Guest editorial - network support for multicast communications

M ANY networked applications rely on multicast communications for efficient operation. These applications include video conferencing, video distribution, computer supported collaborative work (CSCW), distributed games, and wide-scale information dissemination. These applications require a variety of services from the network beyond the provision of efficient routes between participants. Multicast applications require mechanisms for fair bandwidth sharing since they share the network with other multicast and unicast flows. Many applications also require the reliable transfer of data; other applications, such as video and audio applications, require low-delay or low-jitter services. Confidential data and trusted services require authentication and key management protocols, an increasingly important area of research. The papers in this special issue focus on many of those services, and their collection provides a snapshot of current research in the topics covered. It is interesting to contrast the topics covered by this issue with those covered five years ago in the previous IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATION special issue on multicast communications (April 1997). A significant fraction of the papers published five years ago focused on intradomain multicast routing. There was also a large emphasis on protocols for providing reliable multicast based on retransmissions. Last, there was considerable emphasis on asynchronous transfer mode (ATM). Notably absent from that special issue were the topics of application-level multicast and security. The current issue, on the other hand, places a heavy emphasis on various aspects of application-level multicast and on security. In addition, there has been a shift from retransmission-oriented reliable multicast to scalable reliable multicast and to fair congestion control schemes. Several developments in the last few years partly explain these differences. The most important of these is the slow pace of network-level multicast deployment, which has prompted an increased interest on application-level multicast. This appears primarily due to the complexity that the original Internet protocol (IP) multicast service model imposes on intra-and interdomain routing mechanisms. This has resulted in complex and sometimes faulty routing code, ad hoc solutions for routing at the interdomain level, and a reluctance from network administrators to activate multicast. Another contributing factor to this reluctance has been the lack of access controls within the original IP multicast model. The recently proposed Source-Specific Multicast model, proposed in reaction to these problems, may prove to have a positive impact on the acceptance and deployment of native multicast. Reliable multicast, which was a very important research topic five years ago, …