draft-ietf-rtcweb-fec-07.txt   draft-ietf-rtcweb-fec-08.txt 
Network Working Group J. Uberti Network Working Group J. Uberti
Internet-Draft Google Internet-Draft Google
Intended status: Standards Track December 10, 2017 Intended status: Standards Track March 2, 2018
Expires: June 13, 2018 Expires: September 3, 2018
WebRTC Forward Error Correction Requirements WebRTC Forward Error Correction Requirements
draft-ietf-rtcweb-fec-07 draft-ietf-rtcweb-fec-08
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.
skipping to change at page 1, line 31 skipping to change at page 1, line 31
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 13, 2018. This Internet-Draft will expire on September 3, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 20 skipping to change at page 2, line 20
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 . . . . . . . . . . . . . . . . . . . 5 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 . . . . . . . . . . . . . . . . . . . 6 5.2. Negotiating Support . . . . . . . . . . . . . . . . . . . 6
6. FEC for Application Content . . . . . . . . . . . . . . . . . 6 6. FEC for Application Content . . . . . . . . . . . . . . . . . 6
7. Implementation Requirements . . . . . . . . . . . . . . . . . 6 7. Implementation Requirements . . . . . . . . . . . . . . . . . 7
8. Adaptive Use of FEC . . . . . . . . . . . . . . . . . . . . . 7 8. Adaptive Use of FEC . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 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 . . . . . . . . . . . . . . . . . . . . . 10 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12 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 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", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
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 in which this can be
accomplished; this section enumerates the various mechanisms and accomplished; this section enumerates the various mechanisms and
describes their tradeoffs. describes their tradeoffs.
3.1. Separate FEC Stream 3.1. Separate FEC Stream
skipping to change at page 3, line 39 skipping to change at page 3, line 41
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.
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
is about 20-30%, depending on the amount of protection needed. Note is about 20-30%, depending on the amount of protection needed. Note
that this mechanism can only carry redundancy information for the that this mechanism can only carry redundancy information for the
immediately preceding packet; as such the decoder cannot fully immediately preceding packet; as such the decoder cannot fully
skipping to change at page 4, line 30 skipping to change at page 4, line 33
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, [RFC2198]
redundant encoding with lower-fidelity version(s) of the previous redundant encoding with lower-fidelity version(s) of the previous
packet(s) is RECOMMENDED. This provides reasonable protection of the packet(s) is RECOMMENDED. This provides reasonable protection of the
payload with only moderate bitrate increase, as the redundant payload with only moderate bitrate increase, as the redundant
encodings can be significantly smaller than the primary encoding. 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 [RFC2198] redundancy with reduced-bitrate Opus encodings SHOULD be
used instead. 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 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
skipping to change at page 7, line 12 skipping to change at page 7, line 18
be able to receive and make use of the relevant FEC formats for their be able to receive and make use of the relevant FEC formats for their
supported audio codecs, and MUST indicate this support, as described supported audio codecs, and MUST indicate this support, as described
in Section 4. Use of these formats when sending, as mentioned above, in Section 4. Use of these formats when sending, as mentioned above,
is RECOMMENDED. is RECOMMENDED.
The general FEC mechanism described in The general FEC mechanism described in
[I-D.ietf-payload-flexible-fec-scheme] SHOULD also be supported, as [I-D.ietf-payload-flexible-fec-scheme] SHOULD also be supported, as
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
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 [I-D.ietf-payload-flexible-fec-scheme]
retransmissions, which only transmit redundant data when necessary, retransmissions, which only transmit redundant data when necessary,
skipping to change at page 9, line 21 skipping to change at page 9, line 26
[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,
<https://www.rfc-editor.org/info/rfc5956>. <https://www.rfc-editor.org/info/rfc5956>.
[RFC7587] Spittka, J., Vos, K., and JM. Valin, "RTP Payload Format [RFC7587] Spittka, J., Vos, K., and JM. Valin, "RTP Payload Format
for the Opus Speech and Audio Codec", RFC 7587, for the Opus Speech and Audio Codec", RFC 7587,
DOI 10.17487/RFC7587, June 2015, DOI 10.17487/RFC7587, June 2015,
<https://www.rfc-editor.org/info/rfc7587>. <https://www.rfc-editor.org/info/rfc7587>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[TS.26114] [TS.26114]
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-43 (work in progress), December 2017. negotiation-48 (work in progress), January 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.
[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>.
skipping to change at page 10, line 44 skipping to change at page 11, line 7
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 -08:
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.
Changes in draft -06: Changes in draft -06:
o Discuss how multiple streams can be protected by a single FlexFEC o Discuss how multiple streams can be protected by a single FlexFEC
stream. stream.
 End of changes. 14 change blocks. 
15 lines changed or deleted 25 lines changed or added

This html diff was produced by rfcdiff 1.46. The latest version is available from http://tools.ietf.org/tools/rfcdiff/