Skip to Main Content
Group communication plays an important role in the distribution of real-time data for IPTV, multimedia conferencing, or online multiplayer games, but IP multicast remains unsupported in today's global Internet. Hybrid solutions that bridge between overlay and underlay multicast are a promising escape from the deployment dilemma of multicast. In this paper, we examine the real-time capabilities of hybrid multicast in a globally distributed environment based on our adaptive architecture H8Mcast within the Planet-Lab testbed. We present a large-scale measurement study and analysis of one-way packet delay distributions in several realistic group scenarios. The unique results in global traces of hybrid multicast data have been achieved by carefully tracking packets and continuously correcting clock offsets. Companion measurements of unicast-based distribution are part of our analysis, as well as the comparative discussion of our results with previous findings from theory and simulation. Our measurements reveal that about 50% of global group members experience a real-time compliant service within the conversational time bounds of 150 ms.