A Reliable Message Multicast Transport Protocol for Virtual Circuits

Motivated by the need to distribute large volumes of scientific data to large numbers of subscribers, we propose a reliable multicast transport protocol. Specifically, this protocol is developed for use on virtual circuits, since dynamic circuit services are now being offered by large providers, and virtual circuit networking is well suited to multicasting as it eliminates the data-plane congestion control problem of connectionless IP. The new protocol is called Virtual Circuit Multicast Transport Protocol (VCMTP). A key concept is to execute retransmissions (required due to flow control problems) at the end, i.e., after the message (file or memory data) is multicast. This leads to scalability, where the throughput for the receivers that can keep pace with the sending rate is independent of the number of receivers. A prototype was tested on Emulab, and measurements obtained. Our findings are that for disk-to-disk file transfers at a sending rate of 600 Mbps, the Emulab hosts can support multicasting with less than 0.5% retransmission rates, but at a 800 Mbps sending rate, the average throughput is only 650 Mbps because the retransmission rate increases to 9%.