Laura Panizo

Experimental analysis of peer-to-peer streaming in cellular networks

In this paper, we study the adequacy of applying peer-to- peer techniques to mobile networks by conducting a series of experiments using smart phones as peers. We measure important parameters, such as jitter and packet losses, in static and dynamic scenarios, focusing on a video streaming service. Finally, based on the results obtained, we discuss the feasibility of these applications.

Evaluating Video Streaming Over GPRS/UMTS Networks: A Practical Case

In this paper, we focus on analyzing video streaming service performance on real networks. We propose a non intrusive methodology based on mobile devices as clients, instead of using them as modems. Our objective is to provide a more realistic test environment using actual mobile devices in real conditions of network load and radio propagation while taking into account the intrinsic mobility of mobile subscribers. This solution allows us to follow the end to end performance even when handover between different access technologies is performed. Using this methodology we carry out a study of video streaming behavior over GPRS and UMTS networks. Outstanding results related with delays, jitter, lost packets and sequence errors have been obtained. Also other conclusions about video quality, such as PSNR, have been achieved. Moreover, we analyze the impact of mobility issues such as handover or cell reselection.

A practical use of model checking for synthesis: generating a dam controller for flood management

Program synthesis with automated methods has been an active research area for many years; however, we still lack well‐known and accepted techniques for this software engineering task. In this case, the design space to be considered is infinite, even when the solution is restricted to software that meets the requirements. In this paper we propose the use of model checking (MC) techniques to automatically synthesize controllers. Given a goal in the evolution of a plant, MC can be used to search for acceptable software controllers that enable the plant to evolve as desired. We also develop a realistic application in the context of a joint project with a major water reservoir management company. This application generates controllers for dam management during flood seasons. The controllers give the proper orders (open or close the outflow elements) at precise times in order to avoid disasters and to preserve the water level in the dam. Copyright

Extending model checkers for hybrid system verification: the case study of SPIN

A hybrid system is a system that evolves following a continuous dynamic, which may instantaneously change when certain internal or external events occur. Because of this combination of discrete and continuous dynamics, the behaviour of a hybrid system is, in general, difficult to model and analyse. Model checking techniques have been proven to be an excellent approach to analyse critical properties of complex systems. This paper presents a new methodology to extend explicit model checkers for hybrid systems analysis. The explicit model checker is integrated, in a non‐intrusive way, with some external structures and existing abstraction libraries, which store and manipulate the abstraction of the continuous behaviour irrespective of the underlying model checker. The methodology is applied to SPIN using Parma Polyhedra Library. In addition, the authors are currently working on the extension of other model checkers. Copyright

River Basin Management with Spin

This paper presents the use of the Spin model checker as the core engine to build Decision Support Systems (DSSs) to control complex river basins during flood situations. Current DSSs in this domain are mostly based on simulators to predict the rainfall and the water flow along the river basin.

A Simulation Tool for tccp Programs.

The Timed Concurrent Constraint Language tccp is a declarative synchronous concurrent language, particularly suitable for modelling reactive systems. In tccp, agents communicate and synchronise through a global constraint store. It supports a notion of discrete time that allows all non-blocked agents to proceed with their execution simultaneously. In this paper, we present a modular architecture for the simulation of tccp programs. The tool comprises three main components. First, a set of basic abstract instructions able to model the tccp agent behaviour, the memory model needed to manage the active agents and the state of the store during the execution. Second, the agent interpreter that executes the instructions of the current agent iteratively and calculates the new agents to be executed at the next time instant. Finally, the constraint solver components which are the modules that deal with constraints. In this paper, we describe the implementation of these components and present an example of a real system modelled in tccp.

A constraint-based language for modelling intelligent environments

Intelligent environments can be described as hybrid systems, which combine continuous dynamics, modelling the behaviour of physical components, and discrete dynamics, modelling the software components that control the evolution of the physical variables. The growing boom in intelligent environments makes the construction of complex discrete components necessary, which may require the use of more sophisticated concurrent languages. Hy-tccp is a concurrent language for modelling hybrid systems with high-level notations that facilitate the description of computational systems, abstracting away from the implementation details. In this paper, we present an operational semantics based on hybrid automata for Hy-tccp which is a theoretical basis for the analysis and verification of hybrid systems like intelligent environment.

An extension of Java PathFinder for hybrid systems

Hybrid systems are characterized by combining discrete and continuous behaviors. Verification of hybrid systems is, in general, a diffcult task due to the potential complexity of the continuous dynamics. Currently, there are different formalisms and tools which are able to analyze specific types of hybrid systems, model checking being one of the most used approaches. In this paper, we describe an extension of Java PathFinder in order to analyze hybrid systems. We apply a general methodology which has been successfully used to extend Spin. This methodology is non-intrusive, and uses external libraries, such as the Parma Polyhedra Library, to abstract the continuous behavior of the hybrid system.

Developing a Decision Support Tool for Dam Management with SPIN

Analysis of many critical systems is usually based on the simulation of numerical models. This solution is suitable for analyzing systems with continuous and deterministic behaviors that evolve over time. However, real critical systems are more complex and can exhibit non-deterministic behavior due to unexpected events. Furthermore, critical systems present both discrete and continuous behaviors, which interact regularly. Both features can be modeled with hybrid formal methods, taking advantage of exploration techniques like model checking. We have selected dam management as a case study. A dam is a critical system that has a hybrid behavior, there are continuous variables such as the water level, and discrete states such as the opening degrees of the spillways. At present, Decision Support Systems, based on numerical models, are used to manage complete river basins. Dams are modelled as black boxes which store and release water. A Decision Support Tool (DST) for dam management provides information about the possible consequences of dam operator actions, which can help to ensure the safety of the dam, as well as the efficient use of the water. In this work we have used formal methods to model a dam as a hybrid system, and we have obtained decision support information from the analysis performed with model checking.

Integrating river basin DSSs with model checking

This paper presents a decision support system (DSS) based on formal methods for the management of complex river basins in flood scenarios. The DSS is the result of integrating two different DSSs: first, a DSS for dam management that uses the Spin model checker to produce the manoeuvres and the discharged water over time to satisfy user-defined constraints; second, a DSS that performs numeric simulations of rainfall and water flow along the river basin, taking into account the water discharged by dams. By integrating these two DSSs, the user can define constraints over the parameters of the river basin and all the dams. We use Spin to find the sequences of dam manoeuvres that mitigate the effect of floods along the river basin, according to these constraints. This work is part of the SAID project, a European demonstration project whose main goal is to smartly manage river basins by means of the integration of different DSSs. The demonstrator basin is the Guadalhorce river basin, located in the south of Spain. We apply the method to develop a DSS for this river basin in particular, but the approach is general enough that it can be applied to any river basin.