Maya: a Multi-Paradigm Network Modeling Framework
This paper presents Maya, a multi-paradigm, scalableand extensible network modeling framework for emulatingdistributed applications. A novel three-tier architecture isproposed to integrate three disparate modeling paradigms,namely, discrete event models, analytical models and physicalnetwork interfaces into one unified framework of Maya.As the first effort to integrate all three paradigms intoone framework, this paper discusses the implementationsof Maya using Qualnet, fluid flow based TCP model andphysical network interface. It addresses the performanceissues involved in attaining the real time constraints imposedby distributed applications and demonstrates the effectivenessof using analytical models in Maya. Furthermore, it identifies the negative impact on real time performance through the computation intensive ordinary differential equation (ODE) solver in the fluid flow model. A new approach to interleaved executions of the fluid flow model is proposed to hide ODE solver turnaround time. As a result, the percentage of packets missing their deadlines has been reduced from more than 6% to less than 0.2%.

title: An alternative time management mechanism for distributed simulations
abstract: Over the past few years, there has been a keen interest in the management of time in distributed simulation environments. Previous emphasis in time management (TM) services has been based on time stamp ordering, which is both computation and bandwidth intensive. This article discusses an alternative approach to time management based on causal ordering. Traditional causal ordering protocols incur a large amount of communication overhead, which is generally of the order of N2 for a distributed system of N processes. A new causal ordering protocol proposed by the authors, the Modified Schiper-Eggli-Sandoz (MSES) protocol, is presented in this article. This new protocol minimizes the control information overhead of causal ordering by using the direct dependency tracking technique. The MSES protocol works well in both unicast and multicast environments, without relying on information about the underlying network topology and communication pattern among the processes of the distributed system. The MSES protocol has been successfully implemented as a middleware on top of DMSO RTI. Experiments have been conducted to benchmark the performance of the new time management mechanism with respect to the existing TM mechanisms available in DMSO RTI. The simulation scenarios of the experiments vary with different degrees of inter-federate dependency and federate event granularities. The ordering limitations of the causality based TM mechanism are addressed in this article and the trade-off of the degree of event ordering and execution speed of simulations is discussed.

title: TWINE: A Hybrid Emulation Testbed for Wireless Networks and Applications
abstract: In this paper, we present TWINE, a high fidelity, efficient emulation framework that combines the accuracy and realism of emulated and physical networks and the scalability and repeatability of simulation in an integrated testbed, for evaluation of real protocols and applications. Our measurements show that the TWINE emulation kernel has a memory footprint of less than 100KB, and occupies no more than 3.5% CPU cycles. Thanks to such small overhead and the accurate modelling of physical layer events(at microseconds level), application throughput measured in TWINE is within 5% of the measured throughput from an equivalent physical wireless LAN. A single commodity PC in TWINE can emulate at least four wireless hosts or simulate sixty nodes in real time at microseconds granularity. This paper also illustrates TWINE’s novel capabilities via two case studies: a protocol to maintain fairness in mesh networks and an adaptive streaming media application operating in heterogeneous wireless networks. The results from the case studies clearly show the benefit of the TWINE evaluation methodology, by identifying a mismatch between the performance of the protocol or application based on actual user experience versus its performance as measured using traditional network performance metrics such as application throughput.

title: Optimizing parallel execution of detailed wireless network simulation
abstract: With parallel and discrete event simulation (PDES) techniques, the runtime performance of detailed wireless network simulation can be improved significantly without compromising fidelity of the simulation results. However, modelling characteristics of wireless communications such as signal propagation and interference may severely hinder the potential speedup yielded by PDES. This paper proposes various optimization techniques to address three major concerns in achieving efficient parallel execution of wireless network simulation: i.e., (1) reducing communication and computation overhead of simulating signal propagation across multiple logical processes; (2) reducing synchronization overhead among logical processes; (3) minimizing event scheduling overhead within individual logical processes. These techniques have been implemented in a parallel version of GloMoSim and QualNet. The experimental results with mobile ad hoc networking scenarios demonstrate that the proposed optimization techniques can improve the performance of parallel wireless network simulation by up to an order of magnitude.

title: Adaptive range control using directional antennas in mobile ad hoc networks
abstract: This paper presents ARC (Adaptive Range Control), a communication range control mechanism using directional antennas to be implemented across multiple layers. ARC uses directional reception for range control rather than directional transmission such that extended communication links do not increase interference to other ongoing communications. It adaptively controls the communication range by estimating dynamically changing local network density based on the transmission activities around each network node. The experimental results using simulation with detailed physical layer, IEEE 802.11 DCF MAC, and AODV protocol models have shown the successful adaptation of communication range with ARC for varied network densities and traffic loads. ARC improves the packet delivery ratio by a factor of 9 at the maximum for sparse networks while it maintains the increased network capacity for dense networks.

title: Improving scalability of wireless network simulation with bounded inaccuracies
abstract: Discrete event network simulators have emerged as popular tools for verification and performance evaluation of wireless networks. Nevertheless, the desire to model such networks at high fidelity implies high computational costs, limiting most researchers the ability to simulate networks with thousands of nodes. Previous attempts to optimize simulation of large-scale wireless networks have not appropriately modeled accumulation of weak interference, thereby suffering inaccuracies that may be further magnified in the evaluation of upper-layer protocols. This article presents a comprehensive analysis on the effects of common optimization techniques for large-scale wireless network simulation on the overall network performance. Based on the analysis, it formulates distance limit derivation and mobility update reduction that introduce bounded inaccuracy to the radio propagation simulation. It further proposes a novel technique, Lazy Event Scheduling with Corrective Retrospection, that reduces simulation events twenty-five fold without introducing any inaccuracy at all. The experimental results show that these optimizations can substantially improve the runtime performance of an already efficient wireless network simulator, by a factor of up to 55 for wireless networks with 3200 nodes without compromising the simulation's accuracy.

title: An Overlay Subscription Network for Live Internet TV Broadcast
abstract: We propose a framework, called overlay subscription network (OSN), for live Internet TV broadcast, where a subscriber can choose to watch at any time. This framework allows the source server to incrementally build a topology graph that contains the network connections not only from the server to each subscriber, but also among the subscribers themselves. With such a topology graph in place, we consider efficient overlay multicast for scalable OSN services. We first show that idling nodes, which do not receive video data for their own playback, can actually be used for data forwarding to significantly reduce the cost of overlay multicast. In light of this observation, we then propose a novel overlay multicast technique that distinguishes itself from existing schemes with these three aspects. First, the proposed technique is centered on the topology graph and can take advantage of the actual network connections among the subscribing nodes. Second, the new scheme is able to find and incorporate appropriate idling nodes in multicast to reduce network traffic. Third, with our approach, a node can be used in multiple multicast trees for data forwarding to improve the overall system performance. We evaluate the performance of the proposed technique through simulation. Our extensive studies show that the proposed framework has the potential to enable the Internet, a vehicle up to date mainly for transferring text and image data, for large-scale and cost-effective TV broadcast

title: Some Remarks on a Fair Exchange Protocol
abstract: Fair exchange turns out to be an increasingly important topic due to the rapid growth of electronic commerce. An exchange is deemed to be fair if at the end of exchange, either each party receives the expected item or neither party receives any useful information about the other’s item. Several protocols for fair exchange have been proposed in recent years. In this paper, we first examine a newly published fair exchange protocol and point out its flaws and weaknesses. We then put forward a more efficient and secure protocol and give an informal analysis.

title: An intensive survey of fair non-repudiation protocols
abstract: With the phenomenal growth of the Internet and open networks in general, security services, such as non-repudiation, become crucial to many applications. Non-repudiation services must ensure that when Alice sends some information to Bob over a network, neither Alice nor Bob can deny having participated in a part or the whole of this communication. Therefore a fair non-repudiation protocol has to generate non-repudiation of origin evidences intended to Bob, and non-repudiation of receipt evidences destined to Alice. In this paper, we clearly define the properties a fair non-repudiation protocol must respect, and give a survey of the most important non-repudiation protocols without and with trusted third party (TTP). For the later ones we discuss the evolution of the TTP's involvement and, between others, describe the most recent protocol using a transparent TTP. We also discuss some ad-hoc problems related to the management of non-repudiation evidences.

title: Recognition of handwritten numerals by Quantum Neural Network with fuzzy features
abstract: This paper describes a new kind of neural network – Quantum Neural Network (QNN) – and its application to the recognition of handwritten numerals. QNN combines the advantages of neural modelling and fuzzy theoretic principles. Novel experiments have been designed for in-depth studies of applying the QNN to both real data and confusing images synthesized by morphing. Tests on synthesized data examine QNN's fuzzy decision boundary with the intention to illustrate its mechanism and characteristics, while studies on real data prove its great potential as a handwritten numeral classifier and the special role it plays in multi-expert systems. An effective decision-fusion system is proposed and a high reliability of 99.10% has been achieved.

title: On the ascending star subgraph decomposition of star forests
abstract: AbstractLetG be a graph of size
$$\left(  \right)$$
 for some integern≥2. ThenG is said to have an ascending star subgraph decomposition ifG can be decomposed inton subgraphsG1,G2, ...,Gn such that eachGi is a star of sizei with 1≤i≤n. We shall prove in this paper that a star forest with size
$$\left(  \right)$$
, possesses an ascending star subgraph decomposition if the size of each component is at leastn, which is stronger than the conjecture proposed by Y. Alavi, A. J. Boals, G. Chartrand, P. Erdős and O. R. Oellermann.