Network Support for Turn-Taking in Multimedia Collaboration

The e ectiveness 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-speci c. The inherent problem of oor control lacks a systematic methodology. This paper presents a general model on oor control for correct, scalable, ne-grained and fair resource sharing that integrates user interaction with network conditions (Quality-of-Service), and adaptation to various media types. The notion 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 oors. The control semantics of oors derives from concurrency control methodology. An explicit speci cation and veri cation of a novel distributed Floor Control Protocol (FCP) are presented. Hosts assume sharing roles that allow for e cient dissemination of control information, agreeing on a oor holder which is granted mutually exclusive access to a resource. Performance analytic aspects of oor control protocols are also brie y discussed.