Quality of Outcome (QoO)
draft-ietf-ippm-qoo-07
The information below is for an old version of the document.
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| Authors | Bjørn Ivar Teigen , Magnus Olden , Ike Kunze | ||
| Last updated | 2026-03-08 (Latest revision 2026-02-19) | ||
| Replaces | draft-olden-ippm-qoo | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Marcus Ihlar | ||
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draft-ietf-ippm-qoo-07
IP Performance Measurement B. I. T. Monclair
Internet-Draft M. Olden
Intended status: Informational I. Kunze, Ed.
Expires: 23 August 2026 CUJO AI
19 February 2026
Quality of Outcome (QoO)
draft-ietf-ippm-qoo-07
Abstract
This document introduces the Quality of Outcome (QoO) network quality
score and the corresponding QoO framework as an approach to network
quality assessment designed to align with the needs of application
developers, users, and operators.
By leveraging the Quality Attenuation metric, QoO provides a method
for defining and evaluating application-specific, quality-focused
network performance requirements to enable insights for network
optimization and simple Quality of Service scores for end-users.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-ippm-qoo/.
Discussion of this document takes place on the IP Performance
Measurement Working Group mailing list (mailto:ippm@ietf.org), which
is archived at https://mailarchive.ietf.org/arch/browse/ippm/.
Subscribe at https://www.ietf.org/mailman/listinfo/ippm/.
Source for this draft and an issue tracker can be found at
https://github.com/getCUJO/QoOID.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. General Requirements . . . . . . . . . . . . . . . . . . 10
4.2. Requirements from End-Users . . . . . . . . . . . . . . . 11
4.3. Requirements from Application and Platform Developers . . 12
4.4. Requirements from Network Operators and Network Solution
Vendors . . . . . . . . . . . . . . . . . . . . . . . . . 13
5. The QoO Framework . . . . . . . . . . . . . . . . . . . . . . 14
5.1. Measuring Network Conditions . . . . . . . . . . . . . . 14
5.2. Describing Network Performance Requirements . . . . . . . 17
5.3. Calculating QoO . . . . . . . . . . . . . . . . . . . . . 19
5.3.1. Overall QoO Calculation . . . . . . . . . . . . . . . 20
5.3.2. Latency Component . . . . . . . . . . . . . . . . . . 20
5.3.3. Packet Loss Component . . . . . . . . . . . . . . . . 21
5.4. Example . . . . . . . . . . . . . . . . . . . . . . . . . 21
6. Operational Considerations . . . . . . . . . . . . . . . . . 22
6.1. Creating Network Performance Requirement
Specifications . . . . . . . . . . . . . . . . . . . . . 22
6.2. Composability and Use Cases . . . . . . . . . . . . . . . 23
6.3. Deployment Considerations . . . . . . . . . . . . . . . . 24
6.4. Adaptive Applications . . . . . . . . . . . . . . . . . . 24
6.5. Sensitity to Sampling Accuracy . . . . . . . . . . . . . 25
6.6. Insights From User Testing . . . . . . . . . . . . . . . 26
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7. Known Weaknesses and Open Questions . . . . . . . . . . . . . 26
7.1. Volatile Networks . . . . . . . . . . . . . . . . . . . . 27
7.2. Missing Temporal Information in Distributions. . . . . . 27
7.3. Subsampling the Real Distribution . . . . . . . . . . . . 27
7.4. Assuming Linear Relationship Between Optimal Performance
and Unusable . . . . . . . . . . . . . . . . . . . . . . 28
7.5. Binary Bandwidth Threshold . . . . . . . . . . . . . . . 28
7.6. Arbitrary Selection of Percentiles . . . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 28
8.1. Measurement Integrity and Authenticity . . . . . . . . . 29
8.2. Risk of Misuse and Gaming . . . . . . . . . . . . . . . . 29
8.3. Denial-of-Service (DoS) Risks . . . . . . . . . . . . . . 29
8.4. Trust in Application Requirements . . . . . . . . . . . . 30
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 30
10. Comparison To Other Network Quality Metrics . . . . . . . . . 31
10.1. Throughput . . . . . . . . . . . . . . . . . . . . . . . 33
10.2. Mean Latency . . . . . . . . . . . . . . . . . . . . . . 33
10.3. 99th Percentile of Latency . . . . . . . . . . . . . . . 33
10.4. Variance of Latency . . . . . . . . . . . . . . . . . . 34
10.5. Inter-Packet Delay Variation (IPDV) . . . . . . . . . . 34
10.6. Packet Delay Variation (PDV) . . . . . . . . . . . . . . 34
10.7. Trimmed Mean of Latency . . . . . . . . . . . . . . . . 34
10.8. Round-trips Per Minute . . . . . . . . . . . . . . . . . 35
10.9. Quality Attenuation . . . . . . . . . . . . . . . . . . 35
10.10. Quality of Outcome . . . . . . . . . . . . . . . . . . . 35
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
12. Implementation status . . . . . . . . . . . . . . . . . . . . 36
12.1. qoo-c . . . . . . . . . . . . . . . . . . . . . . . . . 36
12.2. goresponsiveness . . . . . . . . . . . . . . . . . . . . 37
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
13.1. Normative References . . . . . . . . . . . . . . . . . . 38
13.2. Informative References . . . . . . . . . . . . . . . . . 38
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43
1. Introduction
This document introduces the Quality of Outcome (QoO) network quality
score. It is designed to be easy to understand, while at the same
time being objective, adaptable to different network quality needs,
and allowing advanced analyses to identify the root cause of network
problems (Section 5.4.3 of [I-D.ietf-opsawg-rfc5706bis]). Centered
around the QoO score, this document defines the QoO framework which
allows application developers to specify quality-focused network
performance requirements (for example, regarding latency, throughput,
and packet loss) and provides a way to derive the user-facing QoO
score by comparing these application-specific performance
requirements to network performance measurements.
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The QoO framework builds on Quality Attenuation [TR-452.1], a network
quality metric that enables network operators to achieve fault
isolation (Section 5.4.4 of [I-D.ietf-opsawg-rfc5706bis]) and
effective network planning through composability [RFC6049]. Quality
Attenuation meets most of the requirements for a meaningful network
quality score set out in Section 4.1: it is composable, captures the
ability of a network to satisfy application requirements, and can be
compared to a variety of application needs. However, interpreting
raw Quality Attenuation values is difficult for end-users and
application developers. The challenge is simplifying the entailed
information to present results in an understandable and unambiguous
way without losing too much precision and accuracy.
The QoO framework takes a probabilistic approach to this challenge
because network stacks and applications adapt dynamically to changing
network conditions. Also, applications and underlying networking
protocols make separate optimizations based on the perceived network
quality over time, making absolute certainty about outcomes
practically impossible. However, educated assessments of expected
outcomes remain achievable for which the QoO framework uses a per-
application, per application-type, or per-Service Level Agreement
(SLA) granularity.
This document assumes that network quality can be represented by a
minimum required throughput, a set of latency percentiles, and packet
loss rates as these measurables will ultimately also capture changes
to additional factors. Application developers, regulatory bodies,
and other interested parties can use this representation to describe
quality-focused network performance requirements. The QoO framework
gives structure to this approach by defining two network quality
thresholds: one for optimal application performance and one for
unacceptable application performance. The QoO score serves as a
linear distance measure between the two distinct thresholds and
allows network conditions to be expressed in easily understood terms
such as "This network provides 94% of optimal conditions for video
conferencing (relative to the threshold for unacceptable
performance)" while supporting both comprehensive end-to-end tests
and analyses from within the network.
The QoO framework is designed to be flexible in its application
scope. QoO scores may be calculated for the complete end-to-end path
(from application client to server), or focused on specific network
segments, such as the customer-facing access network, intermediate
transit networks, or server-side infrastructure. Through the
composability properties of the underlying Quality Attenuation
metric, measurements from different segments can be combined or
decomposed to isolate performance issues regardless of where they
occur in the network path.
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This document defines a minimum viable framework, and often trades
precision for simplicity to facilitate adoption and usability in many
different contexts, such as active testing from applications and
monitoring from network equipment. Assessing the corresponding loss
of precision is important and requires combining measurement results
with a description of the measurement approach; Section 5.1 provides
corresponding guidelines.
Note that this document focuses specifically on the general framework
of using quality-focused network performance requirements and
corresponding network performance measurements to calculate QoO
network quality scores. How applications define and share their
network performance requirements, which format is used to publish
such requirement information, how operators retrieve such data from
applications or services, how the precision of the resulting QoO
scores is assessed, and what levels of precision are considered
acceptable is out of the scope of this document.
2. Terminology
This document uses the following terminology:
Network: The communication infrastructure that facilitates data
transmission between endpoints, including all intermediate
devices, links, and protocols that affect the transmission of
data. This encompasses both the physical infrastructure and the
logical protocols that govern data transmission. The network may
support various communication patterns and may span multiple
administrative domains.
Network Segment: A portion of the complete end-to-end network path
between application endpoints. A network segment may represent a
specific administrative domain (e.g., access network, transit
network, or server-side infrastructure), a particular technology
domain (e.g., Wi-Fi or cellular), or any subset of the path for
which independent quality measurements and analysis are desired.
Quality Attenuation: A network quality metric defined in [TR-452.1]
that combines latency and packet loss distributions in a unified
approach to jointly assess latency and loss characteristics of
network performance.
Quality of Experience (QoE): The degree of delight or annoyance of
the user of an application or service. See also [P.10].
Quality of Service (QoS): The totality of characteristics of a
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telecommunications service that bear on its ability to satisfy
stated and implied needs of the user of the service. See also
[P.10].
Quality of Outcome (QoO): A network quality framework and metric
that evaluates network quality based on how closely measured
network conditions meet application-specific, quality-focused
performance requirements. QoO is a QoS indicator that may be
related to, but cannot be considered the same as, the actual QoE
of end-users.
QoO Score: A numerical value that represents the distance-based
assessment of network quality relative to network performance
requirements for optimal and unacceptable application performance
on a given network for a specific application, typically expressed
as a percentage.
Requirements for Optimal Performance (ROP): The network performance
characteristics at which an application achieves optimal
performance and quality, beyond which further improvements in
network conditions do not result in perceptible improvements in
application performance or user experience. When network
performance exceeds ROP thresholds, any sub-optimal user
experience can be assumed not to be caused by the part of the
network path that has been measured for QoO calculations.
Conditions at the Point of Unacceptable Performance (CPUP): The
network performance threshold below which an application fails to
provide acceptable user experience. Note that 'unacceptable' in
this context refers to degraded performance quality rather than
complete technical failure of the application. There is no
universally strict threshold defining when network conditions
become unacceptable for applications.
Composability: The mathematical property that allows network quality
measurements to be combined across different network segments or
decomposed to isolate specific network components for analysis and
troubleshooting.
Accuracy and Precision: "Accuracy" refers to how close measurements
are to the value that reflects the real conditions. "Precision"
refers to the consistency and repeatability of measurements.
These terms are used with their standard statistical meanings and
are not interchangeable [ISO5725-1].
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3. Overview
The QoO framework produces simple percentage scores that express
network quality in relation to pre-defined, application-specific
network performance requirements. For example: "This network
provides 94% of optimal conditions for video conferencing". This
way, QoO conveys an intuition for how well an application is expected
to perform in the assessed network with higher scores intended to
convey that applications are more likely to have optimal performance.
The QoO framework builds upon Quality Attenuation and evaluates
network conditions using latency distributions, packet loss rates,
and throughput rates. These measured conditions are compared against
application-specific, quality-focused network performance
requirements along multiple dimensions (such as 90th or 95th latency
percentiles or mean packet loss rate) at two thresholds:
* Optimal performance (ROP): Network conditions under which
application performance becomes optimal
* Unacceptable performance (CPUP): Network conditions under which
application performance becomes unacceptable
When the measured network conditions fall between the defined
thresholds for any of the assessed performance dimensions, the QoO
framework calculates a score for each dimension by expressing the
current network quality as a relative position (percentage) on the
linear scale between the corresponding ROP and CPUP thresholds. The
minimum score across all dimensions serves as the overall QoO score
for the assessed network based on the rationale that the most
degraded performance dimension is likely to determine the
application's perceived quality.
The dual-threshold approach of the QoO framework enables meaningful
scores even when networks are not perfect while accounting for
different application sensitivities. The underlying Quality
Attenuation measurements are mathematically composable, enabling
network operators to isolate performance bottlenecks across different
network segments for precise fault diagnosis and network planning.
QoO scores are expected to correlate with QoE metrics, such as Mean
Opinion Score (MOS) [P.800.1], but they are not designed to deliver
MOS or QoE scores directly. QoO measures network service quality,
not subjective user experience.
It is important to note that the QoO framework itself does not define
where QoO scores fall on the spectrum between QoS and QoE metrics.
The position on this spectrum depends primarily on how the ROP and
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CPUP thresholds are chosen. With appropriate threshold selection
based on user-acceptance testing and application performance
analysis, QoO scores can likely be tuned to be close to (if not
identical to) QoE metrics, while still maintaining the objectivity
and composability benefits of QoS metrics.
The remainder of this document outlines requirements for the QoO
framework (Section 4), defines the core QoO framework (Section 5),
discusses operational considerations (Section 6) and known weaknesses
and open questions (Section 7), and compares QoO with existing
quality metrics (Section 10).
4. Requirements
This section describes the features and attributes that a network
quality framework must have to be useful for different stakeholders:
application developers, end-users, and network operators.
At a high level, end-users need an understandable network quality
metric. Application developers require a network quality metric that
allows them to evaluate how well their application is likely to
perform given the measured network performance. Network operators
need a metric that facilitates troubleshooting and optimization of
their networks. Existing network quality metrics and frameworks
address the needs of one or two of these stakeholders, but there is
none that bridges the needs of all three. Examples include
throughput metrics that operators use to prove regulatory compliance
but with little relevance to application performance, or subjective
QoE metrics that are understandable to users but difficult for
operators to collect at meaningful scale.
A key motivation for the QoO framework is to bridge the gap between
the technical aspects of network performance and the practical needs
of those who depend on it. For example, while solutions exist for
many of the problems causing high and unstable latency in the
Internet, such as bufferbloat mitigation techniques [RFC8290] and
improved congestion control algorithms [RFC8033], the incentives to
deploy them have remained relatively weak. A unifying framework for
assessing network quality can serve to strengthen these incentives
significantly.
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Bandwidth alone is necessary but not sufficient for high-quality
modern network experiences. High idle and working latencies, large
delay variations, and unmitigated packet loss are major causes of
poor application outcomes. The impact of latency is widely
recognized in network engineering circles [BITAG], but benchmarking
the quality of network transport remains complex. Most end-users are
unable to relate to metrics other than Mbps, which they have long
been conditioned to think of as the only dimension of network
quality.
Real Time Response under load tests [RRUL] and Responsiveness tests
[RPM] make significant strides toward creating a network quality
metric that is intended to be closer to application outcomes than
bandwidth alone. The latter, in particular, is successful at being
relatively relatable and understandable to end-users. However, as
noted in [RPM], "Our networks remain unresponsive, not from a lack of
technical solutions, but rather a lack of awareness of the problem".
This lack of awareness means that some operators might have little
incentive to improve network quality beyond increasing bandwidth.
For example, despite the availability of open-source solutions such
as FQ_CoDel [RFC8290], which has been available for over a decade,
vendors rarely implement them in widely deployed equipment (e.g., Wi-
Fi routers still commonly exhibit bufferbloat). A universally
accepted network quality framework that successfully captures the
degree to which networks provide the quality required by applications
may help to increase the willingness of vendors to implement such
solutions.
The IAB workshop on measuring Internet quality for end-users
identified a key insight: users care primarily about application
performance rather than network performance. Among the conclusions
was the statement, "A really meaningful metric for users is whether
their application will work properly or fail because of a lack of a
network with sufficient characteristics" [RFC9318]. Therefore, one
critical requirement for a meaningful framework is its ability to
answer the following question: "Will networking conditions prevent an
application from working as intended?".
Answering this question requires several considerations. First, the
Internet is inherently stochastic from the perspective of any given
client, so absolute certainty is unattainable. Second, different
applications have different needs and adapt differently to network
conditions. A framework aiming to answer the stated question must
accommodate such diverse application requirements. Third, end-users
have individual tolerances for degradation in network conditions and
the resulting effects on application experience. These variations
must be factored into the design of a suitable network quality
framework.
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4.1. General Requirements
This section describes the requirements for an objective network
quality framework and metric that is useful for end-users,
application developers, and network operators/vendors alike.
Specifically, this section outlines the three main general
requirements for such a framework while the sections therafter
describe requirements from the perspective of each of the target
groups: end-users (Section 4.2), application developers
(Section 4.3), and network operators (Section 4.4).
In general, all stakeholders ultimately care about the performance of
applications running over a network. Application performance does
not only depend on bandwidth but also on the delay and delay
variation of network links and computational steps involved in making
the application function. These delays depend on how the application
places load on the network, how the network is affected by
environmental conditions, and the behavior of other users and
applications sharing the network resources. Likewise, packet loss
(e.g., caused by congestion) can also negatively impact application
performance in different ways depending on the class of application.
Different applications may have different needs from a network and
may impose different patterns of load. To determine whether an
application will likely work well or fail, a network quality
framework must compare measurements of network performance to a wide
variety of application requirements. It is important that these
measurements reflect the actual network service configuration that
will handle the application flows, including any traffic
prioritization, network slicing, VPN services, or other
differentiated service mechanisms (see Section 6.3). Flexibility in
describing application requirements and the ability to capture the
delay and loss characteristics of a network with sufficient accuracy
and precision are necessary to compute a meaningful QoO network
quality score that can be used to better estimate application
performance.
The framework must also support spatial composition [RFC6049],
[RFC6390] to enable operators to take actions when measurements show
that applications fail too often. In particular, spatial composition
allows results to be divided into sub-results, each measuring the
performance of a required sub-milestone that must be reached in time
for the application to perform adequately.
To summarize, the QoO framework and the corresponding QoO score
should have the following properties in order to be meaningful:
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1. Capture a set of network performance metrics which provably
correlate to the application performance of a set of different
applications as perceived by users.
2. Compare meaningfully to different application requirements.
3. Be composable so operators can isolate and quantify the
contributions of different sub-outcomes and sub-paths of the
network.
Next, the document presents requirements from the perspective of each
of the three target groups: end-users (Section 4.2), application
developers (Section 4.3), and network operators (Section 4.4).
4.2. Requirements from End-Users
The QoO framework should facilitate a metric that is based on
objective QoS measurements (such as throughput [RFC6349], packet loss
[RFC6673][RFC7680], delays [RFC2681][RFC7679], and (one-way) delay
variations [RFC3393]), correlated to application performance, and
relatively understandable for end-users, similar to QoE metrics, such
as MOS [P.800.1].
If these requirements are met, QoO is a middle ground between QoS and
QoE metrics and allows end-users to understand if a network is a
likely source of impairment for what they care about: the outcomes of
applications. Examples are how quickly a web page loads, the
smoothness of a video conference, or whether or not a video game has
any perceptible lag.
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End-users may have individual tolerances of session quality (i.e.,
the quality experienced during a single application usage period,
such as a video call or gaming session), below which their quality of
experience becomes personally unacceptable. However, it may not be
feasible to capture and represent these tolerances per user as the
user group scales. A compromise is for the QoO framework to place
the responsibility for sourcing and representing end-user
requirements onto the application developer. Application developers
are expected to perform user-acceptance testing (UAT) of their
application across a range of users, terminals, and network
conditions to determine the terminal and network requirements that
will meet the acceptability thresholds for a representative subset of
their end-users. Performing UAT helps developers estimate what QoE
new end-users are likely to experience based on the application's
network performance requirements. These requirements can evolve and
improve based on feedback from end-users, and in turn better inform
the application's requirements towards the network. Some real world
examples where 'acceptable levels' have been derived by application
developers include:
* Remote music collaboration: <20ms one-way latency [JamKazam]
* Cloud gaming: >15Mbps downlink throughput and 80ms round-trip time
(RTT) [XboxNetReqs] (specific requirements vary by game and
platform; see [CSGO] for an example study on the impact of latency
on Counter Strike: Global Offensive)
* Virtual reality (VR): <20ms RTT from head motion to rendered
update in VR ([RFC9817]; see [G.1051] for latency measurement and
interactivity scoring)
Note that developers of similar applications may have arrived at
different figures.
4.3. Requirements from Application and Platform Developers
The QoO framework needs to provide developers the ability to describe
the quality-focused network performance requirements of their
applications. The network performance requirements must include all
relevant dimensions of network quality so that applications sensitive
to different network quality dimensions can all evaluate the network
accurately. Not all developers have network expertise, so to make it
easy for developers to use the framework, developers must be able to
specify network performance requirements approximately. Therefore,
it must be possible to describe both simple and complex network
performance requirements. The framework also needs to be flexible so
that it can be used with different kinds of traffic and that extreme
network performance requirements which far exceed the needs of
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today's applications can also be articulated.
If these requirements are met, developers of applications and
platforms can state or test their network requirements and evaluate
whether the network is sufficient for an optimal application outcome.
Both the application developers with networking expertise and those
without can use the framework.
4.4. Requirements from Network Operators and Network Solution Vendors
From an operator perspective, the key is to have a framework that
allows finding the network quality bottlenecks and objectively
comparing different networks, network configurations, and
technologies. To achieve this goal, the framework must support
mathematically sound compositionality ('addition' and 'subtraction')
as network operators rarely manage network traffic end-to-end. If a
test is purely end-to-end, the ability to find bottlenecks may be
gone. If, however, measurements can be taken in both end-to-end
(e.g., a-b-c-d-e) and partial (e.g., a-b-c) fashion, the results can
be decomposed to isolate the areas outside the influence of a network
operator. In other words, the network quality of a-b-c and d-e can
be separated. Compositionality is essential for fault detection and
accountability.
By having mathematically correct composition, a network operator can
measure two segments separately, perhaps even with different
approaches, and combine or correlate the results to understand the
end-to-end network quality.
Another example where composition is useful is troubleshooting a
typical web page load sequence over TCP. If web page load times are
too slow, DNS resolution time, TCP RTT, and the time it takes to
establish TLS connections can be measured separately to get a better
idea of where the problem is. A network quality framework should
support this kind of analysis to be maximally useful for operators.
The framework must be applicable in both lab testing and monitoring
of production networks. It must be useful on different time scales,
and it cannot have a dependency on network technology or OSI layers.
If these requirements are met, network operators can monitor and test
their network and understand where the true bottlenecks are,
regardless of network technology.
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5. The QoO Framework
The QoO framework builds upon the conceptual foundation of the
Quality Attenuation metric as proposed in the Broadband Forum
standard called Quality of Experience Delivered (QED) [TR-452.1].
Quality Attenuation represents quality measurements as distributions.
Using latency distributions to measure network quality has been
proposed by various researchers and practitioners (e.g., [Kelly],
[RFC6049], and [RFC8239]). Quality Attenuation also incorporates a
packet loss distribution, treating packet loss as infinite (or too
late to be of use, e.g., > 5 seconds) latency [TR-452.1], similar to
the One-Way Loss Metric for IP Performance Metrics (IPPM) [RFC7680],
which defines packet loss as packets that fail to arrive within a
specified time threshold. The novelty of Quality Attenuation lies in
its unified treatment of latency and loss within a single
distributional framework, enabling mathematical composition of
network segments as two distributions can be composed using
convolution [TR-452.1].
In line with Quality Attenuation, QoO focuses on latency
distributions and packet loss rates as the basis for network quality
assessment, with the assumption that additional factors which could
in principle be measured but are not explicitly captured will
inevitably influence the observed latency and packet loss behavior,
so that QoO indirectly accounts for their effects through the
measured distributions. The results of corresponding network
performance measurements are compared to pre-defined, application-
specific network performance requirements, which ultimately yield
per-application QoO scores. These scores express network quality as
a relative position (percentage) on a linear scale between two
performance thresholds: one for optimal performance and one for
unacceptable performance.
The following sections first discuss how network conditions can be
measured (Section 5.1), then describe how QoO defines per-application
network performance requirements (Section 5.2), and finally explain
how QoO scores are calculated (Section 5.3) with an example provided
in Section 5.4
5.1. Measuring Network Conditions
One of the key motivations for the QoO framework is that different
applications and application classes fail under different network
conditions. For example, downloads are generally more tolerant of
latency than real-time applications. Video conferences are often
sensitive to high 90th percentile latency and to the difference
between the 90th and 99th percentiles. Online gaming typically has a
low tolerance for high 99th percentile latency. Similar
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considerations apply for a variety of other factors with applications
usually requiring some minimum level of throughput and tolerating
some maximum packet loss rate. Measurement techniques used for QoO
must be able to capture these characteristics with sufficient
resolution to respect the data granularities needed by the different
application classes.
Latency distributions can be gathered via both passive monitoring and
active testing [RFC7799]. The active testing can use any type of
traffic, such as connection-oriented TCP and QUIC or connectionless
UDP. It can be applied across different layers of the protocol stack
and is network technology independent, meaning it can be gathered in
an end-user application, within some network equipment, or anywhere
in between. Passive methods rely on observing and time-stamping
packets traversing the network. Examples of this include TCP SYN and
SYN/ACK packets (Section 2.2 of [RFC8517]) and the QUIC spin bit
[RFC9000][RFC9312]. Similar considerations apply to packet loss
measurements while throughput measurements usually involve active
testing.
This document does not mandate the use of specific measurement
approaches. However, in addition to measurement approaches
standardized in the QED framework [TR-452.1], some relevant
techniques are:
* Active probing with the Two-Way Active Measurement Protocol
(TWAMP) Light [RFC5357], the Simple Two-Way Active Measurement
Protocol (STAMP) [RFC8762], or the Isochronous Round-Trip Tester
(IRTT) [IRTT]
* Latency Under Load Tests
* Speed Tests with latency measures
* Simulating real traffic
* End-to-end measurements of real traffic
* TCP SYN ACK or DNS Lookup RTT Capture
* On-Path Telemetry methods (IOAM [RFC9197], AltMark [RFC9341])
* Estimation
Modeling full latency distributions may be too complex to allow for
easy adoption of the framework. Instead, reporting latency at
selected percentiles offers a practical compromise between accuracy
and deployment considerations, trading off composability, which is
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only possible with distributions, for an easier deployment. A
commonly accepted set of percentiles spanning from the 0th to the
100th in a logarithmic-like progression has been suggested by others
[BITAG] and is recommended here: [0th, 10th, 25th, 50th, 75th, 90th,
95th, 99th, 99.9th, 100th].
The framework is agnostic to traffic direction but mandates that
measurements specify whether latency is one-way or round-trip.
To ensure broad applicability across diverse use cases, the QoO
framework deliberately avoids prescribing specific conditions for
sampling, such as fixed time intervals or defined network load
levels. This flexibility enables deployment in both controlled and
production environments.
When measurements are taken during periods of network load, the
result naturally includes latency under load. In scenarios such as
passive monitoring of production traffic, capturing artificially
loaded conditions may not always be feasible, whereas passively
observing the actual network load may be possible.
Importantly, the framework does not enforce a minimum sample count.
This means that even a small number of samples (e.g., 10) could
technically constitute a distribution but such cases are clearly
insufficient for statistical confidence. The intent is to balance
rigor with practicality, recognizing that constraints vary across
devices, applications, and deployment environments.
To support reproducibility and enable confidence analysis, each
measurement must be accompanied by the following metadata:
* Description of the measurement path, including the endpoints
(source and destination), network segments traversed, measurement
points (if applicable), and direction (uplink, downlink, or
bidirectional)
* Timestamp of first sample
* Total duration of the sampling period
* Number of samples collected
* Sampling method, including:
- Cyclic: One sample every N milliseconds (specify N)
- Burst: X samples every N milliseconds (specify X and N)
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- Passive: Opportunistic sampling of live traffic (non-uniform
intervals)
These metadata elements are essential for interpreting the precision
and reliability of the measurements. As demonstrated in
[QoOSimStudy], low sampling frequencies and short measurement
durations can lead to misleadingly optimistic or imprecise QoO
scores.
To assess the precision of network performance measurements,
implementers should consider:
* The repeatability of measurements under similar network conditions
* The impact of sampling frequency and duration on percentile
estimates, particularly for high percentiles (e.g., 99th, 99.9th)
* The measurement uncertainty introduced by hardware/software timing
jitter, clock synchronization errors, and other system-level noise
sources
* The statistical confidence intervals for percentile estimates
based on sample size
Acceptable levels of precision depend on the use case. Implementers
should document their precision assessment methodology and report
precision metrics alongside QoO scores when precision is critical for
the use case.
5.2. Describing Network Performance Requirements
The QoO framework expresses network performance requirements as a set
of percentile-latency tuples with corresponding packet loss
thresholds and a minimum required throughput. For example, a
requirement might state: at 4Mbps, 90% of packets must arrive within
100ms, and 100% within 200ms, implying 0% packet loss. This list can
be minimal (e.g., 100% within 200ms) or extended as needed and
different percentiles may be used to characterize different
applications. Still, it might be beneficial for future
standardization activities to converge on a fixed set of general
percentiles or for specific applications / application classes to
make QoO measurements between different networks or providers more
comparable. For the sake of simplicity, this document only states
that the latency percentiles specified in the requirements must match
the information provided by the measurements. This means that when
the measurements report full distributions, requirements can use
arbitrary percentiles while the requirement percentiles need to match
one or more of the percentiles reported by the measurements in case
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the simplification described in Section 5.1 is used, i.e., one can
set requirements at the [0th, 10th, 25th, 50th, 75th, 90th, 95th,
99th, 99.9th, 100th] percentiles. Packet loss rates and bandwidth
must be reported as separate values.
Applications do of course have throughput requirements, and thus a
complete framework for application-level network quality must also
take capacity into account. Insufficient bandwidth may give
unacceptable application outcomes without necessarily inducing a lot
of latency or packet loss. Therefore, the network requirements must
include a minimum throughput requirement.
A fully specified requirement can be thought of as specifying the
latency and loss requirements to be met while the end-to-end network
path is loaded in a way that is at least as demanding of the network
as the application itself. This may be achieved by running the
actual application and measuring delay and loss alongside it, or by
generating artificial traffic to a level at least equivalent to the
application traffic load. The QoO framework focuses on latency,
packet loss, and throughput under the assumption that other factors
which could in principle be measured but are not explicitly captured
by QoO will inevitably influence the observed latency and packet loss
behavior, so that QoO indirectly accounts for their effects through
the measured distributions.
Whether the requirements are one-way or two-way must be specified.
Where the requirement is one-way, the direction (user-to-network or
network-to-user) must be specified. In case of a two-way
requirement, a decomposition into uplink and downlink components may
be specified.
Network performance requirements and measurements are already
standardized in the QED framework [TR-452.1]. This document extends
the QED framework with a method that translates the network
performance requirements and measurements into a network quality
score that quantifies how close the provided network conditions are
to the optimal conditions specified by the requirements.
To that aim, first recall the key design goal of establishing a
quantifiable distance between optimal and unacceptable network
conditions, thereby enabling an objective assessment of relative
quality. Accordingly, the requirements specification is extended to
define both the network performance required for achieving optimal
application performance and the lower network performance threshold
below which the application performance is considered unacceptable.
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The two ends of the distance measure correspond to the Requirements
for Optimal Performance (ROP) and the Conditions at the Point of
Unacceptable Performance (CPUP). For example, ROP could be defined
as: at 4Mbps, 99% of packets need to arrive within 100ms, 99.9%
within 200ms, and 0.1% packet loss is acceptable for the outcome to
be as intended. Similarly, CPUP could be defined as: if 99% of the
packets have not arrived after 200ms, or 99.9% within 300ms, the
perceived service will be unacceptable.
If a latency percentile is included in the ROP, it must also be
defined in the CPUP, and vice versa, i.e., neither specification
should define a percentile that is not present in the other. For
example, if the 99.9th percentile is part of the CPUP then the ROP
must also include the 99.9th percentile.
The derivation of ROP and CPUP values requires standardized testing
conditions to ensure consistency and accuracy. Application
developers should publish their testing methodologies, including the
network conditions, hardware configurations, and measurement
procedures used to establish these thresholds. Without such
standardization, the overall accuracy and precision of QoO scores may
be reduced due to variations in testing approaches across different
applications and developers.
Developers are encouraged to follow relevant standards for testing
methodologies, such as ITU-T P-series recommendations for subjective
quality assessment ([P.800], [P.910], [P.1401]) and IETF IPPM
standards for network performance measurement ([RFC7679], [RFC7680],
[RFC6673]). These standards provide guidance on test design,
measurement procedures, and statistical analysis that can help ensure
consistent and reproducible threshold definitions.
This document does not define a standardized approach for creating a
quality-focused network performance requirement specification with
spec-creation only discussing general considerations for creating a
specification.
5.3. Calculating QoO
The QoO score compares the results of network performance
measurements to application-specific network performance requirements
by assessing how close the measured network performance is to the
network conditions needed for optimal application performance,
incorporating both latency and packet loss. There are three key
scenarios:
* The network meets all requirements for optimal performance (ROP).
QoO Score: 100%.
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* The network fails one or more criteria for conditions at the point
of unacceptable performance (CPUP). QoO Score: 0%.
* The network performance falls between optimal and unacceptable.
In this case, a continuous QoO score between 0% and 100% is
computed by taking the worst score derived from latency and packet
loss.
Note that the QoO score should reflect the directionality of the
measurements (one-way or round-trip) as specified in the network
performance requirements. When comparing measurements to
requirements, both must use the same directionality and, for one-way
measurements, the same direction (uplink or downlink).
5.3.1. Overall QoO Calculation
The overall QoO score is the minimum of a latency (QoO_latency) and a
packet loss (QoO_loss) score:
QoO = min(QoO_latency, QoO_loss)
with QoO_latency and QoO_loss as defined in the following.
5.3.2. Latency Component
The QoO latency score bases on linear interpolations of the latency
values at all latency percentiles defined in ROP / CPUP and
represents the minimum value for all percentiles:
for i in latency_percentiles:
m = (ML[i] - ROP[i]) / (CPUP[i] - ROP[i])
metrics[i] = clamp(0, m, 1)
QoO_latency = find_min(metrics) * 100
Where:
* latency_percentiles are the latency percentiles contained in the
ROP and CPUP definitions
* ML[i] is the measured latency at percentile
latency_percentiles[i].
* ROP[i] is the latency as indicated in the requirement for optimal
performance at percentile latency_percentiles[i].
* CPUP[i] is the latency as indicated in the condition at the point
of unacceptable performance at percentile latency_percentiles[i].
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5.3.3. Packet Loss Component
Packet loss is considered as a separate, single measurement that
applies across the entire traffic sample, not at each percentile.
The packet loss score is calculated using a similar interpolation
formula, but based on the total measured packet loss (MLoss) and the
packet loss thresholds defined in the ROP and CPUP:
m = (M_Loss - ROP_Loss) / (CPUP_Loss - ROP_Loss)
QoO_loss = clamp(0, m, 1) * 100
Where:
* M_Loss is the measured packet loss.
* ROP_Loss is the acceptable packet loss for optimal performance.
* CPUP_Loss is the packet loss threshold beyond which the
application becomes unacceptable.
5.4. Example
The following example illustrates the QoO calculations.
Example requirements:
* Minimum bandwidth: 4 Mbps
* ROP: {99%, 200ms}, {99.9%, 300ms}, 1% packet loss
* CPUP: {99%, 500ms}, {99.9%, 600ms}, 5% packet loss
Example measured conditions:
* Measured latency: 99% = 350ms, 99.9% = 375ms
* Measured packet loss: 2%
* Measured minimum bandwidth: 32Mbps / 28Mbps
Latency component:
m1 = (350ms - 200ms) / (500ms - 200ms)
m2 = (375ms - 300ms) / (600ms - 300ms)
metrics = [clamp(0, m1, 1), clamp(0, m2, 1)]
QoO_latency = find_min(metrics) * 100 = 50.00
Packet loss component:
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m = (2% - 1%) / (5% - 1%)
QoO_loss = clamp(0, m, 1) * 100 = 75.00
Overall QoO score:
QoO = min(QoO_latency, QoO_loss) = min(50.00, 75.00) = 50.00
In this example, the network scores 50% on the QoO assessment range
between unacceptable and optimal for the given application when using
the measured network and considering both latency and packet loss.
The score implies that the latency impact dominates the packet loss
impact and that the network overall provides conditions at the midway
point of the performance range.
6. Operational Considerations
This document focuses on the core QoO framework and describes how
quality-focused network performance requirements and corresponding
network performance measurements can be used to calculate QoO network
quality scores. Aiming to ensure broad and easy applicability of the
QoO framework across diverse use cases, the document does not impose
strict mandates. Instead, this section provides general guidance
concerning the operation of the QoO framework based on intuitions and
assumptions that guided the development of the framework. Future
standardization activities are expected to capture and refine best
practices once more operational experience has been gained.
6.1. Creating Network Performance Requirement Specifications
This document does not define a standardized approach for creating a
quality-focused network performance requirement specification.
Instead, this section provides general guidance on and a rough
outline for deriving an admittingly subjective requirement
specification, aiming to create a basis for future standardization
efforts focusing on developing a standardized, objective requirement
creation framework. Additional information is provided in
[QoOAppQualityReqs]. Direct use of the approach described below in
production scenarios is discouraged.
When determining quality-focused network performance requirements for
an application, the goal is to identify the network conditions where
application performance is optimal and where it becomes unacceptable.
There is no universally strict threshold at which network conditions
render an application unacceptable. For optimal performance, some
applications may have clear definitions, but for others, such as web
browsing and gaming, lower latency and loss is always preferable.
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One approach for deriving possible thresholds is to run the
application over a controlled network segment with adjustable quality
and then vary the network conditions while continuously observing the
resulting application-level performance. The latter can be assessed
manually by the entity performing the testing or using automated
methods, such as recording video stall duration within a video
player. Additionally, application developers could set thresholds
for acceptable fps, animation fluidity, i/o latency (voice, video,
actions), or other metrics that directly affect the user experience
and measure these user-facing metrics during tests to correlate the
metrics with the network conditions.
Using this scenario, one can first establish a baseline under
excellent network conditions. Network conditions can then be
gradually worsened by adding delay or packet loss or decreasing
network capacity until the application no longer performs optimally.
The corresponding network conditions identify the minimal
requirements for optimal performance (ROP). Continuing to worsen the
network conditions until the application fails completely eventually
yields the network conditions at the point of unacceptable
performance (CPUP).
Note that different users may have different tolerance levels for
application degradation. Hence, tests conducted by a single entity
likely result in highly subjective thresholds. The thresholds
established should represent acceptable performance for the target
user base, which may require user studies or market research to
determine appropriate values.
As stated at the beginning of this section, this document does not
define a standardized approach for creating a quality-focused network
performance requirement specification and directly using the approach
described above is discouraged.
6.2. Composability and Use Cases
One of the key strengths of the QoO framework is the mathematical
composability of the underlying Quality Attenuation metric, allowing
network quality measurements to be combined across segments using
convolution [TR-452.1]. This approach requires sharing the measured
distributions for the involved segments among relevant stakeholders,
which can be challenging across different operators or networks.
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However, even without sharing distributions across all networks of an
end-to-end path, QoO remains valuable for analyzing and
troubleshooting individual network segments. Operators can use QoO
to assess specific segments within their own networks, and end-users
can gain insights into their own connectivity as long as their
network providers support QoO. Hence, QoO is well-suited for
incremental deployment.
6.3. Deployment Considerations
The QoO framework assumes that measurements reflect the actual
connectivity service that will be provided to application flows.
However, networks may offer multiple connectivity service levels
(e.g., VPN services [RFC2764], corporate customer tiers, and network
slicing configurations [RFC9543]). In such deployments, it is
important to ensure that:
* Measurements are taken using the same connectivity service level
that will be used by the application
* The measurement methodology accounts for any traffic
prioritization, differentiated services, or quality-of-service
mechanisms that may affect application performance
* Network configurations and policies that will apply to application
traffic are reflected in the measurement conditions
Failing to align measurements with the actual service delivery may
result in QoO scores that do not accurately reflect the application's
expected performance.
6.4. Adaptive Applications
Many modern applications are adaptive, meaning they can adjust their
behavior based on network conditions. For example, video streaming
applications may reduce bit rate when bandwidth is limited, or
increase buffer size when latency is high.
For adaptive applications, there are typically different levels of
optimal performance rather than a single absolute threshold. For
example, a video streaming application might provide different
available video resolutions, ranging from 4K to 480p resolution.
Combined with different transmission latencies, each of these
resolutions can induce varying levels of perceived usability.
The QoO framework can accommodate such applications by defining
multiple ROP/CPUP thresholds corresponding to different quality
levels. The framework can then assess how well the application will
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achieve each quality level, providing a more nuanced view of
application performance than a simple binary pass/fail metric.
Another, less complex approach at the cost of reduced fidelity in the
QoO score, is to set the threshold for optimal performance at the
highest rendition available for the video stream, and the threshold
for unacceptability where the lowest rendition cannot be delivered
without resulting in stalling events.
Application developers implementing adaptive applications should
consider publishing quality profiles that define network performance
requirements for different adaptation levels, enabling more accurate
QoO assessment.
6.5. Sensitity to Sampling Accuracy
While the QoO framework itself places no strict requirement on
sampling patterns or measurement technology, a simulation study
[QoOSimStudy] conducted to inform the creation of this document
examined the metric's real-world applicability under varying
conditions and made the following conclusions:
1. Sampling Frequency: Slow sampling rates (e.g., <1Hz) risk missing
rare, short-lived latency spikes, resulting in overly optimistic
QoO scores.
2. Measurement Noise: Measurement errors on the same scale as the
thresholds (ROP, CPUP) can distort high-percentile latencies and
cause artificially lower QoO.
3. Requirement Specification: Slightly adjusting the latency
thresholds or target percentiles can cause significant changes in
QoO, especially when the measurement distribution is near a
threshold.
4. Measurement Duration: Shorter tests with sparse sampling tend to
underestimate worst-case behavior for heavy-tailed latency
distributions, biasing QoO in a positive direction.
In summary, overly noisy or inaccurate latency samples can
artificially inflate worst-case percentiles, thereby driving QoO
scores lower than actual network conditions would warrant.
Conversely, coarse measurement intervals can miss short-lived spikes
entirely, resulting in an inflated QoO.
From these findings, we deduce the following guidelines for practical
application:
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* Calibrate the combination of sampling rate and total measurement
period to capture fat-tailed distributions of latency with
sufficient accuracy.
* Avoid or account for significant measurement noise where possible
(e.g., by calibrating time sources, accounting for clock drift,
considering hardware/software measurement jitter).
* Thoroughly test application requirement thresholds so that the
resulting QoO scores accurately reflect application performance.
These guidelines are non-normative but reflect empirical evidence on
how QoO performs.
6.6. Insights From User Testing
While subjective QoE testing as specified in the ITU-T P-series
recommendations ([P.800], [P.910], and [P.1401]) is out of scope of
this document, a study involving 25 participants tested the QoO
framework in real-world settings [QoOUserStudy]. Participants used
specially equipped routers in their homes for ten days, providing
both network performance data and feedback through pre- and post-
trial surveys.
Participants found QoO scores more intuitive and actionable than
traditional metrics (e.g., speed tests). QoO directly aligned with
their self-reported experiences, increasing trust and engagement.
These results indicate that users find it easier to correlate QoO
scores with real-world application performance than, for example, a
speed test. As such, QoO is expected to help bridge technical
metrics with application performance. However, the specific impact
of QoO should be studied further, for example, via comparative
studies with blinded methodologies that compare QoO to other QoS-type
approaches or application-provided QoE ratings as the mentioned
study's design might have introduced different forms of bias.
7. Known Weaknesses and Open Questions
The described QoO framework simplifies the comparison between network
performance requirements from applications and Quality Attenuation
measurements. This simplification introduces several artifacts, the
significance of which may vary depending on the context. The
following section discusses some known limitations. A general
assumption underlying the framework is that factors which could in
principle be measured but are not explicitly captured by QoO (such as
temporal packet ordering, fine-grained bandwidth variations, or the
full shape of the latency distribution) will inevitably influence the
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observed latency and packet loss behavior, so that QoO indirectly
accounts for their effects through the measured distributions.
7.1. Volatile Networks
Volatile networks - in particular, mobile cellular networks - pose a
challenge for network quality prediction, with the level of assurance
of the prediction likely to decrease as session duration increases.
Historic network conditions for a given cell may help indicate times
of network load or reduced transmission power, and their effect on
throughput/latency/loss. However, as terminals are mobile, the
signal bandwidth available to a given terminal can change by an order
of magnitude within seconds due to physical radio factors. These
include whether the terminal is at the edge of a cell for a radio
network, or undergoing cell handover, the radio interference and
fading from the local environment, and any switch between radio
bearers with differing signal bandwidth and transmission-time
intervals (e.g., 3GPP 4G and 5G). This suggests a requirement for
measuring Quality Attenuation to and from an individual terminal, as
that can account for the factors described above. How that facility
is provisioned onto individual terminals and how terminal-hosted
applications can trigger a Quality Attenuation query, is an open
question.
7.2. Missing Temporal Information in Distributions.
The two latency series (1,200,1,200,1,200,1,200,1,200) and
(1,1,1,1,1,200,200,200,200,200) have identical distributions, but may
have different application performance. Ignoring this information is
a tradeoff between simplicity and precision. To capture all
information necessary to adequately capture outcomes quickly gets
into extreme levels of overhead and high computational complexity.
An application's performance depends on reactions to varying network
conditions, meaning nearly all different series of latencies may have
different application outcomes.
7.3. Subsampling the Real Distribution
Additionally, it is not feasible to capture latency for every packet
transmitted. Probing and sampling can be performed, but some aspects
will always remain unknown. This introduces an element of
uncertainty and perfect predictions cannot be achieved; rather than
disregarding this reality, it is more practical to acknowledge it.
Therefore, discussing the assessment of outcomes provides a more
accurate and meaningful approach.
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7.4. Assuming Linear Relationship Between Optimal Performance and
Unusable
It has been shown that, for example, interactivity cannot be modeled
by a linear scale [G.1051]. Thus, the linear modeling proposed here
adds an error in estimating the perceived performance of interactive
applications.
One can conjure up scenarios where 50ms latency is actually worse
than 51ms latency as developers may have chosen 50ms as the threshold
for changing quality, and the threshold may be imperfect. Taking
these scenarios into account would add another magnitude of
complexity to determining network performance requirements and
finding a distance measure (between requirement and actual measured
capability).
7.5. Binary Bandwidth Threshold
Choosing a binary bandwidth threshold is to reduce complexity, but it
must be acknowledged that many applications are not that simple.
Network requirements can be set up per quality level (resolution,
frames per-second, etc.) for the application if necessary.
7.6. Arbitrary Selection of Percentiles
A selection of percentiles is necessary for simplicity, because more
complex methods may slow adoption of the framework. The 0th
(minimum) and 50th (median) percentiles are commonly used for their
inherent significance. According to [BITAG], the 90th, 98th, and
99th percentiles are particularly important for certain applications.
Generally, higher percentiles provide more insight for interactive
applications, but only up to a certain threshold beyond which
applications may treat excessive delays as packet loss and adapt
accordingly. The choice between percentiles such as the 95th, 96th,
96.5th, or 97th is not universally prescribed and may vary between
application types. Therefore, percentiles must be selected
arbitrarily, based on the best available knowledge and the intended
use case.
8. Security Considerations
The QoO framework introduces a method for assessing network quality
based on probabilistic outcomes derived from latency, packet loss,
and throughput measurements. While the framework itself is primarily
analytical and does not define a new protocol, some security
considerations arise from its deployment and use.
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8.1. Measurement Integrity and Authenticity
QoO relies upon accurate and trustworthy measurements of network
performance. If an attacker can manipulate these measurements,
either by injecting falsified data or tampering with the measurement
process, they could distort the resulting QoO scores. This could
mislead users, operators, or regulators into making incorrect
assessments of network quality.
To mitigate this risk:
* Measurement agents have to authenticate with the systems
collecting or analyzing QoO data.
* Measurement data has to be transmitted over secure channels (e.g.,
(D)TLS) to ensure confidentiality and integrity.
* Digital signatures may be used to verify the authenticity of
measurement reports.
8.2. Risk of Misuse and Gaming
As QoO scores may influence regulatory decisions, SLAs, or user
trust, there is a risk that network operators or application
developers might attempt to "game" the system. For example, they
might optimize performance only for known test conditions or falsify
requirement thresholds to inflate QoO scores.
Mitigations include:
* Independent verification of application requirements and
measurement methodologies.
* Use of randomized testing procedures.
* Transparency in how QoO scores are derived and what assumptions
are made.
8.3. Denial-of-Service (DoS) Risks
Active measurement techniques used to gather QoO data (e.g., TWAMP,
STAMP, and synthetic traffic generation) can place additional load on
a network. If not properly rate-limited, this may inadvertently
degrade services offered by a network or be exploited by malicious
actors to launch DoS attacks.
To mitigate these risks, the following is recommended:
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* Implement rate-limiting and access control for active measurement
tools.
* Ensure that measurement traffic does not interfere with critical
services.
* Monitor for abnormal measurement patterns that may indicate abuse.
8.4. Trust in Application Requirements
QoO depends on application developers to define ROP and CPUP. If
these are defined inaccurately-either unintentionally or maliciously-
the resulting QoO scores may be misleading.
To address such risks, the following recommendations are made:
* Encourage peer review and publication of application requirement
profiles.
* Where QoO is used for regulatory or SLA enforcement, require
independent validation of requirement definitions.
9. Privacy Considerations
QoO measurements may involve collecting detailed performance data
from end-user devices or applications. Depending on the deployment
model, this includes metadata such as IP addresses, timestamps, or
application usage patterns.
To protect user privacy:
* Data collection should be subject to user consent prior to
collecting data.
* Data collection should follow the principle of data minimization,
only collecting what is strictly necessary.
* Privacy-sensitive information (e.g., Personally Identifiable
Information (PII)) should be anonymized or pseudonymized where
possible.
* Users should be informed about what data is collected and how it
is used, in accordance with applicable privacy regulations (e.g.,
General Data Protection Regulation (GDPR)).
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10. Comparison To Other Network Quality Metrics
Numerous network quality metrics and associated frameworks have been
proposed, adopted, and, at times, misapplied over the years. The
following is a brief overview of several key network quality metrics
in comparison to QoO.
Each metric is evaluated against the three criteria established in
Section 4.1. Table 1 summarizes the properties of each of the
surveyed metrics.
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+=============+=====================+==============+==============+
| Metric | Can Assess How Well | Easy to | Composable |
| | Applications Are | Articulate | |
| | Expected to Work | Application | |
| | | Requirements | |
+=============+=====================+==============+==============+
| Throughput | Yes for some | Yes | No |
| | applications | | |
+-------------+---------------------+--------------+--------------+
| Mean | Yes for some | Yes | Yes |
| latency | applications | | |
+-------------+---------------------+--------------+--------------+
| 99th | No | No | No |
| Percentile | | | |
| of Latency | | | |
+-------------+---------------------+--------------+--------------+
| Variance of | No | No | Yes |
| latency | | | |
+-------------+---------------------+--------------+--------------+
| IPDV | Yes for some | No | No |
| | applications | | |
+-------------+---------------------+--------------+--------------+
| PDV | Yes for some | No | No |
| | applications | | |
+-------------+---------------------+--------------+--------------+
| Trimmed | Yes for some | Yes | No |
| mean of | applications | | |
| latency | | | |
+-------------+---------------------+--------------+--------------+
| Round Trips | Yes for some | Yes | No |
| Per Minute | applications | | |
+-------------+---------------------+--------------+--------------+
| Quality | Yes | No | Yes |
| Attenuation | | | |
+-------------+---------------------+--------------+--------------+
| Quality of | Yes | Yes | Yes (Through |
| Outcome | | | Quality |
| | | | Attenuation) |
+-------------+---------------------+--------------+--------------+
Table 1: Summary of Performance Metrics Properties
The column "Can Assess How Well Applications Are Expected to Work"
indicates whether a metric can, in principle, capture relevant
information to assess application performance, assuming that
measurements cover the properties of the end-to-end network path that
the application uses. "Easy to Articulate Application Requirements"
refers to the ease with which application-specific requirements can
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be expressed using the respective metric. "Composable" indicates
whether the metric supports mathematical composition to enable
detailed network analysis.
10.1. Throughput
Throughput is related to user-observable application outcomes because
there must be enough bandwidth available. Adding extra bandwidth
above a certain threshold will, at best, receive diminishing returns
(and any returns are often due to reduced latency). It is not
possible to assess optimal or unacceptable application performance
based on throughput alone for most applications. Throughput can be
compared to a variety of application requirements, but since there is
no direct correlation between throughput and application performance,
it is not possible to conclude that an application will work well
even if it is known that enough throughput is available.
Throughput cannot be composed.
10.2. Mean Latency
Mean latency relates to user-observable application outcomes in the
sense that the mean latency must be low enough to support a good
experience. However, it is not possible to conclude that a general
application will work well if the mean latency is good enough
[BITAG].
Mean latency can be composed. For example, if the mean latency
values of links a-b and b-c are known, then the mean latency of the
composition a-b-c is the sum of a-b and b-c.
10.3. 99th Percentile of Latency
The 99th percentile of latency relates to user-observable application
outcomes because it captures some information about how bad the tail
latency is. If an application can handle 1% of packets being too
late, for instance by maintaining a playback buffer, then the 99th
percentile can be a good metric for measuring application
performance. It does not work as well for applications that are very
sensitive to overly delayed packets because the 99th percentile
disregards all information about the delays of the worst 1% of
packets.
It is not possible to compose 99th-percentile values.
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10.4. Variance of Latency
The variance of latency can be calculated from any collection of
samples, but network latency is not necessarily normally distributed.
As such, it can be difficult to extrapolate from a measure of the
variance of latency to how well specific applications will work.
The variance of latency can be composed. For example, if the
variance values of links a-b and b-c are known, then the variance of
the composition a-b-c is the sum of the variances a-b and b-c.
10.5. Inter-Packet Delay Variation (IPDV)
The most common definition of IPDV [RFC5481] measures the difference
in one-way delay between subsequent packets. Some applications are
very sensitive to this performance characteristic because of time-
outs that cause later-than-usual packets to be discarded. For some
applications, IPDV can be useful in assessing application
performance, especially when it is combined with other latency
metrics. IPDV does not contain enough information to assess how well
a wide range of applications will work.
IPDV cannot be composed.
10.6. Packet Delay Variation (PDV)
The most common definition of PDV [RFC5481] measures the difference
in one-way delay between the smallest recorded latency and each value
in a sample.
PDV cannot be composed.
10.7. Trimmed Mean of Latency
The trimmed mean of latency is the mean computed after the worst x
percent of samples have been removed. Trimmed means are typically
used in cases where there is a known rate of measurement errors that
should be filtered out before computing results.
In the case where the trimmed mean simply removes measurement errors,
the result can be composed in the same way as the mean latency. In
cases where the trimmed mean removes real measurements, the trimming
operation introduces errors that may compound when composed.
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10.8. Round-trips Per Minute
Round-trips per minute [RPM] is a metric and test procedure
specifically designed to measure delays as experienced by
application-layer protocol procedures, such as HTTP GET, establishing
a TLS connection, and DNS lookups. Hence, it measures something very
close to the user-perceived application performance of HTTP-based
applications. RPM loads the network before conducting latency
measurements and is, therefore, a measure of loaded latency (also
known as working latency), and well-suited to detecting bufferbloat
[Bufferbloat].
RPM is not composable.
10.9. Quality Attenuation
Quality Attenuation is a network quality metric that combines
dedicated latency and packet loss distributions into a single
variable [TR-452.1]. It relates to user-observable outcomes in the
sense that they can be measured using the Quality Attenuation metric
directly, or the Quality Attenuation value describing the time-to-
completion of a user-observable outcome can be computed if the
Quality Attenuation of each sub-goal required to reach the desired
outcome is known [Haeri22].
Quality Attenuation is composable because the convolution of Quality
Attenuation values allows computing the time it takes to reach
specific outcomes given the Quality Attenuation of each sub-goal and
the causal dependency conditions between them [Haeri22].
10.10. Quality of Outcome
Quality of Outcome (QoO) builds upon Quality Attenuation by adding
application-specific, dual-threshold network performance requirements
(ROP and CPUP) and translating the comparison between measured
network conditions and these requirements into a percentage-based
score. By incorporating latency distributions, packet loss rates,
and throughput measurements, QoO can assess how well a wide range of
applications are expected to perform under given network conditions.
The underlying Quality Attenuation measurements used in QoO are
mathematically composable, as latency distributions can be composed
using convolution [TR-452.1]. This composability extends to QoO in
the sense that operators can measure individual network segments,
compose the underlying Quality Attenuation distributions, and then
compute QoO scores from the composed result.
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11. IANA Considerations
This document has no IANA actions.
12. Implementation status
Note to RFC Editor: This section must be removed before publication
of the document.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
12.1. qoo-c
* Link to the open-source repository:
https://github.com/getCUJO/qoo-c
* The organization responsible for the implementation:
CUJO AI
* A brief general description:
A C library for calculating Quality of Outcome
* The implementation's level of maturity:
A complete implementation of the specification described in this
document
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* Coverage:
The library is tested with unit tests
* Licensing:
MIT
* Implementation experience:
Tested by the author. Needs additional testing by third parties.
* Contact information:
Bjørn Ivar Teigen Monclair: bjorn.monclair@cujo.com
* The date when information about this particular implementation was
last updated:
27th of May 2025
12.2. goresponsiveness
* Link to the open-source repository:
https://github.com/network-quality/goresponsiveness
The specific pull-request: https://github.com/network-
quality/goresponsiveness/pull/56
* The organization responsible for the implementation:
University of Cincinatti for goresponsiveness as a whole, Domos
for the QoO part.
* A brief general description:
A network quality test written in Go. Capable of measuring RPM
and QoO.
* The implementation's level of maturity:
Under active development; partial QoO support integrated.
* Coverage:
The QoO part is tested with unit tests
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* Licensing:
GPL 2.0
* Implementation experience:
Needs testing by third parties
* Contact information:
Bjørn Ivar Teigen Monclair: bjorn.monclair@cujo.com
William Hawkins III: hawkinwh@ucmail.uc.edu
* The date when information about this particular implementation was
last updated:
10th of January 2024
13. References
13.1. Normative References
[RFC6049] Morton, A. and E. Stephan, "Spatial Composition of
Metrics", RFC 6049, DOI 10.17487/RFC6049, January 2011,
<https://www.rfc-editor.org/rfc/rfc6049>.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
DOI 10.17487/RFC6390, October 2011,
<https://www.rfc-editor.org/rfc/rfc6390>.
[TR-452.1] Broadband Forum, "TR-452.1: Quality Attenuation
Measurement Architecture and Requirements", September
2020,
<https://www.broadband-forum.org/download/TR-452.1.pdf>.
13.2. Informative References
[BITAG] BITAG, "Latency Explained", October 2022,
<https://www.bitag.org/documents/
BITAG_latency_explained.pdf>.
[Bufferbloat]
"Bufferbloat: Dark buffers in the Internet", n.d.,
<https://queue.acm.org/detail.cfm?id=2071893>.
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[CSGO] Xu, X., Liu, S., and M. Claypool, "The Effects of Network
Latency on Counter-strike: Global Offensive Players",
IEEE, 2022 14th International Conference on Quality of
Multimedia Experience (QoMEX) pp. 1-6,
DOI 10.1109/qomex55416.2022.9900915, September 2022,
<https://doi.org/10.1109/qomex55416.2022.9900915>.
[G.1051] ITU-T, "Latency measurement and interactivity scoring
under real application data traffic patterns",
ITU-T G.1051, March 2023,
<https://www.itu.int/rec/T-REC-G.1051>.
[Haeri22] "Mind Your Outcomes: The ΔQSD Paradigm for Quality-Centric
Systems Development and Its Application to a Blockchain
Case Study", n.d.,
<https://www.mdpi.com/2073-431X/11/3/45>.
[I-D.ietf-opsawg-rfc5706bis]
Claise, B., Clarke, J., Farrel, A., Barguil, S.,
Pignataro, C., and R. Chen, "Guidelines for Considering
Operations and Management in IETF Specifications", Work in
Progress, Internet-Draft, draft-ietf-opsawg-rfc5706bis-01,
17 December 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-opsawg-rfc5706bis-01>.
[IRTT] "Isochronous Round-Trip Tester", n.d.,
<https://github.com/heistp/irtt>.
[ISO5725-1]
ISO, "Accuracy (trueness and precision) of measurement
methods and results Part 1: General principles and
definitions", ISO 5725-1:2023, July 2022,
<https://www.iso.org/standard/69418.html>.
[JamKazam] Wilson, D., "What is Latency and Why does it matter?",
n.d., <https://jamkazam.freshdesk.com/support/solutions/
articles/66000122532-what-is-latency-why-does-it-
matter-?>.
[Kelly] Kelly, F. P., "Networks of Queues", n.d.,
<https://www.cambridge.org/core/journals/advances-in-
applied-probability/article/abs/networks-of-
queues/38A1EA868A62B09C77A073BECA1A1B56>.
[P.10] ITU-T, "Vocabulary for performance, quality of service and
quality of experience", ITU-T P.10/G.100, November 2017,
<https://www.itu.int/rec/T-REC-P.10>.
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[P.1401] ITU-T, "Methods, metrics and procedures for statistical
evaluation, qualification and comparison of objective
quality prediction models", ITU-T P.1401, January 2020,
<https://www.itu.int/rec/T-REC-P.1401>.
[P.800] ITU-T, "Methods for subjective determination of
transmission quality", ITU-T P.800, August 1996,
<https://www.itu.int/rec/T-REC-P.800>.
[P.800.1] ITU-T, "Mean opinion score (MOS) terminology",
ITU-T P.800.1, July 2016,
<https://www.itu.int/rec/T-REC-P.800.1>.
[P.910] ITU-T, "Subjective video quality assessment methods for
multimedia applications", ITU-T P.910, October 2023,
<https://www.itu.int/rec/T-REC-P.910>.
[QoOAppQualityReqs]
Østensen, T., "Performance Measurement of Web
Applications", n.d., <https://domos.ai/storage/
U6TlxIlbcl1dQfcNhnCleziJWF23P5w0xWzOARh8-published.pdf>.
[QoOSimStudy]
Monclair, B. I. T., "Quality of Outcome Simulation Study",
n.d., <https://github.com/getCUJO/qoosim>.
[QoOUserStudy]
Monclair, B. I. T., "Application Outcome Aware Root Cause
Analysis", n.d., <https://domos.ai/storage/
LaiW4tJQ2kj4OOTiZbnf48MbS22rQHcZQmCriih9-published.pdf>.
[RFC2681] Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
Delay Metric for IPPM", RFC 2681, DOI 10.17487/RFC2681,
September 1999, <https://www.rfc-editor.org/rfc/rfc2681>.
[RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A.
Malis, "A Framework for IP Based Virtual Private
Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000,
<https://www.rfc-editor.org/rfc/rfc2764>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393,
DOI 10.17487/RFC3393, November 2002,
<https://www.rfc-editor.org/rfc/rfc3393>.
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[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, DOI 10.17487/RFC5357, October 2008,
<https://www.rfc-editor.org/rfc/rfc5357>.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, DOI 10.17487/RFC5481,
March 2009, <https://www.rfc-editor.org/rfc/rfc5481>.
[RFC6349] Constantine, B., Forget, G., Geib, R., and R. Schrage,
"Framework for TCP Throughput Testing", RFC 6349,
DOI 10.17487/RFC6349, August 2011,
<https://www.rfc-editor.org/rfc/rfc6349>.
[RFC6673] Morton, A., "Round-Trip Packet Loss Metrics", RFC 6673,
DOI 10.17487/RFC6673, August 2012,
<https://www.rfc-editor.org/rfc/rfc6673>.
[RFC7679] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Delay Metric for IP Performance Metrics
(IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
2016, <https://www.rfc-editor.org/rfc/rfc7679>.
[RFC7680] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Loss Metric for IP Performance Metrics
(IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January
2016, <https://www.rfc-editor.org/rfc/rfc7680>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/rfc/rfc7799>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/rfc/rfc7942>.
[RFC8033] Pan, R., Natarajan, P., Baker, F., and G. White,
"Proportional Integral Controller Enhanced (PIE): A
Lightweight Control Scheme to Address the Bufferbloat
Problem", RFC 8033, DOI 10.17487/RFC8033, February 2017,
<https://www.rfc-editor.org/rfc/rfc8033>.
[RFC8239] Avramov, L. and J. Rapp, "Data Center Benchmarking
Methodology", RFC 8239, DOI 10.17487/RFC8239, August 2017,
<https://www.rfc-editor.org/rfc/rfc8239>.
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[RFC8290] Hoeiland-Joergensen, T., McKenney, P., Taht, D., Gettys,
J., and E. Dumazet, "The Flow Queue CoDel Packet Scheduler
and Active Queue Management Algorithm", RFC 8290,
DOI 10.17487/RFC8290, January 2018,
<https://www.rfc-editor.org/rfc/rfc8290>.
[RFC8517] Dolson, D., Ed., Snellman, J., Boucadair, M., Ed., and C.
Jacquenet, "An Inventory of Transport-Centric Functions
Provided by Middleboxes: An Operator Perspective",
RFC 8517, DOI 10.17487/RFC8517, February 2019,
<https://www.rfc-editor.org/rfc/rfc8517>.
[RFC8762] Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple
Two-Way Active Measurement Protocol", RFC 8762,
DOI 10.17487/RFC8762, March 2020,
<https://www.rfc-editor.org/rfc/rfc8762>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
Ed., "Data Fields for In Situ Operations, Administration,
and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
May 2022, <https://www.rfc-editor.org/rfc/rfc9197>.
[RFC9312] Kühlewind, M. and B. Trammell, "Manageability of the QUIC
Transport Protocol", RFC 9312, DOI 10.17487/RFC9312,
September 2022, <https://www.rfc-editor.org/rfc/rfc9312>.
[RFC9318] Hardaker, W. and O. Shapira, "IAB Workshop Report:
Measuring Network Quality for End-Users", RFC 9318,
DOI 10.17487/RFC9318, October 2022,
<https://www.rfc-editor.org/rfc/rfc9318>.
[RFC9341] Fioccola, G., Ed., Cociglio, M., Mirsky, G., Mizrahi, T.,
and T. Zhou, "Alternate-Marking Method", RFC 9341,
DOI 10.17487/RFC9341, December 2022,
<https://www.rfc-editor.org/rfc/rfc9341>.
[RFC9543] Farrel, A., Ed., Drake, J., Ed., Rokui, R., Homma, S.,
Makhijani, K., Contreras, L., and J. Tantsura, "A
Framework for Network Slices in Networks Built from IETF
Technologies", RFC 9543, DOI 10.17487/RFC9543, March 2024,
<https://www.rfc-editor.org/rfc/rfc9543>.
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[RFC9817] Kunze, I., Wehrle, K., Trossen, D., Montpetit, M., de Foy,
X., Griffin, D., and M. Rio, "Use Cases for In-Network
Computing", RFC 9817, DOI 10.17487/RFC9817, August 2025,
<https://www.rfc-editor.org/rfc/rfc9817>.
[RPM] "Responsiveness under Working Conditions", July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-ippm-
responsiveness>.
[RRUL] "Real-time response under load test specification", n.d.,
<https://www.bufferbloat.net/projects/bloat/wiki/
RRUL_Spec/>.
[XboxNetReqs]
Microsoft, "Understanding your remote play setup test
results", n.d., <https://support.xbox.com/en-US/help/
hardware-network/connect-network/console-streaming-test-
results>.
Acknowledgments
The authors would like to thank Karl Magnus Kalvik, Olav Nedrelid,
and Knut Joar Strømmen for their conceptual and technical
contributions to the QoO framework.
The authors would like to thank Gavin Young, Brendan Black, Kevin
Smith, Gino Dion, Mayur Sarode, Greg Mirsky, Wim De Ketelaere, Peter
Thompson, and Neil Davies for their contributions to the initial
version of this document.
The authors would like to thank Paul Aitken, Mohamed Boucadair,
Stuart Cheshire, Neil Davies, Guiseppe Fioccola, Ruediger Geib, Will
Hawkins, Marcus Ihlar, Mehmet Şükrü Kuran, Paul Kyzivat, Jason
Livingood, Greg Mirsky, Tal Mizrahi, Luis Miguel Contreras Murillo,
Tommy Pauly, Alexander Raake, Werner Robitza, Kevin Smith, Martin
Thomson, and Michael Welzl for their feedback and input to this
document throughout the IETF process.
Authors' Addresses
Bjørn Ivar Teigen Monclair
CUJO AI
Gaustadalléen 21
0349
Norway
Email: bjorn.monclair@cujo.com
Monclair, et al. Expires 23 August 2026 [Page 43]
Internet-Draft QoO February 2026
Magnus Olden
CUJO AI
Gaustadalléen 21
0349
Norway
Email: magnus.olden@cujo.com
Ike Kunze (editor)
CUJO AI
Gaustadalléen 21
0349
Norway
Email: ike.kunze@cujo.com
Monclair, et al. Expires 23 August 2026 [Page 44]