Angel Fernández

State exploration by transformation with LOLA

LOTOS is a Formal Description Technique developed within ISO to specify services and protocols. This paper describes a tool for doing LOTOS to LOTOS transformations. It has applications in state exploration, deadlock detection, testing, validation and in design by stepwise refinement. The transformations are: expansion (transformation of parallelism into summation and prefix); parameterized expansion; i action removal. The transformations obtain LOTOS specifications which relate to the original one through strong (expansion and parameterized expansion) or weak (i-action removal) bisimulation congruence.

A LOTOS based performance evaluation tool

Abstract This paper describes a LOTOS (ISO International Standard 8807) based technique (LOTOS-TP), and a performance evaluation tool (TOPO-SIM) based on it. LOTOS-TP is able to cope with the modeling of timing and probabilistic system characteristics. It is applied to the modeling and performance evaluation of discrete event systems. The performance evaluation is obtained with TOPO-SIM simulation tool which has been developed using an existing full LOTOS compiler. The structure of the discrete event simulation tool and the simulation machine are described.

A DTN System for Nanosatellite-based Sensor Networks using a New ALOHA Multiple Access with Gateway Priority

This paper presents and evaluates a new communications architecture to provide services to terrestrial sensor networks using a space delay-tolerant networking (DTN)?based solution. We propose a new multiple access mechanism based on extended unslotted ALOHA that takes into account the priority of gateway traffic, which we call ALOHA multiple access with gateway priority (ALOHAGP). We assume a finite sensor population model and a saturated traffic condition where every sensor always has frames to transmit. The performance was evaluated in terms of effective throughput, delay and system fairness. In addition, a DTN convergence layer (ALOHAGP-CL) has been defined as a subset of the standard TCP-CL (Transmission Control Protocol-Convergence Layer). Through simulations, this paper reveals that ALOHAGP/CL adequately supports the proposed DTN scenario, mainly when reactive fragmentation is used.

LOTOS Extended with Probabilistic Behaviours

A common characteristic of process algebras is that they permit us the partial description of concurrent systems by including non-deterministic behaviours. These non-deterministic components are abstractions of the actual ones, and they can be detailed in successive refinements. This paper proposes an enrichment of the above abstraction. It defines a formal description technique which is able to characterize the non-determinism in a probabilistic way. The proposed technique, called LOTOS-P is an upward compatible extension of LOTOS. The compatibility includes also the possibility of specifying non-deterministic behaviours; that is, without probabilistic characterization.The contents of the paper are mainly related to the definition of probabilistic models based on process algebras, and the study of the observable behaviour of systems by using testing relations. The advantage of the proposed model with respect to previous works is twofold. First, the model is simpler, and second, the compatibility with LOTOS is achieved. The simplicity does not make the model useless because its expressive power permits us to express random behaviours in the same way they are being expressed with classical techniques of discrete systems modeling.The probabilistic evaluation of the properties of the system can be done by applying the defined calculus, but also bysimulation. Simulation means that we are able to obtain the desired results with a given confidence level.

Development of Satellite Communication Networks Based on LOTOS

Abstract This paper shows how LOTOS has been applied to the design and development of real communication systems in many stages of the software life cycle. These stages commence with the system analysis, and end with its final implementation. The system analysis is based on queues and simulation techniques. It is followed with several specifications of the system covering the conceptual modeling, the architectural design, and the matching to the hardware architecture. The implementation is hand made but methodologically derived from the text of the last specification of the system. The development of two satellite communication systems is presented: PRODAT (1985–87) and CODE (1989–1992). Both of them are compared from the point of view of the evolution of the engineering based on LOTOS.

PRODAT, a multi-functional satellite mobile communication system

The authors describe the design and development of terminals for the mobile communications system PRODAT. They consider the network topology and the solutions relating to different technology fields, such as forward error correction codes, multiple access methods, and link level protocols. Experience with using the formal specification technique LOTOS for software development along with the hardware architecture for the mobile terminal is analyzed.<<ETX>>

LOTOS based derivation methodology in the PRODAT project

Abstract The article describes an experience on using the formal description technique LOTOS for developing a protocol architecture on a real time embedded multiprocessor systems. The product developed during the project is a satellite communications mobile terminal 1 to be installed on board of aircrafts, ships, or trucks. The objective of the experiment has been evaluating the impact of using formal languages for systems specification and design, in the software life cycle. The use of behaviour equivalences and hiding in LOTOS, as well as its precise semantical definition, give a powerful basis for analyzing the design of a system which clearly supersedes the normal approach to design analysis based on walk-throughs, inspections, reachability analysis , etc, hellip;. The main phases of the project development are analyzed, with emphasis on the influence of using LOTOS in the design cycle.