Many studies conducted in non-virtual activities have shown that flow significantly influences performance, yet studies in virtual activities often reveal only a weak association. This paper begins by building a theoretical explanatory model, and then conducts 3 empirical studies to explore this question. Study 1 exams the mechanism of weak association in two virtual activities. Study 2 tests the effectiveness of a potential approach to strengthen this association. In Study 3 we applied our proposed model and design approach to optimize a VR tennis game. Results show that the influence of flow on performance was not significant in those virtual activities where the primary task and the operation of interactive artifacts were less congruent such that the artifacts can lead to flow experience that is independently of the primary task. Our research offers a theoretical and empirical basis on how to optimize virtual environment design and maximize positive effect of the flow experience.

With the fast development of virtual reality games, one of the key research questions is how players may express their creativity and participate in the process of game design. In this paper, we present a new game genre which combines user-controlled game design in physical space with game play in virtual space on a mobile device. The new system supports authoring by anyone, creating virtual reality games that can be easily modified or developed for physical space, and be used anywhere by novice end-users without any knowledge of tracking technology. We present the design and implementation of the system, as well as a user experiment. Findings illustrate that the proposed system promotes participation and provides a richer, more interactive and engaging experience.

In virtual learning environment, both personality and emotional features of animated pedagogical agents (APAs) may influence learning. To investigate this question, we developed four APAs with two distinct personality types and two sets of gestures expressing distinct emotional feedback. Effects of APAs' personality types and emotional feedback strategies on learning experiences and performance were assessed experimentally using a virtual Tai Chi training system. Fifty six participants completed the experiment. Results showed that positive emotional feedback strategy led to better learning experiences and performance than negative feedback strategy. Moreover, personality type had significant effect on learning. Choleric APAs led to better performance than Phlegmatic APAs. Personality types moderated the effect of emotional feedback on learning satisfaction. Our study demonstrates that APAs with distinct personality types and emotional feedback are important design parameters for virtual learning environments.

Interactive surfaces are increasingly common in museums and other informal learning environments where they are seen as a medium for promoting social engagement. However, despite their increasing prevalence, we know very little about factors that contribute to collaboration and learning around interactive surfaces. In this paper we present analyses of visitor engagement around several multi-touch tabletop science exhibits. Observations of 629 visitors were collected through two widely used techniques: video study and shadowing. We make four contributions: 1) we present an algorithm for identifying groups within a dynamic flow of visitors through an exhibit hall; 2) we present measures of group-level engagement along with methods for statistically analyzing these measures; 3) we assess the effect of observational techniques on visitors' engagement, demonstrating that consented video studies do not necessarily reflect visitor behavior in more naturalistic circumstances; and 4) we present an analysis showing that groups of two, groups with both children and adults, and groups that take turns spend longer at the exhibits and engage more with scientific concepts.

In this paper we describe visitor interaction with an interactive tabletop exhibit on evolution that we designed for use in natural history museums. We video recorded 30 families using the exhibit at the Harvard Museum of Natural History. We also observed an additional 50 social groups interacting with the exhibit without video recording. The goal of this research is to explore ways to develop "successful" interactive tabletop exhibits for museums. To determine criteria for success in this context, we borrow the concept of Active Prolonged Engagement (APE) from the science museum literature. Research on APE sets a high standard for visitor engagement and learning, and it offers a number of useful concepts and measures for research on interactive surfaces in the wild. In this paper we adapt and expand on these measures and apply them to our tabletop exhibit. Our results show that visitor groups collaborated effectively and engaged in focused, on-topic discussion for prolonged periods of time. To understand these results, we analyze visitor conversation at the exhibit. Our analysis suggests that social practices of game play contributed substantially to visitor collaboration and engagement with the exhibit.

Phylogenetic trees are representations of evolutionary relationships amongst species. Interviews of instructors and students have revealed that novice biologists have difficulty understanding phylogenetics. Moreover, misinterpretations of phylogenetics are common among college-level students. In this paper we present Phylo-Genie, a tabletop interface for fostering collaborative learning of phylogenetics. We conducted an experimental study with 56 participants, comparing students' conceptual learning and engagement using Phylo-Genie as: 1) a multi-touch tabletop interface and 2) a pen and paper activity. Our findings show that the tabletop implementation fosters collaborative learning by engaging users in the activity. We also shed light on the way in which our design principles facilitated engagement and collaborative learning in a tabletop environment.

Multi-touch technology lends itself to collaborative crowd interaction (CI). However, common tap-operated widgets are impractical for CI, since they are susceptible to accidental touches and interference from other users. We present a novel multi-touch interface called FlowBlocks in which every UI action is invoked through a small sequence of user actions: dragging parametric UI-Blocks, and dropping them over operational UI-Docks. The FlowBlocks approach is advantageous for CI because it a) makes accidental touches inconsequential; and b) introduces design parameters for mutual awareness, concurrent input, and conflict management. FlowBlocks was successfully used on the floor of a busy natural history museum. We present the complete design space and describe a year-long iterative design and evaluation process which employed the Rapid Iterative Test and Evaluation (RITE) method in a museum setting.

In this paper, we present the DeepTree exhibit, a multi-user, multi-touch interactive visualization of the Tree of Life. We developed DeepTree to facilitate collaborative learning of evolutionary concepts. We will describe an iterative process in which a team of computer scientists, learning scientists, biologists, and museum curators worked together throughout design, development, and evaluation. We present the importance of designing the interactions and the visualization hand-in-hand in order to facilitate active learning. The outcome of this process is a fractal-based tree layout that reduces visual complexity while being able to capture all life on earth; a custom rendering and navigation engine that prioritizes visual appeal and smooth fly-through; and a multi-user interface that encourages collaborative exploration while offering guided discovery. We present an evaluation showing that the large dataset encouraged free exploration, triggers emotional responses, and facilitates visitor engagement and informal learning.

We present CThru, a self-guided video-based educational environment in a large multi-display setting. We employ a video-centered approach, creating and combining multimedia contents of different formats with a story-telling education video. With the support of new display form factors in the environment, viewing a sequential educational video thread is replaced by the immersive learning experience of hands-on exploration and manipulation in a multi-dimensional information space. We demonstrate CThru with an animation clip in cellular biology, supplementing visible objects in the video with rich domain-specific multimedia information and interactive 3D models. We describe CThru's design rationale and implementation. We also discuss a pilot study and what it revealed with respect to CThru's interface and the usage pattern of the tabletop and the associated large wall display.

We present WeSpace -- a collaborative work space that integrates a large data wall with a multi-user multi-touch table. WeSpace has been developed for a population of scientists who frequently meet in small groups for data exploration and visualization. It provides a low overhead walk-up and share environment for users with their own personal applications and laptops. We present our year-long effort from initial ethnographic studies, to iterations of design, development and user testing, to the current experiences of these scientists carrying out their collaborative research in the WeSpace. We shed light on the utility, the value of the multi-touch table, the manifestation, usage patterns and the changes in their workflow that WeSpace has brought about.

True multi-user, multimodal interaction over a digital table lets co-located people simultaneously gesture and speak commands to control an application. We explore this design space through a case study, where we implemented an application that supports the KJ creativity method as used by industrial designers. Four key design issues emerged that have a significant impact on how people would use such a multi-user multimodal system. First, parallel work is affected by the design of multimodal commands. Second, individual mode switches can be confusing to collaborators, especially if speech commands are used. Third, establishing personal and group territories can hinder particular tasks that require artefact neutrality. Finally, timing needs to be considered when designing joint multimodal commands. We also describe our model view controller architecture for true multi-user multimodal interaction.

Many research projects have demonstrated the benefits of bimanual interaction for a variety of tasks. When choosing bimanual input, system designers must select the input device that each hand will control. In this paper, we argue for the use of pen and touch two-handed input, and describe an experiment in which users were faster and committed fewer errors using pen and touch input in comparison to using either touch and touch or pen and pen input while performing a representative bimanual task. We present design principles and an application in which we applied our design rationale toward the creation of a learnable set of bimanual, pen and touch input commands.

The interoperability of disparate data types and sources has been a long standing problem and a hindering factor for the efficacy and efficiency in visual exploration applications. In this paper, we present a solution, called LivOlay, that enables the rapid visual overlay of live data rendered in different applications. Our tool addresses datasets in which visual registration of the information is necessary in order to allow for thorough understanding and visual analysis. We also discuss initial evaluation and user feedback of LivOlay.

We investigate the differences -- in terms of bothquantitative performance and subjective preference -- between direct-touch and mouse input for unimanual andbimanual tasks on tabletop displays. The results of twoexperiments show that for bimanual tasks performed ontabletops, users benefit from direct-touch input. However,our results also indicate that mouse input may be moreappropriate for a single user working on tabletop tasksrequiring only single-point interaction.

Co-located collaborators often work over physical tabletops using combinations of expressive hand gestures and verbal utterances. This paper provides the first observations of how pairs of people communicated and interacted in a multimodal digital table environment built atop existing single user applications. We contribute to the understanding of these environments in two ways. First, we saw that speech and gesture commands served double duty as both commands to the computer, and as implicit communication to others. Second, in spite of limitations imposed by the underlying single-user application, people were able to work together simultaneously, and they performed interleaving acts: the graceful mixing of inter-person speech and gesture actions as commands to the system. This work contributes to the intricate understanding of multi-user multimodal digital table interaction.

Information shown on a tabletop display can appear distorted when viewed by a seated user. Even worse, the impact of this distortion is different depending on the location of the information on the display. In this paper, we examine how this distortion affects the perception of the basic graphical elements of information visualization shown on displays at various angles. We first examine perception of these elements on a single display, and then compare this to perception across displays, in order to evaluate the effectiveness of various elements for use in a tabletop and multi-display environment. We found that the perception of some graphical elements is more robust to distortion than others. We then develop recommendations for building data visualizations for these environments.

Touch is a compelling input modality for interactive devices; however, touch input on the small screen of a mobile device is problematic because a user's fingers occlude the graphical elements he wishes to work with. In this paper, we present LucidTouch, a mobile device that addresses this limitation by allowing the user to control the application by touching the back of the device. The key to making this usable is what we call pseudo-transparency: by overlaying an image of the user's hands onto the screen, we create the illusion of the mobile device itself being semi-transparent. This pseudo-transparency allows users to accurately acquire targets while not occluding the screen with their fingers and hand. Lucid Touch also supports multi-touch input, allowing users to operate the device simultaneously with all 10 fingers. We present initial study results that indicate that many users found touching on the back to be preferable to touching on the front, due to reduced occlusion, higher precision, and the ability to make multi-finger input.

Co-located collaborators often work over physical tabletops with rich geospatial information. Previous research shows that people use gestures and speech as they interact with artefacts on the table and communicate with one another. With the advent of large multi-touch surfaces, developers are now applying this knowledge to create appropriate technical innovations in digital table design. Yet they are limited by the difficulty of building a truly useful collaborative application from the ground up. In this paper, we circumvent this difficulty by: (a) building a multimodal speech and gesture engine around the Diamond Touch multi-user surface, and (b) wrapping existing, widely-used off-the-shelf single-user interactive spatial applications with a multimodal interface created from this engine. Through case studies of two quite different geospatial systems -- Google Earth and Warcraft III -- we show the new functionalities, feasibility and limitations of leveraging such single-user applications within a multi user, multimodal tabletop. This research informs the design of future multimodal tabletop applications that can exploit single-user software conveniently available in the market. We also contribute (1) a set of technical and behavioural affordances of multimodal interaction on a tabletop, and (2) lessons learnt from the limitations of single user applications.

Tables have historically played a key role in many real-time collaborative environments, often referred to as "war rooms". Today, these environments have been transformed by computational technology into spaces with large vertical displays surrounded by numerous desktop computers. However, despite significant research activity in the area of tabletop computing, very little is known about how to best integrate a digital tabletop into these multi-surface environments. In this paper, we identify various design requirements for the implementation of a system intended to support such an environment. We then present a set of designs that demonstrate how an interactive tabletop can be used in a real-time operations center to facilitate collaborative situation-assessment and decision-making.

In many environments, it is often the case that input is made to displays that are positioned non-traditionally relative to one or more users. This typically requires users to perform interaction tasks under transformed input-display spatial mappings, and the literature is unclear as to how such transformations affect performance. We present two experiments that explore the impact of display space position and input control space orientation on user's subjective preference and objective performance in a docking task. Our results provide guidelines as to optimal display placement and control orientation in collaborative computing environments with one or more shared displays.

Visual search is the subject of countless psychology studies in which people search for target items within a scene. The bulk of this literature focuses on the individual with the goal of understanding the human perceptual system. In life, visual search is performed not only by individuals, but also by groups -- a team of doctors may study an x-ray and a team of analysts may study a satellite photograph. In this paper, we examine the issues one should consider when searching as a group. We present the details of an experiment designed to investigate the impact of group size on visual search performance, and how different display configurations affected that performance. We asked individuals, pairs, and groups of four people to participate in a baggage screening task in which these teams searched simulated x-rays for prohibited items. Teams conducted these searches on single monitors, a row of four monitors, and on a single horizontal display. Our findings suggest that groups commit far fewer errors in visual search tasks, although they may perform slower than individuals under certain conditions. The interaction between group size and display configuration turned out to be an important factor as well.

Most commercial software applications are designed for a single user using a keyboard/mouse over an upright monitor. Our interest is exploiting these systems so they work over a digital table. Mirroring what people do when working over traditional tables, we want to allow multiple people to interact naturally with the tabletop application and with each other via rich speech and hand gestures. In previous papers, we illustrated multi-user gesture and speech interaction on a digital table for geospatial applications -- Google Earth, Warcraft III and The Sims. In this paper, we describe our underlying architecture: GSI Demo. First, GSI Demo creates a run-time wrapper around existing single user applications: it accepts and translates speech and gestures from multiple people into a single stream of keyboard and mouse inputs recognized by the application. Second, it lets people use multimodal demonstration -- instead of programming -- to quickly map their own speech and gestures to these keyboard/mouse inputs. For example, continuous gestures are trained by saying "Computer, when I do [one finger gesture], you do [mouse drag]". Similarly, discrete speech commands can be trained by saying "Computer, when I say [layer bars], you do [keyboard and mouse macro]". The end result is that end users can rapidly transform single user commercial applications into a multi-user, multimodal digital tabletop system.

In this paper, we discuss our adaptation of a single-display, single-user commercial application for use in a multi-device, multi-user environment. We wrap Google Earth, a popular geospatial application, in a manner that allows for synchronized coordinated views among multiple instances running on different machines in the same co-located environment. The environment includes a touch-sensitive tabletop display, three vertical wall displays, and a TabletPC. A set of interaction techniques that allow a group to manage and exploit this collection of devices is presented.

We explore the design space of a two-sided interactive touch table, designed to receive touch input from both the top and bottom surfaces of the table. By combining two registered touch surfaces, we are able to offer a new dimension of input for co-located collaborative groupware. This design accomplishes the goal of increasing the relative size of the input area of a touch table while maintaining its direct-touch input paradigm. We describe the interaction properties of this two-sided touch table, report the results of a controlled experiment examining the precision of user touches to the underside of the table, and a series of application scenarios we developed for use on inverted and two-sided tables. Finally, we present a list of design recommendations based on our experiences and observations with inverted and two-sided tables.

Supporting groups of individuals exploring large maps and design diagrams on interactive tabletops is still an open research problem. Today's geospatial, mechanical engineering and CAD design applications are mostly single-user, keyboard and mouse-based desktop applications. In this paper, we present the design of and experience with DTLens, a new zoom-in-context, multi-user, two-handed, multi-lens interaction technique that enables group exploration of spatial data with multiple individual lenses on the same direct-touch interactive tabletop. DTLens provides a set of consistent interactions on lens operations, thus minimizes tool switching by users during spatial data exploration.

DiamondSpin is a toolkit for the efficient prototyping of and experimentation with multi-person, concurrent interfaces for interactive shared displays. In this paper, we identify the fundamental functionality that tabletop user interfaces should embody, then present the toolkit's architecture and API. DiamondSpin provides a novel real-time polar to Cartesian transformation engine that has enabled new, around-the-table interaction metaphors to be implemented. DiamondSpin allows arbitrary document positioning and orientation on a tabletop surface. Polygonal tabletop layouts such as rectangular, octagonal, and circular tabletops can easily be constructed. DiamondSpin also supports multiple work areas within the same digital tabletop. Multi-user operations are offered through multi-threaded input event streams, multiple active objects, and multiple concurrent menus. We also discuss insights on tabletop interaction issues we have observed from a set of applications built with DiamondSpin.

The status quo for co-located groupware is to assume that "social protocols" (standards of polite behavior) are sufficient to coordinate the actions of a group of users; however, prior studies of groupware use as well as our own observations of groups using a shared tabletop display suggest potential for improving groupware interfaces by incorporating coordination policies - direct manipulation mechanisms for avoiding and resolving conflicts. We discuss our observations of group tabletop usage and present our coordination framework. We conclude with example usage scenarios and discuss future research suggested by this framework.

Interactive tabletops have been previously proposed and studied in the domain of co-located group applications. However, little fundamental research has been done to explore the issue of size. In this paper we identify a number of size considerations for tabletop design, and present an experiment to explore some of these issues, in particular the effects of group size and table size on the speed at which the task was performed, the distribution of work among group members, issues of shared resources, and user preference for table size. Our findings shed light on (1) how work strategies are affected by group size, (2) how social interaction varies with respect to table size, and (3) how the speed of task performance is influenced by group size but not by table size. In addition, our experiments revealed that for larger groups, designers might need to add additional vertical displays for shared information. This finding opens the door for extending singledisplay groupware to shared-display groupware settings that involve multiple, shared displays.

This paper presents a new multi-path selection scheme for video streaming on overlay networks. Our scheme uses an overlay network architecture that makes minimal assumptions about the knowledge of the underlying network. We first propose a new QoS metric link correlation and a path correlation model for multi-path selection problem. After discussing the tractability of minimal correlation multi-path selection problem, we present an efficient algorithm called correlation cost routing to select multi-path in overlay networks. The simulation results show that the average peak signal-to-noise ratio (PSNR) of the transmitted multiple descriptions coding (MDC) video using our multi-path selection algorithm improves by up to 3.2 dB over maximally link-disjoint multi-path selection method. Furthermore our new algorithm is more efficient than previous methods since it shares the same complexity with Dijsktra algorithm.

This paper proposes an enhancement layer truncation scheme for the fine-granularity-scalability (FGS) video. Our target is to minimize the quality variation of different parts within each frame when the last transmitted enhancement layer is truncated according to the available network bandwidth. We propose to redistribute the bits in the enhancement layer that can only be partially kept with the available bit-budget so that it is able to cover the whole frame area to raise the quality of different parts uniformly. Simulation results confirm the effectiveness of the proposed method in improving the decoded visual quality and reducing the intra-frame quality variation.

The Personal Digital Historian (PDH) is an ongoing research project aimed at allowing small groups of people co-present to casually browse, embellish, and explore large collections of their personal data, such as pictures, video, or more business-related items such as spreadsheets or PowerPoint slides. In this interactive poster, we demonstrate our initial prototype system which is designed for a tabletop display. The interface allows people to organize their images along the four questions essential to storytelling: who?, when?, where?, and what? Users are provided with a wide variety of flexible interaction methods, including region of interest query specification with in-place freeform stroke input, image-based book marking, suggestion generation via automatic query relaxation, and output summarization. With this interface, the users can enjoy their conversation while having the photos at their fingertips, rather than being distracted by the effort of formulating queries.

This paper presents visualization and layout schemes developed for a novel circular user interface designed for a round, tabletop display. Since all the displayed items are in a polar coordinate system, many interface and visualization schemes must be revisited to account for this new layout of UI elements. We discuss the direct implications of such a circular interface on document orientation. We describe two types of fisheye deformation of the circular layout and explain how to use them in a multi-person collaborative interface. These two schemes provide a general layout framework for circular interfaces. We have also designed a new visualization technique derived from the particularities of the circular layout we have highlighted. In this technique the user controls the layout of the elements of a hierarchical tree. Our approach is to provide the user rich interaction possibilities to easily and quickly produce a layout comparable to the hyperbolic view developed at Xerox PARC. The visualization work presented in this paper is part of our ongoing Personal Digital Historian (PDH) research project. The overall goal of PDH is to investigate ways to effectively and intuitively organize, navigate, browse, present and visualize digital data in an interactive multi-person conversational setting.

Organizations, families, institutions evolve a shared culture and history. In this work, we describe a system to facilitate conversation and storytelling about this collective past. Users explore digital archives of shared materials such as photographs, video, and text documents on a tabletop interface. Both the software and the interface encourage natural conversation and reflection. This work is an application of our ongoing research on systems for multiple, co-present users to explore digital collections. In this paper, we present a case study of our own group history along with the software extensions developed for this scenario. These extensions include methods for easily branching off from and returning to previous threads of the exploration, incorporating background contexts that support a variety of view points and flexible story sharing, and supporting the active and passive discovery of relevant information.

We present visualization and layout algorithms that can enhance informal story-telling using personal digital data such as photos in a face-to-face social setting. In order to build a more intuitive browser for retrieval, navigation and story-telling, we introduce a novel optimized layout technique for large image sets, which respects (context-sensitive) mutual similarities as visualized on a shared 2-D display (a table-top). The experimental results show a more perceptually intuitive and informative visualization of traditional CBIR-based retrievals, providing not only a better understanding of the query context but also aiding the user informing new queries. A framework for user-modeling is also introduced and tested. This allows the system to adapt to the user's preference and integrate relevance feedback.

This paper presents a new scheduling scheme to support a premium service in the differentiated service (DiffServ) architecture. It is based on weighted packet scheduling policies such as weighted round robin or fair queueing. The key feature of the new scheduling scheme is to change the scheduling weights of behavior aggregates adaptively. By adaptively adjusting the weights according to the dynamics of the average queue size of the premium service, the proposed scheme can achieve low loss rate, low delay and delay jitter for the premium service. Moreover, it requires neither rigid admission control nor accurate traffic conditioning to support the premium service in the DiffServ architecture. This adaptive packet scheduling is shown to absorb the transient burstiness of the expedited forwarding (EF) aggregate-which is caused by the traffic distortion inside the network-without incurring packet loss or increasing the queueing delay.

Presents CReMeS (CORBA-compliant Reflective Memory-based Service), a CORBA-compliant design and implementation of a new real-time (RT) communication service. The CReMeS architecture is based on MidART's RT-CRM (Real-Time Channel-based Reflective Memory), which supports the separation of QoS specification between data producers and consumers and employs a user-level scheduling scheme for communicating RT tasks. Although RT-CRM provides a predictable and scalable asynchronous communication infrastructure for applications, it is not a standard middleware. To make its service widely available, we developed CReMeS by adapting RT-CRM for CORBA environments. As a result, CReMeS provides efficient, predictable and scalable communication between information producers and consumers. Since CReMeS provides a CORBA interface to applications and demands no changes to the ORB layer and the language mapping layer, it can run on non-RT off-the-shelf ORBs and enables applications on these ORBs to have scalable and end-to-end predictable asynchronous communication facility. In addition, an application designer can select whether to use an out-of-band channel or the ORB GIOP (General Inter-ORB Protocol)/IIOP (Internet Inter-ORB Protocol) for data communication. This permits a tradeoff between performance, predictability and reliability. Our architecture achieves better performance and predictability than a RT implementation of the CORBA Event Service when the out-of-band channel is employed for data communication; it delivers better predictability with comparable performance when the ORB GIOP/IIOP is used.

In this paper, we propose and present Real-Time Channel-based Reflective Memory (RT-CRM)-a useful programming model and middleware communication service for constructing distributed real-time applications on platforms, open systems. RT-CRM provides remote real-time data reflection abstraction using a simple writer-push model. This writer-push approach enables us to easily decouple the QoS characteristics of the writers from that of the readers. This decoupling is crucial in supporting different kinds of remote data transfer and access needs that one often finds in distributed real-time systems. We describe the design of RT-CRM, along with a set of easy-to-use API to access the RT-CRM service. We have implemented RT-CRM as part of a larger real-time middleware project, MidART. We address many of the important implementation issues, including buffer management and QoS support. We demonstrate the feasibility of RT-CRM through a discussion of our application programming support and performance data.

We present an adaptive network layer protocol for VBR video transport. It: (1) minimizes the buffer requirement in the network while guaranteeing that packets of VBR encoded video flows will not be lost, and (2) minimizes the end-to-end delay and jitter of frames. To achieve the former objective, we utilize a receiver-oriented adaptive credit-based flow control algorithm, and derive the necessary and sufficient number of buffers that should be reserved for ensuring its reliability. To minimize the end-to-end delay and jitter for VBR encoded video streams, we: (1) present bandwidth estimation techniques which exploit the structure of the video traffic, and (2) define a new fairness criteria for buffer allocation and then present a fair buffer/bandwidth allocation algorithm. We experimentally evaluate this protocol for a wide range of parameters and many network configurations, and demonstrate its adaptability. We also compare the performance of the protocol with numerous other schemes and demonstrate its suitability for video transport.

We address the problem of middleware design for constructing ATM LAN based distributed industrial plant monitoring and control systems. In particular, we present a real-time client-server programming model based on a uniform ATM network. This model is being realized in our middleware called MidART. The middleware provides a set of industrial application specific but network transparent programming abstractions and application programming interface (API) that support individual application QoS requirements. In order to achieve on-demand transmission of plant data, we have developed a concept called selective real-time channels to be supported by MidART. We present the design and protocols of selective real-time channels and describe how QoS requirements of applications are guaranteed.

The asynchronous transfer mode (ATM) is expected to be the multiplexing and switching technique for the future broadband integrated service digital networks (BISDNs) which can transport almost all types of traffic including bursty data traffic and continuous voice/video frames. However, this capability cannot be realized without a proper congestion-control scheme. This paper discusses the suitability of the real-time channel approach for congestion control in ATM networks. A main contribution of the paper is the development of a new message-transmission scheme for real-time channels which does not require each cell to carry deadline information which is difficult to do with the standard ATM cell format. This makes our scheme compatible with, and implementable in, ATM networks. The new scheme also has a number of advantages over existing ones. The achievable quality of service with the proposed approach would make ATM networks capable of supporting both real-time services and dynamic bandwidth sharing which have been promised but not yet fully realized.>

Most real-time scheduling algorithms schedule tasks with regard to their worst case computation times. Resources reclaiming refers to the problem of utilizing the resources left unused by a task when it executes in less than its worst case computation time, or when a task is deleted from the current schedule. Dynamic resource reclaiming algorithms that are effective, avoid any run time anomalies, and have bounded overhead costs that are independent of the number of tasks in the schedule are presented. Each task is assumed to have a worst case computation time, a deadline, and a set of resource requirements. The algorithms utilize the information given in a multiprocessor task schedule and perform online local optimization. The effectiveness of the algorithms is demonstrated through simulation studies.>

Resource reclaiming refers to the problem of utilizing the resources left unused by a task when it executes in less than its worst-case computation time, or when a task is deleted from the current schedule. In dynamic real-time multiprocessor environments, resource reclaiming can be used to improve the average performance. Dynamic resource reclaiming algorithms must be effective in reclaiming unused time and also avoiding any anomalies. The authors present resource reclaiming algorithms with these properties. These algorithms are designed to have time complexity independent of the number of tasks in a schedule. The effectiveness of the algorithms is demonstrated through simulation studies. The algorithms have also been implemented in the Spring Kernel.>