< draft-ietf-rtcweb-fec-08.txt   draft-ietf-rtcweb-fec-09.txt >
Network Working Group J. Uberti Network Working Group J. Uberti
Internet-Draft Google Internet-Draft Google
Intended status: Standards Track March 2, 2018 Intended status: Standards Track Jul 3, 2019
Expires: September 3, 2018 Expires: January 4, 2020
WebRTC Forward Error Correction Requirements WebRTC Forward Error Correction Requirements
draft-ietf-rtcweb-fec-08 draft-ietf-rtcweb-fec-09
Abstract Abstract
This document provides information and requirements for how Forward This document provides information and requirements for how Forward
Error Correction (FEC) should be used by WebRTC implementations. Error Correction (FEC) should be used by WebRTC implementations.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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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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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 3, 2018. This Internet-Draft will expire on January 4, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 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
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carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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6. FEC for Application Content . . . . . . . . . . . . . . . . . 6 6. FEC for Application Content . . . . . . . . . . . . . . . . . 6
7. Implementation Requirements . . . . . . . . . . . . . . . . . 7 7. Implementation Requirements . . . . . . . . . . . . . . . . . 7
8. Adaptive Use of FEC . . . . . . . . . . . . . . . . . . . . . 7 8. Adaptive Use of FEC . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
12.1. Normative References . . . . . . . . . . . . . . . . . . 8 12.1. Normative References . . . . . . . . . . . . . . . . . . 8
12.2. Informative References . . . . . . . . . . . . . . . . . 9 12.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 11 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
In situations where packet loss is high, or perfect media quality is In situations where packet loss is high, or perfect media quality is
essential, Forward Error Correction (FEC) can be used to proactively essential, Forward Error Correction (FEC) can be used to proactively
recover from packet losses. This specification provides guidance on recover from packet losses. This specification provides guidance on
which FEC mechanisms to use, and how to use them, for WebRTC which FEC mechanisms to use, and how to use them, for WebRTC
implementations. implementations.
2. Terminology 2. Terminology
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Types of FEC 3. Types of FEC
FEC describes the sending of redundant information in an outgoing FEC describes the sending of redundant information in an outgoing
packet stream so that information can still be recovered even in the packet stream so that information can still be recovered even in the
face of packet loss. There are multiple ways in which this can be face of packet loss. There are multiple ways this can be
accomplished; this section enumerates the various mechanisms and accomplished for RTP media streams [RFC3550]; this section enumerates
describes their tradeoffs. the various mechanisms available and describes their tradeoffs.
3.1. Separate FEC Stream 3.1. Separate FEC Stream
This approach, as described in [RFC5956], Section 4.3, sends FEC This approach, as described in [RFC5956], Section 4.3, sends FEC
packets as an independent SSRC-multiplexed stream, with its own SSRC packets as an independent RTP stream with its own synchronization
and payload type. While this approach can protect multiple packets source (SSRC, [RFC3550]) and payload type, multiplexed with the
primary encoding. While this approach can protect multiple packets
of the primary encoding with a single FEC packet, each FEC packet of the primary encoding with a single FEC packet, each FEC packet
will have its own IP+UDP+RTP+FEC header, and this overhead can be will have its own IP+UDP+RTP+FEC header, and this overhead can be
excessive in some cases, e.g., when protecting each primary packet excessive in some cases, e.g., when protecting each primary packet
with a FEC packet. with a FEC packet.
This approach allows for recovery of entire RTP packets, including This approach allows for recovery of entire RTP packets, including
the full RTP header. the full RTP header.
3.2. Redundant Encoding 3.2. Redundant Encoding
This approach, as descibed in [RFC2198], allows for redundant data to This approach, as described in [RFC2198], allows for redundant data
be piggybacked on an existing primary encoding, all in a single to be piggybacked on an existing primary encoding, all in a single
packet. This redundant data may be an exact copy of a previous packet. This redundant data may be an exact copy of a previous
packet, or for codecs that support variable-bitrate encodings, payload, or for codecs that support variable-bitrate encodings,
possibly a smaller, lower-quality representation. In certain cases, possibly a smaller, lower-quality representation. In certain cases,
the redundant data could include multiple prior packets. the redundant data could include encodings of multiple prior audio
frames.
Since there is only a single set of packet headers, this approach Since there is only a single set of packet headers, this approach
allows for a very efficient representation of primary + redundant allows for a very efficient representation of primary + redundant
data. However, this savings is only realized when the data all fits data. However, this savings is only realized when the data all fits
into a single packet (i.e. the size is less than a MTU). As a into a single packet (i.e. the size is less than a MTU). As a
result, this approach is generally not useful for video content. result, this approach is generally not useful for video content.
As described in [RFC2198], Section 4, this approach cannot recover As described in [RFC2198], Section 4, this approach cannot recover
certain parts of the RTP header, including the marker bit, CSRC certain parts of the RTP header, including the marker bit, CSRC
information, and header extensions. information, and header extensions.
3.3. Codec-Specific In-band FEC 3.3. Codec-Specific In-band FEC
Some audio codecs, notably Opus [RFC6716] and AMR [RFC4867], support Some audio codecs, notably Opus [RFC6716] and AMR [RFC4867], support
their own in-band FEC mechanism, where redundant data is included in their own in-band FEC mechanism, where redundant data is included in
the codec payload. the codec payload. This is similar to the redundant encoding
mechanism described above, but as it adds no additional framing, it
can be slightly more efficient.
For Opus, packets deemed as important are re-encoded at a lower For Opus, audio frames deemed important are re-encoded at a lower
bitrate and added to the subsequent packet, allowing partial recovery bitrate and appended to the next payload, allowing partial recovery
of a lost packet. This scheme is fairly efficient; experiments of a lost packet. This scheme is fairly efficient; experiments
performed indicate that when Opus FEC is used, the overhead imposed performed indicate that when Opus FEC is used, the overhead imposed
is about 20-30%, depending on the amount of protection needed. Note is only about 20-30%, depending on the amount of protection needed.
that this mechanism can only carry redundancy information for the Note that this mechanism can only carry redundancy information for
immediately preceding packet; as such the decoder cannot fully the immediately preceding audio frame; as such the decoder cannot
recover multiple consecutive lost packets, which can be a problem on fully recover multiple consecutive lost packets, which can be a
wireless networks. See [RFC6716], Section 2.1.7 for complete problem on wireless networks. See [RFC6716], Section 2.1.7, and this
details. Opus mailing list post [OpusFEC] for more details.
For AMR/AMR-WB, packets can contain copies or lower-quality encodings For AMR/AMR-WB, packets can contain copies or lower-quality encodings
of multiple prior audio frames. This mechanism is similar to the of multiple prior audio frames. See [RFC4867], Section 3.7.1 for
[RFC2198] mechanism described above, but as it adds no additional details on this mechanism.
framing, it can be slightly more efficient. See [RFC4867],
Section 3.7.1 for details on this mechanism.
In-band FEC mechanisms cannot recover any of the RTP header. In-band FEC mechanisms cannot recover any of the RTP header.
4. FEC for Audio Content 4. FEC for Audio Content
The following section provides guidance on how to best use FEC for The following section provides guidance on how to best use FEC for
transmitting audio data. As indicated in Section 8 below, FEC should transmitting audio data. As indicated in Section 8 below, FEC should
only be activated if network conditions warrant it, or upon explicit only be activated if network conditions warrant it, or upon explicit
application request. application request.
4.1. Recommended Mechanism 4.1. Recommended Mechanism
When using variable-bitrate codecs without an internal FEC, [RFC2198] When using variable-bitrate codecs without an internal FEC, redundant
redundant encoding with lower-fidelity version(s) of the previous encoding (as described in Section 3.2) with lower-fidelity version(s)
packet(s) is RECOMMENDED. This provides reasonable protection of the of the previous packet(s) is RECOMMENDED. This provides reasonable
payload with only moderate bitrate increase, as the redundant protection of the payload with only moderate bitrate increase, as the
encodings can be significantly smaller than the primary encoding. redundant encodings can be significantly smaller than the primary
encoding.
When using the Opus codec, use of the built-in Opus FEC mechanism is When using the Opus codec, use of the built-in Opus FEC mechanism is
RECOMMENDED. This provides reasonable protection of the audio stream RECOMMENDED. This provides reasonable protection of the audio stream
against individual losses, with minimal overhead. Note that, as against individual losses, with minimal overhead. Note that, as
indicated above, the built-in Opus FEC only provides single-frame indicated above, the built-in Opus FEC only provides single-frame
redundancy; if multi-packet protection is needed, the aforementioned redundancy; if multi-packet protection is needed, the aforementioned
[RFC2198] redundancy with reduced-bitrate Opus encodings SHOULD be redundant encoding with reduced-bitrate Opus encodings SHOULD be used
used instead. instead.
When using the AMR/AMR-WB codecs, use of their built-in FEC mechanism When using the AMR/AMR-WB codecs, use of their built-in FEC mechanism
is RECOMMENDED. This provides slightly more efficient protection of is RECOMMENDED. This provides slightly more efficient protection of
the audio stream than [RFC2198]. the audio stream than redundant encoding.
When using constant-bitrate codecs, e.g. PCMU, use of [RFC2198] When using constant-bitrate codecs, e.g., PCMU [RFC5391], redundant
redundant encoding MAY be used, but note that this will result in a encoding MAY be used, but this will result in a potentially
potentially significant bitrate increase, and that suddenly significant bitrate increase, and suddenly increasing bitrate to deal
increasing bitrate to deal with losses from congestion may actually with losses from congestion may actually make things worse.
make things worse.
Because of the lower packet rate of audio encodings, usually a single Because of the lower packet rate of audio encodings, usually a single
packet per frame, use of a separate FEC stream comes with a higher packet per frame, use of a separate FEC stream comes with a higher
overhead than other mechanisms, and therefore is NOT RECOMMENDED. overhead than other mechanisms, and therefore is NOT RECOMMENDED.
As mentioned above, the recommended mechanisms do not allow recovery As mentioned above, the recommended mechanisms do not allow recovery
of parts of the RTP header that may be important in certain audio of parts of the RTP header that may be important in certain audio
applications, e.g., CSRCs and RTP header extensions like those applications, e.g., CSRCs and RTP header extensions like those
specified in [RFC6464] and [RFC6465]. Implementations SHOULD account specified in [RFC6464] and [RFC6465]. Implementations SHOULD account
for this and attempt to approximate this information, using an for this and attempt to approximate this information, using an
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To process the incoming FEC stream, the receiver can demultiplex it To process the incoming FEC stream, the receiver can demultiplex it
by SSRC, and then correlate it with the appropriate primary stream(s) by SSRC, and then correlate it with the appropriate primary stream(s)
via the CSRC(s) present in the RTP header of flexfec repair packets, via the CSRC(s) present in the RTP header of flexfec repair packets,
or the SSRC field present in the FEC header of flexfec retransmission or the SSRC field present in the FEC header of flexfec retransmission
packets. packets.
5.2. Negotiating Support 5.2. Negotiating Support
Support for a SSRC-multiplexed flexfec stream to protect a given RTP Support for a SSRC-multiplexed flexfec stream to protect a given RTP
stream SHOULD be indicated by including one of the formats described stream SHOULD be indicated by including one of the formats described
in [I-D.ietf-payload-flexible-fec-scheme], Section 5.1, as an in [I-D.ietf-payload-flexible-fec-scheme], Section 5.1.2, as an
additional supported media type for the associated m= section in the additional supported media type for the associated m= section in the
SDP offer [RFC3264]. As mentioned above, when BUNDLE is used, only a SDP offer [RFC3264]. As mentioned above, when BUNDLE is used, only a
single flexfec repair stream will be created for each BUNDLE group, single flexfec repair stream will be created for each BUNDLE group,
even if flexfec is negotiated for each primary stream. even if flexfec is negotiated for each primary stream.
Answerers can reject the use of SSRC-multiplexed FEC, by not Answerers can reject the use of SSRC-multiplexed FEC, by not
including the offered FEC formats in the corresponding m= section in including the offered FEC formats in the corresponding m= section in
the SDP answer. the SDP answer.
Use of FEC-only m-lines, and grouping using the SDP group mechanism Use of FEC-only m-lines, and grouping using the SDP group mechanism
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Implementations MAY support additional FEC mechanisms if desired, Implementations MAY support additional FEC mechanisms if desired,
e.g., [RFC5109]. e.g., [RFC5109].
8. Adaptive Use of FEC 8. Adaptive Use of FEC
Because use of FEC always causes redundant data to be transmitted, Because use of FEC always causes redundant data to be transmitted,
and the total amount of data must remain within any bandwidth limits and the total amount of data must remain within any bandwidth limits
indicated by congestion control and the receiver, this will lead to indicated by congestion control and the receiver, this will lead to
less bandwidth available for the primary encoding, even when the less bandwidth available for the primary encoding, even when the
redundant data is not being used. This is in contrast to methods redundant data is not being used. This is in contrast to methods
like RTX [RFC4588] or flexfec [I-D.ietf-payload-flexible-fec-scheme] like RTX [RFC4588] or flexfec's retransmission mode (
retransmissions, which only transmit redundant data when necessary, [I-D.ietf-payload-flexible-fec-scheme], Section 1.1.7), which only
at the cost of an extra roundtrip. transmit redundant data when necessary, at the cost of an extra
roundtrip.
Given this, WebRTC implementations SHOULD consider using RTX or Given this, WebRTC implementations SHOULD consider using RTX or
flexfec retransmissions instead of FEC when RTT is low, and SHOULD flexfec retransmissions instead of FEC when RTT is low, and SHOULD
only transmit the amount of FEC needed to protect against the only transmit the amount of FEC needed to protect against the
observed packet loss (which can be determined, e.g., by monitoring observed packet loss (which can be determined, e.g., by monitoring
transmit packet loss data from RTCP Receiver Reports [RFC3550]), transmit packet loss data from RTCP Receiver Reports [RFC3550]),
unless the application indicates it is willing to pay a quality unless the application indicates it is willing to pay a quality
penalty to proactively avoid losses. penalty to proactively avoid losses.
Note that when probing bandwidth, i.e., speculatively sending extra Note that when probing bandwidth, i.e., speculatively sending extra
data to determine if additional link capacity exists, FEC SHOULD be data to determine if additional link capacity exists, FEC SHOULD be
used in all cases. Given that extra data is going to be sent used in all cases. Given that extra data is going to be sent
regardless, it makes sense to have that data protect the primary regardless, it makes sense to have that data protect the primary
payload; in addition, FEC can be applied in a way that increases payload; in addition, FEC can be applied in a way that increases
bandwidth only modestly, which is necessary when probing. bandwidth only modestly, which is necessary when probing.
When using FEC with layered codecs, e.g., [RFC6386], where only base When using FEC with layered codecs, e.g., [RFC6386], where only base
layer frames are critical to the decoding of future frames, layer frames are critical to the decoding of future frames,
implementations SHOULD only apply FEC to these base layer frames. implementations SHOULD only apply FEC to these base layer frames.
9. Security Considerations Finally, it should be noted that although applying redundancy is
This document makes recommendations regarding the use of FEC.
Generally, it should be noted that although applying redundancy is
often useful in protecting a stream against packet loss, if the loss often useful in protecting a stream against packet loss, if the loss
is caused by network congestion, the additional bandwidth used by the is caused by network congestion, the additional bandwidth used by the
redundant data may actually make the situation worse, and can lead to redundant data may actually make the situation worse, and can lead to
significant degradation of the network. significant degradation of the network.
As described in [RFC3711], Section 10, the default processing when 9. Security Considerations
using FEC with SRTP is to perform FEC followed by SRTP at the sender,
and SRTP followed by FEC at the receiver. This ordering is used for In the WebRTC context, FEC is specifically concerned with recovering
all the SRTP Protection Profiles used in DTLS-SRTP [RFC5763], as data from lost packets; any corrupted packets will be discarded by
described in [RFC5764], Section 4.1.2. the SRTP [RFC3711] decryption process. Therefore, as described in
[RFC3711], Section 10, the default processing when using FEC with
SRTP is to perform FEC followed by SRTP at the sender, and SRTP
followed by FEC at the receiver. This ordering is used for all the
SRTP Protection Profiles used in DTLS-SRTP [RFC5763], which are
enumerated in [RFC5764], Section 4.1.2.
Additional security considerations for each individual FEC mechanism Additional security considerations for each individual FEC mechanism
are enumerated in their respective documents. are enumerated in their respective documents.
10. IANA Considerations 10. IANA Considerations
This document requires no actions from IANA. This document requires no actions from IANA.
11. Acknowledgements 11. Acknowledgements
Several people provided significant input into this document, Several people provided significant input into this document,
including Bernard Aboba, Jonathan Lennox, Giri Mandyam, Varun Singh, including Bernard Aboba, Jonathan Lennox, Giri Mandyam, Varun Singh,
Tim Terriberry, Magnus Westerlund, and Mo Zanaty. Tim Terriberry, Magnus Westerlund, and Mo Zanaty.
12. References 12. References
12.1. Normative References 12.1. Normative References
[I-D.ietf-payload-flexible-fec-scheme] [I-D.ietf-payload-flexible-fec-scheme]
Singh, V., Begen, A., Zanaty, M., and G. Mandyam, "RTP Zanaty, M., Singh, V., Begen, A., and G. Mandyam, "RTP
Payload Format for Flexible Forward Error Correction Payload Format for Flexible Forward Error Correction
(FEC)", draft-ietf-payload-flexible-fec-scheme-05 (work in (FEC)", draft-ietf-payload-flexible-fec-scheme-20 (work in
progress), July 2017. progress), May 2019.
[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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[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,
DOI 10.17487/RFC2198, September 1997, DOI 10.17487/RFC2198, September 1997,
skipping to change at page 9, line 41 skipping to change at page 9, line 41
3GPP, "IP Multimedia Subsystem (IMS); Multimedia 3GPP, "IP Multimedia Subsystem (IMS); Multimedia
telephony; Media handling and interaction", 3GPP TS 26.114 telephony; Media handling and interaction", 3GPP TS 26.114
15.0.0, September 2017. 15.0.0, September 2017.
12.2. Informative References 12.2. Informative References
[I-D.ietf-mmusic-sdp-bundle-negotiation] [I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C., Alvestrand, H., and C. Jennings, Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session "Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle- Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
negotiation-48 (work in progress), January 2018. negotiation-54 (work in progress), December 2018.
[I-D.ietf-rtcweb-data-channel] [I-D.ietf-rtcweb-data-channel]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
Channels", draft-ietf-rtcweb-data-channel-13 (work in Channels", draft-ietf-rtcweb-data-channel-13 (work in
progress), January 2015. progress), January 2015.
[OpusFEC] Terriberry, T., "Opus FEC", January 2013.
[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, DOI 10.17487/RFC3550, Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>. July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[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, DOI 10.17487/RFC3711, March 2004, RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>. <https://www.rfc-editor.org/info/rfc3711>.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588, Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
DOI 10.17487/RFC4588, July 2006, DOI 10.17487/RFC4588, July 2006,
<https://www.rfc-editor.org/info/rfc4588>. <https://www.rfc-editor.org/info/rfc4588>.
[RFC5109] Li, A., Ed., "RTP Payload Format for Generic Forward Error [RFC5109] Li, A., Ed., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, DOI 10.17487/RFC5109, December Correction", RFC 5109, DOI 10.17487/RFC5109, December
2007, <https://www.rfc-editor.org/info/rfc5109>. 2007, <https://www.rfc-editor.org/info/rfc5109>.
[RFC5391] Sollaud, A., "RTP Payload Format for ITU-T Recommendation
G.711.1", RFC 5391, DOI 10.17487/RFC5391, November 2008,
<https://www.rfc-editor.org/info/rfc5391>.
[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework [RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
for Establishing a Secure Real-time Transport Protocol for Establishing a Secure Real-time Transport Protocol
(SRTP) Security Context Using Datagram Transport Layer (SRTP) Security Context Using Datagram Transport Layer
Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May
2010, <https://www.rfc-editor.org/info/rfc5763>. 2010, <https://www.rfc-editor.org/info/rfc5763>.
[RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer
Security (DTLS) Extension to Establish Keys for the Secure Security (DTLS) Extension to Establish Keys for the Secure
Real-time Transport Protocol (SRTP)", RFC 5764, Real-time Transport Protocol (SRTP)", RFC 5764,
DOI 10.17487/RFC5764, May 2010, DOI 10.17487/RFC5764, May 2010,
skipping to change at page 11, line 7 skipping to change at page 11, line 17
to-Client Audio Level Indication", RFC 6465, to-Client Audio Level Indication", RFC 6465,
DOI 10.17487/RFC6465, December 2011, DOI 10.17487/RFC6465, December 2011,
<https://www.rfc-editor.org/info/rfc6465>. <https://www.rfc-editor.org/info/rfc6465>.
[RFC6716] Valin, JM., Vos, K., and T. Terriberry, "Definition of the [RFC6716] Valin, JM., Vos, K., and T. Terriberry, "Definition of the
Opus Audio Codec", RFC 6716, DOI 10.17487/RFC6716, Opus Audio Codec", RFC 6716, DOI 10.17487/RFC6716,
September 2012, <https://www.rfc-editor.org/info/rfc6716>. September 2012, <https://www.rfc-editor.org/info/rfc6716>.
Appendix A. Change log Appendix A. Change log
Changes in draft -09:
o Editorial changes from IETF LC.
o Added new reference for Opus FEC.
Changes in draft -08: Changes in draft -08:
o Switch to RFC 8174 boilerplate. o Switch to RFC 8174 boilerplate.
Changes in draft -07: Changes in draft -07:
o Clarify how bandwidth management interacts with FEC. o Clarify how bandwidth management interacts with FEC.
o Make 3GPP reference normative. o Make 3GPP reference normative.
 End of changes. 28 change blocks. 
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