Network Working Group Z. Sarker
Internet-Draft Ericsson AB
Intended status: Informational V. Singh
Expires: December 23, 2018 callstats.io
X. Zhu
M. Ramalho
Cisco Systems
June 21, 2018
Test Cases for Evaluating RMCAT Proposals
draft-ietf-rmcat-eval-test-06
Abstract
The Real-time Transport Protocol (RTP) is used to transmit media in
multimedia telephony applications, these applications are typically
required to implement congestion control. This document describes
the test cases to be used in the performance evaluation of such
congestion control algorithms.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 23, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Sarker, et al. Expires December 23, 2018 [Page 1]
Internet-Draft Test Scenarios for RMCAT June 2018
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Structure of Test cases . . . . . . . . . . . . . . . . . . . 3
4. Recommended Evaluation Settings . . . . . . . . . . . . . . . 7
4.1. Evaluation metrics . . . . . . . . . . . . . . . . . . . 8
4.2. Path characteristics . . . . . . . . . . . . . . . . . . 8
4.3. Media source . . . . . . . . . . . . . . . . . . . . . . 9
5. Basic Test Cases . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Variable Available Capacity with a Single Flow . . . . . 10
5.2. Variable Available Capacity with Multiple Flows . . . . . 13
5.3. Congested Feedback Link with Bi-directional Media Flows . 14
5.4. Competing Media Flows with same Congestion Control
Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 17
5.5. Round Trip Time Fairness . . . . . . . . . . . . . . . . 19
5.6. Media Flow Competing with a Long TCP Flow . . . . . . . . 21
5.7. Media Flow Competing with Short TCP Flows . . . . . . . . 23
5.8. Media Pause and Resume . . . . . . . . . . . . . . . . . 25
6. Other potential test cases . . . . . . . . . . . . . . . . . 27
6.1. Media Flows with Priority . . . . . . . . . . . . . . . . 27
6.2. Explicit Congestion Notification Usage . . . . . . . . . 27
6.3. Multiple Bottlenecks . . . . . . . . . . . . . . . . . . 27
7. Wireless Access Links . . . . . . . . . . . . . . . . . . . . 29
8. Security Considerations . . . . . . . . . . . . . . . . . . . 29
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
11.1. Normative References . . . . . . . . . . . . . . . . . . 30
11.2. Informative References . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
This memo describes a set of test cases for evaluating congestion
control algorithm proposals for real-time interactive media. It is
based on the guidelines enumerated in [I-D.ietf-rmcat-eval-criteria]
and the requirements discussed in [I-D.ietf-rmcat-cc-requirements].
The test cases cover basic usage scenarios and are described using a
common structure, which allows for additional test cases to be added
to those described herein to accommodate other topologies and/or the
modeling of different path characteristics. The described test cases
Sarker, et al. Expires December 23, 2018 [Page 2]
Internet-Draft Test Scenarios for RMCAT June 2018
in this memo SHOULD be used to evaluate any proposed congestion
control algorithm for real-time interactive media.
2. Terminology
The terminology defined in RTP [RFC3550], RTP Profile for Audio and
Video Conferences with Minimal Control [RFC3551], RTCP Extended
Report (XR) [RFC3611], Extended RTP Profile for RTCP-based Feedback
(RTP/AVPF) [RFC4585], and Support for Reduced-Size RTCP [RFC5506]
apply.
3. Structure of Test cases
All the test cases in this document follow a basic structure allowing
implementers to describe a new test scenario without repeatedly
explaining common attributes. The structure includes a general
description section that describes the test case and its motivation.
Additionally the test case defines a set of attributes that
characterize the testbed, for example, the network path between
communicating peers and the diverse traffic sources.
o Define the test case:
* General description: describes the motivation and the goals of
the test case.
* Expected behavior: describes the desired rate adaptation
behavior.
* Define a list of metrics to evaluate the desired behavior: this
indicates the minimum set of metrics (e.g., link utilization,
media sending rate) that a proposed algorithm needs to measure
to validate the expected rate adaptation behavior. It should
also indicate the time granularity (e.g., averaged over 10ms,
100ms, or 1s) for measuring certain metrics. Typical
measurement interval is 200ms.
o Define testbed topology: every test case needs to define an
evaluation testbed topology. Figure 1 shows such an evaluation
topology. In this evaluation topology, S1..Sn are traffic
sources. These sources generate media traffic and use either
congestion control algorithm under investigation. R1..Rn are the
corresponding receivers. A test case can have one or more such
traffic sources (S) and their corresponding receivers (R). The
path from the source to destination is denoted as "forward" and
the path from a destination to a source is denoted as "backward".
The following basic structure of the test case has been described
from the perspective of media generating endpoints attached on the
Sarker, et al. Expires December 23, 2018 [Page 3]
Internet-Draft Test Scenarios for RMCAT June 2018
left-hand side of Figure 1. In this setup, the media flows are
transported in forward direction and corresponding feedback/
control messages are transported in the backward direction.
However, it is also possible to set up the test with media in both
forward and backward directions. In that case, unless otherwise
specified by the test case, it is expected that the backward path
does not introduce any congestion related impairments and has
enough capacity to accommodate both media and feedback/control
messages. It should be noted that depending on the test cases it
is possible to have different path characteristics in either of
the directions.
+---+ +---+
|S1 |====== \ Forward --> / =======|R1 |
+---+ \\ // +---+
\\ //
+---+ +-----+ +-----+ +---+
|S2 |=======| A |------------------------------>| B |=======|R2 |
+---+ | |<------------------------------| | +---+
+-----+ +-----+
(...) // \\ (...)
// <-- Backward \\
+---+ // \\ +---+
|Sn |====== / \ ======|Rn |
+---+ +---+
Figure 1: Example of A Testbed Topology
In a testbed environment where real equipments are used to create
a laboratory, there may exist a significant amount of traffic on
portions of the network path between the endpoints that is not
desired for the purposes of the tests described in the document.
Some of this traffic may be generated by other processes on the
endpoints themselves (e.g., discovery protocols) or by other
endpoints not presently under test. It is recommended not to
route traffic generated by endpoints that are not under test
through the test bed and route those traffic generated by the
endpoints under test around the bottleneck links specified herein.
o Define testbed attributes:
* Duration: defines the duration of the test in seconds.
* Path characteristics: defines the end-to-end transport level
path characteristics of the testbed for a particular test case.
Two sets of attributes describe the path characteristics, one
for the forward path and the other for the backward path. The
path characteristics for a particular path direction is
Sarker, et al. Expires December 23, 2018 [Page 4]
Internet-Draft Test Scenarios for RMCAT June 2018
applicable to all the Sources "S" sending traffic on that path.
If only one attribute is specified, it is used for both path
directions, however, unless specified the reverse path has no
capacity restrictions and no path loss.
+ Path direction: forward or backward.
+ Bottleneck-link capacity: defines minimum capacity of the
end-to-end path
+ Reference bottleneck capacity: defines a reference value for
the bottleneck capacity for test cases with time-varying
bottleneck capacities. All bottleneck capacities will be
specified as a ratio with respect to the reference capacity
value.
+ One-way propagation delay: describes the end-to-end latency
along the path when network queues are empty, i.e., the time
it takes for a packet to go from the sender to the receiver
without encountering any queuing delay.
+ Maximum end-to-end jitter: defines the maximum jitter that
can be observed along the path.
+ Bottleneck queue type: for example, Droptail, FQ-CoDel, or
PIE.
+ Bottleneck queue size: defines the size of queue in terms of
queuing time when the queue is full (in milliseconds).
+ Path loss ratio: characterizes the non-congested, additive,
losses to be generated on the end-to-end path. MUST
describe the loss pattern or loss model used to generate the
losses.
* Application-related: defines the traffic source behavior for
implementing the test case
+ Media traffic Source: defines the characteristics of the
media sources. When using more than one media source, the
different attributes are enumerated separately for each
different media source.
- Media type: Video/Voice
- Media flow direction: forward, backward or both.
Sarker, et al. Expires December 23, 2018 [Page 5]
Internet-Draft Test Scenarios for RMCAT June 2018
- Number of media sources: defines the total number of
media sources
- Media codec: Constant Bit Rate (CBR) or Variable Bit Rate
(VBR)
- Media source behavior: describes the media encoder
behavior. It defines the main parameters that affect the
adaptation behavior. This may include but is not limited
to:
o Adaptability: describes the adaptation options. For
example, in the case of video it defines the following
ranges of adaptation: bit rate, frame rate, video
resolution. Similarly, in the case of voice, it
defines the range of bit rate adaptation, the sampling
rate variation, and the variation in packetization
interval.
o Output variation : for a VBR encoder it defines the
encoder output variation from the average target rate
over a particular measurement interval. For example,
on average the encoder output may vary between 5% to
15% above or below the average target bit rate when
measured over a 100 ms time window. The time interval
over which the variation is specified must be
provided.
o Responsiveness to a new bit rate request: the lag in
time between a new bit rate request from the
congestion control algorithm and actual rate changes
in encoder output. Depending on the encoder, this
value may be specified in absolute time (e.g. 10ms to
1000ms) or other appropriate metric (e.g. next frame
interval time).
More detailed discussions on expected media source
behavior, including those from synthetic video traffic
sources, is at [I-D.ietf-rmcat-video-traffic-model].
- Media content: describes the chosen media sequences; For
example, test sequences are available at: [xiph-seq] and
[HEVC-seq].
- Media timeline: describes the point when the media source
is introduced and removed from the testbed. For example,
the media source may start transmitting immediately when
the test case begins, or after a few seconds.
Sarker, et al. Expires December 23, 2018 [Page 6]
Internet-Draft Test Scenarios for RMCAT June 2018
- Startup behavior: the media starts at a defined bit rate,
which may be the minimum, maximum bit rate, or a value in
between (in Kbps).
+ Competing traffic source: describes the characteristics of
the competing traffic source, the different types of
competing flows are enumerated in
[I-D.ietf-rmcat-eval-criteria].
- Traffic direction: forward, backward or both.
- Type of sources: defines the types of competing traffic
sources. Types of competing traffic flows are listed in
[I-D.ietf-rmcat-eval-criteria]. For example, the number
of TCP flows connected to a web browser, the mean size
and distribution of the content downloaded.
- Number of sources: defines the total number of competing
sources of each media type per traffic direction.
- Congestion control: enumerates the congestion control
used by each type of competing traffic.
- Traffic timeline: describes when the competing traffic
starts and ends in the test case.
* Additional attributes: describes attributes essential for
implementing a test case which are not included in the above
structure. These attributes MUST be well defined, so that the
other implementers of that particular test case are able to
implement it easily.
Any attribute can have a set of values (enclosed within "[]"). Each
member value of such a set MUST be treated as different value for the
same attribute. It is desired to run separate tests for each such
attribute value.
The test cases described in this document follow the above structure.
4. Recommended Evaluation Settings
This section describes recommended test case settings and could be
overwritten by the respective test cases.
Sarker, et al. Expires December 23, 2018 [Page 7]
Internet-Draft Test Scenarios for RMCAT June 2018
4.1. Evaluation metrics
To evaluate the performance of the candidate algorithms the
implementers MUST log enough information to visualize the following
metrics at a fine enough time granularity:
1. Flow level:
A. End-to-end delay for the congestion controlled media flow.
B. Variation in sending bit rate and goodput. Mainly observing
the frequency and magnitude of oscillations.
C. Packet losses observed at the receiving endpoint.
D. Feedback message overhead.
E. Convergence time - time to reach steady state for the
congestion controlled media flow(s).
2. Transport level:
A. Bandwidth utilization.
B. Queue length (milliseconds at specified path capacity):
+ average over the length of the session.
+ 5 and 95 percentile.
+ median, maximum, minimum.
4.2. Path characteristics
Each path between a sender and receiver as described in Figure 1 have
the following characteristics unless otherwise specified in the test
case.
o Path direction: forward and backward.
o Reference bottleneck capacity: 1Mbps.
o One-Way propagation delay: 50ms. Implementers are encouraged to
run the experiment with additional propagation delays mentioned in
[I-D.ietf-rmcat-eval-criteria]
o Maximum end-to-end jitter: 30ms. Jitter models are described in
[I-D.ietf-rmcat-eval-criteria]
Sarker, et al. Expires December 23, 2018 [Page 8]
Internet-Draft Test Scenarios for RMCAT June 2018
o Bottleneck queue type: Drop tail. Implementers are encouraged to
run the experiment with other AQM schemes, such as FQ-CoDel and
PIE.
o Bottleneck queue size: 300ms.
o Path loss ratio: 0%.
Examples of additional network parameters are discussed in
[I-D.ietf-rmcat-eval-criteria].
For test cases involving time-varying bottleneck capacity, all
capacity values are specified as a ratio with respect to a reference
capacity value, so as to allow flexible scaling of capacity values
along with media source rate range. There exist two different
mechanisms for inducing path capacity variation: a) by explicitly
modifying the value of physical link capacity; or b) by introducing
background non-adaptive UDP traffic with time-varying traffic rate.
Implementers are encouraged to run the experiments with both
mechanisms for test cases specified in Section 5.1, Section 5.2, and
Section 5.3.
4.3. Media source
Unless otherwise specified, each test case will include one or more
media sources as described below.
o Media type: Video
* Media codec: VBR
* Media source behavior:
+ Adaptability:
- Bit rate range: 150 Kbps - 1.5 Mbps. In real-life
applications the bit rate range can vary a lot depending
on the provided service, for example, the maximum bit
rate can be up to 4Mbps. However, for running tests to
evaluate the congestion control algorithms it is more
important to have a look at how they are reacting to
certain amount of bandwidth change. Also it is possible
that the media traffic generator used in a particular
simulator or testbed is not capable of generating higher
bit rate. Hence we have selected a suitable bit rate
range typical of consumer-grade video conferencing
applications in designing the test case. If a different
bit rate range is used in the test cases, then the end-
Sarker, et al. Expires December 23, 2018 [Page 9]
Internet-Draft Test Scenarios for RMCAT June 2018
to-end path capacity values will also need to be scaled
accordingly.
- Frame resolution: 144p - 720p (or 1080p). This
resolution range is selected based on the bit rate range.
If a different bit rate range is used in the test cases
then the frame resolution range also need to be selected
suitably.
- Frame rate: 10fps - 30fps. This frame rate range is
selected based on the bit rate range. If a different bit
rate range is used in the test cases then the frame rate
range also need to be adjusted suitably.
+ Variation from target bit rate: +/-5%. Unless otherwise
specified in the test case(s), bit rate variation SHOULD be
calculated over one (1) second period of time.
+ Responsiveness to new bit rate request: 100ms
* Media content: The media content should represent a typical
video conversational scenario with head and shoulder movement.
We recommend to use Foreman video sequence.
* Media startup behavior: 150Kbps. It should be noted that
applications can use smart ways to select an optimal startup
bit rate value for a certain network condition. In such cases
the candidate proposals MAY show the effectiveness of such
smart approach as an additional information for the evaluation
process.
o Media type: Audio
* Media codec: CBR
* Media bit rate: 20Kbps
5. Basic Test Cases
5.1. Variable Available Capacity with a Single Flow
In this test case the bottleneck-link capacity between the two
endpoints varies over time. This test is designed to measure the
responsiveness of the candidate algorithm. This test tries to
address the requirements in [I-D.ietf-rmcat-cc-requirements], which
requires the algorithm to adapt the flow(s) and provide lower end-to-
end latency when there exists:
Sarker, et al. Expires December 23, 2018 [Page 10]
Internet-Draft Test Scenarios for RMCAT June 2018
o an intermediate bottleneck
o change in available capacity (e.g., due to interface change,
routing change, abrupt arrival/departure of background non-
adaptive traffic).
o maximum media bit rate is greater than link capacity. In this
case, the application will attempt to ramp up to its maximum bit
rate, since the link capacity is limited to a value lower, the
congestion control scheme is expected to stabilize the sending bit
rate close to the available bottleneck capacity.
It should be noted that the exact variation in available capacity due
to any of the above depends on the underlying technologies. Hence,
we describe a set of known factors, which may be extended to devise a
more specific test case targeting certain behaviors in a certain
network environment.
Expected behavior: the candidate algorithm is expected to detect the
path capacity constraint, converges to the bottleneck link's capacity
and adapt the flow to avoid unwanted oscillation when the sending bit
rate is approaching the bottleneck link's capacity. The oscillations
occur when the media flow(s) attempts to reach its maximum bit rate
but overshoots the usage of the available bottleneck capacity then to
rectify, it reduces the bit rate and starts to ramp up again.
Evaluation metrics : as described in Section 4.1.
Testbed topology: One media source S1 is connected to the
corresponding R1. The media traffic is transported over the forward
path and corresponding feedback/control traffic is transported over
the backward path.
Forward -->
+---+ +-----+ +-----+ +---+
|S1 |=======| A |------------------------------>| B |=======|R1 |
+---+ | |<------------------------------| | +---+
+-----+ +-----+
<-- Backward
Figure 2: Testbed Topology for Limited Link Capacity
Testbed attributes:
o Test duration: 100s
o Path characteristics: as described in Section 4.2
Sarker, et al. Expires December 23, 2018 [Page 11]
Internet-Draft Test Scenarios for RMCAT June 2018
o Application-related:
* Media Traffic:
+ Media type: Video
- Media direction: forward.
- Number of media sources: one (1)
- Media timeline:
o Start time: 0s.
o End time: 99s.
+ Media type: Audio
- Media direction: forward.
- Number of media sources: one (1)
- Media timeline:
o Start time: 0s.
o End time: 99s.
* Competing traffic:
+ Number of sources : zero (0)
o Test Specific Information:
* One-way propagation delay: [ 50 ms, 100 ms]. on the forward
path direction
* This test uses bottleneck path capacity variation as listed in
Table 1
* When using background non-adaptive UDP traffic to induce time-
varying bottleneck , the physical path capacity remains at
4Mbps and the UDP traffic source rate changes over time as
(4-x)Mbps, where x is the bottleneck capacity specified in
Table 1
Sarker, et al. Expires December 23, 2018 [Page 12]
Internet-Draft Test Scenarios for RMCAT June 2018
+--------------------+--------------+-----------+-------------------+
| Variation pattern | Path | Start | Path capacity |
| index | direction | time | ratio |
+--------------------+--------------+-----------+-------------------+
| One | Forward | 0s | 1.0 |
| Two | Forward | 40s | 2.5 |
| Three | Forward | 60s | 0.6 |
| Four | Forward | 80s | 1.0 |
+--------------------+--------------+-----------+-------------------+
Table 1: Path capacity variation pattern for forward direction
5.2. Variable Available Capacity with Multiple Flows
This test case is similar to Section 5.1. However in addition this
test will also consider persistent network load due to competing
traffic.
Expected behavior: the candidate algorithm is expected to detect the
variation in available capacity and adapt the media stream(s)
accordingly. The flows stabilize around their maximum bit rate as
the maximum link capacity is large enough to accommodate the flows.
When the available capacity drops, the flows adapt by decreasing
their sending bit rate, and when congestion disappears, the flows are
again expected to ramp up.
Evaluation metrics : as described in Section 4.1.
Testbed Topology: Two (2) media sources S1 and S2 are connected to
their corresponding destinations R1 and R2. The media traffic is
transported over the forward path and corresponding feedback/control
traffic is transported over the backward path.
+---+ +---+
|S1 |===== \ / =======|R1 |
+---+ \\ Forward --> // +---+
\\ //
+-----+ +-----+
| A |------------------------------>| B |
| |<------------------------------| |
+-----+ +-----+
// \\
// <-- Backward \\
+---+ // \\ +---+
|S2 |====== / \ ======|R2 |
+---+ +---+
Figure 3: Testbed Topology for Variable Available Capacity
Sarker, et al. Expires December 23, 2018 [Page 13]
Internet-Draft Test Scenarios for RMCAT June 2018
Testbed attributes:
Testbed attributes are similar as described in Section 5.1 except the
test specific capacity variation setup.
Test Specific Information: This test uses path capacity variation as
listed in Table 2 with a corresponding end time of 125 seconds. The
reference bottleneck capacity is 2Mbps. When using background non-
adaptive UDP traffic to induce time-varying bottleneck for congestion
controlled media flows, the physical path capacity is 4Mbps and the
UDP traffic source rate changes over time as (4-x)Mbps, where x is
the bottleneck capacity specified in Table 2.
+--------------------+--------------+-----------+-------------------+
| Variation pattern | Path | Start | Path capacity |
| index | direction | time | ratio |
+--------------------+--------------+-----------+-------------------+
| One | Forward | 0s | 2.0 |
| Two | Forward | 25s | 1.0 |
| Three | Forward | 50s | 1.75 |
| Four | Forward | 75s | 0.5 |
| Five | Forward | 100s | 1.0 |
+--------------------+--------------+-----------+-------------------+
Table 2: Path capacity variation pattern for forward direction
5.3. Congested Feedback Link with Bi-directional Media Flows
Real-time interactive media uses RTP hence it is assumed that RTCP,
RTP header extension or such would be used by the congestion control
algorithm in the backchannel. Due to asymmetric nature of the link
between communicating peers it is possible for a participating peer
to not receive such feedback information due to an impaired or
congested backchannel (even when the forward channel might not be
impaired). This test case is designed to observe the candidate
congestion control behavior in such an event.
It is expected that the candidate algorithms are able to cope with
the lack of feedback information and adapt to minimize the
performance degradation of media flows in the forward channel.
It should be noted that for this test case: logs are compared with
the reference case, i.e, when the backward channel has no
impairments.
Evaluation metrics : as described in Section 4.1.
Sarker, et al. Expires December 23, 2018 [Page 14]
Internet-Draft Test Scenarios for RMCAT June 2018
Testbed topology: One (1) media source S1 is connected to
corresponding R1, but both endpoints are additionally receiving and
sending data, respectively. The media traffic (S1->R1) is
transported over the forward path and corresponding feedback/control
traffic is transported over the backward path. Likewise media
traffic (S2->R2) is transported over the backward path and
corresponding feedback/control traffic is transported over the
forward path.
+---+ +---+
|S1 |===== \ Forward --> / =======|R1 |
+---+ \\ // +---+
\\ //
+-----+ +-----+
| A |------------------------------>| B |
| |<------------------------------| |
+-----+ +-----+
// \\
// <-- Backward \\
+---+ // \\ +---+
|R2 |===== / \ ======|S2 |
+---+ +---+
Figure 4: Testbed Topology for Congested Feedback Link
Testbed attributes:
o Test duration: 100s
o Path characteristics:
* Reference bottleneck capacity: 1Mbps.
o Application-related:
* Media Source:
+ Media type: Video
- Media direction: forward and backward
- Number of media sources: two (2)
- Media timeline:
o Start time: 0s.
o End time: 99s.
Sarker, et al. Expires December 23, 2018 [Page 15]
Internet-Draft Test Scenarios for RMCAT June 2018
+ Media type: Audio
- Media direction: forward and backward
- Number of media sources: two (2)
- Media timeline:
o Start time: 0s.
o End time: 99s.
* Competing traffic:
+ Number of sources : zero (0)
o Test Specific Information: this test uses path capacity variations
to create congested feedback link. Table 3 lists the variation
patterns applied to the forward path and Table 4 lists the
variation patterns applied to the backward path. When using
background non-adaptive UDP traffic to induce time-varying
bottleneck for congestion controlled media flows, the physical
path capacity is 4Mbps for both directions and the UDP traffic
source rate changes over time as (4-x)Mbps in each direction,
where x is the bottleneck capacity specified in Table 4.
+--------------------+--------------+-----------+-------------------+
| Variation pattern | Path | Start | Path capacity |
| index | direction | time | ratio |
+--------------------+--------------+-----------+-------------------+
| One | Forward | 0s | 2.0 |
| Two | Forward | 20s | 1.0 |
| Three | Forward | 40s | 0.5 |
| Four | Forward | 60s | 2.0 |
+--------------------+--------------+-----------+-------------------+
Table 3: Path capacity variation pattern for forward direction
+--------------------+--------------+-----------+-------------------+
| Variation pattern | Path | Start | Path capacity |
| index | direction | time | ratio |
+--------------------+--------------+-----------+-------------------+
| One | Backward | 0s | 2.0 |
| Two | Backward | 35s | 0.8 |
| Three | Backward | 70s | 2.0 |
+--------------------+--------------+-----------+-------------------+
Table 4: Path capacity variation pattern for backward direction
Sarker, et al. Expires December 23, 2018 [Page 16]
Internet-Draft Test Scenarios for RMCAT June 2018
5.4. Competing Media Flows with same Congestion Control Algorithm
In this test case, more than one media flows share the bottleneck
link and each of them uses the same congestion control algorithm.
This is a typical scenario where a real-time interactive application
sends more than one media flow to the same destination and these
flows are multiplexed over the same port. In such a scenario it is
likely that the flows will be routed via the same path and need to
share the available bandwidth amongst themselves. For the sake of
simplicity it is assumed that there are no other competing traffic
sources in the bottleneck link and that there is sufficient capacity
to accommodate all the flows individually. While this appears to be
a variant of the test case defined in Section 5.2, it focuses on the
capacity sharing aspect of the candidate algorithm. The previous
test case, on the other hand, measures adaptability, stability, and
responsiveness of the candidate algorithm.
Expected behavior: It is expected that the competing flows will
converge to an optimum bit rate to accommodate all the flows with
minimum possible latency and loss. Specifically, the test introduces
three media flows at different time instances, when the second flow
appears there should still be room to accommodate another flow on the
bottleneck link. Lastly, when the third flow appears the bottleneck
link should be saturated.
Evaluation metrics : as described in Section 4.1.
Testbed topology: Three media sources S1, S2, S3 are connected to R1,
R2, R3 respectively. The media traffic is transported over the
forward path and corresponding feedback/control traffic is
transported over the backward path.
+---+ +---+
|S1 |===== \ Forward --> / =======|R1 |
+---+ \\ // +---+
\\ //
+---+ +-----+ +-----+ +---+
|S2 |=======| A |------------------------------>| B |=======|R2 |
+---+ | |<------------------------------| | +---+
+-----+ +-----+
// \\
// <-- Backward \\
+---+ // \\ +---+
|S3 |====== / \ ======|R3 |
+---+ +---+
Figure 5: Testbed Topology for Multiple congestion controlled media
Flows
Sarker, et al. Expires December 23, 2018 [Page 17]
Internet-Draft Test Scenarios for RMCAT June 2018
Testbed attributes:
o Test duration: 120s
o Path characteristics:
* Reference bottleneck capacity: 3.5Mbps
* Path capacity ratio: 1.0
o Application-related:
* Media Source:
+ Media type: Video
- Media direction: forward.
- Number of media sources: three (3)
- Media timeline: new media flows are added sequentially,
at short time intervals. See test specific setup below.
+ Media type: Audio
- Media direction: forward.
- Number of media sources: three (3)
- Media timeline: new media flows are added sequentially,
at short time intervals. See test specific setup below.
* Competing traffic:
+ Number of sources : zero (0)
o Test Specific Information: Table 5 defines the media timeline for
both media type.
Sarker, et al. Expires December 23, 2018 [Page 18]
Internet-Draft Test Scenarios for RMCAT June 2018
+---------+------------+------------+----------+
| Flow ID | Media type | Start time | End time |
+---------+------------+------------+----------+
| 1 | Video | 0s | 119s |
| 2 | Video | 20s | 119s |
| 3 | Video | 40s | 119s |
| 4 | Audio | 0s | 119s |
| 5 | Audio | 20s | 119s |
| 6 | Audio | 40s | 119s |
+---------+------------+------------+----------+
Table 5: Media Timeline for Video and Audio media sources
5.5. Round Trip Time Fairness
In this test case, multiple media flows share the bottleneck link,
but the end-to-end path latency for each flow is different. For the
sake of simplicity it is assumed that there are no other competing
traffic sources in the bottleneck link and that there is sufficient
capacity to accommodate all the flows. While this appears to be a
variant of test case 5.2, it focuses on the capacity sharing aspect
of the candidate algorithm under different RTTs.
It is expected that the competing flows will converge to bit rates to
accommodate all the flows with minimum possible latency and loss.
Specifically, the test introduces five media flows at the same time
instance.
Evaluation metrics : as described in Section 4.1.
Testbed Topology: Five (5) media sources S1,S2,..,S5 are connected to
their corresponding media sinks R1,R2,..,R5. The media traffic is
transported over the forward path and corresponding feedback/control
traffic is transported over the backward path. The topology is the
same as in Section 5.4. The end-to-end path delays are: 10ms for
S1-R1, 25ms for S2-R2, 50ms for S3-R3, 100ms for S4-R4, and 150ms
S5-R5, respectively.
Testbed attributes:
o Test duration: 300s
o Path characteristics:
* One-Way propagation delay for each flow: 10ms, 25ms, 50ms,
100ms, 150ms.
o Application-related:
Sarker, et al. Expires December 23, 2018 [Page 19]
Internet-Draft Test Scenarios for RMCAT June 2018
* Media Source:
+ Media type: Video
- Media direction: forward
- Number of media sources: five (5)
- Media timeline: new media flows are added sequentially,
at short time intervals. See test specific setup below.
+ Media type: Audio
- Media direction: forward.
- Number of media sources: five (5)
- Media timeline: new media flows are added sequentially,
at short time intervals. See test specific setup below.
* Competing traffic:
+ Number of sources : zero (0)
o Test Specific Information: Table 6 defines the media timeline for
both media type.
+---------+------------+------------+----------+
| Flow IF | Media type | Start time | End time |
+---------+------------+------------+----------+
| 1 | Video | 0s | 299s |
| 2 | Video | 10s | 299s |
| 3 | Video | 20s | 299s |
| 4 | Video | 30s | 299s |
| 5 | Video | 40s | 299s |
| 6 | Audio | 0 | 299s |
| 7 | Audio | 10s | 299s |
| 8 | Audio | 20s | 299s |
| 9 | Audio | 30s | 299s |
| 10 | Audio | 40s | 299s |
+---------+------------+------------+----------+
Table 6: Media Timeline for Video and Audio media sources
Sarker, et al. Expires December 23, 2018 [Page 20]
Internet-Draft Test Scenarios for RMCAT June 2018
5.6. Media Flow Competing with a Long TCP Flow
In this test case, one or more media flows share the bottleneck link
with at least one long lived TCP flow. Long lived TCP flows download
data throughout the session and are expected to have infinite amount
of data to send and receive. This is a scenario where a multimedia
application co-exists with a large file download. The test case
measures the adaptivity of the candidate algorithm to competing
traffic. It addresses the requirement 3 in
[I-D.ietf-rmcat-cc-requirements].
Expected behavior: depending on the convergence observed in test case
5.1 and 5.2, the candidate algorithm may be able to avoid congestion
collapse. In the worst case, the media stream will fall to the
minimum media bit rate.
Evaluation metrics : following metrics in addition to as described in
Section 4.1.
1. Flow level:
A. TCP throughput.
B. Loss for the TCP flow
Testbed topology: One (1) media source S1 is connected to the
corresponding media sink, R1. In addition, there is a long-live TCP
flow sharing the same bottleneck link. The media traffic is
transported over the forward path and corresponding feedback/control
traffic is transported over the backward path. The TCP traffic goes
over the forward path from, S_tcp with acknowledgment packets go over
the backward path from, R_tcp.
Sarker, et al. Expires December 23, 2018 [Page 21]
Internet-Draft Test Scenarios for RMCAT June 2018
+--+ +--+
|S1|===== \ Forward --> / =======|R1|
+--+ \\ // +--+
\\ //
+-----+ +-----+
| A |---------------------------->| B |
| |<----------------------------| |
+-----+ +-----+
// \\
// <-- Backward \\
+-----+ // \\ +-----+
|S_tcp|=== / \ ===|R_tcp|
+-----+ +-----+
Figure 6: Testbed Topology for TCP vs congestion controlled media
Flows
Testbed attributes:
o Test duration: 120s
o Path characteristics:
* Reference bottleneck capacity: 2Mbps
* Path capacity ratio: 1.0
* Bottleneck queue size: [300ms, 1000ms]
o Application-related:
* Media Source:
+ Media type: Video
- Media direction: forward
- Number of media sources: one (1)
- Media timeline:
o Start time: 5s.
o End time: 119s.
+ Media type: Audio
- Media direction: forward
Sarker, et al. Expires December 23, 2018 [Page 22]
Internet-Draft Test Scenarios for RMCAT June 2018
- Number of media sources: one (1)
- Media timeline:
o Start time: 5s.
o End time: 119s.
* Additionally, implementers are encouraged to run the experiment
with multiple media sources.
* Competing traffic:
+ Number and Types of sources : one (1) and long-lived TCP
+ Traffic direction : forward
+ Congestion control: default TCP congestion control[RFC5681].
+ Traffic timeline:
- Start time: 0s.
- End time: 119s.
o Test Specific Information: none
5.7. Media Flow Competing with Short TCP Flows
In this test case, one or more congestion controlled media flow
shares the bottleneck link with multiple short-lived TCP flows.
Short-lived TCP flows resemble the on/off pattern observed in the web
traffic, wherein clients (browsers) connect to a server and download
a resource (typically a web page, few images, text files, etc.) using
several TCP connections (up to 4). This scenario shows the
performance of a multimedia application when several browser windows
are active. The test case measures the adaptivity of the candidate
algorithm to competing web traffic, it addresses the requirements 1.E
in [I-D.ietf-rmcat-cc-requirements].
Depending on the number of short TCP flows, the cross-traffic either
appears as a short burst flow or resembles a long TCP flow. The
intention of this test is to observe the impact of short-term burst
on the behavior of the candidate algorithm.
Evaluation metrics : following metrics in addition to as described in
Section 4.1.
Sarker, et al. Expires December 23, 2018 [Page 23]
Internet-Draft Test Scenarios for RMCAT June 2018
1. Flow level:
A. Variation in the sending rate of the TCP flow.
B. TCP throughput.
Testbed topology: The topology described here is same as the one
described in Figure 6.
Testbed attributes:
o Test duration: 300s
o Path characteristics:
* Reference bottleneck capacity: 2.0Mbps
* Path capacity ratio: 1.0
o Application-related:
* Media source:
+ Media type: Video
- Media direction: forward
- Number of media sources: two (2)
- Media timeline:
o Start time: 5s.
o End time: 299s.
+ Media type: Audio
- Media direction: forward
- Number of media sources: two (2)
- Media timeline:
o Start time: 5s.
o End time: 299s.
* Competing traffic:
Sarker, et al. Expires December 23, 2018 [Page 24]
Internet-Draft Test Scenarios for RMCAT June 2018
+ Number and Types of sources : ten (10), short-lived TCP
flows.
+ Traffic direction : forward
+ Congestion algorithm: default TCP Congestion control
[RFC5681].
+ Traffic timeline: each short TCP flow is modeled as a
sequence of file downloads interleaved with idle periods.
Not all short TCP flows start at the same time, 2 of them
start in the ON state while rest of the 8 flows start in an
OFF stats. For description of short TCP flow model see test
specific information below.
o Test Specific Information:
* Short-TCP traffic model: The short TCP model to be used in this
test is described in [I-D.ietf-rmcat-eval-criteria].
5.8. Media Pause and Resume
In this test case, more than one real-time interactive media flows
share the link bandwidth and all flows reach to a steady state by
utilizing the link capacity in an optimum way. At this stage one of
the media flows is paused for a moment. This event will result in
more available bandwidth for the rest of the flows as they are on a
shared link. When the paused media flow resumes it would no longer
have the same bandwidth share on the link. It has to make it's way
through the other existing flows in the link to achieve a fair share
of the link capacity. This test case is important specially for
real-time interactive media which consists of more than one media
flows and can pause/resume media flows at any point of time during
the session. This test case directly addresses the requirement
number 5 in [I-D.ietf-rmcat-cc-requirements]. One can think it as a
variation of test case defined in Section 5.4. However, it is
different as the candidate algorithms can use different strategies to
increase its efficiency, for example in terms of fairness,
convergence time, reduce oscillation etc, by capitalizing the fact
that they have previous information of the link.
Evaluation metrics : following metrics in addition to as described in
Section 4.1.
1. Flow level:
A. Variation in sending bit rate and goodput. Mainly observing
the frequency and magnitude of oscillations.
Sarker, et al. Expires December 23, 2018 [Page 25]
Internet-Draft Test Scenarios for RMCAT June 2018
Testbed Topology: Same as test case defined in Section 5.4
Testbed attributes: The general description of the testbed parameters
are same as Section 5.4 with changes in the test specific setup as
below-
o Other test specific setup:
* Media flow timeline:
+ Flow ID: one (1)
+ Start time: 0s
+ Flow duration: 119s
+ Pause time: not required
+ Resume time: not required
* Media flow timeline:
+ Flow ID: two (2)
+ Start time: 0s
+ Flow duration: 119s
+ Pause time: at 40s
+ Resume time: at 60s
* Media flow timeline:
+ Flow ID: three (3)
+ Start time: 0s
+ Flow duration:119s
+ Pause time: not required
+ Resume time: not required
Sarker, et al. Expires December 23, 2018 [Page 26]
Internet-Draft Test Scenarios for RMCAT June 2018
6. Other potential test cases
It has been noticed that there are other interesting test cases
besides the basic test cases listed above. In many aspects, these
additional test cases can help further evaluation of the candidate
algorithm. They are listed as below.
6.1. Media Flows with Priority
In this test case media flows will have different priority levels.
This will be an extension of Section 5.4 where the same test will be
run with different priority levels imposed on each of the media
flows. For example, the first flow (S1) is assigned a priority of 2
whereas the remaining two flows (S2 and S3) are assigned a priority
of 1. The candidate algorithm MUST reflect the relative priorities
assigned to each media flow. In the previous example, the first flow
(S1) MUST arrive at a steady-state rate approximately twice of that
of the other two flows (S2 and S3).
The candidate algorithm can use a coupled congestion control
mechanism for the bandwidth distribution according to the respective
media flow priority.
6.2. Explicit Congestion Notification Usage
This test case requires to run all the basic test cases with the
availability of Explicit Congestion Notification (ECN) [RFC6679]
feature enabled. The goal of this test is to exhibit that the
candidate algorithms do not fail when ECN signals are available.
With ECN signals enabled the algorithms are expected to perform
better than their delay based variants.
6.3. Multiple Bottlenecks
In this test case one congestion controlled media flow, S1->R2,
traverses a path with multiple bottlenecks. As illustrated in
Figure 7, the first flow (S1->R1) competes with the second congestion
controlled media flow (S2->R2) over the link between A and B which is
close to the sender side; again, that flow (S1->R1) competes with the
third congestion controlled media flow (S3->R3) over the link between
C and D which is close to the receiver side. The goal of this test
is to ensure that the candidate algorithms work properly in the
presence of multiple bottleneck links on the end to end path.
Expected behavior: the candidate algorithm is expected to achieve
full utilization at both bottleneck links without starving any of the
three congestion controlled media flows.
Sarker, et al. Expires December 23, 2018 [Page 27]
Internet-Draft Test Scenarios for RMCAT June 2018
Forward ---->
+---+ +---+ +---+ +---+
|S2 | |R2 | |S3 | |R3 |
+---+ +---+ +---+ +---+
| | | |
| | | |
+---+ +-----+ +-----+ +-----+ +-----+ +---+
|S1 |=======| A |------>| B |----->| C |---->| D |=======|R1 |
+---+ | |<------| |<-----| |<----| | +---+
+-----+ +-----+ +-----+ +-----+
1st 2nd
Bottleneck (A->B) Bottleneck (C->D)
<------ Backward
Figure 7: Testbed Topology for Multiple Bottlenecks
Testbed topology: Three media sources S1, S2, and S3 are connected to
respective destinations R1, R2, and R3. For all three flows the
media traffic is transported over the forward path and corresponding
feedback/control traffic is transported over the backward path.
Testbed attributes:
o Test duration: 300s
o Path characteristics:
* Reference bottleneck capacity: 2Mbps.
* Path capacity ratio between A and B: 1.0
* Path capacity ratio between B and C: 4.0.
* Path capacity ratio between C and D: 0.75.
* One-Way propagation delay:
1. Between S1 and R1: 100ms
2. Between S2 and R2: 40ms
Sarker, et al. Expires December 23, 2018 [Page 28]
Internet-Draft Test Scenarios for RMCAT June 2018
3. Between S3 and R3: 40ms
o Application-related:
* Media Source:
+ Media type: Video
- Media direction: Forward
- Number of media sources: Three (3)
- Media timeline:
o Start time: 0s.
o End time: 299s.
+ Media type: Audio
- Media direction: Forward
- Number of media sources: Three (3)
- Media timeline:
o Start time: 0s.
o End time: 299s.
* Competing traffic:
+ Number of sources : Zero (0)
7. Wireless Access Links
Additional wireless network (both cellular network and WiFi network)
specific test cases are defined in [I-D.ietf-rmcat-wireless-tests].
8. Security Considerations
Security issues have not been discussed in this memo.
9. IANA Considerations
There are no IANA impacts in this memo.
Sarker, et al. Expires December 23, 2018 [Page 29]
Internet-Draft Test Scenarios for RMCAT June 2018
10. Acknowledgements
Much of this document is derived from previous work on congestion
control at the IETF.
The content and concepts within this document are a product of the
discussion carried out in the Design Team.
11. References
11.1. Normative References
[I-D.ietf-rmcat-eval-criteria]
Singh, V., Ott, J., and S. Holmer, "Evaluating Congestion
Control for Interactive Real-time Media", draft-ietf-
rmcat-eval-criteria-07 (work in progress), May 2018.
[I-D.ietf-rmcat-video-traffic-model]
Zhu, X., Cruz, S., and Z. Sarker, "Modeling Video Traffic
Sources for RMCAT Evaluations", draft-ietf-rmcat-video-
traffic-model-04 (work in progress), January 2018.
[I-D.ietf-rmcat-wireless-tests]
Sarker, Z., Johansson, I., Zhu, X., Fu, J., Tan, W., and
M. Ramalho, "Evaluation Test Cases for Interactive Real-
Time Media over Wireless Networks", draft-ietf-rmcat-
wireless-tests-04 (work in progress), May 2017.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551,
DOI 10.17487/RFC3551, July 2003,
<https://www.rfc-editor.org/info/rfc3551>.
[RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,
"RTP Control Protocol Extended Reports (RTCP XR)",
RFC 3611, DOI 10.17487/RFC3611, November 2003,
<https://www.rfc-editor.org/info/rfc3611>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
DOI 10.17487/RFC4585, July 2006,
<https://www.rfc-editor.org/info/rfc4585>.
Sarker, et al. Expires December 23, 2018 [Page 30]
Internet-Draft Test Scenarios for RMCAT June 2018
[RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size
Real-Time Transport Control Protocol (RTCP): Opportunities
and Consequences", RFC 5506, DOI 10.17487/RFC5506, April
2009, <https://www.rfc-editor.org/info/rfc5506>.
[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <https://www.rfc-editor.org/info/rfc6679>.
11.2. Informative References
[HEVC-seq]
HEVC, "Test Sequences",
http://www.netlab.tkk.fi/~varun/test_sequences/ .
[I-D.ietf-rmcat-cc-requirements]
Jesup, R. and Z. Sarker, "Congestion Control Requirements
for Interactive Real-Time Media", draft-ietf-rmcat-cc-
requirements-09 (work in progress), December 2014.
[RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
<https://www.rfc-editor.org/info/rfc5681>.
[xiph-seq]
Xiph.org, "Video Test Media",
http://media.xiph.org/video/derf/ .
Authors' Addresses
Zaheduzzaman Sarker
Ericsson AB
Luleae, SE 977 53
Sweden
Phone: +46 10 717 37 43
Email: zaheduzzaman.sarker@ericsson.com
Varun Singh
Nemu Dialogue Systems Oy
Runeberginkatu 4c A 4
Helsinki 00100
Finland
Email: varun.singh@iki.fi
URI: http://www.callstats.io/
Sarker, et al. Expires December 23, 2018 [Page 31]
Internet-Draft Test Scenarios for RMCAT June 2018
Xiaoqing Zhu
Cisco Systems
12515 Research Blvd
Austing, TX 78759
USA
Email: xiaoqzhu@cisco.com
Michael A. Ramalho
Cisco Systems, Inc.
6310 Watercrest Way Unit 203
Lakewood Ranch, FL 34202-5211
USA
Phone: +1 919 476 2038
Email: mramalho@cisco.com
Sarker, et al. Expires December 23, 2018 [Page 32]