Negative-acknowledgment (NACK)-Oriented Reliable Multicast (NORM) Protocol
RFC 3940

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Network Working Group                                         B. Adamson
Request for Comments: 3940                                           NRL
Category: Experimental                                        C. Bormann
                                                 Universitaet Bremen TZI
                                                              M. Handley
                                                                     UCL
                                                               J. Macker
                                                                     NRL
                                                           November 2004

                Negative-acknowledgment (NACK)-Oriented
                   Reliable Multicast (NORM) Protocol

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document describes the messages and procedures of the Negative-
   acknowledgment (NACK) Oriented Reliable Multicast (NORM) protocol.
   This protocol is designed to provide end-to-end reliable transport of
   bulk data objects or streams over generic IP multicast routing and
   forwarding services.  NORM uses a selective, negative acknowledgment
   mechanism for transport reliability and offers additional protocol
   mechanisms to allow for operation with minimal "a priori"
   coordination among senders and receivers.  A congestion control
   scheme is specified to allow the NORM protocol to fairly share
   available network bandwidth with other transport protocols such as
   Transmission Control Protocol (TCP).  It is capable of operating with
   both reciprocal multicast routing among senders and receivers and
   with asymmetric connectivity (possibly a unicast return path) between
   the senders and receivers.  The protocol offers a number of features
   to allow different types of applications or possibly other higher
   level transport protocols to utilize its service in different ways.
   The protocol leverages the use of FEC-based repair and other IETF
   reliable multicast transport (RMT) building blocks in its design.

Adamson, et al.               Experimental                      [Page 1]
RFC 3940                     NORM Protocol                 November 2004

Table of Contents

   1.  Introduction and Applicability. . . . . . . . . . . . . . . .   3
       1.1. NORM Delivery Service Model. . . . . . . . . . . . . . .   4
       1.2. NORM Scalability . . . . . . . . . . . . . . . . . . . .   6
       1.3. Environmental Requirements and Considerations. . . . . .   7
   2.  Architecture Definition . . . . . . . . . . . . . . . . . . .   7
       2.1. Protocol Operation Overview. . . . . . . . . . . . . . .   9
       2.2. Protocol Building Blocks . . . . . . . . . . . . . . . .  10
       2.3. Design Tradeoffs . . . . . . . . . . . . . . . . . . . .  11
   3.  Conformance Statement . . . . . . . . . . . . . . . . . . . .  12
   4.  Message Formats . . . . . . . . . . . . . . . . . . . . . . .  13
       4.1. NORM Common Message Header and Extensions. . . . . . . .  14
       4.2. Sender Messages. . . . . . . . . . . . . . . . . . . . .  16
            4.2.1. NORM_DATA Message . . . . . . . . . . . . . . . .  16
            4.2.2. NORM_INFO Message . . . . . . . . . . . . . . . .  24
            4.2.3. NORM_CMD Messages . . . . . . . . . . . . . . . .  26
       4.3. Receiver Messages. . . . . . . . . . . . . . . . . . . .  43
            4.3.1. NORM_NACK Message . . . . . . . . . . . . . . . .  43
            4.3.2. NORM_ACK Message. . . . . . . . . . . . . . . . .  50
       4.4. General Purpose Messages . . . . . . . . . . . . . . . .  52
            4.4.1. NORM_REPORT Message . . . . . . . . . . . . . . .  52
   5.  Detailed Protocol Operation . . . . . . . . . . . . . . . . .  52
       5.1. Sender Initialization and Transmission . . . . . . . . .  54
            5.1.1. Object Segmentation Algorithm . . . . . . . . . .  55
       5.2. Receiver Initialization and Reception. . . . . . . . . .  57
       5.3. Receiver NACK Procedure. . . . . . . . . . . . . . . . .  57
       5.4. Sender NACK Processing and Response. . . . . . . . . . .  59
            5.4.1. Sender Repair State Aggregation . . . . . . . . .  60
            5.4.2. Sender FEC Repair Transmission Strategy . . . . .  61
            5.4.3. Sender NORM_CMD(SQUELCH) Generation . . . . . . .  62
            5.4.4. Sender NORM_CMD(REPAIR_ADV) Generation. . . . . .  62
       5.5. Additional Protocol Mechanisms . . . . . . . . . . . . .  63
            5.5.1. Greatest Round-trip Time Collection . . . . . . .  63
            5.5.2. NORM Congestion Control Operation . . . . . . . .  64
            5.5.3. NORM Positive Acknowledgment Procedure. . . . . .  72