Challenges and approaches in providing QoS monitoring

C omputer networks are evolving to support multimedia applications with diverse performance requirements. To provide quality of service (QoS) guarantees to these applications and ensure that the agreed QoS is sustained, it is not sufficient to just commit resources since QoS degradation is often unavoidable. Any fault or weakening of the performance of a network element may result in the degradation of the contracted QoS. Thus, QoS monitoring is required to track the ongoing QoS, compare the monitored QoS against the expected performance, detect possible QoS degradation, and then tune network resources accordingly to sustain the delivered QoS.1,14 The mechanisms for QoS monitoring can be classified into two categories, end-to-end QoS monitoring and QoS distribution monitoring,9 according to the QoS information that can be obtained from them. In an end-to-end QoS monitoring approach, only the end-to-end QoS between the sender and receiver of a real-time flow is monitored. In a QoS distribution monitoring approach, however, the QoS distribution experienced by the flow in different network segments is monitored in addition to the end-to-end QoS. In recent years, several mechanisms have been proposed for QoS monitoring.4,15 In addition, based on the information offered by QoS monitoring, a lot of studies have been conducted to perform further QoS-related analysis or operations. However, most of the current QoS monitoring-related mechanisms are concerned with end-to-end QoS monitoring or based on the assumption that necessary QoS information, such as QoS distribution information, can be obtained from other mechanisms. Few of them address the problem of QoS distribution monitoring directly. On the other hand, the real-time flow of a multimedia application usually crosses several network segments that provide different levels of QoS. Clearly, to locate the network segment(s) causing possible QoS degradation, QoS distribution monitoring is needed rather than endto-end QoS monitoring, i.e., the network manager should monitor the distribution of QoS experienced by the flow in different network segments.9 The purpose of this paper is to identify the challenges involved in providing QoS distribution monitoring. A second goal is to propose possible approaches to meet these challenges. With these approaches, when monitoring a real-time flow, the network manager can locate relevant monitors that are metering the flow. By retrieving and consolidating traffic information from these relevant monitors embedded in different network segments, not only the end-to-end QoS but also the QoS distribution of the flow can be derived. In addition, with the monitored QoS distribution,