draft-ietf-rmcat-eval-criteria-00.txt   draft-ietf-rmcat-eval-criteria-01.txt 
RMCAT WG V. Singh RMCAT WG V. Singh
Internet-Draft J. Ott Internet-Draft J. Ott
Intended status: Informational Aalto University Intended status: Informational Aalto University
Expires: August 04, 2014 January 31, 2014 Expires: September 11, 2014 March 10, 2014
Evaluating Congestion Control for Interactive Real-time Media Evaluating Congestion Control for Interactive Real-time Media
draft-ietf-rmcat-eval-criteria-00 draft-ietf-rmcat-eval-criteria-01
Abstract Abstract
The Real-time Transport Protocol (RTP) is used to transmit media in The Real-time Transport Protocol (RTP) is used to transmit media in
telephony and video conferencing applications. This document telephony and video conferencing applications. This document
describes the guidelines to evaluate new congestion control describes the guidelines to evaluate new congestion control
algorithms for interactive point-to-point real-time media. algorithms for interactive point-to-point real-time media.
Status of This Memo Status of This Memo
skipping to change at page 1, line 33 skipping to change at page 1, line 33
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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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 August 04, 2014. This Internet-Draft will expire on September 11, 2014.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. RTP Log Format . . . . . . . . . . . . . . . . . . . . . 5 3.1. RTP Log Format . . . . . . . . . . . . . . . . . . . . . 4
4. Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Avoiding Congestion Collapse . . . . . . . . . . . . . . 5 4.1. Avoiding Congestion Collapse . . . . . . . . . . . . . . 5
4.2. Stability . . . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Stability . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Media Traffic . . . . . . . . . . . . . . . . . . . . . . 6 4.3. Media Traffic . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Start-up Behaviour . . . . . . . . . . . . . . . . . . . 6 4.4. Start-up Behaviour . . . . . . . . . . . . . . . . . . . 5
4.5. Diverse Environments . . . . . . . . . . . . . . . . . . 6 4.5. Diverse Environments . . . . . . . . . . . . . . . . . . 6
4.6. Varying Path Characteristics . . . . . . . . . . . . . . 7 4.6. Varying Path Characteristics . . . . . . . . . . . . . . 6
4.7. Reacting to Transient Events or Interruptions . . . . . . 7 4.7. Reacting to Transient Events or Interruptions . . . . . . 6
4.8. Fairness With Similar Cross-Traffic . . . . . . . . . . . 7 4.8. Fairness With Similar Cross-Traffic . . . . . . . . . . . 7
4.9. Impact on Cross-Traffic . . . . . . . . . . . . . . . . . 7 4.9. Impact on Cross-Traffic . . . . . . . . . . . . . . . . . 7
4.10. Extensions to RTP/RTCP . . . . . . . . . . . . . . . . . 8 4.10. Extensions to RTP/RTCP . . . . . . . . . . . . . . . . . 7
5. Minimum Requirements for Evaluation . . . . . . . . . . . . . 8 5. Minimum Requirements for Evaluation . . . . . . . . . . . . . 7
6. Evaluation Parameters . . . . . . . . . . . . . . . . . . . . 8 6. Status of Proposals . . . . . . . . . . . . . . . . . . . . . 7
6.1. Bottleneck Traffic Flows . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6.2. Access Links . . . . . . . . . . . . . . . . . . . . . . 9 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6.3. Example Bottleneck Link Parameters . . . . . . . . . . . 9 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
6.4. DropTail Router Queue Parameters . . . . . . . . . . . . 10 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
6.5. Media Flow Parameters . . . . . . . . . . . . . . . . . . 11 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.6. Cross-traffic Parameters . . . . . . . . . . . . . . . . 11 11.1. Normative References . . . . . . . . . . . . . . . . . . 8
7. Status of Proposals . . . . . . . . . . . . . . . . . . . . . 11 11.2. Informative References . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 Appendix A. Application Trade-off . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 A.1. Measuring Quality . . . . . . . . . . . . . . . . . . . . 10
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 10
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 B.1. Changes in draft-ietf-rmcat-eval-criteria-01 . . . . . . 10
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 B.2. Changes in draft-ietf-rmcat-eval-criteria-00 . . . . . . 10
12.1. Normative References . . . . . . . . . . . . . . . . . . 12 B.3. Changes in draft-singh-rmcat-cc-eval-04 . . . . . . . . . 10
12.2. Informative References . . . . . . . . . . . . . . . . . 13 B.4. Changes in draft-singh-rmcat-cc-eval-03 . . . . . . . . . 11
Appendix A. Application Trade-off . . . . . . . . . . . . . . . 14 B.5. Changes in draft-singh-rmcat-cc-eval-02 . . . . . . . . . 11
A.1. Measuring Quality . . . . . . . . . . . . . . . . . . . . 14 B.6. Changes in draft-singh-rmcat-cc-eval-01 . . . . . . . . . 11
Appendix B. Proposal to evaluate Self-fairness of RMCAT Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
congestion control algorithm . . . . . . . . . . . . 14
B.1. Evaluation Parameters . . . . . . . . . . . . . . . . . . 15
B.1.1. Media Traffic Generator . . . . . . . . . . . . . . . 15
B.1.2. Bottleneck Link Bandwidth . . . . . . . . . . . . . . 16
B.1.3. Bottleneck Link Queue Type and Length . . . . . . . . 16
B.1.4. RMCAT flows and delay legs . . . . . . . . . . . . . 16
B.1.5. Impairment Generator . . . . . . . . . . . . . . . . 17
B.2. Proposed Passing Criteria . . . . . . . . . . . . . . . . 17
B.3. Extensibility of the Experiment . . . . . . . . . . . . . 17
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 18
C.1. Changes in draft-ietf-rmcat-eval-criteria-00 . . . . . . 18
C.2. Changes in draft-singh-rmcat-cc-eval-04 . . . . . . . . . 18
C.3. Changes in draft-singh-rmcat-cc-eval-03 . . . . . . . . . 18
C.4. Changes in draft-singh-rmcat-cc-eval-02 . . . . . . . . . 19
C.5. Changes in draft-singh-rmcat-cc-eval-01 . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction 1. Introduction
This memo describes the guidelines to help with evaluating new This memo describes the guidelines to help with evaluating new
congestion control algorithms for interactive point-to-point real congestion control algorithms for interactive point-to-point real
time media. The requirements for the congestion control algorithm time media. The requirements for the congestion control algorithm
are outlined in [I-D.ietf-rmcat-cc-requirements]). This document are outlined in [I-D.ietf-rmcat-cc-requirements]). This document
builds upon previous work at the IETF: Specifying New Congestion builds upon previous work at the IETF: Specifying New Congestion
Control Algorithms [RFC5033] and Metrics for the Evaluation of Control Algorithms [RFC5033] and Metrics for the Evaluation of
Congestion Control Algorithms [RFC5166]. Congestion Control Algorithms [RFC5166].
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Each experiment is expected to log every incoming and outgoing packet Each experiment is expected to log every incoming and outgoing packet
(the RTP logging format is described in Section 3.1). The logging (the RTP logging format is described in Section 3.1). The logging
can be done inside the application or at the endpoints using pcap can be done inside the application or at the endpoints using pcap
(packet capture, e.g., tcpdump, wireshark). The following are (packet capture, e.g., tcpdump, wireshark). The following are
calculated based on the information in the packet logs: calculated based on the information in the packet logs:
1. Sending rate, Receiver rate, Goodput 1. Sending rate, Receiver rate, Goodput
2. Packet delay 2. Packet delay
3. Packet loss 3. Packet loss
4. If using, retransmission or FEC: residual loss 4. If using, retransmission or FEC: residual loss
5. Packets discarded from the playout or de-jitter buffer 5. Packets discarded from the playout or de-jitter buffer
[Open issue (1): The "unfairness" test is (measured at 1s intervals): [Open issue (1): The "unfairness" test is (measured at 1s intervals):
1. Do not trigger the circuit breaker. 1. Does not trigger the circuit breaker.
2. Over 3 times or less than 1/3 times the throughput for an RMCAT 2. Over 3 times or less than 1/3 times the throughput for an RMCAT
media stream compared to identical RMCAT streams competing on a media stream compared to identical RMCAT streams competing on a
bottleneck, for a case when the competing streams have similar RTTs. bottleneck, for a case when the competing streams have similar RTTs.
3. Over 3 times delay compared to RTT measurements performed before 3. Over 3 times delay compared to RTT measurements performed before
starting the RMCAT flow or for the case when competing with identical starting the RMCAT flow or for the case when competing with identical
RMCAT streams having similar RTTs. RMCAT streams having similar RTTs.
] ]
[Open issue (2): Possibly using Jain-fairness index.] [Open issue (2): Possibly using Jain-fairness index.]
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receiver rate, goodput, latency) can be visualized in graphs as receiver rate, goodput, latency) can be visualized in graphs as
variation over time, the measurements in the plot are at 1 second variation over time, the measurements in the plot are at 1 second
intervals. Additionally, from the logs it is possible to plot the intervals. Additionally, from the logs it is possible to plot the
histogram or CDF of packet delay. histogram or CDF of packet delay.
3.1. RTP Log Format 3.1. RTP Log Format
The log file is tab or comma separated containing the following The log file is tab or comma separated containing the following
details: details:
Send or receive timestamp (unix) Send or receive timestamp (unix)
RTP payload type RTP payload type
SSRC SSRC
RTP sequence no RTP sequence no
RTP timestamp RTP timestamp
marker bit marker bit
payload size payload size
If the congestion control implements, retransmissions or FEC, the If the congestion control implements, retransmissions or FEC, the
evaluation should report both packet loss (before applying error- evaluation should report both packet loss (before applying error-
resilience) and residual packet loss (after applying error- resilience) and residual packet loss (after applying error-
resilience). resilience).
4. Guidelines 4. Guidelines
A congestion control algorithm should be tested in simulation or a A congestion control algorithm should be tested in simulation or a
testbed environment, and the experiments should be repeated multiple testbed environment, and the experiments should be repeated multiple
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The evaluation may be done in two stages. In the first stage, the The evaluation may be done in two stages. In the first stage, the
endpoint generates traffic at the rate calculated by the congestion endpoint generates traffic at the rate calculated by the congestion
controller. In the second stage, real codecs or models of video controller. In the second stage, real codecs or models of video
codecs are used to mimic application-limited data periods and varying codecs are used to mimic application-limited data periods and varying
video frame sizes. video frame sizes.
4.4. Start-up Behaviour 4.4. Start-up Behaviour
The congestion control algorithm should be assessed with different The congestion control algorithm should be assessed with different
start-rates. The main reason is to observe the behavior of the start-rates. The main reason is to observe the behavior of the
congestion control in different evaluation scenarios, such as when congestion control in different test scenarios, such as when
competing with varying amount of cross-traffic or how quickly does competing with varying amount of cross-traffic or how quickly does
the congestion control algorithm achieve a stable sending rate. the congestion control algorithm achieve a stable sending rate.
[Editor's note: requires a robust definition for unfriendliness and
convergence time.]
4.5. Diverse Environments 4.5. Diverse Environments
The congestion control algorithm should be assessed in heterogeneous The congestion control algorithm should be assessed in heterogeneous
environments, containing both wired and wireless paths. Examples of environments, containing both wired and wireless paths. Examples of
wireless access technologies are: 802.11, GPRS, HSPA, or LTE. One of wireless access technologies are: 802.11, GPRS, HSPA, or LTE. One of
the main challenges of the wireless environments for the congestion the main challenges of the wireless environments for the congestion
control algorithm is to distinguish between congestion induced loss control algorithm is to distinguish between congestion induced loss
and transmission (bit-error corruption) loss. Congestion control and transmission (bit-error) loss. Congestion control algorithms may
algorithms may incorrectly identify transmission loss as congestion incorrectly identify transmission loss as congestion loss and reduce
loss and reduce the media encoding rate by too much, which may cause the media encoding rate by too much, which may cause oscillatory
oscillatory behavior and deteriorate the users' quality of behavior and deteriorate the users' quality of experience.
experience. Furthermore, packet loss may induce additional delay in Furthermore, packet loss may induce additional delay in networks with
networks with wireless paths due to link-layer retransmissions. wireless paths due to link-layer retransmissions.
4.6. Varying Path Characteristics 4.6. Varying Path Characteristics
The congestion control algorithm should be evaluated for a range of The congestion control algorithm should be evaluated for a range of
path characteristics such as, different end-to-end capacity and path characteristics such as, different end-to-end capacity and
latency, varying amount of cross traffic on a bottleneck link and a latency, varying amount of cross traffic on a bottleneck link and a
router's queue length. For the moment, only DropTail queues are router's queue length. For the moment, only DropTail queues are
used. However, if new Active Queue Management (AQM) schemes become used. However, if new Active Queue Management (AQM) schemes become
available, the performance of the congestion control algorithm should available, the performance of the congestion control algorithm should
be again evaluated. be again evaluated.
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handovers, etc. In wired networks the end-to-end capacity may vary handovers, etc. In wired networks the end-to-end capacity may vary
due to changes in resource reservation. due to changes in resource reservation.
4.8. Fairness With Similar Cross-Traffic 4.8. Fairness With Similar Cross-Traffic
The congestion control algorithm should be evaluated when competing The congestion control algorithm should be evaluated when competing
with other RTP flows using the same or another candidate congestion with other RTP flows using the same or another candidate congestion
control algorithm. The proposal should highlight the bottleneck control algorithm. The proposal should highlight the bottleneck
capacity share of each RTP flow. capacity share of each RTP flow.
[Editor's note: If we define Unfriendliness then that criteria should
be applied here.]
4.9. Impact on Cross-Traffic 4.9. Impact on Cross-Traffic
The congestion control algorithm should be evaluated when competing The congestion control algorithm should be evaluated when competing
with standard TCP. Short TCP flows may be considered as transient with standard TCP. Short TCP flows may be considered as transient
events and the RTP flow may give way to the short TCP flow to events and the RTP flow may give way to the short TCP flow to
complete quickly. However, long-lived TCP flows may starve out the complete quickly. However, long-lived TCP flows may starve out the
RTP flow depending on router queue length. RTP flow depending on router queue length.
The proposal should also measure the impact on varied number of The proposal should also measure the impact on varied number of
cross-traffic sources, i.e., few and many competing flows, or mixing cross-traffic sources, i.e., few and many competing flows, or mixing
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The congestion control algorithm should indicate if any protocol The congestion control algorithm should indicate if any protocol
extensions are required to implement it and should carefully describe extensions are required to implement it and should carefully describe
the impact of the extension. the impact of the extension.
5. Minimum Requirements for Evaluation 5. Minimum Requirements for Evaluation
[Editor's Note: If needed, a minimum evaluation criteria can be based [Editor's Note: If needed, a minimum evaluation criteria can be based
on the above guidelines or defined tests/scenarios.] on the above guidelines or defined tests/scenarios.]
6. Evaluation Parameters 6. Status of Proposals
An evaluation scenario is created from a list of network, link and
flow characteristics. The example parameters discussed in the
following subsections are meant to aid in creating evaluation
scenarios and do not describe an evaluation scenario. The scenario
discussed in Appendix B takes into account all these parameters.
6.1. Bottleneck Traffic Flows
The network scenario describes the types of flows sharing the common
bottleneck with a single RMCAT flow, they are:
1. A single RMCAT flow by itself.
2. Competing with similar RMCAT flows. These competing flows may
use the same algorithm or another candidate RMCAT algorithm.
3. Compete with long-lived TCP.
4. Compete with bursty TCP.
5. Compete with LEDBAT flows.
6. Compete with unresponsive interactive media flows (i.e., not only
CBR).
Figure 1 shows an example evaluation topology, where S1..Sn are
traffic sources, these sources are either RMCAT or a mixture of
traffic flows listed above. R1..Rn are the corresponding receivers.
A and B are routers that can be configured to introduce impairments.
Access links are in between the sender/receiver and the router, while
the bottleneck link is between the Routers A and B.
+---+ Access Access +---+
|S1 |======= \ / =======|R1 |
+---+ link \\ // link +---+
\\ //
+---+ +-----+ Bottleneck +-----+ +---+
|S2 |=======| A |------------------------------>| B |=======|R2 |
+---+ | |<------------------------------| | +---+
+-----+ Link +-----+
(...) // \\ (...)
// \\
+---+ // \\ +---+
|Sn |====== / \ ======|Rn |
+---+ +---+
Figure 1: Simple Topology
[Open Issue: Discuss more complex topologies]
6.2. Access Links
The media senders and receivers are typically connected to the
bottleneck link, common access links are:
1. Ethernet (LAN)
2. Wireless LAN (WLAN)
3. 3G/LTE
[Open issue: point to a reference containing parameters or traces to
model WLAN and 3G/LTE.]
A real-world network typically consists of a mixture of links, the
most important aspect is to identify the location of the bottleneck
link. The bottleneck link can move from one node to another
depending on the amount of cross-traffic or due to the varying link
capacity. The design of the experiments should take this into
account. In the simplest case the access link may not be the
bottleneck link but an intermediate node.
6.3. Example Bottleneck Link Parameters
The bottleneck link carries multiple flows, these flows may be other
RMCAT flows or other types of cross-traffic. The experiments should
dimension the bottleneck link based on the number of flows and the
expected behavior. For example, if 5 media flows are expected to
share the bottleneck link equally, the bottleneck link is set to 5
times the desired transmission rate.
If the experiment carries only media in one direction, then the
upstream (sender to receiver) bottleneck link carries media packets
while the downstream (receiver to sender) bottleneck carries the
feedback packets. The bottleneck link parameters discussed in this
section apply only to a single direction, hence the bottleneck link
in the reverse direction can choose the same or have different
parameters.
The link latency corresponds to the propagation delay of the link,
i.e., the time it takes for a packet to traverse the bottleneck link,
it does not include queuing delay. In an experiment with several
links the experiment should describe if the links add latency or not.
It is possible for experiments to have multiple hops with different
link latencies. Experiments are expected to verify that the
congestion control is able to work in challenging situations, for
example over trans-continental and/or satellite links. The
experiment should pick link latency values from the following:
1. Very low latency: 0-1ms
2. Low latency: 50ms
3. High latency: 150ms
4. Extreme latency: 300ms
Similarly, to model lossy links, the experiments can choose one of
the following loss rates, the fractional loss is the ratio of packets
lost and packets sent.
1. no loss: 0%
2. 1%
3. 5%
4. 10%
5. 20%
These fractional losses can be generated using traces, Gilbert-Elliot
model, randomly (uncorrelated) loss.
6.4. DropTail Router Queue Parameters
The router queue length is measured as the time taken to drain the
FIFO queue, they are:
1. QoS-aware (or short): 70ms
2. Nominal: 500ms
3. Buffer-bloated: 2000ms
However, the size of the queue is typically measured in bytes or
packets and to convert the queue length measured in seconds to queue
length in bytes:
QueueSize (in bytes) = QueueSize (in sec) x Throughput (in bps)/8
6.5. Media Flow Parameters
The media sources can be modeled in two ways. In the first, the
sources always have data to send, i.e., have no data limited
intervals and are able to generate the media rate requested by the
RMCAT congestion control algorithm. In the second, the traffic
generator models the behavior of a media codec, mainly the burstiness
(time-varying data produced by a video GOP).
At the beginning of the session, the media sources are configured to
start at a given start rate, they are:
1. 200 kbps
2. 800 kbps
3. 1300 kbps
4. 4000 kbps
6.6. Cross-traffic Parameters
Long-lived TCP flows will download data throughout the session and
are expected to have infinite amount of data to send or receive.
[Open issue: short-lived/bursty TCP cross-traffic parameters are
still TBD.
7. Status of Proposals
Congestion control algorithms are expected to be published as Congestion control algorithms are expected to be published as
"Experimental" documents until they are shown to be safe to deploy. "Experimental" documents until they are shown to be safe to deploy.
An algorithm published as a draft should be experimented in An algorithm published as a draft should be experimented in
simulation, or a controlled environment (testbed) to show its simulation, or a controlled environment (testbed) to show its
applicability. Every congestion control algorithm should include a applicability. Every congestion control algorithm should include a
note describing the environments in which the algorithm is tested and note describing the environments in which the algorithm is tested and
safe to deploy. It is possible that an algorithm is not recommended safe to deploy. It is possible that an algorithm is not recommended
for certain environments or perform sub-optimally for the user. for certain environments or perform sub-optimally for the user.
[Editor's Note: Should there be a distinction between "Informational" [Editor's Note: Should there be a distinction between "Informational"
and "Experimental" drafts for congestion control algorithms in RMCAT. and "Experimental" drafts for congestion control algorithms in RMCAT.
[RFC5033] describes Informational proposals as algorithms that are [RFC5033] describes Informational proposals as algorithms that are
not safe for deployment but are proposals to experiment with in not safe for deployment but are proposals to experiment with in
simulation/testbeds. While Experimental algorithms are ones that are simulation/testbeds. While Experimental algorithms are ones that are
deemed safe in some environments but require a more thorough deemed safe in some environments but require a more thorough
evaluation (from the community).] evaluation (from the community).]
8. Security Considerations 7. Security Considerations
Security issues have not been discussed in this memo. Security issues have not been discussed in this memo.
9. IANA Considerations 8. IANA Considerations
There are no IANA impacts in this memo. There are no IANA impacts in this memo.
10. Contributors 9. Contributors
The content and concepts within this document are a product of the The content and concepts within this document are a product of the
discussion carried out in the Design Team. discussion carried out in the Design Team.
Michael Ramalho provided the text for the scenario discussed in Michael Ramalho provided the text for a specific scenario, which is
Appendix B. now covered in [I-D.sarker-rmcat-eval-test].
11. Acknowledgements 10. Acknowledgements
Much of this document is derived from previous work on congestion Much of this document is derived from previous work on congestion
control at the IETF. control at the IETF.
The authors would like to thank Harald Alvestrand, Luca De Cicco, The authors would like to thank Harald Alvestrand, Luca De Cicco,
Wesley Eddy, Lars Eggert, Kevin Gross, Vinayak Hegde, Stefan Holmer, Wesley Eddy, Lars Eggert, Kevin Gross, Vinayak Hegde, Stefan Holmer,
Randell Jesup, Piers O'Hanlon, Colin Perkins, Michael Ramalho, Randell Jesup, Piers O'Hanlon, Colin Perkins, Michael Ramalho,
Zaheduzzaman Sarker, Timothy B. Terriberry, Michael Welzl, and Mo Zaheduzzaman Sarker, Timothy B. Terriberry, Michael Welzl, and Mo
Zanaty for providing valuable feedback on earlier versions of this Zanaty for providing valuable feedback on earlier versions of this
draft. Additionally, also thank the participants of the design team draft. Additionally, also thank the participants of the design team
for their comments and discussion related to the evaluation criteria. for their comments and discussion related to the evaluation criteria.
12. References 11. References
12.1. Normative References 11.1. Normative References
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551, Video Conferences with Minimal Control", STD 65, RFC 3551,
July 2003. July 2003.
[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
skipping to change at page 13, line 20 skipping to change at page 9, line 16
"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.
[RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size [RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size
Real-Time Transport Control Protocol (RTCP): Opportunities Real-Time Transport Control Protocol (RTCP): Opportunities
and Consequences", RFC 5506, April 2009. and Consequences", RFC 5506, April 2009.
[I-D.ietf-rmcat-cc-requirements] [I-D.ietf-rmcat-cc-requirements]
Jesup, R., "Congestion Control Requirements For RMCAT", Jesup, R., "Congestion Control Requirements For RMCAT",
draft-ietf-rmcat-cc-requirements-00 (work in progress), draft-ietf-rmcat-cc-requirements-02 (work in progress),
July 2013. February 2014.
[I-D.ietf-avtcore-rtp-circuit-breakers] [I-D.ietf-avtcore-rtp-circuit-breakers]
Perkins, C. and V. Singh, "RTP Congestion Control: Circuit Perkins, C. and V. Singh, "Multimedia Congestion Control:
Breakers for Unicast Sessions", draft-ietf-avtcore-rtp- Circuit Breakers for Unicast RTP Sessions", draft-ietf-
circuit-breakers-01 (work in progress), October 2012. avtcore-rtp-circuit-breakers-05 (work in progress),
February 2014.
12.2. Informative References 11.2. Informative References
[RFC5033] Floyd, S. and M. Allman, "Specifying New Congestion [RFC5033] Floyd, S. and M. Allman, "Specifying New Congestion
Control Algorithms", BCP 133, RFC 5033, August 2007. Control Algorithms", BCP 133, RFC 5033, August 2007.
[RFC5166] Floyd, S., "Metrics for the Evaluation of Congestion [RFC5166] Floyd, S., "Metrics for the Evaluation of Congestion
Control Mechanisms", RFC 5166, March 2008. Control Mechanisms", RFC 5166, March 2008.
[RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion [RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
Control", RFC 5681, September 2009. Control", RFC 5681, September 2009.
[I-D.sarker-rmcat-eval-test]
Sarker, Z., Singh, V., Zhu, X., and M. Ramalho, "Test
Cases for Evaluating RMCAT Proposals", draft-sarker-rmcat-
eval-test-00 (work in progress), February 2014.
[SA4-EVAL] [SA4-EVAL]
R1-081955, 3GPP., "LTE Link Level Throughput Data for SA4 R1-081955, 3GPP., "LTE Link Level Throughput Data for SA4
Evaluation Framework", 3GPP R1-081955, 5 2008. Evaluation Framework", 3GPP R1-081955, 5 2008.
[SA4-LR] S4-050560, 3GPP., "Error Patterns for MBMS Streaming over [SA4-LR] S4-050560, 3GPP., "Error Patterns for MBMS Streaming over
UTRAN and GERAN", 3GPP S4-050560, 5 2008. UTRAN and GERAN", 3GPP S4-050560, 5 2008.
[TCP-eval-suite] [TCP-eval-suite]
Lachlan, A., Marcondes, C., Floyd, S., Dunn, L., Guillier, Lachlan, A., Marcondes, C., Floyd, S., Dunn, L., Guillier,
R., Gang, W., Eggert, L., Ha, S., and I. Rhee, "Towards a R., Gang, W., Eggert, L., Ha, S., and I. Rhee, "Towards a
Common TCP Evaluation Suite", Proc. PFLDnet. 2008, August Common TCP Evaluation Suite", Proc. PFLDnet. 2008, August
2008. 2008.
Appendix A. Application Trade-off Appendix A. Application Trade-off
Application trade-off is yet to be defined. see RMCAT requirements Application trade-off is yet to be defined. see RMCAT requirements
[I-D.ietf-rmcat-cc-requirements] document. Perhaps each experiment [I-D.ietf-rmcat-cc-requirements] document. Perhaps each experiment
should define the application's expectation or trade-off. should define the application's expectation or trade-off.
A.1. Measuring Quality A.1. Measuring Quality
No quality metric is defined for performance evaluation, it is No quality metric is defined for performance evaluation, it is
currently an open issue. However, there is consensus that congestion currently an open issue. However, there is consensus that congestion
control algorithm should be able to show that it is useful for control algorithm should be able to show that it is useful for
interactive video by performing analysis using a real codec and video interactive video by performing analysis using a real codec and video
sequences. sequences.
Appendix B. Proposal to evaluate Self-fairness of RMCAT congestion Appendix B. Change Log
control algorithm
The goal of the experiment discussed in this section is to initially
take out as many unknowns from the scenario. Later experiments can
define more complex environments, topologies and media behavior.
This experiment evaluates the performance of the RMCAT sender
competing with other similar RMCAT flows (running the same algorithm
or other RMCAT proposals) on the bottleneck link. There are up to 20
RMCAT flows competing for capacity, but the media only flows in one
direction, from senders (S1..S20) to receivers (R1..R20) and the
feedback packets flow in the reverse direction.
Figure 2 shows the experiment setup and it has subtle differences
compared to the simple topology in Figure 1. Groups of 10 receivers
are connected to the bottleneck link through two different routers
(Router C and D). The rationale for adding these additional routers
is to create two delay legs, i.e., two groups of endpoints with
different network latencies and measure the performance of the RMCAT
congestion control algorithm. If fewer than 10 sources are
initialized, all traffic flows experience the same delay because they
share the same delay leg.
Router A has a single forward direction bottleneck link (i.e., the
bottleneck capacity and delay constraints applies only to the media
packets going from the sender to the receiver, the feedback packets
are unaffected). Hence, the Round-Trip Time (RTT) is primarily
composed of the bottleneck queue delay and any forward path
(propagation) latency. The main reason for not applying any
constraints on the return path is to provide the best-case
performance scenario for the congestion control algorithm. In later
experiments, it is possible to add similar capacity and delay
constraints on the return path.
+---+
/ === |R1 |
+---+ +-----+ // +---+
|S1 |======= \ / =| C | //
+---+ \\ // +-----+ \\ (...)
\\ // \\
+---+ +-----+ Bottleneck +-----+ \\ +---+
|S2 |=======| A |-------------------->| B | \ ===|R10|
+---+ | |<--------------------| | +---+
+-----+ Link +-----+
(...) // \\ +---+
// \\ / === |R11|
+---+ // \\ +-----+ // +---+
|S20|====== / \ =| D |//
+---+ +-----+\\ (...)
\\
\\ +---+
\ ===|R20|
+---+
Figure 2: Self-fairness Evaluation Setup
Loss impairments are applied at Router C and Router D, but only to
the feedback flows. If the losses are set to 0%, it represents a
case where the return path is over-provisioned for all traffic. In
later experiments the loss impairments can be added to the media path
as well.
The media sources are configured to send infinite amount of data,
i.e., the sources always have data to send and have no data limited
intervals. Additionally, the media sources are always successful in
generating the media rate requested by the RMCAT congestion control
algorithm. In this experiment, we avoid the potentially complicated
scenario of using media traffic generators that try to model the
behavior of media codecs (mainly the burstiness).
B.1. Evaluation Parameters
B.1.1. Media Traffic Generator
The media source always generates at the rate requested by the
congestion control and has infinite data to send. Furthermore, the
media packet generator is subject to the following constraints:
1. It MUST emit a packet at least once per 100 ms time interval.
2. For low media rate source: when generating data at a rate less
than a maximum length MTU every 100 ms would allow (e.g., 120
kbps = 1500 bytes/packet * 10 packets/sec * 8 bits/byte), the
RMCAT source must modulate the packet size (RTP payload size) of
RTP packets that are sent every 100 ms to attain the desired
rate.
3. For high media rate sources: when generating data at a rate
greater than a maximum length MTU every 100 ms would allow, the
source must do so by sending (approximately) maximum MTU sized
packets and adjusting the inter-departure interval to be
approximately equal. The intent of this to ensure the data is
sent relatively smoothly independent of the bit rate, subject to
the first constraint.
B.1.2. Bottleneck Link Bandwidth
The bottleneck link capacity is dimensioned such that each RMCAT flow
in an ideal situation with perfectly equal capacity sharing for all
the flows on the bottleneck obtains the following throughputs: 200
kbps, 800 kbps, 1.3 Mbps and 4 Mbps.
For example, experiments with five RMCAT flows with an 800 kbps/flow
target rate should set the bottleneck link capacity to 4 Mbps.
B.1.3. Bottleneck Link Queue Type and Length
The bottleneck link queue (Router A) is a simple FIFO queue having a
buffer length corresponding to 70 ms, 500 ms or 2000 ms (defined in
Section 6.4) of delay at the bottleneck link rate (i.e., actual
buffer lengths in bytes are dependent on bottleneck link bandwidth).
B.1.4. RMCAT flows and delay legs
Experiments run with 1, 3, 5, 10 and 20 RMCAT sources, they are
outlined as follows:
1. Experiments with 1, 3, and 5 RMCAT flows, all RMCAT flows
commence simultaneously. A single delay leg is used and the link
latency is set to one of the following : 0 ms, 50 ms and 150 ms.
2. For 10 and 20 source experiments where all RMCAT flows begin
simultaneously the sources are split evenly into two different
bulk delay legs. One leg is set to 0 ms bulk delay leg and the
other is set to 150 ms.
3. For 10 and 20 source experiments where the first set will use 0
ms of bulk delay and the second set will use 150 ms bulk delay.
1. Random starts within interval [0 ms, 500 ms].
2. One "early-coming" flow (i.e., the 1st flow starting and
achieving steady-state before the next N-1 simultaneously
begin).
3. One "late-coming" flow (i.e., the Nth flow starting after
steady-state has occurred for the existing N-1 flows).
These cases assess if there are any early or late-comer
advantages or disadvantages for a particular algorithm and to see
if any unfairness is reproducible or unpredictable.
[Open issue (A.1): which group does the early and late flow belong
to?]
[Open issue (A.2): Start rate for the media flows]
B.1.5. Impairment Generator
Packet loss is created in the reverse path (affects only feedback
packets). Cases of 0%, 1%, 5% and 10% are studied for the 1, 3, and
5 RMCAT flow experiments, losses are not applied to flows with 10 or
20 RMCAT flows.
B.2. Proposed Passing Criteria
[Editor's note: there has been little or no discussion on the below
criteria, however, they are listed here for the sake of completeness.
No unfairness is observed, i.e., at steady state each flow attains a
throughput between [ B/(3*N), (3*B)/N ], where B is the link
bandwidth and N is the number of flows.
No flow experiences packet loss when queue length is set to 500 ms or
greater.
All individual sources must be in their steady state within twenty
LRTTs (where LRTT is defined as the RTT associated with the flow with
the Largest RTT in the experiment). ]
B.3. Extensibility of the Experiment
The above scenario describes only RMCAT sources competing for Note to the RFC-Editor: please remove this section prior to
capacity on the bottleneck link, however, future experiments can use publication as an RFC.
different types of cross-traffic (as described in Section 6.1).
Currently, the forward path (carrying media packets) is characterized B.1. Changes in draft-ietf-rmcat-eval-criteria-01
to add delay and a fixed bottleneck link capacity, in the future
packet losses and capacity changes can be applied to mimic a wireless
link layer (for e.g., WiFi, 3G, LTE). Additionally, only losses are
applied to the reverse path (carrying feedback packets), later
experiments can apply the same forward path (carrying media packets)
impairments to the reverse path.
Appendix C. Change Log o Removed Appendix B.
Note to the RFC-Editor: please remove this section prior to o Removed Section on Evaluation Parameters.
publication as an RFC.
C.1. Changes in draft-ietf-rmcat-eval-criteria-00 B.2. Changes in draft-ietf-rmcat-eval-criteria-00
o Updated references. o Updated references.
o Resubmitted as WG draft. o Resubmitted as WG draft.
C.2. Changes in draft-singh-rmcat-cc-eval-04 B.3. Changes in draft-singh-rmcat-cc-eval-04
o Incorporate feedback from IETF 87, Berlin. o Incorporate feedback from IETF 87, Berlin.
o Clarified metrics: convergence time, bandwidth utilization. o Clarified metrics: convergence time, bandwidth utilization.
o Changed fairness criteria to fairness test. o Changed fairness criteria to fairness test.
o Added measuring pre- and post-repair loss. o Added measuring pre- and post-repair loss.
o Added open issue of measuring video quality to appendix. o Added open issue of measuring video quality to appendix.
o clarified use of DropTail and AQM. o clarified use of DropTail and AQM.
o Updated text in "Minimum Requirements for Evaluation" o Updated text in "Minimum Requirements for Evaluation"
C.3. Changes in draft-singh-rmcat-cc-eval-03 B.4. Changes in draft-singh-rmcat-cc-eval-03
o Incorporate the discussion within the design team. o Incorporate the discussion within the design team.
o Added a section on evaluation parameters, it describes the flow o Added a section on evaluation parameters, it describes the flow
and network characteristics. and network characteristics.
o Added Appendix with self-fairness experiment. o Added Appendix with self-fairness experiment.
o Changed bottleneck parameters from a proposal to an example set. o Changed bottleneck parameters from a proposal to an example set.
C.4. Changes in draft-singh-rmcat-cc-eval-02 o
B.5. Changes in draft-singh-rmcat-cc-eval-02
o Added scenario descriptions. o Added scenario descriptions.
C.5. Changes in draft-singh-rmcat-cc-eval-01 B.6. Changes in draft-singh-rmcat-cc-eval-01
o Removed QoE metrics. o Removed QoE metrics.
o Changed stability to steady-state. o Changed stability to steady-state.
o Added measuring impact against few and many flows. o Added measuring impact against few and many flows.
o Added guideline for idle and data-limited periods. o Added guideline for idle and data-limited periods.
o Added reference to TCP evaluation suite in example evaluation o Added reference to TCP evaluation suite in example evaluation
 End of changes. 39 change blocks. 
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