Initial results of the CD-1 reliable multicast experiment - eScholarship

INITIAL RESULTS OF THE CD-1 RELIABLE MULTICAST EXPERIMENT 1 Deborah A. Agarwal 2 , Richard Stead 3 , Brian Coan, James E. Burns, Nishith Shah 4 , Nicholas Kyriakopoulos 5 Abstract A new version of the CD-1 continuous data protocol has been developed to support a multicasting experiment. This new version was developed to study the use of reliable multicast for sending data to multiple receivers in a single operation. The purpose of the experiment is to evaluate the existing multicasting technology for possible use in the Global Communication Infrastructure. This paper describes the initial results of the experiment. Background IP Multicast On the Internet, a class of applications has emerged that requires the ability to send messages to a group of receivers efficiently. This need has led to the development of the multicast capability in the Internet Protocol (IP). Basic IP multicast is a simple communication mechanism that allows a single message to be sent to a group of receivers as an integral part of the communications services offered at the internetworking level. IP multicast is an unreliable messaging service implemented in the hosts and routers of the network. The multicast addresses are a separate address range recognized by the routers as multicast groups. Multicast packets are sent addressed to a multicast address. Applications that wish to receive the multicast packets open a connection to the multicast address and their host automatically transmits a join message to the nearest router. The router then adds the host to the multicast dissemination tree for the group. The multicast tree is dynamic and provides an efficient means of transmitting a packet through the network to reach all the receivers without traveling any link more than once. The routers at branch points in the tree duplicate the packet and send it down all the tree branches. For more detail regarding the multicast routing protocols, see [5] and [10]. The IP multicast communication mechanisms are gradually becoming a standard part of the Internet protocol suite and they co-exist with the unicast Transmission Control Protocol (TCP)[4] and User Datagram Protocol (UDP) mechanisms. The IP multicast mechanisms do not replace the unicast mechanisms; they instead provide an additional service. Since IP multicast is still a relatively new technology, routers do not come with IP multicast enabled by default. The router administrator must enable it before it can be used in the network. Not many commercial applications make use of IP multicast so many Internet Service Providers (ISP) have not yet enabled the capability. Reliable Multicast Reliable multicast is effectively the multicast equivalent to the TCP protocol. Reliable multicast provides reliable delivery of messages to multiple receivers. It uses IP multicast to provide the message dissemination capability and adds reliable delivery mechanisms. A reliable multicast protocol provides several potential advantages over TCP when there are in fact multiple receivers. With reliable multicast the receivers in a group can be reached by sending a single message. Using TCP the messages would need to be sent to each receiver individually by the original sender or a site acting as a forwarder. Reliable multicast is not yet a standard communication protocol that is part of the The views expressed in this paper are those of the authors and not necessarily those of the United States Government. Ernest Orlando Lawrence Berkeley National Laboratory. Sponsored by U. S. Department of Energy, Office of Nonproliferation and National Security, Office of Research and Development, Contract No. DE-AC03-76SF00098 SAIC Telcordia Technologies. Sponsored by U.S. Department of Defense, Defense Threat Reduction Agency, Contract No. DTRA01-99-C-0025. The George Washington University