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Versions: 00 01 02 rfc2422                               Standards Track
    Network Working Group                                   Greg Vaudreuil
    Internet Draft                                     Lucent Technologies
    Expires in six months                                    Glenn Parsons
    Obsoletes: RFC 1911                                   Northern Telecom
                                                         November 21, 1997
                      Toll Quality Voice - 32 kbit/s ADPCM
                           MIME Sub-type Registration
      Status of this Memo
      This document is an Internet Draft.  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 Drafts.
      Internet Drafts are 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 a "work in progress".
      To learn the current status of any Internet-Draft, please check the
      "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
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      ftp.isi.edu (US West Coast).
      Copyright Notice
      Copyright (C) The Internet Society (1997).  All Rights Reserved.
      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.
    Internet Draft             32 kbit/s ADPCM           November 21, 1997
      1.  Abstract
      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 refines
      an earlier sub-type registration in RFC 1911.
      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
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    Internet Draft             32 kbit/s ADPCM           November 21, 1997
      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: none
           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
           Published specification: ITU-T G.726 with little endian
           Applications which use this media type: primarily voice
           Additional information:
             Magic number(s): ?
             File extension(s): .726
             Macintosh File Type Code(s):  APCM
              Little Endian Ordering:
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    Internet Draft             32 kbit/s ADPCM           November 21, 1997
              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.
              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
             Gregory M. Vaudreuil
           Intended usage: COMMON
           Author/Change controller:
             Glenn W. Parsons & Gregory M. Vaudreuil
      5. Authors' Addresses
      Glenn W. Parsons
      Northern Telecom
      P.O. Box 3511, Station C
      Ottawa, ON  K1Y 4H7
      Phone: +1-613-763-7582
      Fax: +1-613-763-4461
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    Internet Draft             32 kbit/s ADPCM           November 21, 1997
      Gregory M. Vaudreuil
      Lucent Technologies
      17080 Dallas Parkway
      Dallas, TX  75248-1905
      United States
      Phone/Fax: +1-972-733-2722
      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] Greg Vaudreuil and Glenn Parsons, "Voice Profile for
           Internet Mail - version 2", Work in Progress, <draft-ema-vpim-
           07.txt> November 1997.
      [X420] ITU-T Recommendation X.420 (1996) - ISO/IEC 10021-7:1996,
           Message handling systems: Interpersonal messaging.
      7.  Full Copyright Statement
      Copyright (C) The Internet Society (1997).  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 implmentation may be prepared, copied, published
      and distributed, in whole or in part, without restriction of any
      kind, provided that the above copyright notice and this paragraph
      are included on all such copies and derivative works.  However, this
      document itself may not be modified in any way, such as by removing
      the copyright notice or references to the Internet Society or other
      Internet organizations, except as needed for the purpose of
      developing Internet standards in which case the procedures for
      copyrights defined in the Internet Standards process must be
      followed, or as required to translate it into languages other than
      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 an
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