Multicast Transport Protocols: A Survey and Taxonomy

0163-6804/97/$10.00 © 1998 IEEE ulticast transport protocols have been a topic of intense research and development efforts over the past couple of years. Both the Internet Engineering and Internet Research Task Forces (IETF and IRTF) have been heavily involved in coordinating multicast transport protocol research, development, standardization, deployment, and technology transfer activities. This recent “hype” comes in response to the increasing popularity of groupware applications such as real-time conferencing tools and multipoint data distribution services. Most of the recently proposed multicast transport mechanisms address the requirements of the different types of group communication applications. Earlier multicast transport mechanisms were designed as a general solution to the group communication problem. More recently it has been recognized that group communication applications have a much wider range of requirements than unicast applications. Therefore, a Transmission Control Protocol (TCP)-like solution for the multicast case is not possible: a single, generic protocol simply cannot meet the requirements of all types of multicast applications. This protocol design model was first referred to as application-layer framing [1]. We observe that most of the more recent multicast transport mechanisms have been designed with a specific application in mind. For instance, several multicast transport protocols address the requirements of delay-sensitive real-time services, such as multimedia conferencing tools. These applications can tolerate a certain degree of data loss, but are sensitive to packet delay variance. On the other hand, traditional data distribution services, such as multipoint file transfer, are not delay-sensitive but require that objects be delivered in their entirety or the transfer fails. The goal of this article is to present an overview of earlier and current multicast transport protocol research and development. This survey is by no means exhaustive: multicast transport protocols have been an extremely active field and in constant evolution for the past couple of years. We review several existing multicast transport mechanisms and classify them according to a taxonomy consisting of several distinct features. These features are described in the next section. The third section reviews the surveyed protocols, including references to commercial product support, and the fourth section summarizes them according to the proposed taxonomy, discusses the rationale behind the protocols’ design decisions, and presents some current research issues in multicast protocol design.