WDM, Gigabit Ethernet define the future

The world of communications is changing before our eyes. The line between cable companies and telephone companies is fading, as both vie to be leading providers of multiple services. But whether cable or telco, providers that can reliably and cost-effectively deliver video, voice and data services to both consumers and business customers stand the greatest chance of survival in the future.

To survive, both telcos and cable companies must expand their product offerings beyond the core services they once dominated. The ability to concurrently deliver video, voice and data to customers-the "triple play," as it has come to be known-will allow service providers to extract the maximum value from their metro plant infrastructure. This has forced a paradigm shift in metro network design philosophy, resulting in the need for innovative solutions for today's metro network requirements.

Separate service-specific networks are being replaced by solutions that can support convergence-the ability to transport any type of traffic to many customers over a single multipurpose pipe. By converging onto a single metro transport platform, a multitude of services can be offered to the maximum number of subscribers at the lowest cost possible.

But how can it be done? Two technologies, wavelength-division multiplexing (WDM) and Gigabit Ethernet, have been combined to offer service providers the flexibility, scalability and economy they will need for the versatile, reliable and cost-effective metro transport for converged network services. WDM is the great enabler of the telecommunications revolution. Being able to propagate hundreds of wavelengths on a single fiber virtually ensures that there will be ample capacity available for the bandwidth-intensive video, data and voice requirements of the future.

Additionally, innovative hardware and software products that provide wavelength-routing flexibility at the optical level make it possible to design optical networks that support drop-and-forward capability, simultaneous narrowcast and broadcast services, dynamic wavelength provisioning and optical-layer network protection. It is because of the technological merits of WDM that fiber-optic networks have become so attractive to service providers.

As providers continue to streamline operations and offer advanced services (a must for survival in today's hypercompetitive environment), WDM has become a key design tool employed in many network designs. As their bandwidth needs increase, network engineers will continue to rely on WDM as a technology that will enable the delivery of high-bandwidth services for the lowest possible cost.

The optical scalability and capacity provided by WDM is only part of the story, however. Recent advances in Ethernet technology have enabled equipment providers to offer metro Ethernet transport solutions with unprecedented capacity, reach and reliability. Ethernet solutions are available now that provide up to 10 gigabits/second of capacity per wavelength with proven quality-of-service (QoS) and high reliability at low cost to the service provider. Gigabit Ethernet offers network designers a platform that will provide them with the capacity needed to expand well into the future, even as bandwidth-hungry services such as video on demand, high-definition television, peer-to-peer sharing and interactive services gain widespread popularity and sap network resources.

The level of capital investment in Gigabit Ethernet technology over recent years has not only dramatically improved performance and reliability, but has driven costs down as well. The concept of high-bandwidth, narrowcast services has existed for decades, but until recently was deemed prohibitively expensive by service providers. Innovations and refinements with chip sets, software and hardware designs continue to be made, solidifying Gigabit Ethernet as a technology that will continue to evolve for years to come, thus opening the door to sweeping changes in the way future networks will be designed and deployed.

Routing and switching

In addition to capacity and economy, Gigabit Ethernet provides additional levels of routing and switching capability for today's multiservice metro networks. Novel products have been developed that capitalize on the flexibility and standards-based approach of Gigabit Ethernet. A packet-based protocol, it allows multiple narrowcast and broadcast services to be delivered on a single wavelength to multiple locations, thus maximizing the utilization efficiency and overall flexibility of today's networks.

Metro transport requirements can vary dramatically. The number of customers, the ratio of businesses to consumers, geographic constraints and expected growth rates can all drive decisions when devising a metro network design. A key value provided by metro transport equipment manufacturers is a diverse array of products that offer network architects multiple design choices for a wide variety of applications. Modular platforms ensure that numerous design challenges can be met with standard off-the-shelf equipment.

Metro network designs utilizing point-to-point, star or ring architectures can be devised with varying levels of physical-layer protection. Scalable WDM solutions can be employed to enable pay-as-you-grow capacity provisioning that does not require service disruption. Gigabit Ethernet transceivers of various capacities can be employed in the same chassis to maximize transport efficiency and lower capital costs.

Cable networks have traditionally been designed to carry broadcast video traffic. For broadcast video service, bandwidth requirements are high, but reliability requirements are not that stringent. In contrast, traditional voice networks are designed to deliver timing-sensitive traffic with "carrier-class" reliability for low-bandwidth applications. Data networks are engineered to handle bursty traffic for low-bandwidth applications. Because voice and data require relatively little bandwidth, networks can be designed that accommodate both types of traffic quite nicely. Data traffic can easily be transported over a carrier-class voice network because the bandwidth requirements are low.

Metro network solutions using WDM and Gigabit Ethernet technologies can be designed to support the concurrent transport of video, voice and data traffic. What's more, mission-critical voice and data traffic can be delivered with carrier-class reliability, ensuring the quality-of-service that businesses and consumers demand.

Where this becomes particularly important is in the transport of voice traffic. Voice-over-Internet Protocol (VoIP) is coming into its own as a reliable, yet very low-cost, means of providing voice services to consumers and businesses. We traditionally expect ultrahigh reliability when it comes to voice service, however, so Gigabit Ethernet networks must be able to deliver voice traffic with carrier-class reliability. To date, the prognosis is positive. Network elements are in place that enable VoIP service with the high reliability that customers demand.

Software advances

Network hardware is only part of the metro transport story. Advances in network management software have also greatly improved the value proposition of today's metro networks. As network complexity increases, software features must keep up in terms of available information, performance monitoring, service provisioning, capacity utilization and overall reliability.

Software packages allow network operators to monitor and control all network elements from any Internet-accessible computer. Bandwidth provisioning can happen in real-time with the click of a mouse. Potential network performance problems and capacity constraints can be pinpointed and addressed before they affect service. As service providers look to increase revenues, business customers become an import piece of the puzzle.

The convergence capabilities and inherent reliability of WDM and Gigabit Ethernet allow the metro network to be utilized for much more than consumer traffic.

Small to medium-size businesses, universities, hotels and government facilities can all be considered potential customers. However, business customers demand QoS levels above those of consumers. Network downtime for business customers is often not an option.

Designs using WDM and Gigabit Ethernet technologies offer metro network architects ultrahigh reliability on several fronts. Physical path protection and logical protection for Gigabit Ethernet traffic can be combined to provide network reliability that ensures high QoS.

Tim Dodge is director of technical marketing at Optinel Systems Inc. (Elkridge, Md.).