draft-ietf-rtcweb-fec-01.txt   draft-ietf-rtcweb-fec-02.txt 
Network Working Group J. Uberti Network Working Group J. Uberti
Internet-Draft Google Internet-Draft Google
Intended status: Standards Track March 5, 2015 Intended status: Standards Track October 18, 2015
Expires: September 6, 2015 Expires: April 20, 2016
WebRTC Forward Error Correction Requirements WebRTC Forward Error Correction Requirements
draft-ietf-rtcweb-fec-01 draft-ietf-rtcweb-fec-02
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 applications.
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-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 September 6, 2015. This Internet-Draft will expire on April 20, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 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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3.3. Codec-Specific In-band FEC . . . . . . . . . . . . . . . 3 3.3. Codec-Specific In-band FEC . . . . . . . . . . . . . . . 3
4. FEC for Audio Content . . . . . . . . . . . . . . . . . . . . 3 4. FEC for Audio Content . . . . . . . . . . . . . . . . . . . . 3
4.1. Recommended Mechanism . . . . . . . . . . . . . . . . . . 3 4.1. Recommended Mechanism . . . . . . . . . . . . . . . . . . 3
4.2. Negotiating Support . . . . . . . . . . . . . . . . . . . 4 4.2. Negotiating Support . . . . . . . . . . . . . . . . . . . 4
5. FEC for Video Content . . . . . . . . . . . . . . . . . . . . 4 5. FEC for Video Content . . . . . . . . . . . . . . . . . . . . 4
5.1. Recommended Mechanism . . . . . . . . . . . . . . . . . . 4 5.1. Recommended Mechanism . . . . . . . . . . . . . . . . . . 4
5.2. Negotiating Support . . . . . . . . . . . . . . . . . . . 5 5.2. Negotiating Support . . . . . . . . . . . . . . . . . . . 5
6. FEC for Application Content . . . . . . . . . . . . . . . . . 5 6. FEC for Application Content . . . . . . . . . . . . . . . . . 5
7. Implementation Requirements . . . . . . . . . . . . . . . . . 5 7. Implementation Requirements . . . . . . . . . . . . . . . . . 5
8. Adaptive Use of FEC . . . . . . . . . . . . . . . . . . . . . 5 8. Adaptive Use of FEC . . . . . . . . . . . . . . . . . . . . . 5
9. Security Considerations . . . . . . . . . . . . . . . . . . . 5 9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
12.1. Normative References . . . . . . . . . . . . . . . . . . 6 12.1. Normative References . . . . . . . . . . . . . . . . . . 6
12.2. Informative References . . . . . . . . . . . . . . . . . 6 12.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 7 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
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 client
implementations. implementations.
2. Terminology 2. Terminology
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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 For video content, use of a separate FEC stream with the RTP payload
format described in [I-D.ietf-payload-flexible-fec-scheme] is format described in [I-D.ietf-payload-flexible-fec-scheme] is
RECOMMENDED. The receiver can demultiplex the incoming FEC stream by RECOMMENDED. The receiver can demultiplex the incoming FEC stream by
SSRC and correlate it with the primary stream via the ssrc-group SSRC and correlate it with the primary stream via the ssrc-group
mechanism. mechanism.
Note that this only allows the FEC stream to protect a single primary Support for protecting multiple primary streams with a single FEC
stream. Support for protecting multiple primary streams with a stream is complicated by WebRTC's 1-m-line-per-stream policy, which
single FEC stream is complicated by WebRTC's 1-m-line-per-stream does not allow for a m-line dedicated specifically to FEC.
policy and requires further study.
5.2. Negotiating Support 5.2. Negotiating Support
To offer support for a separate FEC stream, the offerer MUST offer To offer support for a separate SSRC-multiplexed FEC stream, the
one of the formats described in offerer MUST offer one of the formats described in
[I-D.ietf-payload-flexible-fec-scheme], Section 5.1, as well as a [I-D.ietf-payload-flexible-fec-scheme], Section 5.1, as well as a
ssrc-group with "FEC-FR" semantics as described in [RFC5956], ssrc-group with "FEC-FR" semantics as described in [RFC5956],
Section 4.3. Section 4.3.
Answerers can reject the use of FEC by not including FEC payloads in Use of FEC-only m-lines, and grouping using the SDP group mechanism,
the answer. is not currently defined for WebRTC, and SHOULD NOT be offered.
Answerers can reject the use of SSRC-multiplexed FEC, by not
including FEC payload types in the answer.
Answerers SHOULD reject any FEC-only m-lines, unless they
specifically know how to handle such a thing in a WebRTC context
(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
While WebRTC also supports the ability to send generic application WebRTC also supports the ability to send generic application data,
data, the fact that the application can control exactly what data to and provides transport-level retransmission mechanisms that the
send allows it to monitor packet statistics and perform its own FEC application can use to ensure that its data is delivered reliably.
when necessary.
Because the application can control exactly what data to send, it has
the ability to monitor packet statistics and perform its own
application-level FEC, if necessary.
As a result, this document makes no recommendations regarding FEC for As a result, this document makes no recommendations regarding FEC for
the underlying data transport. the underlying data transport.
7. Implementation Requirements 7. Implementation Requirements
To support the functionality recommended above, implementations MUST To support the functionality recommended above, implementations MUST
support the redundant encoding mechanism described in [RFC2198] and support the redundant encoding mechanism described in [RFC2198] and
the FEC mechanism described in [RFC5956] and the FEC mechanism described in [RFC5956] and
[I-D.ietf-payload-flexible-fec-scheme]. [I-D.ietf-payload-flexible-fec-scheme].
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Since use of FEC causes redundant data to be transmitted, this will Since use of FEC causes redundant data to be transmitted, this will
lead to less bandwidth available for the primary encoding, when in a lead to less bandwidth available for the primary encoding, when in a
bandwidth-constrained environment. Given this, WebRTC bandwidth-constrained environment. Given this, WebRTC
implementations SHOULD only transmit FEC data when network conditions implementations SHOULD only transmit FEC data when network conditions
indicate that this is advisable (e.g. by monitoring transmit packet indicate that this is advisable (e.g. by monitoring transmit packet
loss data from RTCP Receiver Reports), or the application indicates loss data from RTCP Receiver Reports), or the application indicates
it is willing to pay a quality penalty to proactively avoid losses. it is willing to pay a quality penalty to proactively avoid losses.
9. Security Considerations 9. Security Considerations
This document makes recommendations regarding which FEC mechanisms to This document makes recommendations regarding the use of FEC.
use. The security considerations for each individual mechanism are Generally, it should be noted that although applying redundancy is
enumerated in their respective documents. often useful in protecting a stream against packet loss, if the loss
is caused by network congestion, the additional bandwidth used by the
redundant data may actually make the situation worse, and can lead to
significant degradation of the network.
Additional security considerations for each individual FEC mechanism
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 Jonathan Lennox, Giri Mandyam, Varun Singh, Tim Terriberry, including Jonathan Lennox, Giri Mandyam, Varun Singh, Tim Terriberry,
and Mo Zanaty. and Mo Zanaty.
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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., and M. Zanaty, "RTP Payload Format Singh, V., Begen, A., and M. Zanaty, "RTP Payload Format
for Non-Interleaved and Interleaved Parity Forward Error for Non-Interleaved and Interleaved Parity Forward Error
Correction (FEC)", draft-ietf-payload-flexible-fec- Correction (FEC)", draft-ietf-payload-flexible-fec-
scheme-00 (work in progress), February 2015. scheme-00 (work in progress), February 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<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,
September 1997. DOI 10.17487/RFC2198, September 1997,
<http://www.rfc-editor.org/info/rfc2198>.
[RFC5956] Begen, A., "Forward Error Correction Grouping Semantics in [RFC5956] Begen, A., "Forward Error Correction Grouping Semantics in
the Session Description Protocol", RFC 5956, September the Session Description Protocol", RFC 5956, DOI 10.17487/
2010. RFC5956, September 2010,
<http://www.rfc-editor.org/info/rfc5956>.
12.2. Informative References 12.2. Informative References
[I-D.ietf-payload-rtp-opus] [I-D.ietf-payload-rtp-opus]
Spittka, J., Vos, K., and J. Valin, "RTP Payload Format Spittka, J., Vos, K., and J. Valin, "RTP Payload Format
for the Opus Speech and Audio Codec", draft-ietf-payload- for the Opus Speech and Audio Codec", draft-ietf-payload-
rtp-opus-08 (work in progress), February 2015. rtp-opus-11 (work in progress), April 2015.
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error [RFC5109] Li, A., Ed., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, December 2007. Correction", RFC 5109, DOI 10.17487/RFC5109, December
2007, <http://www.rfc-editor.org/info/rfc5109>.
[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, September 2012. Opus Audio Codec", RFC 6716, DOI 10.17487/RFC6716,
September 2012, <http://www.rfc-editor.org/info/rfc6716>.
Appendix A. Change log Appendix A. Change log
Changes in draft -02:
o Expanded discussion of FEC-only m-lines, and how they should be
handled in offers and answers.
Changes in draft -01: Changes in draft -01:
o Tweaked abstract/intro text that was ambiguously normative. o Tweaked abstract/intro text that was ambiguously normative.
o Removed text on FEC for Opus in CELT mode. o Removed text on FEC for Opus in CELT mode.
o Changed RFC 2198 recommendation for PCMU to be MAY instead of NOT o Changed RFC 2198 recommendation for PCMU to be MAY instead of NOT
RECOMMENDED, based on list feedback. RECOMMENDED, based on list feedback.
o Explicitly called out application data as something not addressed o Explicitly called out application data as something not addressed
 End of changes. 18 change blocks. 
30 lines changed or deleted 58 lines changed or added

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