This study assesses the impact of the Basel III regulatory framework on interbank contagion. It focuses on the direct interbank contagion that spreads via interbank foreign claims among national banking sectors. A balance sheet-based network model employs the quarterly consolidated banking statistics, collected by the Bank for International Settlements, to simulate the consequences of credit and funding shock under stressed market conditions. Compared to the Basel II, the Basel III regulatory framework reduces the probability of interbank contagion (following a simulated default of one banking sector) from 31% to 14% and lowers the impact of contagion by 63% in terms of average loss for a banking sector. The simulations under both regulatory frameworks show that relatively smaller banking sectors can trigger severe interbank contagion comparable to large banking sectors. Throughout the 2005-2009 period, the Basel III regulatory framework stabilizes the fluctuations of the scope of interbank contagion.

Vehicular Ad-hoc Network (VANET) is considered to be a viable technology for inter- vehicle communications for the purpose of improving road safety and efficiency. The En- hanced Distribution Channel Access (EDCA) mechanism and multichannel operations are introduced to ensure the Quality of Service (QoS). Therefore, it is necessary to create an accurate vehicular network simulator that guarantees the vehicular communications will work as described in the protocols. A comprehensive vehicular network simulator should consider the interaction between mobility models and network protocols. In this dissertation, a novel vehicular network simulation environment, VANET Toolbox, designed using discrete-event system (DES) is presented. The APP layer DES Module of the proposed simulator integrates vehicular mo- bility operations with message generation functions. The MAC layer DES module supports single channel and multichannel EDCA operations. The PHY layer DES module supports bit-level processing. Compared with packet-based simulator such as NS-3, the proposed PHY layer is more realistic and accurate. The EDCA scheme is evaluated and compared with the traditional Carrier-Sensing Mul- tiple Access (CSMA) scheme, with the simulations proving that data with different priorities can coexist in the same channel. The multichannel operation for the EDCA scheme is also analyzed in this dissertation. The multichannel switching operation and coordination may cause packet dropping or increased latency to the communication. The simulations show that with heavy network traffic, multichannel communication performs better than single channel communication. From the perspective of safety-related messages, the multichannel operation is able to isolate the interference from the non-safety messages in order to achieve a better packet delivery rate and latency. On the other hand, the non-safety messages can achieve high throughput with reasonable latency from multichannel communication under heavy load traffic scenario.

A new approach to distributed network simulations that eases the burdens on the simulation developer in creating space-parallel simulations is presented. It provides a full-topology knowledge for every federate (simulator instance) to make the best routing decision to destinations simulated at other federates. Later, this technique was used to characterize the benefits of IP Anycast mechanism at large scale. Different IP Anycast scenarios were simulated in a detailed Border Gateway Protocol (BGP) simulator using a realistic large-scale AS topology. Results indicated that Anycast indeed provides higher availability and decreased end-to-end delay. It also showed that Anycast does not provide load balancing, and the BGP overhead associated with a topology change is reduced when Anycast is deployed. In addition, a simulation model of Enhanced Interior Gateway Routing Protocol (EIGRP) was developed and used to present a new approach for host mobility within an AS. The new solution is to allow end systems to retain a fixed IP address as those systems move across subnet boundaries, and to use route advertisement updates (by EIGRP) to inform routers of new or revised routes to reach the mobile hosts as they migrate. The simulation results showed the viability of this approach, and the ability of EIGRP to update routing tables in a timely fashion.

Massively multiplayer online games (MMOGs) have become highly popular in the last decade and now attract millions of users from all over the world to play in an evolving virtual world concurrently over the Internet. The high popularity of MMOGs created a rapidly growing market and this highly dynamic market has forced the game developers to step up competitively. However, MMOG development is a challenging and expensive process. In this study, we have developed a network simulation tool which can be used to model and simulate typical MMOGs that have client-server architectures. The main objective is to provide a simulation environment to MMOG developers that could be used to test, analyze and verify various aspects of the MMOG network architecture. We have also implemented a graphical user interface which allows constructing the simulation model visually. We have demonstrated the use of simulation tool by experimental simulations.

Simulation is a powerful and efficient tool for studying wireless networks. Despite the widespread use of simulation, particularly in the study of IEEE 802.11-style networks (e.g., WLAN, mesh, and ad hoc networks), doubts about the credibility of simulation results still persist in the research community. These concerns stem, in part, from a lack of trust in some of the models used in simulation as they do not always accurately reflect reality. Models of the physical layer (PHY), in particular, are a key source of concern. The behavior of the physical layer varies greatly depending on the specifics of the wireless environment, making it difficult to characterize. Validation is the primary means of establishing trust in such models. We present an approach to validating physical layer models using the direct execution of a real PHY implementation inside the wireless simulation environment. This approach leverages the credibility inherent to testbeds, while maintaining the scalability and repeatability associated with simulation. Specifically, we use the PHY implementation from Hydra, a software-defined radio testbed, to validate the sophisticated physical layer model of a new wireless network simulator, called WiNS. This PHY model is also employed in other state-of-the-art network simulators, including ns-3. As such, this validation study also provides insight into the fidelity of other wireless network simulators using this model. This physical layer model is especially important because it is used to represent the physical layer for systems in 802.11-style networks. Network simulation is a particularly popular method for studying these kinds of wireless networks. We use direct-execution to evaluate the accuracy of our PHY model from the perspectives of different protocol layers. First, we characterize the link-level behavior of the physical layer under different wireless channels and impairments. We identify operating regimes where the model is accurate and show accountable difference where it is not. We then use direct-execution to evaluate the accuracy of the PHY model in the presence of interference. We develop "error-maps" that provide guidance to model users in evaluating the potential impact of model inaccuracy in terms of the interference in their own simulation scenarios. This part of our study helps to develop a better understanding of the fidelity of our model from a physical layer perspective. We also demonstrate the efficacy of direct-execution in evaluating the accuracy of our PHY model from the perspectives of the MAC and network layers. Specifically, we use direct-execution to investigate a rate-adaptive MAC protocol and an ad hoc routing protocol. This part of our study demonstrates how the semantics and policies of such protocols can influence the impact that a PHY model has on network simulations. We also show that direct-execution helps us to identify when a model that is inaccurate from the perspective of the PHY can still be used to generate trustworthy simulation results. The results of this study show that the leading physical layer model employed by WiNS and other state-of-the-art network simulators, including ns-3, is accurate under a limited set of wireless conditions. Moreover, our validation study demonstrates that direct-execution is an effective means of evaluating the accuracy of a PHY model and allows us to identify the operating conditions and protocol configurations where the model can be used to generate trustworthy simulation results. / text

As the field of Delay Tolerant Networking continues to expand and receive more attention, a new class of routing algorithms have been proposed that are specifically tailored to perform in a network where no end to end paths between devices are assumed to exist. As the number of proposed routing algorithms has grown, it has become difficult to fully understand their similarities and differences. Although published results clearly show different performance results between algorithms, it can be difficult to pinpoint which of their characteristics are most responsible for their performance differences. This thesis proposes an architectural framework to define the underlying features that Delay Tolerant Network routing algorithms are composed of. Popular routing algorithms from research are discussed and shown to be compositions of the proposed architectural features, thereby validating the architecture itself. The architectural framework is also shown to be a useful guide to developing a modular and configurable simulation platform. Algorithms from literature were implemented as a composition of features, which can easily be modified and combined later to define and implement new algorithms. Better understanding the underlying structure and similarities between different routing algorithm approaches is key to truly analyzing their performance and obtaining a deep understanding of which components of an algorithm have the most influence, both positively and negatively, on the results. Armed with this knowledge, designers of Delay Tolerant Networks can more easily determine the proper composition of routing algorithm features to best fit their needs. / text

The simulation of mobile networks relies on a reliable movement generation. Random movement patterns are frequently used in simulators. In this report, the performance of the popular setdest movement generator, which is built into the ns2 open source simulator, is investigated using two statistical tests: quadrat count test and the variance to mean ratio (VMR) test. The results show a non-uniform distribution of nodes during the simulation with a bias towards placing the nodes in the center of the simulated area. We propose and implement a di erent method for random movement generation in the ns2 simulator and show that our movement generator improves the randomness of the node distribution during the simulation. The new generator was successfully tested with the ns2 simulator.

Made available in DSpace on 2014-06-12T16:00:28Z (GMT). No. of bitstreams: 2 arquivo6669_1.pdf: 1298139 bytes, checksum: 82c0aa9def52f663c245e3f57be952ef (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2007 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The Transmission Control Protocol (TCP) is responsible for supplying reliable data transport service on the TCP/IP stack and for carrying most than 90% of all Internet traffic. In addition, the stability and efficiency of the actual TCP congestion control mechanisms have been extensively studied and are indeed well known by the networking community. However, new Internet applications and functionalities continuously modify its traffic characteristics, demanding new research in order to adapt TCP to the new reality of the Internet. In particular, a traffic phenomenon known as "mice and elephants" has been motivating important researches around the TCP. The main point is that the standard TCP congestion control mechanisms were designed for elephants leading small flows to experience poor performance. This is caused by the exponential behavior of Slow Start which often causes multiple packet losses due their aggressive increase. This work examines minutely the problems caused by the standard TCP congestion control to mice flows as well as it studies the most important proposals to solve them. Thus, based on such research studies, a modified TCP startup mechanism was proposed. The Burst TCP (B-TCP) is an intuitive TCP modification that employs a responsive congestion window growth scheme based on the current window size, to improve performance for small flows. Moreover, B-TCP is easy to implement and requires TCP adjustment at the sender side only. Simulation experiments show that B-TCP can significantly reduce both transfer times and packet losses for small flows without causing damage to large flows

Network simulation is an indispensable tool for studying Internet-scale networks due to the heterogeneous structure, immense size and changing properties. It is crucial for network simulators to generate representative traffic, which is necessary for effectively evaluating next-generation network protocols and applications. With network simulation, we can make a distinction between foreground traffic, which is generated by the target applications the researchers intend to study and therefore must be simulated with high fidelity, and background traffic, which represents the network traffic that is generated by other applications and does not require significant accuracy. The background traffic has a significant impact on the foreground traffic, since it competes with the foreground traffic for network resources and therefore can drastically affect the behavior of the applications that produce the foreground traffic. This dissertation aims to provide a solution to meaningfully generate background traffic in three aspects. First is realism. Realistic traffic characterization plays an important role in determining the correct outcome of the simulation studies. This work starts from enhancing an existing fluid background traffic model by removing its two unrealistic assumptions. The improved model can correctly reflect the network conditions in the reverse direction of the data traffic and can reproduce the traffic burstiness observed from measurements. Second is scalability. The trade-off between accuracy and scalability is a constant theme in background traffic modeling. This work presents a fast rate-based TCP (RTCP) traffic model, which originally used analytical models to represent TCP congestion control behavior. This model outperforms other existing traffic models in that it can correctly capture the overall TCP behavior and achieve a speedup of more than two orders of magnitude over the corresponding packet-oriented simulation. Third is network-wide traffic generation. Regardless of how detailed or scalable the models are, they mainly focus on how to generate traffic on one single link, which cannot be extended easily to studies of more complicated network scenarios. This work presents a cluster-based spatio-temporal background traffic generation model that considers spatial and temporal traffic characteristics as well as their correlations. The resulting model can be used effectively for the evaluation work in network studies.

This thesis deals with modelling and simulation of management protocols on the data-link layer in OMNeT++ tool. Namely protocol CDP, LLDP and ODR routing. These protocols are described in the first thesis' half and in the second half is described their design and implementation in ANSA project. Correctness of implementation is verified by comparison between simulated and real network examples. Also dependencies on module DeviceConfiguratoru were removed from ANSAINET library.