Information received from disparate individual monitors that are concurrently measuring a predetermined property of a predetermined resource in a network are compared in a reliability computation engine to compute a metric of the degree of similarity between their measurements, and thus to determine a measure of the reliability of one or more of the individual monitors. This information can be used by a provisioning engine to select or reject individual resources for use in meeting service requirements on the basis of the reliability of the reports of their performance, as well as the reported performance itself. Monitors identified as unreliable can also be reported to a fault diagnosis function.