Issues in Designing Transport La yer Multicas t Facilities

Multicasting denotes a facility in a communications system for providing efficient delivery from a message's source to some well-defined set of locations using a single logical address. While modem network hardware supports multidestination delivery, first generation Transport Layer protocols (e.g. the DoD Transmission Control Protocol (TCP) [15] and ISO TP-4 [41]) did not anticipate the changes over the past decade in underlying network hardware, transmission speeds, and communication patterns that have enabled and driven the interest in reliable multicast. Much recent research has focused on integrating the underlying hardware multicast capability with the reliable services of Transport Layer protocols. In this paper we explore the communication issues surrounding the design of such a reliable multicast mechanism. Approaches and solutions from the literature are discussed, and four experimental Transport Layer protocols that incorporate reliable multicast are examined. 2 The Transport Layer is layer four in the International Standards Organization Open Systems Interconnect (ISO OSI) Reference Model ([28]).