Sharif Digital Repository

Continuous-time Stochastic Game (CTSG) can be seen as a proper model to analyze probabilistic, nondeterministic, and competitive behaviors as found in Stochastic Multi-Player Game (SMG). The difference is that in an SMG, the system under design is analyzed in the discrete-time setting. In comparison, in a CTSG, the system transitions occur in the continuous-time setting with exponentially distributed delays. This thesis focuses on the model checking of CTSGs with bounded transition rates. We present a uniformization-based algorithm to approximate the optimal time-bounded reachability probabilities with an arbitrary error bound. To illustrate the strength points of our algorithm, we compare... 

This thesis presents an integrated formal method for modeling and model checking of component based computing systems. Both components and coordination subsystems are modeled by a variant of standard labeled transition systems called record transition systems. A record transition system is a labeled transition system whose transition labels are records. We use records to model the concurrency of input – output operations in the ports of the system. The concurrency of the executions with respect to common transition labels are modeled by standard parallel composition operator and also a new defined operator called join which is analogous to the join operator defined to compose constraint... 

In this thesis, we propose a method for verifing software component connectors. In this method, correctness of specification expressed using Linear Temporal Logic (LTL) will be checked on component connectors of Reo coordination model using Model Checking on Constraint Automata which is the behavioral model proposed for Reo connectors. Since model checking suffers from State Explosion Problem as the size of model increases, we reduce the impact of this problem using two techniques: using equivalence relations and implementing using Binary Decision Diagrams (BDDs). We find the smallest equivalent of our behavioral model according to CFFD equivalence which is weakest equivalence preserving... 

Network coding is realized to have great potential for improving throughput limitation of current multi-hop wireless networks. Existing network coding schemes (e.g. COPE) find coding opportunities and use them in forwarding multiple packets, which are coded together, in a single transmission, and consequently, they achieve several fold increase in the throughput of wireless networks. In this thesis, we propose CAPO, a new protocol for multi-hop wireless networks, which does attaching packets in addition to coding them. CAPO has an attaching module which attaches non-encoded packets together opportunistically. In addition, contrary to COPE that just decodes the coded packets the nexthop or... 

Wireless sensor networks (WSN) is a new technology, foreseen to be used increasingly in the near future, and security is an important issue for it. However because of nodes resource limitations, other schemes proposed for securing general ad hoc networks, are not appropriate for WSNs. Usually some nodes act maliciously and they are able to do different kinds of DoS attacks. In order to make the network more secure, malicious nodes should be isolated from the network. In this thesis, we model the interaction of nodes in WSN and intrusion detection system (IDS) as a Bayesian game formulation and use this idea to make a secure routing protocol. By this approach nodes are motivated to act... 

One of the basic characteristics of Wireless Sensor Networks is their resource limitations. As a result, it is essential to try to decrease costs in such networks. These limitations are more critical in transmitting multimedia data with larger data units. In addition, when transmitting real-time multimedia data, delay is an important factor to consider. According to these limitations, Wireless Multimedia Sensor Networks are congestion prone. In this thesis, a transport layer protocol has been proposed. This protocol consists of three three steps in handling congestion. First, it detects congestion according to the queue length in the node. If the lsength is greater than a minimum threshold,... 

Semi-structured documents are a new type of textual documents which has gained a lot of attention nowadays to itself. A specific document modeling for boosting classifiers is needed more than ever which reflects major document specifications. The main goal of this thesis is presenting new adaptive model based on semi-structured documents features. We also aim to use some problem solving approaches such as Statistical approach, Machine Learning and few Algorithmic solutions. In some cases 10% precision optimization can be seen compare to the best approaches available nowadays  

Emerging technologies enable a set of distributed resources across a network tobe linked together and used in a coordinated fashion to solve a particular parallel applicationat the same time. Such applications are often abstracted as directed acyclicgraphs (DAGs), in which vertices represent application tasks and edges represent datadependencies between tasks.The problem of scheduling in a distributed environment is that ofdeciding where to place tasks, and when to start execution of the tasks. Effective scheduling mechanisms for DAG applicationsare essential to exploit the potential of computational resources. Fault tolerance is an important requirement in distributed computing systems when... 

Wireless sensor network is composed of a large number of sensor nodes which are densely deployed to monitor the environment and collect information from physical events. There are different modelsfor sending collected data to users; one of them is query-driven models, in which according to user interest and via declarative queries collected data is delivered. Wireless sensor networks are energy constrained; regarding this issue, it is necessary to have an energy efficient design. Data aggregation or in network processing is one existing solution to reduce energy consumption. Data correlation or redundancy is also can be used with this method to save energy even more. In this thesis, an... 

Routing is one of the most challenging areas in wireless sensor networks because it has a significant impact on energy usage, transmit delay and network fault tolerance. In many situations, network nodes move around and it cause numerous challenges, namely changes in routing paths, failure in sending packets or maybe there is no end-to-end path. Opportunistic routing is one of the best solutions to these problems in mobile wireless sensor networks, thus it provides more efficient routing and less energy consumption in comparison with traditional routings.
In opportunistic routing, nodes try to utilize every opportunity to send their packets to sink. When two nodes are encountered, the... 

Self-organized public key management scheme in mobile ad hoc networks (MANETs) is an inevitable solution to achieve different security services. The aim of such schemes is to find an efficient protocol which makes the node able to obtain the authenticated public key of another node. Public key transmission and verification is achieved using certificate chain or message authentication code, thus it needs other nodes cooperation. It is also notable that in heterogeneous MANETs which include malicious nodes, this method suffers from low throughput and spoofing attack. In this thesis, a novel certificateless, on-demand self-organized public key management scheme is proposed which is based on the... 

Recent advancements in wireless communications and also a tendency to use low cost, tiny, and autonomous high performance products have led to the emergence of wireless sensor networks (WSNs). As the main source of power in a sensor node is a limited and irreplaceable battery, energy is the main important issue. Data aggregation, as an in-network processing method, is a promised technique aiming to conserve energy by reducing the number of packet transmissions through the network. It is a key, yet time-consuming functionality in WSNS, where we hold packets in intermediate nodes to promote aggregation efficiency. However, the requirement of real-time communications is becoming more and more... 

consumption is an economical and environmental concern in nowadays world. Data centers (DC) are an important and energy power hunger part of modern life infrastructure. Many researches have shown that by considering special properties of DCs (e.g. redundancy) the energy consumption can be reduced. However new advances in hardware and software technologies have made DCs equipment more power proportional, i.e. they consume power proportional to their load. Unfortunately this new feature and many previous works do not have synergy. Also the performance of the DCs is so important that no DC owner is willing to trade it for lower power bills. Therefore algorithms that don’t consider the... 

Online social networks (OSNs) can be considered as huge success. However, this success costs users their privacy and loosing own rship of their own data; Sometimes the operators of social networking sites, have some business incentives adverse to users' expectations of privacy. These sort of privacy breaches have inspired research toward privacy-preserving alternatives for social networking in a decentralized fashion. Yet almost all alternatives lack proper feasibility and efciency, which is because of a huge mismatch between aforementioned goal and today's network's means of achieving it. Current Internet architecture is showing signs of age. Among a variety of proposed directions for a new... 

Mobile ad hoc networks have been attracted the attention of many researchers during last years. One of the major concerns faces such networks is the security issue. The root of this concern is the fact that the intermediate nodes have the responsibility of packet transportation and forwarding. The nodes inside the mobile ad hoc networks assumed to be trusty while they can read, change or drop the transported packets. Cryptography as the cornerstone of the security could be play an essential role in such networks. Any cryptosystem need some keys to be able to secure communications. In large scale mobile ad hoc networks storing the whole keys in all nodes is inefficient, if possible, due to... 

In auction-based cloud investment environments, consumers desire the least possible cost and high satisfaction, while providers seek strategies to maximize profit and return on investment. In these environments designing an adequate resource allocation that can satisfy both consumers and providers is of utmost importance. Yet, most available models in resource allocation focus on providers’ needs and do not concern themselves with the consumers. Therefore the present study aims to present an efficient and optimum model for resource allocation problem that takes into account various factors, e.g. resource price, service quality, reputation and fairness, and is capable of satisfying all honest... 

Today's, organizations tend to use cloud services to increase efficiency and reduce IT costs. At the other hand, the growth in diversity of cloud services in aspects of virtual machines cost, technical specifications and locations intricate the process of suitable cloud service selection. In addition to satisfying user requests' requirements, the chosen service must reduce the IT costs. Because of this service diversity and efficiency increase, software modules can be placed in different data centers. And considering this distributivity adds to selection complexity. However, only small amounts of researches have considered communications costs and only have considered qualitative values. As... 

The rapid growth in demand for computational resources driven by new applications and services had led to establishment of new cloud data centers. Such Data Centers consume enormous amount of electrical energy resulting in high costs and carbon emissions. Dynamic Consolidation of virtual machines and turning idle hosts off allow cloud providers to reduce energy consumption. But consolidation of virtual machines may leads to quality of service(QoS) degradation and Service level Agreement(SLA) violation. One of the most important reasons for QoS degradation is the migration overhead, therefore the number of VM migrations should be controlled. Over the last few years, VM consolidation problem... 

Increasing the workload of physical machines in data centers, performance of the system decreases and energy consumption increases. Various methods have been proposed to overcome this challenge and solve the problem. One of these solutions is the migration of virtual machines (VMs) from the over-loaded physical machine (PM) to another one, namely the under-loaded PM, in the clouds, which is effective in increasing the performance of the system and improving energy consumption When the performance of a PM is less than a certain threshold, due to overload, migration of the selected VM to a candidate PM can improve performance, if it is done in an intelligent way. Choosing the best suitable VM... 

Virtualizing the cloud data center as multiple VMs running parallel on a cloud server is a practical solution to the exponentially grown number of cloud users. The fluctuations in the number of required resources, like networking, storage, and computing resources, can be met by dynamic VM migration. The method by which cloud providers manage VMs and hardware resources to decrease costs and ensure the quality of services is of great importance, especially when the cloud is under a heavy workload. VM migration is one of the most fundamental and practical practices in managing the clouds. Despite all the benefits of VM migration, it also brings overhead on the source host, destination host, and...