The derivation of performance expressions for communication protocols from timed Petri net models

Petri Net models have been extended in a variety of ways and have been used to prove the correctness and evaluate the performance of communication protocols. Several extensions have been proposed to model time. This work uses a form of Timed Petri Nets and presents a technique for symbolically deriving expressions which describe system performance. Unlike past work on performance evaluation of Petri Nets which assumes a priori knowledge of specific time delays, the technique presented here applies to a wide range of time delays so long as the delays satisfy a set of timing constraints. The technique is demonstrated using a simple communication protocol

Estimating the feasibility of transition paths in extended finite state machines

There has been significant interest in automating testing on the basis of an extended finite state machine (EFSM) model of the required behaviour of the implementation under test (IUT). Many test criteria require that certain parts of the EFSM are executed. For example, we may want to execute every transition of the EFSM. In order to find a test suite (set of input sequences) that achieves this we might first derive a set of paths through the EFSM that satisfy the criterion using, for example, algorithms from graph theory. We then attempt to produce input sequences that trigger these paths. Unfortunately, however, the EFSM might have infeasible paths and the problem of determining whether a path is feasible is generally undecidable. This paper describes an approach in which a fitness function is used to estimate how easy it is to find an input sequence to trigger a given path through an EFSM. Such a fitness function could be used in a search-based approach in which we search for a path with good fitness that achieves a test objective, such as executing a particular transition, and then search for an input sequence that triggers the path. If this second search fails then we search for another path with good fitness and repeat the process. We give a computationally inexpensive approach (fitness function) that estimates the feasibility of a path. In order to evaluate this fitness function we compared the fitness of a path with the ease with which an input sequence can be produced using search to trigger the path and we used random sampling in order to estimate this. The empirical evidence suggests that a reasonably good correlation (0.72 and 0.62) exists between the fitness of a path, produced using the proposed fitness function, and an estimate of the ease with which we can randomly generate an input sequence to trigger the path

The QoS Manager Interactions for News-on-Demand Prototype

: Emerging high-speed networks and powerful end-systems give rise to a new class of applications such as video-ondemand and teleconferencing. Such applications are very demanding on Quality of Service (QoS) because of the isochronous nature of media they are using. This implies stringent requirements from the underlying systems to support requested QoS. Hence this new type of applications need QoS management to ensure that the requirements of the users are satisfied. To investigate the impact of dynamically changing QoS on the design of applications and to develop management of the QoS related resources within a distributed environment, we implemented a prototype of the design described in this paper as part of a news-on-demand system. The report mainly presents the QoS manager interactions with the other components of remote access to multimedia database system and instantiates the results in the context of our prototype. Thus the implementation structure of the interactions and the Q..

On the architectural design of the formal specification of the session standards in LOTOS

An approach to structuring formal specifications of services and protocols in LOTOS is proposed. The approach is based on experience with the application of LOTOS to the specification of the ISO session standards, and is therefore exemplified with parts of their formal description. It is argued that the structuring of formal specifications of service and underlying protocol should emphasize to the largest extent their commonalities, in order to simplify the proof of their mutual consistency. The conclusion drawn is that the structuring principles for the session specifications may be of more general use for the specification of services and protocols