The Multimedia Collaboration project was funded by ONR at the University of California, Santa Cruz (UCSC).

This project was part of the research carried out within the Computer Communication Research Group (CCRG) of the Baskin Center for Computer Engineering and Computer and Information Sciences at UCSC. This project completed in 1999.

The principal investigator of this project was J.J. Garcia-Luna-Aceves.



Internet computing is gradually migrating from the standard unicast transmission model to multicasting. In the IP multicasting model, a source needs to send a packet only once to the network interface, and multicast routers replicate the packet on its transmission path to multiple receivers. The Internet Group Management Protocol (IGMP) allows a host to join a multicast group by informing its local router to forward multicast traffic for this group to the leaf subnetwork where the host resides. Protocols such as DVMRP, MOSPF, and PIM perform the construction of multicast delivery trees and enable packet forwarding between routers. With IP multicast, no guarantees are given for reliable or order-preserving delivery of packets, and a message is delivered on a best-effort basis to all members of a multicast group. These shortcomings have spurred much research on reliable multicast between end hosts, and on mechanisms to refine IP multicast, such as using addressing information to enable subcasting or anycasting. Subcasting delivers or retrieves data between a source and select members of a multicast group, and anycasting transfers data to any one member of a group, for example the nearest proxy from a group of servers. While IGMP targets group membership, and multicasting routing protocols are concerned with delivery, no protocols exist to tackle an emerging problem of multisite communication, which is group coordination. This problem surfaces especially for tightly-coupled sessions featuring explicit conference membership control.

Group coordination denotes services to support distributed hosts in coordinating their joint activities, including synchronization of flows from different sources, ordered delivery of distributed event information, and the concurrent use of and access to shared resources, referred to as floor control. Our work on group coordination centered around multiparty collaboration with a variety of multimedia tools. This area of work entails conferencing, groupware, Computer-Supported-Cooperative-Work (CSCW) and studies on Human-Computer Interaction. Currently two major trends can be observed: a shift towards synchronous collaboration over multimedia-enabled platforms, and towards larger groups of users on an Internet scope.

This paradigm shift in online collaboration creates new problems, as characterized in the group coordination framework:

  • Floor control of shared, distributed multimedia objects, that is access or concurrency control of continuous and multimodal data
  • Synchronization algorithms for distributed workspaces, their intermedia mixing and presentation facing high user interactivity
  • Ordering algorithms for distributed events, looking at specific dissemination geometries
  • Security issues such as authentication and encryption in collaborative workspaces
  • Deployment of such protocols and algorithms in small handheld and wireless devices to widen the scope of interactivity and collaboration

Although some specific protocols for group coordination services have been proposed in the literature, they often lack more precise description, analysis, or avaliability. In addition, the tools featuring these services are often properietary, monolithic, or nonportable.



Our resarch focused on protocol design and analysis for group coordination services, with the goal to achieve a better understanding of the processes and effects of coordination and cooperation in large groups and improve on the methodology to engineer multiparty collaboration software. Our work integrated network protocol design from various areas previously considered as separate under one coherent framework. We presented a novel way of looking at group services, integrating membership, dissemination, and access issues in a unified model.

We developed, validated, and analyzed new protocols to handle the variety of media and data-streams in multimedia-supported conferencing and collaboration, allowing for fine-grained sharing of objects and data. Since interaction is different for each type of multimedia (text, video, audio etc.), we looked at the characteristics of each medium to derive properties that allow to design a generic protocol suite to cover diverse media in an adaptive manner. We investigated, what quality-of-service parameters must be observed by cooperative protocols in order to mitigate between users and the network state.




  • Developed a formal semantics ("reference model") of group coordination that takes into account causality of interactive groupwork, based on a model of turn-taking from psycholinguistics. This work provides a link between user-level cooperative behavior and cooperation within network layers;
  • Provided a framework for floor control, furthering work on distributed mutual exclusion and concurrency control. This includes a taxonomy and comparative analysis of floor control protocols, a model of incorporating quality-of-service into distributed access control in interactive group work, and specification of several novel protocols, one of which uses extended multicast services to improve on the efficacy of how access control information is disseminated in a control geometry;
  • Specification of a novel adaptive intermedia synchronization protocol for distributed presentation of intermixed media streams, with the goal to maintain synchronicity and consistency among remote workspaces without needing a global clock.
  • Specification of a novel algorithm to achieve ordering among distributed events in a collaborative session that uses a multicast tree for data dissemination. Previous algorithms for ordering are ring-based or do not take advantage of a given control geometry. This contribution is especially relevant because of the fact that many current collaborative architectures use multicast trees for information dissemination, and need ordering services, which otherwise would need to be recoded and deployed at the application-layer. Distributed floor control above the transport layer may rely on a common delivery semantics as provided by ordered reliable multicast.
  • Implemented test application for collaboration such as a web-based control interface for a motorized camera w/ floor control. This work can be considered as a forerunner for more sophisticated interfaces, for example to surgical or exploratory instruments that are shared and concurrently controlled by multiple users or computational agents. We also worked on an API for floor controlled applications and a Java-based collaborative "interaction board".


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Ordered End-to-End Multicast for Distributed Multimedia Systems", Proc. 33rd Hawaii International Conference on System Sciences (HICSS-33), New Trends in Multimedia Systems, Software Technology Track, Maui, Hawaii, January 4-7, 2000.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Multisites Coordination in Shared Multicast Trees", Special Session on Coordination in Parallel and Distributed Applications and Activities, Proc. Int. Conf. on Parallel and Distributed Processing Techniques and Applications (PDPTA'99), Las Vegas, NV, June 28 - July 1, 1999.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Group Coordination Support for Synchronous Internet Collaboration", IEEE Internet Computing Magazine , Special Issue on "Collaboration - Internet-style", March/April 1999.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Efficacy of Floor Control Protocols in Distributed Multimedia Collaboration", Cluster Computing Journal, Special issue on Multimedia Collaborative Environments, Vol. 2, No. 1, 1999.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Comparison of Floor Control Protocols for Collaborative Multimedia Environments", Proc. SPIE Symposium on Voice, Video, and Data Communications,Boston, MA, November 2-5, 1998.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "A Novel Group Coordination Protocol for Collaborative Multimedia Systems", Proc. IEEE International Conference on Systems, Man, and Cybernetics 1998,San Diego, CA, October 11-14, 1998.
    Winner of Best Student Paper Award.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Network Support for Turn-Taking in Multimedia Collaboration", Proc. IS&T/SPIE Symposium on Electronic Imaging: Multimedia Computing and Networking 1997, San Jose, CA, February 1997.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Floor Control for Multimedia Conferencing and Collaboration", Multimedia Systems (ACM/Springer), Vol. 5, No. 1, January 1997.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Floor Control for Networked Multimedia Applications", ACM SIGCOMM'95 Workshop on Middleware , Cambridge, MA, August 28-September 1, 1995.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Floor Control for Activity Coordination in Networked Multimedia Applications", Proc. Second Asian-Pacific Conference on Communications (APCC) 1995,Osaka, Japan, June 12-16, 1995.


  • H.-P. Dommel and J.J. Garcia-Luna-Aceves, "Design Issues for Floor Control Protocols", Proc. IS&T / SPIE Symposium on Electronic Imaging: Multimedia Computing and Networking 1995, Vol. 2417, San Jose, CA, February 1995.

A related article is the following:

  • Alex T. Pang, Craig M. Wittenbrink, and T. Goodman, ``CSpray: a collaborative scientific visualization application'' Proceedings IS&T/SPIE Symposium on Electronic Imaging: Multimedia Computing and Networking, Vol. 2417, pages 317-326, Feb. 1995.