draft-ietf-rtcweb-fec-09.txt   draft-ietf-rtcweb-fec-10.txt 
Network Working Group J. Uberti Network Working Group J. Uberti
Internet-Draft Google Internet-Draft Google
Intended status: Standards Track Jul 3, 2019 Intended status: Standards Track Jul 16, 2019
Expires: January 4, 2020 Expires: January 17, 2020
WebRTC Forward Error Correction Requirements WebRTC Forward Error Correction Requirements
draft-ietf-rtcweb-fec-09 draft-ietf-rtcweb-fec-10
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-
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 January 4, 2020. This Internet-Draft will expire on January 17, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 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
(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
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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's retransmission mode ( like RTX [RFC4588] or flexfec's retransmission mode (
[I-D.ietf-payload-flexible-fec-scheme], Section 1.1.7), which only [I-D.ietf-payload-flexible-fec-scheme], Section 1.1.7), which only
transmit redundant data when necessary, at the cost of an extra transmit redundant data when necessary, at the cost of an extra
roundtrip. roundtrip and thereby increased media latency.
Given this, WebRTC implementations SHOULD consider using RTX or Given this, WebRTC implementations SHOULD prefer using RTX or flexfec
flexfec retransmissions instead of FEC when RTT is low, and SHOULD retransmissions instead of FEC when the connection RTT is within the
only transmit the amount of FEC needed to protect against the application's latency budget, and otherwise SHOULD only transmit the
observed packet loss (which can be determined, e.g., by monitoring amount of FEC needed to protect against the observed packet loss
transmit packet loss data from RTCP Receiver Reports [RFC3550]), (which can be determined, e.g., by monitoring transmit packet loss
unless the application indicates it is willing to pay a quality data from RTCP Receiver Reports [RFC3550]), unless the application
penalty to proactively avoid losses. indicates it is willing to pay a quality 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 data SHOULD
used in all cases. Given that extra data is going to be sent be used as the additional data. Given that extra data is going to be
regardless, it makes sense to have that data protect the primary sent 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 typically be applied in a way that
bandwidth only modestly, which is necessary when probing. 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.
Finally, it should be noted that although applying redundancy is Finally, 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.
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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 -10:
o Additional editorial changes from IETF LC.
Changes in draft -09: Changes in draft -09:
o Editorial changes from IETF LC. o Editorial changes from IETF LC.
o Added new reference for Opus FEC. 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.
 End of changes. 7 change blocks. 
17 lines changed or deleted 22 lines changed or added

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