We present the formal specification and verification of a lip synchronisation algorithm using the real-time model checker UPPAAL. A number of specifications of this algorithm can be found in the literature, but this is the first automatic verification. We take a published specification of the algorithm, code it up in the UPPAAL timed automata notation and then verify whether the algorithm satisfies the key properties of jitter and skew. The verification reveals some flaws in the algorithm. In particular, it shows that for certain sound and video streams the algorithm can timelock before reaching a prescribed error state.

As continuous interaction devices and techniques become increasingly common, it is important to consider how we might model interactive systems in a way which allows us to reason about both the discrete and continuous aspects of such systems. Hybrid systems are systems which contain both discrete components (very often for control), and continuous components. Hybrid automata have been developed to allow the specification and computer assisted analysis of such systems. In this paper we explore the use of hybrid automata for the specification and analysis of interactive systems, and apply the approach to the analysis of a flight deck instrument for monitoring and controlling the hydraulics subsystem.

Abstract: The pervasive nature of mobile and wireless systems has led to increased concerns over Quality of Service (QoS). In the prevailing models for QoS management, QoS resolution is achieved by table look-up, a feature that makes table access the focal point of activity. This approach suffers from two limitations, namely, an inability to deal with unexpected QoS requests, and a reliance on human intervention for update of information. This paper is concerned with the presentation of an architecture for supporting automated QoS resolution through verification. The architecture is modular and the QoS resolution function is performed by a subsidiary component, which combines knowledge base with resolution mechanism. This separation of concerns and the support for flexible QoS management has the advantage of

MONA implements an e#cient decision procedure for the weak second-order logic WS1S, and has already been applied in many non-trivial problems. Among these, we follow on from the work of Smith and Klarlund on the verification of a sliding-window protocol. This paper extends the scope of MONA to the verification of time-dependent protocols. We present Discrete Timed Automata (DTA) as a suitable formalism to specify and verify such protocols. In this paper our case study will be the specification and verification of a multimedia stream.

It is now well recognised that the next generation of distributed systems will be distributed multimedia systems. Central to multimedia systems is quality of service, which defines the nonfunctional requirements on the system. In this paper we investigate how stochastic process algebra can be used in order to determine the quality of service properties of distributed multimedia systems. We use a simple multimedia stream as our basic example. We describe it in the Stochastic Process Algebra PEPA and then we analyse whether the stream satisfies a set of quality of service parameters: throughput, end-to-end latency, jitter and error rates. 1 Introduction It is now well recognised that the next generation of distributed systems will be distributed multimedia systems, supporting multimedia applications such as video conferencing. Importantly though, multimedia imposes a number of new requirements on distributed computing, not least of which is the need to ensure "timely" transmissio...

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Abstract. One of the main challenges of the design of object-based Distributed Multimedia Systems is to address the performance related issues such as the Quality of Service (QoS). The specification of QoS is a crucial part of architectural object-based methods such as Open Distributed Processing (ODP). In the ODP, a QoS property assigned to an object is modelled via two clauses of required and provided QoS statements, which specify the level of QoS required/provided by an object from/to its environment, respectively. An over-demanding QoS statement can be beyond the physical limitation of the system and might result in inconsistencies. In particular, to produce a correct design, it is crucial to study the effect of QoS statements of components on the overall behaviour of the system in earlier stages of the design. This paper develops a theory for the verification of Timeliness QoS properties such as Jitter, Throughput and Latency. The approach adopted is basedontheideaofTest Automata. We shall present a formal definition of Timeliness QoS properties, which is used for the creation of Test Automata. Such Test Automata, which we shall refer to as QoS Timed Automata, can be used to verify the corresponding QoS Timeliness property. The method is illustrated by the verification of Throughput in a Video Player systems via the model checker UPPAAL.

Abstract. A Time Action Lock is a state of a Real-time system at which neither time can progress nor an action can occur. Time Action Locks are often seen as signs of errors in the model or inconsistencies in the specification. As a result, finding out and resolving Time Action Locks is a major task for the designers of Real-time systems. Verification is one of the methods of discovering deadlocks. However, due to state explosion, the verification of deadlock freeness is computationally expensive. The aim of this paper is to present a computationally cheap testing method for Timed Automata models and pointing out any source of possible Time Action Locks to the designer. We have implemented the approach presented in the paper, which is based on the geometry of Timed Automata, via a Testing Tool called TALC (Time Action Lock Checker). TALC, which is used in the conjunction with the model checker UP-PAAL, tests the UPPAAL model and provides feedback to the designer. We have illustrated our method by applying TALC to a model of a simple communication protocol.