Audio/Video Transport Internet Draft R. Kreuter Document: draft-kreuter-avt-rtp-clearmode-00.txt Siemens AG Expires: February 2003 August 2002 RTP payload format for a 64 kbit/s voice band data 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]. Table of Contents 1. Introduction...................................................2 2. Data stream handling and RTP header parameters.................2 3. Registration of audio/CLEARMODE................................3 Kreuter Expires - February 2003 [Page 1] 64kbit/s voice band data call August 2002 4. Security Considerations........................................3 5. References.....................................................4 6. Author's Address...............................................4 1. Introduction Voice over IP media gateways need to carry all data streams generated by analog TDM or ISDN narrowband terminals via an IP network. ISDN data terminals e.g. will produce data streams that are not compatible with a non-linear encoding as is used for voice. For these purposes, there exists a necessity for a transparent transport of 64 kbit/s data streams in RTP packets. This mode is often referred to as ôclear-channel dataö. 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 can be used for plain data streams (e.g. ISDN data), also referred to as ôclear-channel dataö. It is in accordance with RFC 2736 [8], which provides a guideline for the specification of new RTP payload formats. 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. Data stream handling and RTP header parameters CLEARMODE does not use any encoding or decoding. It just provides packetization. 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. By leaving one or more bits per octed unused, it is possible to transport lower transmission rates (56 kbit/s, 48 kbit/s, à) too. The Timestamp SHALL be set according [5] Kreuter Expires -February 2003 [Page 2] 64kbit/s voice band data call August 2002 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 Applications which use this media type: Media Gateways, transferring ISDN 64 kb/s data or other VoIP-related 64 kb/s data streams via an 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 Kreuter Expires -February 2003 [Page 3] 64kbit/s voice band data call August 2002 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. 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, ôGuidelines for Writers of RTP Payload Format Specificationsö, RFC 2736, December 1999 6. Author's Address Ruediger Kreuter Siemens AG 81359 Munich, Germany Phone: +49 89 722 62553 Email: Ruediger.Kreuter@icn.siemens.de Kreuter Expires -February 2003 [Page 4]