Fredrik Orava

An algebraic verification of a mobile network

In a mobile communication network some nodes change locations, and are therefore connected to different other nodes at different points in time. We show how some important aspects of such a network can be formally defined and verified using theπ-calculus, which is a development of CCS (Calculus of Communicating Systems) allowing port names to be sent as parameters in communication events. As an example of a mobile network we consider the Public Land Mobile Network currently being developed by the European Telecommunication Standards Institute and concentrate on the handover procedure which controls the dynamic topology of the network.

Refining Interfaces of Communicating Systems

There are now several theories for describing and reasoning about the behavior of communicating systems, where the behavior of a communicating system is described in terms of its capabilities to perform communication actions in cooperation with its environment. In such theories, preorders or equivalences are defined as criteria for when one system is an acceptable substitute or implementation of another. Existing theories of communicating systems define preorders or equivalence relations only between systems with identical sets of communication actions. In many practical design situations, however, it may be desirable to refine a system by changing its set of communication actions. We present a simple method for carrying out such refinements. The method is first formulated in a general setting, and then elaborated in more detail in the trace model and a simple version of the failure model. We illustrate the usefulness of our method by an application to I.451, an ISDN access protocol.

Global growth of open access networks: from warchalking and connection sharing to sustainable business

This paper discusses the evolution of W-LAN starting from the mere extension of LAN services indoors, through the widespread diffusion of outdoors coverage with free and often un-authorized access, to the business models supporting their evolution to public coverage HotSpots. Besides, the idea of Open Access Networks (OANs) going beyond wireless HotSpots to become a shared access infrastructure fostering service operators competition is introduced and discussed.The concept of Open Access Networks (OAN) is detailed, highlighting its difference with the more traditional model of vertical integration of the access network into the global service. Arguing on OANs development, it is shown how to support the quick and smooth evolution of the infrastructure toward a widespread and reliable communication support. References to existing projects, starting from StockholmOpen.net and Wilma are given.Business models are discussed by mentioning the different actors, the market organization and different organization forms.The final part of the paper is devoted to technical challenges such as access control, security, privacy, roaming, resource exploitation and service differentiation.

Modelling Dynamic Communication Structures in LOTOS

Abstract We study how to formally specify dynamically changing communication structures in the specification language LOTOS. We present a method for modelling dynamic communication structures by encoding link names as data values together with a sufficient condition on the communication structure guaranteeing that the modelling is possible. As an example we formally specify the handover procedure in the GSM protocols. Using automated tools we prove the specification equivalent with a more abstract description of the system.

Formal design of communication protocols

We report partial results from a project aiming at defining guidelines for the specification and verification of communica tion protocols and services. A simple specification mediod is proposed. Using this technique we obtain verifiable specifications. These specifications can be used as the starting point for specification in description techniques, such as: LOTOS, Estelle, or SDL. Guidelines for specification and verification of communication protocols and services are given. It is argued that specifications should be expressed formally and that they should be well structured in order to facilitate verification, Examples of specification and verification are included.

Formalising and Prototyping a Concurrent Object-Based Language

This document aims to provide a formal semantics for an object-oriented language with constructs for concurrency and distribution. The semantics is defined via a translation into the π-calculus process algebra. As is (perhaps regrettably) standard when giving the semantics of a language in such a way, we concentrate on faithfully capturing the program dynamics while abstracting away from many important aspects of object-oriented languages, most notably inheritance.