Network Working Group                                          JM. Valin
Internet-Draft                                              Octasic Inc.
Intended status: Standards Track                          P. Saint-Andre
Expires: April 10, 2010                                            Cisco
                                                              S. Borilin
                                                              SPIRIT DSP
                                                                  K. Vos
                                                           C. Montgomery
                                                     Xiph.Org Foundation
                                                                 R. Chen
                                                    Broadcom Corporation
                                                         October 7, 2009

              Guidelines for Proposed CODEC Working Group

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on April 10, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of

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   publication of this document (
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

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   This document provides general guidelines for work on specifying
   audio codecs within the IETF.  These guidelines cover the development
   process, evaluation and requirements conformance, and intellectual
   property issues.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Development Process  . . . . . . . . . . . . . . . . . . . . .  6
   3.  Evaluation, Testing, and Characterization  . . . . . . . . . .  9
   4.  Requirements Conformance . . . . . . . . . . . . . . . . . . . 10
   5.  Intellectual Property  . . . . . . . . . . . . . . . . . . . . 12
   6.  Relationship with Other SDOs . . . . . . . . . . . . . . . . . 14
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 18
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 19
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21

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1.  Introduction

   This document describes a suggested process for the specification of
   easily distributable audio codecs within the Internet Standards
   Process [PROCESS].  Although several easily distributable audio
   codecs have been developed "in the wild" outside the IETF or any
   other standards development organization (SDO), there are several
   reasons for pursuing such work within the IETF:

   o  The IETF has produced a large "stack" of easily distributable
      protocols and formats for use in a wide variety of Internet
      applications.  However, feedback received from application
      developers and service operators indicates that the lack of
      standardized and easily distributable audio codecs has inhibited
      the development and deployment of interoperable Internet audio

   o  Specification of such codecs within the Internet Standards Process
      would ensure more transparent, stringent, and trusted change
      control than is currently available "in the wild".

   o  In order to develop audio codecs that are optimized for use over
      the Internet, it is important to gain input from the entire
      Internet community and to incorporate cross-area review from the
      full range of technical experts who work within the IETF,
      including areas such as transport, routing, operations,
      architecture, applications, and security.

   o  The Internet Standards Process provides a transparent process for
      the development of Internet technologies, in which any interested
      member of the Internet community can participate.

   o  The IETF's policies toward Intellectual Property Rights (IPR), as
      codified in BCP 79 [IPR], facilitate the development of Internet
      audio codecs that will be easily distributable to all parties that
      might want to implement or deploy such codecs.

   This document describes suggested processes for work on development
   of easily distributable Internet audio codecs within the Internet
   Standards Process, in particular as guidance to the proposed Codec
   Working Group.  Nothing in this document shall be taken to override
   official IETF policies and procedures as codified in BCP 9, BCP 78,
   BCP 79, or any other approved document.  In case the suggestions in
   this document conflict with official policies and procedures, the
   official policies and procedures shall rule.

   Although the authors of this document consider formation of a working
   group to be the most productive path forward because of the

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   consensus-building mechanisms inherent to working groups, work could
   also be pursued through independent submissions, to which the
   procedural guidelines suggested here would apply.

   In addition, although this document sometimes speaks of "codec" in
   the singular in order to simplify the text, IETF participants could
   develop more than one codec; any decisions about the number of codecs
   to work on would be subject to normal consensus processes within the

   The authors welcome discussion and comments related to the topics
   presented in this document.  The preferred venue is the
   <> mailing list, for which archives and subscription
   information are available at

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2.  Development Process

   The process outlined here is intended to maximize the transparency of
   work on codecs within the IETF.  Such work might involve development
   of one or more completely new codecs, adaptation of an existing codec
   to meet the requirements specified in the accompanying requirements
   document [REQS], or integration between two or more existing codecs
   that results in an improved codec combining the best aspects of each
   codec.  To enable such procedural transparency, the contributor of an
   existing codec must be willing to cede change control to the IETF and
   should have sufficient knowledge of the codec to assist in the work
   of adapting it or applying some of its technology to other codecs.
   Furthermore, contributors need to be aware that any codec that
   results from work within the IETF is likely to be different from any
   existing codec that was contributed to the Internet Standards

   Work on codec development is expected to proceed as follows:

   1.  One or more IETF participants will identify the requirements to
       be met by Internet codecs, in the form of an Internet-Draft.

   2.  Interested parties will actively solicit the contribution of
       existing or proposed new codecs to the Internet Standards
       Process.  Ideally these contributions will occur in the form of
       Internet-Drafts to enable the widest community review, although
       any contributions made in accordance with BCP 78 and BCP 79 will
       be acceptable (e.g., via mailing list or a presentation during a
       WG session).  If there is any IPR related to a contributed codec,
       the contribution should be accompanied by an appropriate IPR
       disclosure (IPR issues are described in more detail under
       Section 5).

   3.  As contributions are received and discussed within the working
       group, the group will gain a clearer understanding of what is
       achievable within the design space.  As a result, the authors of
       the requirements document [REQS] should iteratively clarify and
       improve their document to reflect the emerging working group
       consensus.  In parallel, interested parties should evaluate the
       contributions at a higher level to see which requirements might
       be met by each codec.

   4.  Once a sufficient number of proposals has been received, the
       interested parties will identify the strengths, weaknesses, and
       innovative aspects of the contributed codecs.  This step will
       consider not only the codecs as a whole, but also key features of
       the individual algorithms (predictors, quantizers, transforms,

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   5.  It is expected that none of the contributed codecs will meet all
       of the defined requirements.  Therefore, it is expected that IETF
       participants will choose a _starting point_ for the reference
       implementation to facilitate the development process.  This codec
       will meet as many of the requirements as possible, but probably
       will need to be adjusted through an iterative development process
       in order to meet all of the requirements (or as many requirements
       as possible).  The starting point codec might be one of the
       contributed codecs (especially if it is the only codec that meets
       most of the requirements), a combination of two or more of the
       contributed codecs, or an entirely new codec.  None of the
       decisions taken at this step will be definitive.  In particular,
       IETF participants will not provide a "rubber stamp" for any
       contributed codec.

   6.  IETF participants will attempt to iteratively improve each
       component of the starting point reference implementation, where
       by "component" we mean individual algorithms such as predictors,
       transforms, quantizers, and entropy coders.  The participants
       will proceed by trying new designs, applying ideas from the
       contributed codecs, evaluating "proof of concept" ideas, and
       using their expertise in codec development to improve the
       starting point codec.  Any aspect of the starting point codec
       might be changed (even the fundamental principles of the codec)
       or the participants might start over entirely by scrapping the
       starting point codec and designing a completely new one.  The
       overriding goal shall be to design a codec that will meet the
       requirements defined in the requirements document.  Given the
       IETF's open standards process, any interested party will be able
       to contribute to this work, whether or not they submitted an
       Internet-Draft for one of the contributed codecs.  The codec
       itself will be normatively specified with code in an Internet-

   7.  In parallel with work on the codec reference implementation,
       developers and other interested parties should perform evaluation
       of the codec as described under Section 3, IETF participants
       should define (within the AVT Working Group) the codec's payload
       format for use with the Real-time Transport Protocol [RTP], and
       application developers should start testing the codec by
       implementing it in code and deploying it in actual Internet audio
       applications to identify any potential problems.

   8.  Once IETF participants agree that the codec being developed meets
       the requirements (e.g., through consensus calls on the relevant
       discussion list or via a working group last call if a working
       group is formed), IETF participants can begin the task of
       characterizating the codec.  The characterization process is

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       described under Section 3.

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3.  Evaluation, Testing, and Characterization

   Lab evaluation of the codecs should happen throughout the development
   process because it will help ensure that progress is being made
   toward fulfillment of the requirements.  There are many ways in which
   continuous evaluation can be performed.  For minor, uncontroversial
   changes to the codec it should usually be sufficient to use objective
   measurements (e.g., PESQ, PEAQ, and SegSNR) validated by listening to
   a few samples.  For more complex changes (e.g., when psychoacoustic
   aspects are involved) or for controversial issues, internal testing
   should be performed.  An example of internal testing would be to have
   individual participants rate audio samples using one of the
   established testing methodologies, such as ITU-R BS.1534 (MUSHRA).

   Throughout the process, it will be important to make use of the
   Internet community at large for real-world distributed testing.  This
   will enable many different people with different equipment and use
   cases to test the codec and report any problems they experience.  In
   the same way, third-party software developers will be encouraged to
   integrate the codec (with a warning about the bit-stream not being
   final) and provide feedback on its performance in real-world use

   Characterization of the final codec must be based on the reference
   implementation only (and not on any "private implementation").  This
   can be performed by independent testing labs or, if this is not
   possible, using the testing labs of the organizations that contribute
   to the Internet Standards Process.  Packet loss robustness should be
   evaluated using actual loss patterns collected from use over the
   Internet, rather than theoretical models.  The goals of the
   characterization phase are to:

   o  ensure that the requirements have been fulfilled

   o  guide the IESG in its evaluation of the resulting work

   o  assist application developers in understanding whether the codec
      is suitable for a particular application.

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4.  Requirements Conformance

   It is the responsibility of the working group to define criteria for
   evaluating conformance, including but not limited to comparison tools
   and test vectors.  The following text provides suggestions for
   consideration by the working group.

   First, any codec specified by the IETF must include source code for a
   normative reference implementation, specified in an Internet-Draft.
   This will aid in interoperability testing and requirements

   Second, it is best to use the minimum number of normative
   requirements that will ensure complete interoperability between
   implementations.  In practice this generally means that only the
   decoder needs to be normative, so that the encoder can improve over
   time.  This also enables different tradeoffs between quality and

   Third, to reduce the risk of bias towards certain CPU/DSP
   architectures, ideally the decoder specification would not have a
   "bit-exact" definition.  The output of a decoder implementation
   should only be "close enough" to the output of the reference decoder.
   A comparison tool should be used to verify objectively that the
   output of a decoder is likely to be perceptually indistinguishable
   from that of the reference decoder.  The packet loss concealment
   (PLC) algorithm need not be normative.  However, if any part of the
   PLC requires specific information (in the bit-stream) transmitted by
   the encoder, than the corresponding aspect of the reference encoder
   must be normative.

   Fourth, an encoder implementation should not be required to be able
   to generate all the "features" in the bit-stream definition.
   However, it may be required (by the codec specification) to be able
   to generate any possible bit-rates.  Unless any "profile" is defined
   in the specification, the decoder must be able to decode all features
   of the bit-stream.  The decoder must also be able to handle any
   combination of bits, even if that combination cannot be generated by
   the reference encoder.  It is recommended that the decoder
   specification defines exactly how the decoder should react to
   "impossible" packets.

   Compressed test vectors should be provided as a means to verify
   conformance with the decoder specification.  These test vectors
   should exercise all paths in the decoder (100% code coverage).

   While the exact encoder will not be specified, it is recommended to
   specify objective measurement targets for an encoder, below which use

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   of a particular encoder implementation is not recommended.  For
   example, one such specification could be: "the use of an encoder
   whose PESQ MOS is less than 0.1 below the reference encoder in the
   following conditions is not recommended".

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5.  Intellectual Property

   The codec should be easily distributable, with as few restrictions as
   possible.  This can be achieved by handling IPR issues in accordance
   with BCP 78 [TRUST] and BCP 79 [IPR].  IPR is a very important issue
   for the following reasons:

   o  The IETF already provides a comprehensive "stack" of easily
      distributable protocols for communication over the Internet.
      However, there is a conspicuous gap in this stack for media

   o  Many market segments are moving from selling hard-coded hardware
      devices to freely distributing end-user software, including large
      application providers and even telcos themselves.

   o  It is beneficial to have low-cost options whenever possible
      because standalone voice services are being commoditized and
      small, innovative development teams often cannot afford to pay
      per-channel royalties.

   o  Most applications provided in the Internet space will benefit from
      easily distributable codecs.

   In accordance with BCP 78 [TRUST], the source code for the reference
   implementation should be available under the BSD license or whatever
   license is defined as acceptable by the IETF Trust when the relevant
   Internet-Drafts are published.  Also, in accordance with BCP 79
   [IPR], the codecs should preferably use technologies with no known
   IPR claims or technologies with an offer of royalty-free (RF)
   licensing.  Compatibility with the licensing of typical open source
   applications requires the avoidance of restrictive IPR claims.

   There are several ways to maximize the odds that the codec will be
   royalty-free.  First, when a technology under consideration is known
   to be covered by a patent, the patent holder should be contacted and
   asked to license the patent under acceptable RF terms.  If the patent
   holder is also a contributor, the license may have already been
   specified in the IPR disclosure.  In cases where no RF license can be
   obtained regarding a patent, then alternative algorithms or methods
   should be considered, even if they result in lower quality, higher
   complexity, or otherwise less desirable characteristics.  In most
   cases, the degradation will likely be small once the best alternative
   has been identified.

   IETF participants should be aware that, given the way patents work in
   most countries, the resulting codecs can never be guaranteed to be
   free of patent claims because:

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   o  Some patents may not be known to the contributors.

   o  Some patents applications may not be disclosed at the time the
      codec is developed.

   o  Only the courts can determine the validity and breadth of patent

   However, these observations are no different within the Internet
   Standards Process than they are for standardization of codecs within
   other SDOs (or development of codecs outside the context of any SDO)
   and are no different than for other technologies worked on within the
   IETF.  In all these cases, the best approach is to minimize the risk
   of unknowingly incurring encrumbrance on existing patents.

   To help minimize the risk of unknowingly incurring encumbrance on
   existing patents, the WG should prefer technologies that were
   published more than twenty years in the past over more recent
   technologies, at least when the two are mostly equivalent.
   Similarly, whenever possible the WG should use technologies that are
   perceived to be safer by the participants.  Despite these
   precautions, the participants need to understand that, practically
   speaking, it is nearly impossible to guarantee that implementors will
   not incur encumbrance on existing patents.

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6.  Relationship with Other SDOs

   It is understood that other SDOs are also involved in the development
   and standardization of media codecs, including but not necessarily
   limited to:

   o  The Telecommunication Standardization Sector (ITU-T) of the
      Internatioal Telecommunication Union (ITU), in particular Study
      Group 16

   o  The Moving Picture Experts Group (MPEG)

   o  The European Telecommunications Standards Institute (ETSI)

   o  The 3rd Generation Partnership Project (3GPP)

   o  The 3rd Generation Partnership Project 2 (3GPP2)

   By specifying guidelines for working on media codecs within the
   Internet Standards Process, IETF participants are not attempting to
   duplicate work being performed by other SDOs.  Clearly, there is no
   "natural monopoly" over codec work, since SDOs such as ITU-T, MPEG,
   ETSI, 3GPP, and 3GPP2 have defined codecs in parallel.

   With regard to Study Group 16 of the ITU-T, the work envisioned
   within the Internet Standards Process differs as follows:

   o  The codec(s) produced within the Internet Standards Process will
      specifically address problems related to transmission on the

      *  The codec(s) will be optimized for transport using the Real-
         time Transport Protocol [RTP], including secure transport as
         described in [SRTP]

      *  The codec(s) will take into account end-to-end parameter
         negotiation using Internet signalling technologies such as
         Session Initiation Protocol [SIP], Session Description Protocol
         [SDP], and the Extensible Messaging and Presence Protocol
         [XMPP] extensions for media negotiation as specified in

      *  Robustness to packet loss will be a very important aspect to

      *  Purely wireless applications will not be considered

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      *  Issues with circuit-switched networks will not be considered

   o  As discussed under Section 5, IPR issues will be handled in
      accordance with IETF IPR policies, with the goal of developing
      easily distributable codecs

   With regard to MPEG, the work envisioned within the Internet
   Standards Process differs as follows:

   o  The focus will be on interactive audio transmission rather than

   o  As discussed under Section 5, IPR issues will be handled in
      accordance with IETF IPR policies, with the goal of developing
      easily distributable codecs

   o  The emphasis will be on the quality of the reference
      implementations (encoder and decoder), which will be the basis for

   Although there is already sufficient expertise available among
   participants who are active within the IETF, additional contributions
   are welcome.  Because IETF work happens through the efforts of
   individuals, individuals who contribute to the work of other SDOs, as
   well as the SDOs themselves, are welcome to contribute to the work
   within the Internet Standards Process, in the in the following ways:

   o  Contributors to other SDOs can participate in the Internet
      Standards Process, as can any other interested parties

   o  The ITU-T can contribute its existing characterization and
      evaluation techniques, methods, experience and expertise, and thus
      facilitate the testing process

   o  Any other SDO can provide input to the process through liaison

   However, it is important to note that final responsibility for the
   development process and the resulting codecs will remain with the
   IETF as governed by BCP 9 [PROCESS].

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7.  Security Considerations

   The procedural guidelines for codec development do not have security
   considerations.  However, the resulting codec needs to take
   appropriate security considerations into account, for example as
   outlined in [DOS] and [SECGUIDE].

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8.  IANA Considerations

   This document has no actions for IANA.

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9.  Acknowledgments

   We would like to thank all the other people who contributed directly
   or indirectly to this document, including Jason Fischl, Gregory
   Maxwell, Alan Duric, Jonathan Christensen, Julian Spittka, and Henry
   Sinnreich.  We also like to thank Cullen Jennings and Gregory
   Lebovitz for their advice.

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10.  References

10.1.  Normative References

   [IPR]      Bradner, S., "Intellectual Property Rights in IETF
              Technology", BCP 79, RFC 3979, March 2005.

   [PROCESS]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [TRUST]    Bradner, S. and J. Contreras, "Rights Contributors Provide
              to the IETF Trust", BCP 78, RFC 5378, November 2008.

10.2.  Informative References

   [DOS]      Handley, M., Rescorla, E., and IAB, "Internet Denial-of-
              Service Considerations", RFC 4732, December 2006.

   [Jingle]   Ludwig, S., Saint-Andre, P., Egan, S., McQueen, R., and D.
              Cionoiu, "Jingle RTP Sessions", XSF XEP 0167, June 2009.

   [REQS]     Valin, J., Borilin, S., Vos, K., Montgomery, C., and J.
              Chen, "Codec Requirements",
              draft-valin-codec-requirements-00 (work in progress),
              September 2009.

   [RTP]      Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [SDP]      Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

              Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

   [SIP]      Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [SRTP]     Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

   [XMPP]     Saint-Andre, P., Ed., "Extensible Messaging and Presence

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              Protocol (XMPP): Core", RFC 3920, October 2004.

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Authors' Addresses

   Jean-Marc Valin
   Octasic Inc.
   4101, Molson Street
   Montreal, Quebec


   Peter Saint-Andre


   Slava Borilin


   Koen Vos


   Christopher Montgomery
   Xiph.Org Foundation


   Raymond (Juin-Hwey) Chen
   Broadcom Corporation


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