Real-time Transport Protocol (RTP) Payload Format for internet Low Bit Rate Codec (iLBC) Speech
RFC 3952
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RFC - Experimental
(December 2004; No errata)
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Authors |
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Alan Duric
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Soren Andersen
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Last updated |
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2013-03-02
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IETF
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(None)
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Document shepherd |
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No shepherd assigned
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IESG |
IESG state |
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RFC 3952 (Experimental)
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Consensus Boilerplate |
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Unknown
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Telechat date |
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Responsible AD |
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Allison Mankin
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Send notices to |
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<csp@csperkins.org>, <magnus.westerlund@ericsson.com>, <mankin@psg.com>
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Network Working Group A. Duric
Request for Comments: 3952 Telio
Category: Experimental S. Andersen
Aalborg University
December 2004
Real-time Transport Protocol (RTP) Payload Format
for internet Low Bit Rate Codec (iLBC) Speech
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This document describes the Real-time Transport Protocol (RTP)
payload format for the internet Low Bit Rate Codec (iLBC) Speech
developed by Global IP Sound (GIPS). Also, within the document there
are included necessary details for the use of iLBC with MIME and
Session Description Protocol (SDP).
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Background. . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. RTP Payload Format. . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Bitstream definition . . . . . . . . . . . . . . . . . . . 3
3.2. Multiple iLBC frames in a RTP packet . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Storage Mode . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. MIME registration of iLBC. . . . . . . . . . . . . . . . . 8
5. Mapping to SDP Parameters . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 11
7. References. . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 13
Duric & Andersen Experimental [Page 1]
RFC 3952 RTP Payload Format for iLBC Speech December 2004
1. Introduction
This document describes how compressed iLBC speech, as produced by
the iLBC codec [1], may be formatted for use as an RTP payload type.
Methods are provided to packetize the codec data frames into RTP
packets. The sender may send one or more codec data frames per
packet depending on the application scenario or based on the
transport network condition, bandwidth restriction, delay
requirements and packet-loss tolerance.
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 BCP 14, RFC 2119 [2].
2. Background
Global IP Sound (GIPS) has developed a speech compression algorithm
for use in IP based communications [1]. The iLBC codec enables
graceful speech quality degradation in the case of lost frames, which
occurs in connection with lost or delayed IP packets.
This codec is suitable for real time communications such as,
telephony and videoconferencing, streaming audio, archival and
messaging.
The iLBC codec [1] is an algorithm that compresses each basic frame
(20 ms or 30 ms) of 8000 Hz, 16-bit sampled input speech, into output
frames with rate of 400 bits for 30 ms basic frame size and 304 bits
for 20 ms basic frame size.
The codec supports two basic frame lengths: 30 ms at 13.33 kbit/s and
20 ms at 15.2 kbit/s, using a block independent linear-predictive
coding (LPC) algorithm. When the codec operates at block lengths of
20 ms, it produces 304 bits per block which MUST be packetized in 38
bytes. Similarly, for block lengths of 30 ms it produces 400 bits
per block which MUST be packetized in 50 bytes. This algorithm
results in a speech coding system with a controlled response to
packet losses similar to what is known from pulse code modulation
(PCM) with a packet loss concealment (PLC), such as ITU-T G711
standard [7], which operates at a fixed bit rate of 64 kbit/s. At
the same time, this algorithm enables fixed bit rate coding with a
quality-versus-bit rate tradeoff close to what is known from code-
excited linear prediction (CELP).
Duric & Andersen Experimental [Page 2]
RFC 3952 RTP Payload Format for iLBC Speech December 2004
3. RTP Payload Format
The iLBC codec uses 20 or 30 ms frames and a sampling rate clock of 8
kHz, so the RTP timestamp MUST be in units of 1/8000 of a second. The
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