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Photonics: A gamble that will pay

Posted: 16 Jul 2003 ?? ?Print Version ?Bookmark and Share

Keywords:photonics? transparent photonic switching? oeo? optical-electrical-optical? photonic switch?

The introduction of transparent photonic switching into communications networks is sure to provide savings in several areas. Photonic switching is likely to supplement current deployment initiatives for STS-1 grooming resources. Using photonic switching, designers will be able to combine transparent trunking, transponder, optical-electrical-optical (OEO) conversion optimization, banded wavelength routing and trunk grooming to provide the critical bottom-line business impact.

The baseline model assumes ongoing buildout of an STS-1-based grooming switch infrastructure. With this initiative in process, why would any provider consider installation of a photonic switch? The bad economy and drop in demand for high-speed optical connections means service providers now consider grooming switches a necessity. Since switching requirements at the optical level (2.5Gbps and 10Gbps) are small, service providers can offset the growth/scalability argument of a photonic switch with the capital-expenditure penalty of a few 2.5Gbps and/or 10Gbps ports. Simply, they trade functionality for price. They are willing to pay more by running 2.5Gbps and 10Gbps transit traffic less efficiently through the grooming switch.

However, a slight glitch has emerged. Developers are introducing grooming switches as de facto mesh core solution switches even though these devices may have a price penalty if the network starts growing again. Networks will grow again at some point; they will have to absorb the traffic when the economy picks up again. Conversely, if one switch or technology supports multiple functions in the network, the integration with the BSS/OSS systems becomes easier.

So when does photonic switching prove itself? Almost immediately. Inserting a photonic switch in a D-WDM hub results in immediate capital-expenditure benefits, even if the amount of drop traffic is low. Mature MEMS design and high-yield manufacturing, combined with new optical packaging, have created reliable, low-cost photonic switches that are one-quarter of the OC-48 per-port price of electronic fabric systems now being deployed; for OC-192, that factor becomes one-sixteenth. This demonstrates the economic advantage of switching at the optical layer.

Distinct advantage

While there are distinct advantages to and a definite need for STS-1 grooming switches, deploying them as core network trunking switches carries a cost inherent to the switch architecture in general, and the lack of "transparent" ports in particular. Advances in line systems require wholesale upgrades of the I/O ports, if not the switching systems themselves. On a more microscopic level, we observe that there are two aspects to the problem of providing efficient and cost-effective switching solutions: first is the need to maximize the number of revenue-generating service ports; second is to make efficient use of the new higher-speed transport systems.

In view of the constantly evolving traffic dynamics, it is difficult to arrive at an optimal solution, at any one switching hub. OEO switches have fixed and rigid switching capacities, and the total capacity must be divided between the needs of the line systems and the revenue ports with the above objectives in mind.

Data interfaces are migrating to higher speeds, approaching those of the line systems themselves. Past solutions meant provisioning these circuits directly on the line systems via patch panels. This is acceptable when the number of circuits is low, but becomes unmanageable when the number of circuits increases. Even with low circuit counts, performance guarantees and liabilities imposed by service level agreements demand that circuits be provisioned on manageable network elements, the most appropriate being optical switches.

But provisioning of such circuits on OEO switches further burdens the already constrained capacity. The problems are not insurmountable. Developers have produced new network elements to handle these trouble spots. The availability of reliable and low-cost photonic switches, for example, offers practical solutions that address technical, operational and business aspects of the problems at hand.

- Charles Corbalis

President and CEO

Calient Networks Inc.

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