Introduction and Applicability

The Negative-ACKnowledgment (NACK) Oriented Reliable Multicast (NORM) protocol can provide reliable transport of data from one or more senders 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 self-adapting to a wide range of dynamic network conditions with little or no pre-configuration. The protocol is tolerant of inaccurate timing estimations or lossy conditions that can occur in many networks including mobile and wireless. The protocol can also converge and maintain efficient operation even in situations of heavy packet loss and large queuing or transmission delays. This document obsoletes the Experimental RFC 3940 specification.

This document is a product of the IETF RMT working group and follows the guidelines provided in the Author Guidelines for Reliable Multicast Transport (RMT) Building Blocks and Protocol Instantiation documents [RFC3269].

Statement of Intent

This memo contains the definitions necessary to fully specify a Reliable Multicast Transport protocol in accordance with the criteria of IETF Criteria for Evaluating Reliable Multicast Transport and Application Protocols [RFC2357]. The NORM specification described in this document was previously published in the Experimental Category [RFC3940]. It was the stated intent of the RMT working group to resubmit this specifications as an IETF Proposed Standard in due course. This Proposed Standard specification is thus based on RFC 3940 and has been updated according to accumulated experience and growing protocol maturity since the publication of RFC 3940. Said experience applies both to this specification itself and to congestion control strategies related to the use of this specification. The differences between RFC 3940 and this document are listed in Section 10.