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Computationally Efficient Scheduling with the Physical Interference Model for Throughput Improvement in Wireless Mesh Networks
 in Wireless Mesh Networks,” in Proc. ACM MobiCom
, 2006
"... Wireless mesh networks are expected to be widely used to provide Internet access in the near future. In order to fulfill the expectations, these networks should provide high throughput simultaneously to many users. Recent research has indicated that, due to its conservative CSMA/CA channel access sc ..."
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Cited by 90 (9 self)
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Wireless mesh networks are expected to be widely used to provide Internet access in the near future. In order to fulfill the expectations, these networks should provide high throughput simultaneously to many users. Recent research has indicated that, due to its conservative CSMA/CA channel access scheme and RTS/CTS mechanism, 802.11 is not suitable to achieve this goal. In this paper, we investigate throughput improvements achievable by replacing CSMA/CA with an STDMA scheme where transmissions are scheduled according to the physical interference model. To this end, we present a computationally efficient heuristic for computing a feasible schedule under the physical interference model and we prove, under uniform random node distribution, an approximation factor for the length of this schedule relative to the shortest schedule possible with physical interference. This represents the first known polynomialtime algorithm for this problem with a proven approximation factor. We also evaluate the throughput and execution time of this algorithm on representative wireless mesh network scenarios through packetlevel simulations. The results show that throughput with STDMA and physicalinterferencebased scheduling can be up to three times higher than 802.11 for the parameter values simulated. The results also show that our scheduling algorithm can schedule networks with 2000 nodes in about 2.5 minutes.
SimGrid: a Generic Framework for LargeScale Distributed Experiments
 In 10th IEEE International Conference on Computer Modeling and Simulation
, 2008
"... Distributed computing is a very broad and active research area comprising fields such as cluster computing, computational grids, desktop grids and peertopeer (P2P) systems. Unfortunately, it is often impossible to obtain theoretical or analytical results to compare the performance of algorithms ta ..."
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Cited by 76 (20 self)
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Distributed computing is a very broad and active research area comprising fields such as cluster computing, computational grids, desktop grids and peertopeer (P2P) systems. Unfortunately, it is often impossible to obtain theoretical or analytical results to compare the performance of algorithms targeting such systems. One possibility is to conduct large numbers of backtoback experiments on real platforms. While this is possible on tightlycoupled platforms, it is infeasible on modern distributed platforms as experiments are laborintensive and results typically not reproducible. Consequently, one must resort to simulations, which enable reproducible results and also make it possible to explore wide ranges of platform and application scenarios. In this paper we describe the SimGrid framework, a simulationbased framework for evaluating cluster, grid and P2P algorithms and heuristics. This paper focuses on SimGrid v3, which greatly improves on previous versions thanks to a novel and validated modular simulation engine that achieves higher simulation speed without hindering simulation accuracy. Also, two new user interfaces were added to broaden the targeted research community. After surveying existing tools and methodologies we describe the key features and benefits of SimGrid. 1
Largescale network simulation – how big? how fast
 In Symposium on Modeling, Analysis and Simulation of Computer Telecommunication Systems (MASCOTS
, 2003
"... Parallel and distributed simulation tools are emerging that offer the ability to perform detailed, packetlevel simulations of largescale computer networks on an unprecedented scale. The stateoftheart in largescale network simulation is characterized quantitatively. For this purpose, a metric b ..."
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Cited by 35 (5 self)
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Parallel and distributed simulation tools are emerging that offer the ability to perform detailed, packetlevel simulations of largescale computer networks on an unprecedented scale. The stateoftheart in largescale network simulation is characterized quantitatively. For this purpose, a metric based on the number of Packet Transmissions that can be processed by a simulator per Second of wallclock time (PTS) is used as a means to quantitatively assess packetlevel network simulator performance. An approach to realizing scalable network simulations that leverages existing sequential simulation models and software is described. Results from a recent performance study are presented concerning largescale network simulation on a variety of platforms ranging from workstations to cluster computers to supercomputers. These experiments include runs utilizing as many as 1536 processors yielding performance as high as 106 Million PTS. The performance of packetlevel simulations of web and ftp traffic, and Denial of Service attacks on networks containing millions of network nodes are briefly described, including a run demonstrating the ability to simulate a million web traffic flows in near realtime. New opportunities and research challenges to fully exploit this capability are discussed. 1.
To Infinity and Beyond: TimeWarped Network Emulation
 In Proceedings of the 3rd USENIX Symposium on Networked Systems Design and Implementation
, 2006
"... The goal of this work is to subject unmodified applications running on commodity operating systems and stock hardware to network speeds orders of magnitude faster than available at any given point in time. This paper describes our approach to time dilation, a technique to uniformly and accurately sl ..."
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Cited by 31 (4 self)
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The goal of this work is to subject unmodified applications running on commodity operating systems and stock hardware to network speeds orders of magnitude faster than available at any given point in time. This paper describes our approach to time dilation, a technique to uniformly and accurately slow the passage of time from the perspective of an operating system by a specified factor. As a side effect, physical devices— including the network—appear relatively faster to both applications and operating systems. Both qualitative and statistical evaluations indicate our prototype implementation is accurate across several orders of magnitude. We demonstrate time dilation’s utility by conducting highbandwidth headtohead TCP stack comparisons and application evaluation. 1
A Federated Approach to Distributed Network Simulation
 ACM Transactions on Modeling and Computer Simulation
, 2004
"... We describe an approach and our experiences in applying federated simulation techniques to create largescale parallel simulations of computer networks. Using the federated approach, the topology and the protocol stack of the simulated network is partitioned into a number of submodels, and a simulat ..."
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Cited by 21 (3 self)
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We describe an approach and our experiences in applying federated simulation techniques to create largescale parallel simulations of computer networks. Using the federated approach, the topology and the protocol stack of the simulated network is partitioned into a number of submodels, and a simulation process is instantiated for each one. Runtime infrastructure software provides services for interprocess communication and synchronization (time management). We first describe issues that arise in homogeneous federations where a sequential simulator is federated with itself to realize a parallel implementation. We then describe additional issues that must be addressed in heterogeneous federations composed of different network simulation packages, and describe a dynamic simulation backplane mechanism that facilitates interoperability among different network simulators. Specifically, the dynamic simulation backplane provides a means of addressing key issues that arise in federating different network simulators: differing packet representations, incomplete implementations of network protocol models, and differing levels of detail among the simulation processes. We discuss two different methods for using the backplane for interactions between heterogeneous simulators: the crossprotocol stack method and the splitprotocol stack method. Finally, results from an experimental study are presented for both the homogeneous and
Yet Another Network Simulator
 In WNS2’06: Proc. of the 2006 workshop on ns2
, 2006
"... We report on the design objectives and initial design of a new discreteevent network simulator for the research community. Creating Yet Another Network Simulator (yans, ..."
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Cited by 20 (3 self)
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We report on the design objectives and initial design of a new discreteevent network simulator for the research community. Creating Yet Another Network Simulator (yans,
Getting urban pedestrian flow from simple observation: Realistic mobility generation in wireless network simulation
 in Proc. of 8th ACM/IEEE International Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems (MSWiM
"... In order for precise evaluation of MANET applications, more realistic mobility models are needed in wireless network simulations. In this paper, we focus on the behavior of pedestrians in urban areas and propose a new method to generate a mobility scenario called Urban Pedestrian Flows (UPF). In the ..."
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Cited by 18 (7 self)
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In order for precise evaluation of MANET applications, more realistic mobility models are needed in wireless network simulations. In this paper, we focus on the behavior of pedestrians in urban areas and propose a new method to generate a mobility scenario called Urban Pedestrian Flows (UPF). In the proposed method, we classify pedestrians in a simulation field into multiple groups by their similar behavior patterns (simply called flows hereafter, which indicate how they move around geographic points). Given the observed road density in the target field, we derive using linear programming techniques how many pedestrians per minute follow each flow. Using the derived flows, we generate a UPF scenario which can be used in network simulators. In particular, we have enhanced a network simulator called MobiREAL, which has been developed in our research group, so that we can generate and use the UPF scenario. MobiREAL simulator has three main facilities: the behavior simulator, network simulator and animator. The behavior simulator can generate/delete mobile nodes according to the UPF scenario. The network simulator can simulate MANET protocols and applications. The animator offers elegant visualization of simulation traces as well as graphical user interfaces for facilitating derivation of UPF scenarios. Through several case studies, we show similarity of the derived flows to the observed ones, as well as the metrics that characterize the mobility of the scenario.
Distributed optimal estimation from relative measurements
 in Proc. 3rd Int. Conf. Intelligent Sensing Information Processing (ICISIP), 2005
, 2006
"... Abstract. We consider the problem of estimating vectorvalued variables from noisy “relative ” measurements. The measurement model can be expressed in terms of a graph, whose nodes correspond to the variables being estimated and the edges to noisy measurements of the difference between the two varia ..."
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Cited by 13 (9 self)
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Abstract. We consider the problem of estimating vectorvalued variables from noisy “relative ” measurements. The measurement model can be expressed in terms of a graph, whose nodes correspond to the variables being estimated and the edges to noisy measurements of the difference between the two variables. This type of measurement model appears in several sensor network problems, such as sensor localization and time synchronization. We consider the optimal estimate for the unknown variables obtained by applying the classical Best Linear Unbiased Estimator, which achieves the minimum variance among all linear unbiased estimators. We propose a new algorithm to compute the optimal estimate in an iterative manner, the Overlapping Subgraph Estimator algorithm. The algorithm is distributed, asynchronous, robust to temporary communication failures, and is guaranteed to converges to the optimal estimate even with temporary communication failures. Simulations for a realistic example show that the algorithm can reduce energy consumption by a factor of two compared to previous algorithms, while achieving the same accuracy. 1
A primer for realtime simulation of largescale networks
 In Proceedings of the 41st Annual Simulation Symposium (ANSS’08
, 2008
"... Realtime network simulation refers to simulating computer networks in real time so that the virtual network can interact with real implementations of network protocols, network services, and distributed applications. In this paper, we present the motivation behind realtime network simulation and c ..."
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Cited by 10 (10 self)
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Realtime network simulation refers to simulating computer networks in real time so that the virtual network can interact with real implementations of network protocols, network services, and distributed applications. In this paper, we present the motivation behind realtime network simulation and compare it against other major networking research tools, including analytical models, physical testbeds, simulation, and emulation. We introduce PRIME, a parallel realtime network simulator, and provide a summary of techniques that allow PRIME to model largescale networks and interact with many real applications under the realtime constraint. We also discuss ongoing research efforts that will allow realtime network simulation to assume important roles at supporting future networking research. 1.
The SCREAM Approach for Efficient Distributed Scheduling with Physical Interference in Wireless Mesh Networks ∗
"... It is known that CSMA/CA channel access schemes are not well suited to meet the high traffic demand of wireless mesh networks. One possible way to increase traffic carrying capacity is to use a spatial TDMA (STDMA) approach in conjunction with the physical interference model, which allows more aggre ..."
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Cited by 9 (3 self)
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It is known that CSMA/CA channel access schemes are not well suited to meet the high traffic demand of wireless mesh networks. One possible way to increase traffic carrying capacity is to use a spatial TDMA (STDMA) approach in conjunction with the physical interference model, which allows more aggressive scheduling than the protocol interference model on which CSMA/CA is based. While an efficient centralized solution for STDMA with physical interference has been recently proposed, no satisfactory distributed approaches have been introduced so far. In this paper, we first prove that no localized distributed algorithm can solve the problem of building a feasible schedule under the physical interference model. Motivated by this, we design a global primitive, called SCREAM, which is used to verify the feasibility of a schedule during an iterative distributed scheduling procedure. Based on this primitive, we present two distributed protocols for efficient, distributed scheduling under the physical interference model, and we prove an approximation bound for one of the protocols. We also present extensive packetlevel simulation results, which show that our protocols achieve schedule lengths very close to those of the centralized algorithm and have running times that are practical for mesh networks. 1