Concast: design and implementation of an active network service

Concast is a network layer service that provides many-to-one channels: multiple sources send messages toward one destination, and the network delivers a single "merged" copy to that destination. As we have defined it, the service is generic but the relationship between the sent and received messages can be customized for particular applications. We describe the concast service and show how it can be implemented in a back ward-compatible manner in the Internet. We describe its use to solve a problem that has eluded scalable end-system-only solutions: collecting feedback in multicast applications. Our preliminary analysis of concasting effectiveness shows that it provides significant benefits, even with partial deployment. We argue that concast has the characteristics needed for a programmable service to be widely accepted and deployed in the Internet.