Sharif Digital Repository

Large scale decentralized communication systems have motivated a new trend towards online routing where routing decisions are performed based on a limited and localized knowledge of the network. Geometrical greedy routing has been among the simplest and most common online routing schemes. While a geometrical online routing scheme is expected to deliver each packet to the point in the network that is closest to the destination, geometrical greedy routing, when applied over generalized substrate graphs, does not guarantee such delivery as its forwarding decision might deliver packets to a localized minimum instead. This letter investigates the necessary and sufficient conditions of greedy... 

Peer to Peer networks have received considerable attention during the past decade and have been the focus of many research and development activities. New applications such as video streaming or gaming would benefit from multicast topologies and creating such trees in peer to peer networks is a challenging task. Proper multicast trees should minimize the traffic delay and bandwidth consumption. At the same time, construction of these trees should not be very complicated in terms of the required processing power so they can be implemented easily. The required time for construction of multicast trees should also be minimized and that helps with their adaptation to the dynamics of the network.... 

Effectiveness of P2P systems highly depends on efficiency of their search algorithms. With existence of malicious and dishonest nodes, reputation systems are essential to evaluate the trustworthiness of participating peers and to combat subversive peer behaviours. Surprisingly majority of the available reputation systems, ignore the underlying search algorithm and assume it pre-existing. In this paper we propose TBSearch, a robust and efficient trust based search algorithm for unstructured P2P networks. TBSearch maintains limited size routing indexes combining search and trust data, to guide queries to most reputable nodes. We introduce a low overhead method of estimating peers' reputation... 

Peer-to-peer networks are beginning to form the infrastructure of future applications. The use of semantic information to organize nodes in a P2P network is a prosperous approach. In this paper we present a novel method, called Semantic Partition Tree, which organizes nodes in a semantic space, using an upper ontology. In this approach each node can find a target in a time proportioned to the depth of the upper ontology, which is significantly less than the number of nodes in the network. Also we simulated our method with several configurations and measured its performance. The results of the simulation show that our scheme is highly scalable and can be used by real P2P networks. © 2007 IEEE... 

One of the challenges of P2P systems is to perform load balancing efficiently. A distributed hash table (DHT) abstraction, heterogeneous nodes, and non uniform distribution of objects cause load imbalance in structured P2P overlay networks. Several solutions are suggested to solve this problem but they have some restrictions. They assume the homogeneous capabilities of nodes, unawareness of the link latency during transferring load and imposing logical structures to collect and reassign load. This paper presents a distributed load balancing algorithm with topology awareness using the concept of virtual servers. In our proposed approach, each node collects neighborhood load information from... 

Network coding was first introduced in information theory for increasing the multicast rate in the networks with directed links. We can model many of the content distribution networks and overlay networks with such a network. Therefore, the solutions introduced in information theory can be used in these networks. In this paper, we analyze using of network coding in uncoordinated cooperative content distribution systems. Reaching the optimum performance in an uncoordinated system needs blocks of the system to be "equally important". In that case, we can retrieve the whole data without need of central controller or complex algorithms. In part of this paper, we exactly define the concept of... 

To support the increasing data traffic demand in wireless communications networks, a multi-tier architecture that consists of multiple small cells is adopted in traditional (macro) cellular networks. Nevertheless, due to the expansion of various wireless devices and services, there is still a need to increase the network capacity in new generation networks such as 5G. Hence, the integration of Device-to-Device (D2D) communication as a promising technology with heterogeneous networks has been proposed. This integration not only increases network capacity but also improves spectral efficiency and alleviates the traffic load of base stations. However, the co/cross-tier interferences between D2D... 

This article proposes a new architecture for distributed data management and update massage exchange in massively multiuser virtual environments. The key points in the design of such environments are scalability and QoS-aware message delivery. Therefore it requires robust distributed algorithms in a dynamic peer-to-peer system with frequent node arrivals and departures. Our proposed approach is mainly based on distributed hash tables (DHTs) in order to achieve a decentralized system where any participating node can efficiently retrieve the updates associated with a given object. Therefore, the responsibility of maintaining the mapping from names to values is distributed among the nodes in a... 

In this paper, we propose a novel algorithm for rate allocation in multiple-source media streaming peer to peer networks. Our algorithm is based on ant-colony optimization and capable of handling network changes which occur quite often in unstructured P2P networks. The suggested algorithm does not need any information about the topology of the network. Moreover, it could get over uncertainties in network state information, particularly the rate of media provider nodes that could happen due to lack of accurate measurements. We show that our algorithm will reach the maximum achievable rate of the network quite fast and with relatively little overhead. In our simulations, we have demonstrated... 

Peer-to-peer (P2P) networks are beginning to form the infrastructure of future applications. Heavy network traffic limits the scalability of P2P networks. Indexing is a method to reduce this traffic. But indexes tend to become large with the growth of the network. Also, limiting the size of these indexes causes loss of indexing information. In this paper we introduce a novel ontology based index (OI) which limits the size of the indexes without sacrificing indexing information. We show that the method can be employed by many P2P networks. The OI sits on top of routing and maintenance modules of a P2P network and enhances it. The OI prunes branches of search trees which have no chance to... 

The simplicity, low cost, preserving anonymity, and availability of Peer-to-peer (P2P) systems, especially with the advent of file-sharing networks, make them a favorite architecture for users. To reach this infrastructure, there are some challenges that must be addressed. One of the most important challenges is providing service security and trust. But due to the properties of P2P networks, it is difficult and complicated to design and implement a trust system. Some of the trust systems consider only one criterion to evaluate trust; it's simple but not so effective and has restricted applications. On the other side, considering multi-criteria is more effective but needs a systematic way to...