One document matched: draft-ietf-vpim-vpimv2r2-32k-00.txt
Network Working Group Greg Vaudreuil
Internet Draft Lucent Technologies
Document: <draft-ietf-vpim-vpimv2r2-32k-00.txt> Glenn Parsons
Obsoletes: RFC 2422 Nortel Networks
Category: Standards Track November 16, 2000
Toll Quality Voice - 32 kbit/s ADPCM
MIME Sub-type Registration
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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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.
This document obsoletes RFC 2422.
2. Conventions used in this document
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 RFC-2119.
3. ITU-T Definition
Recommendation G.726 [G726] defines the characteristics that are
recommended for the conversion of a 64 kbit/s A-law or mu-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
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(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.
4. MIME Definition
4.1 audio/32KADPCM
CCITT Recommendation G.726 [G726] describes the algorithm recommended
for conversion of a 64 kbit/s A-law or mu-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.
4.2 VPIM Usage
The audio/32KADPCM sub-type is a primary component of the VPIM
specification [VPIM2R2]. 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.
5. 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:
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32 kbit/s ADPCM November 16, 2000
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
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
+--+--+--+--+--+--+--+--+
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32K ADPCM / Octet Mapping
Person & email address to contact for further information:
Glenn W. Parsons
gparsons@nortelnetworks.com
Gregory M. Vaudreuil
gregv@lucent.com
Intended usage: COMMON
Author/Change controller:
Glenn W. Parsons & Gregory M. Vaudreuil
6. 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.
7. References
[ADPCM] G. Vaudreuil and G. Parsons, "Toll Quality Voice - 32 kbit/s
ADPCM: MIME Sub-type Registration", RFC 2422, September 1998.
[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] Freed, N., Klensin, J., and J. Postel, "Multipurpose Internet
Mail Extensions (MIME) Part Four: Registration Procedures", RFC 2048,
November 1996.
[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.
[VPIM2R2] Vaudreuil, G., and G. Parsons, "Voice Profile for Internet
Mail - version 2", <draft-ietf-vpim-vpimv2r2-01.txt>, November 2000.
[X420] ITU-T Recommendation X.420 (1996) - ISO/IEC 10021-7:1996,
Message handling systems: Interpersonal messaging.
8. Authors' Addresses
Glenn W. Parsons
Nortel Networks
P.O. Box 3511, Station C
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Ottawa, ON K1Y 4H7
Canada
Phone: +1-613-763-7582
Fax: +1-416-597-7005
EMail: gparsons@nortelnetworks.com
Gregory M. Vaudreuil
Lucent Technologies
17080 Dallas Parkway
Dallas, TX 75248-1905
United States
Phone/Fax: +1-972-733-2722
EMail:gregv@lucent.com
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9. Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
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or assist in its implementation may be prepared, copied, published
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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
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English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
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TASK FORCE DISCLAIMS 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.
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