The Internet has been designed as a best-effort network, which does not provide any additional services to applications using the network. Overlay networks, which form an application layer network on top of the underlying Internet, have emerged as popular means to provide specific services and greater control to applications. Overlay networks offer a wide range of services, including content distribution, multicast and multimedia streaming. In my thesis, I focus on overlay networks for content distribution, used by applications such as bulk data transfer, file sharing and web retrieval. I first investigate the construction of such overlay networks by studying the bootstrapping functionality in an example network (the Gnutella peer-to-peer system). This study comprises the analysis and performance measurements of Gnutella servents and measurement of the GWebCache system that helps new peers find existing peers on the Gnutella network. Next, I look at fairness issues due to the retrieval of data at a client in the form of multipoint-to-point sessions, formed due to the use of content distribution networks. A multipoint-to-point session comprises multiple connections from multiple servers to a single client over multiple paths, initiated to retrieve a single application-level object. I investigate fairness of rate allocation from a session point of view, and propose fairness definitions and algorithms to achieve these definitions. Finally, I consider the problem of designing an overlay network for content distribution, which is fair to competing overlay networks, while maximizing the total end-to-end throughput of the data it carries. As a first step, I investigate this design problem for a single path in an Overlay-TCP network. I propose two schemes that dynamically provision the number of TCP connections on each hop of an Overlay-TCP path to maximize the end-to-end throughput using few extraneous connections. Next, I design an Overlay-TCP network, with the secondary goal of intra-overlay network fairness. I propose four schemes for deciding the number of TCP connections to be used on each overlay hop. I show that one can vary the proportion of sharing between competing overlay networks by varying the maximum number of connections allowed on overlay hops in each competing network.

Due to the World Wide Web (WWW) has expanded speedily, the interaction between the user and the Web site is becoming persistently. Most proposed load control schemes developed based on the traditional Web site providing static files are not suitable for the Web site today. The new generation of WWW provides more varied and secure services. The greater part of applications are belonging to the session-based service. In order to provide better quality of services for the users, Web cluster architecture becomes the popular solution for most Web sites. This architecture combines serveral servers to work together and deals satisfied with the exponential increasing in service on WWW. In this paper, we proposed a session-based admission control and load balancing mechanism for Web cluster systems. The admission control scheme is used to prevent Web system from becoming overload by determining whether an establishment of TCP connection is admitted or not. The load balancing scheme assigns new sessions to the suitable back-end server and achieves good load balancing among back-end servers, which also increases the throughput of system. The simulation results demonstrate that our mechanism utilizes system resource efficiently and takes system utilization and percentage of completed session into account simultaneously. Therefore, our mechanism can ensure the sessions would not be aborted midway. To compare with others, our mechanism can attain higher throughput and maintain the request average delay time. Furthermore, whether the back-end servers are identical in capacity or not, their load always get good balance.

Le déploiement sensible au contexte et la reconfiguration des applications dans les sessions collaboratives sont les processus permettant de gérer la distribution initiale et ultérieure des outils collaboratifs sur les nSuds des participants en prenant en compte diverses contraintes. Ces contraintes proviennent de la structure de la session, des environnements d'exécution et des relations entre les participants. La majorité des travaux liés au déploiement et à la reconfiguration proposent des solutions qui couvrent essentiellement les deux premiers points mais qui n'accordent pas beaucoup d'importance au dernier point. Ainsi, les applications déployées couvrent les besoins des utilisateurs et sont compatibles avec le contexte local mais l'interopérabilité avec les applications déjà déployées sur les nSuds des voisins n'est pas vérifiée. De plus, le contrôle du déploiement et la découverte des applications requises se fait de façon centralisée et nécessite l'intervention humaine. Nous proposons une approche de déploiement et de reconfiguration automatique basée sur un algorithme décentralisé qui s'exécute sur chaque nSud de déploiement. Cet algorithme utilise des modèles abstraits pour générer des configurations de déploiement valides permettant de respecter les diverses contraintes. Nous avons développé une plate-forme Pair-à-Pair offrant des modules génériques pour supporter cet algorithme. Enfin, nous avons réalisé des prototypes et nous avons mené des tests de performance afin d'évaluer expérimentalement notre approche.

Le formalisme CSP (Problème de Satisfaction de Contraintes) permet de représenter de nombreux problèmes de manière simple et efficace. Cependant, une partie de ces problèmes ne peut être résolue de manière classique et centralisée. Les causes peuvent être diverses : temps de rapatriement des données prohibitif, sécurité des données non garantie, etc. Les CSP Distribués(DisCSP), domaine intersectant celui des SMA et des CSP, permettent de modéliser et de résoudre ces problèmes naturellement distribués. Les raisonnements intra-agent et inter-agents sont alors basés sur un ensemble de relations entre différentes variables. Les agents interagissent afin de construire une solution globale à partir des solutions locales. Nous proposons, dans ce travail, un algorithme de résolution de DisCSP nommé Distributed Backtracking with Sessions (DBS) permettant de résoudre des DisCSP où chaque agent dispose d'un problème local complexe. DBS a la particularité de ne pas utiliser de nogoods comme la majorité des algorithmes de résolution de DisCSP mais d'utiliser à la place des sessions. Ces sessions sont des nombres permettant d'attribuer un contexte à chaque agent ainsi qu'à chaque message échangé durant la résolution du problème. Il s'agit d'un algorithme complet permettant l'utilisation de filtres sur les messages échangés sans remettre en cause la preuvede complétude. Notre proposition est évaluée, dans les cas mono-variable et multi-variables par agents, sur différents benchmarks classiques (les problèmes de coloration de graphes distribués et les DisCSP aléatoires) ainsi que sur un problème d'exploration en environnement inconnu.

Darbe atlikta teorinė analizė atskleidė, kad sutrikusios klausos mokiniai susiduria su verbalinės raiškos problemomis dėl turimo skurdaus žodyno ir paveikto gebėjimo priimti, suprasti, išreikšti lingvistinę informaciją. Šias problemas galima spręsti dailės terapijos sesijose, kurių metu, sudarant sąlygas, įgyjama dailinės ir verbalinės raiškos patirtis, lavinami įgūdžiai. Iškelta hipotezė, kad dailės terapijos sesijose yra skatinama klausos sutrikimų turinčių mokinių verbalinė raiška. Veiklos (veiksmo) metodu buvo atliktas tyrimas, kurio tikslas – ištirti dailės terapijos poveikį skatinant sutrikusios klausos mokinių verbalinę raišką. Panaudojus literatūros analizės rezultatus, organizuotos dailės terapijos sesijos, kuriose buvo stebimos dailinės raiškos inspiravimo ir verbalinės raiškos skatinimo apraiškos. Tyrime dalyvavo 5 (2 neprigirdintys ir 3 kurti) klausos sutrikimų turintys 10-14 metų amžiaus mokiniai. Empirinėje dalyje nagrinėti sutrikusios klausos mokinių verbalinės raiškos skatinimo rezultatai bei atliktos content ir fenomenografinės analizės atskleidė svarbiausias tyrimo išvadas: 1. Retrospektyvus dailės terapijos sesijų stebėjimas atskleidė, kad grupės dalyvių verbalinė raiška yra skatinama tiesioginiu poveikiu – sudarant sąlygas išsisakyti, papasakoti apie savo dailinės raiškos kūrinį, atsakyti į mokytojos ir kitų grupės dalyvių klausimus bei netiesioginiu poveikiu – stebint mokytojos bendravimą, kitų dalyvių pasisakymus, išreiškiant spontaniškai kilusias... [toliau žr. visą tekstą] / The theoretical research performed in the paper revealed that the pupils with hearing impairments confronted with the problems of verbal expression concerning their poor vocabulary and their affected ability to accept, perceive, and express linguistic information. These problems can be solved in sessions of art therapy, which capacitate acquiring experience of artistic and verbal expression and development of skills. We have hypothesized that the verbal expression of pupils with hearing impairments is stimulated during the sessions of art therapy. The research, which aim was the ascertainment of the effect of the art therapy on stimulation of the verbal expression of the pupils with hearing impairments, was performed by the method of activity (action). By using the results of the literature analysis, the sessions of art therapy were organised, during which we observed the manifestations of artistic activity inspiration and stimulation of verbal expression. 5 pupils with hearing impairments (2 hard of hearing and 3 deaf) of 10 – 14 years old participated in the research. The results of verbal expression stimulation of the pupils with hearing impairments analysed in the empirical part and the content and phenomenographic analyses revealed the following main conclusions of the research: 1. The retrospective observation of the art therapy sessions revealed that the verbal expression of the participants of the group was stimulated by the direct impact – by allowing opening... [to full text]

This quantitative study investigated the effect of client self-disclosure on the physiological arousal of the therapist and subsequent ratings of the therapeutic alliance, session smoothness, and session depth. Three therapists and 10 clients participated in a 40-minute videotaped therapy session while being attached to sensors that measured heart rate and skin conductance. The participants completed self-report questionnaires designed to assess the therapeutic alliance and session smoothness and depth immediately following the therapy session. The videotaped therapy sessions were later transcribed and coded by two independent coders for the occurrence of client self-disclosure. Correlation analyses were utilized to determine whether or not a relationship existed between client self-disclosure and the physiological arousal of the therapist. No significant relationships were found to exist between client self-disclosure and the physiological arousal of the therapist. Positive correlations were found to exist between the occurrence of client self-disclosure and the physiological arousal of the therapist as well as between the occurrence of client self-disclosure and the therapeutic alliance. The physiological arousal of the therapist was also found to be positively correlated with the strength of the therapeutic alliance.

In this thesis, a new reactive session reconstruction method &#039 / Smart-SRA&#039 / is introduced. Web usage mining is a type of web mining, which exploits data mining techniques to discover valuable information from navigations of Web users. As in classical data mining, data processing and pattern discovery are the main issues in web usage mining. The first phase of the web usage mining is the data processing phase including session reconstruction. Session reconstruction is the most important task of web usage mining since it directly affects the quality of the extracted frequent patterns at the final step, significantly. Session reconstruction methods can be classified into two categories, namely &#039 / reactive&#039 / and &#039 / proactive&#039 / with respect to the data source and the data processing time. If the user requests are processed after the server handles them, this technique is called as &lsquo / reactive&rsquo / , while in &lsquo / proactive&rsquo / strategies this processing occurs during the interactive browsing of the web site. Smart-SRA is a reactive session reconstruction techique, which uses web log data and the site topology. In order to compare Smart-SRA with previous reactive methods, a web agent simulator has been developed. Our agent simulator models behavior of web users and generates web user navigations as well as the log data kept by the web server. In this way, the actual user sessions will be known and the successes of different techniques can be compared. In this thesis, it is shown that the sessions generated by Smart-SRA are more accurate than the sessions constructed by previous heuristics.

<p>SIP is receiving much attention these days and it seems to be the most promising candidate as a signaling protocol for the current and future IP telephony services. Realizing this, there is the obvious need to provide a certain level of quality comparable to the traditional telephone service signalling system. Thus, we identified the major costs of SIP, which were found to be delay and security. This thesis discusses the costs of SIP, the solutions for the major costs, and the development of a low cost SIP application. The literature review of the components used to develop such a service is discussed, the networks in which the SIP is used are outlined, and some SIP applications and services previously designed are discussed. A simulation environment is then designed and implemented for the instant messaging service for wireless devices. This environment simulates the average delay in LAN and WLAN in different scenarios, to analyze in which scenario the system has the lowest costs and delay constraints.</p>

Intrusion Detection systems are now an essential component in the overall network and data security arsenal. With the rapid advancement in the network technologies including higher bandwidths and ease of connectivity of wireless and mobile devices, the focus of intrusion detection has shifted from simple signature matching approaches to detecting attacks based on analyzing contextual information which may be specific to individual networks and applications. As a result, anomaly and hybrid intrusion detection approaches have gained significance. However, present anomaly and hybrid detection approaches suffer from three major setbacks; limited attack detection coverage, large number of false alarms and inefficiency in operation. / In this thesis, we address these three issues by introducing efficient intrusion detection frameworks and models which are effective in detecting a wide variety of attacks and which result in very few false alarms. Additionally, using our approach, attacks can not only be accurately detected but can also be identified which helps to initiate effective intrusion response mechanisms in real-time. Experimental results performed on the benchmark KDD 1999 data set and two additional data sets collected locally confirm that layered conditional random fields are particularly well suited to detect attacks at the network level and user session modeling using conditional random fields can effectively detect attacks at the application level. / We first introduce the layered framework with conditional random fields as the core intrusion detector. Layered conditional random field can be used to build scalable and efficient network intrusion detection systems which are highly accurate in attack detection. We show that our systems can operate either at the network level or at the application level and perform better than other well known approaches for intrusion detection. Experimental results further demonstrate that our system is robust to noise in training data and handles noise better than other systems such as the decision trees and the naive Bayes. We then introduce our unified logging framework for audit data collection and perform user session modeling using conditional random fields to build real-time application intrusion detection systems. We demonstrate that our system can effectively detect attacks even when they are disguised within normal events in a single user session. Using our user session modeling approach based on conditional random fields also results in early attack detection. This is desirable since intrusion response mechanisms can be initiated in real-time thereby minimizing the impact of an attack.

The present research sought to understand patient experiences during Hyperbaric Oxygen Therapy (HBOT) by using 24 HBOT patients (17 men, 7 women) to examine the relationship between individual variables and anxiety, and providing One Session Exposure Therapy (OSET; Öst, 1989) if necessary. Pre-HBOT participants completed the following measures: State-Trait Anxiety Inventory (STAI; Spielberger, 1983), Claustrophobia Questionnaire (CLQ; Radomsky, Rachman, Thordarson, McIsaac, & Teachman, 2001), Anxiety Sensitivity Index (ASI; Reiss, Peterson, Gursky, & McNally, 1986), and Treatment Credibility/Expectancy Questionnaire (CEQ; Devilly & Borkovec, 2000). State Anxiety was assessed pre-HBOT and at the tenth and last sessions. Findings suggest Dispositional Anxiety (STAI-Trait + ASI), Expectancy of symptom improvement (CEQ), and gender were significantly predictive of State Anxiety before and during HBOT. Limitations and directions for future research are discussed.