File Multicast Transport Protocol (FMTP)

This paper describes a new reliable transport protocol designed to run on top of a multicast network service for delivery of continuously generated files. The motivation for this work is to support scientific computing Grid applications that require file transfers between geographically distributed data enters. For example, atmospheric research scientists at various universities subscribe to real-time meteorology data that is being distributed by the University Corporation for Atmospheric Research (UCAR). UCAR delivers 30 different feed types, such as radar data and satellite imagery, to over 240 institutions. The current solution uses an application-layer (AL) multicast tree with uncast TCP connections between the AL servers. Recently, Internet2 and other research-and-education networks have deployed a Layer-2 service using OpenFlow/Software Defined Network (SDN) technologies. Our new transport protocol, FMTP, is designed to run on top of a multipoint Layer-2 topology. A key design aspect of FMTP is the tradeoffs between file delivery throughput of fast receivers and robustness (measure of successful reception) of slow receivers. A configurable parameter, called the retransmission timeout factor, is used to trade off these two metrics. In a multicast setting, it is difficult to achieve full reliability without sacrificing throughput under moderate-to-high loads, and throughput is important in scientific computing grids. A backup solution allows receivers to use uncast TCP connections to request files that were not received completely via multicast. For a given load and a multicast group of 30 receivers, robustness increased significantly from 81.4 to 97.5% when the retransmission timeout factor was increased from 10 to 50 with a small drop in average throughput from 85 to 82.8 Mbps.