Sharif Digital Repository

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... 

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 (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... 

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... 

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... 

The aim of this research is to fabricate Mg based nanocomposite by friction stir processing and investigation of the process parameters on the microstructure and mechanical properties of the nanocomposite. In order to this aim, alumina nanoparticles as reinforcement were poured in the groove, with 5mm depth, and due to rotation of friction stir tool, these nanoparticles were mixed with the matrix and nanocomposite was produced. To reach to the best condition in nanocomposite fabrication, the effect of friction stir processing parameters such as, tool rotation speed, tool design, number of friction stir passes, cooling media and reinforcement percent on microstructure, hardness, tensile... 

Nowadays, the significance of securing data and information is undeniable. Cryptography is being used to provide data security. In addition, cryptanalysis is required to evaluate the effectiveness of cryptography methods, and hence, it is an essential concept for securing data. In general, the cryptography functions shall be designed in a way to impose a high load of time-intensive operations to prevent an adversary from accessing the main data from the encrypted data. As a result, cryptography and cryptanalysis algorithms need high performance computations. So far, a number of methods have been proposed to support the required performance. These methods include: distributed computing and... 

Congestion is an important issue in the network environment. To keep stable the perfor-mance of the network, congestion control algorithms have been extensively studied. Queue management method employed by the routers is one of the important issues in the congestion control study. Active Queue Management (AQM) has been proposed for early detection of congestion inside the network. AQM mechanisms control the queue length in a router by dropping arriving packets. The Random Early Detection (RED) is the most popular AQM mechanism used in routers on the Intenet to allow network users to simultaneously achieve high throughput and low average delay. The RED algorithm may cause heavy oscillation of... 

Protocol identification and reverse engineering have recently received much attention due to their importance in many communication and security applications. In this field, the main challenges are: protocol identification, clustering unknown protocols, extracting protocol fields, and finding the protocol format based on these fields and their relations. Most of the proposed methods for the first two parts (protocol identification and clustering) use machine learning and AI techniques. For the last part, some bioinformatics techniques like sequence alignment algorithms are used. In this thesis, after reviewing different methods for protocol identification and reverse engineering, some... 

Generating realistic network traffic serves capacity planning, traffic engineering, understanding internet service performance and anomaly detection. A useful traffic generator must generate characteristics in flows and packets, and add known internet anomalies to legitimate traffic. In this dissertation, we develop a tool for generating realistic and anomalous traffic. This generator can generate traffic in a scalable, reproducible and stochastic manner. Two methods are proposed for this purpose. In the first method, the traffic is generated according to statistical distribution of packets and flow charactristics. In the second method, traffic is generated by modeling the behavior of... 

With prominent features such as lower power consumption, shock resistance, and smaller size, SSDs are widely being used in portable applications. In addition, SSDs are becoming more popular in data storage systems and servers due to their even access and fast response time. Several efforts have been made in the past few years to improve the performance of SSDs. One common technique to improve performance is designing an Input/Output (IO) scheduler based on SSD organization.
In this thesis, we propose an IO scheduling algorithm to improve both performance and endurance of SSDs. Since in-place update is not allowed in flash chips, erasure before any data overwriting is required. As... 

Many congestion control protocols proposed so far to alleviate the problems encountered by TCP protocol in high-speed networks and wireless links have to estimate the parameters of the network. For example, the TCP WESTWOOD congestion window is adjusted based on available bandwidth estimation, or TCP Vegas detects the congestion status based on RTT (Round Trip Time) estimation, and XCP protocol operates according to network traffic load. In this paper, we proposed a novel estimation algorithm that is based on burst identification techniques in router. we show through analysis and simulation that during burst periods this method can estimate the congestion window size of the specific flow... 

Today road accidents take the lives of millions of people on a yearly basis through the world. Also, numerous attempts have been proposed to increase safety on the roads. Vehicular Ad hoc Network (VANET) is a subclass of mobile ad hoc networks (MANET); the main goal of which is to increase the safety and efficiency of road traffics and trips. However, like other networks, routing protocols are one of the most important parts of VANET. But, due to the unique characteristics of VANET (high mobility, short radio coverage area, etc.), the process of data dissemination is a more challenging task than other networks. Therefore, the need for efficient, reliable and safe routing protocols which can... 

Nowadays, using smart buildings to improve performance and welfare of residents is of interest. Usually, these systems consist of safety systems that provide safety and security for residents. For example, fire detection system, sound the alarm and activating sprinkler in the building. For different types of critical events that can occur, variety of safety systems has been designed. Response time of these systems should be less than the deadline and the correct operation must be compeleted. As a result, analyzing and checking out the real-time and logical features of safety systems are the issues that we treat and investigate in this thesis.
In general, these systems are either... 

The visible growth in usage of computer networks in daily human life has significantly increased the importance of their correct and flawless operation. Various solutions have been offered to evaluate the operation correctness of network equipment. One of the most important issues in this context is evaluating the performance of such equipment. Due to the increase in speed of network ports, design and implementation of performance evaluation tools have become a challenging issue in terms of parameters such as speed, time accuracy, power consumption and cost. In this thesis, a hardware-based system for testing network equipment with 10 Gbps ports has been designed and implemented. This system... 

The attempt of this project is to propose a simple model for traffic analysis which eventually leads to the presentation of an online classifier for network traffic anomaly detection. In this research, e show empirically that despite the variety of data networks in size, number of users, applications, and load, the inter-arrival times of normal TCP flows comply with the Weibull distribution whereas specific irregularities (anomalies) causes deviations from the distribution. Consequently, any type of anomalies affecting TCP flows, including intentional intrusions or unintended faults and network failures in general, can be detected by analyzing the discrepancy of TCP flow inter-arrival times... 

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... 

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... 

Flux-cored arc welding has become prevalent in the recent decades worldwide. One of the variants of this welding method is self-shielded welding which requires no external shielding, neither with mineral flux nor with shielding gases. In this study, the variation of microstructure and mechanical properties of flux-cored self-shielded welds was investigated and optimization of this properties was also carried out. For this purpose, a basic combination of powders was chosen from the literature to fabricate the flux-cored wire. These powders contain fluorine, calcium carbonate, aluminum, magnesium and iron. Then, same amount of alloying elements such as molybdenum and nickel was added to this... 

Friction stir soldering (FSS) or brazing (FSB) as an emerging joining process, was first developed to resolve some shortcomings in FSLW and FSSLW such as excessive IMC layer thickness and confined bond area. Although it has advantages over conventional furnace soldering and/or brazing, including localized heating, less detrimental thermal effects on the substrates and capability to reduce the amount of voids at the joint interface. The aim of this study is to investigate the effects of rotational speed, traverse speed and plunge depth of the pinless tool on the shear strength and electrical resistivity of the copper-coated graphite-copper FSSed joints with the aid of Sn-37Pb solder alloy. At...