draft-ietf-rmcat-cc-requirements-05.txt   draft-ietf-rmcat-cc-requirements-06.txt 
Network Working Group R. Jesup Network Working Group R. Jesup
Internet-Draft Mozilla Internet-Draft Mozilla
Intended status: Informational July 4, 2014 Intended status: Informational October 7, 2014
Expires: January 5, 2015 Expires: April 10, 2015
Congestion Control Requirements For RMCAT Congestion Control Requirements For RMCAT
draft-ietf-rmcat-cc-requirements-05 draft-ietf-rmcat-cc-requirements-06
Abstract Abstract
Congestion control is needed for all data transported across the Congestion control is needed for all data transported across the
Internet, in order to promote fair usage and prevent congestion Internet, in order to promote fair usage and prevent congestion
collapse. The requirements for interactive, point-to-point real time collapse. The requirements for interactive, point-to-point real time
multimedia, which needs low-delay, semi-reliable data delivery, are multimedia, which needs low-delay, semi-reliable data delivery, are
different from the requirements for bulk transfer like FTP or bursty different from the requirements for bulk transfer like FTP or bursty
transfers like Web pages. Due to an increasing amount of RTP-based transfers like Web pages. Due to an increasing amount of RTP-based
real-time media traffic on the Internet (e.g. with the introduction real-time media traffic on the Internet (e.g. with the introduction
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on January 5, 2015. This Internet-Draft will expire on April 10, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 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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1. The congestion control algorithm must attempt to provide as-low- 1. The congestion control algorithm must attempt to provide as-low-
as-possible-delay transit for real-time traffic while still as-possible-delay transit for real-time traffic while still
providing a useful amount of bandwidth. There may be lower providing a useful amount of bandwidth. There may be lower
limits on the amount of bandwidth that is useful, but this is limits on the amount of bandwidth that is useful, but this is
largely application-specific and the application may be able to largely application-specific and the application may be able to
modify or remove flows in order allow some useful flows to get modify or remove flows in order allow some useful flows to get
enough bandwidth. (Example: not enough bandwidth for low- enough bandwidth. (Example: not enough bandwidth for low-
latency video+audio, but enough for audio-only.) latency video+audio, but enough for audio-only.)
A. It should provide this as-low-as-possible-delay transit even A. Jitter (variation in the bitrate over short timescales) also
is relevant, though moderate amounts of jitter will be
absorbed by jitter buffers. Transit delay should be
considered to track the short-term maximums of delay
including jitter.
B. It should provide this as-low-as-possible-delay transit even
when faced with intermediate bottlenecks and competing when faced with intermediate bottlenecks and competing
flows. Competing flows may limit what's possible to flows. Competing flows may limit what's possible to
achieve. achieve.
B. It should handle routing changes which may alter or remove C. It should handle routing changes which may alter or remove
bottlenecks or change the bandwidth available, and react bottlenecks or change the bandwidth available, and react
quickly, especially if there is a reduction in available quickly, especially if there is a reduction in available
bandwidth or increase in bottleneck delay. bandwidth or increase in observed delay.
C. It should handle interface changes (WLAN to 3G data, etc) D. It should handle interface changes (WLAN to 3G data, etc)
which may radically change the bandwidth available or which may radically change the bandwidth available or
bottlenecks, and react quickly, especially if there is a bottlenecks, and react quickly, especially if there is a
reduction in available bandwidth or increase in bottleneck reduction in available bandwidth or increase in bottleneck
delay. It is assumed that an interface change can generate delay. It is assumed that an interface change can generate
a notification to the algorithm. a notification to the algorithm.
D. The offered load may be less than the available bandwidth at E. The offered load may be less than the available bandwidth at
any given moment, and may vary dramatically over time, any given moment, and may vary dramatically over time,
including dropping to no load and then resuming a high load, including dropping to no load and then resuming a high load,
such as in a mute operation. The reaction time between a such as in a mute operation. The reaction time between a
change in the bandwidth available from the algorithm and a change in the bandwidth available from the algorithm and a
change in the offered load is variable, and may be different change in the offered load is variable, and may be different
when increasing versus decreasing. when increasing versus decreasing.
E. The algorithm must not overreact to short-term bursts (such F. The algorithm must not overreact to short-term bursts (such
as web-browsing) which can quickly saturate a local- as web-browsing) which can quickly saturate a local-
bottleneck router or link, but also clear quickly, and bottleneck router or link, but also clear quickly, and
should recover quickly when the burst ends. This is should recover quickly when the burst ends. This is
inherently at odds with the need to react quickly-enough to inherently at odds with the need to react quickly-enough to
avoid queue buildup. avoid queue buildup.
F. Similarly periodic bursty flows such as MPEG DASH G. Similarly periodic bursty flows such as MPEG DASH
[MPEG_DASH] or proprietary media streaming algorithms may [MPEG_DASH] or proprietary media streaming algorithms may
compete in bursts with the algorithm, and may not be compete in bursts with the algorithm, and may not be
adaptive within a burst. They are often layered on top of adaptive within a burst. They are often layered on top of
TCP. The algorithm must avoid too much delay buildup during TCP. The algorithm must avoid too much delay buildup during
those bursts, and quickly recover. Note that this competing those bursts, and quickly recover. Note that this competing
traffic may on a shared access link, or the traffic burst traffic may on a shared access link, or the traffic burst
may cause a shift in the location of the bottleneck for the may cause a shift in the location of the bottleneck for the
duration of the burst. duration of the burst.
2. The algorithm must be fair to other flows, both realtime flows 2. The algorithm must be fair to other flows, both realtime flows
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This document is the result of discussions in various fora of the This document is the result of discussions in various fora of the
WebRTC effort, in particular on the rtp-congestion@alvestrand.no WebRTC effort, in particular on the rtp-congestion@alvestrand.no
mailing list. Many people contributed their thoughts to this. mailing list. Many people contributed their thoughts to this.
6. References 6. References
6.1. Normative References 6.1. Normative References
[I-D.ietf-rtcweb-overview] [I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-10 Browser-based Applications", draft-ietf-rtcweb-overview-11
(work in progress), June 2014. (work in progress), August 2014.
[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, March 1997.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control "Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July
2006. 2006.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for
Real-time Transport Control Protocol (RTCP)-Based Feedback Real-time Transport Control Protocol (RTCP)-Based Feedback
(RTP/SAVPF)", RFC 5124, February 2008. (RTP/SAVPF)", RFC 5124, February 2008.
6.2. Informative References 6.2. Informative References
[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-10 (work in Channels", draft-ietf-rtcweb-data-channel-12 (work in
progress), June 2014. progress), September 2014.
[I-D.welzl-rmcat-coupled-cc] [I-D.welzl-rmcat-coupled-cc]
Welzl, M., Islam, S., and S. Gjessing, "Coupled congestion Welzl, M., Islam, S., and S. Gjessing, "Coupled congestion
control for RTP media", draft-welzl-rmcat-coupled-cc-03 control for RTP media", draft-welzl-rmcat-coupled-cc-03
(work in progress), May 2014. (work in progress), May 2014.
[MPEG_DASH] [MPEG_DASH]
"Dynamic adaptive streaming over HTTP (DASH) -- Part 1: "Dynamic adaptive streaming over HTTP (DASH) -- Part 1:
Media presentation description and segment formats", April Media presentation description and segment formats", April
2012. 2012.
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