Subject: I-D ACTION:draft-ietf-rmt-pi-alc-00.txt

From: [email-masked]
Date: Mon, 13 Mar 2000 06:19:21 -0500

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Reliable Multicast Transport Working Group of the IETF.

	Title		: Asynchronous Layered Coding A scalable reliable       
                          multicast protocol
 	Author(s)	: M. Luby, L. Vicisano et.al
	Filename	: draft-ietf-rmt-pi-alc-00.txt
	Pages		: 28
	Date		: 10-Mar-00
	
This document describes Asynchronous Layered Coding, a scalable reli-
able multicast protocol, hereafter referred to as ALC.   ALC can be
used to reliably transmit objects to multiple receivers.  An object
can be any well-defined piece of data.  Examples include any type of
file such as a group of pictures in an MPEG stream, a MP3 music file,
a JPEG image, and a collection of files that are zipped into one
file.  In addition, the ALC delivery model is fairly flexible, e.g.,
on demand or a push delivery.  When using ALC, the payload of the
packets that flow from senders to receivers in no way depend on net-
work conditions or the reaction of receivers to these conditions,
although the rate of flow of the packets in various parts of the net-
work does depend on network conditions. Receivers may join or leave
an existing packet stream in an asynchronous manner independent of
other receivers. Congestion control is achieved by sending several
packet streams ordered in a layered fashion and delivering only a
subset of these to individual receivers. The number of streams
received is dictated by the local bandwidth availability and network
conditions. A possible way to achieve this is by using a distinct
multicast address for each stream.   Receivers join the lowest layer
stream they are not currently joined to at coordinated points in time
when there is more available bandwidth between those receivers and
the sender.  Similarly, receivers leave one or more highest layer
streams they are currently joined to as soon as they feel congestion
(typically as evidenced by packet loss).  Another possibility to
achieve this form of congestion control is through router-assisted
schemes. Reliability is achieved via FEC coding only, i.e. there is
no request for feedback for retransmission from receivers that miss
packets for whatever reason.

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