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Versions: 00 01 02 03 RFC 3802

    Network Working Group                                   Greg Vaudreuil
    Internet Draft                                     Lucent Technologies
    Expires in six months                                    Glenn Parsons
    Obsoletes: RFC 2422                                    Nortel Networks
                                                         February 14, 2002
    
    
                      Toll Quality Voice - 32 kbit/s ADPCM
                           MIME Sub-type Registration
    
                      <draft-ietf-vpim-vpimv2r2-32k-03.txt>
    
    
    Status of this Memo
    
       This document is an Internet-Draft and is in full conformance with
       all provisions of Section 10 of RFC2026.
    
       Internet-Drafts are working documents of the Internet Engineering
       Task Force (IETF), its areas, and its working groups. Note that
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     Abstract
    
       This document is an Internet-Draft and is in full conformance with
       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 RFC 2422.
    
    
     Copyright Notice
    
       Copyright (C) The Internet Society (2002).  All Rights Reserved.
    
    
    

    
    
    Internet Draft             32 kbit/s ADPCM           February 14, 2002
    
    
    
      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].
    
    
      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.
    
    
    
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    Internet Draft             32 kbit/s ADPCM           February 14, 2002
    
    
      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 Specifcation for proper usage.
    
    
      4.  IANA Registration
    
           To: ietf-types@iana.org
           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
    
    
    
    
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    Internet Draft             32 kbit/s ADPCM           February 14, 2002
    
    
           Additional information:
    
             Magic number(s): ?
             File extension(s): .726
             Macintosh File Type Code(s):  APCM
    
              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
             gparsons@NortelNetworks.com
    
             Gregory M. Vaudreuil
             GregV@ieee.org
    
           Intended usage: COMMON
    
           Author/Change controller:
    
             Glenn W. Parsons & Gregory M. Vaudreuil
    
    
    
    
    
    
    
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    Internet Draft             32 kbit/s ADPCM           February 14, 2002
    
    
       4. 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.
    
    
      5. Authors' Addresses
    
       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: gparsons@nortelnetworks.com
    
    
       Gregory M. Vaudreuil
       Lucent Technologies
       7291 Williamson Rd
       Dallas, TX  75214
       United States
    
       Phone/Fax: +1-972-733-2722
       Email: gregv@ieee.org
    
    
    
      6. 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).
    
      [MIME4] N. Freed and N. Borenstein,  "Multipurpose Internet Mail
           Extensions (MIME) Part Four: Registration Procedures", RFC
           2048, Innosoft, First Virtual, Nov 1996.
    
      [VPIM1] Vaudreuil, Greg, "Voice Profile for Internet Mail", RFC
           1911, Feb 1996.
    
      [VPIM2] Vaudreuil, G., and G. Parsons, "Voice Profile for Internet
           Mail - version 2", RFC 2421, September 1998.
    
      [VPIM2R2] Vaudreuil, G., and G. Parsons, "Voice Profile for Internet
           Mail - version 2", <draft-ietf-vpim-vpimv2r2-04.txt>, October
           22, 2001.
    
    
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    Internet Draft             32 kbit/s ADPCM           February 14, 2002
    
    
      [X420] ITU-T Recommendation X.420 (1996) - ISO/IEC 10021-7:1996,
           Message handling systems: Interpersonal messaging.
    
      [REQ] S. Bradner, "Key words for use in RFCs to Indicate Requirement
           Levels", RFC 2119, March 1997.
    
    
    
      7.  Changes from RFC 2422
    
       Only editoral and boilerplate changes from RFC 2424 have been made
       to this document.
    
    
      8.  Full Copyright Statement
    
       Copyright (C) The Internet Society (2002).  All Rights Reserved.
    
       This document and translations of it may be copied and furnished to
       others, and derivative works that comment on or otherwise explain
       it or assist in its implementation may be prepared, copied,
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       of any kind, provided that the above copyright notice and this
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       However, this document itself may not be modified in any way, such
       as by removing the copyright notice or references to the Internet
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       purpose of developing Internet standards in which case the
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       other than English.
    
       The limited permissions granted above are perpetual and will not be
       revoked by the Internet Society or its successors or assigns.
    
       This document and the information contained herein is provided on
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