Increases in Internet bandwidth have spurred a growing interest in using it to solve problems in coordinating geographically distributed project teams. Supporting these teams requires applications such as real-time video conferencing and group editing tools. Other organizations are interested in delivering entertainment, group games, and lectures. All of these applications need to be able to transmit simultaneously and e ciently to many hosts. In order to preserve network bandwidth, the routers in the Internet backbone provide a capability to send a message to many hosts without duplicating the message while it travels on the backbone. This service is called IPmulticasting. However, IP-multicasting is a best e ort service without guarantees about delivery or correctness. These services are left to the transport protocol. Therefore, it is up to the multicast transport protocol to implement the reliability. This paper surveys the two issues of reliability and routing. It begins by discussing the terms used in multicast protocols and discussing several experimental protocols. It then gives an overview of the theoretical performance limits for the various types of reliable multicast protocols. Next, it discusses current multicast routing algorithms. Finally, a survey of current and experimental multicast routing protocols is given.
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