





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]

