Talking quiescence: a rigorous theory that supports parallel composition, action hiding and determinisation

The notion of quiescence - the absence of outputs - is vital in both behavioural modelling and testing theory. Although the need for quiescence was already recognised in the 90s, it has only been treated as a second-class citizen thus far. This paper moves quiescence into the foreground and introduces the notion of quiescent transition systems (QTSs): an extension of regular input-output transition systems (IOTSs) in which quiescence is represented explicitly, via quiescent transitions. Four carefully crafted rules on the use of quiescent transitions ensure that our QTSs naturally capture quiescent behaviour. We present the building blocks for a comprehensive theory on QTSs supporting parallel composition, action hiding and determinisation. In particular, we prove that these operations preserve all the aforementioned rules. Additionally, we provide a way to transform existing IOTSs into QTSs, allowing even IOTSs as input that already contain some quiescent transitions. As an important application, we show how our QTS framework simplifies the fundamental model-based testing theory formalised around ioco.Comment: In Proceedings MBT 2012, arXiv:1202.582

Performance Evaluation of Severe Congestion Handling Solutions for Multilevel Service in RMD Domains

To address the ever-increasing demands of real-time multimedia networking applications, several QoS frameworks have been developed. One of these is RMD, which is a reducedstate resource reservation protocol, meaning that the interior nodes of the RMD domain deal with per-class states instead of per-flow states. Though reduced-state operation has many advantages, such as scalability and flexibility, it also means that the handling of severe congestion is far from a trivial task. In this paper two severe congestion handling solutions for RMD are introduced and evaluated using simulations, with special emphasis on their support for traffic with multiple levels of precedence