Managing Services Quality through Admission Control and Active Monitoring Solange Lima, Paulo Carvalho, Alexandre Santos, and Vasco Freitas Universidade do Minho, Dept. de Inform´ atica, 4710-057 Braga, Portugal {solange,paulo,alex,vf}@uminho.pt Abstract. We propose a lightweight traffic admission control scheme based on on-line monitoring which ensures multimedia services quality both intra-domain and end-to-end. TheAC strategy is distributed, service-oriented and allows to con- trol QoS and SLS without adding complexity to the network core. For each service class, AC decisions are driven by rate-based SLS control rules and QoS parameters control rules, defined and parameterized according to each service characteristics. These rules are essentially based on systematic on-line measurements of relevant QoS and performance parameters. Thus, from a practical perspective, we discuss and evaluate methodologies and mechanisms for parameter estimation. The AC criteria is evaluated as regards its ability to ensure service commitments while achieving high network utilization. The results show that the proposed model pro- vides a good compromise between simplicity, service level guarantee and network usage, even for services with strict QoS requirements. 1 Introduction The deployment of multimedia services in the Internet has been fostering the adoption of QoS models and related traffic control mechanisms in order to handle different applica- tions QoS requirements while using network resources efficiently. Class of service (CoS) networks, such as Diffserv, are a step forward in pursuing this objective, where flows with similar characteristics and service requirements are aggregated in the same class. Controlling the admission of flows sharing a class allows to support new traffic flows conveniently without compromising existing QoS commitments. An admission control (AC) strategy should consider three vectors: (i) assurance level; (ii) control complexity; and (iii) network resources usage. Overprovisioning is currently the most common way to provide QoS guarantees in network backbones. Although for some ISPs overprovi- sioning is an attainable solution, in general, it is either not available or a solution too expensive. In our opinion, some degree of overprovisioning is recommended so that the AC process can be relaxed and simplified. The level of service guarantee to be provided is closely related to the complexity of the underlying traffic control strategy. In fact, either using centralized or decentralized AC approaches, the provision of guaranteed services, e.g. for hard real-time traffic, involves controlling the state and load of traffic aggregates in the core nodes [1,2,3]. These solutions tend to require significant network state information and, in many cases, changes in all network nodes [3]. Furthermore, as they are closely tied to network topology and routing, their complexity increases with A. Marshall and N. Agoulmine: MMNS 2003, LNCS 2839, pp. 142–154, 2003. c  IFIP International Federation for Information Processing 2003