scope:

General

This Recommendation presents the general principles for employing performance monitoring features and capabilities on international transmission systems and equipment for maintenance purposes. Performance monitoring data is one category of maintenance information as described in Recommendation M.20, § 5.4.

As an example, the need for performance monitoring may be seen by considering a defective transmission system or equipment which will increasingly degrade for a period of time prior to total failure. In the early stages, the failing system or equipment generates errors over isolated short duration intervals, possibly causing short losses of frame alignment. As the severity of the degradation increases with time, the quantities and densities of errors and losses of frame alignment increase to more severe levels. Since these error bursts and losses of frame alignment are usually too short in duration to initiate automatic-protection switching or to generate alarms, they will propagate through the network unchecked and affect customers. The degradation process may last for days, weeks or even months if not corrected before a detectable failure occurs. In many cases, the defective equipment will never completely fail, but continually generate errors and losses of frame alignment.

This Recommendation describes a possible strategy to employ performance monitoring features and capabilities. The choice of applying this strategy and the actual arrangements to provide it are left to the discretion of the Administrations.