In one embodiment, a head-end node of a tunnel, relative to a tail-end node, receives a trace request, and in response, generates an out-of-tunnel trace request based on the trace-request. The first sensor array is arranged to monitor the fracturing operation. The chromatic dispersion compensator comprises at least a first chromatic dispersion compensation unit and a second chromatic dispersion compensation unit connected with the first chromatic dispersion compensation unit in series.