CAIRO: a concurrent engineering meeting environment for virtual design teams

This paper presents the software architecture for a next generation concurrent engineering environment that helps geographically separated designers and engineers to collaborate effectively. The paper highlights research in computer-supported collaboration work (CSCW) based on various models of group interaction, social communication theory, negotiation theory and distributed artificial intelligence concepts. The paper describes CAIRO (Collaborative Agent Interaction and synchROnization) system, a distributed conferencing architecture for managing designers and engineers in a distributed design meeting. The CAIRO system allows designers and engineers to work together in virtual teams by supporting multi-media interactions over computer networks. CAIRO aids the concurrent engineering effort by relaxing the physical, temporal and organizational constraints experienced in traditional design meeting environments. CAIRO provides both media synchronization, i.e. ensuring that all information exchanged between users is synchronized, and agent synchronization, i.e. ensuring effective structuring and control of a distributed conference. This paper also details the prototype CAIRO system with a detailed example, illustrating its use in concurrent design settings.     

Towards a Smarter Meeting Record—Capture and Access of Meetings Revisited

Multimedia records of meetings contain a rich amount of project information. However, finding detailed information in a meeting record can be difficult because there is no structural information other than time to aid navigation. In this paper we survey and discuss various ways of indexing meeting records by categorizing existing approaches along multiple dimensions. We then introduce the notion of creating indices based upon user interaction with domain-specific artifacts. As an example to illustrate the use of domain-specific artifacts to create meaningful pointers into the meeting record, we describe capture and access in a prototype system that supports general meeting artifacts. Werner Geyer is a Research Staff Member at the IBM T.J. Watson Research Lab in Cambridge, Massachusetts, in the Collaborative User Experience Group (CUE). He is leading research projects in the areas of activity-centric collaboration, ad hoc collaboration, and virtual meetings. His research focuses on the intersections of egocentric vs. public, informal vs. formal, unstructured vs. structured types of collaboration. Before joining CUE, Werner was a Post Doc at IBM Research in New York where he worked on new web-based team support technologies and on capture and access of distributed meetings. He holds a Ph.D. in Computer Science from the University of Mannheim, Germany. He also earned a M.S. in Information Technology, which combines Computer Science and Business Administration, from the University of Mannheim. Heather Richter is an Assistant Professor in the Department of Software and Information Systems at the University of North Carolina at Charlotte. She received her Ph.D. in Computer Science from the Georgia Institute of Technology in 2005, and her B.S. in Computer Science from Michigan State University in 1995. Her research interests are in the areas of Human Computer Interaction, Computer Supported Cooperative Work, Ubiquitous Computing, and Software Engineering. Gregory D. Abowd is an Associate Professor in the College of Computing at the Georgia Institute of Technology. He leads the Ubiquitous Computing Research Group in examining issues involved in building and evaluating ubiquitous computing applications that impact our everyday lives. Dr. Abowd initiated, and now co-directs, the Aware Home Research Initiative at Georgia Tech. He is an Associate Editor for the Human Computer Interaction Journal and the IEEE Pervasive Computing Magazine. He received a B.S. in Mathematics in 1986 from the University of Notre Dame and the degrees of M.Sc. in 1987 and D.Phil in 1991 in Computation from Oxford University.     

Distributed Java applets for project management on the Web

The rapid evolution of our data communications infrastructure is making distributed projects increasingly viable. Without a common infrastructure, computer-supported collaborative tools for distributed teams have been prohibitively expensive to build and maintain. However, the increasing availability of the Internet is enabling companies to develop cost-effective collaborative solutions. Traditional desktop project management software is designed as a single-user tool that lets the project manager track tasks, milestones and deliverables. As teams spread over geographic distances with multiple centers of control, the communication, coordination, and tracking of ongoing project activity become key issues for project success. This article looks beyond the traditional planning focus of project management applications to a network-centric focus on collaboration. It describes the implementation of ActionPlan, a 100 percent Java-based application from Netmosphere that supports real-time collaboration among Java thin clients to facilitate distributed project management     

Telepresence in concurrent lifecycle design and construction

Construction projects usually involve transient ‘virtual organisations’ made up of members of a project team (involving several disparate disciplines) working together on the design and construction of a facility. Team members are often non-co-located, particularly at the early stages of the design process, and tend to work independently while taking decisions that affect others. The adoption of concurrent engineering principles by the construction industry is increasingly being seen as vital for reducing the problems posed by the industry's fragmentation, and enhancing its competitiveness. An important aspect of concurrent engineering in construction is the need for an effective communications infrastructure able to transmit project information between members of the project team and across all stages in the constructed facility's lifecycle. This paper describes the development of such a communications infrastructure that is based on the concept of Telepresence. The intention is to create a persistent space to support interaction between project personnel throughout the design and construction phases of projects. The paper first highlights the key communications issues that need to be addressed, introduces ‘Telepresence’ and describes an initial prototype system. The approach being adopted in the development of an advanced Telepresence environment for construction project teams is also presented. The Telepresence environment is intended to help people who cannot be together to work together.     

Athena, Andrew and Stanford: a look at implementation and evaluation in three large projects

Abstract Massachusetts Institute of Technology and Carnegie Mellon University have both embarked on enormous projects designed to implement workstation environments for use in academic endeavours. Project Athena at MIT is a network designed to service teaching and learning only, while the Andrew network at CMU is to service both teaching and research. Stanford University's computer-intensive environment for teaching and learning owes no allegiance to either the Athena or the Andrew model. The environments at these three universities are summarized and placed in context.     

InfoFilter: Supporting quality of service for fresh information delivery

With the explosive growth of the Internet and World Wide Web comes a dramatic increase in the number of users that compete for the shared resources of distributed system environments. Most implementations of application servers and distributed search software do not distinguish among requests to different web pages. This has the implication that the behavior of application servers is quite unpredictable. Applications that require timely delivery of fresh information consequently suffer the most in such competitive environments. This paper presents a model of quality of service (QoS) and the design of a QoS-enabled information delivery system that implements such a QoS model. The goal of this development is two-fold. On one hand, we want to enable users or applications to specify the desired quality of service requirements for their requests so that application-aware QoS adaptation is supported throughout the Web query and search processing. On the other hand, we want to enable an application server to customize how it should respond to external requests by setting priorities among query requests and allocating server resources using adaptive QoS control mechanisms. We introduce the Infopipe approach as the systems support architecture and underlying technology for building a QoS-enabled distributed system for fresh information delivery. Ling Liu, Ph.D.: She is an associate professor at the College of Computing, Georgia Institute of Technology. She received her Ph.D. from Tilburg University, The Netherlands in 1993. Her research interests are in the area of large-scale data intensive systems and its applications in distributed, mobile, multimedia, and Internet computing environments. Her work has focused on systems support for creating, searching, manipulating, and monitoring streams of information in wide area networked information systems. She has published more than 70 papers in internal journals or international conferences, and has served on more than 20 program committees in the area of data engineering, databases, and knowledge and information management. Calton Pu, Ph. D.: He is a Professor and John P. Imlay, Jr. Chair in Software at the College of Computing, Georgia Institute of Technology. Calton received his Ph.D. from University of Washington in 1986. He leads the Infosphere expedition project, which is building the system software to support the next generation information flow applications. Infosphere research includes adaptive operating system kernels, communications middleware, and distributed information flow applications. His past research included operating system projects such as Synthetix and Microfeedback, extended transaction projects such as Epsilon Serializability, and Internet data management. He has published more than 125 journal and conference papers, and served on more than 40 program committees. Karsten Schwan, Ph.D.: He is a professor in the College of Computing at the Georgia Institute of Technology. He received the M.Sc. and Ph.D. degrees from Carnegie-Mellon University in Pittsburgh, Pennsylvania. He directs the IHPC project for high performance cluster computing at Georgia Tech. His current research addresses the interactive nature of modern high performance applications (i.e., online monitoring and computational steering), the development of efficient and object-based middleware, the operating system support for distributed and parallel programs, and the online configuration of applications for distributed real-time applications and for communication protocols. Jonathan Walpole, Ph.D.: He is a Professor in the Computer Science and Engineering Department at oregon Graduate Institute of Science and Technology. He received his Ph.D. in Computer Science from Lancaster University, U.K. in 1987. His research interests are in the area of adaptive systems software and its application in distributed, mobile, multimedia computing environments. His work has focused on quality of service specification, adaptive resource management and dynamic specialization for enhanced performance, survivability and evolvability of large software systems, and he has published extensively in these areas.     

Behavioural notions for elementary net systems

We study the relationships between a number of behavioural notions that have arisen in the theory of distributed computing. In order to sharpen the under-standing of these relationships we apply the chosen behavioural notions to a basic net-theoretic model of distributed systems called elementary net systems. The behavioural notions that are considered here are trace languages, non-sequential processes, unfoldings and event structures. The relationships between these notions are brought out in the process of establishing that for each elementary net system, the trace language representation of its behaviour agrees in a strong way with the event structure representation of its behaviour. M. Nielsen received a Master of Science degree in mathematics and computer science in 1973, and a Ph.D. degree in computer science in 1976 both from Aarhus University, Denmark. He has held academic positions at Department of Computer Science, Aarhus University, Denmark since 1976, and was visiting researcher at Computer Science Department, University of Edinburgh, U.K., 1977–79, and Computer Laboratory, Cambridge University, U.K., 1986. His research interest is in the theory of distributed computing. Grzegorz Rozenberg received a master of engineering degree from the Department of Electronics (section computers) of the Technical University of Warsaw in 1964 and a Ph.D. in mathematics from the Institute of Mathematics of the Polish Academy of Science in 1968. He has held acdeemic positions at the Institute of Mathematics of the Polish Academy of Science, the Department of Mathematics of Utrecht University, the Department of Computer Science at SUNY at Buffalo, and the Department of Mathematics of the University of Antwerp. He is currently Professor at the Department of Computer Science of Leiden University and Adjoint Professor at the Department of Computer Science of the University of Colorado at Boulder. His research interests include formal languages and automata theory, theory of graph transformations, and theory of concurrent systems. He is currently President of the European Association for Theoretical Computer Science (EATCS). P.S. Thiagarajan received the Bachelor of Technology degree from the Indian Institute of Technology, Madras, India in 1970. He was awarded the Ph.D. degree by Rice University, Houston Texas, U.S.A, in 1973. He has been a Research Associate at the Massachusetts Institute of Technology, Cambridge a Staff Scientist at the Geosellschaft für Mathematik und Datenverarbeitung, St. Augustin, a Lektor at Århus University, Århus and an Associate Professor at the Institute of Mathematical Sciences, Madras. He is currently a Professor at the School of Mathematics, SPIC Science Foundation, Madras. He research intest is in the theory of distributed computing.     

Transaction commit in a realistic timing model

Animportant problem in the construction of fault-tolerant distributed database systems is the design of nonblocking transaction commit protocols. This problem has been extensively studied for synchronous systems (i.e., systems where no messages ever arrive late). In this paper, the synchrony assumption is relaxed. A new partially synchronous timing model is described. Developed for this model is a new nonblocking randomized transaction commit protocol, which incorporates an agreement protocol of Ben-Or. The new protocol works as long as fewer than half the processors fail. A matching lower bound is proved, showing that the number of processor faults tolerated is optimal. If half or more of the processors fail, the protocol degrades gracefully: it blocks, but no processor produces a wrong answer. A notion of asynchronous round is defined, and the protocol is shown to terminate in a small constant expected number of asynchronous rounds. In contrast it is shown that no protocol in this model can guarantee that a processor terminates in a bounded expected number of its own steps, even if processors are synchronous. Brian A. Coan received the B.S.E. degree in electrical engineering and computer science from Princeton University, Princeton, New Jersey, in 1977; the M.S. degree in computer engineering from Stanford University, Stanford, California, in 1979; and the Ph.D. degree in computer science from the Massachusetts Institute of Technology, Cambridge, Massachusetts, in 1987. He has worked for Amdahl Corporation and AT & T Bell Laboratories. Currently he is a member of the technical staff at Bellcore. His main research interest is fault tolerance in distributed systems. Jennifer Lundelius Welch received her B.A. in 1979 from the University of Texas at Austin, and her S.M. and Ph.D. from the Massachusetts Institute of Technology in 1984 and 1988 respecively. She was a member of technical staff at GTE Laboratories Incorporated in Waltham, Massachusetts, from 1988 to 1989. She is currently an assistant professor at the University of North Carolina in Chapel Hill. Her research interests include algorithms and lower bounds for distributed computing.The authors were with the MIT Laboratory for Computer Science when the bulk of this work was done. This work was supported in part by the Advanced Research Projects Agency of the Department of Defense under Contract N00014-83-K-0125, the National Science Foundation under Grant DCR-83-02391, the Office of Army Research under Contract DAAG29-84-K-0058, and the Office of Naval Research under Contract N00014-85-K-0168. A preliminary version of this paper appears in theProceedings of the Fifth Annual ACM Symposium on Principles of Distributed Computing [2]     

Knowledge in shared memory systems

Summary We study the relation between knowledge and space. That is, we analyze how much shared memory space is needed in order to learn certain kinds of facts. Such results are useful tools for reasoning about shared memory systems. In addition we generalize a known impossibility result, and show that results about how knowledge can be gained and lost in message passing systems also hold for shared memory systems. Michael Merritt received a B.S. degree in Philosophy and in Computer Science from Yale College in 1978, the M.S. and Ph.D. degrees in Information and Computer Science in 1980 and 1983, respectively, from the Georgia Institute of Technology. Since 1983 he has been a member of technical staff at AT & T Bell Laboratories, and has taught as an adjunct or visiting lecturer at Stevens Institute of Technology, Massachusetts Institute of Technology, and Columbia University. In 1989 he was program chair for the ACM Symposium on Principles of Distributed Computing. His research interests include distributed and concurrent computation, both algorithms and formal methods for verifying their correctness, cryptography, and security. He is an editor for Distributed Computing and for Information and Computation, recently co-authored a book on database concurrency control algorithms, and is a member of the ACM and of Computer Professionals for Social Responsibility. Gadi Taubenfeld received the B.A., M.Sc. and Ph.D. degrees in Computer Science from the Technion (Israel Institute of Technology), in 1982, 1984 and 1988, respectively. From 1988 to 1990 he was a research scientist at Yale University. Since 1991 he has been a member of technical staff at AT & T Bell Laboratories. His primary research interests are in concurrent and distributed computing.A preliminary version of this work appeared in the Proceedings of the Tenth Annual ACM Symposium on Principles of Distributed Computing, pages 189–200, Montreal, Canada, August 1991     

Designing systolic,distributed buffers with bounded response time

Several buffer designs are derived by applying a design methodology that is based on so-called abstract states. Abstract states are euivalence classes of communication histories. These abstract states are very useful in the verification of program transformations, since they facilitate the definition of a function mapping the states of the transformed automaton onto the states of the original one. Three kinds of bufferes are discussed: the stack, the first-in first-out queue, and the priority queue. The designs are systolic and offer bounded response time, which means that all permissible communications are accepted within a time bounded by a constant. The design of the stack offers maximum storage utilization as well. We show that the properties of bounded response time and maximum storage utilization cannot be combined in distributed systolic queues. Joep L.W. Kessels received an M.Sc. (Honors) degree in electrical engineering from the Eindhoven University of Technology, The Netherlands, in 1967. In 1969 he joined the Philips Research Laboratories in Eindhoven, where he has been involved in three major projects in the following research areas: applicative programming, distributed processing, and local area networks. Currently, he is engaged in the formal derivation of VLSI designs. His main research interests are design methodology and distributed processing. Martin Rem obtained an M.Sc. degree in mathematics at the University of Amsterdam in 1971 and a Ph.D. degree in computing science at the Eindhoven University of Technology in 1976. He is currently professor of mathematics and computing science at Eindhoven and part-time visiting professor at California Institute of Technology. Professor Rem is consultant for Philips Research and editor of Science of Computer Programming and Integration.     

Highly concurrent logically synchronous multicast

We define thelogically synchronous multicast problem which imposes a natural and useful structure on message delivery order in an asynchronous system. In this problem, a computation proceeds by a sequence ofmulticasts, in which a process sends a message to some arbitrary subset of the processes, including itself. A logically synchronous multicast protocol must make it appear to every process as if each multicast occurs simultaneously at all participants of that multicast (sender plus receivers). Furthermore, if a process continually wishes to send a message, it must eventually be permitted to do so.We present a highly concurrent solution in which each multicast requires at most 4|S| messages, whereS is the set of participants in that multicast. The protocol's correctness is shown using a careful problem specification stated in the I/O automaton model. We conclude the paper by describing how the logically synchronous multicast protocol can be used for distributed simulation of algorithms expressed as I/O automata. Kenneth J. Goldman received the Sc.B. degree in Computer Science from Brown University in 1984, the S.M. degree in Electrical Engineering and Computer Science from the Massachusetts Institute of Technology in 1987, and the Ph.D. degree in Electrical Engineering and Computer Science from the Massachusetts Institute of Technology in 1990. As part of his doctoral work, he designed and implemented the Spectrum Simulation System, a distributed algorithm development tool based on the I/O automaton model of Lynch and Tuttle. His publications include papers in the areas of models for distributed computing, database concurrency control, human interfaces, and image processing. He is currently Assistant Professor in the Department of Computer Science at Washington University in St. Louis.A preliminary version of this paper appeared in the Proceedings of the 3rd International Workshop on Distributed Algorithms, Lecture Notes in Computer Science 392, Bermond and Raynal, Eds., Springer-Verlag, Berlin, 1989, pp 94–109.This research was conducted at the Massachusetts Institute of Technology Laboratory for Computer Science and was supported in part by the National Science Foundation under Grant CCR-86-11442, by the Office of Naval Research under Contract N00014-85-K-0168, by the Defense Advanced Research Projects Agency (DARPA) under Contract N00014-83-K-0125, and by an Office of Naval Research graduate fellowship     

An orientation update message filtering algorithm in collaborative virtual environments

Orientation update message filtering is an important issue in collaborative virtual environments (CVEs). Dead-reckoning (DR) is a known effective mechanism for update message filtering. Yet, previous deadreckoning techniques mainly focus on the update message filtering for positions. The existing orientation deadreckoning algorithms are based on fixed threshold values. The drawbacks of fixed thresholding for orientations (FTO) are discussed in this paper. We propose a variable thresholding for orientations (VTO) based on average recent angular velocity. The main advantage of the proposed VTO is the ability of balancing the number of state update messages and shift frequency of direction and speed of rotation.     

A platform for virtual collaboration spaces and educational communities: the case of EVE

This paper presents the design, implementation and evaluation of EVE Community Prototype, which is an educational virtual community aiming to meet the requirements of a Virtual Collaboration Space and to support e-learning services. Furthermore, this paper describes the design and implementation of an integrated platform for Networked Virtual Environments, called EVE Platform, which supports the afore-mentioned educational community. This platform supports stable event sharing and creation of multi-user three dimensional (3D) places, H.323-based voice over IP services integrated in 3D spaces as well as multiple concurrent virtual worlds. Christos Bouras obtained his Diploma and PhD from the Department Of Computer Engineering and Informatics of Patras University (Greece). He is currently an Associate Professor in the above department. Also he is a scientific advisor of Research Unit 6 in Research Academic Computer Technology Institute (CTI), Patras, Greece. His research interests include Analysis of Performance of Networking and Computer Systems, Computer Networks and Protocols, Telematics and New Services, QoS and Pricing for Networks and Services, e-Learning Networked Virtual Environments and WWW Issues. He has extended professional experience in Design and Analysis of Networks, Protocols, Telematics and New Services. He has published 200 papers in various well-known refereed conferences and journals. He is a co-author of seven books in Greek. He has been a PC member and referee in various international journals and conferences. He has participated in R&D projects such as RACE, ESPRIT, TELEMATICS, EDUCATIONAL MULTIMEDIA, ISPO, EMPLOYMENT, ADAPT, STRIDE, EUROFORM, IST, GROWTH and others. Also he is member of experts in the Greek Research and Technology Network (GRNET), Advisory Committee Member to the World Wide Web Consortium (W3C), Member of WG3.3 and WG6.4 of IFIP, Task Force for Broadband Access in Greece, ACM, IEEE, EDEN, AACE and New York Academy of Sciences. Eleftheria Giannaka obtained her Diploma from the Informatics Department of the Aristotelian University of Thessaloniki (Greece) and her Masters Degree from the Computer Engineering and Informatics Department of Patras University. She is currently a PhD Candidate of the Department of Computer Engineer and Informatics of Patras University. Furthermore, she is working as an R&D Computer Engineer at the Research Unit 6 of the Computer Technology Institute in Patra (Greece). Her interests include Computer Networks, Virtual Networks, System Architecture, Internet Applications, Electronic Commerce, Database Implementation and Administration, Virtual Reality applications, Performance Evaluation and Programming. Alexandros Panagopoulos was born in Pyrgos, Greece, 1981. He obtained his Diploma, from the Computer Engineering and Informatics Department of Patras University (Greece). In 2000 he became a member of Research Unit 6 of the Computer Technology Institute (CTI). His interests include Computer Networks, Multiuser Virtual Environments, Telematics, and C/C++ and Java programming. Dr. Thrasyvoulos Tsiatsos obtained his Diploma, his Master's Degree and his PhD from the Computer Engineering and Informatics Department of Patras University (Greece). He is currently an R&D Computer Engineer at the Research Unit 6 of Computer Technology Institute, Patras, Greece. His research interests include Computer Networks, Telematics, Distributed Systems, Networked Virtual Environments, Multimedia and Hypermedia. More particular he is engaged in Distant Education with the use of Computer Networks, Real Time Protocols and Networked Virtual Environments. He has published nine papers in journals and 30 papers in well-known refereed conferences. He has participated in R&D projects such as OSYDD, RTS-GUNET, ODL-UP, VES, ODL-OTE, INVITE, VirRAD and EdComNet.     

Using mappings to prove timing properties

Summary A new technique for proving timing properties for timing-based algorithms is described; it is an extension of the mapping techniques previously used in proofs of safety properties for asynchronous concurrent systems. The key to the method is a way of representing a system with timing constraints as an automaton whose state includes predictive timing information. Timing assumptions and timing requirements for the system are both represented in this way. A multi-valued mapping from the assumptions automaton to the requirements automaton is then used to show that the given system satisfies the requirements. One type of mapping is based on a collection of progress functions providing measures of progress toward timing goals. The technique is illustrated with two examples, a simple resource manager and a two-process race system. Nancy A. Lynch received the B.S. degree in mathematics from Brooklyn College, Brooklyn, NY, in 1968, and the Ph.D. degree in mathematics from the Massachusetts Institute of Technology, Cambridge, MA, in 1972. She is presently a professor of computer science and electrical engineering at Massachusetts Institute of Technology. She has also been on the computer science faculty at Georgia Institute of Technology and on the mathematics faculty at Tufts University and the University of Southern California. Her research interests are in distributed and real-time computing and theoretical computer science. In particular, she has worked on formal models and verification methods, on algorithm design and analysis, and on impossibility results. She also likes to hike and ski. Hagit Attiya received the B.Sc. degree in Mathematics and Computer Science from the Hebrew University of Jerusalem, in 1981, the M.Sc. and Ph.D. degrees in Computer Science from the Hebrew University of Jerusalem, in 1983 and 1987, respectively. She is presently a senior lecturer at the department of Computer Science at the Technion, Israel Institute of Technology. Prior to this, she has been a post-doctoral research associate at the Laboratory for Computer Science at M.I.T. Her general research interests are distributed computation and theoretical computer science. More specific interests include fault-tolerance, timing-based and asynchronous algorithms.This work was supported by ONR contracts N00014-85-K-0168 and N00014-91-J-1046, by NSF grants CCR-8611442 and CCR-8915206, and by DARPA contracts N00014-87-K-0825 and N00014-89-J-1988     

Distributed scheduling for disconnected cooperation

Ability to cooperate on common tasks in a distributed setting is key to solving a broad range of computation problems ranging from distributed search such as SETI to distributed simulation and multi-agent collaboration. In such settings there exists a trade-off between computation and communication: both resources must be managed to decrease redundant computation and to ensure efficient computational progress. This paper deals with scheduling issues for distributed collaboration. Specifically, we examine the extreme situation where initially collaboration must occur without communication. That is, we consider the extent to which efficient collaboration is possible if all resources are directed to computation at the expense of communication. The results summarized here precisely characterize the ability of distributed agents to collaborate on a known collection of independent tasks by means of local scheduling decisions that require no communication and that achieve low redundancy in task executions. Such scheduling solutions exhibit an interesting connection between the distributed collaboration problem and the design theory. The lower bounds presented here along with the randomized and deterministic schedule constructions show the limitations on such low-redundancy cooperation and show that schedules with near-optimal redundancy can be efficiently constructed by processors working in isolation. The work of G. Malewicz was done when he was a Ph.D. student at the University of Connecticut, and in part during a visit to the Specification and Algorithm Research Department, AT&T Shannon Lab, and the Supercomputing Technologies Group, Massachusetts Institute of Technology. Parts of this article appeared in a preliminary form in the Proceedings of the 14th International Symposium on Distributed Computing [24], Springer LNCS Vol. 1914, pp. 119–133, in the Proceedings of the 8th International Colloquium on Structural Information and Communication Complexity [23], and the doctoral thesis of the first author.     

Visual wheel sinkage measurement for planetary rover mobility characterization

Wheel sinkage is an important indicator of mobile robot mobility in natural outdoor terrains. This paper presents a vision-based method to measure the sinkage of a rigid robot wheel in rigid or deformable terrain. The method is based on detecting the difference in intensity between the wheel rim and the terrain. The method uses a single grayscale camera and is computationally efficient, making it suitable for systems with limited computational resources such as planetary rovers. Experimental results under various terrain and lighting conditions demonstrate the effectiveness and robustness of the algorithm. Christopher Brooks is a graduate student in the Mechanical Engineering department of the Massachusetts Institute of Technology. He received his B.S. degree with honor in engineering and applied science from the California Institute of Technology in 2000, and his M.S. degree from the Massachusetts Institute of Technology in 2004. He is a student collaborator on the Mars Exploration Rover science mission. His research interests include mobile robot control, terrain sensing, and their application to improving autonomous robot mobility. He is a member of Tau Beta Pi. Karl Iagnemma is a research scientist in the Mechanical Engineering department of the Massachusetts Institute of Technology. He received his B.S. degree summa cum laude in mechanical engineering from the University of Michigan in 1994, and his M.S. and Ph.D. from the Massachusetts Institute of Technology, where he was a National Science Foundation graduate fellow, in 1997 and 2001, respectively. He has been a visiting researcher at the Jet Propulsion Laboratory. His research interests include rough-terrain mobile robot control and motion planning, robot-terrain interaction, and robotic mobility analysis. He is author of the monograph Mobile Robots in Rough Terrain: Estimation, Motion Planning, and Control with Application to Planetary Rovers (Springer, 2004). He is a member of IEEE and Sigma Xi. Steven Dubowsky received his Bachelor's degree from Rensselaer Polytechnic Institute of Troy, New York in 1963, and his M.S. and Sc.D. degrees from Columbia University in 1964 and 1971. He is currently a Professor of Mechanical Engineering at M.I.T and Director of the Mechanical Engineering Field and Space Robotics Laboratory. He has been a Professor of Engineering and Applied Science at the University of California, Los Angeles, a Visiting Professor at Cambridge University, Cambridge, England, and Visiting Professor at the California Institute of Technology. During the period from 1963 to 1971, he was employed by the Perkin-Elmer Corporation, the General Dynamics Corporation, and the American Electric Power Service Corporation. Dr. Dubowsky's research has included the development of modeling techniques for manipulator flexibility and the development of optimal and self-learning adaptive control procedures for rigid and flexible robotic manipulators. He has authored or co-authored nearly 300 papers in the area of the dynamics, control and design of high performance mechanical and electromechanical systems. Professor Dubowsky is a registered Professional Engineer in the State of California and has served as an advisor to the National Science Foundation, the National Academy of Science/Engineering, the Department of Energy, and the US Army. He is a fellow of the ASME and IEEE and is a member of Sigma Xi and Tau Beta Pi.     

Practical uses of synchronized clocks in distributed systems

Summary Synchronized clocks are interesting because they can be used to improve performance of a distributed system by reducing communications. Since they have only recently become a reality in distributed systems, their use in distributed algorithms has received relatively little attention. This paper discusses a number of distributed algorithms that make use of synchronized clocks and analyzes how clocks are used in these algorithms Barbara Liskov received her B.A. in mathematics from the University of California at Berkeley and her M.S. and Ph.D. in computer science from Stanford University. She is currently a member of the faculty at the Massachusetts Institute of Technology, where she is NEC Professor of Software Science and Engineering. Her research and teaching interests include programming languages, programming methodology, distributed computing, and parallel computing. Her work on data abstraction led to the development of the CLU programming language and to a programming methodology based on data abstraction and specifications. This work is described in her book Abstraction and Specification in Program Development. Her subsequent research in distributed computing resulted in the Argus programming language, which supports robust distributed programs that survive hardware failures, and the Mercury communications mechanism, which supports efficient communication in a heterogeneous distributed system. At present Prof. Liskov is continuing her work in distributed computing, including development of replication algorithms for implementing highly-available systems. She is working on Harp, a replicated Unix file system for use via NFS, and on the design and implementation of Thor, a highly available object repository for use in a heterogeneous distributed environment. She is a member of ACM, IEEE, the National Academy of Engineering, and is a fellow of the American Academy of Arts and Sciences.This research was supported in part by the Advanced Research Projects Agency of the Department of Defense, monitored by the Office of Naval Research under contract N00014-89-J-1988, and in part by the National Science Foundation under grant CCR-8822158.     

Open media service architecture for advanced collaboration environments

Advanced collaboration environments are extensively utilized for distance learning, e-science, and other distributed global collaboration events. In such environments, high-quality and seamless media services play an important role in improving the quality of user experience to participants. In this paper, to support high-quality media-based services, we design open media service architecture for advanced collaboration environments, by combining the open interface for state-of-the-art media tools, the performance monitoring tools for devices and networks, and application-level adaptation schemes for media streaming. By implementing the proposed architecture on top of an open-source Access Grid (AG) collaboration toolkit, we verify that high-quality collaboration among several collaboration sites can be effectively realized over a multicast-enabled network testbed with improved media quality experience.

CDIO教育模式下工程型软件人才培养的探讨(英文)

From the perspective of cultivation of engineering-type software talents,we combine with the CDIO engineering education pattern reformation of American Massachusetts Institute of Technology,adopt four step engineering content including Conceive,Design,Implement and Operate as the cultivating goal of students' ability,and analyze the current talent cultivation pattern,summarize the intensive talent cultivation of Software College,Shandong University in recent years,and bring forward an innovation on talent cultivation pattern,and illustrate practicing process under the new pattern,and report the results and achievements of talents cultivation.     

Fault-tolerant atomic computations in an object-based distributed system

A distributed system can support fault-tolerant applications by replicating data and computation at nodes that have independent failure modes. We present a scheme called parallel execution threads (PET) which can be used to implement fault-tolerant computations in an object-based distributed system. In a system that replicates objects, the PET scheme can be used to replicate a computation by creating a number of parallel threads which execute with different replicas of the invoked objects. A computation can be completed successfully if at least one thread does not encounter any failed nodes and its completion preserves the consistency of the objects. The PET scheme can tolerate failures that occur during the execution of the computation as long as all threads are not affected by the failures. We present the algorithms required to implement the PET scheme and also address some performance issues. Mustaque Ahamad received his B.E. (Hons.) degree in Electrical Engineering from the Birla Institute of Technology and Science, Pilani, India. He obtained his M.S. and Ph.D. degrees in Computer Science from the State University of New York at Stony Brook in 1983 and 1985 respectively. Since September 1985, he is an Assistant Professor in the School of Information and Computer Science at the Georgia Institute of Technology, Atlanta. His research interests include distributed operating systems, distributed algorithms, faulttolerant systems and performance evaluation. Partha Dasgupta is an Assistant Professor at Georgia Tech since 1984. He has a Ph.D. in Computer Science from the State University of New York at Stony Brook. He is the technical project director of the Clouds distributed operating systems project, as well as a coprincipal investigator of Georgia Tech's NSF-CER award. His research interests include building distributed operating systems, distributed algorithms, fault-tolerant systems and distributed programming support. Richard J. LeBlanc, Jr. received the B.S. degree in physics from Louisiana State University in 1972 and the M.S. and Ph.D. degrees in computer sciences from the University of Wisconsin-Madison in 1974 and 1977, respectively. He is currently a Professor in the School of Information and Computer Science of the Georgia Institute of Technology. His research interests include programming language design and implementation, programming environments, and software engineering. Dr. LeBlanc's current research work involves application of these interests in distributed processing systems. As co-director of the Clouds Project, he is studying language concepts and software engineering methodology for utilizing a highly reliable, object-based distributed system. He is also interested in specification-based software development methodologies and tools. Dr. LeBlanc is a member of the Association for Computing Machinery, the IEEE Computer Society and Sigma Xi.This work was supported in part by NSF grants CCR-8619886 and CCR-8806358, and RADC contract number F30602-86-C-0032