Audio/Video Transport Internet Draft R. Kreuter Document: draft-ietf-avt-rtp-clearmode-00.txt Siemens AG Expires: October 2003 April 2003 RTP payload format for a 64 kbit/s transparent call Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. 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 describes how to carry 64 kbit/s data streams trans- parently in RTP packets, using a pseudo-codec called "Clearmode". It also serves as registration for a related MIME type called "audio/clearmode". "Clearmode" is a basic feature of VoIP media gateways. 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 RFC2119 [2]. Kreuter Expires - October 2003 [Page 1] RTP-Clearmode April 2003 Table of Contents 1. Introduction..................................................2 2. 64 kbit/s data stream handling and RTP header parameters......2 3. Registration of audio/clearmode...............................3 4. Mapping to SDP parameters.....................................4 5. Security Considerations.......................................5 6. References....................................................5 7. Author's Address..............................................6 8. IPR Notice....................................................6 9. Full Copyright Statement......................................6 1. Introduction Voice over IP media gateways need to carry all data streams generated by analog or ISDN terminals via an IP network. ISDN wideband speech terminals do not rely on a voice data processing (e.g. echo cancellation or DTMF detection) within a Voice over IP media gateway. And ISDN data terminals e.g. will produce data streams that are not compatible with a non-linear encoding as is used for voice. For such applications, there exists a necessity for a transparent relay of 64 kbit/s data streams in RTP packets. This mode is often referred to as "clear-channel data" or "64 kbit/s unrestricted". No encoder/decoder is needed in that case, but a unique RTP [6] payload type is necessary and a related MIME type is to be registered for signaling purposes. This payload format document describes a pseudo-codec called "Clearmode", for sample-oriented 64 kbit/s data streams with 8 bits per sample. It is in accordance with RFC 2736 [3], which provides a guideline for the specification of new RTP payload formats. Examples for the use of Clearmode in current VoIP media gateways are the transfer of "ISDN 7 kHz voice" and "ISDN data". This document also serves as the MIME type registration according RFC 2048 [5], which defines procedures for registration of new MIME types within the IETF tree. 2. 64 kbit/s data stream handling and RTP header parameters Clearmode does not use any encoding or decoding. It just provides packetization. Kreuter Expires -October 2003 [Page 2] RTP-Clearmode April 2003 Clearmode assumes that the data to be handled is sample oriented with one octet (8bits) per sample. There is no restriction on the number of samples per packet. The payload handling for Clearmode is similar to the PCMU or PCMA handling described in [7]. Each Clearmode octet SHALL be octet- aligned in a RTP packet. A sample rate of 8000 Hz is used. This calculates to a 64 kbit/s transmission rate per channel. The Timestamp SHALL be set according to [6]. The marker bit is always zero. Silence suppression is not applicable for Clearmode data streams. The payload type is dynamically assigned by means outside the scope of this document. This document specifies the use of RTP over unicast and multicast UDP as well as TCP. (This does not preclude the use of this definition when RTP is carried by other lower-layer protocols.) 3. Registration of audio/clearmode To: ietf-types@iana.org Subject: Registration of MIME media type audio/clearmode MIME media type name: audio MIME subtype name: clearmode Required parameters: none Optional parameters: ptime, maxptime "ptime" gives the length of time in milliseconds represented by the media in a packet [9]. "maxptime" represents the maximum amount of media which can be encapsulated in each packet, expressed as time in milliseconds [9]. Encoding considerations: This type is defined for transfer via RTP [6]. Security considerations: Implementations using the profile defined in this Kreuter Expires -October 2003 [Page 3] RTP-Clearmode April 2003 specification are subject to the security considerations discussed in the RTP specification [6]. Interoperability considerations: none Published specification: This document Applications which use this media type: Voice over IP Media Gateways, transferring "ISDN 64 kb/s data" or "ISDN 7 kHz voice" or other VoIP-related 64 kbit/s data streams via a RTP connection. Additional information: none Intended usage: COMMON Author/Change controller: This registration is part of the IETF registration tree. 4. Mapping to SDP parameters Parameters are mapped to SDP [9] in a standard way. o The MIME type (audio) goes in SDP "m=" as the media name. o The MIME subtype (clearmode) goes in SDP "a=rtpmap" as the encoding name. o The optional parameters "ptime" and "maxptime" go in the SDP "a=ptime" and "a=maxptime" attributes, respectively. An example mapping is as follows: audio/clearmode; ptime=10 m=audio 12345 RTP/AVP 97 a=rtpmap:97 CLEARMODE/8000 a=ptime:10 Note that the payload format (encoding) names defined in the RTP Profile are commonly shown in upper case. MIME subtypes are commonly shown in lower case. These names are case-insensitive in both places. Similarly, parameter names are case-insensitive both in MIME types and in the default mapping to the SDP a=fmtp attribute. Kreuter Expires -October 2003 [Page 4] RTP-Clearmode April 2003 5. Security Considerations Implementations using the profile defined in this specification are subject to the security considerations discussed in the RTP specification [6]. This profile does not specify any different security services. The primary function of this profile is to add a transparent transport for a 64 kbit/s data stream. Confidentiality of the media streams is achieved by encryption. Since there is no processing of the data stream other than packetization and depacketization, there is no interference to an end-to-end encryption mechanism. 6. References [1] S. Bradner, "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [2] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 [3] M. Handley and C. Perkins, "Guidelines for Writers of RTP Payload Format Specifications", RFC 2736, December 1999 [4] N. Freed, N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies ", RFC 2045, November 1996. [5] N. Freed, J. Klensin and J. Postel, "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures", RFC 2048, November 1996. [6] H. Schulzrinne, S. Casner, R. Frederick and V. Jacobson, "RTP: transport protocol for real-time applications", revision of RFC 1889 work in Progress. [7] H. Schulzrinne, S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", revision of RFC 1890 work in Progress [8] S. Casner and P. Hoschka, "MIME type registration of RTP payload formats", Work in Progress. [9] M. Handley, V. Jacobson and C. Perkins, "SDP: Session Description Protocol", revision of 2327, work in progress. Kreuter Expires -October 2003 [Page 5] RTP-Clearmode April 2003 [10] H. Schulzrinne, S. Casner, R. Frederick and V. Jacobson, "RTP: a transport protocol for real-time applications", RFC 1889, January 1996. [11] H. Schulzrinne "RTP Profile for Audio and Video Conferences with Minimal Control", RFC 1890, January 1996. [12] M. Handley and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. 7. Author's Address Ruediger Kreuter Siemens AG 81359 Munich, Germany Phone: +49 89 722 62553 Email: ruediger.kreuter@siemens.com 8. IPR Notice The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to per- tain 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 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 implementers 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 (date). All Rights Reserved. Kreuter Expires -October 2003 [Page 6] 64kbit/s voice band data call April 2003 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. Kreuter Expires -October 2003 [Page 7]