draft-ietf-avtext-client-to-mixer-audio-level-01.txt   draft-ietf-avtext-client-to-mixer-audio-level-02.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: September 15, 2011 Jitsi Expires: December 4, 2011 Jitsi
E. Marocco E. Marocco
Telecom Italia Telecom Italia
March 14, 2011 June 2, 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-01 draft-ietf-avtext-client-to-mixer-audio-level-02
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
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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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 September 15, 2011. This Internet-Draft will expire on December 4, 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 . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 8.2. Informative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 8 Appendix A. Changes From Earlier Versions . . . . . . . . . . . . 9
Appendix A. Open issues . . . . . . . . . . . . . . . . . . . . . 9 A.1. Changes From Draft -01 . . . . . . . . . . . . . . . . . . 9
Appendix B. Changes From Earlier Versions . . . . . . . . . . . . 9 A.2. Changes From Draft -00 . . . . . . . . . . . . . . . . . . 9
B.1. Changes From Draft -01 . . . . . . . . . . . . . . . . . . 10 A.3. Changes From Individual Submission Draft -01 . . . . . . . 10
A.4. Changes From Individual Submission Draft -00 . . . . . . . 10
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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centralized server needs to decode, measure audio levels, and centralized server needs to decode, measure audio levels, and
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 than, but
with, the one defined in complementary with, the one defined in
[I-D.ietf-avtext-mixer-to-client-audio-level], which defines a [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.
3. Audio Levels 3. Audio Levels
The audio level header extension carries both the level of the audio The audio level header extension element carries the level of the
carried in the RTP payload of the packet it is associated with, as audio in the RTP payload of the packet it is associated with, and
well as an indication as to whether voice activity has been detected also an indication as to whether voice activity has been detected in
in the packet. the packet. This information is carried in an RTP header extension
element as defined by [RFC5285].
The form of the audio level extension block is as follows: The payload of the audio level header extension element is as
follows:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID | len=0 |V| level | | ID | len=0 |V| level |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Figure 1
The length field takes the value 0 to indicate that 1 byte follows. The length field takes the value 0 to indicate that 1 byte follows.
The audio level is defined in the same manner as is audio noise level The two-byte header defined in RFC 5285 [RFC5285] may also be used.
in the RTP Comfort Noise [RFC3389] specification. In that
specification, the overall magnitude of the noise level is encoded
into the first byte of the payload, with spectral information about
the noise in subsequent bytes. This specification's audio level
parameter is defined so as to be identical to the comfort noise
payload's noise-level byte.
The magnitude of the audio level is packed into the seven least The magnitude of the audio level is packed into the seven least
significant bits of the single byte of the header extension, shown in significant bits of the single byte of the header extension, shown in
Figure 1. The least significant bit of the audio level magnitude is Figure 1. The least significant bit of the audio level magnitude is
packed into the least significant bit of the byte. The most packed into the least significant bit of the byte. The most
significant bit of the byte is used as a separate flag bit "V", significant bit of the byte is used as a separate flag bit "V",
defined below. defined below.
The audio level is expressed in -dBov, with values from 0 to 127 The audio level is expressed in -dBov, with values from 0 to 127
representing 0 to -127 dBov. dBov is the level, in decibels, relative representing 0 to -127 dBov. dBov is the level, in decibels, relative
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 The audio level for digital silence, for example for a muted audio
[I-D.ietf-avtext-mixer-to-client-audio-level] provides a sample source, MAY be represented as 127 (-127 dBov), regardless of the
dynamic range of the encoded audio format.
Implementations MAY choose to measure audio levels prior to encoding
them in the payload carried in the RTP payload, e.g. on raw linear
PCM input.
The audio level header extension only carries the level of the audio
in the RTP payload of the packet it is associated with, with no long-
term averaging or smoothing applied.
To simplify implementation of the encoding procedures described here,
the reference implementation section in
[I-D.ietf-avtext-mixer-to-client-audio-level] provides a sample Java
implementation of an audio level calculator that helps obtain such implementation of an audio level calculator that helps obtain such
values from raw audio samples. values from raw linear PCM 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
example for a muted audio source, MAY be represented as 127 (-127
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
Payload for Redundant Audio Data [RFC2198], the header's data Payload for Redundant Audio Data [RFC2198], the header's data
describes the contents of the primary encoding. describes the contents of the primary encoding.
Note: This audio level is defined in the same manner as is audio
noise level in the RTP Payload Comfort Noise specification [RFC3389].
In the comfort noice specification, the overall magnitude of the
noise level in comfort noise is encoded into the first byte of the
payload, with spectral information about the noise in subsequent
bytes. This specification's audio level parameter is defined so as
to be identical to the comfort noise payload's noise-level byte.
4. Signaling (Setup) Information 4. Signaling (Setup) Information
The URI for declaring this header extension in an extmap attribute is The URI for declaring this header extension in an extmap attribute is
"urn:ietf:params:rtp-hdrext:audio-level". There is no additional "urn:ietf:params:rtp-hdrext:ssrc-audio-level". There is no
setup information needed for this extension (no extensionattributes). additional setup information needed for this extension (i.e. no
extensionattributes).
5. Considerations on Use 5. Considerations on Use
Mixers and forwarders generally should not base audio forwarding Mixers and forwarders generally should not base audio forwarding
decisions directly on packet-by-packet audio level information, but decisions directly on packet-by-packet audio level information, but
rather should apply some analysis of the audio levels and trends. rather should apply some analysis of the audio levels and trends.
This general rule applies whether audio levels are provided by This general rule applies whether audio levels are provided by
endpoints (as defined in this document), or are calculated at a endpoints (as defined in this document), or are calculated at a
server, as would be done in the absence of this information. This server, as would be done in the absence of this information. This
section discusses several issues that mixers and forwarders may wish section discusses several issues that mixers and forwarders may wish
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filtering must be balanced with the need to avoid clipping of the filtering must be balanced with the need to avoid clipping of the
beginning of a speaker's speech. beginning of a speaker's speech.
Additionally, different participants may have their audio input set Additionally, different participants may have their audio input set
differently. It may be useful to apply some sort of automatic gain differently. It may be useful to apply some sort of automatic gain
control to the audio levels. There are a number of possible control to the audio levels. There are a number of possible
approaches to acheiving this, e.g. by measuring peak audio levels, by approaches to acheiving this, e.g. by measuring peak audio levels, by
average audio levels during speech, or by measuring background audio average audio levels during speech, or by measuring background audio
levels (average audio level levels during non-speech). levels (average audio level levels during non-speech).
6. Limitations 6. Security Considerations
The audio levels carried by the extension header defined by this
document are defined as dBov, decibels below system overload.
In principle, it could be more useful to have, instead, dB SPL,
decibels of sound pressure level. In traditional telephony systems,
telephone handsets were calibrated such that a particular (e.g.)
u-law audio level, or analog voltage, corresponded to a particular
sound pressure level at the handset's mouthpiece.
However, in many environments, this information is not available.
Notably, PC soundcard hardware can only determine the levels of mic-
or line-in at the hardware input, and operating systems usually allow
further adjustments of audio input levels without providing
information about these transformations to applications.
Furthermore, in many circumstances, such as speech synthesis or mixed
audio, an "audio" signal may in fact never have actually existed as
sound pressure at all.
Thus, while information about the correspondance between dB SPL and
dBov, or encoded audio, could be useful, this document does not
attempt to define it. If there are circumstances in which this
information would be useful, a separate header extension would be
straightforward to define. (The information carried by such a header
extension could indeed be useful independently from the information
in the header extension defined by this document.)
7. Security Considerations
A malicious endpoint could choose to set the values in this header A malicious endpoint could choose to set the values in this header
extension falsely, so as to falsely claim that audio or voice is or extension falsely, so as to falsely claim that audio or voice is or
is not present. It is not clear what could be gained by falsely is not present. It is not clear what could be gained by falsely
claiming that audio is not present, but an endpoint falsely claiming claiming that audio is not present, but an endpoint falsely claiming
that audio is present could perform a denial-of-service attack on an that audio is present could perform a denial-of-service attack on an
audio conference, so as to send silence to suppress other conference audio conference, so as to send silence to suppress other conference
members' audio. Thus, a device relying on audio level data from members' audio. Thus, a device relying on audio level data from
untrusted endpoints SHOULD periodically audit the level information untrusted endpoints SHOULD periodically audit the level information
transmitted, taking appropriate corrective action if endpoints appear transmitted, taking appropriate corrective action if endpoints appear
to be sending incorrect data. (Note that endpoints MAY choose to to be sending incorrect data. (Note that as it is valid for an
measure audio levels prior to encoding, so some degree of discrepancy endpoint to choose to measure audio levels prior to encoding, some
SHOULD be tolerated.) degree of discrepancy SHOULD be tolerated.)
In the Secure Real-Time Transport Protocol (SRTP) [RFC3711], RTP In the Secure Real-Time Transport Protocol (SRTP) [RFC3711], RTP
header extensions are authenticated but not encrypted. When this header extensions are authenticated but not encrypted. When this
header extension is used, audio levels are therefore visible on a header extension is used, audio levels are therefore visible on a
packet-by-packet basis to an attacker passively observing the audio packet-by-packet basis to an attacker passively observing the audio
stream. As discussed in [I-D.perkins-avt-srtp-vbr-audio], such an stream. As discussed in [I-D.perkins-avt-srtp-vbr-audio], such an
attacker might be able to infer information about the conversation, attacker might be able to infer information about the conversation,
possibly with phoneme-level resolution. In scenarios where this is a possibly with phoneme-level resolution. In scenarios where this is a
concern, additional mechanisms SHOULD be used to protect the concern, additional mechanisms SHOULD be used to protect the
confidentiality of the header extension. One solution would be confidentiality of the header extension. One solution is header
header extension encryption extension encryption [I-D.lennox-avtcore-srtp-encrypted-header-ext].
[I-D.lennox-avt-srtp-encrypted-extension-headers].
8. IANA Considerations 7. IANA Considerations
This document defines a new extension URI to the RTP Compact Header This document defines a new extension URI to the RTP Compact Header
Extensions subregistry of the Real-Time Transport Protocol (RTP) Extensions subregistry of the Real-Time Transport Protocol (RTP)
Parameters registry, according to the following data: Parameters registry, according to the following data:
Extension URI: urn:ietf:params:rtp-hdrext:audio-level Extension URI: urn:ietf:params:rtp-hdrext:ssrc-audio-level
Description: Audio Level Description: Audio Level
Contact: jonathan@vidyo.com Contact: jonathan@vidyo.com
Reference: RFC XXXX Reference: RFC XXXX
9. References Note to RFC Editor: please replace "RFC XXXX" with the number of this
RFC.
9.1. Normative References 8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2198] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., [RFC2198] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V.,
Handley, M., Bolot, J., Vega-Garcia, A., and S. Fosse- Handley, M., Bolot, J., Vega-Garcia, A., and S. Fosse-
Parisis, "RTP Payload for Redundant Audio Data", RFC 2198, Parisis, "RTP Payload for Redundant Audio Data", RFC 2198,
September 1997. September 1997.
[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 8.2. Informative References
[I-D.ietf-avtext-mixer-to-client-audio-level] [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) Header Extension for Mixer-to- Transport Protocol (RTP) Header Extension for Mixer-to-
Client Audio Level Indication", Client Audio Level Indication",
draft-ietf-avtext-mixer-to-client-audio-level-01 (work in draft-ietf-avtext-mixer-to-client-audio-level-02 (work in
progress), March 2011. progress), May 2011.
[I-D.lennox-avt-srtp-encrypted-extension-headers] [I-D.lennox-avtcore-srtp-encrypted-header-ext]
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-avtcore-srtp-encrypted-header-ext-00 (work in
in progress), October 2010. progress), March 2011.
[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",
draft-perkins-avt-srtp-vbr-audio-05 (work in progress), draft-perkins-avt-srtp-vbr-audio-05 (work in progress),
December 2010. December 2010.
[ITU.G711.1988] [ITU.G711.1988]
International Telecommunications Union, "Pulse Code International Telecommunications Union, "Pulse Code
Modulation (PCM) of Voice Frequencies", ITU- Modulation (PCM) of Voice Frequencies", ITU-
T Recommendation G.711, November 1988. T Recommendation G.711, November 1988.
[ITU.P56.1993]
International Telecommunications Union, "Objective
Measurement of Active Speech Level", ITU-T Recommendation
P.56, March 1988.
[RFC3389] Zopf, R., "Real-time Transport Protocol (RTP) Payload for [RFC3389] Zopf, R., "Real-time Transport Protocol (RTP) Payload for
Comfort Noise (CN)", RFC 3389, September 2002. Comfort Noise (CN)", RFC 3389, September 2002.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)", Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004. RFC 3711, March 2004.
Appendix A. Open issues Appendix A. Changes From Earlier Versions
o In order to more accurately determine signal-to-noise ratio, it
would be useful for a sender to also send its estimate of its
current audio noise floor. If so, it's unclear whether this would
be better as a separate header extension element, or added to this
header extension element.
o It has been suggested to reference ITU P.56 [ITU.P56.1993] for
level measurement. This needs to be investigated.
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 Draft -01 A.1. Changes From Draft -01
o Changed the URI for declaring this header extension from
"urn:ietf:params:rtp-hdrext:audio-level" to
"urn:ietf:params:rtp-hdrext:ssrc-audio-level" for consistency with
[I-D.ietf-avtext-mixer-to-client-audio-level].
o Removed the "Limitations" section; it was discussing a potential
extension that consensus indicated was out of scope of this
document.
o Closed the P.56 open issue. It was agreed on IETF 80 that P.56 is
mostly about speech levels and the levels transported by the
extension defined here should also be able to serve as an
indication for noise.
o Closed the open issue about transmitting noise floor information.
Noise floor is (loosely) inferrable by observing the per-packet
level information over a period of time, so the additional
complexity seemed unnecessary.
o Editorial changes for consistency with
[I-D.ietf-avtext-mixer-to-client-audio-level].
o Moved several descriptions of normative items that previously had
only been described in informative sections of the text.
o Other editorial clarifications.
A.2. Changes From Draft -00
o Added references to the sample level calculator in o Added references to the sample level calculator in
[I-D.ietf-avtext-mixer-to-client-audio-level]. [I-D.ietf-avtext-mixer-to-client-audio-level].
o Changed affiliation for Emil Ivov. o Changed affiliation for Emil Ivov.
A.3. Changes From Individual Submission 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.
A.4. 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.ietf-avtext-mixer-to-client-audio-level].
o The header extension format has been changed from a two-byte to a
one-byte payload, eliminating the 7 reserved bits and the one
must-be-zero bit.
o The sections Considerations on Use (Section 5) and Limitations
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-avtcore-srtp-encrypted-header-ext] 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
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