Supporting group applications via satellite constellations with multicast

Construction of low-earth-orbiting satellite constellations for global wireless communication to small user terminals has begun with the launch of a number of Motorola's Iridium satellites in 1997 and the building of a number of Qualcomm's Globalstar satellites for launch in 1998. These early constellations, and their competitors, aim to provide low-bandwidth satellite telephony world-wide, including paging, faxing and 2400bps modem services. Future satellite constellations have been proposed for high-bandwidth wireless data transmission. These include Teledesic, Alcatel's SkyBridge, formerly known as Sativod, and Motorola's Celestri, whose components were formerly known as M-Star and Millennium. In providing data networking services, the ability to internetwork with pre-existing ground networks will be an important requirement for these constellations. Proponents of these schemes have stressed their advantages over existing geostationary satellite networking solutions of higher overall capacity, due to frequency reuse, and of decreased latency in communication due to the decrease in propagation delay in going from high-altitude geostationary orbit (GEO) to low-altitude low earth orbit (LEO). However, support for low-latency group applications, such as multiparty videoconferencing, is problematical. Here, the networking aspects of the broadband satellite constellations are discussed, and the suitability of the constellations for multicast is assessed.