Asynchronous Layered Coding (ALC) Protocol Instantiation
RFC 3450

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Network Working Group                                            M. Luby
Request for Comments: 3450                              Digital Fountain
Category: Experimental                                        J. Gemmell
                                                               Microsoft
                                                             L. Vicisano
                                                                   Cisco
                                                                L. Rizzo
                                                              Univ. Pisa
                                                            J. Crowcroft
                                                         Cambridge Univ.
                                                           December 2002

        Asynchronous Layered Coding (ALC) Protocol Instantiation

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 (2002).  All Rights Reserved.

Abstract

   This document describes the Asynchronous Layered Coding (ALC)
   protocol, a massively scalable reliable content delivery protocol.
   Asynchronous Layered Coding combines the Layered Coding Transport
   (LCT) building block, a multiple rate congestion control building
   block and the Forward Error Correction (FEC) building block to
   provide congestion controlled reliable asynchronous delivery of
   content to an unlimited number of concurrent receivers from a single
   sender.

Table of Contents

   1. Introduction.................................................2
     1.1 Delivery service models...................................3
     1.2 Scalability...............................................5
     1.3 Environmental Requirements and Considerations.............6
   2. Architecture Definition......................................8
     2.1 LCT building block........................................9
     2.2 Multiple rate congestion control building block..........10
     2.3 FEC building block.......................................11
     2.4 Session Description......................................13

Luby, et. al.               Experimental                        [Page 1]
RFC 3450               ALC protocol instantiation          December 2002

     2.5 Packet authentication building block.....................14
   3. Conformance Statement.......................................14
   4. Functionality Definition....................................14
     4.1 Packet format used by ALC................................15
     4.2 Detailed Example of Packet format used by ALC............16
     4.3 Header-Extension Fields..................................23
     4.4 Sender Operation.........................................26
     4.5 Receiver Operation.......................................27
   5. Security Considerations.....................................29
   6. IANA Considerations.........................................31
   7. Intellectual Property Issues................................31
   8. Acknowledgments.............................................31
   9. References..................................................31
   Authors' Addresses.............................................33
   Full Copyright Statement.......................................34

1. Introduction

   This document describes a massively scalable reliable content
   delivery protocol, Asynchronous Layered Coding (ALC), for multiple
   rate congestion controlled reliable content delivery.  The protocol
   is specifically designed to provide massive scalability using IP
   multicast as the underlying network service.  Massive scalability in
   this context means the number of concurrent receivers for an object
   is potentially in the millions, the aggregate size of objects to be
   delivered in a session ranges from hundreds of kilobytes to hundreds
   of gigabytes, each receiver can initiate reception of an object
   asynchronously, the reception rate of each receiver in the session is
   the maximum fair bandwidth available between that receiver and the
   sender, and all of this can be supported using a single sender.

   Because ALC is focused on reliable content delivery, the goal is to
   deliver objects as quickly as possible to each receiver while at the
   same time remaining network friendly to competing traffic.  Thus, the
   congestion control used in conjunction with ALC should strive to
   maximize use of available bandwidth between receivers and the sender
   while at the same time backing off aggressively in the face of
   competing traffic.

   The sender side of ALC consists of generating packets based on
   objects to be delivered within the session and sending the
   appropriately formatted packets at the appropriate rates to the