Incentive-Informed Inter-Domain Multicast

IP multicast enables reduced link loads for multiple recipients with overlapping data paths. In inter-domain settings, however, the costs and benefits of multicast redundancy elimination fall on different economic entities. Hence, in the absence of multicast specific inter-domain contracts and compensation, IP multicast has remained mostly an intra-domain endeavor. We propose incentive-informed inter-domain multicast, with which domains base multicast operation solely on their local unicast- derived incentives. Multicast forking will be provided only by domains that find it locally beneficial. Multicast traffic will pass through other domains using unicast paths. We find that, overall, up to 95% of the optimal IP multicast link load reduction can be attained, varying by the multicast group size. Link loads near the multicast sources can still remain high, mostly due to the considerable uphill diversity in the Internet topology. However, causal dynamics seem to exist for top tier transit providers to offer multicast as a service, significantly reducing the effective uphill diversity, thus enabling highly reduced link loads also on uphill paths. In this case the overall efficiency is also better than with optimal IP multicast.