Context-aware computing is a mobile computing paradigm in which applications can discover and take advantage of contextual information (such as user location, time of day, nearby people and devices, and user activity). Since it was proposed about a decade ago, many researchers have studied this topic and built several context-aware applications to demonstrate the usefulness of this new technology. Context-aware applications (or the system infrastructure to support them), however, have never been widely available to everyday users. In this survey of research on context-aware systems and applications, we looked in depth at the types of context used and models of context information, at systems that support collecting and disseminating context, and at applications that adapt to the changing context. Through this survey, it is clear that context-aware research is an old but rich area for research. The difficulties and possible solutions we outline serve as guidance for researchers hoping to make context-aware computing a reality. 1.

This paper is an answer to the question: "What is unique and conceptually different about mobile computing? " The paper begins by describing a set of constraints intrinsic to mobile computing, and examining the impact of these constraints on the design of distributed systems. Next, it summarizes the key results of the Coda and Odyssey systems. Finally, it describes the research opportunities in five important topics relevant to mobile computing: caching metrics, semantic callbacks and validators, resource revocation, analysis of adaptation, and global estimation from local observations. 1.2. The Need for Adaptation Mobility exacerbates the tension between autonomy and interdependence that is characteristic of all distributed systems. The relative resource poverty of mobile elements as well as their lower trust and robustness argues for reliance on static servers. But the need to cope with unreliable and low-performance networks, as well as the need to be sensitive to power consumption argues for self-reliance. 1.

A common problem facing mobile computing is disconnected operation, or computing in the absence of a network. Hoarding eases disconnected operation by selecting a subset of the user's files for local storage. We describe a hoarding system that can operate without user intervention, by observing user activity and predicting future needs. The system calculates a new measure, semantic distance, between individual files, and uses this to feed a clustering algorithm that chooses which files should be hoarded. A separate replication system manages the actual transport of data; any of a number of replication systems may be used. We discuss practical problems encountered in the real world and present usage statistics showing that our system outperforms previous approaches by factors that can exceed 10:1. 1 Introduction The face of computing today is rapidly being changed by the advent of mobility, but the utility of the portable computer is seriously challenged by the problem of disconnect...

The ability to access information on demand when mobile will be a critical capability in the 21st century. In this paper, we examine the fundamental forces at work in mobile computing systems and explain how they constrain the problem of mobile information access. From these constraints, we derive the importance of adaptivity as a crucial requirement of mobile clients. We then develop a taxonomy of adaptation strategies, and summarize our research in application-transparent and application-aware adaptation in the Coda and Odyssey systems respectively.

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 present designers with unprecedented challenges in the areas of modularity and dependability. So far, the literature on mobile computing is dominated by concerns having to do with the development of protocols and services. This paper complements this perspective by considering the nature of the underlying formal models that will enable us to specify and reason about such computations. The basic research goal is to characterize fundamental issues facing mobile computing. We want to achieve this in a manner analogous to the way concepts such as shared variables and message passing help us understand distributed computing. The pragmatic objective is to develop techniques that facilitate the verification and design of dependable mobile systems. Towards this goal we employ the methods of UNITY. To focus on what is essential we center our study on ad-hoc networks whose singular nature is bound to reveal the ultimate impact of movement on the way one computes and communicates in a mobile environment. To understand interactions we start with the UNITY concepts of union and superposition and consider direct generalizations to transient interactions. The motivation behind the transient nature of the interactions comes

ions for Mobile Computing Peter J. McCann, Gruia-Catalin Roman Abstract--- Recent advances in wireless networking technology and the increasing demand for ubiquitous, mobile connectivity demonstrate the importance of providing reliable systems for managing reconfiguration and disconnection of components. Design of such systems requires tools and techniques appropriate to the task. Many formal models of computation, including UNITY, are not adequate for expressing reconfiguration and disconnection and are therefore inappropriate vehicles for investigating the impact of mobility on the construction of modular and composable systems. Algebraic formalisms such as the ß-calculus have been proposed for modeling mobility. This paper addresses the question of whether UNITY, a state-based formalism with a foundation in temporal logic, can be extended to address concurrent, mobile systems. In the process, we examine some new abstractions for communication among mobile components that express re...

Mobile computing adds a new wrinkle to the ageold problem of caching. Today's wireless links are both slow and expensive, and are not always available to a user. Therefore, when a mobile user is disconnected, a cache miss means (at best) a substantial cost in time and money, or (at worst) a complete halt to work if critical information has not been cached. Existing solutions to this problem rely on some combination of explicit hoard profiles and spying on a user's file accesses.

Mobile computing introduces a new form of distributed computation in which communication is most often intermittent, low-bandwidth, or expensive, thus providing only weak connectivity. In this paper, we present a replication scheme tailored for such environments. Bounded inconsistency is defined by allowing controlled deviation among copies located at weakly connected sites. A dual database interface is proposed that in addition to read and write operations with the usual semantics supports weak read and write operations. In contrast to the usual read and write operations that read consistent values and perform permanent updates, weak operations access only local and potentially inconsistent copies and perform updates that are only conditionally committed. Exploiting weak operations supports disconnected operation, since mobile clients can employ them to continue operate even while disconnected. The extended database interface coupled with bounded inconsistency offers a flexible mechan...

this document we will use the term transaction to mean IOT when there is no ambiguity. running committed resolution pending user invocation with partitioned file accesses without partitioned file accesses automatic or manual resolution validation fail validation succeed & reintegration first class transaction second class transaction Figure 1: A State Transition Diagram for IOT Execution 4. Why Isolation Only?

RPC latencies and other network-related delays can frustrate mobile users of a distributed file system. Disconnected operation helps, but fails to use networking opportunities to their full advantage. In this paper we describe partially connected operation, an extension of disconnected operation that resolves cache misses and preserves client cache consistency, but does not incur the write latencies of a fully connected client. Benchmarks of partially connected mode over a slow network indicate overall system performance comparable to fully connected operation over Ethernet.