Hans-Peter Dommel

Floor control for multimedia conferencing and collaboration

Abstract.Floor control allows users of networked multimedia applications to utilize and share resources such as remote devices, distributed data sets, telepointers, or continuous media such as video and audio without access conflicts. Floors are temporary permissions granted dynamically to collaborating users in order to mitigate race conditions and guarantee mutually exclusive resource usage. A general framework for floor control is presented. Collaborative environments are characterized and the requirements for realization of floor control will be identified. The differences to session control, as well as concurrency control and access control are elicited. Based upon a brief taxonomy of collaboration-relevant parameters, system design issues for floor control are discussed. Floor control mechanisms are discerned from service policies and principal architectures of collaborative systems are compared. The structure of control packets and an application programmers interface are proposed and further implementation aspects are elaborated. User-related aspects such as floor presentation, assignment, and the timely stages of floor-controlled interaction in relation to user-interface design are also presented.

Group coordination support for synchronous Internet collaboration

Current research on networked multimedia applications such as distributed interactive simulations concentrates on transport issues like multicast routing and presentation and session management, including session orchestration and quality-of-service support in media delivery. Session orchestration includes mechanisms to coordinate fair and exclusive access to shared resources whose semantics do not allow for concurrent usage, in order to prevent conflicts and inconsistencies in the shared workspace. The authors discuss the current state of research with regard to such services, which they refer to as group coordination, and present a new approach that integrates group coordination with extended multicast services.

Network support for turn-taking in multimedia collaboration

The effectiveness of collaborative multimedia systems depends on the regulation of access to their shared resources, such as continuous media or instruments used concurrently by multiple parties. Existing applications use only simple protocols to mediate such resource contention. Their cooperative rules follow a strict agenda and are largely application-specific. The inherent problem of floor control lacks a systematic methodology. This paper presents a general model on floor control for correct, scalable, fine-grained and fair resource sharing that integrates user interaction with network conditions, and adaptation to various media types. The motion of turn-taking known from psycholinguistics in studies on discourse structure is adapted for this framework. Viewed as a computational analogy to speech communication, online collaboration revolves around dynamically allocated access permissions called floors. The control semantics of floors derives from concurrently control methodology. An explicit specification and verification of a novel distributed Floor Control Protocol are presented. Hosts assume sharing roles that allow for efficient dissemination of control information, agreeing on a floor holder which is granted mutually exclusive access to a resource. Performance analytic aspects of floor control protocols are also briefly discussed.

A novel group coordination protocol for collaborative multimedia systems

Group collaboration in distributed multimedia environments extends gradually to larger groups and wide area networks. While reliable multicasting has made significant advancements in recent years, effective mechanisms to synchronize and coordinate work within large multicast groups and across long distances are still lacking. Group coordination is here understood as the mediated access to shared remote resources in synchronous groupwork, as for example in telecollaboration and distributed simulation environments, complementing protocols for group membership, media synchronization and reliable ordered multicast. A comparative analytic model for known classes of group coordination mechanisms, ranging from socially mediated control to floor control in ring and tree topologies, is presented. It is shown that hierarchical group coordination is the most efficient and scalable approach to date. Based on these findings, a novel protocol is described, which dynamically organizes participants in a multilevel control tree and aggregates resource sharing directives on the paths between interacting stations.

Design Issues for Floor Control Protocols

Floor control allows users of networked multimedia applications to remotely share resources like cursors, data views, video and audio channels, or entire applications without access conflicts. Floors are mutually exclusive permissions, granted dynamically to collaborating users, mitigating race conditions and guaranteeing fair and deadlock- free resource access. Although floor control is an early concept within computer-supported cooperative work, no framework exists and current floor control mechanisms are often limited to simple objects. While small-scale collaboration can be facilitated by social conventions, the importance of floors becomes evident for large-scale application sharing and teleconferencing orchestration. In this paper, the concept of a scalable session protocol is enhanced with floor control. Characteristics of collaborative environments are discussed, and session and floor control are discerned. The systems and users requirements perspectives are discussed, including distributed storage policies, packet structure and user-interface design for floor presentation, manipulation, and triggering conditions for floor migration. Interaction stages between users, and scenarios of participant withdrawal, late joins, and establishment of subgroups are elicited with respect to floor generation, bookkeeping, and passing. An API is proposed to standardize and integrate floor control among shared applications. Finally, a concise classification for existing systems with a notion of floor control is introduced.

Comparison of floor control protocols for collaborative multimedia environments

Improvements in networking allow for increasingly complex collaboration environments with regard to sessions scale, range of shared tasks, and distance between remote parties. Floor control protocols add an access discipline to such environments that allows to mitigate race conditions on shared resources and throttle media transmission. Primary causes for resource competition among users may be the lack of mutual awareness sand formal session orchestration, or network and shot limitations. Various, often proprietary and unscalable solutions for floor control have been implemented for telemedicine, video conferencing, or distributed interactive simulation. To this date, an analytic comparison of the efficacy of these solutions is lacking. With efficacy, we mean the proportion of time that a protocol takes to allocate a resource, accounting for social and technical overhead for muser behavior, protocol cost, and network conditions. We present a novel taxonomy an comparative performance analysis of known classes of floor control protocols, including socially driven protocols, collision sensing on shared resource, floor taken passing in fully-connected and ring topologies, and, innovatively, across shared control trees. Accordingly, aggregated and selective transmission of control information over a multicast control tree offers the best scalability and efficacy. A novel hierarchical floor control protocol correlating in its operation with tree-based reliable multicast is outlined.

A coordination architecture for Internet groupwork

This paper discusses a group coordination architecture to support Internet-wide distributed collaboration in the context of legacy Internet protocols. Group coordination in distributed systems and multimedia systems has many faces manifested in a variety of user interfaces and network protocols. To date, no standardized methodology for engineering group coordination protocols exists. We perceive coordination as the third complementary component in the trinity of group-communication services, next to membership and dissemination. With the current surge in e-commerce and Web-leveraged information exchange among users, the need for systems offering better telepresence and interaction capabilities becomes tangible. Services to support distributed group interaction at (near) real-time, with user-specified quality-of-service, and at Internet scope are of particular interest in this mosaic of telepresence and remote collaboration. We propose a general group coordination architecture for heterogeneous networks, as a framework to leverage the rapid development of group-oriented distributed collaborative applications in the Internet, for example for distance education, distributed scientific simulation or visualization, and similar applications.

Ordered end-to-end multicast for distributed multimedia systems

We address the problem of message ordering for reliable multicast communication. End-to-end multicast ordering is useful for ensuring the collective integrity and consistency of distributed operations. It is applicable for distributed multiparty collaboration or other multipoint applications, where the ordered reception of messages at all hosts is critical. Existing reliable multicast protocols largely lack support for ordering Our novel mechanism can be added to existing reliable multicast services at low cost by performing cascaded total ordering of messages among on-tree hosts en route from senders to receivers. The protocol operates directly on a given end-to-end multicast tree, contrasting other tree-based approaches requiring a separate propagation graph to be built to compute ordering information. For better load distribution, resilience, and ordered subcasting of messages within multicast groups, sequencer nodes are elected dynamically based on address extensions to hosts in the multicast tree. A taxonomy of broadcast and multicast ordering solutions and comparative cost analysis show that reliable message delivery integrated with staggered ordering in end-to-end multicast trees is more efficient, scalable, and less costly to deploy.

A coordination framework and architecture for Internet groupware

We discuss a group coordination architecture to support Internet-wide distributed collaboration, in particular for WWW-based distance education. With the current surge in e-commerce and Web-centric information exchange among users, the need for systems offering better telepresence and interaction capabilities becomes tangible. Group coordination in distributed systems and networked multimedia systems has many faces manifested in a variety of user interfaces and network protocols. However, to date no general methodology exists for engineering group coordination protocols to streamline the deployment of remote learning and collaboration environments. The objective of this article is to identify the key elements of a general group coordination framework, complementing existing group membership and multicast dissemination models, and to set the cornerstones for a coordination architecture which may be used to leverage the rapid development of group-oriented distributed collaborative applications in the Internet, for example for distance education, distributed scientific simulation and visualization, or similar applications.

The challenges of ambient collaboration

Collaborative capabilities are a hallmark of a new generation of networked applications. While traditional collaboration puts the computer in the foreground to help users interface through personal computing portholes, ambient collaboration reverses this paradigm by placing the machine in the background and enabling users to synergistically share a workspace with focus on mutual presence and tasks rather than tools. Although various ambient collaborative systems have been deployed in recent years, the field itself lacks a conceptual framework, in particular in contrast with legacy collaborative technologies. We introduce a simple systematics and roadmap for ambient collaboration to identify opportunities and challenges unique to this class of computing.