VMR-WB Extension RTP: Real-Time Transport Protocol (RTP) Payload Format for the Variable-Rate Multimode Wideband (VMR-WB) Extension Audio Codec
A small update to the RTP payload format for the VMR-WB speech codec so it can carry the new mode 4.
Ahmadi, S., "Real-Time Transport Protocol (RTP) Payload Format for the Variable-Rate Multimode Wideband (VMR-WB) Extension Audio Codec", RFC 4424, DOI 10.17487/RFC4424, February 2006, <https://www.rfc-editor.org/info/rfc4424>.
@misc{rfc4424,
series = {Request for Comments},
number = 4424,
howpublished = {RFC 4424},
publisher = {RFC Editor},
doi = {10.17487/RFC4424},
url = {https://www.rfc-editor.org/info/rfc4424},
author = {S. Ahmadi},
title = {{Real-Time Transport Protocol (RTP) Payload Format for the Variable-Rate Multimode Wideband (VMR-WB) Extension Audio Codec}},
pagetotal = 8,
year = 2006,
month = feb,
} RFC text
Contents
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
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
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.
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].
+-------+----------------------------------------------------------+
| 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].
+----+--------------------------------------------+-----------------+
| 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.
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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Copyright (C) The Internet Society (2006).
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AI ELI5
On this page
§1An Addendum to RFC 4348
This document is an addendum to RFC 4348. It contains the updates needed to support the new operating mode of the 3GPP2 VMR-WB standard, called VMR-WB mode 4.
Mode 4 runs at a lower data rate but has similar characteristics to the existing modes, such as variable bit rate, narrowband and wideband processing, and continuous and discontinuous transmission. For that reason all provisions and restrictions of RFC 4348 apply to every mode including the new one, and no new media type registration is required.
The file format for storing VMR-WB data covers the new mode as well, and is specified outside this RFC.
This is a short add-on page to an existing rulebook. The new setting follows the same rules, so almost nothing needs to change.
§3What VMR-WB Is and What Changed
VMR-WB is a wideband speech-coding standard developed by 3GPP2 for encoding and decoding wideband and narrowband speech in multimedia services on 3G CDMA cellular systems. It is source-controlled and variable-rate, with several operating modes. Each mode trades voice quality against average data rate, and the mode is chosen based on network traffic conditions and the desired quality of service.
The new mode works at lower average data rates, which improves system capacity in IP and non-IP networks. To add it, certain reserved table entries in RFC 4348 are used. The existing entries, such as the frame types, stay unchanged, and the original modes are not affected.
Because RFC 4348 already allowed for future extensions, the addition does not affect interoperability with earlier implementations. Implementation, congestion control and security provisions stay identical to RFC 4348.
The codec is like a dimmer for voice quality. The new setting uses less data, and it fits into a slot that was left empty on purpose.
§4.1Rates and Mode Requests
Table 1 of RFC 4348 lists the frame types permitted on a CDMA2000 system with their sizes and encoding rates. RFC 4424 replaces it with a table that adds the new permissible rates, which correspond to CDMA2000 rate-set I. Examples are a 171-bit full-rate frame at 8.55 kbps and a 16-bit eighth-rate frame at 0.8 kbps.
Table 2 of RFC 4348 maps Codec Mode Request (CMR) values to VMR-WB operating modes. The update adds CMR value 7 for VMR-WB mode 4 and CMR value 8 for mode 4 with maximum half-rate encoding. These replace values that were reserved. CMR 15 still means no preference, and 9 to 14 stay reserved.
A mode request is a number you hold up to ask for a setting. Numbers 7 and 8 used to be blank, and now they ask for the new setting.
- 6Mode 2, max half-rate — VMR-WB mode 2 with maximum half-rate encoding.
- 7Mode 4 — VMR-WB mode 4; replaces a reserved value.
- 8Mode 4, max half-rate — VMR-WB mode 4 with maximum half-rate encoding; replaces a reserved value.
- 9-14Reserved — Still reserved.
- 15No Preference — No mode request is present.
§4.2New Frame Types
Table 3 of RFC 4348 lists the payload frame types (FTs) for real-time transport. The update fills three reserved entries: FT 7 is full-rate at 8.55 kbps with 171 bits, FT 8 is half-rate at 4.0 kbps with 80 bits, and FT 10 is eighth-rate at 0.8 kbps with 16 bits. Existing entries do not change.
The RFC points out that the frame sizes are unique and different, which allows a header-free payload format for all modes of operation.
Every kind of voice packet has a different size, so the receiver can tell which kind it got just by measuring it. The new kinds have new sizes.
- 7Full-Rate 8.55 kbps — 171 bits; replaces a reserved entry.
- 8Half-Rate 4.0 kbps — 80 bits; replaces a reserved entry.
- 10Eighth-Rate 0.8 kbps — 16 bits; replaces a reserved entry.
§4.3Negotiating Mode 4
The mode-set MIME parameter value 4 is defined to show that VMR-WB mode 4 is supported and used. The active modes are negotiated and agreed by the IP terminals through the offer/answer model in Section 9.3 of RFC 4348.
Two phones agree on which settings they will both use before they start talking, and now setting 4 can be on that list.
§5Security Considerations
The security section is a single line: the considerations are the same as in RFC 4348. The introduction to the update also says that implementation, congestion control and security provisions are identical to that RFC.
Nothing new is risky here, so the safety rules from the older rulebook still apply.
§7Changes to the Media Type Registration
This document updates the media type registered by RFC 4348. IANA added this RFC as a reference to that registration and modified the optional mode-set parameter.
The registration text changes from modes 0, 1, 2 and 3 to modes 0, 1, 2, 3 and 4, and from the set 0 to 3 to the set 0 to 4. The original VMR-WB document is 3GPP2 C.S0052-A v1.0, and RFC 4424 is IANA's second reference.
The official list of allowed settings was edited so that setting 4 is now written on it.