The deployment of IP Multicast has fostered the development of a suite of applications, collectively known as the MBone tools, for real-time multimedia conferencingover the Internet. Two of these tools --- nv from Xerox PARC and ivs from INRIA --- provide video transmission using softwarebased codecs. We describe a new video tool, vic, that extends the groundbreaking work of nv and ivs with a more flexible system architecture. This flexibility is characterized by network layer independence, support for hardware-based codecs, a conference coordination model, an extensible user interface, and support for diverse compression algorithms. We also propose a novel compression scheme called "IntraH. 261". Created as a hybrid of the nv and ivs codecs, IntraH. 261 provides a factor of 2-3 improvement in compression gain over the nv encoder (6 dB of PSNR) as well as a substantial improvement in run-time performance over the ivs H.261 coder. KEYWORDS Conferencing protocols; digital video; image ...

This paper presents an overview of GroupKit, a groupware toolkit that lets developers build applications for synchronous and distributed computer-based conferencing. GroupKit was constructed from our belief that programming groupware should be only slightly harder than building functionally similar single-user systems. We have been able to significantly reduce the implementation complexity of groupware through the key features that comprise GroupKit. A runtime infrastructure automatically manages the creation, interconnection, and communications of the distributed processes that comprise conference sessions. A set of groupware programming abstractions allows developers to control the behaviour of distributed processes, to take action on state changes, and to share relevant data. Groupware widgets let interface features of value to conference participants to be easily added to groupware applications. Session managers⎯interfaces that let people create and manage their meetings⎯are decoupled from groupware applications and are built by developers to accommodate the group’s working style. Example GroupKit applications in a variety of domains have been implemented with only modest effort.

This paper exposes the concurrency control problem in groupware when it is implemented as a distributed system. Traditional concurrency control methods cannot be applied directly to groupware because system interactions include people as well as computers. Methods, such as locking, serialization, and their degree of optimism, are shown to have quite different impacts on the interface and how operations are displayed and perceived by group members. The paper considers both human and technical considerations that designers should ponder before choosing a particular concurrency control method. It also reviews our work-in-progress designing and implementing a library of concurrency schemes in GROUPIUT, a groupware toolkit.

This paper introduces COAST, an object-oriented toolkit for the development of synchronous groupware, which enhances the usability and simplifies the development of such applications. COAST offers basic and generic components for the design of synchronous groupware and is complemented by a methodology for groupware development. Basic features of the toolkit include transaction-controlled access to replicated shared objects, transparent replication management, and a fully optimistic concurrency control. Development support is provided by a session concept supporting the flexible coupling of shared objects' aspects between concurrent users and by a fully transparent updating concept for displays which is based on declarative programming. KEYWORDS: toolkit, synchronous collaboration, groupware, replicated objects, sessions, display updating, concurrency control 1 INTRODUCTION Groupware allows several geographically distributed people to work together with the aid of a computerized envi...

In just a few years the "Internet Multicast Backbone", or MBone, has risen from a small, research curiosity to a large scale and widely used communications infrastructure. A driving force behind this growth was our development of multipoint audio, video, and shared whiteboard conferencing applications that are now used daily by the large and growing MBone community. Because these real-time media are transmitted at a uniform rate to all the receivers in the network, the source must either run below the bottleneck rate or overload portions of the multicast distribution tree. In this dissertation, we propose a solution to this problem by moving the burden of rate-adaptation from the source to the receivers with a scheme we call Receiver-driven Layered Multicast, or RLM. In RLM, a source distr...

The rich person-to-person interaction afforded by shared physical workspaces allows people to maintain up-to-the minute knowledge about others ’ interaction with the workspace. This knowledge is workspace awareness, part of the glue that allows groups to collaborate effectively. In real-time groupware systems that provide a shared virtual workspace, the possibilities for interaction are impoverished when compared with physical workspaces, partly because support for workspace awareness has not generally been a priority in groupware design. In this paper, we present the concept of workspace awareness as one key to supporting the richness evident in face-to-face interaction. We construct a conceptual framework that describes the elements and mechanisms of workspace awareness, and then show several widgets that can be embedded in relaxed-WYSIWIS groupware systems to support the maintenance of workspace awareness.

Workflow management is a technology that is considered strategically important by many businesses, and its market growth shows no signs of abating. It is, however, often viewed with skepticism by the research community, conjuring up visions of oppressed workers performing rigidly-defined tasks on an assembly line. Although the potential for abuse no doubt exists, worlcflow management can instead be used to help individuals manage their work and to provide a clear context for performing that work. A key challenge in the realization of this ideal is the reconciliation of workflow process models and software with the rich variety of activities and behaviors that comprise "real" work. Our experiences with the InConcert workflow management system are used as a basis for outlining several issues that will need to be addressed in meeting this challenge. This is intended as an invitation to CSCW researchers to influence this important technology in a constructive manner by drawing on research and experience. KEYWORDS: Workflow, business process reengineering.

We have developed a high-level and flexible framework for supporting the construction of multi-user user-interfaces. The framework is based on a generalized editing interaction model, which allows users to view programs as active data that can be concurrently edited by multiple users. It consists of several novel components including a refinement of both the Seeheim UIMS architecture and the distributed graphics architecture that explicitly addresses multi-user interaction; the abstractions of shared active variables and interaction variables, which allow users and applications to exchange information; a set of default collaboration rules designed to keep the collaboration-awareness low in multi- user programs; and a small but powerful set of primitives for overriding these rules. The framework allows users to be dynamically added and removed from a multi-user session, different users to use different user interfaces to interact with an application, the modules interacting with a particular user to execute on the local workstation, and program- mers to incrementally trade automation for flexibility. We have implemented the framework as part of a system called Suite. This paper motivates, describes, and illustrates the framework using the concrete example of Suite, discusses how it can be implemented in other kinds of systems, compares it with related work, discusses its shortcom- ings, and suggests directions for future work.

: We review systems that support the management of collaborative interaction, and propose a classification framework built on a simple model of coaching. Our framework distinguishes between mirroring systems, which display basic actions to collaborators, metacognitive tools, which represent the state of interaction via a set of key indicators, and coaching systems, which offer advice based on an interpretation of those indicators. The reviewed systems are further characterized by the type of interaction data they assimilate, the processes they use for deriving higher-level data representations, and the type of feedback they provide to users. Keywords: CSCL systems, interaction management, mirroring, coaching collaboration 1 Introduction Over the past decade, we have seen an explosion of network-based technologies that enable traditional and non-traditional distance learners alike to learn collaboratively. These environments enhance traditional distance learning curricula by ...

The ability to share synchronized views of interactions with an application is critical to supporting synchronous collaboration. This paper suggests a simple synchronous collaboration paradigm in which the sharing of the views of user/application interactions occurs at the window level within a multi-user, multi-window application. The paradigm is incorporated in a toolkit, DistView, that allows some of the application windows to be shared at a fine-level of granularity, while still allowing other application windows to be private. The toolkit is intended for supporting synchronous collaboration over wide-area networks. To keep bandwidth requirements and interactive response time low in such networks, DistView uses an object-level replication scheme, in which the application and interface objects that need to be shared among users are replicated. We discuss the design of DistVlew and present our preliminary experience with a prototype version of the system.