Maria R. Ebling

Experience with disconnected operation in a mobile computing environment

In this paper we present qualitative and quantitative data on file access in a mobile computing environment. This information is based on actual usage experience with the Coda File System over a period of about two years. Our experience confirms the viability and effectiveness of disconnected operation. It also exposes certain deficiencies of the current implementation of Coda, and identifies new functionality that would enhance its usefulness for mobile computing. The paper concludes with a description of what we are doing to address these issues.

Remote health-care monitoring using personal care connect

Caring for patients with chronic illnesses is costly-nearly

An open ecosystem for mobile-cloud convergence

1.27 trillion today and predicted to grow much larger. To address this trend, we have designed and built a platform, called Personal Care Connect (PCC), to facilitate the remote monitoring of patients. By providing caregivers with timely access to a patients health status, they can provide patients with appropriate preventive interventions, helping to avoid hospitalization and to improve the patients quality of care and quality of life. PCC may reduce health-care costs by focusing on preventive measures and monitoring instead of emergency care and hospital admissions. Although PCC may have features in common with other remote monitoring systems, it differs from them in that it is a standards-based, open platform designed to integrate with devices from device vendors and applications from independent software vendors. One of the motivations for PCC is to create and propagate a working environment of medical devices and applications that results in innovative solutions. In this paper, we describe the PCC remote monitoring system, including our pilot tests of the system.

On the contributions of different empirical data in usability testing

We show how a disruptive force in mobile computing can be created by extending todays unmodified cloud to a second level consisting of self-managed data centers with no hard state called cloudlets. These are located at the edge of the Internet, just one wireless hop away from associated mobile devices. By leveraging lowlatency offload, cloudlets enable a new class of real-time cognitive assistive applications on wearable devices. By processing high data rate sensor inputs such as video close to the point of capture, cloudlets can reduce ingress bandwidth demand into the cloud. By serving as proxies for distant cloud services that are unavailable due to failures or cyberattacks, cloudlets can improve robustness and availability. We caution that proprietary software ecosytems surrounding cloudlets will lead to a fragmented marketplace that fails to realize the full business potential of mobile-cloud convergence. Instead, we urge that the software ecosystem surrounding cloudlets be based on the same principles of openness and end-to-end design that have made the Internet so successful.

Overcoming the Network Bottleneck in Mobile Computing

Many sources of empirical data can be used to evaluate an interface (e.g., time to learn, time to perform benchmark tasks, number of errors on benchmark tasks, answers on questionnaires, comments made in verbal protocols). This paper examines the relative contributions of both quantiðtaðtive and qualitative data gathered during a usability study. For each usability problem uncovered by this study, we trace each contributing piece of evidence back to its empirical source. For this usability study, the verbal protocol provided the sole source of evidence for more than one third of the most severe problems and more than two thirds of the less severe problems. Thus, although the verbal protocol provided the bulk of the evidence, other sources of data contributed disproportionately to the more critical problems. This work suggests that further research is required to determine the relative value of different forms of empirical evidence.

Enabling location-based applications

System designers have traditionally treated the network as an inexhaustible resource, focusing their efforts on optimizing CPU and storage usage. For instance, the popular NFS file system [8] supports diskless operation, thereby avoiding use of local secondary storage at the expense of increased network usage. But in mobile computing, it is the network, rather than CPU or storage, that will be the scarce resource. The time has come when we must treat the network as a first-class resource, expending the CPU and storage resources necessary to use it intelligently. In this paper we argue that prescient caching and smart scheduling are key techniques/or overcoming the network bottleneck. We use the Coda file system [9] as a case study to substantiate our position.

Matrix: adaptive middleware for distributed multiplayer games

We identify a number of factors that may hinder the commercial success of location-based applications: the concern of privacy, the need to consider context beyond location, the presence of voluminous resources, and the constrained interfaces available on mobile devices. We describe an end-to-end system architecture with integrated support to address these issues. In particular, the architecture includes a Secure Context Service that provides broad context information to applications and allows people to flexibly control the release of their private information, an Intelligent Service Discovery Service that allows for personalized selection of physical and virtual services, and a multi-modal interaction mechanism that enables users to exploit multiple synchronized access channels to interact with an application and to switch among channels at any time. Our goals are to improve user experience, to reduce user distraction and to facilitate awareness of the physical world.

SynRGen: an extensible file reference generator

Building a distributed middleware infrastructure that provides the low latency required for massively multiplayer games while still maintaining consistency is non-trivial. Previous attempts have used static partitioning or client-based peer-to-peer techniques that do not scale well to a large number of players, perform poorly under dynamic workloads or hotspots, and impose significant programming burdens on game developers. We show that it is possible to build a scalable distributed system, called Matrix, that is easily usable by game developers. We show experimentally that Matrix provides good performance, especially when hotspots occur.

The importance of translucence in mobile computing systems

SynRGen, a synthetic file reference generator operating at the system call level, is capable of modeling a wide variety of usage environments. It achieves realism through trace-inspired micromodels and flexibility by combining these micromodels stochastically. A micromodel is a parameterized piece of code that captures the distinctive signature of an application. We have used SynRGen extensively for stress testing the Coda File System. We have also performed a controlled experiment that demonstrates SynRGens ability to closely emulate real users—within 20% of many key system variables. In this paper we present the rationale, detailed design, and evaluation of SynRGen, and mention its applicability to broader uses such as performance evaluation.

Bar Codes Everywhere You Look

Mobile computing has been an active area of research for the past decade, but its importance will increase substantially in the decade to come. One problem faced by designers of mobile systems is that of maintaining the illusion of connectivity even when network performance is poor or non-existent. The Coda file system uses its cache to maintain this illusion. Extensive experience with the system suggests that, although users find the functionality provided by the system extremely valuable, new users face an arduous learning curve and even experienced users are sometimes confused by the systems behavior. The fundamental problem is that the lack of a strong network connection causes the system to violate a key property of caching: transparency. To overcome this problem, we have built an interface, called the CodaConsole, that makes caching translucent to users through controlled exposure of cache management internals. The interface exposes critical aspects of caching to support the mobile user while hiding noncritical details to preserve usability. This article presents the design, implementation, and usability evaluation of this interface. The CodaConsole successfully makes caching translucent in the presence of disconnected or weakly connected operation. The most surprising result was that novice Coda users performed almost as well as experienced Coda users.