Two main approaches can be identified for QoS management, the first is oriented to infrastructure management and the second deals with alignment of service delivery with business objectives. This paper addresses the main issues arising under the second perspective. A critical issue is to provide an effective way to define and evaluate service level indicators. Two evaluation modes naturally arise: on-line and off-line. On-line methods compute indicators values when a related event occurs whereas off-line methods do at the end of a pre-defined assessment period. This work focuses on techniques for on-line evaluation of service level indicators. It presents an architecture for implementing service quality management (SQM) systems and the details of the mechanisms for on-line evaluation.