Group coordination support in networked multimedia systems
Jose Joaquin Garcia-Luna-Aceves, Hans‐Peter Dommel · 1999
Advances in computer hardware and networking technology have incited the deployment of large-scale group-oriented applications for delivery or interactive development of multimedia content in the Internet. There is a growing number of protocols and techniques for group communication and membership services in the IP-multicast framework, however, group coordination support for telecollaborative tasks such as videoconferencing or distributed interactive simulation has received little attention. In this dissertation, we address network control and coordination functions to orchestrate synchronous multimedia groupwork, establishing a sharing discipline on multimedia resources and guaranteeing consistency of distributed activities with ordered multicasting. We introduce a formal framework for group coordination and a turn-taking abstraction useful for evaluating coordination protocols. Elemental design choices for group coordination architectures and the concept of aggregated processing of coordination information are discussed. A floor control methodology is presented to implement concurrency control for interactive, rather than transactive cooperation among users. Floors are dynamically generated, ephemeral permissions for using discrete or continuous media such as GUI objects, audio and video channels, or remote instruments. Floor control regulates user interaction and bandwidth consumption by throttling sources in sending information flows according to receiver interest. A novel taxonomy of floor control protocols and a comparative throughput analysis show that large-scale group coordination is most effectively supported by hierarchical host organization. Two new protocols are presented to provide floor control in fully-connected networks and in multicast trees, where the addition of group-relative address information permits more sophisticated coordination among end-nodes. Finally, we discuss the problem of out-of-sequence delivery in multicasting. A new taxonomy for ordered multicasting protocols and a comparison of message complexities elicit the benefits of aggregated, ordered multicasting. We present a novel multicast ordering protocol for more efficient total-order delivery of messages from multiple sources to multiple, potentially overlapping receiver groups in multicast trees. Previous solutions require the computation of a separate propagation graph to structure ordering relations and incur high cost, if sources change frequently. Our proposed mechanism is more flexible and efficient, because it relays ordering information in accordance with the hierarchical organization of end-hosts maintained by an underlying tree-based reliable multicast protocol.