draft-ietf-fecframe-req-01.txt   draft-ietf-fecframe-req-02.txt 
FECFRAME Working Group Watson FECFRAME Working Group M. Watson
Internet-Draft Digital Fountain Internet-Draft Digital Fountain
Intended status: Informational October 20, 2006 Intended status: Informational December 3, 2007
Expires: April 23, 2007 Expires: June 5, 2008
FECFRAME requirements FECFRAME requirements
draft-ietf-fecframe-req-01 draft-ietf-fecframe-req-02
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2007).
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
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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 group will be re-used, specifically the FEC Building Block [RFC5052]
[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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3. Motivation 3. Motivation
One approach to the problem addressed in this document would be to One approach to the problem addressed in this document would be to
arrange the source packet flows into a sequence of 'objects' and then arrange the source packet flows into a sequence of 'objects' and then
apply FEC protection using the mechanisms defined by the RMT working apply FEC protection using the mechanisms defined by the RMT working
group for object transport. This section describes the motivation group for object transport. This section describes the motivation
for following a separate approach, although one that draws heavily on for following a separate approach, although one that draws heavily on
the RMT work. the RMT work.
FEC Schemes defined according to the RMT FEC Building Block FEC Schemes defined according to the RMT FEC Building Block [RFC5052]
[I-D.ietf-rmt-fec-bb-revised] envisage objects with a finite size. envisage objects with a finite size. Mapping arbitrary flows to this
Mapping arbitrary flows to this environment one would need to environment one would need to consider the flows as a sequence of
consider the flows as a sequence of such objects (also known as such objects (also known as Source Blocks). For each object, the RMT
Source Blocks). For each object, the RMT FEC Schemes expect FEC FEC Schemes expect FEC Object Transmission Information to be
Object Transmission Information to be communicated with the object. communicated with the object. In many cases some or all of this
In many cases some or all of this information will be the same for information will be the same for every block. Thus there is some
every block. Thus there is some advantage in explicitly introducing advantage in explicitly introducing the concept of a flow (or bundle
the concept of a flow (or bundle of flows) for which some or all of of flows) for which some or all of the FEC Object Transmission
the FEC Object Transmission Information can be the same for every Information can be the same for every source block. As well as
source block. As well as reducing overhead, it is advantageous to be reducing overhead, it is advantageous to be able to inform the
able to inform the receiver that these parameters won't change during receiver that these parameters won't change during the lifetime of
the lifetime of the flow or flows. the flow or flows.
A second issue is that FEC Schemes in RMT generally also include A second issue is that FEC Schemes in RMT generally also include
recommendations for parameter settings, which are based on single- recommendations for parameter settings, which are based on single-
object delivery. Recommendations for protection of packet flows may object delivery. Recommendations for protection of packet flows may
be different from these for a variety of reasons. There is a need, be different from these for a variety of reasons. There is a need,
therefore, for FEC-Scheme specific specification material which is therefore, for FEC-Scheme specific specification material which is
specific to the case of arbitrary packet flows and different from the specific to the case of arbitrary packet flows and different from the
recommendations for single-object delivery. One of the key aspects recommendations for single-object delivery. One of the key aspects
of the FEC Framework contemplated here is that it provides a context of the FEC Framework contemplated here is that it provides a context
for such material, in the form of an explicit description of the for such material, in the form of an explicit description of the
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this FEC Framework are distinct from FEC Schemes defined for object this FEC Framework are distinct from FEC Schemes defined for object
delivery in the context of the RMT FEC Building Block. However, it 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 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 Scheme into one which can be used with both the RMT protocols and
this FEC Framework will be a simple one. this FEC Framework will be a simple one.
4. Essential requirements 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 [RFC5052] (including short and long block FEC codes, systematic
codes, systematic and non-systematic codes). Specifically, the and non-systematic codes). Specifically, the FEC Framework shall
FEC Framework shall define the requirements that FEC code define the requirements that FEC code specifications shall meet in
specifications shall meet in order to be used with the framework, order to be used with the framework, re-using, as far as possible,
re-using, as far as possible, the FEC code specification approach the FEC code specification approach and requirements from the FEC
and requirements from the FEC Building Block and specifying any Building Block and specifying any further requirements that must
further requirements that must be met for the FEC Framework. be met for the FEC Framework.
Req-20: The FEC Framework shall support a wide range of application Req-20: The FEC Framework shall support a wide range of application
protocols, using the abstractions of the FEC Building Block protocols, using the abstractions of the FEC Building Block
[I-D.ietf-rmt-fec-bb-revised]. Specifically, the FEC Framework [RFC5052]. Specifically, the FEC Framework shall define the
shall define the requirements that application protocol requirements that application protocol specifications shall meet
specifications shall meet in order to be used with the framework, in order to be used with the framework, re-using, as far as
re-using, as far as possible, the Content Delivery Protocol possible, the Content Delivery Protocol specification approach and
specification approach and requirements from the FEC Building requirements from the FEC Building Block and specifying any
Block and specifying any further requirements that must be met for 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-35: The FEC Framework shall support variable protection amounts, Req-35: The FEC Framework shall support variable protection amounts,
including dynamic 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
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6. 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.
7. References 7. References
[I-D.ietf-rmt-fec-bb-revised] [RFC5052] Watson, M., Luby, M., and L. Vicisano, "Forward Error
Watson, M., "Forward Error Correction (FEC) Building Correction (FEC) Building Block", RFC 5052, August 2007.
Block", draft-ietf-rmt-fec-bb-revised-04 (work in
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
Full Copyright Statement Full Copyright Statement
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