Deliver Multimedia Streams with Flexible QoS via a Multicast DAG

In this paper, we investigate the problem of delivering real time multimedia streams in a MAN environment. Most research in this area presumes the scenario where all packets of a stream are transmitted along a single path from the sender to a receiver. In this paper, we propose a new application layer multicast scheme, namely ROME, to better fulfill heterogeneous QoS requirements from various receivers simultaneously by setting up multiple paths. Instead of enforcing a multicast tree structure, a multicast DAG (Directed Acyclic Graph) is constructed in ROME, where multiple nodes in the multicast group may share the responsibility to deliver the stream to a node. To achieve this, each stream is partitioned into a set of stream shares. A QoS oriented share assignment technique is proposed to distribute stream shares progressively among delivery paths to maximize the number of fulfilled clients while minimizing the overall bandwidth usage. Moreover, both the delivery paths and the stream partition can be adapted easily on the fly to accommodate multicast group membership change during the real time delivery. Last but not least, we evaluate our scheme via simulations and show that the proposed scheme can fulfill a larger number of clients with higher QoS requirements than existing approaches under the same network capacity