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
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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
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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
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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.
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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
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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)
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