PoK

Authors: Christine Julien, Jamie Payton, Gruia-Catalin Roman

Description:
Context-awareness is emerging as an important computing paradigm designed to address the special needs of applications that must accommodate or exploit the highly dynamic environments that occur in the presence of physical or logical mobility. A number of formal models are available for reasoning about concurrency. Models designed to capture the specifics of mobility are fewer but still well represented (e.g., Mobile Ambients, phi-Calculus, and Mobile UNITY). These models do not, however, provide constructs necessary for explicit modeling of context-aware interactions. This paper builds upon earlier efforts on state-based formal reasoning about mobility and explores the process by which a model such as Mobile UNITY can be transformed to explicitly capture context-awareness. Starting with an examination of the essential features of context-aware systems, this paper explores a range of constructs designed to facilitate a highly decoupled style of programming among context-aware components. The result of this exoration is a model called Context UNITY.

Authors: Chien-Liang Fok, Gruia-Catalin Roman, Gregory Hackmann

Description:
This paper presents Limone, a new coordination model that facilitates rapid application development over ad hoc networks consisting of logically mobile agents and physically mobile hosts. Limone assumes an agent-centric perspective on coordination by allowing each agent to define its own acquaintance policy and by limiting all agent-initiated interactions to agents that satisfy the policy. Agents that satisfy this acquaintance policy are stored in an acquaintance list, which is automatically maintained by the system. This asymmetric style of coordination allows each agent to focus only on relevant peers. Coordination activities are restricted solely to tuple spaces owned by agents in the acquaintance list. Limone tailors Linda-like primitives for mobile environments by eliminating remote blocking and complex group operations. It also provides timeouts for all distributed operations and reactions, which enable asynchronous communication with agents in the acquaintance list. Finally, Limone minimizes the granularity of atomic operations and the set of assumptions about the environment. In this paper we introduce Limone, explain its key features, and explore its capabilities as a coordination model. A universal remote control implementation using Limone provides a concrete illustration of the model and the applications it can support.

Authors: G. Varghese, Amy L. Murphy, Gruia-Catalin Roman

Description:
Mobile computing is emerging as a novel paradigm with its own characteristic problems, models, and algorithms. Much effort is being directed to integrate mobile units with fixed networks, providing bridges to connect wireless to wired. The result is a fixed core of wireconnected static nodes and a fluid fringe of wireless mobile units, a computing system similar to the cellular telephone network. The model we put forward uses the graph of fixed nodes as a foundation and models the mobile units themselves as persistent messages moving through this network graph. Such a model allows algorithms from traditional distributed computing to be directly implemented in the mobile environment, however, it has been shown that the unique properties of mobility, such as limited bandwidth and disconnection, make such direct translation impractical. This paper presents a fundamentally different idea. Instead of recreating the functionality of distributed algorithms in the mobile domain, we show how distributed algorithms can be adapted to solve problems unique to the mobile environment. Specifically we focus on the problem of dependably delivering a message to a moving unit. We demonstrate this technique with two new algorithms, the first based on distributed snapshots and the second on diffusing computations.

Authors: Radu Handorean, Rohan Sen, Gregory Hackmann, Gruia-Catalin Roman

Description:
The increasing ubiquity of wireless mobile devices is promoting unprecedented levels of electronic collaboration among devices interoperating to achieve a common goal. Issues related to host interoperability are addressed partially by the principles of the service-oriented computing paradigm. However, certain technical concerns relating to predictable interactions among hosts in mobile ad hoc networks have not yet received much attention. We introduce “follow-me sessions,” where interactions occur between a client and a service, rather than a specific service provider. A client may thus exploit several service providers during the course of its interaction with a given service. This redundancy mitigates the effects of mobility-induced disconnections, thereby facilitating reliable communication. The switching of service providers is done using a combination of strong process migration, context-sensitive binding, and location-agnostic communication protocols. This paper covers the architecture and implementatio of a middleware that supports follow-me sessions and shows how this middleware mitigates issues related to proxy-based service-oriented architectures in mobile ad hoc networks. We support our claims via a technical evaluation of our approach.

Authors: Gruia-Catalin Roman, Peter J. McCann, Jerome Plun

Description:
Mobile computing represents a major point of departure from the traditional distributed computing paradigm. The potentially very large number of independent computing units, a decoupled computing style, frequent disconnections, continuous position changes, and the location-dependent nature of the behavior and communication patterns of the individual components present designers with unprecedented challenges in the areas of modularity and dependability. This paper describes two ideas regarding a modular approach to specifying and reasoning about mobile computing. The novelty of our approach rests with the notion of allowing transient interactions among programs which move in space. In this paper we restrict our concern to pairwise interactions involving variable sharing and action synchronization. The motivation behind the transient nature of the interactions comes from the fact that components can communicate with each other only when they are within a certain range. The notation we propose is meant to simplify the writing of mobile applications and is a direct extension of that used in UNITY. Reasoning about mobile computations relies on the UNITY proof logic.