draft-ietf-rtcweb-fec-05.txt   draft-ietf-rtcweb-fec-06.txt 
Network Working Group J. Uberti Network Working Group J. Uberti
Internet-Draft Google Internet-Draft Google
Intended status: Standards Track May 23, 2017 Intended status: Standards Track July 3, 2017
Expires: November 24, 2017 Expires: January 4, 2018
WebRTC Forward Error Correction Requirements WebRTC Forward Error Correction Requirements
draft-ietf-rtcweb-fec-05 draft-ietf-rtcweb-fec-06
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 applications. 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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This Internet-Draft will expire on November 24, 2017. This Internet-Draft will expire on January 4, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 15 skipping to change at page 2, line 15
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Types of FEC . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Types of FEC . . . . . . . . . . . . . . . . . . . . . . . . 2
3.1. Separate FEC Stream . . . . . . . . . . . . . . . . . . . 3 3.1. Separate FEC Stream . . . . . . . . . . . . . . . . . . . 3
3.2. Redundant Encoding . . . . . . . . . . . . . . . . . . . 3 3.2. Redundant Encoding . . . . . . . . . . . . . . . . . . . 3
3.3. Codec-Specific In-band FEC . . . . . . . . . . . . . . . 3 3.3. Codec-Specific In-band FEC . . . . . . . . . . . . . . . 3
4. FEC for Audio Content . . . . . . . . . . . . . . . . . . . . 4 4. FEC for Audio Content . . . . . . . . . . . . . . . . . . . . 4
4.1. Recommended Mechanism . . . . . . . . . . . . . . . . . . 4 4.1. Recommended Mechanism . . . . . . . . . . . . . . . . . . 4
4.2. Negotiating Support . . . . . . . . . . . . . . . . . . . 4 4.2. Negotiating Support . . . . . . . . . . . . . . . . . . . 5
5. FEC for Video Content . . . . . . . . . . . . . . . . . . . . 5 5. FEC for Video Content . . . . . . . . . . . . . . . . . . . . 5
5.1. Recommended Mechanism . . . . . . . . . . . . . . . . . . 5 5.1. Recommended Mechanism . . . . . . . . . . . . . . . . . . 5
5.2. Negotiating Support . . . . . . . . . . . . . . . . . . . 5 5.2. Negotiating Support . . . . . . . . . . . . . . . . . . . 6
6. FEC for Application Content . . . . . . . . . . . . . . . . . 6 6. FEC for Application Content . . . . . . . . . . . . . . . . . 6
7. Implementation Requirements . . . . . . . . . . . . . . . . . 6 7. Implementation Requirements . . . . . . . . . . . . . . . . . 6
8. Adaptive Use of FEC . . . . . . . . . . . . . . . . . . . . . 6 8. Adaptive Use of FEC . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
12.1. Normative References . . . . . . . . . . . . . . . . . . 7 12.1. Normative References . . . . . . . . . . . . . . . . . . 8
12.2. Informative References . . . . . . . . . . . . . . . . . 8 12.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 8 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
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 client which FEC mechanisms to use, and how to use them, for WebRTC
implementations. implementations.
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 [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Types of FEC 3. Types of FEC
By its name, FEC describes the sending of redundant information in an FEC describes the sending of redundant information in an outgoing
outgoing packet stream so that information can still be recovered packet stream so that information can still be recovered even in the
even in the face of packet loss. There are multiple ways in which face of packet loss. There are multiple ways in which this can be
this can be accomplished; this section enumerates the various accomplished; this section enumerates the various mechanisms and
mechanisms and describes their tradeoffs. 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 SSRC-multiplexed stream, with its own SSRC
and payload type. While by far the most flexible, each FEC packet and payload type. While this approach can protect multiple packets
will have its own IP+UDP+RTP+FEC header, leading to additional of the primary encoding with a single FEC packet, each FEC packet
overhead of the FEC stream. 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
with a FEC packet.
This approach allows for recovery of entire RTP packets, including
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 descibed in [RFC2198], allows for redundant data to
be piggybacked on an existing primary encoding, all in a single 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, packet, 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 multiple prior packets.
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
certain parts of the RTP header, including the marker bit, CSRC
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.
For Opus, packets deemed as important are re-encoded at a lower For Opus, packets deemed as important are re-encoded at a lower
bitrate and added to the subsequent packet, allowing partial recovery bitrate and added to the subsequent packet, 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
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recover multiple consecutive lost packets, which can be a problem on recover multiple consecutive lost packets, which can be a problem on
wireless networks. See [RFC6716], Section 2.1.7 for complete wireless networks. See [RFC6716], Section 2.1.7 for complete
details. 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. This mechanism is similar to the
[RFC2198] mechanism described above, but as it adds no additional [RFC2198] mechanism described above, but as it adds no additional
framing, it can be slightly more efficient. See [RFC4867], framing, it can be slightly more efficient. See [RFC4867],
Section 3.7.1 for details on this mechanism. Section 3.7.1 for details on this mechanism.
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]
redundant encoding with lower-fidelity version(s) of the previous
packet(s) is RECOMMENDED. This provides reasonable protection of the
payload with only moderate bitrate increase, as the 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 typical losses, with modest overhead. Note that as indicated against individual losses, with minimal overhead. Note that as
above the built-in Opus FEC only provides single-frame redundancy; if indicated above the built-in Opus FEC only provides single-frame
multi-packet protection is needed, the built-in FEC should be redundancy; if multi-packet protection is needed, the aforementioned
combined with [RFC2198] redundancy to protect the N-2th, N-3rd, etc. [RFC2198] redundancy with reduced-bitrate Opus encodings SHOULD be
packets. used 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 [RFC2198].
When using variable-bitrate codecs without an internal FEC, [RFC2198]
redundant encoding with lower-fidelity version(s) of previous
packet(s) is RECOMMENDED. This provides reasonable protection of the
payload with moderate overhead.
When using constant-bitrate codecs, e.g. PCMU, use of [RFC2198] When using constant-bitrate codecs, e.g. PCMU, use of [RFC2198]
redundant encoding MAY be used, but note that this will result in a redundant encoding MAY be used, but note that this will result in a
potentially significant bitrate increase, and that suddenly potentially significant bitrate increase, and that suddenly
increasing bitrate to deal with losses from congestion may actually increasing bitrate to deal 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
of parts of the RTP header that may be important in certain audio
applications, e.g., CSRCs and RTP header extensions like those
specified in [RFC6464] and [RFC6465]. Implementations SHOULD account
for this and attempt to approximate this information, using an
approach similar to those described in [RFC2198], Section 4, and
[RFC6464], Section 5.
4.2. Negotiating Support 4.2. Negotiating Support
Support for redundant encoding MUST be indicated by offering "red" as Support for redundant encoding of a given RTP stream SHOULD be
a supported payload type in the offer. Answerers can reject the use indicated by including audio/red [RFC2198] as an additional supported
of redundant encoding by not including "red" as a supported payload media type for the associated m= section in the SDP offer [RFC3264].
type in the answer. Answerers can reject the use of redundant encoding by not including
the audio/red media type in the corresponding m= section in the SDP
answer.
Support for codec-specific FEC mechanisms are typically indicated via Support for codec-specific FEC mechanisms are typically indicated via
"a=fmtp" parameters. "a=fmtp" parameters.
For Opus, a receiver MUST indicate that it is prepared to use For Opus, a receiver MUST indicate that it is prepared to use
incoming FEC data with the "useinbandfec=1" parameter, as specified incoming FEC data with the "useinbandfec=1" parameter, as specified
in [RFC7587]. This parameter is declarative and can be negotiated in [RFC7587]. This parameter is declarative and can be negotiated
separately for either media direction. separately for either media direction.
For AMR/AMR-WB, support for redundant encoding, and the maximum For AMR/AMR-WB, support for redundant encoding, and the maximum
supported depth, are controlled by the 'max-red' parameter, as supported depth, are controlled by the 'max-red' parameter, as
specified in [RFC4867], Section 8.1. Receivers MUST include this specified in [RFC4867], Section 8.1. Receivers MUST include this
parameter, and set it to an appropriate value, as specified in parameter, and set it to an appropriate value, as specified in
[3GPP.26.114], Table 6.3. [TS.26114], Table 6.3.
5. FEC for Video Content 5. FEC for Video 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 video data. As indicated in Section 8 below, FEC should transmitting video 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.
5.1. Recommended Mechanism 5.1. Recommended Mechanism
For video content, use of a separate FEC stream with the RTP payload Video frames, due to their size, often require multiple RTP packets.
format described in [I-D.ietf-payload-flexible-fec-scheme] is As discussed above, a separate FEC stream can protect multiple
RECOMMENDED. The receiver can demultiplex the incoming FEC stream by packets with a single FEC packet. In addition, the "flexfec" FEC
SSRC and correlate it with the primary stream via the SSRC field mechanism described in [I-D.ietf-payload-flexible-fec-scheme] is also
present in the FEC header. capable of protecting multiple RTP streams via a single FEC stream,
including all the streams that are part of a BUNDLE
[I-D.ietf-mmusic-sdp-bundle-negotiation] group. As a result, for
video content, use of a separate FEC stream with the flexfec RTP
payload format is RECOMMENDED.
Support for protecting multiple primary streams with a single FEC To process the incoming FEC stream, the receiver can demultiplex it
stream is complicated by WebRTC's 1-m-line-per-stream policy, which by SSRC, and then correlate it with the appropriate primary stream(s)
does not allow for a m-line dedicated specifically to FEC. 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
packets.
5.2. Negotiating Support 5.2. Negotiating Support
To offer support for a SSRC-multiplexed FEC stream that is associated Support for a SSRC-multiplexed flexfec stream to protect a given RTP
with a given primary stream, the offerer MUST offer the formats stream SHOULD be indicated by including one of the formats described
supported for the primary stream, as well as one of the formats in [I-D.ietf-payload-flexible-fec-scheme], Section 5.1, as an
described in [I-D.ietf-payload-flexible-fec-scheme], Section 5.1. additional supported media type for the associated m= section in the
SDP offer [RFC3264]. As mentioned above, when BUNDLE is used, only a
single flexfec repair stream will be created for each BUNDLE group,
even if flexfec is negotiated for each primary stream.
Answerers can reject the use of SSRC-multiplexed FEC, by not
including the offered FEC formats in the corresponding m= section in
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
as described in [RFC5956], Section 4.1 is not currently defined for as described in [RFC5956], Section 4.1 is not currently defined for
WebRTC, and SHOULD NOT be offered. WebRTC, and SHOULD NOT be offered.
Answerers can reject the use of SSRC-multiplexed FEC, by not
including FEC formats in the answer.
Answerers SHOULD reject any FEC-only m-lines, unless they Answerers SHOULD reject any FEC-only m-lines, unless they
specifically know how to handle such a thing in a WebRTC context specifically know how to handle such a thing in a WebRTC context
(perhaps defined by a future version of the WebRTC specifications). (perhaps defined by a future version of the WebRTC specifications).
This ensures that implementations will not malfunction when said
future version of WebRTC enables offers of FEC-only m-lines.
6. FEC for Application Content 6. FEC for Application Content
WebRTC also supports the ability to send generic application data, WebRTC also supports the ability to send generic application data,
and provides transport-level retransmission mechanisms to support and provides transport-level retransmission mechanisms to support
full and partial (e.g. timed) reliability. See full and partial (e.g. timed) reliability. See
[I-D.ietf-rtcweb-data-channel] for details. [I-D.ietf-rtcweb-data-channel] for details.
Because the application can control exactly what data to send, it has Because the application can control exactly what data to send, it has
the ability to monitor packet statistics and perform its own the ability to monitor packet statistics and perform its own
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mentioned in Section 5. mentioned in Section 5.
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
Since use of FEC always causes redundant data to be transmitted, this Since use of FEC always causes redundant data to be transmitted, this
will lead to less bandwidth available for the primary encoding when will lead to less bandwidth available for the primary encoding when
in a bandwidth-constrained environment. This is in contrast to in a bandwidth-constrained environment. This is in contrast to
methods like RTX [RFC4588], which only transmits redundant data when methods like RTX [RFC4588] or flexfec
necessary, at the cost of an extra roundtrip. [I-D.ietf-payload-flexible-fec-scheme] retransmissions, which only
transmit redundant data when necessary, at the cost of an extra
roundtrip.
Given this, WebRTC implementations SHOULD consider using RTX instead Given this, WebRTC implementations SHOULD consider using RTX or
of FEC when RTT is low, and SHOULD only transmit the amount of FEC flexfec retransmissions instead of FEC when RTT is low, and SHOULD
needed to protect against the observed packet loss (which can be only transmit the amount of FEC needed to protect against the
determined, e.g., by monitoring transmit packet loss data from RTCP observed packet loss (which can be determined, e.g., by monitoring
Receiver Reports [RFC3550]), unless the application indicates it is transmit packet loss data from RTCP Receiver Reports [RFC3550]),
willing to pay a quality penalty to proactively avoid losses. unless the application indicates it is willing to pay a quality
penalty to proactively avoid losses.
Note that when probing bandwidth, i.e., speculatively sending extra
data to determine if additional link capacity exists, FEC SHOULD be
used in all cases. Given that extra data is going to be sent
regardless, it makes sense to have that data protect the primary
payload; in addition, FEC can be applied in a way that increases
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 9. Security Considerations
This document makes recommendations regarding the use of FEC. This document makes recommendations regarding the use of FEC.
Generally, it should be noted that although applying redundancy is 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
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], as
described 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 Singh, V., Begen, A., Zanaty, M., 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-04 (work in (FEC)", draft-ietf-payload-flexible-fec-scheme-05 (work in
progress), March 2017. progress), July 2017.
[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,
<http://www.rfc-editor.org/info/rfc2119>. <http://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,
<http://www.rfc-editor.org/info/rfc2198>. <http://www.rfc-editor.org/info/rfc2198>.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002,
<http://www.rfc-editor.org/info/rfc3264>.
[RFC4867] Sjoberg, J., Westerlund, M., Lakaniemi, A., and Q. Xie,
"RTP Payload Format and File Storage Format for the
Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband
(AMR-WB) Audio Codecs", RFC 4867, DOI 10.17487/RFC4867,
April 2007, <http://www.rfc-editor.org/info/rfc4867>.
[RFC5956] Begen, A., "Forward Error Correction Grouping Semantics in [RFC5956] Begen, A., "Forward Error Correction Grouping Semantics in
the Session Description Protocol", RFC 5956, the Session Description Protocol", RFC 5956,
DOI 10.17487/RFC5956, September 2010, DOI 10.17487/RFC5956, September 2010,
<http://www.rfc-editor.org/info/rfc5956>. <http://www.rfc-editor.org/info/rfc5956>.
[RFC7587] Spittka, J., Vos, K., and JM. Valin, "RTP Payload Format
for the Opus Speech and Audio Codec", RFC 7587,
DOI 10.17487/RFC7587, June 2015,
<http://www.rfc-editor.org/info/rfc7587>.
12.2. Informative References 12.2. Informative References
[I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
negotiation-38 (work in progress), April 2017.
[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.
[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, <http://www.rfc-editor.org/info/rfc3550>. July 2003, <http://www.rfc-editor.org/info/rfc3550>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<http://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,
<http://www.rfc-editor.org/info/rfc4588>. <http://www.rfc-editor.org/info/rfc4588>.
[RFC4867] Sjoberg, J., Westerlund, M., Lakaniemi, A., and Q. Xie,
"RTP Payload Format and File Storage Format for the
Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband
(AMR-WB) Audio Codecs", RFC 4867, DOI 10.17487/RFC4867,
April 2007, <http://www.rfc-editor.org/info/rfc4867>.
[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, <http://www.rfc-editor.org/info/rfc5109>. 2007, <http://www.rfc-editor.org/info/rfc5109>.
[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
for Establishing a Secure Real-time Transport Protocol
(SRTP) Security Context Using Datagram Transport Layer
Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May
2010, <http://www.rfc-editor.org/info/rfc5763>.
[RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer
Security (DTLS) Extension to Establish Keys for the Secure
Real-time Transport Protocol (SRTP)", RFC 5764,
DOI 10.17487/RFC5764, May 2010,
<http://www.rfc-editor.org/info/rfc5764>.
[RFC6386] Bankoski, J., Koleszar, J., Quillio, L., Salonen, J., [RFC6386] Bankoski, J., Koleszar, J., Quillio, L., Salonen, J.,
Wilkins, P., and Y. Xu, "VP8 Data Format and Decoding Wilkins, P., and Y. Xu, "VP8 Data Format and Decoding
Guide", RFC 6386, DOI 10.17487/RFC6386, November 2011, Guide", RFC 6386, DOI 10.17487/RFC6386, November 2011,
<http://www.rfc-editor.org/info/rfc6386>. <http://www.rfc-editor.org/info/rfc6386>.
[RFC6464] Lennox, J., Ed., Ivov, E., and E. Marocco, "A Real-time
Transport Protocol (RTP) Header Extension for Client-to-
Mixer Audio Level Indication", RFC 6464,
DOI 10.17487/RFC6464, December 2011,
<http://www.rfc-editor.org/info/rfc6464>.
[RFC6465] Ivov, E., Ed., Marocco, E., Ed., and J. Lennox, "A Real-
time Transport Protocol (RTP) Header Extension for Mixer-
to-Client Audio Level Indication", RFC 6465,
DOI 10.17487/RFC6465, December 2011,
<http://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, <http://www.rfc-editor.org/info/rfc6716>. September 2012, <http://www.rfc-editor.org/info/rfc6716>.
[RFC7587] Spittka, J., Vos, K., and JM. Valin, "RTP Payload Format [TS.26114]
for the Opus Speech and Audio Codec", RFC 7587, 3GPP, "IP Multimedia Subsystem (IMS); Multimedia
DOI 10.17487/RFC7587, June 2015, telephony; Media handling and interaction", 3GPP TS 26.114
<http://www.rfc-editor.org/info/rfc7587>. 13.3.0, March 2016.
Appendix A. Change log Appendix A. Change log
Changes in draft -06:
o Discuss how multiple streams can be protected by a single FlexFEC
stream.
o Discuss FEC for bandwidth probing.
o Add note about recovery of RTP headers and header extensions.
o Add note about FEC/SRTP ordering.
o Clarify flexfec demux text, and mention retransmits.
o Clarify text regarding offers/answers.
o Make RFC2198 support SHOULD strength.
o Clean up references.
Changes in draft -05:
o No changes.
Changes in draft -04: Changes in draft -04:
o Discussion of layered codecs. o Discussion of layered codecs.
o Discussion of RTX. o Discussion of RTX.
o Clarified implementation requirements. o Clarified implementation requirements.
o FlexFEC MUST -> SHOULD. o FlexFEC MUST -> SHOULD.
 End of changes. 37 change blocks. 
76 lines changed or deleted 190 lines changed or added

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