Audio/Video Transport Internet Draft R. Kreuter Document: draft-kreuter-avt-rtp-clearmode-02.txt Siemens AG Expires: August 2003 February 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 transparently in RTP packets, using a pseudo-codec called "CLEARMODE". It also serves as registration for a related MIME type called "audio/CLEARMODE". 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 [2]. Kreuter Expires - August 2003 [Page 1] 64kbit/s voice band data call February 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. Security Considerations.......................................4 5. References....................................................4 6. Author's Address..............................................5 1. Introduction Voice over IP media gateways need to carry all data streams generated by analog TDM 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 [5] 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 [8], 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 [4], which defines procedures for registration of new MIME types within the IETF tree. 2. 64 kbit/s data stream handling and RTP header parameters The profile 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.) CLEARMODE does not use any encoding or decoding. It just provides packetization. Kreuter Expires -August 2003 [Page 2] 64kbit/s voice band data call February 2003 The payload handling for CLEARMODE is similar to the PCMU or PCMA handling described in [9]. Each CLEARMODE octet is octet-aligned in a RTP packet. The sign bit of each CLEARMODE octet corresponds to the most significant bit of the octet in the RTP packet (i.e., assuming the CLEARMODE samples are handled as octets on the host machine, the sign bit is the most significant bit of the octet as defined by the host machine format). A sample rate of 8000 Hz is used. Note, that the payload format described here assumes that the data to be handled is sample oriented with one octet (8bits) per sample. Together with the 8000 Hz sample rate this calculates to a 64 kbit/s transmission rate per channel. The Timestamp SHALL be set according [5] 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. 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 This represents the packet length in milliseconds [7]. Encoding considerations: This type is only defined for transfer via RTP [5]. Security considerations: Implementations using the profile defined in this specification are subject to the security considerations discussed in the RTP specification [5]. Interoperability considerations: none Published specification: This document Kreuter Expires -August 2003 [Page 3] 64kbit/s voice band data call February 2003 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. Security Considerations Implementations using the profile defined in this specification are subject to the security considerations discussed in the RTP specification [5]. 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. 5. References 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 2 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 3 Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures", RFC 2048, November 1996. 4 Casner, S. and P. Hoschka, "MIME type registration of RTP payload formats", Work in Progress. 5 Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: a transport protocol for real-time applications", RFC 1889, January 1996. Kreuter Expires -August 2003 [Page 4] 64kbit/s voice band data call February 2003 6 Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: transport protocol for real-time applications", Work in Progress. 7 Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. 8 Handley, M. and C. Perkins, "Guidelines for Writers of RTP Payload Format Specifications", RFC 2736, December 1999 9 Schulzrinne, H., Casner, S., "RTP Profile for Audio and Video Conferences with Minimal Control", Work in Progress 6. Author's Address Ruediger Kreuter Siemens AG 81359 Munich, Germany Phone: +49 89 722 62553 Email: ruediger.kreuter@siemens.com Kreuter Expires -August 2003 [Page 5]