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Versions: (draft-jones-avt-text-red) 00 01 02 03 04 05 RFC 4102

AVT Working Group
Internet Draft                                                 P. Jones
<draft-ietf-avt-text-red-00.txt>                    Cisco Systems, Inc.
Expires: May 2004                                         December 2003

                Registration of the text/red MIME Sub-Type

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   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
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   This document defines the text/red MIME sub-type.  The actual RTP
   packetization for this MIME type is specified in RFC 2198.

1. Introduction

   Text is an important component of any multimedia communication
   system.  Like audio, the transport of text can benefit from the use
   of redundancy in order to improve reliability and end-user

   RFC 2198 [2] defines an RTP [3] payload format for audio data.  The
   format defined in that document is quite suitable for providing
   redundancy for text, as well as audio.

   RFC 2793 [1] specifies one usage of RFC 2198 and this MIME type for
   the transport of redundant text data.

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              Registration of the text/red MIME Sub-Type December 2003

   This memo provides the MIME sub-type registration information for
   text/red.  While this document focuses on the use of this MIME sub-
   type in SDP [6], the application of this MIME sub-type is not
   restricted to SDP.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [4].

3. IANA Considerations

   One new MIME sub-type is to be registered, as described below:

      MIME media type name: text

      MIME subtype name: RED

      Required parameters:
        rate: the RTP clock rate of the payload carried within the
        RTP packet.  Typically, this rate is 1000, but other rates
        may be specified.

        pt: a comma-separated list of RTP payload types.  Because
        comma is a special character, the list must be a quoted-string
        (enclosed in double quotes).  For static payload types, each
        list element is simply the type number.  For dynamic payload
        types, each list element is a mapping of the dynamic payload
        type number to an embedded MIME content-type specification for
        the payload format corresponding to the dynamic payload type.
        The format of the mapping is:

           dynamic-payload-type "=" content-type

        If the content-type string includes a comma, then the
        content-type string MUST be a quoted-string.  If the content-
        type string does not include a comma, it MAY still be quoted.
        Since it is part of the list which must itself be a quoted-
        string, that means the quotation marks MUST be quoted with
        backslash quoting as specified in RFC 2045 [5].  If the content-
        type string itself contains a quoted-string, then the
        requirement for backslash quoting is recursively applied.

      Optional parameters: ptime, maxptime

      Encoding considerations:
        This type is only defined for transfer via RTP.

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              Registration of the text/red MIME Sub-Type December 2003

      Security considerations: Refer to section 4.

      Interoperability considerations: none

      Published specification: RFC 2198

      Applications which use this media type:
        Text streaming and conferencing tools.

      Additional information: none

      Person & email address to contact for further information:
        Paul E. Jones
        E-mail: paulej@packetizer.com

      Intended usage: COMMON

      Author                        / Change controller:
        Paul E. Jones               | IETF avt WG
        paulej@packetizer.com       |

4. Mapping to SDP Parameters

   The information carried in the MIME media type specification has a
   specific mapping to fields in the Session Description Protocol (SDP)
   [11], which is commonly used to describe RTP sessions.  When SDP is
   used to specify sessions employing the RFC 2198 in a text session,
   the mapping is as follows:

   -  The MIME type ("text") goes in SDP "m=" as the media name.

   -  The MIME subtype (RED) goes in SDP "a=rtpmap"
      as the encoding name.  The RTP clock rate in "a=rtpmap" MUST be
      set equal to the text payload formats carried as primary encoding.

   -  The parameters "ptime" and "maxptime" go in the SDP "a=ptime"
      and "a=maxptime" attributes, respectively.

   -  The pt parameter is mapped to an a=fmtp attribute by eliminating
      the parameter name (pt) and changing the commas to slashes.  For
      example, 'pt="101,102"' maps to 'a=fmtp:99 101/102'

   An example of SDP is:

       m=text 11000 RTP/AVP 98 100
       a=rtpmap:98 t140/1000
       a=rtpmap:100 red/1000

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              Registration of the text/red MIME Sub-Type December 2003

       a=fmtp:100 98/98

5. Security Considerations

   The security considerations listed in RFC 2198 apply.  Further, it
   should be understood that text data, perhaps even more so than audio
   data, is susceptible to unwanted modification that may lead to
   undesired results.

6. Normative References

   [1] Hellstrom, G., "RTP Payload for Text Conversation", RFC 2793,
       May 2000.

   [2] Perkins, C., et al., "RTP Payload for Redundant Audio Data", RFC
       2198, September 1997.

   [3] Schulzrinne, et al., "RTP: A Transport Protocol for Real-Time
       Applications", RFC 3550, July 2003.

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

   [5] Freed, N., Borenstein, N., "Multipurpose Internet Mail
       Extensions (MIME) Part One: Format of Internet Message Bodies",
       RFC 2045, November 1996.

   [6] Handley, M., Jackson, V., "SDP: Session Description Protocol",
       RFC 2327, April 1998.

   [7] Casner, S., Hoschka, P., "MIME Type Registration of RTP Payload
       Formats", RFC 3555, July 2003.

7. Author's Address

   Paul E. Jones
   Cisco Systems, Inc.
   7025 Kit Creek Rd.
   Research Triangle Park, NC 27709
   Phone: +1 919 392 6948
   Email: paulej@packetizer.com

8. Intellectual Property Right Considerations

   The IETF takes no position regarding the validity or scope of any
   intellectual property 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; neither does it represent that it

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              Registration of the text/red MIME Sub-Type December 2003

   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication 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 implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive

9. Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an


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

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