The initial specifications of Web Services cope with the issues of service publishing and service discovery but not with the issue of service selection. Service discovery, handled by UDDI and WSDL, alone is not sufficient to find the most appropriate server that can deliver customers' required quality of service (QoS). In this paper, we consider a broker-based approach to provide QoS support in Web Services and deal with the selection issue. The broker may implement various selection policies that can range from static policies to dynamic ones, which take into account the current state of servers. Besides, Servers may deliver different levels of service to their customers. We model this QoS broker-based scheme by a multi-class queuing model and we study its performance with a probabilistic splitting policy for server selection.

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The successful integration of the Service Oriented Architecture (SOA) in large distributed environments greatly depends on their support of quality of service (QoS) management. The aim of QoS management is to guarantee diverse QoS levels to users issuing requests from a variety of platforms and underlying networks. In this paper, we present our policy-based framework for QoS management in SOA environment with both usual and mobile users. The framework is based on a federation of QoS Brokers that are in charge of mediating between service requestors and service providers, and carrying out various QoS management operations. We describe an auction-based ranking algorithm of functionally equivalent services, which ranks services according to their ability to fulfill the service requestor QoS requirements. The brokers are also in charge of handling appropriately service requests from mobile users equipped with various handheld devices. 

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