Network Working Group S. Ahmadi Request for Comments: 4424 February 2006 Updates: 4348 Category: Standards Track Real-Time Transport Protocol (RTP) Payload Format for the Variable-Rate Multimode Wideband (VMR-WB) Extension Audio Codec 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 (2006). Abstract This document is an addendum to RFC 4348, which specifies the RTP payload format for the Variable-Rate Multimode Wideband (VMR-WB) speech codec. This document specifies some updates in RFC 4348 to enable support for the new operating mode of VMR-WB standard (i.e., VMR-WB mode 4). These updates do not affect the existing modes of VMR-WB already specified in RFC 4348. The payload formats and their associated parameters, as well as all provisions, restrictions, use cases, features, etc., that are specified in RFC 4348 are applicable to the new operating mode with no exception. Table of Contents 1. Introduction ....................................................2 2. Conventions and Acronyms ........................................2 3. The Variable-Rate Multimode Wideband (VMR-WB) Extension .........2 4. The Necessary Updates in RFC 4348 ...............................4 5. Security Considerations .........................................6 6. Public Specification ............................................6 7. IANA Considerations .............................................7 8. References ......................................................7 8.1. Normative References .......................................7 8.2. Informative References .....................................7 Ahmadi Standards Track [Page 1]
RFC 4424 VMR-WB Extension RTP Payload Format February 2006 1. Introduction This document is an addendum to RFC 4348 [2] and contains the necessary updates for the support of the new operating mode of 3GPP2 VMR-WB standard [1]. The new mode of VMR-WB standard (VMR-WB mode 4), although operating at a lower data rate, has similar characteristics and functionalities compared to the existing modes of VMR-WB already included in RFC 4348 (e.g., variable bit rate, narrowband/wideband input/output speech/audio processing capability, continuous and discontinuous transmission, etc.). Therefore, all provisions and restrictions specified in RFC 4348 are applicable to all modes of the VMR-WB standard including the new mode, which is specified in this document. As a result, no new media type registration is required. The VMR-WB file format for transport of VMR-WB speech data in storage mode applications is specified in [1,4] and includes support for the new mode of operation. The following sections provide the necessary updates to RFC 4348 to enable support of VMR-WB mode 4. 2. Conventions and Acronyms 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]. The following acronyms are used in this document: 3GPP2 - Third Generation Partnership Project 2 CDMA - Code Division Multiple Access VMR-WB - Variable-Rate Multimode Wideband CMR - Codec Mode Request DTX - Discontinuous Transmission RTP - Real-Time Transport Protocol MIME - Multipurpose Internet Mail Extensions 3. The Variable-Rate Multimode Wideband (VMR-WB) Extension VMR-WB is the wideband speech-coding standard developed by the Third Generation Partnership Project 2 (3GPP2) for encoding/decoding wideband/narrowband speech content in multimedia services in 3G CDMA cellular systems [1]. VMR-WB is a source-controlled variable-rate multimode wideband speech codec. It has a number of operating modes, where each mode is a trade-off between voice quality and average data rate. The operating mode in VMR-WB (as shown in Table 2) is chosen based on the traffic condition of the network and the desired quality Ahmadi Standards Track [Page 2]
RFC 4424 VMR-WB Extension RTP Payload Format February 2006 of service. The desired average data rate (ADR) in each mode is obtained by encoding speech frames at permissible rates (as shown in Tables 1 and 3) compliant with CDMA2000 system depending on the instantaneous characteristics of input speech and the maximum and minimum rate constraints imposed by the network operator. The capabilities of the VMR-WB codec were extended through the addition of a new mode operating at lower average data rates, resulting in improved system capacity in IP and non-IP networks [1]. As a result of this extension, certain reserved table entries in RFC 4348 are used to include support for the new operating mode. VMR-WB mode 4 is compliant with all applicable provisions and restrictions specified in RFC 4348 [2]. Note that the existing table entries of RFC 4348 remain unchanged (e.g., frame types) and the original modes of VMR-WB are not affected by these updates. The existing flexibility in RFC 4348 for future extensions allows the addition of the new mode without any impact on the interoperability with earlier implementations of RFC 4348. The following sections provide the necessary updates that are required to be made in RFC 4348. The provisions and considerations for implementation, congestion control, and security remain identical to those specified in RFC 4348. Ahmadi Standards Track [Page 3]
RFC 4424 VMR-WB Extension RTP Payload Format February 2006 4. The Necessary Updates in RFC 4348 Table 1 of RFC 4348 is updated as follows: +---------------------------+-----------------+---------------+ | Frame Type | Bits per Packet | Encoding Rate | | | (Frame Size) | (kbps) | +---------------------------+-----------------+---------------+ | Full-Rate | 266 | 13.3 | | Full-Rate | 171 | 8.55 | | Half-Rate | 124 | 7.2 | | Half-Rate | 80 | 4.0 | | Quarter-Rate | 54 | 2.7 | | Quarter-Rate | 40 | 2.0 | | Eighth-Rate | 20 | 1.0 | | Eighth-Rate | 16 | 0.8 | | Blank | 0 | - | | Erasure | 0 | - | | Full-Rate with Bit Errors | 171 | 8.55 | +---------------------------+-----------------+---------------+ Table 1: CDMA2000 system permissible frame types and their associated encoding rates Note that the new permissible rates correspond to CDMA2000 rate-set I and have been added to the table. Table 2 of RFC 4348 is updated as follows to include VMR-WB mode 4 and VMR-WB mode 4 with maximum half-rate similar to that described in Section 2.4 of the revised VMR-WB specification [1]. Ahmadi Standards Track [Page 4]
RFC 4424 VMR-WB Extension RTP Payload Format February 2006 +-------+----------------------------------------------------------+ | CMR | VMR-WB Operating Modes | +-------+----------------------------------------------------------+ | 0 | VMR-WB mode 3 (AMR-WB interoperable mode at 6.60 kbps) | | 1 | VMR-WB mode 3 (AMR-WB interoperable mode at 8.85 kbps) | | 2 | VMR-WB mode 3 (AMR-WB interoperable mode at 12.65 kbps) | | 3 | VMR-WB mode 2 | | 4 | VMR-WB mode 1 | | 5 | VMR-WB mode 0 | | 6 | VMR-WB mode 2 with maximum half-rate encoding | | 7 | VMR-WB mode 4 | | 8 | VMR-WB mode 4 with maximum half-rate encoding | | 9-14 | (reserved) | | 15 | No Preference (no mode request is present) | +-------+----------------------------------------------------------+ Table 2: List of valid CMR values and their associated VMR-WB operating modes Note that CMR values 7 and 8 replace the reserved values in Table 2 of RFC 4348. Table 3 of RFC 4348 is updated as follows to include new frame types (FTs) associated with VMR-WB mode 4. Note that the sizes of the frames are unique and different, allowing for the use of header-free payload format for all modes of operations [2]. Ahmadi Standards Track [Page 5]
RFC 4424 VMR-WB Extension RTP Payload Format February 2006 +----+--------------------------------------------+-----------------+ | FT | Encoding Rate |Frame Size (Bits)| +----+--------------------------------------------+-----------------+ | 0 | Interoperable Full-Rate (AMR-WB 6.60 kbps) | 132 | | 1 | Interoperable Full-Rate (AMR-WB 8.85 kbps) | 177 | | 2 | Interoperable Full-Rate (AMR-WB 12.65 kbps)| 253 | | 3 | Full-Rate 13.3 kbps | 266 | | 4 | Half-Rate 6.2 kbps | 124 | | 5 | Quarter-Rate 2.7 kbps | 54 | | 6 | Eighth-Rate 1.0 kbps | 20 | | 7 | Full-Rate 8.55 kbps | 171 | | 8 | Half-Rate 4.0 kbps | 80 | | 9 | CNG (AMR-WB SID) | 35 | | 10 | Eighth-Rate 0.8 kbps | 16 | | 11 | (reserved) | - | | 12 | (reserved) | - | | 13 | (reserved) | - | | 14 | Erasure (AMR-WB SPEECH_LOST) | 0 | | 15 | Blank (AMR-WB NO_DATA) | 0 | +----+--------------------------------------------+-----------------+ Table 3: VMR-WB payload frame types for real-time transport Note that the new FT types associated with VMR-WB mode 4 replace the reserved entries 7, 8, and 10 in Table 3 of RFC 4348 and there are no changes in the existing entries of Table 3 of RFC 4348. The 'mode-set' MIME parameter value 4 is defined to indicate that VMR-WB mode 4 is supported and used. Note that the active modes of operation are negotiated and agreed by the IP terminals through the offer/answer model provided in Section 9.3 of RFC 4348 [2]. 5. Security Considerations Same as RFC 4348. 6. Public Specification The VMR-WB speech codec including the new mode is specified in following 3GPP2 specification C.S0052-A version 1.0. Transfer methods are specified in RFC 4348. Ahmadi Standards Track [Page 6]
RFC 4424 VMR-WB Extension RTP Payload Format February 2006 7. IANA Considerations This document updates the media type registered in [2]. IANA has added this document as reference to that media type registration and has modified the optional parameter mode-set in the registration. Section 9.1 of RFC 4348 [2] reads: Currently, this list includes modes 0, 1, 2, and 3 [1], but MAY be extended in the future. If such mode-set is specified during session initiation, the encoder MUST NOT use modes outside of the subset. If not present, all operating modes in the set 0 to 3 are allowed for the session. IANA will change "modes 0, 1, 2 and 3 [1]" to "modes 0, 1, 2, 3, and 4 [1] [2]", and change "modes in the set 0 to 3" to "modes in the set 0 to 4". [1] will be the IANA's reference to the original VMR-WB document (3GPP2 C.S0052-A v1.0) and [2] will be IANA's reference to this document (RFC 4424). 8. References 8.1. Normative References [1] 3GPP2 C.S0052-A v1.0 "Source-Controlled Variable-Rate Multimode Wideband Speech Codec (VMR-WB) Service Options 62 and 63 for Spread Spectrum Systems", 3GPP2 Technical Specification, April 2005, http://www.3gpp2.org/. [2] Ahmadi, S., "Real-Time Transport Protocol (RTP) Payload Format for the Variable-Rate Multimode Wideband (VMR-WB) Audio Codec", RFC 4348, January 2006. [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 8.2. Informative References [4] 3GPP2 C.S0050-A v1.0 "3GPP2 File Formats for Multimedia Services", 3GPP2 Technical Specification, October 2005, http://www.3gpp2.org/. Author's Address Dr. Sassan Ahmadi EMail: sassan.ahmadi@ieee.org Ahmadi Standards Track [Page 7]
RFC 4424 VMR-WB Extension RTP Payload Format February 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). 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 provided by the IETF Administrative Support Activity (IASA). Ahmadi Standards Track [Page 8]