Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575331
Engin Leloglu, Tolga Ayav, B. Aslan
With the significant growth in the cloud-based systems, many industries give their attention to cloud computing solutions. E-learning is a promising application area since its typical requirements such as dynamically allocation of computation and storage resources, coincide well with cloud characteristics. This paper presents some possible cloud solutions in e-learning environments by emphasizing its pros and cons. It is of paramount importance to choose the most suitable cloud model for an e-learning application or an educational organization in terms of scalability, portability and security. We distinguish various deployment alternatives of cloud computing and discuss their benefits against typical e-learning requirements.
{"title":"A review of cloud deployment models for e-learning systems","authors":"Engin Leloglu, Tolga Ayav, B. Aslan","doi":"10.1109/DSN.2013.6575331","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575331","url":null,"abstract":"With the significant growth in the cloud-based systems, many industries give their attention to cloud computing solutions. E-learning is a promising application area since its typical requirements such as dynamically allocation of computation and storage resources, coincide well with cloud characteristics. This paper presents some possible cloud solutions in e-learning environments by emphasizing its pros and cons. It is of paramount importance to choose the most suitable cloud model for an e-learning application or an educational organization in terms of scalability, portability and security. We distinguish various deployment alternatives of cloud computing and discuss their benefits against typical e-learning requirements.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116437506","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575332
N. Silva, R. Barbosa, J. Cunha, M. Vieira
Fault injection is a well-known technology that enables assessing dependability attributes of computer systems. Many works on fault injection have been developed in the past, and fault injection has been used in different application domains. This fast abstract briefly revises previous applications of fault injection, especially for embedded systems, and puts forward ideas on its future use, both in terms of application areas and business markets.
{"title":"A view on the past and future of fault injection","authors":"N. Silva, R. Barbosa, J. Cunha, M. Vieira","doi":"10.1109/DSN.2013.6575332","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575332","url":null,"abstract":"Fault injection is a well-known technology that enables assessing dependability attributes of computer systems. Many works on fault injection have been developed in the past, and fault injection has been used in different application domains. This fast abstract briefly revises previous applications of fault injection, especially for embedded systems, and puts forward ideas on its future use, both in terms of application areas and business markets.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"69 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122136405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575356
Nosayba El-Sayed, Bianca Schroeder
As the component count in supercomputing installations continues to increase, system reliability is becoming one of the major issues in designing HPC systems. These issues will become more challenging in future Exascale systems, which are predicted to include millions of CPU cores. Even with relatively reliable individual components, the sheer number of components will increase failure rates to unprecedented levels. Efficiently running those systems will require a good understanding of how different factors impact system reliability. In this paper we use a decade worth of field data made available by Los Alamos National Lab to study the impact of a diverse set of factors on the reliability of HPC systems. We provide insights into the nature of correlations between failures, and investigate the impact of factors, such as the power quality, temperature, fan and chiller reliability, system usage and utilization, and external factors, such as cosmic radiation, on system reliability.
{"title":"Reading between the lines of failure logs: Understanding how HPC systems fail","authors":"Nosayba El-Sayed, Bianca Schroeder","doi":"10.1109/DSN.2013.6575356","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575356","url":null,"abstract":"As the component count in supercomputing installations continues to increase, system reliability is becoming one of the major issues in designing HPC systems. These issues will become more challenging in future Exascale systems, which are predicted to include millions of CPU cores. Even with relatively reliable individual components, the sheer number of components will increase failure rates to unprecedented levels. Efficiently running those systems will require a good understanding of how different factors impact system reliability. In this paper we use a decade worth of field data made available by Los Alamos National Lab to study the impact of a diverse set of factors on the reliability of HPC systems. We provide insights into the nature of correlations between failures, and investigate the impact of factors, such as the power quality, temperature, fan and chiller reliability, system usage and utilization, and external factors, such as cosmic radiation, on system reliability.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"71 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125707472","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575341
Domenico Cotroneo, A. Pecchia, S. Russo
Cyber attacks have become surprisingly sophisticated over the past fifteen years. While early infections mostly targeted individual machines, recent threats leverage the widespread network connectivity to develop complex and highly coordinated attacks involving several distributed nodes [1]. Attackers are currently targeting very diverse domains, e.g., e-commerce systems, corporate networks, datacenter facilities and industrial systems, to achieve a variety of objectives, which range from credentials compromise to sabotage of physical devices, by means of smarter and smarter worms and rootkits. Stuxnet is a recent worm that well emphasizes the strong technical advances achieved by the attackers' community. It was discovered in July 2010 and firstly affected Iranian nuclear plants [2]. Stuxnet compromises the regular behavior of the supervisory control and data acquisition (SCADA) system by reprogramming the code of programmable logic controllers (PLC). Once compromised, PLCs can progressively destroy a device (e.g., components of a centrifuge, such as the case of the Iranian plant) by sending malicious control signals. Stuxnet combines a relevant number of challenging features: it exploits zero-days vulnerabilities of the Windows OS to affect the nodes connected to the PLC; it propagates either locally (e.g., by means of USB sticks) or remotely (e.g., via shared folders or the print spooler vulnerability); it is able to modify its behavior during the progression of the attack, and communicates with a remote command and control server. More importantly, Stuxnet can remain undetected for many months [3] because it is able to fool the SCADA system by emulating regular monitoring signals.
{"title":"Towards secure monitoring and control systems: Diversify!","authors":"Domenico Cotroneo, A. Pecchia, S. Russo","doi":"10.1109/DSN.2013.6575341","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575341","url":null,"abstract":"Cyber attacks have become surprisingly sophisticated over the past fifteen years. While early infections mostly targeted individual machines, recent threats leverage the widespread network connectivity to develop complex and highly coordinated attacks involving several distributed nodes [1]. Attackers are currently targeting very diverse domains, e.g., e-commerce systems, corporate networks, datacenter facilities and industrial systems, to achieve a variety of objectives, which range from credentials compromise to sabotage of physical devices, by means of smarter and smarter worms and rootkits. Stuxnet is a recent worm that well emphasizes the strong technical advances achieved by the attackers' community. It was discovered in July 2010 and firstly affected Iranian nuclear plants [2]. Stuxnet compromises the regular behavior of the supervisory control and data acquisition (SCADA) system by reprogramming the code of programmable logic controllers (PLC). Once compromised, PLCs can progressively destroy a device (e.g., components of a centrifuge, such as the case of the Iranian plant) by sending malicious control signals. Stuxnet combines a relevant number of challenging features: it exploits zero-days vulnerabilities of the Windows OS to affect the nodes connected to the PLC; it propagates either locally (e.g., by means of USB sticks) or remotely (e.g., via shared folders or the print spooler vulnerability); it is able to modify its behavior during the progression of the attack, and communicates with a remote command and control server. More importantly, Stuxnet can remain undetected for many months [3] because it is able to fool the SCADA system by emulating regular monitoring signals.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130773467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575299
Peng Li, Debin Gao, M. Reiter
This paper presents StopWatch , a system that defends against timing-based side-channel attacks that arise from coresidency of victims and attackers in infrastructure-as-a-service clouds. StopWatch triplicates each cloud-resident guest virtual machine (VM) and places replicas so that the three replicas of a guest VM are coresident with nonoverlapping sets of (replicas of) other VMs. StopWatch uses the timing of I/O events at a VM's replicas collectively to determine the timings observed by each one or by an external observer, so that observable timing behaviors are similarly likely in the absence of any other individual, coresident VM. We detail the design and implementation of StopWatch in Xen, evaluate the factors that influence its performance, and address the problem of placing VM replicas in a cloud under the constraints of StopWatch so as to still enable adequate cloud utilization.
{"title":"Mitigating access-driven timing channels in clouds using StopWatch","authors":"Peng Li, Debin Gao, M. Reiter","doi":"10.1109/DSN.2013.6575299","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575299","url":null,"abstract":"This paper presents StopWatch , a system that defends against timing-based side-channel attacks that arise from coresidency of victims and attackers in infrastructure-as-a-service clouds. StopWatch triplicates each cloud-resident guest virtual machine (VM) and places replicas so that the three replicas of a guest VM are coresident with nonoverlapping sets of (replicas of) other VMs. StopWatch uses the timing of I/O events at a VM's replicas collectively to determine the timings observed by each one or by an external observer, so that observable timing behaviors are similarly likely in the absence of any other individual, coresident VM. We detail the design and implementation of StopWatch in Xen, evaluate the factors that influence its performance, and address the problem of placing VM replicas in a cloud under the constraints of StopWatch so as to still enable adequate cloud utilization.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125142392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575319
J. Muppala, M. Hiltunen, R. Campbell, P. Veríssimo
The Third International Workshop on Dependability of Clouds, Data Centers, and Virtual Machine Technology (DCDV 2013) features papers covering various aspects of dependability and security in Clouds and Data Centers. Four sessions covering Cloud and Data Center Networking, Dependability Evaluation, Mobile and Cloud Computing, and Virtualization and Cloud include eleven papers.
{"title":"The Third International Workshop on Dependability of Clouds, Data Centers and Virtual Machine Technology DCDV 2013","authors":"J. Muppala, M. Hiltunen, R. Campbell, P. Veríssimo","doi":"10.1109/DSN.2013.6575319","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575319","url":null,"abstract":"The Third International Workshop on Dependability of Clouds, Data Centers, and Virtual Machine Technology (DCDV 2013) features papers covering various aspects of dependability and security in Clouds and Data Centers. Four sessions covering Cloud and Data Center Networking, Dependability Evaluation, Mobile and Cloud Computing, and Virtualization and Cloud include eleven papers.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"160 4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125941513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575339
F. Machida, Jianwen Xiang, Kumiko Tadano, Y. Maeno, T. Horikawa
Design of storage system configuration is one of the key issues for providing dependable IT systems. An appropriate RAID storage configuration should consider both performance and availability. To assist the design, this paper presents the performability models for RAID10 and RAID6 that can be used to compare the configuration quantitatively. A performability advantage of RAID6 over RAID10 in sequential read access is discovered by the numerical study in conjunction with performance benchmark results.
{"title":"Performability analysis of RAID10 versus RAID6","authors":"F. Machida, Jianwen Xiang, Kumiko Tadano, Y. Maeno, T. Horikawa","doi":"10.1109/DSN.2013.6575339","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575339","url":null,"abstract":"Design of storage system configuration is one of the key issues for providing dependable IT systems. An appropriate RAID storage configuration should consider both performance and availability. To assist the design, this paper presents the performability models for RAID10 and RAID6 that can be used to compare the configuration quantitatively. A performability advantage of RAID6 over RAID10 in sequential read access is discovered by the numerical study in conjunction with performance benchmark results.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"174 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127583758","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575355
Javier Alonso, Michael Grottke, A. Nikora, Kishor S. Trivedi
Faults in software systems can have different characteristics. In an earlier paper, the anomaly reports for a number of JPL/NASA missions were analyzed and the underlying faults were classified as Bohrbugs, non-aging-related Mandelbugs, and aging-related bugs. In another paper the times to failure for each of these fault types were examined to identify trends within missions as well as across the missions. The results of those papers are now starting to provide guidance to improve the dependability of space mission software. Just as there are different types of faults, there are different kinds of mitigations of faults and failures. This paper analyzes the mitigations associated with each fault studied in our previous papers. We identify trends of mitigation type proportions within missions as well as from mission to mission. We also look for relationships between fault types and mitigation types. The results will be used to increase the reliability of space mission software.
{"title":"An empirical investigation of fault repairs and mitigations in space mission system software","authors":"Javier Alonso, Michael Grottke, A. Nikora, Kishor S. Trivedi","doi":"10.1109/DSN.2013.6575355","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575355","url":null,"abstract":"Faults in software systems can have different characteristics. In an earlier paper, the anomaly reports for a number of JPL/NASA missions were analyzed and the underlying faults were classified as Bohrbugs, non-aging-related Mandelbugs, and aging-related bugs. In another paper the times to failure for each of these fault types were examined to identify trends within missions as well as across the missions. The results of those papers are now starting to provide guidance to improve the dependability of space mission software. Just as there are different types of faults, there are different kinds of mitigations of faults and failures. This paper analyzes the mitigations associated with each fault studied in our previous papers. We identify trends of mitigation type proportions within missions as well as from mission to mission. We also look for relationships between fault types and mitigation types. The results will be used to increase the reliability of space mission software.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131307803","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575363
E. Anceaume, Yann Busnel, B. Sericola
We consider the problem of achieving uniform node sampling in large scale systems in presence of a strong adversary. We first propose an omniscient strategy that processes on the fly an unbounded and arbitrarily biased input stream made of node identifiers exchanged within the system, and outputs a stream that preserves Uniformity and Freshness properties. We show through Markov chains analysis that both properties hold despite any arbitrary bias introduced by the adversary. We then propose a knowledge-free strategy and show through extensive simulations that this strategy accurately approximates the omniscient one. We also evaluate its resilience against a strong adversary by studying two representative attacks (flooding and targeted attacks). We quantify the minimum number of identifiers that the adversary must insert in the input stream to prevent uniformity. To our knowledge, such an analysis has never been proposed before.
{"title":"Uniform node sampling service robust against collusions of malicious nodes","authors":"E. Anceaume, Yann Busnel, B. Sericola","doi":"10.1109/DSN.2013.6575363","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575363","url":null,"abstract":"We consider the problem of achieving uniform node sampling in large scale systems in presence of a strong adversary. We first propose an omniscient strategy that processes on the fly an unbounded and arbitrarily biased input stream made of node identifiers exchanged within the system, and outputs a stream that preserves Uniformity and Freshness properties. We show through Markov chains analysis that both properties hold despite any arbitrary bias introduced by the adversary. We then propose a knowledge-free strategy and show through extensive simulations that this strategy accurately approximates the omniscient one. We also evaluate its resilience against a strong adversary by studying two representative attacks (flooding and targeted attacks). We quantify the minimum number of identifiers that the adversary must insert in the input stream to prevent uniformity. To our knowledge, such an analysis has never been proposed before.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123917545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-06-24DOI: 10.1109/DSN.2013.6575302
V. Sundaram, P. Eugster
Wireless sensor networks (WSNs) deployments are subjected not infrequently to complex runtime failures that are difficult to diagnose. Alas, debugging techniques for traditional distributed systems are inapplicable because of extreme resource constraints in WSNs, and existing WSN-specific debugging solutions address either only specific types of failures, focus on individual nodes, or exhibit high overheads hampering their scalability. Message tracing is a core issue underlying the efficient and effective debugging of WSNs. We propose a message tracing solution which addresses key challenges in WSNs - besides stringent resource constraints, these include out-of-order message arrivals and message losses - while being streamlined for the common case of successful in-order message transmission. Our approach reduces energy overhead significantly (up to 95% and on average 59% smaller) compared to state-of-the-art message tracing approaches making use of Lamport clocks. We demonstrate the effectiveness of our approach through case studies of several complex faults in three well-known distributed protocols.
{"title":"Lightweight message tracing for debugging wireless sensor networks","authors":"V. Sundaram, P. Eugster","doi":"10.1109/DSN.2013.6575302","DOIUrl":"https://doi.org/10.1109/DSN.2013.6575302","url":null,"abstract":"Wireless sensor networks (WSNs) deployments are subjected not infrequently to complex runtime failures that are difficult to diagnose. Alas, debugging techniques for traditional distributed systems are inapplicable because of extreme resource constraints in WSNs, and existing WSN-specific debugging solutions address either only specific types of failures, focus on individual nodes, or exhibit high overheads hampering their scalability. Message tracing is a core issue underlying the efficient and effective debugging of WSNs. We propose a message tracing solution which addresses key challenges in WSNs - besides stringent resource constraints, these include out-of-order message arrivals and message losses - while being streamlined for the common case of successful in-order message transmission. Our approach reduces energy overhead significantly (up to 95% and on average 59% smaller) compared to state-of-the-art message tracing approaches making use of Lamport clocks. We demonstrate the effectiveness of our approach through case studies of several complex faults in three well-known distributed protocols.","PeriodicalId":163407,"journal":{"name":"2013 43rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124549045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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