Distributed management of exclusive resources in collaborative multimedia systems

Collaborative multimedia systems encompass many Internet applications such as desk-top conferencing and interactive distance learning. These applications often contain resources , such as audio, video and shared applications, that must be accessed exclusively by one participant at a time. In this paper, we present a distributed algorithm that manages the access to these exclusive resources. The algorithm is based on the assumption that the transport layer provides reliable multicasting. Resources are classiied into two main classes: primitive and composite. Composite resources consist of a set of two or more primitive resources. A token is associated with each resource unit, and a participant must obtain the resource's token before using the resource. To use a resource, certain permissions may be needed from certain entities such as the session coordinator, the current resource holder and, in some cases, the resource itself. Resources that are not used by any participant are held by a special entity called the free resource holder. The participant processes in our algorithm uses two types of multicast messages, one to request resources and the other to grant resources. The algorithm guarantees that at any given time, the resource is held by exactly one participant, either an actual participant or the free resource holder. The token of any resource will never be lost under all possible failure conditions.