Christopher K. Hess

A middleware infrastructure for active spaces

The paper discusses the Gaia metaoperating system which extends the reach of traditional operating systems to manage ubiquitous computing habitats and living spaces as integrated programmable environments. Gaia exports services to query, access, and use existing resources and context, and provides a framework to develop user-centric, resource-aware, multidevice, context-sensitive, and mobile applications.

Gaia: a middleware platform for active spaces

We envision a future where peoples living spaces are interactive and programmable. Users interact with their offices, homes, cars, malls and airports to request information, benefit from the resources available, and configure the habitats behavior. Data and tasks are always accessible and are mapped dynamically to convenient resources present in the current location. Users may extend the habitat with personal devices that seamlessly integrate with the environment. Such user-oriented interactive environments may require a novel software infrastructure to operate their resources, sense context properties, and assist in the development and execution of applications. In this article, we present an experimental middleware infrastructure called Gaia that we have used to prototype the resource management of and provide the user-oriented interfaces for such physical spaces populated with network-enabled computing resources.

Building Applications for Ubiquitous Computing Environments

Ubiquitous computing embodies a fundamental change from traditional desktop computing. The computational environment is augmented with heterogeneous devices, choice of input and output devices, mobile users, and contextual information. The design of systems and applications needs to accommodate this new operating environment. In this paper, we present our vision of future computing environments we term User Virtual Spaces, the challenges facing developers, and how they motivate the need for new application design. We present our approach for developing applications that are portable across ubiquitous computing environments and describe how we use contextual information to store and organize application data and user preferences. We present an application we have implemented that illustrates the advantages of our techniques in this new computing environment.

An application of a context-aware file system

Ubiquitous computing environments stretch the requirements of traditional infrastructures used to facilitate the development of applications. Activities are often supported by collections of applications, some of which are automatically launched with little or no human intervention. This task-driven environment challenges existing application construction and data management techniques. In this paper, we describe a file system that organises application data based on contextual information, imports user data based on its physical presence, and supports format conversions to accommodate device context. We describe several applications that we have developed within our ubiquitous computing infrastructure and show how they leverage the novel features of our file system to simplify their complexity.

A context-aware data management system for ubiquitous computing applications

One of the factors that differentiates ubiquitous computing from traditional distributed computing is context. Context, such as time, location, and situation, allows a system to adapt to the current surroundings in order to facilitate the use of the computational environment. In this paper, we present a file system for ubiquitous computing applications that is context-aware. Context is used to support the types of applications and devices that are found in ubiquitous computing spaces. Novel features of the system include how the view of data adapts to the activity being currently performed and how user data is imported into the local environment. Our system is evaluated as part of a ubiquitous computing infrastructure deployed in a seminar room to investigate issues of performance, scalability, and usability.

Integrating PDAs into Distributed Systems: 2K and PalmORB

In this paper we describe an application model for seamless mobile data access using handheld devices and wireless links. We go beyond the current model in which handhelds are used as smart organizers augmented with stripped down versions of popular desktop programs. Instead, we propose to integrate handheld devices seamlessly in a distributed computing environment. Componentized applications, adaptable middleware frameworks, and standardized protocols play a significant role in this new paradigm. We also describe an implementation within this paradigm using PalmORB, a CORBA client for the 3Com Palm devices.

Media Streaming Protocol: an adaptive protocol for the delivery of audio and video over the Internet

The introduction of audio and video content on the World Wide Web has greatly increased traffic on the Internet. Congestion within the network may delay the reception of frames and cause them to miss presentation deadlines. A new protocol, the Media Streaming Protocol (MSP), has been developed to stream audio and video over the Internet, which is fair in its consumption of network bandwidth. The protocol incorporates a novel technique to identify congestion within the system. The algorithm monitors the state of the system and is able to quickly adjust to the changing capacity of the network. The protocol reduces the amount of data being transmitted and minimizes the aural and visual defects during playback. Such a protocol is critical as network bandwidth is increasingly being consumed by audio and video applications.

Design and performance of MPEG video streaming to palmtop computers

Todays wide variety of computing devices offer a large range of resource availability. These resources include CPU speed, bandwidth, and memory. Workstations and PCs typically are rich in resources, whereas palmtop devices are generally quite limited. This disparity offers challenges to integrating these heterogeneous devices into a single distributed system. Services must be available to each device, but it may be necessary to modify certain services if the connected device does not have the required resources to support them. Proxies may be introduced into the system to off-load computations that would preclude certain services to resource-deprived devices. We have implemented one such proxy that enables the viewing of live MPEG video on the 3Com PalmPilot. The proxy is able to transform the video feed on-the-fly, removing extraneous information, thereby reducing CPU and memory requirements and allowing palm devices to participate in video sessions. This paper discusses the design and performance of our video proxy targeted for 3Com PalmPilot handheld computers. Several protocols are compared and the advantages of each are discussed.

VistaMail: an integrated multimedia mailing system

VistaMail, a fully integrated multimedia mailing system, lets users easily create, send, and view audio and video components. The system treats these components as part of a single unified message rather than as additions to the text portion. This article discusses the design of the multimedia mail system and some of the issues involved in implementing it.