RFC 4424

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

📅 published February 2006, from ietf

RFC 4424 💖 Real-Time Transport Protocol (RTP) Payload Format for the Variable-Rate Multimode Wideband (VMR-WB) Extension Audio Codec

Okay bestie, let's start with the basics 🎀. This one is by S. Ahmadi and it's dated February 2006 📅. It's a Standards Track doc, which means it's an official Internet spec and not just a vibe. It came out of the Network Working Group 🌸, and it updates RFC 4348 ✨. That's the doc it's basically an addendum to, so you'll want to keep 4348 open in another tab 💅.

Status of This Memo 📜

So this document is an Internet standards track protocol for the Internet community, and it's asking for discussion and suggestions for improvements 🫶. If you want to know where this protocol stands, check the current edition of the "Internet Official Protocol Standards" (STD 1). Also, distribution of this memo is unlimited, so share it with everyone 🦋.

Copyright Notice 🌈

Copyright (C) The Internet Society (2006). Yep, that's the legal bit, and it's all there ✨.

Abstract 🔮

Okay, big picture. This doc is an addendum to RFC 4348, which covers the RTP payload format for the VMR-WB speech codec 🎤. What's new is that it adds support for a new operating mode of VMR-WB, called VMR-WB mode 4 🍓. The updates don't touch the existing modes that RFC 4348 already covers, so those are totally safe 🙈.

The payload formats, their parameters, and all the provisions, restrictions, use cases, features, and so on from RFC 4348 still apply to the new mode, with no exceptions 👑. Literally everything carries over.

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 doc is an addendum to RFC 4348 [2], and it has the updates needed to support the new operating mode of the 3GPP2 VMR-WB standard [1] 🧚. VMR-WB mode 4 runs at a lower data rate, but it's giving the same energy as the modes RFC 4348 already has. It's still variable bit rate, it still handles narrowband and wideband input and output for speech and audio, and it still does continuous and discontinuous transmission 🎀. So everything in RFC 4348 applies to every mode, including this new one. Which means no new media type registration is required 💅.

The VMR-WB file format for carrying VMR-WB speech in storage mode applications is defined in [1,4], and it already supports the new mode 📂.

The next sections list the updates to RFC 4348 that turn on 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] 📖. These are the capital-letter key words, so pay attention to them 👀.

Here are the acronyms used in this doc 💜:

   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 🌸

Okay, so VMR-WB is the wideband speech codec that 3GPP2 developed for encoding and decoding wideband and narrowband speech in multimedia services on 3G CDMA cellular systems [1] 📱. It's source-controlled and variable-rate, and it has a bunch of operating modes 🎶. Each mode is a trade-off between voice quality and average data rate, so it's always a balancing act ⚖️.

The mode gets picked based on the network's traffic conditions and the quality of service you want. Check Table 2 for the list 📋. The average data rate (ADR) for each mode comes from encoding speech frames at the permissible rates (see Tables 1 and 3) that are compliant with the CDMA2000 system. The rate depends on what the input speech is doing moment to moment, plus the maximum and minimum rate limits the network operator sets 🔥.

The capabilities of VMR-WB got an upgrade with a new mode that runs at lower average data rates. That means better system capacity in both IP and non-IP networks [1] 🚀.

Because of this extension, some reserved table entries in RFC 4348 are now used to support the new mode 🧩. VMR-WB mode 4 follows all the applicable provisions and restrictions in RFC 4348 [2] 💖. The existing table entries in RFC 4348 stay exactly the same (frame types included), and the original VMR-WB modes aren't affected by any of this, so no drama there 🫶.

RFC 4348 was built with room for future extensions, so adding this mode doesn't break interoperability with earlier RFC 4348 implementations ✨. It's honestly so clean.

Next up, the sections spell out the updates that have to be made to RFC 4348 📝. The provisions and considerations for implementation, congestion control, and security are the same as in RFC 4348, so you don't need to relearn any of that 🌈.

7. IANA Considerations ✨

Okay bestie, this part is all about the paperwork 📋 IANA (the folks who keep the official registries) gets a little glow-up here. This document updates the media type registered in [2]. IANA has added this document as a 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.

So IANA is changing "modes 0, 1, 2 and 3 [1]" to "modes 0, 1, 2, 3, and 4 [1] [2]", and changing "modes in the set 0 to 3" to "modes in the set 0 to 4". 💅 [1] will be 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). Iconic. 🎀

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

Full Copyright Statement

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.

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Acknowledgement

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📦 where this page comes from

ietf: rfc4424 2006-02
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