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    Improving the Scalability of Blockchain Systems

    , M.Sc. Thesis Sharif University of Technology Azimi, Navid (Author) ; Eghlidos, Taraneh (Supervisor) ; Mohajeri, Javad (Co-Supervisor)
    Blockchain systems are considered a subclass of distributed systems and have drawn a lot of attention from academia in recent years. The deployment of these systems in various contexts has been the focus of extensive studies. Because of their design, which places a strong focus on security and decentralization, blockchain systems have some challenges. The most prominent challenge is the one that involves scalability. A blockchain's scalability refers to its capacity to achieve a target throughput and solid performance in confirming transactions with an ever-increasing workload or number of nodes in the network. A solid performance suggests that the blockchain system can sustain its... 

    A topology-aware load balancing algorithm for P2P systems

    , Article 4th International Conference on Digital Information Management, ICDIM 200916 December 2009 ; 2009 , Pages 97-102 ; 9781424442539 (ISBN) Mirrezaei, S. I ; Shahparian, J ; Ghodsi, M ; Sharif University of Technology
    One of the challenges of P2P systems is to perform load balancing efficiently. A distributed hash table (DHT) abstraction, heterogeneous nodes, and non uniform distribution of objects cause load imbalance in structured P2P overlay networks. Several solutions are suggested to solve this problem but they have some restrictions. They assume the homogeneous capabilities of nodes, unawareness of the link latency during transferring load and imposing logical structures to collect and reassign load. This paper presents a distributed load balancing algorithm with topology awareness using the concept of virtual servers. In our proposed approach, each node collects neighborhood load information from... 

    LOADER: A location-aware distributed virtual environment architecture

    , Article 2008 IEEE International Conference on Virtual Environments, Human-Computer Interfaces, and Measurement Systems, IEEE VECIMS 2008, Istanbul, 14 July 2008 through 16 July 2008 ; 2008 , Pages 97-101 ; 9781424419289 (ISBN) Hariri, B ; Shirmohammadi, S ; Pakravan, M. R ; Sharif University of Technology
    This article proposes a new architecture for distributed data management and update massage exchange in massively multiuser virtual environments. The key points in the design of such environments are scalability and QoS-aware message delivery. Therefore it requires robust distributed algorithms in a dynamic peer-to-peer system with frequent node arrivals and departures. Our proposed approach is mainly based on distributed hash tables (DHTs) in order to achieve a decentralized system where any participating node can efficiently retrieve the updates associated with a given object. Therefore, the responsibility of maintaining the mapping from names to values is distributed among the nodes in a... 

    Semantic partitioning of peer-to-peer search space

    , Article Computer Communications ; Volume 32, Issue 4 , 2009 , Pages 619-633 ; 01403664 (ISSN) Rostami, H ; Habibi, J ; Livani, E ; Sharif University of Technology
    Peer-to-peer (P2P) networks are beginning to form the infrastructure of future applications. Computers are organized in P2P overlay networks to facilitate search queries with reasonable cost. So, scalability is a major aim in design of P2P networks. In this paper, to obtain a high factor of scalability, we partition network search space using a consistent static shared upper ontology. We name our approach semantic partition tree (SPT). All resources and queries are annotated using the upper ontology and queries are semantically routed in the overlay network. Also, each node indexes addresses of other nodes that possess contents expressible by the concept it maintains. So, our approach can be... 

    Topology control modeling and measurement for networked virtual environments

    , Article VECIMS 2007 - IEEE International Conference on Virtual Environments, Human-Computer Interfaces, and Measurement Systems, Ostuni, 25 June 2007 through 27 June 2007 ; June , 2007 , Pages 155-159 ; 1424408202 (ISBN); 9781424408207 (ISBN) Hariri, B ; Shirmohammadi, S ; Pakravan, M. R ; Sharif University of Technology
    In this paper we will propose a novel distributed architecture for overlay tree construction in collaborative virtual environments that is unlimitedly scalable due to its fully decentralized nature. The routing issue over this architecture will later be discussed and several forwarding schemes based on distributed hash tables (DHT) will be proposed. One of the main concerns for a routing algorithm is to keep a trade-off between the algorithm locality and the algorithm performance. In a global algorithm where nodes make the forwarding decision based on the information gathered from all other nodes in the network, the routing performance may obviously be better. However such a large group...