Imperial College London

ProfessorWilliamKnottenbelt

Faculty of EngineeringDepartment of Computing

Professor of Applied Quantitative Analysis
 
 
 
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Contact

 

+44 (0)20 7594 8331w.knottenbelt Website

 
 
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Location

 

371Huxley BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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162 results found

Zamyatin A, Wolter K, Werner S, Mulligan CEA, Harrison PG, Knottenbelt WJet al., Swimming with fishes and sharks: beneath the surface of queue-based ethereum mining pools, 25th Annual Meeting of the IEEE International Symposium on Modelling, Analysis and Simulation of Computer and Telecommunication Systems, Publisher: IEEE

Cryptocurrency mining can be said to be the modernalchemy, involving as it does the transmutation of electricityinto digital gold. The goal of mining is to guess the solutionto a cryptographic puzzle, the difficulty of which is determinedby the network, and thence to win the block reward andtransaction fees. Because the return on solo mining has a veryhigh variance, miners band together to create so-called miningpools. These aggregate the power of several individual miners,and, by distributing the accumulated rewards according to somescheme, ensure a more predictable return for participants.In this paper we formulate a model of the dynamics of a queue-based reward distribution scheme in a popular Ethereum miningpool and develop a corresponding simulation. We show that theunderlying mechanism disadvantages miners with above-averagehash rates. We then consider two-miner scenarios and show howlarge miners may perform attacks to increase their profits at theexpense of other participants of the mining pool. The outcomes ofour analysis show the queue-based reward scheme is vulnerableto manipulation in its current implementation.

CONFERENCE PAPER

Pesu T, Knottenbelt WJ, 2017, Optimising hidden stochastic PERT networks, Pages: 133-136

Copyright © 2016 EAI. This paper introduces a technique for minimising subtask dispersion in hidden stochastic PERT networks. The technique improves on existing research in two ways. Firstly, it enables subtask dispersion reduction in DAG structures, whereas previous techniques have only been applicable to single-layer split-merge or fork-join systems. Secondly, the exact distributions of subtask processing times do not need to be known, so long as there is some means of generating samples. The technique is further extended to use a metric which trades off subtask dispersion and task response time.

CONFERENCE PAPER

Harrison PG, Patel NM, Knottenbelt WJ, 2016, Energy--Performance Trade-Offs via the EP Queue, ACM Transactions on Modeling and Performance Evaluation of Computing Systems, Vol: 1, Pages: 1-31, ISSN: 2376-3639

JOURNAL ARTICLE

Haughian G, Osman R, Knottenbelt WJ, 2016, Benchmarking Replication in Cassandra and MongoDB NoSQL Datastores, 27th International Conference on Database and Expert Systems Applications (DEXA), Publisher: SPRINGER INT PUBLISHING AG, Pages: 152-166, ISSN: 0302-9743

CONFERENCE PAPER

Kelly J, Knottenbelt WJ, 2016, Does disaggregated electricity feedback reduce domestic electricity consumption? A systematic review of the literature., CoRR, Vol: abs/1605.00962

JOURNAL ARTICLE

McGinn D, Birch D, Akroyd D, Molina-Solana M, Guo Y, Knottenbelt WJet al., 2016, Visualizing Dynamic Bitcoin Transaction Patterns, BIG DATA, Vol: 4, Pages: 109-119, ISSN: 2167-6461

JOURNAL ARTICLE

Tsimashenka I, Knottenbelt WJ, Harrison PG, 2016, Controlling variability in split-merge systems and its impact on performance, ANNALS OF OPERATIONS RESEARCH, Vol: 239, Pages: 569-588, ISSN: 0254-5330

JOURNAL ARTICLE

Bradley J, Knottenbelt W, Thomas N, 2015, Preface, Electronic Notes in Theoretical Computer Science, Vol: 310, Pages: 1-3, ISSN: 1571-0661

JOURNAL ARTICLE

Chen X, Knottenbelt WJ, 2015, A performance tree-based monitoring platform for clouds, Pages: 97-98

Copyright © 2015 ACM. Cloud-based software systems are expected to deliver reli- able performance under dynamic workload while eficiently managing resources. Conventional monitoring frameworks provide limited support for exible and intuitive performance queries. In this paper, we present a prototype monitor- ing and control platform for clouds that is a better fit to the characteristics of cloud computing (e.g. extensible, user- defined, scalable). Service Level Objectives (SLOs) are ex- pressed graphically as Performance Trees, while violated SLOs trigger mitigating control actions.

CONFERENCE PAPER

Chen X, Rupprecht L, Osman R, Pietzuch P, Knottenbelt W, Franciosi Fet al., 2015, CloudScope: Diagnosing and Managing Performance Interference in Multi-Tenant Clouds, 23rd International Symposium on Modeling, Analysis, and Simulation of Computer and Telecommunication Systems (MASCOTS), Publisher: IEEE, Pages: 164-173, ISSN: 1526-7539

CONFERENCE PAPER

Kelly J, Knottenbelt WJ, 2015, Neural NILM: Deep Neural Networks Applied to Energy Disaggregation., CoRR, Vol: abs/1507.06594

JOURNAL ARTICLE

Kelly J, Knottenbelt WJ, 2015, Neural NILM: Deep Neural Networks Applied to Energy Disaggregation., Publisher: ACM, Pages: 55-64

CONFERENCE PAPER

Parson O, Fisher G, Hersey A, Batra N, Kelly J, Singh A, Knottenbelt W, Rogers Aet al., 2015, Dataport and NILMTK: A Building Data Set Designed for Non-intrusive Load Monitoring, IEEE Global Conference on Signal and Information Processing (GlobalSIP), Publisher: IEEE, Pages: 210-214

CONFERENCE PAPER

Pesu T, Knottenbelt WJ, 2015, Dynamic Subtask Dispersion Reduction in Heterogeneous Parallel Queueing Systems, ELECTRONIC NOTES IN THEORETICAL COMPUTER SCIENCE, Vol: 318, Pages: 129-142, ISSN: 1571-0661

JOURNAL ARTICLE

Wu H, Knottenbelt WJ, Wolter K, 2015, Analysis of the Energy-Response Time Tradeoff for Mobile Cloud Offloading Using Combined Metrics., Publisher: IEEE, Pages: 134-142

CONFERENCE PAPER

Wu H, Seidenst├╝cker D, Sun Y, Nieto CM, Knottenbelt WJ, Wolter Ket al., 2015, An Optimal Offloading Partitioning Algorithm in Mobile Cloud Computing., CoRR, Vol: abs/1510.07986

JOURNAL ARTICLE

, 2015, 8th International Conference on Performance Evaluation Methodologies and Tools, VALUETOOLS 2014, Bratislava, Slovakia, December 9-11, 2014, Publisher: ICST

CONFERENCE PAPER

Batra N, Kelly J, Parson O, Dutta H, Knottenbelt WJ, Rogers A, Singh A, Srivastava MBet al., 2014, NILMTK: an open source toolkit for non-intrusive load monitoring., Publisher: ACM, Pages: 265-276

CONFERENCE PAPER

Chen X, Ho CP, Osman R, Harrison PG, Knottenbelt WJet al., 2014, Understanding, modelling, and improving the performance of web applications in multicore virtualised environments, Pages: 197-207

As the computing industry enters the Cloud era, multicore architectures and virtualisation technologies are replacing traditional IT infrastructures. However, the complex relationship between applications and system resources in multi-core virtualised environments is not well understood. Workloads such as web services and on-line financial applications have the requirement of high performance but benchmark analysis suggests that these applications do not optimally benefit from a higher number of cores. In this paper, we try to understand the scalability behaviour of network/CPU intensive applications running on multicore architectures. We begin by benchmarking the Petstore web application, noting the systematic imbalance that arises with respect to per-core workload. Having identified the reason for this phenomenon, we propose a queueing model which, when appropriately parametrised, reflects the trend in our benchmark results for up to 8 cores. Key to our approach is providing a fine-grained model which incorporates the idiosyncrasies of the operating system and the multiple CPU cores. Analysis of the model suggests a straightforward way to mitigate the observed bottleneck, which can be practically realised by the deployment of multiple virtual NICs within our VM. Next we make blind predictions to forecast performance with multiple virtual NICs. The validation results show that the model is able to predict the expected performance with relative errors ranging between 8 and 26%. Copyright is held by the owner/author(s). Publication rights licensed to ACM.

CONFERENCE PAPER

Danila R, Nika M, Wilding T, Knottenbelt WJet al., 2014, Uncertainty in on-the-fly epidemic fitting, Pages: 135-148, ISSN: 0302-9743

The modern world features a plethora of social, technological and biological epidemic phenomena. These epidemics now spread at unprecedented rates thanks to advances in industrialisation, transport and telecommunications. Effective real-time decision making and management of modern epidemic outbreaks depends on the two factors: the ability to determine epidemic parameters as the epidemic unfolds, and the ability to characterise rigorously the uncertainties inherent in these parameters. This paper presents a generic maximum- likelihoodbased methodology for online epidemic fitting of SIR models from a single trace which yields confidence intervals on parameter values. The method is fully automated and avoids the laborious manual efforts traditionally deployed in the modelling of biological epidemics. We present case studies based on both synthetic and real data. © 2014 Springer International Publishing.

CONFERENCE PAPER

Gandini A, Gribaudo M, Knottenbelt WJ, Osman R, Piazzolla Pet al., 2014, Performance evaluation of NoSQL databases, Pages: 16-29, ISSN: 0302-9743

NoSQL databases have emerged as a backend to support Big Data applications. NoSQL databases are characterized by horizontal scalability, schema-free data models, and easy cloud deployment. To avoid overprovisioning, it is essential to be able to identify the correct number of nodes required for a specific system before deployment. This paper benchmarks and compares three of the most common NoSQL databases: Cassandra, MongoDB and HBase. We deploy them on the Amazon EC2 cloud platform using different types of virtual machines and cluster sizes to study the effect of different configurations. We then compare the behavior of these systems to high-level queueing network models. Our results show that the models are able to capture the main performance characteristics of the studied databases and form the basis for a capacity planning tool for service providers and service users. © 2014 Springer International Publishing.

CONFERENCE PAPER

Huang W-C, Knottenbelt WJ, 2014, Self-Adaptive Containers: Interoperability Extensions and Cloud Integration., Publisher: IEEE Computer Society, Pages: 433-440

CONFERENCE PAPER

Kelly J, Batra N, Parson O, Dutta H, Knottenbelt WJ, Rogers A, Singh A, Srivastava MBet al., 2014, NILMTK v0.2: A Non-intrusive Load Monitoring Toolkit for Large Scale Data Sets., CoRR, Vol: abs/1409.5908

JOURNAL ARTICLE

Kelly J, Batra N, Parson O, Dutta H, Knottenbelt WJ, Rogers A, Singh A, Srivastava MBet al., 2014, NILMTK v0.2: a non-intrusive load monitoring toolkit for large scale data sets: demo abstract., Publisher: ACM, Pages: 182-183

CONFERENCE PAPER

Kelly J, Knottenbelt WJ, 2014, Metadata for Energy Disaggregation., Publisher: IEEE Computer Society, Pages: 578-583

CONFERENCE PAPER

Kelly J, Knottenbelt WJ, 2014, `UK-DALE': A dataset recording UK Domestic Appliance-Level Electricity demand and whole-house demand., CoRR, Vol: abs/1404.0284

JOURNAL ARTICLE

Kelly J, Knottenbelt WJ, 2014, Metadata for Energy Disaggregation., CoRR, Vol: abs/1403.5946

JOURNAL ARTICLE

Nika M, Fiems D, De Turck K, Knottenbelt WJet al., 2014, Modelling Interacting Epidemics in Overlapping Populations, ANALYTICAL AND STOCHASTIC MODELLING TECHNIQUES AND APPLICATIONS, Vol: 8499, Pages: 33-45, ISSN: 0302-9743

JOURNAL ARTICLE

Nika M, Wilding T, Fiems D, De Turck K, Knottenbelt WJet al., 2014, Going multi-viral: Synthedemic modelling of internet-based spreading phenomena, Pages: 50-57

© Copyright 2015 ICST. Epidemics of a biological and technological nature pervade modern life. For centuries, scientific research focused on biological epidemics, with simple compartmental epidemiological models emerging as the dominant explanatory paradigm. Yet there has been limited translation of this effort to explain internet-based spreading phenomena. Indeed, singleepidemic models are inadequate to explain the multimodal nature of complex phenomena. In this paper we propose a novel paradigm for modelling internet-based spreading phenomena based on the composition of multiple compartmental epidemiological models. Our approach is inspired by Fourier analysis, but rather than trigonometric wave forms, our components are compartmental epidemiological models. We show results on simulated multiple epidemic data, swine u data and BitTorrent downloads of a popular music artist. Our technique can characterise these multimodal data sets utilising a parsimonous number of subepidemic models.

CONFERENCE PAPER

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