This paper presented ALMI, an application level multicast infrastructure, that has been designed and built to provide a solution for multi-sender multicast communication which scales to a large number of communication groups with small number of members, and does not depend on multicast support at the IP layer. This solution provides a multicast middleware which is implemented above the sockets layer. Application level multicast offers accelerated deployment, simplified configuration and better access control at the cost of small additional traffic load in the network. Simulation results, along with initial experimentation results indicate that the performance tradeoff is quite small and that ALMI multicast trees are close to the efficiency of IP multicast trees. Since application level multicast is implemented in the user space, it allows more flexibility in customizing some application related modules, e.g. data transcoding, error recovery, flow control, scheduling, differentiated message handling and security.
We plan to extend this work in multiple ways. We are enhancing the performance evaluation work to include experiments with a larger number of nodes, as well as integrating with real life applications so that, besides control, data performance characteristics can be studied in detail. In addition, we plan to implement and study in more detail application specific modules such as end-to-end reliability, naming and security. In terms of speeding the performance of our middleware, we will explore options of moving parts of the forwarding functionality to an OS kernel and defining an interface between ALMI and the OS specific parts.