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

Network Working Group
Internet Draft                                                 P. Jones
<draft-ietf-avt-text-red-05.txt>                    Cisco Systems, Inc.
Expires: October 2004                                          May 2004



                 Registration of the text/red MIME Sub-Type


Status of this Memo

    By submitting this Internet-Draft, I (we) certify that any applicable
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    This document is a submission of the IETF AVT WG. Comments should be
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Abstract

    This document defines the text/red MIME sub-type.  The actual RTP
    packetization for this MIME type is specified in RFC 2198.

    [Note to RFC Editor: All references to RFC XXXX are to be replaced by
    references to the RFC number of this memo when published.]

1.   Introduction





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    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
    experience.

    RFC 2198 [1] defines an RTP [2] payload format for redundant audio
    data.  The format defined in that document is quite suitable for
    providing redundancy for text, as well as audio.

    RFC 2793 [7] specifies one usage of RFC 2198 and the text/red MIME
    type for the transport of redundant text data.

    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 [5], 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",
    "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
    document are to be interpreted as described in RFC 2119 [3].

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.  This parameter MUST be set equal to the clock rate
          of the text payload format carried as the primary encoding.

          pt: a comma-separated ordered list of RTP payload types
          enumerating the primary, secondary, etc., in accordance with
          RFC 2198.  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 "=3D" content-type



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          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 [4].  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.

       Security considerations: Refer to section 5 of RFC XXXX.

       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)
    [5], 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=3D" as the media name.

    -  The value of the parameter "rate" goes in SDP "a=3Drtpmap".

    -  The MIME subtype (RED) goes in SDP "a=3Drtpmap"
       as the encoding name.


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    -  The parameters "ptime" and "maxptime" go in the SDP "a=3Dptime"
       and "a=3Dmaxptime" attributes, respectively.

    -  The pt parameter is mapped to an a=3Dfmtp attribute by eliminating
       the parameter name (pt) and changing the commas to slashes.  For
       example, 'pt=3D"101,102"' maps to 'a=3Dfmtp:99 101/102', where =
'99' is
       the payload type of the redundancy frames.  Note that the single
       quote marks (') used in this example is not present in the
       actual message encoding, but is present here only for readability.
       The level of redundancy is shown by the number of elements in the
       payload type list.

    Any dynamic payload type in the list MUST be represented by its
    payload type number and not by its content-type. The mapping of
    payload types to the content-type is done using the normal SDP
    procedures with "a=3Drtpmap".

    An example of SDP is:

        m=3Dtext 11000 RTP/AVP 98 100
        a=3Drtpmap:98 t140/1000
        a=3Drtpmap:100 red/1000
        a=3Dfmtp:100 98/98

    For each redundancy payload type defined, the ordering of the primary
    and redundancy encoding(s) is fixed. If more than one combination of
    primary and redundancy encoding(s) is desired, multiple redundancy
    payload types needs to be defined.

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.  To prevent modification of the primary, secondary
    or header information, payload integrity protection over at least the
    complete RTP packet is RECOMMENDED, for example using SRTP [8].

6.   Normative References

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

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

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


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

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

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

7.   Informative References

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

    [8] Baugher, et al., "The Secure Real-time Transport Protocol", RFC
        3711, March 2004.

8.   Author's Address

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

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.

Disclaimer

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    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




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Acknowledgement

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

























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