Architecture and Performance Evaluation for Redundant Multicast Transmission Supporting Adaptive QoS

In this paper we describe the architecture of an application that was developed for the transmission of multimedia data, using the multicast mechanism, over the Internet. There are two major issues that have to be considered when designing and implementing such a service, the fairness and the adaptation schemes. The fairness problem results from the fact that Clients with different capabilities have to be served. In our application we use a mechanism that categorizes the Clients into a number of groups according to each Client's capabilities and (the mechanism) serves each group of Clients with a different multicast stream. With the term capabilities we do not only mean the processing power of the Client, but also the capacity and the condition of the network path towards that Client. Because of today's Internet heterogeneity and the lack of Quality of Service (QoS) support, the Server cannot assume that the Clients will permanently be able to handle a specific bit rate. We have therefore implemented an additional mechanism for the intra-stream bit rate adaptation. The proposed mechanism uses a friendly to the network users congestion control policy to control the transmission of the data. We evaluate the adaptive multicast transmission mechanism through a number of experiments and a number of simulations in order to examine its behaviour to a heterogeneous group of Clients and its behaviour against TCP and UDP data streams.