riginal fault has on other network elements. In spite of working properly, they are not able to carry traffic due to the original fault, and therefore they are detected as faulty. For instance a transmission repeater fault may lead to fault indications at different levels on the transmission system, a rather high number of declared faults on associated routes, and also fault indications switching devices utilizing those routes. The process through which the original fault is obtained from a rather high number of alarm indications is called alarm (or fault) correlation. Alarm correlation becomes more complex with network heterogeneity and increased number of network elements. Some systems have the possibility to learn from previous network faults experiences and from network expert indications, to improve alarm correlation. Suppression of secondary alarms is a recognized method. Fault management has advanced alarm correlation tools, which allow the operator better understanding of the real alarm situation, and leads to shorter times for service recovery and fault repair. Performance management portraits the network performance through diagrams and reports, either standardized or specially selected by the network administrator. The net- work status in each moment is usually compared with the performance corresponding to some level of network activity defined as a reference. This reference consists of the network status when working without network element's faults and with normal traffic conditions. The reference is often mentioned as the 'net- work baseline' or the 'network normal condition'. Also comparison of the network status with the baseline raises alarms when the measured traffic or workload goes over certain threshold values, defined by the network administrator. Understanding Changing Telecommunications - Building a Successful Telecom Business In this case, alarms are emitted to alert the network operator about abnormal traffic conditions. This information permits the operator to act in advance to any pos