Sharif Digital Repository

An Ad-Hoc wireless network consists of a collection of geographically distributed nodes that communicate with each other over a wireless medium. These networks don’t use any infrastructure or base station to channel allocation. The important difference between wireless networks and wired networks is the broadcast nature of wireless communications. In these networks, each node transmits data to all of the nodes in the transmission range which may cause an increase in interference and data loss. On the other hand, due to mobility of users, fading the channel between them and change of routing, the probability of data loss increases. The extensive and successful employment of TCP variants in... 

This research presents an efficient thermal-aware routing protocol based on Shortest Hop Routing algorithms for implanted bi medical sensor network. Implanted biomedical sensor networks provide a major application of sensor networks in the near future. These in-vivo sensor nodes collect desired biometric data and communicate the data wirelessly to a base-station through a multi-hop network. They generate the heat due to wireless communication and circuitry power consumption. A high temperature of the in-vivo nodes for a prolonged period might damage the surrounding tissues. Most of the protocols for sensor networks don’t take the thermal issue as a factor in the routing of packets. In its... 

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... 

Multicasting has gained a lot of research attentions in facilitating group communications in wireless networks. Applying multicast mechanisms in Wireless Mesh Networks, brings a lot of benefits to these networks. In our research, we have introduced Cost-aware On-Demand Multicast Routing Protocol (C-ODMRP) as an extension of ODMRP that supports QoS provisioning for high quality applications in WMNs. In C-ODMRP, the nodes are prevented from applying the links that do not meet the QoS requirements. The multicast receivers are provided with resource-aware information to efficiently compute the cost of the routes when multiple routes from source to destination nodes are established. C-ODMRP takes... 

Wireless networks with the shared media require Medium Access Control (MAC) protocol that provides contention resolution mechanism. The design of MAC protocol is a challenging issue because of limited energy source and high propagation delay in UnderWater Acoustic Sensor Networks (UWASNs). The most important goal of the MAC design for underwater sensor networks is to resolve data packet collision efficiently with respect to energy consumption. So, selection of MAC protocol is an important task because it has significant impact on the system efficiency. A suitable MAC protocol must consider some factors such as fairness, energy consumption, latency and throughput based on various... 

Wireless sensor networks (WSNs) use many tiny sensors to monitor phenomena such as temperature, humidity, brightness and traffic, and then transmit this information to a base station using wireless channels. WSNs find applications in military, ecological, urban and health related areas. Hierarchical wireless sensor networks are kind of sensor networks that use communication entities with different capabilities in terms of energy, processing power, bandwidth, communication range and etc. In this thesis, an introduction to WSNs and their applications, characteristics and designing factors is expressed. It continues on studying the infrastructures and the role of cryptography in enhancing... 

Today many communications take place over asynchronous insecure networks which do not provide any guarantee of security (as Internet); hence there is a must in authenticating party or parties with which we are going to interact. In many cases, more than two parties (entities) are going to interact, resulting in need of group authentication. Since authentication is inseparable from key exchange, we are going to introduce a new authenticated group key exchange protocol in this thesis which benefits from all known features for such a protocol in the literature such as contributiveness and deniability. To overcome the problem of concurrency, we use a framework dedicated to security in concurrent... 

Security protocols are mostly verified using tools based on model checking approach. These tools are automatic but they can be used for verifying protocols with low complexity and limited number of participants. The other approach that can be used in these cases is theorem proving. Inductive method is a theorem proving approach which is based on induction in mathematics. Inductive method has been applied for verifying several classical and real-world protocols.
The basic concepts in this method are event and trace. Using the concept of event, the network traffic can be modeled through various events occurring in the network. Atrace is a list of events and model a history of the network.... 

Nowadays, distributed embedded systems are extensively employed in safety-critical automotive applications, e.g. Steer-By-Wire and Brake-By-Wire. Moreover, according to the present and future needs of the automotive industry of Iran, in this Ph.D. thesis, fault tolerance in safety-critical distributed automotive communication networks has been improved. This thesis consists of three research layers. In the first layer, several comprehensive studies on all automotive communication protocols and their architectures have been done. Among the protocols, the FlexRay communication protocol has been selected to employ in safety-critical distributed embedded systems. In the second layer, the fault... 

Distributed computation has an important role in data mining. Data mining, usually requires a lot of resources both in terms of storage space and computing time. To reach scalability, some mechanisms for the distribution of work is required. Moreover, in many systems today, data is distributed in several databases. In this case, due to traffic overload in network, transferring all data to a central server and applying process centrally is inefficient and is subject to privacy issues. Distributed data mining provides some techniques for efficient mining in decentralized mode. Identifying frequent itemsets is one of the important branches of data mining. Frequent patterns are set of items,... 

Identifying clusters is an important aspect of analyzing large data sets. In many popular applications like peer-to-peer systems, large amounts of data, is distributed among multiple dispersed data sources. In such decentralized platforms, transmission of data to a central server is infeasible due to processing, storage and transmission costs. Furthermore, the data rarely remains static and frequent data changes, quickly out dates previously extracted clustering models. In this thesis, we propose a fully decentralized partition-based clustering algorithm which is capable of clustering dynamic and distributed data sets, without requiring a central control or message flooding. In this... 

In this thesis, we present a new identification protocol which is based on lattice problems. Lattice-based cryptographic algorithms are, in general, faster than those based on number theory. Moreover, instead of algorithms based on number theory problems, such as Factoring and Discrete Logarithm, lattice-based ones are resistant against quantum computers. In addition, lattice problems have worst-case/average-case hardness relation; so become suitable choices for cryptographic purposes. However, there are few lattice-based identification protocols which are efficient. The protocol introduced in this thesis, is statistical zero-knowledge which means no verifier, even computationally unbounded... 

In recent years, frequent involvements in claims have been inevitable due to unpredictable economic changes and increasing complexities in construction industry. Therefore, even appropriately made contracts are not exempted from claims. On the other hand, construction contract claims are time-consuming, expense-involving and most likely leading to unsatisfactory results. However, there may be some positive outcomes, such as time extension or compensation of damages. To launch investigationson claim management, a list of important and frequent claims in oil and gas industry projects of Iran was extracted after a succinct documents review. Further, the most important claim causes were... 

In decentralized Supply Chains, each member decides based on his own interests. Conflict of interests results in suboptimal decisions and poor performance for entire supply chains, as well seriously harms credibly information sharing across them. In this thesis, coordination of decisions in supply chains in the context of Capacity Procurement problem are studied in different situations in form of three models. In first model, a dyadic supply chain with stochastic demand and exogenous price is investigated by taking various costs into account. PARD and RCRS contracts are designed and proposed in order for coordination of decisions respectively in full and partial information updating... 

Video communications over mobile ad hoc networks is increasingly deployable as these networks become deployed in various applications such as disaster recovery. Error-prone nature of the mobile ad hoc networks and the vulnerability of compressed video to packet losses have brought many challenges to realize video transmission over MANETs. In this thesis, it is tried to achieve a good quality of service by resilient video coding and multipath transmission over mobile ad hoc networks. To generate error resilient video, a hybrid method is used by combining scalable video coding and multiple description video coding techniques. First, the video sequence is coded to two layers and then each layer... 

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... 

Cooperative control of autonomous multi-agent systems is one of the challenging problems in control theory. According to existing enhancements in communication networks and broad application of multi-agent systems in various engineering fields, coordinated motion control in multi-agent systems has been attracted the attention of researchers in control science. In this thesis, flocking algorithms in multi-agent systems with undirected interactions (bidirectional information flow) is considered and new convergence results and final characteristics are obtained. Also, geometric optimization methods are used to propose a new optimization problem to reduce the number of informed agents of the... 

Identification protocols facilitates two participants A and B to identify themselves to each other. Beside identification, A and B can exchange a secret value along with the identification process as the key exchange identification protocol.A secure key exchange identification protocol hould utilize perfect forward secrecy (PFS) property. PFS means if an attacker could compromise an entity in future and gain its long-term key, he cannot succeed to extract previous session keys. So, he will be unable to decrypt previous messages and they will remain secure. Because of the low power and storage of light devices, updating secret shared keys is a solution to reach PFS in such protocols. A major... 

In this thesis all the information about different techniques and methods used in Local Area Network (LAN) are described and organized as follows:
Chapter 1: The network properties are described including Network definitions and different types of LAN and their relative applications
Chapter 2 :Different techniques and protocols of data transfer and switching methods are being described and compared.
Chapter 3 : Network technology consists of different topologies for physical connections and various transfer Medias are covered.
Chapter 4 :All network protocols are described including different methods of DATA access in LOOP, RING and BUS topologies and the ISO and IEEE...