In transparent optical networks, signals propagate over all-optical lightpaths. The absence of regenerating devices that act in the electrical domain renders end-to-end monitoring difficult. Quality of transmission (QoT) metrics quantify the degradation in quality that a signal experiences as it traverses a lightpath. Hardware monitors that can directly measure QoT are expensive, which motivates the development of monitoring schemes that require fewer monitors but can still generate accurate QoT estimates. In this paper we describe a monitoring scheme that estimates the QoT of multiple lightpaths in a network. Our focus is on estimating bit-error-rates (BERs), but the methodology is also applicable for other metrics. One of the primary innovations in this monitoring framework is the establishment of “active lightpaths”—lightpaths that carry no useful data but are instead used as measurement probes. We describe a method for choosing where to establish the active lightpaths in order to maximize the information gain. We demonstrate with simulations the possibility to trade off the amount of costly hardware monitoring equipment with cheaper, temporary active lightpaths, while still achieving accurate monitoring.
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