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Real-Time Transport Protocol (RTP) Payload Format for the Variable-Rate Multimode Wideband (VMR-WB) Extension Audio Codec

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 4424.
Author Sassan Ahmadi
Last updated 2018-12-20 (Latest revision 2005-10-21)
Replaces draft-ahmadi-avt-rtp-vmr-wb-extension
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
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IESG IESG state Became RFC 4424 (Proposed Standard)
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Responsible AD Allison J. Mankin
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Audio Video Transport WG                                  Sassan Ahmadi
Expires: April 19, 2006                                October 19, 2005

      Real-Time Transport Protocol (RTP) Payload Format for the         
   Variable-Rate Multimode Wideband (VMR-WB) Extension Audio Codec 

Status of this Memo

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   This document is an addendum to RFC xxxx, which specifies the 
   RTP payload format for the Variable-Rate Multimode Wideband (VMR-WB) 
   speech codec. This document specifies some updates in RFC xxxx 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 xxxx. 

   The payload formats and their associated parameters, as well as all 
   provisions, restrictions, use cases, features, etc. that are 
   specified in RFC xxxx are applicable to the new operating mode with 
   no exception. 

Sassan Ahmadi                Standards Track                   [page 1]

INTERNET-DRAFT    VMR-WB Extension RTP Payload Format    October 2005

Table of Contents

2.Conventions and Acronyms.....................................2
3.The Variable-Rate Multimode Wideband (VMR-WB) Extension......3
4.The Necessary Updates in RFC xxxx............................3
5.Security Considerations......................................5
6.Public Specification.........................................5
7.IANA Considerations..........................................5
   Normative References........................................5
   Informative References......................................6
Author's Address...............................................6
IPR Notice.....................................................6
Copyright Notice...............................................7

1. Introduction

   This document is an addendum to RFC xxxx [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; i.e., VMR-WB
   mode 4, while operating at a lower data rate, has similar 
   characteristics and functionalities compared to the existing modes 
   of VMR-WB already included in RFC xxxx (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 xxxx 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; i.e., 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 xxxx to enable support of VMR-WB mode 4.

2. Conventions and Acronyms

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   document are to be interpreted as described in RFC2119 [3].

   The following acronyms are used in this document:

    3GPP2  - The Third Generation Partnership Project 2
    CDMA   - Code Division Multiple Access
    VMR-WB - Variable-Rate Multimode Wideband Codec
    CMR    - Codec Mode Request
    DTX    - Discontinuous Transmission

Sassan Ahmadi                Standards Track                   [page 2]

INTERNET-DRAFT    VMR-WB Extension RTP Payload Format    October 2005

    RTP    - Real-Time Transport Protocol
    MIME   - Multipurpose Internet Mail Extension

3. The Variable-Rate Multimode Wideband (VMR-WB) Extension

   VMR-WB is the wideband speech-coding standard developed by
   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 tradeoff 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 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 xxxx 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 xxxx [2]. Note that the existing table 
   entries of RFC xxxx remain unchanged (e.g., frame types, etc.) and 
   the original modes of VMR-WB are not affected by these updates.

   The existing flexibility in RFC xxxx for future extensions allows 
   the addition of the new mode without any impact on the 
   interoperability with earlier implementations of RFC xxxx.

   The following sections provide the necessary updates that are 
   required to be made in RFC xxxx.

   The provisions and considerations for implementation, congestion 
   control, and security remain identical to those specified in
   RFC xxxx. 

4. The Necessary Updates in RFC xxxx

   Table 1 of RFC xxxx is updated as follows:

Sassan Ahmadi                Standards Track                   [page 3]

INTERNET-DRAFT    VMR-WB Extension RTP Payload Format    October 2005
   |        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 have been added to the table.
   Table 2 of RFC xxxx 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].   

   | 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 xxxx.

   Table 3 of RFC xxxx is updated as follows to include new frame types
   (FT) associated with VMR-WB mode 4.

   Note that the size of the frames are unique and different, allowing 
   for the use of header-free payload format for all modes of 
   operations [2].

Sassan Ahmadi                Standards Track                   [page 4]

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| 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 xxxx and there are 
   no changes in the existing entries of Table 3 of RFC xxxx.

   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 xxxx [2].

5. Security Considerations

   Same as RFC xxxx

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 xxxx.

7. IANA Considerations


Normative References

Sassan Ahmadi                Standards Track                   [page 5]

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   [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.

   [2]  S. Ahmadi, "Real-Time Transport Protocol (RTP) Payload Formats 
        for the Variable-Rate Multimode Wideband (VMR-WB) Audio Codec", 
        RFC xxxx, Internet Engineering Task Force, October 2005.

   [3]  S. Bradner, "Key words for use in RFCs to Indicate
        Requirement Levels", BCP 14, RFC 2119, Internet Engineering 
        Task Force, March 1997.

Informative References

   [4]  3GPP2 C.S0050-A v1.0 "3GPP2 File Formats for Multimedia 
        Services", 3GPP2 Technical Specification, October 2005. 
   Any 3GPP2 document can be downloaded from the 3GPP2 web 
   server, "", see specifications.

Author's Address

    Dr. Sassan Ahmadi             Email: 

    This Internet-Draft expires in six months from October 19, 2005.

RFC Editor Considerations

    The RFC editor is requested to replace all occurrences of xxxx with
    the RFC number that reference [2] will receive.

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Sassan Ahmadi                Standards Track                   [page 6]

INTERNET-DRAFT    VMR-WB Extension RTP Payload Format    October 2005

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Copyright Notice

    Copyright (C) The Internet Society (2005).  This document is 
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    This document and the information contained herein are provided on

Sassan Ahmadi                Standards Track                   [page 7]