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Ending the Anomaly: Achieving Low Latency and Airtime Fairness in WiFi
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013). (DISCO)ORCID iD: 0000-0001-5241-6815
Tieto Poland, Szczecin, Poland.
TekLibre, San Francisco, CA USA.
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013). (DISCO)ORCID iD: 0000-0002-8731-2482
Show others and affiliations
2017 (English)In: Proceedings of the 2017 USENIX Annual Technical Conference (USENIX ATC ’17), USENIX - The Advanced Computing Systems Association, 2017, p. 139-151Conference paper, Published paper (Refereed)
Abstract [en]

With more devices connected, delays and jitter at the WiFi hop become more prevalent, and correct functioning during network congestion becomes more important. However, two important performance issues prevent modern WiFi from reaching its potential: increased latency under load caused by excessive queueing (i.e. bufferbloat) and the 802.11 performance anomaly.

To remedy these issues, we present a novel two-part solution. We design a new queueing scheme that eliminates bufferbloat in the wireless setting. Leveraging this queueing scheme, we then design an airtime fairness scheduler that operates at the access point and doesn't require any changes to clients.

We evaluate our solution using both a theoretical model and experiments in a testbed environment, formulating a suitable analytical model in the process. We show that our solution achieves an order of magnitude reduction in latency under load, large improvements in multi-station throughput, and nearly perfect airtime fairness for both TCP and downstream UDP traffic. Further experiments with application traffic confirm that the solution provides significant performance gains for real-world traffic.We develop a production quality implementation of our solution in the Linux kernel, the platform powering most access points outside of the managed enterprise setting. The implementation has been accepted into the mainline kernel distribution, making it available for deployment on billions of devices running Linux today.

Place, publisher, year, edition, pages
USENIX - The Advanced Computing Systems Association, 2017. p. 139-151
Series
2017 Usenix Annual Technical Conference (Usenix Atc '17)
National Category
Computer Sciences
Research subject
Computer Science
Identifiers
URN: urn:nbn:se:kau:diva-47000ISI: 000428763500011ISBN: 978-1-931971-38-6 (print)OAI: oai:DiVA.org:kau-47000DiVA, id: diva2:1043930
Conference
2017 USENIX Annual Technical Conference (USENIX ATC 17). July 12–14, 2017, Santa Clara, CA, USA
Available from: 2016-11-01 Created: 2016-11-01 Last updated: 2018-11-13Bibliographically approved
In thesis
1. On the Bleeding Edge: Debloating Internet Access Networks
Open this publication in new window or tab >>On the Bleeding Edge: Debloating Internet Access Networks
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

As ever more devices are connected to the internet, and applications turn ever more interactive, it becomes more important that the network can be counted on to respond reliably and without unnecessary delay. However, this is far from always the case today, as there can be many potential sources of unnecessary delay. In this thesis we focus on one of them: Excess queueing delay in network routers along the path, also known as bufferbloat.

We focus on the home network, and treat the issue in three stages. We examine latency variation and queueing delay on the public internet and show that significant excess delay is often present. Then, we evaluate several modern AQM algorithms and packet schedulers in a residential setting, and show that modern AQMs can almost entirely eliminate bufferbloat and extra queueing latency for wired connections, but that they are not as effective for WiFi links. Finally, we go on to design and implement a solution for bufferbloat at the WiFi link, and also design a workable scheduler-based solution for realising airtime fairness in WiFi.

Also included in this thesis is a description of Flent, a measurement tool used to perform most of the experiments in the other papers, and also used widely in the bufferbloat community.

Place, publisher, year, edition, pages
Karlstad: Karlstad University Press, 2016. p. 20
Series
Karlstad University Studies, ISSN 1403-8099 ; 2016:49
Keywords
Bufferbloat, WiFi, AQM, queueing, network measurement, performance evaluation, fairness
National Category
Computer Sciences
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-47001 (URN)978-91-7063-732-2 (ISBN)
Presentation
2016-12-06, 1B309 (Sjöströmsalen), Karlstads Universitet, Universitetsgatan 2, Karlstad, 13:15 (English)
Opponent
Supervisors
Available from: 2016-11-16 Created: 2016-11-01 Last updated: 2019-07-12Bibliographically approved
2. Bufferbloat and Beyond: Removing Performance Barriers in Real-World Networks
Open this publication in new window or tab >>Bufferbloat and Beyond: Removing Performance Barriers in Real-World Networks
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The topic of this thesis is the performance of computer networks. While network performance has generally improved with time, over the last several years we have seen examples of performance barriers limiting network performance. In this work we explore such performance barriers and look for solutions.

The problem of excess persistent queueing latency, known as bufferbloat, serves as our starting point; we examine its prevalence in the public internet, and evaluate solutions for better queue management, and explore how to improve on existing solutions to make them easier to deploy.

Since an increasing number of clients access the internet through WiFi networks, examining WiFi performance is a natural next step. Here we also look at bufferbloat, as well as the so-called performance anomaly, where stations with poor signal strengths can severely impact the performance of the whole network. We present solutions for both of these issues, and additionally design a mechanism for assigning policies for distributing airtime between devices on a WiFi network. We also analyse the “TCP Small Queues” latency minimisation technique implemented in the Linux TCP stack and optimise its performance over WiFi networks.

Finally, we explore how high-speed network processing can be enabled in software, by looking at the eXpress Data Path framework that has been gradually implemented in the Linux kernel as a way to enable high-performance programmable packet processing directly in the operating system’s networking stack.

A special focus of this work has been to ensure that the results are carried forward to the implementation stage, which is achieved by releasing implementations as open source software. This includes parts that have been accepted into the Linux kernel, as well as a separate open source measurement tool, called Flent, which is used to perform most of the experiments presented in this thesis, and also used widely in the bufferbloat community.

Abstract [en]

The topic of this thesis is the performance of computer networks in general, and the internet in particular. While network performance has generally improved with time, over the last several years we have seen examples of performance barriers limiting network performance. In this work we explore such performance barriers and look for solutions.

Our exploration takes us through three areas where performance barriers are found: The bufferbloat phenomenon of excessive queueing latency, the performance anomaly in WiFi networks and related airtime resource sharing problems, and the problem of implementing high-speed programmable packet processing in an operating system. In each of these areas we present solutions that significantly advance the state of the art.

The work in this thesis spans all three aspects of the field of computing, namely mathematics, engineering and science. We perform mathematical analysis of algorithms, engineer solutions to the problems we explore, and perform scientific studies of the network itself. All our solutions are implemented as open source software, including both contributions to the upstream Linux kernel, as well as the Flent test tool, developed to support the measurements performed in the rest of the thesis.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2018
Series
Karlstad University Studies, ISSN 1403-8099 ; 2018:42
Keywords
Bufferbloat, AQM, WiFi, XDP, TSQ, Flent, network measurement, performance evaluation, fairness, queueing, programmable packet processing
National Category
Computer Sciences
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-69416 (URN)978-91-7063-878-7 (ISBN)978-91-7063-973-9 (ISBN)
Public defence
2018-11-23, 21A342, Eva Erikssonsalen, Karlstad, 09:15 (English)
Opponent
Supervisors
Available from: 2018-10-26 Created: 2018-09-27 Last updated: 2019-03-13Bibliographically approved

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Høiland-Jørgensen, TokeHurtig, PerBrunström, Anna

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