Simulation Of Multi-core Systems And Interconnections And Evaluation Of Fat-Mesh Networks

Simulators are very important in computer architecture research as they enable the exploration of new architectures to obtain detailed performance evaluation without building costly physical hardware. Simulation is even more critical to study future many-core architectures as it provides the opportunity to assess currently non-existing computer systems. In this thesis, a multiprocessor simulator is presented based on a cycle accurate architecture simulator called SESC. The shared L2 cache system is extended into a distributed shared cache (DSC) with a directory-based cache coherency protocol. A mesh network module is extended and integrated into SESC to replace the bus for scalable inter-processor communication. While these efforts complete an extended multiprocessor simulation infrastructure, two interconnection enhancements are proposed and evaluated. A novel non-uniform fat-mesh network structure similar to the idea of fat-tree is proposed. This non-uniform mesh network takes advantage of the average traffic pattern, typically all-to-all in DSC, to dedicate additional links for connections with heavy traffic (e.g., near the center) and fewer links for lighter traffic (e.g., near the periphery). Two fat-mesh schemes are implemented based on different routing algorithms. Analytical fat-mesh models are constructed by presenting the expressions for the traffic requirements of personalized all-to-all traffic. Performance improvements over the uniform mesh are demonstrated in the results from the simulator. A hybrid network consisting of one packet switching plane and multiple circuit switching planes is constructed as the second enhancement. The circuit switching planes provide fast paths between neighbors with heavy communication traffic. A compiler technique that abstracts the symbolic expressions of benchmarks' communication patterns can be used to help facilitate the circuit establishment

Networking - A Statistical Physics Perspective

Efficient networking has a substantial economic and societal impact in a broad range of areas including transportation systems, wired and wireless communications and a range of Internet applications. As transportation and communication networks become increasingly more complex, the ever increasing demand for congestion control, higher traffic capacity, quality of service, robustness and reduced energy consumption require new tools and methods to meet these conflicting requirements. The new methodology should serve for gaining better understanding of the properties of networking systems at the macroscopic level, as well as for the development of new principled optimization and management algorithms at the microscopic level. Methods of statistical physics seem best placed to provide new approaches as they have been developed specifically to deal with non-linear large scale systems. This paper aims at presenting an overview of tools and methods that have been developed within the statistical physics community and that can be readily applied to address the emerging problems in networking. These include diffusion processes, methods from disordered systems and polymer physics, probabilistic inference, which have direct relevance to network routing, file and frequency distribution, the exploration of network structures and vulnerability, and various other practical networking applications.Comment: (Review article) 71 pages, 14 figure

On Detection Mechanisms and Their Performance for Packet Dropping Attack in Ad Hoc Networks

Ad hoc networking has received considerable attention in the research community for seamless communications without an existing infrastructure network. However, such networks are not designed with security protection in mind and they are prone to several security attacks. One such simple attack is the packet dropping attack, where a malicious node drops all data packets, while participating normally in routing information exchange. This attack is easy to deploy and can significantly reduce the throughput in ad hoc networks.In this dissertation, we study this problem through analysis and simulation. The packet dropping attack can be a result of the behavior of a selfish node or pernicious nodes that launch blackhole or a wormhole attacks. We are only interested in detecting this attack but not the causes of the attack. In this dissertation, for simple static ad hoc networks, analysis of the throughput drop due to this attack along with its improvement when mitigated are presented. A watchdog and a newly proposed "cop" detection mechanisms are studied for mitigating the throughput degradation after detection of the attack. The watchdog mechanism is a detection mechanism that has to be typically implemented in every node in the network. The cop detection mechanism is similar to the watchdog mechanism but only a few nodes opportunistically detect malicious nodes instead of all nodes performing this function. For multiple flows in static and mobile ad hoc networks, simulations are used to study and compare both mechanisms. The study shows that the cop mechanism can improve the throughput of the network while reducing the detection load and complexity for other nodes

Themelio: a new blockchain paradigm

Public blockchains hold great promise in building protocols that uphold security properties like transparency and consistency based on internal, incentivized cryptoeconomic mechanisms rather than preexisting trust in participants. Yet user-facing blockchain applications beyond "internal" immediate derivatives of blockchain incentive models, like cryptocurrency and decentralized finance, have not achieved widespread development or adoption. We propose that this is not primarily due to "engineering" problems in aspects such as scaling, but due to an overall lack of transferable endogenous trust—the twofold ability to uphold strong, internally-generated security guarantees and to translate them into application-level security. Yet we argue that blockchains, due to their foundation on game-theoretic incentive models rather than trusted authorities, are uniquely suited for building transferable endogenous trust, despite their current deficiencies. We then engage in a survey of existing public blockchains and the difficulties and crises that they have faced, noting that in almost every case, problems such as governance disputes and ecosystem inflexibility stem from a lack of transferable endogenous trust. Next, we introduce Themelio, a decentralized, public blockchain designed to support a new blockchain paradigm focused on transferable endogenous trust. Here, the blockchain is used as a low-level, stable, and simple root of trust, capable of sharing this trust with applications through scalable light clients. This contrasts with current blockchains, which are either applications or application execution platforms. We present evidence that this new paradigm is crucial to achieving flexible deployment of blockchain-based trust. We then describe the Themelio blockchain in detail, focusing on three areas key to its overall theme of transferable, strong endogenous trust: a traditional yet enhanced UTXO model with features that allow powerful programmability and light-client composability, a novel proof-of-stake system with unique cryptoeconomic guarantees against collusion, and Themelio's unique cryptocurrency "mel", which achieves stablecoin-like low volatility without sacrificing decentralization and security. Finally, we explore the wide variety of novel, partly off-chain applications enabled by Themelio's decoupled blockchain paradigm. This includes Astrape, a privacy-protecting off-chain micropayment network, Bitforest, a blockchain-based PKI that combines blockchain-backed security guarantees with the performance and administration benefits of traditional systems, as well as sketches of further applications

Parallel and Distributed Computing

The 14 chapters presented in this book cover a wide variety of representative works ranging from hardware design to application development. Particularly, the topics that are addressed are programmable and reconfigurable devices and systems, dependability of GPUs (General Purpose Units), network topologies, cache coherence protocols, resource allocation, scheduling algorithms, peertopeer networks, largescale network simulation, and parallel routines and algorithms. In this way, the articles included in this book constitute an excellent reference for engineers and researchers who have particular interests in each of these topics in parallel and distributed computing

State of the art in Wireless Mesh Networks - delivrable L3.01 - RNRT project "Airnet"

This delivrable presents a state of the art on management related issues in Wireless Mesh Networks. We describe existant work focusing on the five functional domains of the management plane: fault management, configuration management, accounting, performance and security

Allocation of SISAL program graphs to processors using BLAS

There are a number of well known techniques for extracting parallelism from a given program. They range from hardware implementations, building restructuring compilers or reorganizing of programs so as to specify all the available parallelism. The success rate of any of the known techniques is rather poor over all types of programs. This has pushed the research community to explore new languages and design different architectures to exploit program parallelism. The principles of dataflow architectures have addressed the problem of exploiting parallelism in systems by executing dataflow graphs. These graphs or programs represent data dependencies among instructions and execution of the graph proceeds in a data-driven manner. That is, an instruction is executed as soon as all its operands are available, without waiting for any program counter to sequence its execution, as is the case in conventional von Neumann architectures. In this thesis, data flow graphs are generated during the intermediate compilation of a functional language called SISAL (Streams and Iterations in a Single Assignment Language). The Intermediate Form (IFl) is a graphical language consisting of multiple acyclic function graphs that represent a given program. Each graph consists of a sequence of nodes and edges. The nodes specify the operation and the edges indicate the dependencies between the nodes. The graphs are further connected to each other by means of implicit dependencies. The Automator package developed in this project, preprocesses these multiple IF1 graphs and translates them into a single connected graph. It converts all implicit dependencies into actual ones. Additionally, complex language constructs like For All, loops and if-then-else are treated in special ways together with their nested levels by the Automator. There is virtually no limit to the number of nested levels that can be translated by this package. The Automator's prime contribution is in translating real programs written in SISAL into a specified format required by an allocation algorithm called the Balanced Layered Allocation Scheme (BLAS). BLAS partitions a connected graph into independent tasks and assigns them to processors in a multicomputer system. The problem of program allocation lies in maximizing parallelism while minimizing interprocessor communication costs. Hence, allocation is based on the best choice of communication to execution ratio for each task. BLAS utilizes heuristic rules to find a balance between computation and communication costs in the target system. Here the target architecture is a simulated nCUBE 3E computer, having a hypercube topology. Simulations show that, BLAS is effective in reducing the overall execution time of a program by considering the communication costs on the execution times. The results will help in understanding the effects in packing nodes (grain-packing), routing issues in the network and in general, the allocation problem to any processor in a network. In addition, tasks have also been assigned to adjacent processors only, instead of any processor on the hypercube network. The adjacent allocation to processors helps to determine trade-offs required between achieved speed-ups and the time it takes to completely allocate large graphs on compilation