88 research outputs found

    Simulation and evaluation of the reactive virtual node layer

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    Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 65-67).Developing software in a wireless, ad hoc environment is an intrinsically difficult problem. One way to mitigate it is to add an abstraction layer between the software and the individual mobile devices. This thesis describes one such abstraction, the Reactive Virtual Node (RVN) Layer [1, 2, 3, 4], as well as a new simulation framework written in Python. Additionally, this thesis uses the simulator to characterize an RVN-based routing service for multihop mobile ad hoc networks. The performance of the routing service is compared to the Ad hoc On-Demand Distance Vector routing protocol, as well as a greedy geographic routing protocol.by Mike Spindel.M.Eng

    The Speedup of Discrete Event Simulations by Utilizing CPU Caching

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    Pending Event Set Implementation

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    Táto práca sa zaoberá vytvorením knižnice v C++, ktorá implementuje rôzne varianty kalendára udalostí, ktorý sa používa na riadenia diskrétnych simulácií. Knižnica zahŕňa deväť rôznych implementácií kalendára udalostí, ktoré sú prístupné cez jednotné rozhranie. Toto rozhranie je navrhnuté tak, aby bolo jednoduché knižnicu rozšíriť o ďalšie implementácie. Okrem samotnej knižnice sa práca zaoberá aj návrhom a popisom testovacej aplikácie a zhodnotením časových zložitostí jednotlivých implementácií.This work aims to create a library in C++, which implements various variants of the pending event set, which is used in discrete simulations. The library includes nine different implementations of the pending event set, accessible through a single interface. This interface is designed to make it easy to extend the library with additional implementations. In addition to the library itself, the work also describes the design of the test application and evaluates the time complexity of individual implementations.

    FlexQueue: Simple and Efficient Priority Queue for System Software

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    Existing studies of priority queue implementations often focus on improving canonical operations such as insert and deleteMin, while sacrificing design simplicity and pre- dictable worst-case latency. Design simplicity is sacrificed as the algorithm becomes more and more optimized, taking into account characteristics of the input workload distribution. Predictable worst-case latency is sacrificed when operations such as memory allocation and structural re-organization are deferred until absolutely necessary. While these techniques often yield performance improvement to some degree, it is possible to take a step back and ask a more basic question: is it possible to achieve similar performance while retaining a simple design? By combining techniques such as hierarchical bit-vector and dynamic horizon resizing, all of which are straight-forward in principle, this thesis presents a new priority queue design called FlexQueue, that answers this question with a definitive “yes”

    Downward wage rigidity and automatic wage indexation: evidence from monthly micro wage data

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    This paper assesses the degree of downward wage rigidity in Luxembourg using an administrative monthly data set on individual wages covering the entire economy over the period from January 2001 to January 2007. After limiting for measurement error, which would otherwise bias downwards the estimates of wage rigidity, we conclude that nearly all workers in Luxembourg are potentially subject to downward real wage rigidity. Our results are robust to different procedures to adjust for measurement error and methods for estimation of downward wage rigidity. We report relatively small differences in the frequency of nominal wage cuts across occupational groups and sectors. In addition, the observed rigidity does not seem to be driven predominantly by the absence of negative shocks. We show that the real wage rigidity is related to the automatic wage indexation, while additional factors might be necessary to explain the high degree of downward wage rigidity. JEL Classification: J31downward wage rigidity, wage indexation

    Downward wage rigidity for different workers and firms : an evaluation for Belgium using the IWFP procedure

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    This paper evaluates the extent of downward nominal and real wage rigidity for different categories of workers and firms using the methodology recently developed by the International Wage Flexibility Project (Dickens and Goette, 2006). The analysis is based on an administrative data set on individual earnings, covering one-third of employees of the private sector in Belgium over the period 1990-2002. Our results show that Belgium is characterised by strong real wage rigidity and very low nominal wage rigidity, consistent with the Belgian wage formation system of full indexation. Real rigidity is stronger for white-collar workers than for blue-collar workers. Real rigidity decreases with age and wage level. Wage rigidity appears to be lower in firms experiencing downturns. Finally, smaller firms and firms with lower job quit rates appear to have more rigid wages. Our results are robust to alternative measures of rigiditywage rigidity, matched employer-employee data.

    An investigation into pilot and system response to critical in-flight events, volume 2

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    Critical in-flight event is studied using mission simulation and written tests of pilot responses. Materials and procedures used in knowledge tests, written tests, and mission simulations are include

    An investigation into pilot and system response to critical in-flight events. Volume 2: Appendix

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    Materials relating to the study of pilot and system response to critical in-flight events (CIFE) are given. An annotated bibliography and a trip summary outline are presented, as are knowledge surveys with accompanying answer keys. Performance profiles of pilots and performance data from the simulations of CIFE's are given. The paper and pencil testing materials are reproduced. Conditions for the use of the additive model are discussed. A master summary of data for the destination diversion scenario is given. An interview with an aircraft mechanic demonstrates the feasibility of system problem diagnosis from a verbal description of symptoms and shows the information seeking and problem solving logic used by an expert to narrow the list of probable causes of aircraft failure

    Congestion Control for Streaming Media

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    The Internet has assumed the role of the underlying communication network for applications such as file transfer, electronic mail, Web browsing and multimedia streaming. Multimedia streaming, in particular, is growing with the growth in power and connectivity of today\u27s computers. These Internet applications have a variety of network service requirements and traffic characteristics, which presents new challenges to the single best-effort service of today\u27s Internet. TCP, the de facto Internet transport protocol, has been successful in satisfying the needs of traditional Internet applications, but fails to satisfy the increasingly popular delay sensitive multimedia applications. Streaming applications often use UDP without a proper congestion avoidance mechanisms, threatening the well-being of the Internet. This dissertation presents an IP router traffic management mechanism, referred to as Crimson, that can be seamlessly deployed in the current Internet to protect well-behaving traffic from misbehaving traffic and support Quality of Service (QoS) requirements of delay sensitive multimedia applications as well as traditional Internet applications. In addition, as a means to enhance Internet support for multimedia streaming, this dissertation report presents design and evaluation of a TCP-Friendly and streaming-friendly transport protocol called the Multimedia Transport Protocol (MTP). Through a simulation study this report shows the Crimson network efficiently handles network congestion and minimizes queuing delay while providing affordable fairness protection from misbehaving flows over a wide range of traffic conditions. In addition, our results show that MTP offers streaming performance comparable to that provided by UDP, while doing so under a TCP-Friendly rate
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