of 10 gigabit-per-second systems. If fiber is enclosed in a pipeline, installed in a tunnel, buried under a street or strung along a high-voltage transmission line, upgrade plans should not call for more deployment of fiber. Service providers are maximizing their existing fiber resources. Upgrading their OC-48 electronics to the OC-192 provides a 4:1 fiber utilization, a 4:1 network element reduction and bandwidth management across the pipeline.

What is the next step? In the year 2000, a service provider will be considering deployment of multiwavelength technologies to implement advanced optical networks. Optical amplifiers will require flat gain across multiple wavelengths. Another technical challenge will be the development of passive devices, which split and redirect a large number of wavelengths with high isolation between channels. Manufacturers need to fabricate new laser arrays with multiple wavelengths, separated by nanometers.

The network of the future will push such network elements as Sonet terminals and ATM multiplexers into the end-user environment. The service provider will create an all-fiber network with higher utilization and capacity than is possible today. Interface ports will no longer be electrical. Consequently, there will be fewer of them, and the backbone will finally become all fiber. The technology challenges to be overcome include multiwavelength-division multiplexing routing and operational visibility of optical network elements. With continued investment in the Sonet pipelines of today, optical backbones will become a reality. u

Wilf Cameron is vice president for transport network marketing and Rob Koslowsky is director of account marketing at Northern Telecom Broadband Networks, Atlanta, a division of Northern Telecom Inc.

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