draft-ietf-avtcore-rtp-circuit-breakers-16.txt   draft-ietf-avtcore-rtp-circuit-breakers-17.txt 
AVTCORE Working Group C. Perkins AVTCORE Working Group C. Perkins
Internet-Draft University of Glasgow Internet-Draft University of Glasgow
Updates: 3550 (if approved) V. Singh Updates: 3550 (if approved) V. Singh
Intended status: Standards Track callstats.io Intended status: Standards Track callstats.io
Expires: December 13, 2016 June 11, 2016 Expires: January 21, 2017 July 20, 2016
Multimedia Congestion Control: Circuit Breakers for Unicast RTP Sessions Multimedia Congestion Control: Circuit Breakers for Unicast RTP Sessions
draft-ietf-avtcore-rtp-circuit-breakers-16 draft-ietf-avtcore-rtp-circuit-breakers-17
Abstract Abstract
The Real-time Transport Protocol (RTP) is widely used in telephony, The Real-time Transport Protocol (RTP) is widely used in telephony,
video conferencing, and telepresence applications. Such applications video conferencing, and telepresence applications. Such applications
are often run on best-effort UDP/IP networks. If congestion control are often run on best-effort UDP/IP networks. If congestion control
is not implemented in these applications, then network congestion can is not implemented in these applications, then network congestion can
lead to uncontrolled packet loss, and a resulting deterioration of lead to uncontrolled packet loss, and a resulting deterioration of
the user's multimedia experience. The congestion control algorithm the user's multimedia experience. The congestion control algorithm
acts as a safety measure, stopping RTP flows from using excessive acts as a safety measure, stopping RTP flows from using excessive
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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 December 13, 2016. This Internet-Draft will expire on January 21, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. RTP Circuit Breakers for Systems Using the RTP/AVP Profile . 7 4. RTP Circuit Breakers for Systems Using the RTP/AVP Profile . 7
4.1. RTP/AVP Circuit Breaker #1: RTCP Timeout . . . . . . . . 10 4.1. RTP/AVP Circuit Breaker #1: RTCP Timeout . . . . . . . . 10
4.2. RTP/AVP Circuit Breaker #2: Media Timeout . . . . . . . . 11 4.2. RTP/AVP Circuit Breaker #2: Media Timeout . . . . . . . . 11
4.3. RTP/AVP Circuit Breaker #3: Congestion . . . . . . . . . 12 4.3. RTP/AVP Circuit Breaker #3: Congestion . . . . . . . . . 12
4.4. RTP/AVP Circuit Breaker #4: Media Usability . . . . . . . 16 4.4. RTP/AVP Circuit Breaker #4: Media Usability . . . . . . . 16
4.5. Ceasing Transmission . . . . . . . . . . . . . . . . . . 17 4.5. Ceasing Transmission . . . . . . . . . . . . . . . . . . 17
5. RTP Circuit Breakers and the RTP/AVPF and RTP/SAVPF Profiles 17 5. RTP Circuit Breakers and the RTP/AVPF and RTP/SAVPF Profiles 17
6. Impact of RTCP Extended Reports (XR) . . . . . . . . . . . . 19 6. Impact of RTCP Extended Reports (XR) . . . . . . . . . . . . 19
7. Impact of Explicit Congestion Notification (ECN) . . . . . . 19 7. Impact of Explicit Congestion Notification (ECN) . . . . . . 19
8. Impact of Bundled Media and Layered Coding . . . . . . . . . 20 8. Impact of Bundled Media and Layered Coding . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 21 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
12.1. Normative References . . . . . . . . . . . . . . . . . . 22 12.1. Normative References . . . . . . . . . . . . . . . . . . 21
12.2. Informative References . . . . . . . . . . . . . . . . . 22 12.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction 1. Introduction
The Real-time Transport Protocol (RTP) [RFC3550] is widely used in The Real-time Transport Protocol (RTP) [RFC3550] is widely used in
voice-over-IP, video teleconferencing, and telepresence systems. voice-over-IP, video teleconferencing, and telepresence systems.
Many of these systems run over best-effort UDP/IP networks, and can Many of these systems run over best-effort UDP/IP networks, and can
suffer from packet loss and increased latency if network congestion suffer from packet loss and increased latency if network congestion
occurs. Designing effective RTP congestion control algorithms, to occurs. Designing effective RTP congestion control algorithms, to
adapt the transmission of RTP-based media to match the available adapt the transmission of RTP-based media to match the available
network capacity, while also maintaining the user experience, is a network capacity, while also maintaining the user experience, is a
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SR packets, RTCP RR packets, or RTCP XR ECN Summary Report packets, SR packets, RTCP RR packets, or RTCP XR ECN Summary Report packets,
are used by the RTP circuit breaker algorithm. are used by the RTP circuit breaker algorithm.
7. Impact of Explicit Congestion Notification (ECN) 7. Impact of Explicit Congestion Notification (ECN)
The use of ECN for RTP flows does not affect the RTCP timeout circuit The use of ECN for RTP flows does not affect the RTCP timeout circuit
breaker (Section 4.1) or the media timeout circuit breaker breaker (Section 4.1) or the media timeout circuit breaker
(Section 4.2), since these are both connectivity checks that simply (Section 4.2), since these are both connectivity checks that simply
determinate if any packets are being received. determinate if any packets are being received.
There is no consensus on what would be the correct response of the At the time of this writing, there's no consensus on how the receipt
congestion circuit breaker (Section 4.3) to ECN-CE marked packets. of ECN feedback will impact the congestion circuit breaker
The guidelines in [RFC3168] and [RFC6679] are that the response to (Section 4.3) or indeed whether the congestion circuit breaker ought
receipt of an ECN-CE marked packet needs to be essentially the same to take ECN feedback into account. A future version of this memo is
as the response to a lost packet for congestion control purposes. expected to provide guidance for implementers.
Since the RTP congestion circuit breaker responds to the same
congestion signals, this suggests that it ought to consider ECN-CE
marked packets as lost packets when calculating the TCP throughput
estimate to determine if the congestion circuit breaker triggers.
More recent work, however, has suggested that the response to an ECN-
CE mark ought to be less severe than the response to packet loss.
For example, the TCP ABE proposal
[I-D.khademi-tcpm-alternativebackoff-ecn] makes the argument that TCP
congestion control ought to back-off less in response to an ECN-CE
mark than to packet loss, because networks that generate ECN-CE marks
tend to use AQM schemes with much smaller buffers. For RTP
congestion control, both NADA [I-D.ietf-rmcat-nada] and SCREAM
[I-D.ietf-rmcat-scream-cc] suggest responding differently to ECN-CE
marked packets than to lost packets, for quality of experience
reasons, but make different proposals for how the response ought to
change. Such proposals would imply that a different circuit breaker
threshold be used for congestion signalled by ECN-CE marks than for
congestion signalled by packet loss, but unfortunately they offer no
clear guidance on how the threshold ought to be changed.
Finally, there are suggestions that forthcoming AQM proposals
[I-D.briscoe-aqm-dualq-coupled] might mark packets with ECN-CE in a
significantly more aggressive manner that at present. Any such
deployment would likely be incompatible with deployed TCP
implementations, so is not a short-term issue, but would require
significant changes to the congestion circuit breaker response.
Given the above issues, implementations MAY ignore ECN-CE marks when
determining if the congestion circuit breaker triggers, since
excessive persistent congestion will eventually lead to packet loss
that will trigger the circuit breaker. Doing this will protect the
network from congestion collapse, but might result in sub-optimal
user experience for competing flows that share the bottleneck queue,
since that queue will be driven to overflow, inducing high latency.
If this is a concern, the only current guidance is for
implementations to treat ECN-CE marked packets as equivalent to lost
packets, whilst being aware that this might trigger the circuit
breaker prematurely in future, depending on how AQM and ECN
deployment evolves. Developers that implement a circuit breaker
based on ECN-CE marks will need to track future developments in AQM
standards and deployed ECN marking behaviour, and ensure their
implementations are updated to match.
For the media usability circuit breaker (Section 4.4), ECN-CE marked For the media usability circuit breaker (Section 4.4), ECN-CE marked
packets arrive at the receiver, and if they arrive in time, they will packets arrive at the receiver, and if they arrive in time, they will
be decoded and rendered as normal. Accordingly, receipt of such be decoded and rendered as normal. Accordingly, receipt of such
packets ought not affect the usability of the media, and the arrival packets ought not affect the usability of the media, and the arrival
of RTCP feedback indicating their receipt is not expected to impact of RTCP feedback indicating their receipt is not expected to impact
the operation of the media usability circuit breaker. the operation of the media usability circuit breaker.
8. Impact of Bundled Media and Layered Coding 8. Impact of Bundled Media and Layered Coding
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for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <http://www.rfc-editor.org/info/rfc6679>. 2012, <http://www.rfc-editor.org/info/rfc6679>.
12.2. Informative References 12.2. Informative References
[Floyd] Floyd, S., Handley, M., Padhye, J., and J. Widmer, [Floyd] Floyd, S., Handley, M., Padhye, J., and J. Widmer,
"Equation-Based Congestion Control for Unicast "Equation-Based Congestion Control for Unicast
Applications", Proceedings of the ACM SIGCOMM Applications", Proceedings of the ACM SIGCOMM
conference, 2000, DOI 10.1145/347059.347397, August 2000. conference, 2000, DOI 10.1145/347059.347397, August 2000.
[I-D.briscoe-aqm-dualq-coupled]
Schepper, K., Briscoe, B., Bondarenko, O., and I. Tsang,
"DualQ Coupled AQM for Low Latency, Low Loss and Scalable
Throughput", draft-briscoe-aqm-dualq-coupled-01 (work in
progress), March 2016.
[I-D.ietf-avtcore-rtp-multi-stream] [I-D.ietf-avtcore-rtp-multi-stream]
Lennox, J., Westerlund, M., Wu, Q., and C. Perkins, Lennox, J., Westerlund, M., Wu, Q., and D. Perkins,
"Sending Multiple RTP Streams in a Single RTP Session", "Sending Multiple RTP Streams in a Single RTP Session",
draft-ietf-avtcore-rtp-multi-stream-11 (work in progress), draft-ietf-avtcore-rtp-multi-stream-11 (work in progress),
December 2015. December 2015.
[I-D.ietf-rmcat-nada]
Zhu, X., Pan, R., Ramalho, M., Cruz, S., Jones, P., Fu,
J., D'Aronco, S., and C. Ganzhorn, "NADA: A Unified
Congestion Control Scheme for Real-Time Media", draft-
ietf-rmcat-nada-02 (work in progress), March 2016.
[I-D.ietf-rmcat-scream-cc]
Johansson, I. and Z. Sarker, "Self-Clocked Rate Adaptation
for Multimedia", draft-ietf-rmcat-scream-cc-04 (work in
progress), June 2016.
[I-D.ietf-tsvwg-circuit-breaker] [I-D.ietf-tsvwg-circuit-breaker]
Fairhurst, G., "Network Transport Circuit Breakers", Fairhurst, G., "Network Transport Circuit Breakers",
draft-ietf-tsvwg-circuit-breaker-15 (work in progress), draft-ietf-tsvwg-circuit-breaker-15 (work in progress),
April 2016. April 2016.
[I-D.ietf-tsvwg-rtcweb-qos] [I-D.ietf-tsvwg-rtcweb-qos]
Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP
Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb- Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb-
qos-17 (work in progress), May 2016. qos-17 (work in progress), May 2016.
[I-D.khademi-tcpm-alternativebackoff-ecn]
Khademi, N., Welzl, M., Armitage, G., and G. Fairhurst,
"TCP Alternative Backoff with ECN (ABE)", draft-khademi-
tcpm-alternativebackoff-ecn-00 (work in progress), May
2016.
[Mathis] Mathis, M., Semke, J., Mahdavi, J., and T. Ott, "The [Mathis] Mathis, M., Semke, J., Mahdavi, J., and T. Ott, "The
macroscopic behavior of the TCP congestion avoidance macroscopic behavior of the TCP congestion avoidance
algorithm", ACM SIGCOMM Computer Communication algorithm", ACM SIGCOMM Computer Communication
Review 27(3), DOI 10.1145/263932.264023, July 1997. Review 27(3), DOI 10.1145/263932.264023, July 1997.
[Padhye] Padhye, J., Firoiu, V., Towsley, D., and J. Kurose, [Padhye] Padhye, J., Firoiu, V., Towsley, D., and J. Kurose,
"Modeling TCP Throughput: A Simple Model and its Empirical "Modeling TCP Throughput: A Simple Model and its Empirical
Validation", Proceedings of the ACM SIGCOMM Validation", Proceedings of the ACM SIGCOMM
conference, 1998, DOI 10.1145/285237.285291, August 1998. conference, 1998, DOI 10.1145/285237.285291, August 1998.
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