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 the π -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.

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 1.451, an ISDN access protocol.

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The restoration time in high capacity optical networks has to be kept as short as possible in order to avoid a huge loss of data. This paper discusses several methods to improve restoration time in optical networks and we propose the use of error codes that will trigger immediately the appropriate layer recovery mechanism, which is the best to handle a given fault.