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 other groups may also distribute working documents as Internet- Drafts. 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 http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract 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. 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. Jones Expires - May 2004 [Page 1]
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", "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. 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. Jones Expires - May 2004 [Page 2]
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 Jones Expires - May 2004 [Page 3]
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 Jones Expires - May 2004 [Page 4]
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 Director. 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 others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph 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 Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Jones Expires - May 2004 [Page 5]
