Reliable Multicast for Coordination of Cooperative Applications

home Author: Eva M. Castro
eva@gsyc.escet.urjc.es


Abstract

Cooperative and distributed applications often involve mutiple participants and require a multicast communication model to transmit data to receivers. For example, CSCW applications in the multimedia conferencing field define a virtual conference room by the interconnection of some distributed real auditoriums providing a good scenario to the multipoint communication. Most of these applications need to solve interaction problems between all participants which require very low latency requirements. Interaction control, also called coordination of the application, is tipically based on the exchange of messages between remote nodes using a reliable multicast protocol in order to mantain a consistent application global state.

We have designed a reliable multicast protocol suitable to coordinate cooperative distributed applications, it defines two kind of messages exchanged by the users of this protocol:
Messages issued to completely represent an application global state.
Messages that provide an incremental state incremental state variation.

In this context, we refer to an application global state as a set of local states of all participating nodes. Some of these global states may be described by using a repository, or profile, of predefined local configurations known by all involved nodes. Hence, it is easy to identify one of these global initial states with a few, probably one, application messages. Departures from these initial states are coordinated through small update messages.

In order to test and debug this communication service model we have used a customizable multiconferencing application which provides advanced video/audio/data conferencing features, ISABEL. This application uses this reliable multicast protocol to maintain an application consistent state.

Related Work.
Requirements.
Protocol Sketch.

home Author: Eva M. Castro
eva@gsyc.escet.urjc.es