SIMULATION: Transactions of The Society for Modeling and Simulation International

Liu, Jason

doi: 10.1177/0037549709341319pmid: N/A

Ke Pan, ; Turner, Stephen John; Wentong Cai, ; Zengxiang Li,

doi: 10.1177/0037549709106328pmid: N/A

The High-Level Architecture (HLA), which is the IEEE standard for distributed simulation, defines six service groups. The Time Management (TM) service group ensures a Time-Stamp-Ordered (TSO) message delivery sequence and correct time advancement of each simulation component (federate) in a HLA-based distributed simulation application (federation). To control time advancement of a federation, a distributed TM algorithm requires each regulating federate to periodically propagate its local time information to all constrained federates for their respective calculation of the Greatest Available Logical Time (GALT). The time information propagated is called conditional information or unconditional information depending on whether it can be guaranteed to be true conditionally or unconditionally. A traditional distributed TM algorithm can be either synchronous or asynchronous. In general, a synchronous algorithm utilizes conditional information while an asynchronous algorithm utilizes unconditional information. However, both synchronous and asynchronous algorithms have their own drawbacks and thus cannot be used for all federation scenarios. To resolve the drawback of each algorithm, this paper proposes a hybrid TM algorithm by combining synchronous and asynchronous algorithms. The three algorithms have been incorporated into a Run-Time Infrastructure (RTI) and experimental results show that the hybrid algorithm effectively combines the advantages of both synchronous and asynchronous algorithms. We also compare the proposed hybrid TM algorithm with the TM algorithm implemented in the Federated Simulations Development Kit (FDK), which also uses both conditional and unconditional information. The hybrid TM algorithm is more scalable than FDK’s TM algorithm with respect to the total number of federates in a federation, because FDK’s TM algorithm has the overhead of redundant GALT calculations.

Ben Hamida, Elyes; Chelius, Guillaume; Gorce, Jean Marie

doi: 10.1177/0037549709106633pmid: N/A

Recent years have witnessed a tremendous growth of research in the field of wireless systems and networking protocols. Consequently, simulation has appeared as the most convenient approach for the performance evaluation of such systems and several wireless network simulators have been proposed in recent years. However, the complexity of the wireless physical layer (PHY) induces a clear tradeoff between the accuracy and the scalability of simulators. Thereby, the accuracy of the simulation results varies drastically from one simulator to another. In this paper, we focus on this tradeoff and we investigate the impact of the physical layer modeling accuracy on both the computational cost and the confidence in simulations. We first provide a detailed discussion on physical layer issues, including the radio range, link and interference modeling, and we investigate how they have been handled in existing popular simulators. We then introduce a flexible and modular new wireless network simulator, called WSNet. Using this simulator, we analyze the influence of the PHY modeling on the performance and the accuracy of simulations. The results show that the PHY modeling, and in particular interference modeling, can have a significant impact on the behavior of the evaluated protocols at the expense of an increased computational overhead. Moreover, we show that the use of realistic propagation models can improve the simulation accuracy without inducing a severe degradation of scalability.

Nicol, David M.; Schear, Nabil

doi: 10.1177/0037549709341292pmid: N/A

Encrypted protocols, such as Secure Socket Layer (SSL), are becoming more prevalent because of the growing use of e-commerce, anonymity services, and secure authentication. Likewise, traffic analysis is becoming more common because it is often the only way to analyze these protocols. Although there are many valid uses for traffic analysis (such as network policy enforcement and intrusion detection), it can also be used to maliciously compromise the secrecy or privacy of a user. While the payload can be strongly protected by encryption, analysis of traffic patterns can yield information about the type and nature of traffic. In this paper we use simulation and analytic models to examine the impact on user experience of a scheme that masks the behavior of real traffic by embedding it in synthetic, encrypted, cover traffic. Through simulation and an analytic model we investigate the effects on the user experience using disparate and similar traffic models. This point provides a novel context where we observe the synergy of simulation and analytic modeling. We show that a detailed simulation model of network traffic characteristics can be used to estimate the parameters of an analytic model of tunneling. We see that the accuracy of the model’s predictions is directly dependent on the accuracy of parameters we obtain from the simulation. However, the simulation model does not need to have any concept of tunneling. Using simulation and analytic modeling together, we obtain an analysis whose whole is greater than the sum of its parts.

Webb, Steven Daniel; Soh, Sieteng; Trahan, Jerry L.

doi: 10.1177/0037549709102918pmid: N/A

Peer-to-Peer (P2P) architectures for Massively Multiplayer Online Games (MMOG) provide better scalability than Client/Server (C/S), however, they increase the possibility of cheating. Recently proposed P2P protocols use trusted referees that simulate/validate the game to provide security equivalent to C/S. When selecting referees from un-trusted peers, selecting non-colluding referees becomes critical. Further, referees should be selected such that the range and length of delays to players is minimized (maximizing game fairness and responsiveness). In this paper we formally define the referee selection problem and propose two secure referee selection algorithms, SRS-1 and SRS-2, to solve it. Both algorithms ensure the probability of corrupt referees controlling a zone/region is below a pre-defined limit, while attempting to maximize responsiveness and fairness. The trade-off between responsiveness and fairness is adjustable for both algorithms. Simulations of three different scenarios show the effectiveness of our algorithms.