Sharif Digital Repository

Transformers are one of the most important equipments in transmission and distribution networks. Transformer unplanned outages have severe impacts on the continuity of power system operation. To improve the reliability of transformers and to achieve an optimum operation cost, online condition monitoring of transformers is inevitable. Information about the quality of the transformers insulation system is known as the best parameter to be monitored in a transformer. Since partial discharge signals are initiated long before the beginning of a severe damage, partial discharge monitoring and its evaluation canbe employed to warn the operator.Data mining on the partial discharge signals extracts... 

Due to climate change and the increase in the emission of greenhouse gasses, the temperature of the large cities is increasing. Tehran, which is the capital of Iran and the most populated city of it, is no exception. One of the significant tools for characterizing heat in the cities is having access to the temperature field of the region. Different tools can be used for achieving the temperature field. Two methods for doing so are remote sensing and numerical models. Each one of the mentioned methods has their own strength and weaknesses. In this research, the WRF-ARW model (version 3.7) is used for deriving meteorological fields for the city of Tehran. One of the many merits of using... 

In real-time systems, jobs that miss their deadline are considered worthless or ineffective. Nowadays, real-time applications (such as multimedia) that communicate through software-defined networks (SDN) are widely used and will continue to expand in the future. SDN is an emerging network architecture in which control plane is separated from data plane to manage it directly. In this research, we make changes to the controller and the switch used in such network to deliver real time packets or real-time flows (such as video) on time, as much as possible. As missed deadline packets are worthless and they waste bandwidth, dropping them is a solution. Moreover, the controller can drop flows that... 

The increasing number of road accidents and fatalities have yielded the introduction of several solutions by related industries such as automobile manufacture. Proposed solutions can be classified into two categories: passive, such as airbags, and active such as ABS ad ITS-based technologies. Inter vehicles communication let the communication between vehicles(V2V) or between vehicles and road infrastructure (V2I) by relying on DSRC technology and standards. Intelligent Transportation System (ITS) has three main types of applications namely safety, traffic and commercial. Safety applications are the main goal of vehicular communication, and real time guarantee in safety applications is so... 

Nowadays, one of the problems of network designers and users is the correctness of network equipment functionality. Since routers play an important role in information transfer between various networks and communicate with each other through a routing protocol, any violation of such protocol can result in the network's failure or defective transfer of data. Thus, being assured of the conformance of the implemented protocol in a router with what has been defined in the protocol's standard is of great significance. To this end, before using or exposing a router, network equipment testers should run protocol conformance tests on it and insure its correct functionality. This brings up the... 

In order to increase the network performance, to discover network security threats, to guarantee the quality of services, to simulate networks and develop new network protocols, network designers and operators need software tools to analyze the network traffic. The first step to do this analysis is network monitoring. This can be done by using various software and hardware tools.
In this research we developed a tool which analyzes the network traffic using appropriate statistical methods. The models which are analyzed in this application are: Poisson, Self-similar and Weibull. This application analyzes the network traffic based on this statistical models and calculates their parameters.... 

Recent advancement in wireless communications, electronics, low power design and also tendency to use high performance low cost products have led to emergence of Wireless Sensor Networks (WSNs). As the main purpose of a WSN is information gathering and it’s transmission to the sink node, the main problem is to deliver information correctly with minimum energy consumption. Besides, whereas the majority of developed applications for WSNs are event-critical applications, achieving reliable data transfer as the main factor of dependability and quality of service seems vital. However, data transmission is unreliable over multi-hop WSN due to the unreliability of wireless links and node failures. ... 

Wireless sensor networks (WSNs) are tiny devices with limited computation and power supply. For such devices, data transmission is a very energy-consuming operation. Data aggregation eliminates redundancy and minimizes the number of transmissions in order to save energy. This research explores the efficiency of data aggregation by focusing on different aspects of the problem such as energy efficiency, latency and accuracy. To achieve this goal, we first investigate data aggregation efficiency with constraint on delay, which can be compatible with other important system properties such as energy consumption and accuracy. By simulation, we will show that, depending on the application, we can... 

Up to now two kinds of hardware have been used in routers: ASIC processors or general purpose processors. These two solutions have their own flaws. ASIC hardwares are fast but they are not flexible for implementation or development of new applications. And general purpose processors are not fast enough for fast data rate of network. On the other hand, there is an ever increasing gap between the memory access speed and network data rate. At this time the main bottleneck in packet processing systems is memory. For solving this problem, two groups of solution have been introduced. The first group tries to reduce the demand for memory by using cache or longer system words. The second group uses... 

Wireless sensor networks have many applications, vary in size, and are deployed in a wide variety of areas. They are often deployed in potentially adverse or even hostile environment so security issues are of much concern in these networks. Key management is a fundamental security issue in sensor networks. In this thesis, we are mainly focusing on key establishment and group rekeying schemes aspects of key management. Due to limited resources of sensor networks, key pre-distribution schemes are currently viewed as the most promising solution. Key predistribution in sensor networks refers to the problem of distributing secret keys among sensor nodes prior to deployment. Recently, many key... 

Recent advances in miniaturization and low power design have led to a flurry of activity in wireless sensor networks (WSNs). Sensor networks have different constraints than traditional wired networks. A wireless sensor network is a special network with large numbers of nodes equipped with embedded processors, sensors, and radios. These nodes collaborate to accomplish a common task such as environment monitoring or asset tracking. Many of these applications interface with real world environments and delivery of data is subject to certain constraints. So It is often necessary for communication to meet real-time constraints. Most existing real-time protocols don’t use packet scheduling schemes... 

We use an abstract model to perform hardware/software partitioning for embedded systems. The complexity of partitioning problem in the model is studied and we use a scheme to overcome its NP-Hardness. Partitioning problem can be considered as the main phase of high level synthesis. As it suffers from complexity, heuristic search methods are generally used to overcome its complexity. In this thesis we present a heuristic method (named Tendency algorithm) to increase the performance of heuristic searches, and use it in parallel with other tuning methods. We defind suitable initial point(s) for heuristic searches instead of tuning heuristic parameters. The thesis justifies the logic behind... 

Nowadays, information gathering based on wireless sensor network (WSN) has formed various applications and it also seems to be spreading more in future. Wireless sensor network, is a network composed of multiple nodes, without any infrastructure, each having one or more sensors, wireless communications unit, processing unit, memory, and power supply. Memory capacity, computation power, and power supply are usually considered as valuable resources and limited in nodes. Most of sensor nodes are located in a dense mode and they are susceptible to failure. Therefore network topology may vary dynamically. A sensor network can support real-time communications independent of its type of structure... 

Distributed Denial of Service attacks are threats that target availability of network resources. One feature of this type of attacks is high volume of traffic or service request from huge number of illegitimate attackers that organize botnets together, which cause performance decrease of network. Nowadays, distinguishing huge number of legitimate users during Flash Crowd is one of the most challenging issues for network security experts. Most of proposed methods so far, did not have enough performance or were only applicable in short term, due to increasing attackers’ knowledge in mimicking legitimate users behavior. Methods based on extracting statistic features usually, have better... 

Software Defined Networking (SDN) is an emerging paradigm which makes the network programmable by separating the control plane from data plane and makes both planes to work independently. There is a centralized controller and a programmable data plane in these networks architecture and forwarding data packets is realized by programming the data plane via an open interface called OpenFlow. OpenFlow is a communication protocol between control and data planes. The centralized architecture of these networks provides a global view of the underlying network to upper applications and brings numerous advantages such as routing, traffic engineering and QoS control. Despite these advantages there are... 

In recent years, due to the drawback of rule-based firewalls in detecting unknown attacks, using neural networks has got more attention to be used in firewalls. As the computation load of neural networks are so much there is a need to decrease the processing time and power consumption as they are under load 24/7. Although there have been huge achievements in the usage of graphics processing units (which contain numerous processing cores) in neural networks, their high power consumption has made the scientists think about an alternative to implement neural networks. Field Programmable Gate Array (FPGA) is one of the most serious candidates to be used for implementing neural networks. The goal... 

Software Defined Networking (SDN) is an emerging paradigm which makes the network programmable by separating the control plane from data plane and makes both planes to work independently. There is a centralized controller and a programmable data plane in these networks architecture and forwarding data packets is realized by programming the data plane via an open interface called OpenFlow. OpenFlow is a communication protocol between control and data planes. The centralized architecture of these networks provides a global view of the underlying network to upper applications and brings numerous advantages such as routing, traffic engineering and QoS control. Despite these advantages there are... 

In this project we have designed & implemented a hardware accelerator for domain name service. This hardware accelerator is compatible with existing designs and it could be used standalone as an authoritative DNS server or a hardware accelerator in series of an existing DNS server facility. Two goals, are achieved in this thesis: increasing total DNS throughput and decreasing its response time.In this project, we have surveyed about domain name service, its scientific measurements, theory of caching and its effectiveness, name lookup methods and finally some of the similar designs. Domain name lookup in memory is one of the most challenging operations in every DNS server. We have researched...