Sharif Digital Repository

One of the main parts of peer-to-peer multicast is the structure of overlay network. Most of the existing works utilize some common parameters for constructing overlay tree. These parameters are bandwidth and delay. The mismatch between current overlay structure and underlying network topology causes severe link stress and then leads to high end to end latency. According to these problems, we propose a new overlay construction algorithm called OLT in this thesis that finds the location of peers and tries to connect peers that are as close as possible. OLT exploits a number of heuristic techniques to reach an optimized tree even in case of peer heterogeneity and high churn rate. Our... 

In Mobile Ad hoc Networks (MANETs), nodes depend on each other for routing and forwarding their packets. However, to save power and other resources, nodes belonging to independent authorities may behave selfishly, and not cooperate in network activities. Such selfish behaviour poses a real threat to the proper functioning of MANETs. To cope with this situation, a motivation stimulation mechanism is required to provide sufficient incentives for nodes to forward other nodes’ packets. One Appropriate approach is to have network nodes paid in order to motivate them to cooperate with protocol. To achieve truthfulness, the payment based on the cost of transmission of packets. Since the mentioned... 

For increasing safety of driving, intelligent vehicles in vehicular ad hoc networks (VANETs) communicate with each other by sending announcements. The existence of a system that guarantees the trustworthiness of these announcements seems necessary. The proposed system generating announcements should be preserved from internal and external attackers that attempt to send fake messages. In this thesis, we use a group-based endorsement mechanism based on threshold signatures against internal attackers. We choose NTRUSign as a public key cryptosystem for implementing the Public Key Infrastructure (PKI) for decreasing signature generation and verification times. This approach optimizes the network... 

A parallel computer system is composed of a collection of processors used to speed up running a program or performance of multiple programs. If we consider the processors as nodes and the channels between processors as edges, the constructed graph represents an interconnection networks. Network topology affects performance and energy consumption of interconnection network very much. Some parameters of topology quality are low node degree and diameter, high connectivity degree and bisection width and symmetry. Since some of these parameters are in contrast with others, a network with more parameter improvements, is more desirable. Finding cycles with specific length and particularly ... 

Processalgebras,acompositionalmethodofmodelingsystemsandtheirbehavioural features, have been a key instrument in the verification of systems and have strived to completely span a whole spectrum of verification solutions for diverse areas of applications. In this sense, modeling and analysis of the performance metrics in a Mobile Ad hoc Network (MANET) in contrast to other systems, face different challenges which demand different strategies. Hence, our goal here is to model and analyze the qualitative and quantitative aspects of MANETs within one especially designed compositional framework. To achieve this framework, we will first have a look at the different methods which aim to model MANETs... 

In recent years, we have seen the proliferation of real-time and time-dependent systems. They have increased both in number and in complexity. Due to their increasing complexity, we need to model them and become assured of their correctness. Several formalisms have been devised for time-dependent systems. They include timed automaton and timed extensions of Petri nets. Our focus is on timed extension of activity networks and its model checking. Activity networksare powerful formalisms which allow designers to model the system in a natural, small and conceivable manner. This way, timed extension of activity networks can greatly help modelers. In this thesis, we propose a method to specify the... 

Blackhole and grayhole attacks have been become two of the major security concerns in mobile ad hoc networks (MANET). To achieve security in MANETs, a lot of mechanisms had been proposed by now. Using intrusion detection systems(IDSs) is one of the important mechanism to reach this goal. Thus, a well-known IDS was chosen and analyzed in this thesis. Furthermore, a collaborative bayesian filter approach for this intrusion detection system was proposed to enhance its performance. Then the performance of this approach was considered. This intrusion detection system was analyzed using stochastic modeling like continuous time markov chain(CTMC), stochastic reward net(SRN) and stochastic... 

Modeling and performance evaluation of the real time distributed systems is a significant problem. Stochastic activity network is one of the high level models used for this purpose. This network is an extension of generalized stochastic Petri net which is more powerful and flexible than other Petri net extensions. Checking the satisfiability of properties such as performance, dependability and user's expected properties is considerable in these models. Thus, using the approaches and generating modeling and model checking tools with the mentioned purpose is attractive. A model checker automatically checks the correctness of the system behaviors as properties against the model by getting the... 

The daily growth of cloud computing usage for data based applications and Internet services has caused many challenges in the sense of storage cost, data access performance, QoS provision such as availability, scalability, pay-as-you-go model conformation and etc. Data replication is one of the most important mechanisms for data management in distributed systems. It creates some replicas of data and distributes them to the network. The number of replicas, the time for creating a new replica, the way of their distribution among the nodes and replica replacement strategy in the case of storage unavailability are some important challenges in data replication context. Replication is extensively... 

Web applications and services have been developed and deployed with unprecedented speed, providing various important functionalities to the end user such as office applications, social networking, content sharing, education, and entertainment. Given its popularity and ubiquity, the Web also attracts the attention of malicious entities. Indeed, the Web and its global user community have observed various forms of attack in the past. Among these attacks, using the Web as a channel to distribute malware has become a prominent issue. This type of attack called drive by download attack. This issue has generated a great deal of attention from the security research community . Existing systems to... 

With the growth of spreading information across social networks, users face with many options. More specifically, try to find out information is so troublesome in this context.In response to this problem, recommender systems aim at providing suggestions of interest for end-users. Also, we see many social networks in real-life which have the potential to be used in a variety of recommender systems. In the bipartite networks of users and items weighted edges is formed between each user and each item in the training set. On the other hand, developing a recommender system that takes into account the social network of the user improves the accuracy of traditional recommender systems.The purpose... 

Long and continuous running of software is likely to cause software aging-induced errors and failures. Cloud service centers suffer from such errors because of degradation of virtual machine monitors (VMMs) that oversee the execution of virtual machines (VMs). The proposed solution to prevent such VMM failures is to use a rejuvenation scheme for planned termination and restarting of monitor software. The best measure to determine the optimum time of rejuvenation is the VMM’s age, that is, the cumulative workload carried out since the last reboot, repair, or rejuvenation. This paper provides an analytical model based on stochastic activity network (SAN) tool for performance evaluation of... 

The proliferation of cloud services and drastic growing of IaaS data centers,encourage providers to adopt more intelligent approaches to save more energy and as a result, save more money. Today’s novel techniques such as virtualization and live virtual machine migration, provide effective solutions to service providers to fulfill this need. However, investigate the effect of different resource management and virtual machine migration approaches in virtualized data centers, require great efforts. Therefore, in this research work, we propose a model based on Colored Petri Nets to investigate the effect of live virtual machine migration in cloud data centers. Our proposed model is able to... 

With the ever-growing use of cloud computing by practitioners and also the emphasis placed by researchers from various backgrounds on this field, collaboration between various clouds has emerged as a new research area garnering a lot of attention in recent years. Cloud Federation, in which different clouds interact for purposes such as increased productivity and decreased costs, is one aspect of this new trend, which although faced with many challenges,has the potential to make cloud computing even more pervasive then before.In this thesis, by focusing on statistical multiplexing in the resource usage behavior of cloud requests, we evaluate the efficient and fair partitioning of requests in... 

Named Data Networking is the most promisicing content centric Architecture for the future of Internet. In this architecture, content can be accessed regardless of where it is.Routing is one of the most important and challenging issues in these networks. An efficient router improves the efficiency of network by reducing routers convergence time, stored data related to routing and exchanged routing data traffic. It also reduces the state each router keeps due to routing information. In Named Data Networking routers are smart and some of routing protocol responsibilities can be done by forwarding plane. Therefor netwok churns can be handeled by forwarding plane. Considering this responsibility... 

With the growing of smart device softwares, the speed of applications and energy consumption has become a concern for developers of smart device. The unobtrusive running of applications, when the smartphone processor is occupied, alongside the energy issue, when the user needs an urgent need to use a low power storage device, is of concerns for the use of these devices.In order to overcome this issue, cloud computing platforms, transfer smartphone tasks and duties to the cloud platforms and retrieve the results of the calculations to the phone.Obviously, communicating with the cloud requires a communication channel. The communication channel for the internet can either be the internet in... 

Vehicular ad-hoc networks have attracted the attention of many researchers during the last years due to the emergence of autonomous vehicles and the safety concerns regarding their use in near future. One of the major applications in this domain is the usage of vehicle to vehicle communication for warning message dissemination in dangerous situations to prevent more damage. A number of schemes have been proposed regarding the selection of forwarding nodes in this application and there is a need for developing frameworks for analysis and comparison of the schemes in fair situation. Most of the proposed frameworks make use of simulation techniques for the analysis of schemes. However, due to... 

In recent years, a new architecture named Information-Centric Networks has been proposed to change the current host-centric internet model to a content-centric one. One of the key components of these networks is the ability to store content in the ubiquitous caches of network routers. By caching content in routers, network performance can be improved via delivering content from routers closer to users. In these networks, content can be cached in all the routers of the path. This approach will impose a lot of redundancy on the network and also increases the number of replacements of the routers’ caches. So finding a suitable place for caching content that will improve performance from network... 

Cache networks play a key role in today’s Internet. Inspired by the successful deployment of caching in content delivery networks (CDNs), pervasive caching now is a fundamental concept in storage-assisted future Internet architectures, e.g., information-centric networks (ICN), and 5G. However, despite the clear and increasing economic advantages of caching for the network operators, it does not take place efficiently due to various problems. The emergence of in-network caching has created new challenges for modeling and performance evaluation of networks. In addition, content providers (CPs), who alone have the detailed demand data required for optimal content placement, have no natural... 

5G networks are going to support a variety of vertical services, with a diverse set of key performance indicators (KPIs), by using enabling technologies such as software-defined networking and network function virtualization. It is the responsibility of the network operator to efficiently allocate the available resources to the service requests in such a way to honor KPI requirements, while accounting for the limited quantity of available resources and their cost. A critical challenge is that requests may be highly varying over time, requiring a solution that accounts for their dynamic generation and termination. With this motivation, we seek to make joint decisions for request admission,...