draft-ietf-avtext-client-to-mixer-audio-level-03.txt   draft-ietf-avtext-client-to-mixer-audio-level-04.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: January 6, 2012 Jitsi Expires: February 28, 2012 Jitsi
E. Marocco E. Marocco
Telecom Italia Telecom Italia
July 5, 2011 August 27, 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-03 draft-ietf-avtext-client-to-mixer-audio-level-04
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-
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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
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 January 6, 2012. This Internet-Draft will expire on February 28, 2012.
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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not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
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 . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 8 8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Changes From Earlier Versions . . . . . . . . . . . . 9 Appendix A. Changes From Earlier Versions . . . . . . . . . . . . 10
A.1. Changes From Draft -02 . . . . . . . . . . . . . . . . . . 9 A.1. Changes From Draft -03 . . . . . . . . . . . . . . . . . . 10
A.2. Changes From Draft -01 . . . . . . . . . . . . . . . . . . 9 A.2. Changes From Draft -02 . . . . . . . . . . . . . . . . . . 10
A.3. Changes From Draft -00 . . . . . . . . . . . . . . . . . . 10 A.3. Changes From Draft -01 . . . . . . . . . . . . . . . . . . 10
A.4. Changes From Individual Submission Draft -01 . . . . . . . 10 A.4. Changes From Individual Submission Draft -01 . . . . . . . 11
A.5. Changes From Individual Submission Draft -00 . . . . . . . 10 A.5. Changes From Individual Submission Draft -00 . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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 are intended
forwarded to the other conference participants. to be forwarded to the other conference participants.
In such a scenario, in order to pick the audio streams to forward, a In such a scenario, in order to pick the audio streams to forward, a
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
skipping to change at page 4, line 42 skipping to change at page 4, line 42
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 the level of the audio in The audio level header extension carries the level of the audio in
the RTP payload of the packet it is associated with. This the RTP [RFC3550] payload of the packet it is associated with. This
information is carried in an RTP header extension element as defined information is carried in an RTP header extension element as defined
by the "General Mechanism for RTP Header Extensions" [RFC5285]. by the "General Mechanism for RTP Header Extensions" [RFC5285].
The payload of the audio level header extension element can be The payload of the audio level header extension element can be
encoded using the one or the two-byte header defined in [RFC5285]. encoded using the one-byte or the two-byte header defined in
Figure 1 and Figure 2 show sample audio level encodings with each of [RFC5285]. Figure 1 and Figure 2 show sample audio level encodings
them. with each of them.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sample audio level encoding using the one-byte header format Sample audio level encoding using the one-byte header format
Figure 1 Figure 1
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in the RTP payload of the packet it is associated with, with no long- in the RTP payload of the packet it is associated with, with no long-
term averaging or smoothing applied. That level is measured as a term averaging or smoothing applied. That level is measured as a
root mean square of all the samples in the measured range. root mean square of all the samples in the measured range.
To simplify implementation of the encoding procedures described here, To simplify implementation of the encoding procedures described here,
the reference implementation section in the reference implementation section in
[I-D.ietf-avtext-mixer-to-client-audio-level] provides a sample Java [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 linear PCM 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) optionally indicates whether the
believes the audio packet contains voice activity (1) or does not encoder believes the audio packet contains voice activity. If the V
(0). The voice activity detection algorithm is unspecified and left bit is in use, the value 1 indicates that the encoder believes the
implementation-specific. audio packet contains voice activity, and the value 0 indicates that
the encoder believes it does not. (The voice activity detection
algorithm is unspecified and left implementation-specific.) If the V
bit is not in use, its value is unspecified and MUST be ignored by
receivers. The use of the V bit is signaled using the extension
attribute "vad", discussed in Section 4.
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 Note: This audio level is defined in the same manner as is audio
noise level in the RTP Payload Comfort Noise specification [RFC3389]. noise level in the RTP Payload Comfort Noise specification [RFC3389].
In the comfort noice specification, the overall magnitude of the In the comfort noise specification, the overall magnitude of the
noise level in comfort noise is encoded into the first byte of the noise level in comfort noise is encoded into the first byte of the
payload, with spectral information about the noise in subsequent payload, with spectral information about the noise in subsequent
bytes. This specification's audio level parameter is defined so as bytes. This specification's audio level parameter is defined so as
to be identical to the comfort noise payload's noise-level byte. 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:ssrc-audio-level". There is no "urn:ietf:params:rtp-hdrext:ssrc-audio-level".
additional setup information needed for this extension (i.e. no
extensionattributes). It has a single extension attribute, named "vad". It takes the form
"vad=on" or "vad=off". If the header extension element is signaled
with "vad=on", the "V" bit described in Section 3 is in use, and MUST
be set by senders. If the header extension element is signaled with
"vad=off", the "V" bit is not in use, and its value MUST be ignored
by receivers. If the "vad" extension attribute is not specified, the
default is "vad=on".
An example attribute line in the SDP, for a conference might hence
be:
a=extmap:6 urn:ietf:params:rtp-hdrext:ssrc-audio-level vad=on
The "vad" extension attribute only controls the semantics of this
header extension attribute, and does not make any statement about
whether the sender is using any other voice activity detection
features such as discontinuous transmission, comfort noise, or
silence suppression.
Using the mechanisms of [RFC5285], an endpoint MAY signal multiple
instances of the header extension element, with different values of
the vad attribute, so long as these instances use different values
for the extension identifier. However, again following the rules of
[RFC5285], the semantics chosen for a header extension element
(including its vad setting) for a particular extension identifier
value MUST NOT be changed within an RTP session.
5. Considerations on Use 5. Considerations on Use
Mixers and forwarders generally should not base audio forwarding Mixers and forwarders generally ought 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 ought to 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
to take into account. (Note that this section provides design to take into account. (Note that this section provides design
guidance only, and is not normative.) guidance only, and is not normative.)
First of all, audio levels should generally be measured over longer First of all, audio levels generally ought to be measured over longer
intervals than that of a single audio packet. In order to avoid intervals than that of a single audio packet. In order to avoid
false-positives for short bursts of sound (such as a cough or a false-positives for short bursts of sound (such as a cough or a
dropped microphone), it is often useful to require that a dropped microphone), it is often useful to require that a
participant's audio level be maintained for some period of time participant's audio level be maintained for some period of time
before considering it to be "real", i.e. some type of low-pass filter before considering it to be "real", i.e. some type of low-pass filter
should be applied to the audio levels. Note, though, that such ought to be applied to the audio levels. Note, though, that such
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. Security Considerations 6. 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, if a device relys on audio level data from
untrusted endpoints SHOULD periodically audit the level information untrusted endpoints, it SHOULD periodically audit the level
transmitted, taking appropriate corrective action if endpoints appear information transmitted, taking appropriate corrective action against
to be sending incorrect data. (Note that as it is valid for an endpoints that appear to be sending incorrect data. (However, as it
endpoint to choose to measure audio levels prior to encoding, some is valid for an endpoint to choose to measure audio levels prior to
degree of discrepancy SHOULD be tolerated.) encoding, some degree of discrepancy could be present. This would
not indicate that an endpoint is malicous.)
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 is header confidentiality of the header extension. This mechanism could be
extension encryption [I-D.lennox-avtcore-srtp-encrypted-header-ext]. header extension encryption
[I-D.ietf-avtcore-srtp-encrypted-header-ext], or a lower-level
security and authentication mechanism.
7. 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:ssrc-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
skipping to change at page 8, line 40 skipping to change at page 9, line 26
[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.
8.2. Informative References 8.2. Informative References
[I-D.ietf-avtcore-srtp-encrypted-header-ext]
Lennox, J., "Encryption of Header Extensions in the Secure
Real-Time Transport Protocol (SRTP)",
draft-ietf-avtcore-srtp-encrypted-header-ext-00 (work in
progress), June 2011.
[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-02 (work in draft-ietf-avtext-mixer-to-client-audio-level-03 (work in
progress), May 2011. progress), July 2011.
[I-D.lennox-avtcore-srtp-encrypted-header-ext]
Lennox, J., "Encryption of Header Extensions in the Secure
Real-Time Transport Protocol (SRTP)",
draft-lennox-avtcore-srtp-encrypted-header-ext-00 (work in
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-
skipping to change at page 9, line 28 skipping to change at page 10, line 14
[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. Changes From Earlier Versions Appendix A. 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.
A.1. Changes From Draft -02 A.1. Changes From Draft -03
o Added vad extension attribute to negotiate use of the V bit.
o Addressed editorial comments made on the mailing list.
A.2. Changes From Draft -02
o Changed encoding related text so that it would cover both the one- o Changed encoding related text so that it would cover both the one-
byte and the two-byte header formats. byte and the two-byte header formats.
o Clarified use of root mean square for dBov calculation o Clarified use of root mean square for dBov calculation
o Added references to the sample level calculator in
[I-D.ietf-avtext-mixer-to-client-audio-level].
o Changed affiliation for Emil Ivov.
o Other minor editorial changes. o Other minor editorial changes.
A.2. Changes From Draft -01 A.3. Changes From Draft -01
o Changed the URI for declaring this header extension from o Changed the URI for declaring this header extension from
"urn:ietf:params:rtp-hdrext:audio-level" to "urn:ietf:params:rtp-hdrext:audio-level" to
"urn:ietf:params:rtp-hdrext:ssrc-audio-level" for consistency with "urn:ietf:params:rtp-hdrext:ssrc-audio-level" for consistency with
[I-D.ietf-avtext-mixer-to-client-audio-level]. [I-D.ietf-avtext-mixer-to-client-audio-level].
o Removed the "Limitations" section; it was discussing a potential o Removed the "Limitations" section; it was discussing a potential
extension that consensus indicated was out of scope of this extension that consensus indicated was out of scope of this
document. document.
o Closed the P.56 open issue. It was agreed on IETF 80 that P.56 is 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 mostly about speech levels and the levels transported by the
skipping to change at page 10, line 4 skipping to change at page 10, line 46
extension that consensus indicated was out of scope of this extension that consensus indicated was out of scope of this
document. document.
o Closed the P.56 open issue. It was agreed on IETF 80 that P.56 is 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 mostly about speech levels and the levels transported by the
extension defined here should also be able to serve as an extension defined here should also be able to serve as an
indication for noise. indication for noise.
o Closed the open issue about transmitting noise floor information. o Closed the open issue about transmitting noise floor information.
Noise floor is (loosely) inferrable by observing the per-packet Noise floor is (loosely) inferrable by observing the per-packet
level information over a period of time, so the additional level information over a period of time, so the additional
complexity seemed unnecessary. complexity seemed unnecessary.
o Editorial changes for consistency with o Editorial changes for consistency with
[I-D.ietf-avtext-mixer-to-client-audio-level]. [I-D.ietf-avtext-mixer-to-client-audio-level].
o Moved several descriptions of normative items that previously had o Moved several descriptions of normative items that previously had
only been described in informative sections of the text. only been described in informative sections of the text.
o Other editorial clarifications.
A.3. Changes From Draft -00 o Other editorial clarifications.
o Added references to the sample level calculator in
[I-D.ietf-avtext-mixer-to-client-audio-level].
o Changed affiliation for Emil Ivov.
A.4. Changes From Individual Submission Draft -01 A.4. Changes From Individual Submission Draft -01
o This version is primarily a document refresh. o This version is primarily a document refresh.
o Emil Ivov and Enrico Marocco have been added as co-authors. o Emil Ivov and Enrico Marocco have been added as co-authors.
o Additional open issues listed. o Additional open issues listed.
A.5. Changes From Individual Submission Draft -00 A.5. Changes From Individual Submission Draft -00
o The draft name has been changed to clarify that this document o The draft name has been changed to clarify that this document
defines Client-To-Mixer Audio Levels, to more clearly distinguish defines Client-To-Mixer Audio Levels, to more clearly distinguish
it from [I-D.ietf-avtext-mixer-to-client-audio-level]. 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 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 one-byte payload, eliminating the 7 reserved bits and the one
must-be-zero bit. must-be-zero bit.
o The sections Considerations on Use (Section 5) and Limitations o The sections Considerations on Use (Section 5) and Limitations
have been added. have been added.
o It has been noted that senders MAY indicate -127 dBov for digital o It has been noted that senders MAY indicate -127 dBov for digital
silence, and that level measurement MAY be done prior to encoding silence, and that level measurement MAY be done prior to encoding
audio. audio.
o A reference to [I-D.lennox-avtcore-srtp-encrypted-header-ext] has o A reference to [I-D.ietf-avtcore-srtp-encrypted-header-ext] has
been added to the security considerations. been added to the security considerations.
o The term "header extension" is now used consistentenly throughout o The term "header extension" is now used consistentenly throughout
the document (as opposed to "extension header"). 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
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