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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-01.txt>                    Cisco Systems, Inc.
       Expires: August 2004                                     February 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
          other groups may also distribute working documents as Internet-
          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."
          [Note to the RFC-Editor: Change XXXX to the RFC number of this memo.
               In reference no [7], change reference to RFC number of SRTP when
          The list of current Internet-Drafts can be accessed at
          The list of Internet-Draft Shadow Directories can be accessed at
          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
          experience. The name "red" used comes form the use of redundancy.
          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 February 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",
          "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
          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 that MAY occur in
               the redundancy payload. 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: See 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)
          [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 ( examples of text from SDP are surrounded
          by "" or '' in this memo. These quotes shall be removed in practical
          use of SDP if not otherwise stated here.):
          -  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 rate parameterĀ“s value goes as rate in
             the "a=rtpmap" attribute.
          -  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' where 99 is the
             payload type number used to refer to the redundant format.
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                     Registration of the text/red MIME Sub-Type February 2003
             Any dynamic payload type in the list, SHALL NOT include its
             content-type, only the payload type number. The mapping of payload types
             to the content-type is done using the normal SDP procedures with
          An example of SDP is:
              m=text 11000 RTP/AVP 98 100
              a=rtpmap:98 t140/1000
              a=rtpmap:100 red/1000
              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.
          To prevent modification of the primary, secondary or header
          information, payload integrity protection over at least the
          complete RTP packet is recommend, for example using SRTP [7].
       6. References
       6.1 Informative references
          [1] Hellstrom, G., "RTP Payload for Text Conversation", RFC 2793,
              May 2000.
       6.2. Normative references
          [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] Baugher, McGrew, Carrara, Naslund,Norrman, The Secure Real-Time
              Transport Protocol, draft-ietf-avt-srtp-09.txt, July 2003.
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                     Registration of the text/red MIME Sub-Type February 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
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          pertain to the implementation or use of the technology described in
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          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.
          This document and translations of it may be copied and furnished to
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          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.
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                     Registration of the text/red MIME Sub-Type February 2003
          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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