We study a behavioral theory of Mobile Ambients, a process calculus for modelling mobile agents in wide-area networks, focussing on reduction barbed congruence. Our contribution is threefold. (1) We prove a context lemma which shows that only parallel and nesting contexts need be examined to recover this congruence. (2) We characterize this congruence using a labeled bisimilarity: this requires novel techniques to deal with asynchronous movements of agents and with the invisibility of migrations of secret locations. (3) We develop refined proof methods involving up-to proof techniques, which allow us to verify a set of algebraic laws and the correctness of more complex examples.

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We propose a timed broadcasting process calculus for wireless systems where time-consuming communications are exposed to collisions. The operational semantics of our calculus is given in terms of a labelled transition system. The calculus enjoys a number of desirable time properties such as (i) time determinism: the passage of time is deterministic; (ii) patience: devices will wait indefinitely until they can communicate; (iii) maximal progress: data transmissions cannot be delayed, they must occur as soon as a possibility for communication arises. We use our calculus to model and study MAC-layer protocols with a special emphasis on collisions and security. The main behavioural equality of our calculus is a timed variant of barbed congruence, a standard branching-time and contextually-defined program equivalence. As an efficient proof method for timed barbed congruence we define a labelled bisimilarity. We then apply our bisimulation proof-technique to prove a number of algebraic laws.

The asynchronous π-calculus has been considered as the basis of experimental programming languages (or proposals for programming languages) like Pict, Join and TyCO. However, on closer inspection, these languages are based on an even simpler calculus, called Localised π (Lπ), where: (a) only the output capability of names may be transmitted; (b) there is no matching or similar constructs for testing equality between names. We study the basic operational and algebraic theory of Lπ. We focus on bisimulation-based behavioural equivalences, more precisely, on barbed congruence. We prove two coinductive characterisations of barbed congruence in Lπ, and some basic algebraic laws. We then show applications of this theory, including: the derivability of the delayed input; the correctness of an optimisation of the encoding of call-by-name λ-calculus; the validity of some laws for Join; the soundness of Thielecke's axiomatic semantics of the Continuation Passing Style calculus.

Boxed Ambients (BA) replace Mobile Ambients’ open capability with communication primitives acting across ambient boundaries. The expressiveness of the new communication model is achieved at the price of communication interferences whose resolution requires synchronisation of activities at multiple, distributed locations. We study a variant of BA aimed at controlling communication as well as mobility interferences. Our calculus modifies the communication mechanism of BA, and introduces a new form of co-capability, inspired from Safe Ambients (SA) (with passwords), that registers incoming agents with the receiver ambient while at the same time performing access control. We prove that the new calculus has a rich semantics theory, including a sound and complete coinductive characterisation, and an expressive, yet simple type system. Through a set of examples, and an encoding, we characterise its expressiveness with respect to both BA and SA. © 2005 Elsevier Inc. All rights reserved

We deÿne a typed bisimulation equivalence for the language DPI, a distributed version of the -calculus in which processes may migrate between dynamically created locations. It takes into account resource access policies, which can be implemented in DPI using a novel form of dynamic capability types. The equivalence, based on typed actions between conÿgurations, is justiÿed by showing that it is fully abstract with respect to a natural distributed version of a contextual equivalence.In the second part of the paper we study the e ect of controlling the migration of processes. This a ects the ability to perform observations at speciÿc locations, as the observer may be denied access. We show how the typed actions can be modiÿed to take this into account, and generalise the full-abstraction result to this more delicate scenario.

We develop a semantics theory for SAP, a variant of Levi and Sangiorgi's Safe Ambients, SA.The dynamics of SA relies upon capabilities (and co-capabilities) exercised by mobile agents, called ambients, to interact with each other. These capabilities contain references, the names of ambients with which they wish to interact. In SAP we generalize the notion of capability: in order to interact with an ambient n, an ambient m must exercise a capability indicating both n and a password h to access n; the interaction between n and m takes place only if n is willing to perform a corresponding co-capability with the same password h. The name h can also be looked upon as a port to access ambient n via port h.In SAP, by managing passwords/ports, for example generating new ones and distributing them selectively, an ambient may now program who may migrate into its computation space, and when. Moreover in SAP, an ambient may provide different services/resources depending on the port accessed by the incoming clients. Then we give an lts-based operational semantics for SAP and a labelled bisimulation equivalence, which is proved to coincide with reduction barbed congruence.We use our notion of bisimulation to prove a set of algebraic laws that are subsequently exploited to prove more significant examples.

Abstract. We define a typed bisimulation equivalence for the language Dpi, a distributed version of the π-calculus in which processes may migrate between dynamically created locations. It takes into account resource access policies, which can be implemented in Dpi using a novel form of dynamic capability types. The equivalence, based on typed actions between configurations, is justified by showing that it is fullyabstract with respect to a natural distributed version of a contextual equivalence. In the second part of the paper we study the effect of controlling the migration of processes. This affects the ability to perform observations at specific locations, as the observer may be denied access. We show how the typed actions can be modified to take this into account, and generalise the full-abstraction result to this more delicate scenario.