draft-ietf-fecframe-req-00.txt   draft-ietf-fecframe-req-01.txt 
FECFRAME Working Group Watson FECFRAME Working Group Watson
Internet-Draft Digital Fountain Internet-Draft Digital Fountain
Expires: January 1, 2007 June 30, 2006 Intended status: Informational October 20, 2006
Expires: April 23, 2007
FECFRAME requirements FECFRAME requirements
draft-ietf-fecframe-req-00 draft-ietf-fecframe-req-01
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document defines requirements for a "FEC Framework" to be This document defines requirements for a "FEC Framework" to be
defined by the IETF FECFRAME working group. The object of this group defined by the IETF FECFRAME working group. The object of this group
is primarily to develop specifications for using forward error is primarily to develop specifications for using forward error
correction (FEC) codes with applications in the Internet to provide correction (FEC) codes with applications in the Internet to provide
protection against packet loss. protection against packet loss.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Essential requirements . . . . . . . . . . . . . . . . . . . . 6 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Non-essential requirements . . . . . . . . . . . . . . . . . . 8 4. Essential requirements . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 5. Non-essential requirements . . . . . . . . . . . . . . . . . . 10
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
1. Introduction 1. Introduction
This document defines requirements for a "FEC Framework" to be This document defines requirements for a "FEC Framework" to be
defined by the IETF FECFRAME working group. The purpose of this defined by the IETF FECFRAME working group. The purpose of this
working group is defined in the working group charter as follows: working group is defined in the working group charter as follows:
"The object of this group is to develop specifications for using "The object of this group is to develop specifications for using
forward error correction (FEC) codes with applications in the forward error correction (FEC) codes with applications in the
Internet to provide protection against packet loss. The group Internet to provide protection against packet loss. The group
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application requirements defined in the framework. application requirements defined in the framework.
The FEC protocol framework must therefore define as much as possible The FEC protocol framework must therefore define as much as possible
of a protocol for providing forward error correction for arbitrary of a protocol for providing forward error correction for arbitrary
packet flows over unreliable transport, without defining a particular packet flows over unreliable transport, without defining a particular
FEC code or assuming a particular application. Furthermore, the FEC code or assuming a particular application. Furthermore, the
protocol framework specification will define a clear interface protocol framework specification will define a clear interface
between the specified parts and the unspecified, FEC-code-specific between the specified parts and the unspecified, FEC-code-specific
and application-specific, parts. For this purpose, the building and application-specific, parts. For this purpose, the building
block techniques applied in the Reliable Multicast (RMT) working block techniques applied in the Reliable Multicast (RMT) working
group will be re-used, specifically the FEC Building Block [I-D.ietf- group will be re-used, specifically the FEC Building Block
rmt-fec-bb-revised] [I-D.ietf-rmt-fec-bb-revised]
The term "Forward Error Correction" refers here to application/ The term "Forward Error Correction" refers here to application/
transport layer techniques for recovering lost packets of data. More transport layer techniques for recovering lost packets of data. More
accurately, the term "Forward Erasure Correction" should be used. In accurately, the term "Forward Erasure Correction" should be used. In
many contexts the term "Application Layer FEC (AL-FEC)" is also used, many contexts the term "Application Layer FEC (AL-FEC)" is also used,
although the mechanisms considered here could be considered as either although the mechanisms considered here could be considered as either
application or transport layer (the important point being that they application or transport layer (the important point being that they
are end-to-end). are end-to-end).
Generally, an "FEC Code" is defined in terms of the operations Generally, an "FEC Code" is defined in terms of the operations
required to construct encoded data from source data (at an encoder) required to construct encoded data from source data (at an encoder)
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specification is known as an "FEC Scheme". The FEC Framework will specification is known as an "FEC Scheme". The FEC Framework will
define the requirements that FEC Schemes must meet for use with the define the requirements that FEC Schemes must meet for use with the
framework. framework.
Generally, it is required to add forward error correction to existing Generally, it is required to add forward error correction to existing
applications, for example media streaming applications. In this applications, for example media streaming applications. In this
case, the application protocols must be extended to support this. case, the application protocols must be extended to support this.
The FEC framework will describe the requirements that application The FEC framework will describe the requirements that application
protocols must meet in order to be used with the FEC framework. protocols must meet in order to be used with the FEC framework.
This version of this document is a first draft for discussion in the
FECFRAME working group.
2. Terminology 2. Terminology
'FEC' Forward Erasure Correction. 'FEC' Forward Erasure Correction.
'AL-FEC' Application Layer Forward Erasure Correction 'AL-FEC' Application Layer Forward Erasure Correction
'FEC Framework' The protocol framework which is to be defined by 'FEC Framework' The protocol framework which is to be defined by
FECFRAME and for which this document provides requirements. FECFRAME and for which this document provides requirements.
'Source data flow' The packet flow or flows to which FEC protection 'Source data flow' The packet flow or flows to which FEC protection
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'Repair data flow' The packet flow or flows carrying forward error 'Repair data flow' The packet flow or flows carrying forward error
correction data correction data
'Source protocol' A protocol used for the source data flow being 'Source protocol' A protocol used for the source data flow being
protected - e.g. RTP. protected - e.g. RTP.
'Transport protocol' The protocol used for transport of the source 'Transport protocol' The protocol used for transport of the source
data flow being protected - e.g. UDP, DCCP. data flow being protected - e.g. UDP, DCCP.
'Application protocol' Control protocols used to establish and modify 'Control protocol' Application layer protocols used to establish and
the source data flow being protected - e.g. RTSP. modify the source data flow being protected - e.g. RTSP.
'FEC Code' An algorithm for encoding data such that the encoded dats 'FEC Code' An algorithm for encoding data such that the encoded dats
flow is resiliant to data loss or corruption. flow is resiliant to data loss or corruption.
'FEC Scheme' A specification which defines the additional protocol 'FEC Scheme' A specification which defines the additional protocol
aspects required to use a particular FEC code with the FEC aspects required to use a particular FEC code with the FEC
framework, or (in the context of RMT), with the RMT FEC Building framework, or (in the context of RMT), with the RMT FEC Building
Block. Block.
'Source Block' the group of source data packets which are to be FEC 'Source Block' the group of source data packets which are to be FEC
protected as a single block protected as a single block
'Protection amount' The relative increase in data sent due to the use 'Protection amount' The relative increase in data sent due to the
of FEC. use of FEC.
3. Essential requirements 3. Motivation
One approach to the problem addressed in this document would be to
arrange the source packet flows into a sequence of 'objects' and then
apply FEC protection using the mechanisms defined by the RMT working
group for object transport. This section describes the motivation
for following a separate approach, although one that draws heavily on
the RMT work.
FEC Schemes defined according to the RMT FEC Building Block
[I-D.ietf-rmt-fec-bb-revised] envisage objects with a finite size.
Mapping arbitrary flows to this environment one would need to
consider the flows as a sequence of such objects (also known as
Source Blocks). For each object, the RMT FEC Schemes expect FEC
Object Transmission Information to be communicated with the object.
In many cases some or all of this information will be the same for
every block. Thus there is some advantage in explicitly introducing
the concept of a flow (or bundle of flows) for which some or all of
the FEC Object Transmission Information can be the same for every
source block. As well as reducing overhead, it is advantageous to be
able to inform the receiver that these parameters won't change during
the lifetime of the flow or flows.
A second issue is that FEC Schemes in RMT generally also include
recommendations for parameter settings, which are based on single-
object delivery. Recommendations for protection of packet flows may
be different from these for a variety of reasons. There is a need,
therefore, for FEC-Scheme specific specification material which is
specific to the case of arbitrary packet flows and different from the
recommendations for single-object delivery. One of the key aspects
of the FEC Framework contemplated here is that it provides a context
for such material, in the form of an explicit description of the
requirements that FEC Schemes must meet in order to be used with this
framework.
A third issue is the question of how source data from a packet flow
or flows is formatted into data blocks that an 'object-based' FEC
Scheme could process. RMT FEC Schemes expect an object which is just
a sequence of bytes. We therefore would need to build such an object
out of a sequence of potentially variable-length source packets.
There are several ways this could be done and different FEC Schemes
may require different approaches. Again, the framework contemplated
here provides a context for the definition of these mechanisms
through the concept of FEC Schemes which are adapted for use with
this framework. The RMT work then envisages that both source packets
and repair packets consist of symbols which are extracted from or
generated from (respectively) this source block. In the case of FEC
protection of arbitrary packet flows it is desirable to support cases
where the source packets are transmitted unchanged, thereby providing
backwards compatibility. This is not compatible with in the RMT
approach.
As a result of the considerations above, this document describes
requirements for an FEC Framework for arbitrary packet flows which is
independent of the RMT FEC Building Block, although we draw heavily
on the concepts developed there. FEC Schemes defined for use with
this FEC Framework are distinct from FEC Schemes defined for object
delivery in the context of the RMT FEC Building Block. However, it
is expected that in many cases the task of generalising an RMT FEC
Scheme into one which can be used with both the RMT protocols and
this FEC Framework will be a simple one.
4. Essential requirements
Req-10: The FEC Framework shall support a wide range of FEC codes, Req-10: The FEC Framework shall support a wide range of FEC codes,
using the abstractions of the FEC Building Block defined in RMT using the abstractions of the FEC Building Block defined in RMT
[I-D.ietf-rmt-fec-bb-revised] (including short and long block FEC [I-D.ietf-rmt-fec-bb-revised] (including short and long block FEC
codes, systematic and non-systematic codes). Specifically, the codes, systematic and non-systematic codes). Specifically, the
FEC Framework shall define the requirements that FEC code FEC Framework shall define the requirements that FEC code
specifications shall meet in order to be used with the framework, specifications shall meet in order to be used with the framework,
re-using, as far as possible, the FEC code specification approach re-using, as far as possible, the FEC code specification approach
and requirements from the FEC Building Block and specifying any and requirements from the FEC Building Block and specifying any
further requirements that must be met for the FEC Framework. further requirements that must be met for the FEC Framework.
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specifications shall meet in order to be used with the framework, specifications shall meet in order to be used with the framework,
re-using, as far as possible, the Content Delivery Protocol re-using, as far as possible, the Content Delivery Protocol
specification approach and requirements from the FEC Building specification approach and requirements from the FEC Building
Block and specifying any further requirements that must be met for Block and specifying any further requirements that must be met for
the FEC Framework. the FEC Framework.
Req-30: The FEC Framework shall support variable source block sizes, Req-30: The FEC Framework shall support variable source block sizes,
including real-time variation of source block size between blocks including real-time variation of source block size between blocks
of a given source data flow. of a given source data flow.
Req-30: The FEC Framework shall support variable protection amounts, Req-35: The FEC Framework shall support variable protection amounts,
including real-time variation of protection amount between blocks including dynamic variation of protection amount between blocks
within a given source data flow. within a given source data flow.
Req-40: The FEC Framework shall be independent of the source Req-40: The FEC Framework shall be independent of the source
protocols (provided that source protocol uses one of the supported protocols (provided that source protocol uses one of the supported
transport protocols). transport protocols).
Req-50: The FEC Framework shall place minimal requirements on the Req-50: The FEC Framework shall place minimal requirements on the
application protocols. application protocols.
Req-60: The FEC Framework shall support variable source data flow Req-60: The FEC Framework shall support variable source data flow
rates. rates.
Req-70: The FEC Framework shall support variable source data flow Req-70: The FEC Framework shall support variable source data flow
packet sizes. packet sizes.
Req-80: The FEC Framework shall provide support of combined Req-80: The FEC Framework shall provide support of combined
protection of multiple source data flows. protection of multiple source data flows.
Req-90: The FEC Framework shall provide support of multiple transport Req-90: The FEC Framework shall provide support of multiple
protocols for the source data protocols (UDP, DCCP, others ?). transport protocols for the source data protocols (UDP, DCCP,
others ?).
Req-100: The FEC Framework shall provide support for definition of Req-100: The FEC Framework shall provide support for definition of
backwards-compatible FEC protocols (i.e. where the source packets backwards-compatible FEC protocols (i.e. where the source packets
are not modified in any way). are not modified in any way).
Req-110: The FEC Framework shall provide support for different source Req-110: The FEC Framework shall provide support for different
data protocols (RTP, MIKEY, others ?). source data protocols (RTP, MIKEY, others ?).
Req-120: The FEC Framework shall shall address the security issues, Req-120: The FEC Framework shall shall address the security issues,
if any, associated with the use of FEC. if any, associated with the use of FEC.
4. Non-essential requirements 5. Non-essential requirements
The FEC Framework should be constructed such that the FEC The FEC Framework should be constructed such that the FEC
streaming protocol defined by 3GPP in TS26.346 is a valid protocol streaming protocol defined by 3GPP in TS26.346 is a valid protocol
according to the FEC Framework. according to the FEC Framework.
5. Security Considerations 6. Security Considerations
This document defines requirements for the work of the FECFRAME This document defines requirements for the work of the FECFRAME
working group and includes a requirement that the security working group and includes a requirement that the security
implications of the use of FEC, if any, should be addressed in that implications of the use of FEC, if any, should be addressed in that
work. work.
6. References 7. References
[I-D.ietf-rmt-fec-bb-revised] [I-D.ietf-rmt-fec-bb-revised]
Watson, M., "Forward Error Correction (FEC) Building Watson, M., "Forward Error Correction (FEC) Building
Block", draft-ietf-rmt-fec-bb-revised-03 (work in Block", draft-ietf-rmt-fec-bb-revised-04 (work in
progress), January 2006. progress), September 2006.
Author's Address Author's Address
Mark Watson Mark Watson
Digital Fountain Digital Fountain
39141 Civic Center Dr. 39141 Civic Center Dr.
Suite 300 Suite 300
Fremont, CA 94538 Fremont, CA 94538
US US
Email: mark@digitalfountain.com Email: mark@digitalfountain.com
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ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
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Internet Society. Administrative Support Activity (IASA).
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