High Performance IP Multicasting Over Wireless Satellite- Terrestrial Networks

We describe our recent work on the design and implementation of high performance Internet services over networks consisting of interconnected high data rate satellites including Direct Broadcast Satellite hosts and terrestrial wireless LANs with various capabilities (with rates from 16 kbps to 10Mbps, including LMDS and MMDS systems). The network can use either bi-directional or receive only satellite links for downstream data delivery and wireless and wireline terrestrial or satellite links for the upstream path. A key concept in our work is that of a hybrid terminal, which is a PC connected to a satellite antenna (including just DBS antennas) and to the wireless LAN. The hybrid terminal uses a modem connection for outgoing tra c while receiving incoming information through the VSAT. The hybrid terminal is attached to the Internet through any Internet service provider who supports Serial Line Internet Protocol (SLIP). The tra c from the hybrid terminal is transmitted to the hybrid gateway through IP-within-IP encapsulation, to accomplish asymmetric routing. The hybrid gateway is responsible for decapsulation of tra c from hybrid terminals. It is also responsible for formatting data to suite the satellite transmission. The asymmetric nature of tra c in most networks, as evident in the Internet, is shifting current networking technology trends more towards the development of hybrid networks. Multimedia tra c with its inherent variability in Quality of Service (QoS) requirements further reinforces this trend. Technologies such as DirecPCwhich allow users to send tra c terrestrially and receive tra c through satellite have demonstrated the e ciency of the broadcast nature of satellite communications as a means of delivering high bandwidth tra c to end This work was supported in part by the Center for Satellite and Hybrid Communication Networks under NASA Cooperative Agreement NCC2-528, by Hughes Network Systems and by the State of Maryland under the MIPS program. users. Even though the majority of Internet applications rely on point-to-point transmission (unicast), emerging applications such as teleconferencing and information distribution have necessitated the development of an overlay multicast backbone network in the Internet (MBONE) for point/multipoint-tomultipoint data transmission. A major hurdle in multicasting over the Internet is the potential for high bandwidth tra c to cause congestion in the terrestrial backbone. Introducing hybrid terminals within corporate LANs for incoming multicast streams thus would provide an e ective means of preserving gateway bandwidth for other outgoing tra c. We describe our work on IP multicast extensions to the wireless hybrid network described. We describe e ective extensions of IGMP, and asymmetric multicast algorithms that exploit the asymmetry to increase the number of users, scale-up and improve the loading of the terrestrial components. This requires an asymmetric multicast routing mechanism. We describe enhancements to existing multicast routing protocols such as CBT to the hybrid environment described here. We provide results on performance of our proposed hybrid multicast algorithms with respect to the following performance metrics: time to join a group; time for a packet to reach every member of the multicast group; performance with large multicast groups. Multicasting in Hybrid Networks Traditional multicasting on the MBONE has been used for exchanging information between a group of users in applications such as video or audio conferencing but a major hurdle in multicasting over the Internet is the potential for high bandwidth trafc to cause congestion in the terrestrial backbone. For groups with many members that are sparsely distributed over a wide area, the multicast packets would have to traverse several links before reaching all group members, hence the potential for causing congestion. Some companies may wish to en-