This document outlines a simple protocol framework for reliable multicast dissemination of data files. The general framework was originally developed and used by the Image Multicaster (IMM) application within the Internet MBone for dissemination of satellite imagery. This document describes the more general use of the protocol framework as a reliable bulk file transfer technique. We discuss the present operational modes, some performance issues, and the basic application data units (ADUs) used. This is not intended to be a detailed protocol specification document, but rather a broad description of the basic protocol features and a discussion of issues. Further detailed description of the protocol implementation may be provided in future documents.