Modular Architecture to Build Group Communication Protocols with Several QoS

The dynamic characteristics of the new communication infrastructures widespread in the last few years make it difficult to build applications with every increasing requirements in what concerns dependability and timeliness. Not being always possible, at a given moment, to provide the desired quality-of-service (QoS), it is necessary and convenient to be able to choose between several different QoS as a way to achieve a better adaptation to the evolution of the surrounding environment. The existence of several "working envelopes" makes it possible to provide a better coverage of system properties, avoiding situations that could jeopardize its consistency. To increase the flexibility in obtaining protocols with several QoS, we propose to build them by resorting to a component based architecture and supported in the "quasi-synchronous approach".