Overlay Multicasting for Ad Hoc Networks

In this work, we study the benefits of using application layer multicast in ad hoc networks. We propose a flexible receiver-driven overlay multicast protocol that we call the Application Layer Multicast Algorithm (ALMA). As an application layer protocol, ALMA constructs an overlay multicast tree of logical links between the group members. Our protocol has the advantages of an application layer protocol: a) simplicity of deployment, b) independence from lower layer protocols, and c) capability of exploiting features such as reliability and security that may be provided by the lower layers. In addition, ALMA has all the following characteristics. First, it is receiver-driven: the member nodes find their connections according to their needs. Second, it is flexible, and thus, it can satisfy the performance goals and the needs of a wide range of applications. Third, it is highly adaptive: it reconfigures the tree in response to mobility or congestion. We perform extensive simulations to evaluate the performance of ALMA. First, we show that ALMA outperforms the best previously proposed application layer multicast protocol for ad hoc networks. Second, we find that ALMA compares favorably with arguably the best network layer multicast protocol: ALMA performs significantly better for small group sizes. We conclude that the application layer approach and ALMA seem very promising for ad hoc multicasting.