Dissertations / Theses on the topic 'Goodput'

This dissertation represents a modeling and simulation approach toward determining whether distributed computing architectures (e.g., Cloud Computing) require state of the art servers to ensure top performance, and whether alternate approaches can result in optimized Quality of Service by reducing operating costs while maintaining high overall system performance. The author first investigated the origins of Cloud Computing, to ensure that the model of distributed computing architectures still applied to the Cloud Computing business model. After establishing that Cloud Computing was in fact a new iteration of a current architecture, the author conducted a series of modeling and simulation experiments using the OPNET Modeler system dynamics tool to evaluate whether variations in the server infrastructure altered the overall system performance of a distributed computing architecture environment. This modeling exercise focused on comparing state of the art commodity Information Technology (IT) servers to those meeting the Advanced Telecommunications Association (AdvancedTCA or ATCA) open standard requirements, which are generally at least one generation behind commodity servers in terms of performance benchmarks. After modeling an enterprise IT environment, and simulating network traffic using the OPNET Modeler tool, the author concluded that there is no system-level performance degradation in using AdvancedTCA servers for the consolidation effort, using ANOVA/Tukey and Kruskal-Wallis multivariate data analysis of the simulation results. In order to conduct this comparison, the author developed a system-level performance benchmark, System Goodput (GS) to represent end to end performance of services, a more appropriate measure of the performance of distributed systems such as Cloud Computing. The analysis of the data proved that individual component benchmarks are not an accurate predictor of system-level performance. After establishing that using slower servers (e.g., ATCA) does not affect overall system performance in a Cloud Computing environment, the author developed a model for optimizing system-level Quality of Service (QoS) for Cloud Computing infrastructures by relying on the more rugged ATCA servers to extend the service life of a Cloud Computing environment, resulting in a much lower Total Ownership Cost (TOC) for the Cloud Computing infrastructure provider.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2015-12-01T12:45:13Z No. of bitstreams: 1 robertomussideoliveira.pdf: 1293292 bytes, checksum: 78c6c9fd9415c0b3990a1aaf55b842a2 (MD5)
Made available in DSpace on 2015-12-01T12:45:13Z (GMT). No. of bitstreams: 1 robertomussideoliveira.pdf: 1293292 bytes, checksum: 78c6c9fd9415c0b3990a1aaf55b842a2 (MD5) Previous issue date: 2015-03-11
CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Nesse trabalho, discutimos o uso de protocolos de coopera¸c˜ao na subcamada de controle de acesso ao meio (CMAC) para reduzir a taxa de perda de pacote e aumentar o goodput em um sistema de comunica¸c˜ao banda larga via rede el´etrica (PLC) de ambientes residenciais. Para apoiar essa discuss˜ao, n´os, pela primeira vez, apresentamos uma an´alise estat´ıstica da taxa de erro de pacote (PER) de canais PLC residenciais a partir de dados medidos em um modelo com um ´unico relay. Adicionalmente, n´os esbo¸camos um simples protocolo CMAC capaz de explorar a diversidade oferecida por uma rede el´etrica dom´estica. Usando esse protocolo, nosso objetivo ´e mostrar o impacto da varia¸c˜ao da largura de banda, da varia¸c˜ao da PER e da posi¸c˜ao relativa do relay no desempenho do sistema. Sendo assim, n´os mostramos que a taxa de perda de pacote e o goodput melhoram quando a largura de banda de frequˆencia aumenta. Al´em disso, resultados mostram que a coopera¸c˜ao na camada de enlace n˜ao oferece vantagens caso os valores de PER do enlace direto e do enlace intermediado pelo relay sejam muito altos ou muito baixos. N´os tamb´em notamos que as melhorias estudadas dependem da posi¸c˜ao do n´o relay em rela¸c˜ao ao n´o fonte e ao n´o destino (i.e., notamos melhoras na rede nos casos em que o relay estava situado pr´oximo `a fonte e no meio do caminho entre a fonte e o destino). Finalmente, uma compara¸c˜ao entre os esquemas de acesso m´ultiplo por divis˜ao de frequˆencias ortogonais - acesso m´ultiplo por divis˜ao de tempo (OFDMA-TDMA) e acesso m´ultiplo por divis˜ao de tempo - multiplexa¸c˜ao por divis˜ao ortogonal de frequˆencia (TDMA-OFDM) mostra que o simples protocolo CMAC ´e mais eficaz quando usado juntamente com o primeiro esquema do que com o ´ultimo. Em suma, a nossa contribui¸c˜ao ´e dividida em duas etapas: primeiramente, desenvolvemos um simples protocolo MAC de coopera¸c˜ao que traz melhorias de desempenho na rede quando comparado com um sistema sem a coopera¸c˜ao; em segundo lugar, n´os realizamos uma an´alise sistem´atica de diferentes cen´arios, mostrando os benef´ıcios e limita¸c˜oes da coopera¸c˜ao na camada de enlace de redes PLC.
In this work, we discuss the use of cooperative medium access control (CMAC) protocols to reduce packet loss rate and to improve goodput of in-home broadband power line communication (PLC) systems. To support this discussion, we, for the first time, present a statistical packet error rate (PER) analysis of measured in-home PLC channels by adopting a single relay model. Additionally, we outline a simple CMAC protocol that is capable of exploiting the diversity offered by in-home electric power grids. Using this protocol, we aim to show the impact of bandwidth variation, PER variation and of relative relay location on system performance. Thus, we show that packet loss rate and goodput improve when frequency bandwidth increases. Also, results show that cooperation at the link layer does not offer advantages if the PER values of direct and relayed links are very high or very low. Furthermore, we note that the improvements depend on the location of the node relay in relation to the nodes source and the destination (i.e., network improves if the relay is located near the source or in the midway between the source and the destination). Finally, a comparison between orthogonal frequency division multiple access - time division multiple access (OFDMA-TDMA) and time division multiple access - orthogonal frequency division multiplexing (TDMA-OFDM) schemes show that the simple CMAC protocol is more effective when it is used together with the former scheme than the latter.

In this thesis we investigated whether using compression when sending inter-process communication (IPC) messages can be beneficial or not. A literature study on lossless compression resulted in a compilation of algorithms and techniques. Using this compilation, the algorithms LZO, LZFX, LZW, LZMA, bzip2 and LZ4 were selected to be integrated into LINX as an extra layer to support lossless message compression. The testing involved sending messages with real telecom data between two nodes on a dedicated network, with different network configurations and message sizes. To calculate the effective throughput for each algorithm, the round-trip time was measured. We concluded that the fastest algorithms, i.e. LZ4, LZO and LZFX, were most efficient in our tests.
I detta examensarbete har vi undersökt huruvida komprimering av meddelanden för interprocesskommunikation (IPC) kan vara fördelaktigt. En litteraturstudie om förlustfri komprimering resulterade i en sammanställning av algoritmer och tekniker. Från den här sammanställningen utsågs algoritmerna LZO, LZFX, LZW, LZMA, bzip2 och LZ4 för integrering i LINX som ett extra lager för att stödja komprimering av meddelanden. Algoritmerna testades genom att skicka meddelanden innehållande riktig telekom-data mellan två noder på ett dedikerat nätverk. Detta gjordes med olika nätverksinställningar samt storlekar på meddelandena. Den effektiva nätverksgenomströmningen räknades ut för varje algoritm genom att mäta omloppstiden. Resultatet visade att de snabbaste algoritmerna, alltså LZ4, LZO och LZFX, var effektivast i våra tester.

Cette thèse porte sur l'allocation de ressources dans les réseaux mobiles ad hoc basés sur les protocoles ARQ Hybrides (HARQ), qui offrent une souplesse de déploiement rapide pour des communications à court terme dans le cadre d'applications militaires ou de futurs réseaux intelligents. L'OFDMA (Orthogonal Frequency Division Multiple Access) est considérée en particulier, en tant que solution prometteuse dans les standards de communication sans fil les plus récents. Bien qu'une coordination centralisée des communications soit rendue possible grâce à une organisation en clusters, il est toutefois difficile de remonter au coordinateur des informations fiables sur l'état du canal en vertu de la latence due à l'organisation de ce réseau. Ainsi les performances des liens seront renforcées par des mécanismes de retransmission HARQ, qui permettent de gérer les variations rapides du canal. L'objectif principal de cette thèse est l'allocation des ressources OFDMA dans les réseaux mobiles ad hoc basés sur les protocoles HARQ, en utilisant uniquement les statistiques à long terme du canal. Pour répondre à un besoin industriel, des schémas de modulation et de codage pratiques seront considérés en lieu et place des outils de capacité hérités de la théorie de l'information. En particulier, nous concevons et analysons de nouveaux algorithmes qui optimisent l'attribution de puissance, de largeur de bande, d'ordre de modulation et de rendement de codage, pour les mécanismes HARQ insérés dans le schéma multi-utilisateurs proposé. En raison de la présence de protocoles HARQ dans le réseau, une partie de la thèse est dédiée à l'étude des performances de l'HARQ que nous étendons à de nouveaux contextes.

In the wireless channel, cooperative communications allow one or many relays to assist the communication between the source and the destination. The aim of this thesis is the development of tools for the analysis of cooperative systems, when HARQ techniques are employed to provide cross-layer error protection. The first chapter of the thesis gives background information on network coding in cooperative relay networks, and introduces the motivation for this work. The second chapter is devoted to the analysis of the energetic-fair performance evaluations of FEC, ARQ-STBC and HARQ schemes at the MAC and IP layers. New analytical framework is derived and applied to a point-to-point network scenario. This framework allows to make energetic fair comparisons between the schemes with and without retransmissions. We determine under which channel conditions the cross-layer error protection is energetically more efficient than the simple channel coding. In the third chapter of this thesis we study the cooperative deterministic protocols. The protocols that we consider differ based on the behaviour of the relay(s), source(s), and destination. We consider two major types of cooperative protocols: decode-and forward (DCF), and demodulate-and-forward (DMF). Each of these protocols in its turn is analysed with and without combining mechanisms at the destination. We derive the soft decoders at the destination side for each respective case, and compare the performances of these protocols at the MAC layer. The following quality of service metrics are evaluated: frame error rate, delay, efficiency, goodput. The analysis is done evaluating the steady-state, using finite state Markov chains and a combinatorial approach. The analysis, however, becomes very complex as the number of transmissions and/or nodes in the network increases. The fourth chapter introduces a class of probabilistic communication protocols, where the devices retransmit with a given probability. We prove the existence of an equivalent class of protocols, with the same performances as the deterministic class. Using proofs of concept it is shown that the probabilistic protocol class allows for tractable steady-state analysis, even for many nodes in the network. Based on this, we then derive the QoS metrics and evalute them also by simulations. The derived performance evaluation metrics are then optimized by constraining the frame error rate, and trying to find the most optimal transmissions number and code rates which maximize the goodput. It is furthermore shown, that the equivalent protocol has larger optimal region than the deterministic one.

Inom nätverksbranchen finns en strävan att gå från proprietära lösningar till en öppen standard för hård- och mjukvara. En term för detta är Whiteboxing och det innebär att användaren ges möjlighet att plocka ihop komponenter efter behov, och själv välja vilken mjukvara som används. I sin enklaste form byggs en Whiteboxrouter av en konventionell PC med två nätverkskort och en mjukvarubaserad routingapplikation. Företaget ÅF är intresserade av att veta hur Whitebox-lösningar för routrar står sig prestandamässigt i relation till konventionella routerlösningar med Application Specific Integrated Circuit. Detta arbete har undersökt prestandan genom att mäta throughput och goodput hos en Cisco 2911-router, en Whiteboxrouter med mjukvaran pfSense, samt en Whiteboxrouter som körde pfSense virtualiserat på ESXi. Dessutom undersöktes respektive konfigurations prestanda när trafiken skickades över IPsec VPN. För mätningarna användes filöverföringar med FTP och mätprogrammet Iperf3. Målet med arbetet var att skapa ett beslutsunderlag som klargjorde eventuella prestandaskillnader och utarbetade rekommendationer för framtida val av routerlösning. Resultatet visade att vid generell paketförmedling var prestandan mellan routrarna relativt jämn, dock rekommenderas den virtualiserade Whiteboxroutern då den fick det bästa resultatet. När trafiken sedan krypterades med IPsec VPN var det stora prestandaskillnader mellan enheterna. Bäst prestanda fick Whiteboxroutern. Författaren ser en vinning med Whitebox-tekniken i stort då den medger att serverutrustning som ska utrangeras på grund av prestandakrav, istället kan fungera som nätverksutrustning (routrar och brandväggar) och fortsätta användas under en större del av den tekniska livslängden. Detta kan på sikt leda till minskad miljöpåverkan och besparingar för företaget.

My stories are set in the townships, and move with the vigorous rhythms and jagged structures of township life. Some of them are written in English and others in isiXhosa. Some of the dialogue is township slang, a mixture of languages; and pure isiXhosa. The stories follow no particular pattern and are arranged according to any form of chronology, and different voices, at times as a man/boy and in others as a girl. The characters are not related each story perfectly stands for itself. Some of the stories hark back to the days of apartheid and are seen through the eyes of a child confused by the humiliations of his elders.
Amabali am asekelwe ezilokishini yaye ahambelana neemeko ezimaxongo zokuphila zasezilokishini apho yaye amanye asukela kwixesha lengcinezelo yesizwe esimnyama. Imiba echatshazelwa kula mabali iquka intlupheko, intiyo kwakunye nokuphilisana koluntu ezilokishini, phantsi kwezo meko. Amabali la ndizame ukuwenza alandele indlela yokubalisa yhenkwenkwana enguSkhumba, ethi ibone iqwalasele iimeko zokuphila zabantu bohlanga lwayo. Ingqokelela esisiqendu sokuqala yona ibhalwe ze yangeniswa ngesiNgesi.
This thesis is presented in two parts: English and isiXhosa.

Made available in DSpace on 2014-06-11T19:22:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-11-08Bitstream added on 2014-06-13T18:08:33Z : No. of bitstreams: 1 semensato_m_me_ilha.pdf: 1302035 bytes, checksum: 43c8881f259cd513c7fc585dd25d1307 (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Este trabalho tem o objetivo de abordar a Teoria da Potência Complexa Instantânea, a qual utiliza vetores espaciais instantâneos, e mostrar sua utilidade através de duas aplicações para cargas do sistema trifásico: A ponte retificadora trifásica de seis pulsos e o transitório de partida de um motor de indução trifásico. Os resultados obtidos são comparados com as grandezas de Buchholz-Goodhue no cálculo da potência aparente e do fator de potência, grandezas estas definidas na norma IEEEStd 1459/2000, para sistemas trifásicos operando em regime permanente em condições de desequilíbrio e com formas de onda não-senoidais. Mostra-se a sua utilidade para a análise destes dois sistemas e lança-se um pouco mais de entendimento da relação existente entre estas duas abordagens. A ponte retificadora trifásica é analisada em condições equilibradas, facilitando-se, portanto, a comparação com a teoria convencional para regimes equilibrados e não-senoidais. Com relação ao transitório de partida do motor de indução, fica evidenciado que este pode ser tratado como se estivesse operando em regime para cada valor do escorregamento, durante o período do transitório eletromecânico.
This work aims to show The Instantaneous Complex Power approach, which uses instantaneous space vectors, showing its usefulness through two applications: The six pulse three-phase bridge rectifier and the starting transient of an induction motor. The results are compared to the Buchholz-Goodhue quantities, as defined in IEEE-Std 1459/2000, which deals with three-phase power systems under non-sinusoidal and unbalanced conditions. In this way it is possible to improve our understanding of the theory and the Buchholz- Goodhue approach. As the three-phase bridge rectifier is analyzed under balanced conditions, it facilitates the comparison of these two approaches with the conventional power theory for this case. Concerning the induction motor, it is shown that it can be treated as operating on steady-state sinusoidal conditions for every value of its slip during the electromechanical period of the starting process.

Orientador: Dalgerti Lelis Milanese
Banca: Júlio Borges de Souza
Banca: Haroldo Rodrigues de Azevedo
Resumo: Este trabalho tem o objetivo de abordar a Teoria da Potência Complexa Instantânea, a qual utiliza vetores espaciais instantâneos, e mostrar sua utilidade através de duas aplicações para cargas do sistema trifásico: A ponte retificadora trifásica de seis pulsos e o transitório de partida de um motor de indução trifásico. Os resultados obtidos são comparados com as grandezas de Buchholz-Goodhue no cálculo da potência aparente e do fator de potência, grandezas estas definidas na norma IEEEStd 1459/2000, para sistemas trifásicos operando em regime permanente em condições de desequilíbrio e com formas de onda não-senoidais. Mostra-se a sua utilidade para a análise destes dois sistemas e lança-se um pouco mais de entendimento da relação existente entre estas duas abordagens. A ponte retificadora trifásica é analisada em condições equilibradas, facilitando-se, portanto, a comparação com a teoria convencional para regimes equilibrados e não-senoidais. Com relação ao transitório de partida do motor de indução, fica evidenciado que este pode ser tratado como se estivesse operando em regime para cada valor do escorregamento, durante o período do transitório eletromecânico.
Abstract: This work aims to show The Instantaneous Complex Power approach, which uses instantaneous space vectors, showing its usefulness through two applications: The six pulse three-phase bridge rectifier and the starting transient of an induction motor. The results are compared to the Buchholz-Goodhue quantities, as defined in IEEE-Std 1459/2000, which deals with three-phase power systems under non-sinusoidal and unbalanced conditions. In this way it is possible to improve our understanding of the theory and the Buchholz- Goodhue approach. As the three-phase bridge rectifier is analyzed under balanced conditions, it facilitates the comparison of these two approaches with the conventional power theory for this case. Concerning the induction motor, it is shown that it can be treated as operating on steady-state sinusoidal conditions for every value of its slip during the electromechanical period of the starting process.
Mestre

Made available in DSpace on 2014-06-11T19:22:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-06-09Bitstream added on 2014-06-13T18:06:43Z : No. of bitstreams: 1 motoki_my_me_ilha.pdf: 675184 bytes, checksum: e172c8abc0127eb211d92ea44339f645 (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Realiza-se neste trabalho um estudo da Teoria da Potência Complexa Instantânea aplicada na máquina de indução trifásica, onde são mostrados os vetores espaciais instantâneos (VEI´s), pois estes reduzem os parâmetros para estudo (o sistema trifásico é representado por um equivalente ortogonal). Através dos vetores espaciais instantâneos serão calculadas as grandezas de Buchholz-Goodhue para a determinação do aproveitamento da linha (melhoria do fator de potência) - que são recomendados pela norma IEEE 1459-2000. A máquina estará submetida a variadas condições de assimetria e desequilíbrio possibilitando a apresentação de novos parâmetros, que serão utilizadas para a compensação harmônica.
It takes place in this work a study of the Theory of the Instantaneous Complex Power applied will be accomplished in the three-phase induction machine, where the instantaneous space phasors are shown (ISP´s), because these reduce the parameters for study (the system three-phase is represented by an equivalent orthogonal). Through the instantaneous space phasors the parameters of Buchholz- Goodhue will be calculated for the determination of the use of the line (improvement of the power factor) - that are recommended by the norm IEEE 1459-2000. The machine will be submitted to varied asymmetry conditions and unbalance making possible the presentation of new parameters, which will be used for the harmonic compensation.

Orientador: Dalgerti Lelis Milanese
Banca: Júlio Borges de Souza
Banca: Milton Itsuo Samesima
Resumo: Realiza-se neste trabalho um estudo da Teoria da Potência Complexa Instantânea aplicada na máquina de indução trifásica, onde são mostrados os vetores espaciais instantâneos (VEI's), pois estes reduzem os parâmetros para estudo (o sistema trifásico é representado por um equivalente ortogonal). Através dos vetores espaciais instantâneos serão calculadas as grandezas de Buchholz-Goodhue para a determinação do aproveitamento da linha (melhoria do fator de potência) - que são recomendados pela norma IEEE 1459-2000. A máquina estará submetida a variadas condições de assimetria e desequilíbrio possibilitando a apresentação de novos parâmetros, que serão utilizadas para a compensação harmônica.
Abstract: It takes place in this work a study of the Theory of the Instantaneous Complex Power applied will be accomplished in the three-phase induction machine, where the instantaneous space phasors are shown (ISP's), because these reduce the parameters for study (the system three-phase is represented by an equivalent orthogonal). Through the instantaneous space phasors the parameters of Buchholz- Goodhue will be calculated for the determination of the use of the line (improvement of the power factor) - that are recommended by the norm IEEE 1459-2000. The machine will be submitted to varied asymmetry conditions and unbalance making possible the presentation of new parameters, which will be used for the harmonic compensation.
Mestre

碩士
國立臺灣大學
資訊工程學研究所
102
Internet technology has developed many methods to improve the efficiency of information transmission, The theories designed for heterogeneous networks are also common in the real network. However, in the case of the network is unstable, the message still canoot be sent with better reliability. In this thesis, a flooding-like algorithm is provied to not only maintain the reliability, but also improve the utilization of network bandwidth. It is also designed for heterogeneous network and provides an optimized settings module.

博士
國立臺灣大學
電信工程學研究所
106
Recent research trends exhibit a growing imbalance between the demands of tenants’ software applications and the provisioning of hardware resources. Misalignment of demand and supply gradually hinders workloads from being efficiently mapped to fixed-sized server nodes in traditional data centers. The incurred resource holes not only lower infrastructure utilization but also cripple the capability of a data center for hosting large-sized workloads. This deficiency motivates the development of a new rack-wide architecture referred to as the composable system. The composable system transforms traditional server racks of static capacity into a dynamic compute platform. Specifically, this novel architecture aims to link up all compute components that are traditionally distributed on traditional server boards, such as central processing unit (CPU), random access memory (RAM), storage devices, and other application-specific processors. By doing so, a logically giant compute platform is created and this platform is more resistant against the variety of workload demands by breaking the resource boundaries among traditional server boards. This research is divided into three parts. In the first part, we introduce the concepts of this reconfigurable architecture and design a framework of the composable system for cloud data centers. We then develop mathematical models to describe the resource usage patterns on this platform and enumerate some types of workloads that commonly appear in data centers. From the simulations, we show that the composable system sustains nearly up to 1.6 times stronger workload intensity than that of traditional systems and it is insensitive to the distribution of workload demands. This demonstrates that this composable system is indeed an effective solution to support cloud data center services. In the next part, we extend the framework from a single data center into a network of data centers, where each of them is geographic distributed in the serving area. A workload may need to migrate to the data center that close to its tenants for lower transmission delay. The migration may happen multiple times during its runtime, conditioned on the mobility of its tenants. We develop a two-tier model to tell the overall resource usage patterns. The mobility patterns of tenants are transformed into the effective arrival rates to each data center. Under the conditions of the Poisson arrivals of incoming workloads and probabilistic mobility patterns, the resource usage patterns of each data center can be calculated in parallel. In the last part, we turn our viewpoint to the communication links between workloads. An integrated application may consist of multiple workloads which run inside dedicated VMs. These VMs form a logical network which is physically distributed in the network of data centers. However, traditional protocols used in local area networks may not be applicable for data center networks due to the difference in network topology. Recent research suggests that layer-2-in-layer-3 tunneling protocols may be the solution to address the challenges. We find via testbed experiments that directly applying these tunneling protocols toward network virtualization only results in poor performance due to the scalability problems. Specifically, we observe that the bottlenecks actually reside inside the servers. We then propose a CPU offloading mechanism that exploits a packet steering function to balance packet processing among available CPU threads, thus greatly improving network performance. Compared to a virtualized network created based on VXLAN, our scheme improves the bandwidth for up to almost 300 percent on a 10 Gb/s link between a pair of tunnel endpoints.

碩士
國立中正大學
通訊工程研究所
94
In recent years, wireless local area network (WLAN) has received significant attention from the industry and academia because it enables users, wherever they are, to get abundant information from Internet. It not only offers quite a few advantages, but also raises potential research issues, such as link adaptation, power control and channel estimation. This research will focus on fragmentation and link adaptation for further discussions and researches. In the fragmentation scheme of IEEE 802.11 standard, if the size of the MSDU (Media Access Control Service Data Units) is greater than the fragmentation threshold (aFragmentationThreshold), it is divided into several equal sections of smaller MPDUs (Media Access Control Protocol Data Units). In the past, many researches only considered single fragmentation threshold and link adaptation in order to improve network performances. However, although transmitter can adjust the transmission rate dynamically based on channel information, it transmits the same number of bits for each transmission process. In order to improve network performances effectively, in this thesis, we propose dynamic fragmentation and link adaptation algorithm. Multiple fragmentation thresholds, instead of any single one, can be selected according to different transmission rates when a particular target packet error occurs. Under this circumstance, the channel is able to be more effectively utilized as well. We simulate this algorithm under log-normal shadowing channel model and the results show that the proposed scheme achieves much better performances than other link adaptation schemes.

碩士
國立中山大學
資訊工程研究所
87
Internet Protocol (IP) conformed the ATM network, the complicated way is IP packet and the transform of ATM cell, while the IP packet segment to cells, and the cells reassemble to IP packet make the Internet Protocol link up with messages. Under continual reassemble and segmentation, the completely received of packets have the closely relationship with cell in buffer allocation scheme of ATM backbone switches and how to control it and proceed to the next step to find out the relation of goodput of packet is the point of this research. In this paper, we will focus on shared-buffering schemes. As the multicast traffic increases and multimedia becomes popular, shared-buffering schemes are better choices. Researchers have studied the effects of Per-VC queueing. However, only considering queues of each VC is not enough. As we will show, the buffers needed should be also dependent on output rates. In addition, the number of VCs could be a lot and the management of them could be a problem. Instead, we suggest the idea of per-port queueing here. By per-port queueing, we can lower the complexity by managing ports as well as take into account the channel rate of each output port. By combing per-port queuing with packet discarding schemes, we show the goodput of ATM switches for different proposed schemes. The paper is organized as follows. In section II, we introduce advantages and disadvantages of dedicated-buffering and shared-buffering queueing, and different packet discarding schemes. Several shared-buffering schemes are proposed in section III. Simulation results and comparisons are discussed in section IV. Three different topologies are simulated. Section V is the conclusions.

碩士
國立臺灣師範大學
工業科技教育研究所
90
Armed with the space and time feasibility, web-based instrucation is a easy way for adult learners. The purposes of this study were to develop and applicate the indicators for assessing learning management system on the case study of institute for industry information’s good2u. A planed assessment indicators were firstly drafted from literature analysis and expert interview, and then a questopmmaire was mailed by E-mail to 517 members of good2U. Finally, 303 valid questionnaires were obtained and led to the return rate 58.6 ﹪. The following conclusions were made：(1) Five learning management system assessment indicators were：Accuracy indicator、utility indicator、abundance indicator、interaction indicator、assisstance indicator. (2) 52 items of learning management system of web-based instruction were developed in 5 assessment indicators. (3) There are 43 items of learning management system in Good2U. 42 of them, the importance are above average；5 of them, the quality are below average. (4) Good2U had better equip 10 more items of learning management system . (5) The difference of importance of learning management system , 11 items of learning management system were affected by gender、15 affected by education、7 affected by work locatoion.