1. Introduction and Applicability

   The Negative-acknowledgment (NACK) Oriented Reliable Multicast (NORM)
   protocol is designed to provide reliable transport of data from one
   or more sender(s) to a group of receivers over an IP multicast
   network.  The primary design goals of NORM are to provide efficient,
   scalable, and robust bulk data (e.g., computer files, transmission of
   persistent data) transfer across possibly heterogeneous IP networks
   and topologies.  The NORM protocol design provides support for
   distributed multicast session participation with minimal coordination
   among senders and receivers.  NORM allows senders and receivers to
   dynamically join and leave multicast sessions at will with minimal
   overhead for control information and timing synchronization among
   participants.  To accommodate this capability, NORM protocol message
   headers contain some common information allowing receivers to easily
   synchronize to senders throughout the lifetime of a reliable
   multicast session.  NORM is designed to be self-adapting to a wide
   range of dynamic network conditions with little or no pre-
   configuration.  The protocol is purposely designed to be tolerant of
   inaccurate timing estimations or lossy conditions that may occur in
   many networks including mobile and wireless.  The protocol is also
   designed to exhibit convergence and efficient operation even in
   situations of heavy packet loss and large queuing or transmission
   delays.

   This document is a product of the IETF RMT WG and follows the
   guidelines provided in RFC 3269 [1].  The key words "MUST", "MUST
   NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
   "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
   interpreted as described in BCP 14, RFC 2119 [2].