Multicasting in Overlays with Network Layer Support

Overlay networks are virtual networks formed by cooperating nodes that share an underlying physical network. They represent a flexible and deployable approach for applications to obtain new network semantics without modification of the underlying network, but they suffer from efficiency concerns. We present two router-based primitives that help end-hosts alleviate these inefficiencies. Packet Reflection allows end hosts to request that routers perform routing and duplication for certain packets. Path Painting allows end hosts to determine where their paths to a rendezvous point meet. This knowledge facilitates building overlay topologies that resemble the topology of the underlying network. Both primitives can be incrementally deployed for incremental benefit. We show how these primitives can be used to provide an efficient application-level multicast system and provide experimental results on simulated topologies to show the benefits provided. These results indicate that when all routers support the proposed primitives, the system incurs less than 5% overhead (in terms of link usage and latency). In addition, the benefits gained from deployment are significant even at low levels. When intelligent deployment strategies are used, link usage overhead is less than 30% with less than 10% deployment. Finally, these benefits apply mostly to the area local to the deployed routers, providing a deployment incentive to independent networks.