Network Working Group                                       G. Vaudreuil
Request for Comments: 3802                           Lucent Technologies
Obsoletes: 2422                                               G. Parsons
Category: Standards Track                                Nortel Networks
                                                              June 2004


   Toll Quality Voice - 32 kbit/s Adaptive Differential Pulse Code
            Modulation (ADPCM) MIME Sub-type Registration

Status of this Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2004).

Abstract

  This document describes the registration of the MIME sub-type
  audio/32KADPCM Adaptive Differential Pulse Code Modulation for toll
  quality audio.  This audio encoding is defined by the ITU-T in
  Recommendation G.726.

1.  Introduction

  This document describes the registration of the MIME sub-type
  audio/32KADPCM for toll quality audio.  This audio encoding is
  defined by the ITU-T in Recommendation G.726.  This document
  obsoletes an earlier sub-type registration contained in RFC 1911.
  This document also obsoletes RFC 2422.

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
  document are to be interpreted as described in [REQ].











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2.  ITU-T Definition

  Recommendation G.726 [G726] defines the characteristics that are
  recommended for the conversion of a 64 kbit/s A-law or m-law pulse
  code modulation (PCM) channel at 8000 samples/second to and from a
  40, 32, 24 or 16 kbit/s channel.  The conversion is applied to the
  PCM bit stream using an adaptive differential pulse code modulation
  (ADPCM) transcoding technique.  This Recommendation obsoletes G.721
  which only defined the 32 kbit/s characteristics.

  Recommendation G.726 was prepared by Study Group 15 of the
  Telecommunications Standardization Sector of the International
  Telecommunication Union (ITU-T) and was approved under the ITU's
  Resolution No. 2 procedure on the 14 of December 1990.

3.  MIME Definition

3.1.  audio/32KADPCM

  CCITT Recommendation G.726 [G726] describes the algorithm recommended
  for conversion of a 64 kbit/s A-law or u-law PCM channel to and from
  a 32 kbit/s channel (this is the same algorithm as described in the
  deprecated G.721).  The conversion is applied to the PCM stream using
  an Adaptive Differential Pulse Code Modulation (ADPCM) transcoding
  technique.

  The MIME sub-type audio/32KADPCM is defined to hold binary audio data
  encoded in 32 kbit/s ADPCM exactly as defined by ITU-T Recommendation
  G.726.  No header information shall be included as part of the audio
  data.  The content transfer encoding is typically either binary or
  base64.

  An additional consideration that this document defines for clarity is
  the choice of little endian ordering of the four bit code words. This
  default ordering is defined in ITU-T Recommendation X.420 [X420] for
  the equivalent X.400 body part, but is also detailed below in the
  IANA Registration.

3.2.  VPIM Usage

  The audio/32KADPCM sub-type is a primary component of the VPIM
  specification [VPIM].  In this context, the Content-Description and
  Content-Disposition headers are used to succinctly describe the
  contents of the audio body.  As well, only the little endian bit
  ordering is valid.  Refer to the VPIM Specification for proper usage.






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4.  IANA Registration

     To: [email protected]
     Subject: Registration of MIME media type audio/32KADPCM

     MIME media type name: audio

     MIME subtype name: 32KADPCM

     Required parameters: none

     Optional parameters: none

     Encoding considerations:

        Binary or Base-64 generally preferred

     Security considerations:

        There are no known security risks with the sending or playing
        of raw audio data  Audio data is typically interpreted only by
        an audio codec.  Unintended information introduced into the
        data stream will result in noise.

     Interoperability considerations:

        The four bit code word ordering within a byte may differ
        between existing implementations of G.726 codecs.  Since this
        content only permits the little endian ordering, codecs that
        support the opposite ordering must reorder the code words
        before storing to or retrieving from this content type.

     Published specification:

        ITU-T G.726 with little endian ordering

     Applications which use this media type:

        Primarily voice messaging

     Additional information:

        Magic number(s): ? File extension(s): .726 Macintosh File Type
        Code(s):  APCM







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         Little Endian Ordering:

         The 4-bit code words of the G.726 encoding MUST be packed into
         octets/bytes as follows:  the first code word (A) is placed in
         the four least significant bits of the first octet, with the
         least significant bit (LSB) of the code word (A0) in the least
         significant bit of the octet;  the second code word (B) is
         placed in the four most significant bits of the first octet,
         with the most significant bit (MSB) of the code word (B3) in
         the most significant bit of the octet. Subsequent pairs of the
         code words shall be packed in the same way into successive
         octets, with the first code word of each pair placed in the
         least significant four bits of the octet.  It is preferred
         that the voice sample be extended with silence such that the
         encoded value comprises an even number of code words.
         However, if the voice sample comprises an odd number of code
         words, then the last code word shall be discarded.

                 +--+--+--+--+--+--+--+--+
                 |B3|B2|B1|B0|A3|A2|A1|A0|
                 +--+--+--+--+--+--+--+--+
         MSB ->  | 7| 6| 5| 4| 3| 2| 1| 0|  <- LSB
                 +--+--+--+--+--+--+--+--+

                 32K ADPCM / Octet Mapping

     Person & email address to contact for further information:

       Glenn W. Parsons [email protected]

       Gregory M. Vaudreuil [email protected]

     Intended usage: COMMON

     Author/Change controller:

       Glenn W. Parsons & Gregory M. Vaudreuil

5.  Security Considerations

  There are no known security risks with the sending or playing of raw
  audio data  Audio data is typically interpreted only by an audio
  codec.  Unintended information introduced into the data stream will
  result in noise.







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6.  References

6.1.  Normative References

  [G726]     CCITT Recommendation G.726 (1990), General Aspects of
             Digital Transmission Systems, Terminal Equipment - 40, 32,
             24,16 kbit/s Adaptive Differential Pulse Code Modulation
             (ADPCM).

  [VPIM2R2]  Vaudreuil, G., and G. Parsons, "Voice Profile for Internet
             Mail - version 2 (VPIMv2)", RFC 3801, June 2004.

  [REQ]      Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

6.2.  Informative References

  [RFC 3023] Murata, M., St. Laurent, S. and D. Kohn, "XML Media
             Types", RFC 3023, January 2001.

  [VPIM1]    Vaudreuil, G., "Voice Profile for Internet Mail", RFC
             1911, February 1996.

  [VPIM2]    Vaudreuil, G., and G. Parsons, "Voice Profile for Internet
             Mail - version 2", RFC 2421, September 1998.

  [X420]     ITU-T Recommendation X.420 (1996) - ISO/IEC 10021-7:1996,
             Message handling systems: Interpersonal messaging.

7.  Changes from RFC 2422

  Only editorial and boilerplate changes from RFC 2422 have been made
  to this document.


















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8.  Authors' Addresses

  Gregory M. Vaudreuil
  Lucent Technologies
  7291 Williamson Rd
  Dallas, TX  75214
  United States

  EMail: [email protected]


  Glenn W. Parsons
  Nortel Networks
  P.O. Box 3511, Station C
  Ottawa, ON  K1Y 4H7
  Canada

  Phone: +1-613-763-7582
  Fax:   +1-613-763-2697
  EMail: [email protected]































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9.  Full Copyright Statement

  Copyright (C) The Internet Society (2004).  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.

  This document and the information contained herein are provided on an
  "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
  OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
  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.

Intellectual Property

  The IETF takes no position regarding the validity or scope of any
  Intellectual Property Rights or other rights that might be claimed to
  pertain to the implementation or use of the technology described in
  this document or the extent to which any license under such rights
  might or might not be available; nor does it represent that it has
  made any independent effort to identify any such rights.  Information
  on the procedures with respect to rights in RFC documents can be
  found in BCP 78 and BCP 79.

  Copies of IPR disclosures made to the IETF Secretariat and any
  assurances of licenses to be made available, or the result of an
  attempt made to obtain a general license or permission for the use of
  such proprietary rights by implementers or users of this
  specification can be obtained from the IETF on-line IPR repository at
  http://www.ietf.org/ipr.

  The IETF invites any interested party to bring to its attention any
  copyrights, patents or patent applications, or other proprietary
  rights that may cover technology that may be required to implement
  this standard.  Please address the information to the IETF at ietf-
  [email protected].

Acknowledgement

  Funding for the RFC Editor function is currently provided by the
  Internet Society.









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