Sharif Digital Repository

In this paper, we propose CodedSketch, as a distributed straggler-resistant scheme to compute an approximation of the multiplication of two massive matrices. The objective is to reduce the recovery threshold, defined as the total number of worker nodes that the master node needs to wait for to be able to recover the final result. To exploit the fact that only an approximated result is required, in reducing the recovery threshold, some sorts of pre-compression are required. However, compression inherently involves some randomness that would lose the structure of the matrices. On the other hand, considering the structure of the matrices is crucial to reduce the recovery threshold. In... 

Reconfigurability for a component of a distributed component-based system means ability to replace the component with a new one, in presence of the other components. In this context, substitutability and compatibility of components should be analyzed. In this paper, we use I/O-Constraint Automata to model behavior of components and propose enough formalism for substitutability and compatibility analysis. We show that in the context of distributed non-blocking components, there is a relation weaker than usual simulation relation in automata theory for notion of substitutability. We illustrate the relation between substitutability and compatibility to reason about the reconfigurability of a... 

A component-based computing system consists of two main parts: a set of components and a coordination subsystem. Reo is an exogenous coordination language for compositional construction of the coordination subsystem. Constraint automaton has been defined as the operational semantics of Reo. The main goal of this paper is to prepare a model checking method for verifying linear time temporal properties of component-based systems whose coordinating subsystems are modeled by Reo and components are modeled by labeled transition systems. For this purpose, we introduce modified definitions of constraint automata and their composition operators by which, every constraint automaton can be considered... 

Due to the constraints of P2P networks (such as bandwidth limitation) multiple senders should be employed for reliable multimedia streaming. This paper introduces a mathematic approach to select a set of senders among all available senders to provide the most reliable stream for the receiver. This selection is based on upload bandwidths and availability of peers as well as bandwidth of links connecting the senders and the receiver. Our method is called IPROMISE as it is an improved version of the PROMISE algorithm. Simulation results demonstrate improved media quality delivered to the receiver, while the complexity of sender selection remains the same. © 2007 IEEE  

Peer-to-peer overlay networks provide a useful infrastructure for building distributed applications. These networks provide efficient and fault-tolerant routing and object locating within a self-organizing overlay network. This paper presents a multi-dimensional overlay network called RAQNet which is based on RAQ1. RAQ supports exact match queries and range queries over multi-dimensional data efficiently. Moreover, its routing cost does not depend on the dimension of the search space. In RAQNet, we have improved its original routing algorithms and extended it to have topology awareness property. In RAQNet, nodes are connected to each other if their labels are "close" to each other with... 

In overlay networks, the mechanism of a peer randomly joining and leaving a network, causes a topology mismatch between the overlay and the underlying physical topology. This causes a large volume of redundant traffic in the underlying physical network as well as an extra delay in message delivery in the overlay network. Topology mismatch occurs because overlay networks are not aware of their underlying physical networks. In this paper we present a mathematical model for topology awareness of overlay networks (degree of matching between an overlay and its underlying physical network) and the efficiency of message delivery on them. Then we experimentally show that the model is precise in the... 

The distributed nature and complexity of computer networks and various services provided via them, makes the networks vulnerable to numerous attacks. The TCP/IP presumptions which are based on using this protocol to provide a simple, open communication infrastructure in an academic and collaborative environment, causes this protocol lack of built-in mechanisms for authentication, integrity and privacy. Even though in the last few years a more systematic approach to TCP/IP network security problem has been followed, a formal approach to this problem is lacking. In this paper, we propose using Description Logics as a formal model which could be used to analyze TCP/IP networks against attacks.... 

Peer-to-peer networks are beginning to form the infrastructure of future applications. One of the problems with non structured peer-to-peer networks is their scalability limitation. These networks can't contain a large number of nodes because of the large amount of traffic that they have to handle. HyperCup is a structured overlay network that solves the scalability problem for message broadcasts. This overlay broadcasts search queries throughout the entire network and all nodes receive broadcasted messages. In this paper we introduce Semantic HyperCup, an extension of HyperCup which uses semantic data to route messages and reduce overlay network traffic through search queries. © 2006 IEEE  

This paper suggests a method, called distributed voting, to overcome the problem of the single point of failure in a TMR system used in robotics and industrial control applications. It uses time redundancy and is based on TMR with disagreement detector feature. This method masks faults occurring in the voter where the TMR system can continue its function properly. The method has been evaluated by injecting faults into Vertex2Pro and Vertex4 Xilinx FPGAs. An analytical evolution is also performed. The results of both evaluation approaches show that the proposed method can improve the reliability and the mean time to failure (MTTF) of a TMR system by at least a factor of (2-R v(t)) where Rv(t)... 

Optical character recognition of cursive scripts present a number of challenging problems in both segmentation and recognition processes and this attracts many researches in the field of machine learning. This paper presents a novel approach based on a combination of MLP and SVM to design a trainable OCR for Persian/Arabic cursive documents. The implementation results on a comprehensive database show a high degree of accuracy which meets the requirements of commercial use. © Springer-Verlag Berlin Heidelberg 2005  

This paper presents the SkipTree, a new balanced, distributed data structure for storing data with multidimensional keys in a peer-to-peer network. The SkipTree supports range queries as well as single point queries which are routed in O(log n) hops. SkipTree is fully decentralized with each node being connected to O(logn) other nodes. The memory usage for maintaining the links at each node is O(log n log log n) on average and O(log2 n) in the worst case. Load balance is also guaranteed to be within a constant factor. © Springer-Verlag Berlin Heidelberg 2005  

In peer-to-peer (P2P) overlay networks, the mechanism of a peer randomly joining and leaving a network, causes a topology mismatch between the overlay and the underlying physical topology. This causes a large volume of redundant traffic in the underlying physical network as well as an extra delay in message delivery in the overlay network. Topology mismatch occurs because overlay networks are not aware of their underlying physical networks. In this paper we present a mathematical model for topology awareness of overlay networks (degree of matching between an overlay and its underlying physical network) and the efficiency of message delivery on them. We also after determining the... 

In this paper, a parallel algorithm for data clustering is presented on a multi-computer with star topology. This algorithm is fast and requires a small amount of memory per processing element, which makes it even suitable for SIMD implementation. The proposed parallel algorithm completes in O(K+S 2-T 2) steps for a clustering problem of N data patterns with M features per pattern and K clusters, where N.M = S!, K.M = T!, and M=R!, on a s-star interconnection network. © Springer-Verlag Berlin Heidelberg 2005  

Combination of three-dimensional (3D) IC technology and network on chip (NoC) is an effective solution to increase system scalability and also alleviate the interconnect problem in large-scale integrated circuits. However, because of the increased power density in 3D NoC systems and the destructive effect of high temperatures on chip reliability, applying thermal management solutions becomes crucial in such circuits. In this study, the authors propose a runtime distributed migration algorithm based on game theory to balance the heat dissipation among processing elements (PEs) in a 3D NoC chip multiprocessor. The objective of this algorithm is to minimise the 3D NoC system's peak temperature,... 

The synergy of fundamental factors like changes in governmental policies, global expansions of the manufacturing industries and improvements in technology related to reliability of manufacturing information flow have created the global manufacturing revolution in the first years of the twenty-first century. Although the concept of global manufacturing enterprise has created benefits and opportunities for todays manufacturing enterprises, it has enforced enterprises to endure costs to adopt the global manufacturing solutions. Besides, considering the researches aimed to enable the global manufacturing paradigm, there is still a need for efficient solutions to fulfil the global product... 

Packet loss recovery is an important part of P2P video streaming networks due to inevitable packet loss in today's internet and interdependency of data units in compressed video streams. In addition, the architecture of P2P streaming networks, in which the data delivered to the receivers through chain of peers, can intensify the impact of the internet packet loss on the quality of perceived video at the receivers. FEC and ARQ are the two most important techniques that can be used to overcome the side effect of the internet packet loss in P2P video streaming networks. Based on these two techniques, different packet loss recovery strategies can be applied in different overlay hops of a given... 

In this paper, a new search algorithm in heterogeneous hierarchical unstructured p2p networks is presented which takes into account heterogeneity of peers such as upload bandwidth, life time in the network and process capacity in its peer discovery policy as factors that influence download performance and user satisfaction. One advantage of this algorithm is that it can be performed in a completely unstructured network without imposing any change on network topology and file replication. However, it obviously decreases file download time as it is designed to discover broad-bandwidth nodes with a higher probability. This property results in a fair distribution of load over heterogeneous p2p... 

Combination of three-dimensional (3D) IC technology and network on chip (NoC) is an effective solution to increase system scalability and also alleviate the interconnect problem in large-scale integrated circuits. However, because of the increased power density in 3D NoC systems and the destructive effect of high temperatures on chip reliability, applying thermal management solutions becomes crucial in such circuits. In this study, the authors propose a runtime distributed migration algorithm based on game theory to balance the heat dissipation among processing elements (PEs) in a 3D NoC chip multiprocessor. The objective of this algorithm is to minimise the 3D NoC system's peak temperature,... 

The current multi-channel P2P video streaming architectures still suffer from several performance problems such as low Quality of Service (QoS) in unpopular channels. The P2P systems are inherently dynamic, and their performance problems could be categorized into four groups; peer churn, channel churn, uncooperative peers, and geographical distribution of peers. In this paper, for the first time, we develop a novel locality-incentive framework for multi-channel live video streaming. We propose a hierarchical overlay network architecture by utilizing a dual-mode locality-Awareness method (spatial and temporal). Moreover, an incentive mechanism for encouraging peers to dedicate their upload... 

Inter-wire coupling capacitance may lead to crosstalk faults that significantly limits the reliability of NoCs. In this paper, we propose a numerical-based crosstalk avoidance code that can omit the Triplet Opposite Direction (TOD) transitions produced by crosstalk faults. The proposed coding does not have ambiguity and uses all of the codeword space. Simulations using VHDL for different channel widths show that the proposed method can reduce crosstalk fault in the NoC links with negligible power and area overheads