In large multicast groups, the size of the group membership table maintained by RTP (Real Time Transport Protocol) participants may become unwieldy, particularly for embedded devices with limited memory and processing power. This document discusses mechanisms for sampling of this group membership table in order to reduce the memory requirements. Several mechanisms are proposed, and the performance of each is considered.
RTP, the Real Time Transport Protocol, has gained widespread acceptance as the transport protocol for voice and video on the Internet. It provides services such as timestamping, sequence numbering, and payload identification. It also contains a control component, the Real Time Control Protocol (RTCP), which is used for loose session control, QoS reporting, and media synchronization, among other functions. The RTP specification describes an algorithm for determining the RTCP packet transmission rate at a host participating in a multicast RTP session. This algorithm was designed to allow RTP to be used in sessions with anywhere from one to a million members. However, we have discovered several problems with this algorithm when used with very large groups with rapidly changing group membership. One problem is the flood of RTCP packets which occurs when many users join a multicast RTP session at nearly the same time. To solve this problem, we present a novel adaptive timer algorithm called reconsideration. We present a mathematical analysis of this algorithm, and demonstrate that it performs extremely well, reducing the congestion problem by several orders of magnitude. We also back up these results with simulation.
This document discusses the issues involved in elevating RTP to the status of protocol, equivalent to TCP or UDP. This will result in all RTP packets being explicitly labeled as such in the packet header. This vastly simplifies the problem of classifying real time streams. Such classification operations are essential for successful deployment of RTP header compression, differentiated services, and traffic isolation. We define the format of the RTP protocol header, and discuss issues of backwards compatibility.Discussion at 41st IETF, Los Angeles
Last updated by Henning Schulzrinne