RFC4424: Real-Time Transport Protocol (RTP) Payload Format for the Variable-Rate Multimode Wideband (VMR-WB) Extension Audio Codec
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Related keywords:
(speech codec)
(variable-rate multicode wideband speech codec)
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
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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
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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.
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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].
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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].
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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.
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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
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RFC 4424 VMR-WB Extension RTP Payload Format February 2006
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