Dissertations / Theses on the topic 'Variants TCP'

With the evolution of 3G technologies like Universal Mobile TelecommunicationSystem (UMTS), the usage of TCP has become more popular for a reliable end-to-end (e2e) data delivery. However, TCP was initially designed for wired networks and therefore it suffers performance degradation due to the radio signal getting affected by fading, shadowing and interference. There are many strategies proposed by the research community on how to improve the performance of TCP over wireless links such as introducing link-layer retransmission, explicitly notifying the sender of network conditions or using new variants of TCP.

As UMTS network coverage and availability are currently experiencing rapidgrowth, optimization of various internal components of its wireless network is very important. One of the optimization is the introduction of High Speed Downlink Packet Access (HSDPA). This architecture not only allows higher data rates but also more reliable data transfer by the introduction of Hybrid ARQ (HARQ). With this enhancement to the UMTS network, it becomes vital to see the performance of TCP in such a network. Therefore in this thesis, we try to evaluate two aspects of UMTS networks: first, the impact of HSDPA parameters like scheduling algorithm and RLC/MAC-hs buffer size on overall performance of TCP and second, to study the behavior of two categories of TCP rate and flow control: loss based and delay based. Our simulation shows that delay based TCP tends to perform better than loss based TCP in our selected scenarios. The simulations are performed using the network simulator NS-2 with an e2e network model for enhanced UMTS (EURANE).

Ces dernières années, le domaine du dépannage réseau a suscité un intérêt particulier de la part des chercheurs en raison de la complexité et de l’importance de cette tâche. Le travail présenté dans cette thèse se concentre sur l’automatisation du dépannage réseau à l’aide de mesures de performance extraites des captures de paquets. La première contribution de cette thèse réside dans l’extraction de caractéristiques permettant d’identifier la cause fondamentale d’une anomalie en analysant des traces de paquets TCP montrant des connexions médiocres. Nous avons classé quatre causes de dégradation fréquemment observées : les problèmes de transmission, les problèmes de congestion, les problèmes de gigue et les limitations d’application. La deuxième contribution de cette thèse réside dans le développement d’une méthode automatisée pour détecter l’instant de sortie de l’état Slow-Start. L’importance de cette méthode réside dans le gain de temps précieux dans l’analyse des problèmes réseau, étant donné que l’état Slow-Start est un indicateur clé pour le diagnostic des défauts. La troisième contribution de cette thèse consiste en l’identification de l’algorithme de contrôle de congestion BBR. L’objectif principal est de détecter si un contrôle de l’envoi des paquets (’pacing’) est utilisé dans une connexion TCP. Cette méthode repose sur la modélisation de la distribution de la durée de l’inter-paquet pendant l’état Slow-Start. L’objectif est de reconnaître les distributions monomodales de l’inter-paquet dans le cas de BBR par rapport aux distributions à deux composantes mélangées dans le cas de CUBIC
In recent years, the field of network troubleshooting has garnered significant attention from researchers due to the complexity and importance of this task. The work presented in this thesis focuses on automating network troubleshooting using performance metrics extracted from packet captures. The first contribution of this thesis lies in extracting features to identify the root cause of an anomaly by analyzing TCP packet traces with bad performance. We have categorized four frequently observed causes of degradation: transmission problems, congestion problems, jitter problems, and application-limited problems. The second contribution of this thesis involves developing an automated method to detect the moment of exiting the Slow-Start state. The significance of this method lies in saving valuable time in the analysis of network degradation, as the Slow-Start state serves as a key indicator for fault diagnosis. The third contribution of this thesis revolves around identifying the BBR congestion control algorithm. The primary goal of our approach is to detect whether packet pacing is employed in a TCP connection. This method relies on modeling the distribution of inter-packet duration during the Slow-Start state. The objective is to distinguish unimodal distributions of inter-packet intervals in the case of BBR compared to mixed two component distributions in the case of CUBIC

The Datagram Congestion Control Protocol (DCCP) is a prominent transport protocol that has attracted the attention of the scientific community for its rapid progress and good results. The main novelty of DCCP is the performance priority design, as in UDP, however with congestion control capabilities, as in TCP. Literature about DCCP is still scarce and needs to be complemented to gather enouth scientific elements to support new research properly. In this context, this work joins the efforts of the scientific community to analise, mensure, compare and characterize DCCP in relevant scenarios that cover many real world situations. Three open questions were preliminarly identified in the literature: How DCCP behaves (i) when fighting for the same link bandwidth with other transport protocols; (ii) with highly relevant ones (e.g., Compound TCP, CUBIC) and (iii) fighting for the same link bandwidth with Compound TCP and CUBIC, adopting multimedia applications (e.g., VoIP). In this work, computational simulations are used to compare the performance of two DCCP variants (DCCP CCID2 and DCCP CCID3) with three highly representative TCP variants (Compound TCP, CUBIC and TCP SACK), in real world scenarios, including concurrent use of the same link by protocols, link errors and assorted bandwidths, latencies and traffic patterns. The simulation results show that, under contention, in most scenarios DCCP CCID2 has achieved higher throughput than Compound TCP or TCP SACK. Throughout the simulations there was a tendency of DCCP CCID3 to have lower throughput than the other chosen protocol. However, the results also showed that DCCP CCID3 has achieved significanly better throughput in the presence of link errors and higher values of latency and bandwidth, eventualy outperforming Compound TCP and TCP SACK. Finally, there was a tendency of predominance of CUBIC´ throughtput, which can be explained by its aggressive algorithm (i.e., non-linear) of return of the transmission window to the previous value before the discard event. However, CUBIC has presented the highest packet drop and the lowest delivery rate.
O Datagram Congestion Control Protocol (DCCP) é um proeminente protocolo de transporte que vem atraindo a atenção da comunidade científica pelos seus rápidos avanços e bons resultados. A principal inovação do DCCP é a priorização de desempenho, como ocorre com o UDP, mas com capacidade de realizar controle de congestionamento, como ocorre com o TCP. Entretanto, a literatura sobre o DCCP ainda é escassa e necessita ser complementada para trazer elementos científicos suficientes para novas pesquisas. Neste contexto, este trabalho vem se somar aos esforços da comunidade científica para analisar, mensurar, comparar e caracterizar o DCCP em cenários representativos que incorporem diversas situações de uso. Identificaram-se então três questões alvo, ainda em aberto na literatura: qual é o comportamento do DCCP (i) quando disputa o mesmo enlace com outros protocolos de transporte; (ii) com protocolos de transporte relevantes (e.g., Compound TCP, CUBIC) e (iii) em disputa no mesmo enlace com o Compound TCP e o CUBIC, utilizando aplicações multimídia (e.g., VoIP). Neste trabalho, simulações computacionais são utilizadas para comparar duas variantes do DCCP (CCID2 e CCID3) a três variantes do TCP (Compound TCP, CUBIC e TCP SACK), em cenários onde ocorrem situações de mundo real, incluindo utilização concorrente do enlace pelos protocolos, presença de erros de transmissão no enlace, variação de largura de banda, variação de latência, e variação de padrão e distribuição de tráfego. Os resultados das simulações apontam que, sob contenção, na maioria dos cenários o DCCP CCID2 obteve vazão superior à do Compound TCP, do DCCP CCID3 e do TCP SACK. Ao longo das simulações observou-se uma tendência do DCCP CCID3 a ter vazão inferior à dos demais protocolos escolhidos. Entretanto, os resultados apontaram que o DCCP CCID3 obteve desempenho significativamente melhor na presença de erros de transmissão e com valores maiores de latência e de largura de banda, chegando a ultrapassar a vazão do DCCP CCID2 e do TCP SACK. Por fim, observou-se uma tendência de predominância do protocolo CUBIC no tocante à vazão, que pode ser determinada pelo seu algoritmo agressivo (i.e., não-linear) de retorno da janela de transmissão ao valor anterior aos eventos de descarte. Entretanto, o CUBIC apresentou o maior descarte de pacotes e a menor taxa de entrega.

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Aplicações de dados, que funcionam sobre o Bluetooth, tais como HTTP, FTP e real audio, irão necessitar de protocolos da camada de transporte da arquitetura TCP/IP (TCP e UDP) para enviar pacotes sobre os links wireless. Para aumentar o desempenho destas aplicações é preciso otimizar os recursos existentes, que na maioria dos dispositivos para este tipo de tecnologia são escassos. Alguns fatores influenciam o desempenho do tráfego de dados sobre estes dispositivos, normalmente, de tamanho reduzido e pouca autonomia de uso. Com isso, há uma crescente tentativa de torná-los mais eficientes, através do melhor aproveitamento de seus recursos. Este trabalho contempla a análise e o aumento de performance do tráfego de dados usando o serviço assíncrono Bluetooth. Mostramos, através dos resultados, que o melhor algoritmo de Segmentação e Remontagem (SAR) é o de Melhor Ajuste (BF), que na média, apresenta maior vazão, menor atraso e variação de atraso nas transmissões e menor porcentagem de perda de pacotes. Quanto as variantes do TCP, o Vegas apresentou-se a melhor escolha, com uma vazão média maior, uma menor porcentagem de perda de pacotes, menor atraso e variação de atraso, mas devido não haver implementações dessa variante, a solução mais conveniente é a utilização do New Reno, uma vez que utilizado com o algoritmo SAR-BF obteve melhor desempenho que os demais

La détection infrarouge, autrefois réservée aux applications militaires et spatiales, connait depuis une dizaine d’années une mutation importante et s’ouvre de plus en plus vers des marchés "grand public". Cette démocratisation est principalement liée aux développements rapides que connaissent les technologies utilisant des bolomètres "non refroidis", qui profitent de leurs compatibilités avec les filières de la microélectronique.La technologie utilisée au CEA/LETI repose sur l’utilisation d’un matériau thermomètre à base de silicium amorphe (également noté "a-Si"). Ce dernier comporte de nombreux avantages dont, principalement, son excellente compatibilité avec les outils "classiques" de la microélectronique. Cependant, l’intégration d’un matériau thermomètre plus performant que le a-Si est nécessaire pour répondre aux défis à venir.Conscient de l’importance de cette problématique "matériau" le laboratoire CEA/LETI développe depuis plusieurs années des matériaux à base d’oxydes de métaux de transition déposés en couches minces.Cette étude s’appuie sur l’ensemble des variantes d’oxydes de métaux de transition étudié dans ce cadre. Cette palette de matériaux, qui se sont révélés très différents dans leur structure et, corrélativement, les mesures de transport dans chacun de ces types, nous ont permis de relier structure et mécanismes de conduction spécifiques à chacun. Une attention particulière a été portée aux mesures de TCR, ou « Temperature Coefficient of Resistance », (facteur à maximiser) et de bruit en 1/f (source de bruit à minimiser), les deux paramètres de choix pour le matériau thermistor.Des grandes tendances qui pilotent la performance d’un matériau thermistor pour la bolométrie ont pu être déduites de ces investigations. Les travaux présentés dans cette thèse permettent d’évaluer le potentiel de tel ou tel compétiteur avant d’en entreprendre le développement
InfraRed detection, formerly reserved to defense and spatial applications, is currently undergoing deep changes which open new opportunities. Uncooled microbolometer technologies, compatible with classical semiconductors processes, are now able to produce low cost thermal imagers and this will open the door to customer markets in a close future.The technology developed in the CEA/LETI laboratory use the amorphous silicon (noted "a-Si") as the thermistor material. This material has many advantages, in particular, its excellent compatibility with the classical tools used in microelectronic industry. However, better performance in the thermistor material is still needed to address future applications.To handle this challenge, CEA/LETI laboratory is currently developing thermistors made of transition metal oxides thin films. The study presented hereby is based on various transition metal oxides samples deposited in the CEA/LETI Laboratory.Characterization of the structure and the electronic transport for each of these samples allowed us to put in evidence correlations between microscopic structure and conduction mechanisms. Two main figures of merit impacting the overall material performance were investigated : the TCR, Temperature Coefficient of Resistance (which must be maximized) and the 1/f noise (which must be minimized).Finally we conclude this work by highlighting majors outlines governing the performance of a thermistor

Cette thèse s'inscrit dans une thématique pluridisciplinaire explorant les liens existants entre la théorie de la commande et les réseaux informatiques. L'idée consiste à appliquer les outils de l'Automatique pour la stabilisation du trafic dans les réseaux de communication. Premièrement, nous nous sommes intéressés à l'analyse de stabilité des systèmes à retards variables au travers de deux approches temporelles. D'une part, nous avons considéré la méthode de Lyapunov-Krasovskii dans laquelle nous avons élaboré des fonctionnelles en adéquation avec de nouvelles modélisations du système (segmentation du retard, dérivée temporelle). D'autre part, la stabilité a également été abordée avec une approche entrée-sortie, empruntant alors les outils de l'analyse robuste. Le système à retard est alors réécrit comme l'interconnexion d'une application linéaire avec une matrice constituée d'opérateurs définissant le système original. Après avoir revisité le principe de séparation quadratique, nous développons des opérateurs auxiliaires afin de caractériser au mieux la dynamique retardée et proposer des critères moins pessimistes. Deuxièmement, la méthodologie développée est ensuite utilisée pour le problème de contrôle de congestion d'un routeur lors de communications TCP. Ce protocole de bout en bout est sensible à la perte de paquet et modifie en conséquence son taux d'émission selon l'algorithme du AIMD. Il s'agit alors de commander le taux de perte par l'intermédiaire d'un mécanisme d'Active Queue Management situé au niveau du routeur afin de réguler le trafic. Les résultats théoriques sont ensuite évalués à l'aide du simulateur de réseaux NS-2.

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Introduction: Head and neck cancer is a collective term defined by anatomical and topographical basis to describe malignant tumors of the upper aerodigestive tract. This anatomical region includes the oral cavity, pharynx and larynx, having as the main risk factors smoking and alcoholism. The most representative hystologic type from head and neck cancer was squamous cell carcinoma (HNSCC), with more than 500,000 new cases worldwide every year. Folate deficiency is associated with increased risk of several types of cancer and alterations in folate metabolism may contribute to the process of carcinogenesis by influencing DNA methylation and genomic stability. Polymorphisms in genes encoding enzymes involved in this pathway may alter enzyme activity and consequently interfere in concentrations of homocysteine and Sadenosylmethionine that are important for DNA synthesis and cellular methylation reactions. Objectives: Investigate MTHFD1 G1958A, BHMT G742A, TC2 C776G and TC2 A67G polymorphisms involved in folate metabolism on head and neck cancer risk, and the association between these polymorphisms with primary site, tumor extension, lymph node involvement and prognosis of the disease. Patients and Methods: Were included in the study 694 individuals (240 patients with head and neck cancer and 454 controls). Molecular analysis was made by genomic DNA from peripheral blood and genetic alterations were investigated by Polymerase Chain Reaction-restriction Fragment Length Polymorphism (PCR-RFLP) and Real Time-PCR. Socio-demographic data were obtained from patient´s medical records and interview of the controls. Results: Multiple logistic regression showed that tobacco, alcohol and age over 42 years were predictors for the disease (P<0.05). Hardy-Weinberg equilibrium showed that the genotypic distributions were in equilibrium for both groups in all polymorphisms studied. The MTHFD1 1958GA or AA genotypes associated with tobacco (P=0.04) and alcohol (P=0.03) consumption increase the risk for head and neck cancer (HNSCC). These same genotypes were found in higher proportion in patients with advanced stage tumors (P=0.04) and in patients with lower survival (P=0.01). TC2 C776G polymorphism (P=0.03) were less frequent in patients with age over 52 years and TC2 A67G polymorphism (P=0.04) were less frequent in patients with 52-63 years. TC2 C776G polymorphism was not associated to HNC, however was present in higher proportion in patients with pharynx as primary site of tumor (P=0.02). Conclusions: Are predictors for head and neck cancer, regardless of the gene, tobacco and alcohol consumption and age over 42 years. The presence of MTHFD1 G1958A polymorphism associated to tobacco and alcohol consumption may modulate the risk for disease development.
Introdução: Câncer de cabeça e pescoço é um termo coletivo definido por bases anatômicas e topográficas para descrever tumores malignos do trato aerodigestivo superior. Esta região anatômica inclui a cavidade oral, faringe e laringe, tendo como principais fatores de risco o tabagismo e o etilismo. O tipo histológico mais representativo de todos os cânceres de cabeça e pescoço é o carcinoma espinocelular (HNSCC), com mais de 500 mil casos novos no mundo todos os anos. Deficiência de folato no organismo está associada ao aumento do risco de vários tipos de câncer e alterações neste metabolismo podem contribuir para o processo de carcinogênese por influenciar as reações de metilação do DNA e a estabilidade genômica. Polimorfismos em genes que codificam enzimas envolvidas no metabolismo do folato podem alterar a atividade enzimática e interferir nas concentrações de homocisteína, Sadenosilmetionina e outros produtos do metabolismo, importantes para a síntese de DNA e reações de metilação celular. Objetivos: Avaliar a influência dos polimorfismos MTHFD1 G1958A, BHMT G742A, TC2 C776G e TC2 A67G em pacientes com carcinoma espinocelular de cabeça e pescoço e em indivíduos controle sem história da neoplasia, além de verificar a associação entre os polimorfismos e os sítios primários de ocorrência, extensão do tumor, comprometimento de linfonodos, e o prognóstico da doença. Pacientes e Métodos: Foram incluídos no estudo 694 indivíduos (240 pacientes com câncer de cabeça e pescoço e 454 controles). Foi feita análise molecular através de extração de DNA genômico de sangue periférico e as alterações genéticas foram investigadas por meio das técnicas de Reação em Cadeia da Polimerase (PCR) em tempo real e Análise de Polimorfismo de Comprimento de Fragmento de Restrição (PCR-RFLP). Os dados sócio-demográficos foram obtidos através do prontuário dos pacientes e entrevista dos indivíduos controles. Resultados: Regressão logística múltipla mostrou que tabagismo, etilismo e idade superior a 42 anos foram preditores da doença (P<0,05). As distribuições genotípicas estiveram em equilíbrio de Hardy- Weinberg em ambos os grupos em todos os polimorfismos estudados. Os genótipos MTHFD1 1958GA ou AA associados ao tabagismo (P=0,04) e etilismo (P=0,03) aumentaram o risco de carcinoma espinocelular de cabeça e pescoço. Estes mesmos genótipos estiveram presentes em maior proporção em pacientes com tumores em estadios mais avançados T3 e T4 (P=0,04) e em pacientes com menor sobrevida (P=0,01). O polimorfismo TC2 C776G (P=0.03) esteve presente em menor frequência em pacientes com idade superior a 52 anos e o polimorfismo TC2 C776G (P=0.03) em pacientes com idade entre 52-63 anos. O polimorfismo TC2 C776G não foi relacionado ao risco da doença, porém esteve presente em alta proporção em pacientes que tiveram a faringe como sítio primário de ocorrência do tumor. Conclusões: São preditores para o câncer de cabeça e pescoço, independentemente da variável genética o uso de tabaco, álcool e idade superior a 42 anos. A presença do polimorfismo MTHFD1 G1958A associado aos hábitos tabagista e etilista podem modular o risco para o desenvolvimento da doença.

INTRODUZIONE. L’HCC ha la capacità di secernere nel tessuto sano fattori di crescita per generare attorno a sé una rete vascolare (angiogenesi) che porta nutrimento e ossigeno alla lesione. Per verificare l’efficacia delle recenti terapie anti-angiogeniche è necessario caratterizzare la perfusione del tumore, al fine di osservarne le variazioni nella microvascolatura. L’analisi perfusionale si basa su tecniche di imaging funzionale inclusa la Tomografia Computerizzata perfusionale (TCp). Da scansioni TC ripetute si ricostruiscono le Time Concentration Curve (TCC) che rappresentano l’evoluzione temporale del Mezzo di Contrasto iniettato. Le curve sono rumorose e con artefatti: è necessaria una fase di pre-processing, tra cui la rappresentazione delle TCC mediante modelli di fitting parametrici. OBIETTIVI. Nel lavoro di Tesi si è sviluppato il fitting delle TCC di input vascolari basato su Gamma Variate (GV) a 4 parametri ed applicato alle TCC di aorta e porta degli esami TCp (baseline e un follow-up) di 18 pazienti del Centro più numeroso dello studio SARAH, affetti da HCC e trattati con SIRT. METODI. Il fitting è stato implementato mediante Interior Point (IP), con selezione automatica del set di condizioni iniziali globali di tutti i parametri GV nel caso dell’aorta e di 3 parametri GV per la porta, per la quale il quarto parametro è variato con criterio paziente-specifico. RISULTATI. Le variazioni delle TCC fra baseline e follow-up sono classificabili in 2 famiglie di curve in base a valore di picco e larghezza. Le correlazioni tra i parametri GV trovati con IP e i descrittori calcolati sulle TCC evidenziano l’ottima capacità del fitting di rilevare sia le caratteristiche delle singole TCC sia le variazioni tra baseline e follow-up. Infine, i risultati preliminari dell’analisi perfusionale non evidenziano una variazione nella vascolarizzazione del tumore indotta da SIRT dopo un mese di trattamento.

碩士
大同大學
通訊工程研究所
94
In this thesis we studied the TCPW which requires modifications only in the TCP stack at the source node. Basically it differs from TCP Reno in the TCP congestion control algorithm. It was designed by following the principle of Additive Increase Adaptive Decrease (AIAD), not that of additive increase multiplicative decrease (AIMD, used in TCP Reno. Our simulation considers both the core links and the WLANs. The results show that, TCP Westwood (TCPW) outperforms TCP Reno in terms of average throughput when bursty losses occurred over the wireless channel. The results also show that TCP Westwood (TCPW) is better under bandwidth bottleneck and limited buffer size.

碩士
中興大學
電機工程學系所
95
SCTP(Stream Control Transmission Protocol), a new fourth layer transport protocol, was proposed by the SIGTRAN Working Group of the IETF(Internet Engineering Task Force). The protocol is a connection-oriented and reliable transport service. It also supports multi-homing and multi-streaming mechanisms and can improve the transmission efficiency and enhance the security of traditional TCP. In this thesis we will focus on the congestion control for TCP (Transmission Control Protocol) (Tahoe, NewReno, SACK) and SCTP(SCTP, NewReno) and will compare the performance issue on delivery. We use the NS-2(Network Simulator-Version 2), a network simulation software, to simulate several scenarios of packet loss and congestion window size. The number of packets received, throughput and distribution of packet loss was simulated under two fourth layer transport protocol existing at the same time. The simulation results shows that the design of congestion control of SCTP is better than using TCP. The SCTP can not only reduce the probability of packet loss, but also improve the performance of delivery than TCP while face the suffering of multiple packet loss.