This paper presents the design, implementation and performance of a reliable multicast transport protocol called RMTP. RMTP is based on a hierarchical structure in which receivers are grouped into local regions or domains and in each domain there is a special receiver called a Designated Receiver (DR) which is responsible for sending acknowledgments periodically to the sender, for processing acknowledgements from receivers in its domain and for retransmitting lost packets to the corresponding receivers. Since lost packets are recovered by local retransmissions as opposed to retransmissions from the original sender, end-to-end latency is significantly reduced, and the overall throughput is improved as well. Also, since only the DRs send their acknowledgments to the sender, instead of all receivers sending their acknowledgments to the sender, a single acknowledgement is generated per local region, and this prevents acknowledgement implosion. Receivers in RMTP send their acknowledgments to the DRs periodically, thereby simplifying error recovery. In addition, lost packets are recovered by selective repeat retransmissions, leading to improved throughput at the cost of minimal additional buffering at the receivers. This paper also describes the implementation of RMTP and its performance on the Internet.

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This article describes the network concepts underlying MBone, the importance of bandwidth considerations, various application tools, MBone events, interesting MBone uses (see the two sidebars), and provides guidance on how to connect your Internet site to the MBone.

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Such interactive, distributed multimedia applications as shared whiteboards, group editors, and simulations require reliable concurrent multicast services, i.e., the reliable dissemination of information from multiple sources to all the members of a group. Furthermore, it makes sense to offer that service on top of the increasingly available IP multicast service, which offers unreliable multicasting. This paper establishes that concurrent reliable multicasting over the Internet should be based on reliable multicast protocols based on a shared acknowledgment tree. First, we show that organizing the receivers of a reliable multicast group into an acknowledgment tree and using NAK-avoidance with periodic polling in local groups inside such a tree provides the highest maximum throughput among all classes of reliable multicast protocols proposed to date. Second, we introduce Lorax, which demonstrates the viability of implementing a reliable multicasting approach in the Internet based on ack...

A core-based forwarding multicast protocol uses a core router as a traffic transit center: all multicast packets are first sent to the core, then distributed to destinations on a multicast tree rooted at the core. The purpose of this paper is to evaluate, via simulation, the effect of various core selection methods on multicast performance. Performance metrics of interest include network resource usage, packet delay, the join time of multicast participants, and link congestion. In addition, we assess the feasibility of these heuristics in real-world environments.

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(IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a ‘‘working draft’ ’ or ‘‘work in progress.’ ’ Please check the 1id-abstracts.txt listing contained in the internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net, nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the current status of any Internet Draft. Internet Draft Requirements for IP Routers December 1993 This is a working document only, it should neither be cited nor quoted in any formal document. This document will expire before 26 June 1994. Distribution of this document is unlimited. Please send comments to the editor. If your comment pertains to a particular piece of text, please remember to mention the section number, this document is very large and locating the text solely by context might not be possible. Please also mention the date of this draft (12/21/93) and the revision level (1.47).

This paper describes the design and implementation of a multicast transport protocol called RMTP. RMTP provides sequenced, lossless delivery of bulk data from one sender to a group of receivers. RMTP achieves reliability by using a packet based selective repeat retransmission scheme, in which each acknowledgment (ACK) packet carries a sequence number and a bitmap. ACK handling is based on a multi-level hierarchical approach, in which the receivers are grouped into a hierarchy of local regions, with a Designated Receiver (DR) in each local region. Receivers in each local region periodically send ACKs to their corresponding DR, DRs send ACKs to the higher-level DRs, until the DRs in the highest level send ACKs to the sender, thereby avoiding the ACK-implosion problem. DRs cache received data and respond to retransmission requests of the receivers in their corresponding local regions, thereby decreasing end-to-end latency and improving resource usage. This paper also provides the measurem...

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