Sharif Digital Repository

Predicting latency between nodes on the internet can have a significant impact on the performance of many services that use latency distances among nodes as a decision making input. Coordinate-based approaches are among the family of latency prediction techniques where latency between each pair of nodes is modeled as the virtual distance among those nodes over a virtual system. This article proposes the Decentralized Coordinate System (DCS) as a fully distributed system that does not rely on any infrastructure support from the underlying network. DCS uses a two-phase algorithm: first, each host is assigned rough coordinates, then, the rough estimation is refined in a way that it gradually... 

A novel active queue management (AQM) method is proposed. This method, named NN-RED, is based on the use of a neural network for early congestion prediction. By simulations, it is demonstrated that the performance of the proposed approach is better than the random early detection (RED) method that is currently known as one of the best AQM methods in solving congestion problems. © The Institution of Engineering and Technology 2007  

In this study, a detector/estimator is proposed for compressed sensing radars, which does not need to reconstruct the radar signal, and which works directly from compressive measurements. More precisely, through direct processing of the measurements, and without the need for reconstructing the original radar signal, the system performs target detection, and then estimates range, Doppler frequency shift and radar cross section in the presence of a Gaussian clutter. It can be seen that for large compression ratios, the detection performance and estimation quality is comparable with a common radar system while having a much lower data rate and with less computational load  

The main motivation behind compressive sensing is to reduce the sampling rate at the input of a digital signal processing system. However, if for processing the sensed signal one requires to reconstruct the corresponding Nyquist samples, then the data rate will be again high in the processing stages of the overall system. Therefore, it is preferred that the desired processing task is done directly on the compressive measurements, without the need for the reconstruction of the Nyquist samples. This paper addresses the case in which the processing task is “detection” (the existence) of a sparse signal in additive white Gaussian noise, with applications e.g. in radar systems. Moreover, we will... 

Various methods using different measures have been proposed for ontology alignment. Therefore, it is necessary to evaluate the effectiveness of such measures to select better ones for more quality alignment. Current approaches for comparing these measures, are highly dependent on alignment frameworks, which may cause unreal results. In this paper, we propose a framework independent evaluation method, and discuss results of applying it to famous existing string measures. © Springer-Verlag Berlin Heidelberg 2006  

Resilient Packet Ring (RPR) that has been standardized as IEEE 802.17 is a MAC layer protocol designed for data centric metropolitan area network applications. A well-designed RPR network would be able to offer QoS guarantee for throughput and delay sensitive data classes in addition to providing other types of low cost best effort services. Careful network planning would be required to allow successful provisioning of classA services with strict delay and jitter requirements over RPR networks. This would require the knowledge of the dependency of delay and jitter for classA traffic on the load that is added to the ring. In this article, we propose an algorithm to estimate the dependency of... 

predicting the latency between hosts in the internet can play a significant rolein the improvement of the performance of many services that use latency distances among hosts as a decision making input. Although, the information regarding the point to point delay among internet peers is required in many applications, such information is not easily available to the peers. Latency data acquisition requires a considerableamount of measurements to be performed at each node in order for that node to keep a recordof its latency to all the other nodes. Moreover, the measurements need to be regularly repeated in order to be updatedagainst the network dynamics where the latency values are frequently... 

Massively Multiuser Virtual Environment (MMVE) applications have the challenge of update message exchange among a large number of users. Real-time collaboration in the virtual environments requires the updates to be exchanged with the minimum end-to-end latency and overhead. This article proposes a new clustering technique to improve the update message exchange efficiency in MMVE applications. The proposed solution is based on the use of ant clustering technique in order to cluster the users based on their geographical proximity. These clusters can be used as localized routing regions in the hierarchical routing architecture and prevent local messages to be routed through long distance hops.... 

In this paper we will propose a novel distributed architecture for overlay tree construction in collaborative virtual environments that is unlimitedly scalable due to its fully decentralized nature. The routing issue over this architecture will later be discussed and several forwarding schemes based on distributed hash tables (DHT) will be proposed. One of the main concerns for a routing algorithm is to keep a trade-off between the algorithm locality and the algorithm performance. In a global algorithm where nodes make the forwarding decision based on the information gathered from all other nodes in the network, the routing performance may obviously be better. However such a large group... 

Although collaborative distributed simulations and virtual environments (VE) have been an active area of research in the past few years, they have recently gained even more attention due to the emergence of online gaming, emergency simulation and planning systems, and disaster management applications. Such environments combine graphics, haptics, animations and networking to create interactive multimodal worlds that allows participants to collaborate in real-time. Massively Multiplayer Online Gaming (MMOG), perhaps the most widely deployed practical application of distributed virtual environments, allows players to act together concurrently in a virtual world over the Internet. IP... 

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... 

Massively multi user virtual environment (MMVE) applications must deal with the challenge of update message exchange among a large set of nodes distributed over the Internet. Therefore design of scalable network protocols is a major concern in such large scale distributed architectures. Several approaches have been proposed to aid update exchange in MMVEs. Message localization has always been a key point in the design of such distributed network protocols. Area of Interest Management (AoIM) mainly deals with the issues related to the update message localization with respect to the user's interest. As the number of users in the virtual environment increases, update message localization... 

Online games seem to become major contributors to Internet traffic. Therefore a great deal of effort is being devoted to the analysis and modeling of network game traffic. However the results from the previous measurements have not been unified into a single frame work while gaming traffic model is of high importance to network designers. Considering the fact that Gaming traffic is generated by the player's interaction during game sessions, we propose to model the player's activities and later use this model to extract the traffic pattern. We will propose a model for the gaming player behavior regarding traffic generation based on hierarchical hidden markov model. Player activities are... 

At present study, Endurance Time (ET) method that is a new dynamic pushover procedure is introduced and its application in predicting concrete arch dam behavior in linear domain is investigated. In this method structure is subjected to gradually intensifying acceleration functions. DEZ arch dam was selected as case study. FE model of dam-reservoir-foundation was excited in three levels of MCL, MDL, DBL using six records scaled based on design spectrum of the site and results were compared with those obtained from ET analyses. It was found that results obtained from ET method at equivalent target time are in good agreement with extreme results obtained from exciting the system using natural... 

The mechanism of gold nanowire (AuNW) and nanotube (AuNT) electrodeposition in a cyanide-free solution is investigated for the first time based on the analytical model of Szabo et al. (A. Szabo et al., J. Electroanal. Chem. 217 (1987) 417) for recessed cylindrical ultramicroelectrode (UME). Track-etched Polycarbonate Template (PCT) is served as cylindrical UME ensemble/arrays. Firstly, Au is nucleated through a charge transfer step and when the Nernst thickness exceeds the pore length, the radial diffusion is established around pore mouths. By overlapping of these domains, the planar diffusion toward the whole PCT surface is obtained. An analytic expression for global diffusion coefficient... 

One of the methods in limiting tensile stresses in arch dams and removing stress concentrations at the dam-foundation interface is setting the dam body on a concrete saddle called a Pulvino. In the present study, the effects of Pulvino and peripheral joints on the static behavior and seismic performance of arch dams are investigated. Dez Dam with a height of 203 m was selected as a case study and all contraction joints of the dam body were modeled using the discrete crack approach based on as-built drawings. Also, the surrounding rock was modeled as a mass-less medium tied to Pulvino. The dam-reservoirfoundation system was analyzed under static loads accounting for stage construction...