draft-ietf-avtext-client-to-mixer-audio-level-00.txt   draft-ietf-avtext-client-to-mixer-audio-level-01.txt 
AVT J. Lennox, Ed. AVT J. Lennox, Ed.
Internet-Draft Vidyo Internet-Draft Vidyo
Intended status: Standards Track E. Ivov Intended status: Standards Track E. Ivov
Expires: August 22, 2011 SIP Communicator Expires: September 15, 2011 Jitsi
E. Marocco E. Marocco
Telecom Italia Telecom Italia
February 18, 2011 March 14, 2011
A Real-Time Transport Protocol (RTP) Header Extension for Client-to- A Real-Time Transport Protocol (RTP) Header Extension for Client-to-
Mixer Audio Level Indication Mixer Audio Level Indication
draft-ietf-avtext-client-to-mixer-audio-level-00 draft-ietf-avtext-client-to-mixer-audio-level-01
Abstract Abstract
This document defines a mechanism by which packets of Real-Time This document defines a mechanism by which packets of Real-Time
Transport Protocol (RTP) audio streams can indicate, in an RTP header Transport Protocol (RTP) audio streams can indicate, in an RTP header
extension, the audio level of the audio sample carried in the RTP extension, the audio level of the audio sample carried in the RTP
packet. In large conferences, this can reduce the load on an audio packet. In large conferences, this can reduce the load on an audio
mixer or other middlebox which wants to forward only a few of the mixer or other middlebox which wants to forward only a few of the
loudest audio streams, without requiring it to decode and measure loudest audio streams, without requiring it to decode and measure
every stream that is received. every stream that is received.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 22, 2011. This Internet-Draft will expire on September 15, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Audio Levels . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Audio Levels . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Signaling (Setup) Information . . . . . . . . . . . . . . . . 6 4. Signaling (Setup) Information . . . . . . . . . . . . . . . . 6
5. Considerations on Use . . . . . . . . . . . . . . . . . . . . 6 5. Considerations on Use . . . . . . . . . . . . . . . . . . . . 6
6. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Open issues . . . . . . . . . . . . . . . . . . . . . 9 Appendix A. Open issues . . . . . . . . . . . . . . . . . . . . . 9
Appendix B. Changes From Earlier Versions . . . . . . . . . . . . 9 Appendix B. Changes From Earlier Versions . . . . . . . . . . . . 9
B.1. Changes From Individual Submission Draft -01 . . . . . . . 9 B.1. Changes From Draft -01 . . . . . . . . . . . . . . . . . . 10
B.2. Changes From Individual Submission Draft -00 . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
In a centralized Real-Time Transport Protocol (RTP) [RFC3550] audio In a centralized Real-Time Transport Protocol (RTP) [RFC3550] audio
conference, an audio mixer or forwarder receives audio streams from conference, an audio mixer or forwarder receives audio streams from
many or all of the conference participants. It then selectively many or all of the conference participants. It then selectively
forwards some of them to other participants in the conference. In forwards some of them to other participants in the conference. In
large conferences, it is possible that such a server might be large conferences, it is possible that such a server might be
receiving a large number of streams, of which only a few should be receiving a large number of streams, of which only a few should be
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possibly perform voice activity detection on audio data from a large possibly perform voice activity detection on audio data from a large
number of streams. The need for such processing limits the size or number of streams. The need for such processing limits the size or
number of conferences such a server can support. number of conferences such a server can support.
As an alternative, this document defines an RTP header extension As an alternative, this document defines an RTP header extension
[RFC5285] through which senders of audio packets can indicate the [RFC5285] through which senders of audio packets can indicate the
audio level of the packets' payload, reducing the processing load for audio level of the packets' payload, reducing the processing load for
a server. a server.
The header extension in this draft is different to, but complementary The header extension in this draft is different to, but complementary
with, the one defined in [I-D.ivov-avt-slic], which defines a with, the one defined in
[I-D.ietf-avtext-mixer-to-client-audio-level], which defines a
mechanism by which audio mixers can indicate to clients the levels of mechanism by which audio mixers can indicate to clients the levels of
the contributing sources that made up the mixed audio. the contributing sources that made up the mixed audio.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119] and document are to be interpreted as described in RFC 2119 [RFC2119] and
indicate requirement levels for compliant implementations. indicate requirement levels for compliant implementations.
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to the overload point of the system, i.e. the maximum-amplitude to the overload point of the system, i.e. the maximum-amplitude
signal that can be handled by the system without clipping. (Note: signal that can be handled by the system without clipping. (Note:
Representation relative to the overload point of a system is Representation relative to the overload point of a system is
particularly useful for digital implementations, since one does not particularly useful for digital implementations, since one does not
need to know the relative calibration of the analog circuitry.) For need to know the relative calibration of the analog circuitry.) For
example, in the case of u-law (audio/pcmu) audio [ITU.G711.1988], the example, in the case of u-law (audio/pcmu) audio [ITU.G711.1988], the
0 dBov reference would be a square wave with values +/- 8031. (This 0 dBov reference would be a square wave with values +/- 8031. (This
translates to 6.18 dBm0, relative to u-law's dBm0 definition in Table translates to 6.18 dBm0, relative to u-law's dBm0 definition in Table
6 of G.711.) 6 of G.711.)
The reference implementation section in
[I-D.ietf-avtext-mixer-to-client-audio-level] provides a sample
implementation of an audio level calculator that helps obtain such
values from raw audio samples.
In addition, a flag bit (labeled V) indicates whether the encoder In addition, a flag bit (labeled V) indicates whether the encoder
believes the audio packet contains voice activity (1) or does not believes the audio packet contains voice activity (1) or does not
(0). The voice activity detection algorithm is unspecified and left (0). The voice activity detection algorithm is unspecified and left
implementation-specific. implementation-specific.
The audio level for digital silence (e.g. all-0 pcmu audio), for The audio level for digital silence (e.g. all-0 pcmu audio), for
example for a muted audio source, MAY be represented as 127 (-127 example for a muted audio source, MAY be represented as 127 (-127
dBov), regardless of the dynamic range of the encoded audio format. dBov), regardless of the dynamic range of the encoded audio format.
When this header extension is used with RTP data sent using the RTP When this header extension is used with RTP data sent using the RTP
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[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP
Header Extensions", RFC 5285, July 2008. Header Extensions", RFC 5285, July 2008.
9.2. Informative References 9.2. Informative References
[I-D.ivov-avt-slic] [I-D.ietf-avtext-mixer-to-client-audio-level]
Ivov, E., Marocco, E., and J. Lennox, "A Real-Time Ivov, E., Marocco, E., and J. Lennox, "A Real-Time
Transport Protocol (RTP) Extension Header for Mixer-to- Transport Protocol (RTP) Header Extension for Mixer-to-
client Audio Level Indication", draft-ivov-avt-slic-04 Client Audio Level Indication",
(work in progress), January 2011. draft-ietf-avtext-mixer-to-client-audio-level-01 (work in
progress), March 2011.
[I-D.lennox-avt-srtp-encrypted-extension-headers] [I-D.lennox-avt-srtp-encrypted-extension-headers]
Lennox, J., "Encryption of Header Extensions in the Secure Lennox, J., "Encryption of Header Extensions in the Secure
Real-Time Transport Protocol (SRTP)", Real-Time Transport Protocol (SRTP)",
draft-lennox-avt-srtp-encrypted-extension-headers-02 (work draft-lennox-avt-srtp-encrypted-extension-headers-02 (work
in progress), October 2010. in progress), October 2010.
[I-D.perkins-avt-srtp-vbr-audio] [I-D.perkins-avt-srtp-vbr-audio]
Perkins, C. and J. Valin, "Guidelines for the use of Perkins, C. and J. Valin, "Guidelines for the use of
Variable Bit Rate Audio with Secure RTP", Variable Bit Rate Audio with Secure RTP",
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be better as a separate header extension element, or added to this be better as a separate header extension element, or added to this
header extension element. header extension element.
o It has been suggested to reference ITU P.56 [ITU.P56.1993] for o It has been suggested to reference ITU P.56 [ITU.P56.1993] for
level measurement. This needs to be investigated. level measurement. This needs to be investigated.
Appendix B. Changes From Earlier Versions Appendix B. Changes From Earlier Versions
Note to the RFC-Editor: please remove this section prior to Note to the RFC-Editor: please remove this section prior to
publication as an RFC. publication as an RFC.
B.1. Changes From Individual Submission Draft -01 B.1. Changes From Draft -01
o This version is primarily a document refresh.
o Emil Ivov and Enrico Marocco have been added as co-authors.
o Additional open issues listed.
B.2. Changes From Individual Submission Draft -00
o The draft name has been changed to clarify that this document
defines Client-To-Mixer Audio Levels, to more clearly distinguish
it from [I-D.ivov-avt-slic].
o The header extension format has been changed from a two-byte to a o Added references to the sample level calculator in
one-byte payload, eliminating the 7 reserved bits and the one [I-D.ietf-avtext-mixer-to-client-audio-level].
must-be-zero bit. o Changed affiliation for Emil Ivov.
o The sections Considerations on Use (Section 5) and Limitations
(Section 6) have been added.
o It has been noted that senders MAY indicate -127 dBov for digital
silence, and that level measurement MAY be done prior to encoding
audio.
o A reference to [I-D.lennox-avt-srtp-encrypted-extension-headers]
has been added to the security considerations.
o The term "header extension" is now used consistentenly throughout
the document (as opposed to "extension header").
Authors' Addresses Authors' Addresses
Jonathan Lennox (editor) Jonathan Lennox (editor)
Vidyo, Inc. Vidyo, Inc.
433 Hackensack Avenue 433 Hackensack Avenue
Seventh Floor Seventh Floor
Hackensack, NJ 07601 Hackensack, NJ 07601
US US
Email: jonathan@vidyo.com Email: jonathan@vidyo.com
Emil Ivov Emil Ivov
SIP Communicator Jitsi
Strasbourg 67000 Strasbourg 67000
France France
Email: emcho@sip-communicator.org Email: emcho@jitsi.org
Enrico Marocco Enrico Marocco
Telecom Itialia Telecom Itialia
Via G. Reiss Romoli, 274 Via G. Reiss Romoli, 274
Turin 10148 Turin 10148
Italy Italy
Email: enrico.marocco@telecomitalia.it Email: enrico.marocco@telecomitalia.it
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