Testing the waves.(new testing techniques for optical performance monitoring)(Industry Trend or Event)

The all-optical future calls for new testing techniques. Optical performance monitoring is becoming essential

What do surfers and network managers have in common? Both benefit from watching for wild waves. However, their responses are quite different. Upon seeing rogue waves, surfers grab their surfboards and head out to sea. When network managers see them, they dispatch a technician with a testhead in hand.

Surfers who want to catch the best waves depend on networks of trusted lookouts and weather reports to tell them when the surf is up. Like the surfers, as service providers turn up more and more individual wavelengths on each fiber, network managers will have to keep a steady watch on each of them to keep their networks running smoothly.

However, keeping watch over wavelengths is going to become more challenging. That's because evolving networks will have fewer and fewer points at which wavelengths undergo optical-to-electrical-to-optical (OEO) conversion.

Today, that is where their contents are examined for errors, which are used to pinpoint faults in network elements. As all-optical network elements are deployed and the lengths of spans increase, wavelengths will remain in the optical layer. As a result, OEO conversion will not take place and information about the health of the network will have to be obtained at the optical layer.

"With electronics, we can predict or address problems in the network before a service-affecting failure happens. We want to have that same information that allows us to trend and predict problems in optical networks," says Tom Afferton, district manager for AT & T Network Services.

One option involves the use of "wrappers." Ciena, Lucent Technologies, Marconi and Nortel Networks are implementing digital wrapper technology in their equipment. The wrapper provides a Sonet-like capability to determine bit-error rates of non-Sonet signals as they pass through elements. It also enables providers to see if traffic is routed correctly, helps switch traffic across multiple vendors' networks and automatically switches wavelengths to different routes at pre-set error rates.

However, digital wrapper technology will not become universally useful, especially in multivendor networks, until vendors implement the digital wrapper standard recently ratified by the International Telecommunication Union. …

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