This paper presents a simple, generic source-based end-to-end multicast congestion control (GSC) algorithm for reliable multicast transport (RMT) protocols. The algorithm is completely implemented at the source and leverages the reverse control information ow in RMT protocols like PGM or RMTP [13,44]. Speci cally, itdoes not introduce any new control tra c or new elds in RMT protocol headers. It addresses the drop-to-zero problem [43] by introducing a robust, adaptive timelter based upon RTT estimates collected by observing NAK tra c. This solution allows it to scale for large multicast groups while being very adaptive to congestion situation changes in any part of the tree. The algorithm is friendly to TCP in terms of competition for bandwidth shares. The scheme has minimal control tra c requirements and weak RTT estimation requirements which allows a large deployment space including multi-sender multicast and combination with receiver-based schemes. Key words: reliable multicast, congestion control, transport protocol 1

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards " (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (c) 2008 IETF Trust and the persons identified as the