Sharif Digital Repository

Complex networks have recently become a very noticeable subject because of their remarkable theory on real networks such as rumor spreading. This thesis contributes to a prevention strategy which uses a maximal clique algorithm to find overlapping communities and also uses inverse targeting immunization strategy to immune these communities. By the using maximal clique algorithm combined with inverse targeting strategy we have achieved that the TIK method (targeted immunization using k-clique percolation) obtains 10% of better immunization than HD (highest degree) method which is one of the best methods in targeted immunization strategies. The TIK also demonstrates that rumor spreading is... 

Complex network studies grow by the scientific community, thanks to the increasing availability of real-world network data. The importance of using analysis on this type of network algorithms and community structure is one of the most important problems in the field of complex networks. Community Detection in a multidimensional network is still under investigation in the research community. The aim of this research is to give an algorithm for community discovery. We have reviewed the basis for multidimensional network analysis and will present a solid repertoire of basic concepts and analytical measures, which take into account the general structure of multidimensional networks. Then, we... 

Free and Open-Source Software (FOSS) is grown rapidly and many researches are conducted to study FOSS developments. The studies aim to help FOSS development by finding bugs, analyzing developers, modeling evolution of software and categorizing them. Finding proper developers or key developers of each group is essential in developing software, recommend developers and assigning bugs to proper developers. Community detection detects groups of nodes having dense connections. The groups represent developers which cooperate closely on developing FOSS. The thesis proposes a method based on evolutionary algorithms and topological analysis to detect communities in open-source software development... 

Researching in the field of optimization of network immunizing and epidemic spreading is an active and important area. According to literature review, influential nodes are detected based on global graph metrics such as centrality measures. On the other hand, when a network infrastructure is not available and a direct or straight path between source and destination may not be accessible, one can use opportunistic networks routing protocols in Delay Tolerant Networks to recognize influential users is an appropriate approach. In this work, we use a real world three layer dataset which consists of digital data (social relations and Bluetooth contact traces) of individuals. We convert the real... 

Open source software development is growing rapidly according to request of market. Different types of analysis have done on open source development networks to extract knowledge and help both developers and users to decide better. In this thesis, we try to extract data from one of the biggest open source development repositories GitHub and then a community detection algorithm will apply on these data for different time stamps. Then we propose an evolution tracking model and implement it to detect evolution of communities from 2013 until 2015. Then communities size evolution and changes in communities such as growth, dissolve, merge, split and formation will be discussed. After that we... 

In healthcare field to reduce costs, high availability, increasing reliability, access to data from multiple locations and manage distributed information between centers, doctors and patients; there is a certain need to a distributed system and cloud services are a good option to meet that need. In this thesis different models of service delivery in the healthcare were studied which included traditional and cloud models. Also from the survey, the metrics which we used to compare these models were extracted. These metrics include quantitative metrics such as cost, setup time, availability, multi-regional, elasticity, efficiency and qualitative metrics including integrity, privacy,... 

In this thesis, we propose a QoS-aware routing algorithm for multimedia streaming that uses cross-layer information (application layer and physical layer) in Wireless Multimedia Sensor Networks (WMSN). Our goal is to use cross-layer information to route video packets efficiently and deliver a higher quality video in streaming applications. Our QoS-Aware Multi-Path Selection (QAMPS) method is based on multi-path multi-priority selection algorithm that uses Two-Phase geographic Greedy Forwarding (TPGF) as a routing algorithm. The proposed method guarantees QoS by splitting video streams into I-frames, P-frames and B-frames in the application layer and passes them to the network layer for... 

Nowadays, deployment of peer-to-peer video streaming systems over wireless mesh networks has attained increasing popularity among a large number of users around the world. In this thesis, we present an efficient peer-to-peer live video streaming architecture over multi-hop wireless mesh networks. In our proposed architecture, we take the physical topology of the network into account and based on a distributed locality-aware neighbor selection algorithm in the overlay construction phase, we generate an efficient mesh-based overlay on top of wireless mesh networks. In locality-aware neighbor selection algorithm, instead of choosing randomly, peers find their best neighbors based on their... 

Since the contribution bandwidth of each CDN (Content Delivery Network) node and also each peer are limited, optimal allocation of their bandwidth to their partners is an interesting issue. In this work, an efficient resource allocation algorithm in a hybrid CDN-P2P (Content Delivery Network- peer to peer) video streaming network has been designed and each peer will receive the video chunks with the bit rate according to the number of nodes that the peer supports. We have added this algorithm to Coolstreaming because it does not have a resource allocation mechanism. In Coolstreaming each peer when requests chunks from its neighbors, the neighbors will send the peer the requested chunks with... 

To make Wireless Multimedia Sensor Networks (WMSNs) more practical, researchers have tried to meet its challenges in the last decade. Some factors of WMSNs, such as low bandwidth and channel errors, cause a decrease in the video quality that is declared as distortion. On the other hand, one important requirement in the context of multimedia streaming is its quality. In this thesis, we first introduce and use an adaptive cross-layer error control in the link layer, and then we implement a new cross-layer source rate control Mechanism for efficient and reliable real-time multimedia streaming in wireless sensor networks. Our main objective is to minimize distortion. Some of the used cross-layer... 

According to increase of multimedia applications such as video surveillance and environment monitoring in Wireless Multimedia Sensor Networks (WMSN), energy conservation and prolonging network lifetime become increasingly important. Therefore, energy conservation and maximization of system lifetime are commonly recognized as a key challenge in the design and implementation of WMSNs. In these networks, nodes sense the area with high degree of correlation due to the overlapping Field Of Views (FoVs) and causes wasting network energy. We present “overlapped region detection clustering” as a new clustering method to reduce redundant video streams and overcome waste of the energy. We apply scene... 

Nowadays, a need for intelligent system that can assist web users in acquiring their desired information has been highlighted. In particular a mechanism for web user profiling which involves knowing the users and providing them with their preferred information is recommended to any website. To address this issue, Web Usage Mining (WUM) techniques have attracted many attentions. WUM is a kind of web mining process that tries to extract interesting usage patterns from the data that are obtained from the interaction of users with the web. The most important drawback of conventional, data mining based, WUM system is their inability to continuously learn the evolving patterns of web usage. On the... 

attacks have become such a serious problem that according to the recent security firms’ reports, more than five thousands attacks are launched per day, whichcould lead to lots of damage and loss of online businesses. When a P2P system has millions of concurrently active peers, there is the risk that an attacker misuses these clients, or diverts their generated traffic to launch DDoS attack.As we will see, since BitTorrent has gained more popularity among other P2P protocols,and ithas the most number of concurrent active users,it may lead to destructivedamagesif exploited by attackers for lunching DDoS attack. Thus, we have focused on DDoS detection over this protocol.In this study, first,we... 

Most of current the MAC protocols for Wireless Sensor Networks (WSNs) concern about energy efficiency rather than low latency. The main source of energy consumption in the MAC layer is idle listening, and most of these protocols use duty cycling for reducing energy consumption. But duty cycling method increases packet delivery latency. This problem is very critical in real time applications where packets should meet their deadline. There are some solutions for this problem. For example a node forwards data packets multi hop away instead of one hop in a single cycle. In this research, an efficient cross layer MAC protocol for real time applications is proposed. In this protocol multi hop... 

Web servers and web applications are susceptible to different attacks. In order to detect web-based attacks Intrusion detection systems (IDS) should be equipped with a large number of signatures. Unfortunately various types of web threats are increasingly growing and so detection and prevention of all these new and old attacks is exhaustive and really difficult.This thesis represents a designed system for intrusion detection that uses different techniques to discover vulnerabilities with derived patterns and also some user behavior based attacks against web applications. This was done by using new dataset which was generated by new log file.The primary objective of this thesis shows the... 

Peer-to-peer streaming has developed as a popular application in today’s Internetinfrastructure. In a typical peer-to-peer live streaming system, publishers provide the streaming content and the interested peers receive and deliver data in a distributed manner and also apeer structure is created by forming an overlay inside the network. In reality, peers are strategic and there is no motivation to contribute any of their upload bandwidth toward other peers. To address this issue, we proposed a simple arcade algorithm that makes an arcade based mechanism for peers to facilitate adjacent peers with more bandwidth to achieve a higher bandwidth themselves.Commensurate with our algorithm, if... 

Hybrid CDN-P2P architecture has been introduced to combine scalability advantage of P2P and reliability of CDN networks. Although it has been proved that CDN-P2P is more efficient than other architectures for live video streaming, there is still the question, “How is it possible to be more efficient in providing higher service quality?” Quality degradation in P2P and Hybrid CDN-P2P is mainly connected to the lack of exploiting role of peers’ heterogeneity in the system. Most of currently deployed live video streaming systems don’t adapt to bandwidth of the peers and just send one version of video to all users. To tackle this issue, many researches combine P2P solution with scalable video... 

The emerging peer-to-peer (P2P) networks become more popular among researchers in different applications such as file sharing, and video streaming. Since various P2P networks provide high performance and scalable interaction among peers, they are very efficient in designing distributed multimedia applications such as live streaming, IPTV, VoIP, and multimedia broadcasting. In order to improve the network throughput and downloading performance of P2P networks for multimedia streaming, network coding is a technique which can be used for these purposes. In this thesis, we propose a peer-to-peer (P2P) video streaming protocol which presents an implementation of network coding technique. The... 

The quality of service in Wireless Multimedia Sensor Networks (WMSNs) is related to packet loss rate. Recently dierent studies have been done on developing ecient protocols in the transport layer for controlling packet loss in WMSNs. However, all of these protocols are independent of the characteristics of the multimedia content. In this thesis, a novel transport layer protocol, called User Datagram Dispatcher Protocol (UDDP), is proposed to minimize the packet loss ratio in WMSNs by considering trac characteristics, the inter-arrival pattern of packets and packet priority. UDDP is a new cross-layer transport layer that uses information of MAC and application layers to distribute packet... 

Peer to peer networks and especially peer to peer live video streaming systems are becoming more and more popular these days. To disseminate the video chunks in a live P2P video streaming system all users should contribute in uploading the video chunks; however there are some selfish peers who tend to download video chunks from the network while they do not upload any data to the network; these peers are called free-riders. With incorporating the incentive mechanisms in peer to peer live video streaming systems the chance of free-riders to get the full video or the video with the intended quality will be very low. In this research we propose a push-pull live video streaming system with a...