Search results

Title: Secure and private access control for systems of smart devices
Creator: Le, Tam Dan
Date: 2019
Collection: Electronic Theses & Dissertations
Description: With the emergence of Internet of Things (IoT) technologies and the invasion of smart devices in almost every aspect of our lives, access control that allows only authorized users to access IoT devices becomes an important problem. The limited capabilities of the devices and the distributed nature of IoT environments have presented unique challenges to the design of an effective access control mechanism. First, it should be lightweight enough for the IoT devices to handle due to their...
Show moreWith the emergence of Internet of Things (IoT) technologies and the invasion of smart devices in almost every aspect of our lives, access control that allows only authorized users to access IoT devices becomes an important problem. The limited capabilities of the devices and the distributed nature of IoT environments have presented unique challenges to the design of an effective access control mechanism. First, it should be lightweight enough for the IoT devices to handle due to their resource constraints. Second, the variety of devices and applications and the arbitrary manners of users require the support of fined-grain, flexible access control policies. Last but not least, traditional access control models that are often centralized may not be suitable for distributed IoT. Therefore, a decentralized approach should be considered.In this dissertation, we propose access control solutions that are not only secure and private but also scalable to meet IoT requirements. Our first design is an authorization protocol that supports flexible delegation for smart home applications. The protocol allows users to create and share various permissions within their authorities to other users. In addition, since simple computation operations are used, the protocol is lightweight and supports fast validation at resource-constrained devices. Next, the need to support larger environments and the open problem with the exchange of access keys without a central authority motivate us to seek a decentralized solution from blockchain technology, which is originated from the famous cryptocurrency Bitcoin. The advantages of blockchain, which lie in an immutable distributed ledger that is maintained by a peer-to-peer network of untrusted nodes, can bring decentralization to IoT applications. However, applying blockchain to IoT is not straightforward as it was not originally designed for IoT requirements. We address two main issues in blockchain-based access control for IoT systems. First, since blockchain is a public platform, user privacy is one of the top priorities. Second, resource-constrained IoT devices are often not powerful enough to interact directly with the blockchain but need to rely on certain trusted nodes to retrieve blockchain data.The first issue of user privacy leads to our design of CapChain, a blockchain-based privacy-preserving access control framework that enables the sharing of access capabilities to multiple devices in a secure and private manner. Then, applying similar techniques to CapChain but also extending the use of blockchain by smart contracts, we design a privacy-preserving service that allows users to create IoT automated tasks by defining one of multiple conditional statements that need to be satisfied before a task can be performed. We set up strict privilege at the triggering party, such that it may not trigger the task any time except only when the conditions are satisfied.To address the second issue of resource constrained devices, we propose a method for IoT devices to validate blockchain data without solely being dependent on a central server. In our approach, several witnesses on the network can be selected randomly by the devices to validate access control information. Our method is aided by Bloom filters, which are shown to be lightweight for resource-constrained devices.
Show less

Title: Scheduling for CPU Packing and node shutdown to reduce the energy consumption of high performance computing centers
Creator: Vudayagiri, Srikanth Phani
Date: 2010
Collection: Electronic Theses & Dissertations
Description: During the past decade, there has been a tremendous growth in the high performance computing and data center arenas. The huge energy requirements in these sectors have prompted researchers to investigate possible ways to reduce their energy consumption. Reducing the energy consumption is not only beneficial to an organization economically but also to the environment. In this thesis, we focus our attention on high performance scientific computing clusters. We first perform experiments with the...
Show moreDuring the past decade, there has been a tremendous growth in the high performance computing and data center arenas. The huge energy requirements in these sectors have prompted researchers to investigate possible ways to reduce their energy consumption. Reducing the energy consumption is not only beneficial to an organization economically but also to the environment. In this thesis, we focus our attention on high performance scientific computing clusters. We first perform experiments with the CPU Packing feature available in Linux using programs from the SPEC CPU2000 suite. We then look at an energy-aware scheduling algorithm for the cluster that assumes that CPU Packing is enabled on all the nodes. Using simulations, we compare the scheduling done by this algorithm to that done by the existing, commercial Moab scheduler in the cluster. We experiment with the Moab Green Computing feature and based on our observations, we implement the shutdown mechanism used by Moab in our simulations. Our results show that Moab Green Computing could provide about an 13% energy savings on average for the HPC cluster without any noticeable decrease in the performance of jobs.
Show less

Title: Dynamic process migration for load balancing in distributed systems
Creator: Xu, Chong-Wei
Date: 1986
Collection: Electronic Theses & Dissertations

Title: Estimating available bandwidth for real-time supermedia applications
Creator: Chobanyan, Alexander
Date: 2007
Collection: Electronic Theses & Dissertations

Title: Integration of a statistical method in one way delay trend detection for available bandwidth estimation
Creator: Shafii, Mahnaz
Date: 2008
Collection: Electronic Theses & Dissertations

Title: Co-operative coded communication under network constraints
Creator: Misra, Kiran Mukesh
Date: 2010
Collection: Electronic Theses & Dissertations

Title: Impacts of interactivity from computer-mediated communication in an organizational setting : a study of electronic mail
Creator: Ku, Linlin
Date: 1992
Collection: Electronic Theses & Dissertations

Title: Multicast communication in multicomputer networks
Creator: Lin, Xiaola
Date: 1991
Collection: Electronic Theses & Dissertations

Title: Implementation of a high throughput low power MAC protocol in wireless sensor networks
Creator: Liu, Chin-Jung
Date: 2011
Collection: Electronic Theses & Dissertations
Description: This thesis presents the design, implementation, and evaluation of TATD-MAC, a TDMA-based low duty cycle synchronous MAC protocol that improves throughput by increasing channel uti- lization with a traffic-adaptive time slot scheduling method. Conventional time division multiple access (TDMA) introduces significant end-to-end packet delivery delay and its throughput is lim- ited. TATD-MAC achieves higher throughput by improving TDMA with a novel traffic-adaptive mechanism that assigns time...
Show moreThis thesis presents the design, implementation, and evaluation of TATD-MAC, a TDMA-based low duty cycle synchronous MAC protocol that improves throughput by increasing channel uti- lization with a traffic-adaptive time slot scheduling method. Conventional time division multiple access (TDMA) introduces significant end-to-end packet delivery delay and its throughput is lim- ited. TATD-MAC achieves higher throughput by improving TDMA with a novel traffic-adaptive mechanism that assigns time slots only to nodes that are expecting traffic. Our traffic-adaptive mechanism is a two-phase design, which decomposes the DATA period into traffic notification part and data transmission scheduling part. The two-phase design enables TATD-MAC to optimize the control packets and improve their energy efficiencies according to the characteristics of each phase. The source nodes inform all nodes on the routing path that these sources have outgoing traffic by transmitting traffic notification packets in a "pulse" fashion. With traffic notification packets, ev- ery node on the routing path claims time slots in data transmission part. Therefore, TATD-MAC is able to forward a packet over multiple hops in a single cycle and thus reduce the end-to-end delay. The data transmission scheduling mechanism only assigns time slots to nodes with traf- fic through an ordered schedule negotiation scheme. This innovative traffic-adaptive scheduling mechanism assigns time slots based on traffic and totally eliminates the idle listening slots on nodes with no traffic. Moreover, if any other nodes need more time slots, they are able to claim them, which further improves channel utilization and achievable throughput. We implemented a TATD-MAC prototype on Tmote-Sky running TinyOS 2.1.0. Performance evaluation shows that TATD-MAC significantly improves throughput compared to conventional TDMA and achieves the same throughput as TDMA with slot stealing while having 70% less power consumption.
Show less

Title: The effects of participation and feedback received on the length of time members in online communities remain active
Creator: Sarkar, Chandan
Date: 2013
Collection: Electronic Theses & Dissertations
Description: Online communities support extensive interactions among their members. Membership in most of these communities is voluntary, content supplied by other members is typically a primary attractant to new members, and barriers to admission and exit are minimal (Lampe, 2009; Lampe, 2010). For a community to thrive, it is necessary that members remain active in the community and continue to interact with others. Given that sustaining a solid base of active long-term members is critical to the...
Show moreOnline communities support extensive interactions among their members. Membership in most of these communities is voluntary, content supplied by other members is typically a primary attractant to new members, and barriers to admission and exit are minimal (Lampe, 2009; Lampe, 2010). For a community to thrive, it is necessary that members remain active in the community and continue to interact with others. Given that sustaining a solid base of active long-term members is critical to the sustainability of an online community, it is important that factors that contribute to the length of active membership are identified. Addressing certain limitations of prior studies, this dissertation examines key factors such as rate of participation, rate of feedback received, early participation and early feedback received that may influence the length of time members stay active in a community. A mixed method approach that included server log analyses for two online communities, Everything2 and Sploder, and qualitative interviews with members of Everything2, was used to study how these factors are related to how long members remain active in a community. A Cox proportional hazard rate model and a Granger causality test were employed to analyze the server log data. The results suggest that certain types of early participation (first post submitted in Sploder and first post and first message submitted in Everything2) and certain type of early feedback received (deletion of post in Sploder and first positive and negative vote and deletion of first post in Everything2) are significant predictors of how long a member remains active in Sploder and Everything2. A member's average rate of participation (writeups, votes given, and messages sent) in Everything2 is positively correlated with length of active membership, but not in Sploder. The rate of feedback received is not significantly correlated in either community. It is well-known that correlational evidence is not dispositive proof of a causal link. Therefore, the relationships between the dependent variable and the independent variables identified by the Cox Proportional Hazard Rate model are further examined using a Granger causality test, with which time series data can be employed for a more rigorous test of causality. The results showed no causality between rate of participation and the length of time a member remains active in a community. Findings from the quantitative studies are expanded on, based on interviews with long-term members in the community. These results show that the factors contributing to length of active membership may vary among online communities. While some results may generalize to other communities if the communities are similar enough, not all results do generalize. The findings also suggest that early negative feedback has a strong negative impact on how long a member will remain active in an online community, as both Everything2 and Sploder had a significant negative correlation with deletion of first post. The implications of these results for the design online communities are discussed.
Show less

Title: Flexible spectrum use in channel bonding wireless networks
Creator: Yang, Xi (Software engineer)
Date: 2014
Collection: Electronic Theses & Dissertations
Description: Channel bonding, which assembles multiple narrow channels into one logical channel, can speed up data transmission and achieve better bandwidth utilization in wireless networks. Since introduced in 802.11n, channel bonding has been extended continually to support wider channels, making low-lag high-speed wireless communication possible. However, different radio technologies have different requirements on channel width. Devices that use different channel widths coexist in a contention domain...
Show moreChannel bonding, which assembles multiple narrow channels into one logical channel, can speed up data transmission and achieve better bandwidth utilization in wireless networks. Since introduced in 802.11n, channel bonding has been extended continually to support wider channels, making low-lag high-speed wireless communication possible. However, different radio technologies have different requirements on channel width. Devices that use different channel widths coexist in a contention domain may cause inefficiency and unfairness issues. For example, narrowband devices are easier to obtain medium access opportunities because they do not need to wait for the entire wide band to be idle. Therefore, although wideband devices can provide higher transmission speed, they are at an unfavorable position in contentions with narrowband devices.To this end, we propose a flexible spectrum use channel bonding (FSUB) protocol in which a node is allowed to start a transmission whenever there are some idle narrow channels and gradually increases the channel width during transmission. Because a node dynamically adjusts the channel width in a communication, we use a convolution method to achieve fast spectrum agreement between the transmitter and the receiver. To address contentions between devices in a wide band of spectrum, we introduce a compound preamble to make the collisions detectable in the frequency domain and use a parallel bitwise arbitration mechanism to quickly determine the winner. We implement and evaluate the proposed protocol through both the GNU Radio/USRP platform and ns-2 simulations. The results show that the proposed protocol well addresses the inefficiency and unfairness issues caused by heterogeneous radio coexistence. Channel bonding devices usingFSUB have more medium access opportunities and can aggregate wider channels than using other channel bonding protocols in presence of narrowband interference. The FSUB enables a device to always benefit from channel bonding without concerns about narrowband interference level.
Show less

Title: Inter-partition networking for overlay multicast
Creator: Eetemadi, Sauleh
Date: 2005
Collection: Electronic Theses & Dissertations

Title: Cooperative resource sharing by integrating cellular and mobile Ad Hoc networks
Creator: Zhu, Danyu
Date: 2005
Collection: Electronic Theses & Dissertations

Title: Autoconfiguration and security for wireless networks
Creator: Zhou, Hongbo
Date: 2005
Collection: Electronic Theses & Dissertations

Title: Adaptive key management for secure group communication
Creator: Bezawada, Bruhadeshwar
Date: 2005
Collection: Electronic Theses & Dissertations

Title: Complex network problems in physics, computer science and biology
Creator: Cojocaru, Radu Ionut
Date: 2006
Collection: Electronic Theses & Dissertations

Title: Capacity assurance in hostile networks
Creator: Li, Jian
Date: 2015
Collection: Electronic Theses & Dissertations
Description: Linear network coding provides a new communication diagram to significantly increase the network capacity by allowing the relay nodes to encode the incoming messages. However, this communication diagram is fragile to communication errors and pollution attacks. How to combat errors while maintaining the network efficiency is a challenging research problem. In this dissertation, we study how to combat the attacks in both fixed network coding and random network coding.For fixed network coding,...
Show moreLinear network coding provides a new communication diagram to significantly increase the network capacity by allowing the relay nodes to encode the incoming messages. However, this communication diagram is fragile to communication errors and pollution attacks. How to combat errors while maintaining the network efficiency is a challenging research problem. In this dissertation, we study how to combat the attacks in both fixed network coding and random network coding.For fixed network coding, we provide a novel methodology to characterize linear network coding through error control coding. We propose to map each linear network coding to an error control coding. Under this mapping, these two codes are essentially identical in algebraic aspects. Meanwhile, we propose a novel methodology to characterize a linear network coding through a series of cascaded linear error control codes, and to develop network coding schemes that can combat node compromising attacks. For random network coding, we propose a new error-detection and error-correction (EDEC) scheme to detect and remove malicious attacks. The proposed EDEC scheme can maintain throughput unchanged when moderate network pollution exists with only a slight increase in computational overhead. Then we propose an improved LEDEC scheme by integrating the low-density parity check (LDPC) decoding. Our theoretical analysis, performance evaluation and simulation results using ns-2 simulator demonstrate that the LEDEC scheme can guarantee a high throughput even for heavily polluted network environment.Distributed storage is a natural application of network coding. It plays a crucial role in the current cloud computing framework in that it can provide a design trade-off between security management and storage. Regenerating code based approach attracted unique attention because it can achieve the minimum storage regeneration (MSR) point and minimum bandwidth regeneration (MBR) point for distributed storage. Since then, Reed-Solomon code based regenerating codes (RS-MSR code and RS-MBR code) were developed. They can also maintain the MDS (maximum distance separable) property in code reconstruction. However, in the hostile network where the storage nodes can be compromised and the packets can be tampered with, the storage capacity of the network can be significantly affected.In this dissertation, we propose a Hermitian code based minimum storage regenerating (H-MSR) code and a Hermitian code based minimum bandwidth regenerating (H-MBR) code. We first prove that they can achieve the theoretical MSR bound and MBR bound respectively. We then propose data regeneration and reconstruction algorithms for the H-MSR code and the H-MBR code in both error-free networks and hostile networks. Theoretical evaluation shows that our proposed schemes can detect the erroneous decodings and correct more errors in the hostile network than the RS-MSR/RS-MBR code with the same code rate respectively.Inspired by the novel construction of Hermitian code based regenerating codes, a natural question is how to construct optimal regenerating codes based on the layered structure like Hermitian code in distributed storage. Compared to the Hermitian based code, these codes have simpler structures and are easier to understand and implement. We propose two optimal constructions of MSR codes through rate-matching in hostile networks: 2-layer rate-matched MSR code and m-layer rate-matched MSR code. For the 2-layer code, we can achieve the optimal storage efficiency for given system requirements. Our comprehensive analysis shows that our code can detect and correct malicious nodes with higher storage efficiency compared to the RS-MSR code. Then we propose the m-layer code by extending the 2-layer code and achieve the optimal error correction efficiency by matching the code rate of each layer's MSR code. We also demonstrate that the optimized parameter can achieve the maximum storage capacity under the same constraint. Compared to the RS-MSR code, our code can achieve much higher error correction efficiency. The optimized m-layer code also has better error correction capability than the H-MSR code.
Show less