Skip to main content

Registration of the text/red MIME Sub-Type
RFC 4102

Document Type RFC - Proposed Standard (June 2005) Errata
Updated by RFC 6354
Author Paul Jones
Last updated 2013-03-02
RFC stream Internet Engineering Task Force (IETF)
Formats
Additional resources Mailing list discussion
IESG Responsible AD Allison J. Mankin
Send notices to (None)
RFC 4102
Network Working Group                                           P. Jones
Request for Comments: 4102                           Cisco Systems, Inc.
Category: Standards Track                                      June 2005

               Registration of the text/red MIME Sub-Type

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document defines the text/red MIME sub-type.  "Red" is short for
   redundant.  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.

   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 4103 [8] 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.

Jones                       Standards Track                     [Page 1]
RFC 4102                 text/red MIME Sub-Type                June 2005

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 has been registered by the IANA, 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 "=" 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.  Because it is
      part of the list, which must itself be a quoted-string, 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 (these attributes are originally
      defined in RFC 2327 [5] and RFC 3267 [6], respectively)

   Restrictions on Usage:
      This type is defined only for transfer via RTP.
      It shall not be defined for a storage format.

Jones                       Standards Track                     [Page 2]
RFC 4102                 text/red MIME Sub-Type                June 2005

   Encoding considerations:
      See restrictions on Usage above; this section is included per
      the requirements in RFC 3555 [7].

   Security considerations: Refer to section 5 of RFC 4102.

   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:
      Paul E. Jones
      paulej@packetizer.com

   Change Controller:
      AVT Working Group delegated from the IESG

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=" as the media name.

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

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

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

Jones                       Standards Track                     [Page 3]
RFC 4102                 text/red MIME Sub-Type                June 2005

   -  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 of the redundancy frames.  Note that the
      single quote marks (') used in this example are not present in the
      actual message encoding, but are 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=rtpmap".

   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

   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 [9].

Jones                       Standards Track                     [Page 4]
RFC 4102                 text/red MIME Sub-Type                June 2005

6.  Normative References

   [1] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., Handley, M.,
       Bolot, J., Vega-Garcia, A., and S. Fosse-Parisis, "RTP Payload
       for Redundant Audio Data", RFC 2198, September 1997.

   [2] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
       "RTP: A Transport Protocol for Real-Time Applications", STD 64,
       RFC 3550, July 2003.

   [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.

   [4] Freed, N. and N. Borenstein, "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] Sjoberg, J., Westerlund, M., Lakaniemi, A., and Q. Xie, "Real-
       Time Transport Protocol (RTP) Payload Format and File Storage
       Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate
       Wideband (AMR-WB) Audio Codecs", RFC 3267, June 2002.

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

7.  Informative References

   [8] Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation",
       RFC 4103, June 2005.

   [9] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
       Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC
       3711, March 2004.

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

Jones                       Standards Track                     [Page 5]
RFC 4102                 text/red MIME Sub-Type                June 2005

Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   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.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights 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; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at ietf-
   ipr@ietf.org.

Acknowledgement

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

Jones                       Standards Track                     [Page 6]