Command performance

Performance monitoring is moving front and centre in optical networking, especially as channel speeds increase, channel spacing becomes denser and topologies change.

As speeds increase from 2.5G to 10G to 40G bit/sec, the optical-signal-to-noise ratio decreases, meaning the signal is more susceptible to distortion. As channel spacing becomes denser – from 100 GHz to 50 GHz to 25 GHz – wavelengths are more likely to “drift” into other channels.

And as optical network designs move from point-to-point to rings to meshes, monitoring becomes as complex as the topology.

Performance monitoring is different from dispersion compensation. Dispersion is the gradual degeneration of an optical signal due to transmission at higher speeds over longer distances, resulting in bit errors. Dispersion compensation attempts to reconcile that physical characteristic to minimize the amount of transmission errors.

Performance monitoring analyzes all transmission errors, be they the result of dispersion, drift, power, optical-signal-to-noise ratio or complex topologies.

The latest vendor to address optical network performance monitoring is Proximion, a Swedish company with roots in fibre Bragg gratings (FBG), those little etchings in optical fibre that filter and reflect some wavelengths while letting others pass. Proximion has applied its FBG expertise to “tunable” performance monitoring.

Proximion makes a product called WISTOM, a 1.5-rack-unit-high device that combines optical channel monitoring with spectrum analysis to monitor power levels and drift in one device. WISTOM takes traffic from add/drop multiplexers, optical cross-connects and amplifiers, and filters it through these “tunable” FBGs.

Proximion says it can tune its FBGs without any moving parts – such as mechanical fiber stretchers – but company officials would not say how they do this, citing a patent-pending on the technique. Once the traffic is filtered, a high-resolution spectrum is presented within milliseconds, Proximion says, showing power levels, optical-signal-to-noise ratios, drift and isolating faults.

Millisecond monitoring facilitates sub-50 msec failover, which fosters milli-precise service-level agreements resulting in millions of dollars for the carrier.

Systems vendors will sample WISTOM later this quarter, with volume shipments slated for the first quarter of 2002. Its cost will be competitive with other performance-monitoring devices that cost between US$10,000 and $18,000, Proximion says.