draft-ietf-rmcat-sbd-09.txt		draft-ietf-rmcat-sbd-10.txt
	RTP Media Congestion Avoidance Techniques D. Hayes, Ed.		RTP Media Congestion Avoidance Techniques D. Hayes, Ed.
	Internet-Draft Simula Research Laboratory		Internet-Draft Simula Research Laboratory
	Intended status: Experimental S. Ferlin		Intended status: Experimental S. Ferlin
	Expires: May 30, 2018		Expires: August 20, 2018
	M. Welzl		M. Welzl
	K. Hiorth		K. Hiorth
	University of Oslo		University of Oslo
	November 26, 2017		February 16, 2018
	Shared Bottleneck Detection for Coupled Congestion Control for RTP		Shared Bottleneck Detection for Coupled Congestion Control for RTP
	Media.		Media.
	draft-ietf-rmcat-sbd-09		draft-ietf-rmcat-sbd-10
	Abstract		Abstract
	This document describes a mechanism to detect whether end-to-end data		This document describes a mechanism to detect whether end-to-end data
	flows share a common bottleneck. It relies on summary statistics		flows share a common bottleneck. It relies on summary statistics
	that are calculated based on continuous measurements and used as		that are calculated based on continuous measurements and used as
	input to a grouping algorithm that runs wherever the knowledge is		input to a grouping algorithm that runs wherever the knowledge is
	needed. This mechanism complements the coupled congestion control		needed.
	mechanism in draft-ietf-rmcat-coupled-cc.
	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.
	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 May 30, 2018.		This Internet-Draft will expire on August 20, 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 51 ¶		skipping to change at page 2, line 50 ¶
	4.1.2. Improving the Response of the Variability Estimate . 19		4.1.2. Improving the Response of the Variability Estimate . 19
	4.2. Removing Oscillation Noise . . . . . . . . . . . . . . . 19		4.2. Removing Oscillation Noise . . . . . . . . . . . . . . . 19
	5. Measuring OWD . . . . . . . . . . . . . . . . . . . . . . . . 20		5. Measuring OWD . . . . . . . . . . . . . . . . . . . . . . . . 20
	5.1. Time-stamp Resolution . . . . . . . . . . . . . . . . . . 20		5.1. Time-stamp Resolution . . . . . . . . . . . . . . . . . . 20
	5.2. Clock Skew . . . . . . . . . . . . . . . . . . . . . . . 20		5.2. Clock Skew . . . . . . . . . . . . . . . . . . . . . . . 20
	6. Expected Feedback from Experiments . . . . . . . . . . . . . 20		6. Expected Feedback from Experiments . . . . . . . . . . . . . 20
	7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 21		9. Security Considerations . . . . . . . . . . . . . . . . . . . 21
	10. Change history . . . . . . . . . . . . . . . . . . . . . . . 21		10. Change history . . . . . . . . . . . . . . . . . . . . . . . 21
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 22		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
	11.1. Normative References . . . . . . . . . . . . . . . . . . 22		11.1. Normative References . . . . . . . . . . . . . . . . . . 23
	11.2. Informative References . . . . . . . . . . . . . . . . . 23		11.2. Informative References . . . . . . . . . . . . . . . . . 23
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
	1. Introduction		1. Introduction
	In the Internet, it is not normally known if flows (e.g., TCP		In the Internet, it is not normally known if flows (e.g., TCP
	connections or UDP data streams) traverse the same bottlenecks. Even		connections or UDP data streams) traverse the same bottlenecks. Even
	flows that have the same sender and receiver may take different paths		flows that have the same sender and receiver may take different paths
	and may or may not share a bottleneck. Flows that share a bottleneck		and may or may not share a bottleneck. Flows that share a bottleneck
	link usually compete with one another for their share of the		link usually compete with one another for their share of the
	skipping to change at page 4, line 39 ¶		skipping to change at page 4, line 39 ¶
	Flows that share a common bottleneck may traverse different paths,		Flows that share a common bottleneck may traverse different paths,
	and these paths will often have different base delays. This makes it		and these paths will often have different base delays. This makes it
	difficult to correlate changes in delay or loss. This technique uses		difficult to correlate changes in delay or loss. This technique uses
	the long term shape of the delay distribution as a base for		the long term shape of the delay distribution as a base for
	comparison to counter this.		comparison to counter this.
	2. Definitions		2. Definitions
	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 RFC 2119 [RFC2119].		"OPTIONAL" in this document are to be interpreted as described in BCP
			14 [RFC2119] RFC2119 [RFC2119] RFC8174 [RFC8174] when, and only when,
			they appear in all capitals, as shown here.
	Acronyms used in this document:		Acronyms used in this document:
	OWD -- One Way Delay		OWD -- One Way Delay
	MAD -- Mean Absolute Deviation		MAD -- Mean Absolute Deviation
	RTT -- Round Trip Time		RTT -- Round Trip Time
	SBD -- Shared Bottleneck Detection		SBD -- Shared Bottleneck Detection
	skipping to change at page 9, line 18 ¶		skipping to change at page 9, line 18 ¶
	control mechanisms.		control mechanisms.
	3.1.1. Feedback When All the Logic is Placed at the Sender		3.1.1. Feedback When All the Logic is Placed at the Sender
	Having the sender calculate the summary statistics and determine the		Having the sender calculate the summary statistics and determine the
	shared bottlenecks based on them has the advantage of placing most of		shared bottlenecks based on them has the advantage of placing most of
	the functionality in one place -- the sender.		the functionality in one place -- the sender.
	For every packet, the sender requires accurate relative OWD		For every packet, the sender requires accurate relative OWD
	measurements of adequate precision, along with an indication of lost		measurements of adequate precision, along with an indication of lost
	packets (or the proportion of packets lost over an interval). These		packets (or the proportion of packets lost over an interval). An
	can be provided by [I-D.ietf-avtcore-cc-feedback-message].		method to provide such measurement data with RTCP is described in
			[I-D.ietf-avtcore-cc-feedback-message].
	Sums, var_base_T and skew_base_T are calculated incrementally as		Sums, var_base_T and skew_base_T are calculated incrementally as
	relative OWD measurements are determined from the feedback messages.		relative OWD measurements are determined from the feedback messages.
	When the mechanism has received sufficient measurements to cover the		When the mechanism has received sufficient measurements to cover the
	T base time interval for all flows, the summary statistics (see		T base time interval for all flows, the summary statistics (see
	Section 3.2) are calculated for that T interval and flows are grouped		Section 3.2) are calculated for that T interval and flows are grouped
	(see Section 3.3.1). The exact timing of these calculations will		(see Section 3.3.1). The exact timing of these calculations will
	depend on the frequency of the feedback message.		depend on the frequency of the feedback message.
	3.1.2. Feedback When the Statistics are Calculated at the Receiver and		3.1.2. Feedback When the Statistics are Calculated at the Receiver and
	SBD Performed at the Sender		SBD Performed at the Sender
	This scenario minimizes feedback, but requires receivers to send		This scenario minimizes feedback, but requires receivers to send
	selected summary statistics at an agreed regular interval. We		selected summary statistics at an agreed regular interval. We
	envisage the following exchange of information to initialize the		envisage the following exchange of information to initialize the
	system:		system:
	o An initialization message from the sender to the receiver will		o An initialization message from the sender to the receiver will
	contain the following information:		contain the following information:
	* A protocol identifier (SBD=01). This is to future proof the
	message exchange so that potential advances in SBD technology
	can be easily deployed. All following initialization elements
	relate to the mechanism outlined in this document which will
	have the identifier SBD=01.
	* A list of which key metrics should be collected and relayed		* A list of which key metrics should be collected and relayed
	back to the sender out of a possibly extensible set (pkt_loss,		back to the sender out of a possibly extensible set (pkt_loss,
	var_est, skew_est, freq_est). The grouping algorithm described		var_est, skew_est, freq_est). The grouping algorithm described
	in this document requires all four of these metrics, and		in this document requires all four of these metrics, and
	receivers MUST be able to provide them, but future algorithms		receivers MUST be able to provide them, but future algorithms
	may be able to exploit other metrics (e.g. metrics based on		may be able to exploit other metrics (e.g. metrics based on
	explicit network signals).		explicit network signals).
	* The values of T, N, M, and the necessary resolution and		* The values of T, N, M, and the necessary resolution and
	precision of the relayed statistics.		precision of the relayed statistics.
	o A response message from the receiver acknowledges this message		o A response message from the receiver acknowledges this message
	with a list of key metrics it supports (subset of the senders		with a list of key metrics it supports (subset of the senders
	list) and is able to relay back to the sender.		list) and is able to relay back to the sender.
	This initialization exchange may be repeated to finalize the agreed		This initialization exchange may be repeated to finalize the agreed
	metrics should not all be supported by all receivers.		metrics should not all be supported by all receivers. It is also
			recommendable to include an identifier for the SBD algorithm version
			in the initialization message from the sender, so that potential
			advances in SBD technology can be easily deployed. For reference,
			the mechanism outlined in this document has the identifier SBD=01.
	After initialization the agreed summary statistics are fed back to		After initialization the agreed summary statistics are fed back to
	the sender (nominally every T).		the sender (nominally every T).
	3.1.3. Feedback When Bottlenecks can be Determined at Both Senders and		3.1.3. Feedback When Bottlenecks can be Determined at Both Senders and
	Receivers		Receivers
	This type of mechanism is currently beyond the scope of SBD in RMCAT.		This type of mechanism is currently beyond the scope of the SBD
	It is mentioned here to ensure more advanced sender/receiver		algorithm described in this document. It is mentioned here to ensure
	cooperative shared bottleneck determination mechanisms remain		more advanced sender/receiver cooperative shared bottleneck
	possible in the future.		determination mechanisms remain possible in the future.
	It is envisaged that such a mechanism would be initialized in a		It is envisaged that such a mechanism would be initialized in a
	similar manner to that described in Section 3.1.2.		similar manner to that described in Section 3.1.2.
	After initialization both summary statistics and shared bottleneck		After initialization both summary statistics and shared bottleneck
	determinations should be exchanged, nominally every T.		determinations should be exchanged, nominally every T.
	3.2. Key Metrics and Their Calculation		3.2. Key Metrics and Their Calculation
	Measurements are calculated over a base interval, T and summarized		Measurements are calculated over a base interval, T and summarized
	skipping to change at page 11, line 26 ¶		skipping to change at page 11, line 26 ¶
	3.2.2. Skewness Estimate		3.2.2. Skewness Estimate
	Skewness is difficult to calculate efficiently and accurately.		Skewness is difficult to calculate efficiently and accurately.
	Ideally it should be calculated over the entire period (M * T) from		Ideally it should be calculated over the entire period (M * T) from
	the mean OWD over that period. However this would require storing		the mean OWD over that period. However this would require storing
	every delay measurement over the period. Instead, an estimate is		every delay measurement over the period. Instead, an estimate is
	made over M * T based on a calculation every T using the previous T's		made over M * T based on a calculation every T using the previous T's
	calculation of mean_delay.		calculation of mean_delay.
	The base for the skewness calculation is estimated using a counter		The base for the skewness calculation is estimated using a counter
	initialized every T. It increments for one way delay samples (OWD)		initialized every T. It increments for one way delay (OWD) samples
	below the mean and decrements for OWD above the mean. So for each		below the mean and decrements for OWD above the mean. So for each
	OWD sample:		OWD sample:
	if (OWD < mean_delay) skew_base_T++		if (OWD < mean_delay) skew_base_T++
	if (OWD > mean_delay) skew_base_T--		if (OWD > mean_delay) skew_base_T--
	The mean_delay does not include the mean of the current T interval to		The mean_delay does not include the mean of the current T interval to
	enable it to be calculated iteratively.		enable it to be calculated iteratively.
	skipping to change at page 13, line 20 ¶		skipping to change at page 13, line 20 ¶
	pkt_loss = sum_NT(lost packets) / sum_NT(total packets)		pkt_loss = sum_NT(lost packets) / sum_NT(total packets)
	Note: When pkt_loss is small it is very variable, however, when		Note: When pkt_loss is small it is very variable, however, when
	pkt_loss is high it becomes a stable measure for making grouping		pkt_loss is high it becomes a stable measure for making grouping
	decisions.		decisions.
	3.3. Flow Grouping		3.3. Flow Grouping
	3.3.1. Flow Grouping Algorithm		3.3.1. Flow Grouping Algorithm
	The following grouping algorithm is RECOMMENDED for SBD in the RMCAT		The following grouping algorithm is RECOMMENDED for use of SBD with
	context and is sufficient and efficient for small to moderate numbers		coupled congestion control for RTP media [I-D.ietf-rmcat-coupled-cc]
	of flows. For very large numbers of flows (e.g. hundreds), a more		and is sufficient and efficient for small to moderate numbers of
			flows. For very large numbers of flows (e.g. hundreds), a more
	complex clustering algorithm may be substituted.		complex clustering algorithm may be substituted.
	Since no single metric is precise enough to group flows (due to		Since no single metric is precise enough to group flows (due to
	noise), the algorithm uses multiple metrics. Each metric offers a		noise), the algorithm uses multiple metrics. Each metric offers a
	different "view" of the bottleneck link characteristics, and used		different "view" of the bottleneck link characteristics, and used
	together they enable a more precise grouping of flows than would		together they enable a more precise grouping of flows than would
	otherwise be possible.		otherwise be possible.
	Flows determined to be transiting a bottleneck are successively		Flows determined to be transiting a bottleneck are successively
	divided into groups based on freq_est, var_est, skew_est and		divided into groups based on freq_est, var_est, skew_est and
	skipping to change at page 20, line 27 ¶		skipping to change at page 20, line 27 ¶
	clock offsets should be approximately constant over the measurement		clock offsets should be approximately constant over the measurement
	periods, the offset is subtracted out in the calculation.		periods, the offset is subtracted out in the calculation.
	5.1. Time-stamp Resolution		5.1. Time-stamp Resolution
	The SBD mechanism requires timing information precise enough to be		The SBD mechanism requires timing information precise enough to be
	able to make comparisons. As a rule of thumb, the time resolution		able to make comparisons. As a rule of thumb, the time resolution
	should be less than one hundredth of a typical path's range of		should be less than one hundredth of a typical path's range of
	delays. In general, the coarser the time resolution, the more care		delays. In general, the coarser the time resolution, the more care
	that needs to be taken to ensure rounding errors do not bias the		that needs to be taken to ensure rounding errors do not bias the
	skewness calculation. Timing information described by		skewness calculation. Frequent timing information in millisecond
	[I-D.ietf-avtcore-cc-feedback-message] should be sufficient for the		resolution as described by [I-D.ietf-avtcore-cc-feedback-message]
	sender to calculate relative OWD.		should be sufficient for the sender to calculate relative OWD.
	5.2. Clock Skew		5.2. Clock Skew
	Generally sender and receiver clock skew will be too small to cause		Generally sender and receiver clock skew will be too small to cause
	significant errors in the estimators. Skew_est and freq_est are the		significant errors in the estimators. Skew_est and freq_est are the
	most sensitive to this type of noise due to their use of a mean OWD		most sensitive to this type of noise due to their use of a mean OWD
	calculated over a longer interval. In circumstances where clock skew		calculated over a longer interval. In circumstances where clock skew
	is high, basing skew_est only on the previous T's mean and ignoring		is high, basing skew_est only on the previous T's mean and ignoring
	freq_est provides a noisier but reliable signal.		freq_est provides a noisier but reliable signal.
	A more sophisticated method is to estimate the effect the clock skew		A more sophisticated method is to estimate the effect the clock skew
	is having on the summary statistics, and then adjust statistics		is having on the summary statistics, and then adjust statistics
	accordingly. There are a number of techniques in the literature,		accordingly. There are a number of techniques in the literature,
	including [Zhang-Infocom02].		including [Zhang-Infocom02].
	6. Expected Feedback from Experiments		6. Expected Feedback from Experiments
	The algorithm described in this memo has so far been evaluated using		The algorithm described in this memo has so far been evaluated using
	simulations and small scale experiments. Real network tests using		simulations and small scale experiments. Real network tests using
	RMCAT congestion control algorithms will help confirm the default		RTP Media Congestion Avoidance Techniques (RMCAT) congestion control
	parameter choice. For example, the time interval T may need to be		algorithms will help confirm the default parameter choice. For
	made longer if the packet rate is very low. Implementers and testers		example, the time interval T may need to be made longer if the packet
	are invited to document their findings in an Internet draft.		rate is very low. Implementers and testers are invited to document
			their findings in an Internet draft.
	7. Acknowledgments		7. Acknowledgments
	This work was part-funded by the European Community under its Seventh		This work was part-funded by the European Community under its Seventh
	Framework Programme through the Reducing Internet Transport Latency		Framework Programme through the Reducing Internet Transport Latency
	(RITE) project (ICT-317700). The views expressed are solely those of		(RITE) project (ICT-317700). The views expressed are solely those of
	the authors.		the authors.
	8. IANA Considerations		8. IANA Considerations
	This memo includes no request to IANA.		This memo includes no request to IANA.
	9. Security Considerations		9. Security Considerations
	The security considerations of RFC 3550 [RFC3550], RFC 4585		The security considerations of RFC 3550 [RFC3550], RFC 4585
	[RFC4585], and RFC 5124 [RFC5124] are expected to apply.		[RFC4585], and RFC 5124 [RFC5124] are expected to apply.
	Non-authenticated RTCP packets carrying OWD measurements, shared		Non-authenticated RTCP packets carrying OWD measurements, shared
	bottleneck indications, and/or summary statistics could allow		bottleneck indications, and/or summary statistics could allow
	attackers to alter the bottleneck sharing characteristics for private		attackers to alter the bottleneck sharing characteristics for private
	gain or disruption of other parties' communication.		gain or disruption of other parties' communication. When using SBD
			for coupled congestion control as described in
			[I-D.ietf-rmcat-coupled-cc], the security considerations of
			[I-D.ietf-rmcat-coupled-cc] apply.
	10. Change history		10. Change history
			XX RFC ED - PLEASE REMOVE THIS SECTION XXX
	Changes made to this document:		Changes made to this document:
			WG-09->WG-10 : AD review addressed.
	WG-08->WG-09 : Removed definitions that are no longer used. Added		WG-08->WG-09 : Removed definitions that are no longer used. Added
	pkt_loss definition. Refined c_s recommendation.		pkt_loss definition. Refined c_s recommendation.
	WG-07->WG-08 : Updates addressing https://www.ietf.org/mail-		WG-07->WG-08 : Updates addressing https://www.ietf.org/mail-
	archive/web/rmcat/current/msg01671.html Mainly		archive/web/rmcat/current/msg01671.html Mainly
	clarifications.		clarifications.
	WG-06->WG-07 : Updates addressing		WG-06->WG-07 : Updates addressing
	https://mailarchive.ietf.org/arch/msg/		https://mailarchive.ietf.org/arch/msg/
	rmcat/80B6q4nI7carGcf_ddBwx7nKvOw. Mainly		rmcat/80B6q4nI7carGcf_ddBwx7nKvOw. Mainly
	skipping to change at page 24, line 5 ¶		skipping to change at page 24, line 10 ¶
	[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, DOI 10.17487/RFC5124, February		(RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February
	2008, <https://www.rfc-editor.org/info/rfc5124>.		2008, <https://www.rfc-editor.org/info/rfc5124>.
	[RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind,		[RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind,
	"Low Extra Delay Background Transport (LEDBAT)", RFC 6817,		"Low Extra Delay Background Transport (LEDBAT)", RFC 6817,
	DOI 10.17487/RFC6817, December 2012,		DOI 10.17487/RFC6817, December 2012,
	<https://www.rfc-editor.org/info/rfc6817>.		<https://www.rfc-editor.org/info/rfc6817>.
			[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>.
	[Zhang-Infocom02]		[Zhang-Infocom02]
	Zhang, L., Liu, Z., and H. Xia, "Clock synchronization		Zhang, L., Liu, Z., and H. Xia, "Clock synchronization
	algorithms for network measurements", Proc. the IEEE		algorithms for network measurements", Proc. the IEEE
	International Conference on Computer Communications		International Conference on Computer Communications
	(INFOCOM) pp160-169, September 2002,		(INFOCOM) pp160-169, September 2002,
	<http://dx.doi.org/10.1109/INFCOM.2002.1019257>.		<http://dx.doi.org/10.1109/INFCOM.2002.1019257>.
	Authors' Addresses		Authors' Addresses
	David Hayes (editor)		David Hayes (editor)
End of changes. 20 change blocks.
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