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Context Interactive GPGPU applications requires low response time feedback from events such as user input in order to provide a positive user experience. Communication of these events must be performed asynchronously as to not cause significant performance penalties. Objectives In this study the usage of CPU/GPU shared virtual memory to perform asynchronous communication is explored. Previous studies have shown that shared virtual memory can increase computational performance compared to other types of memory. Methods A communication technique that aimed to utilize the performance increasing properties of shared virtual memory was developed and implemented. The implemented technique was then compared to an implementation using explicitly transferred memory in an experiment measuring the performance of the various stages involved in the technique. Results The results from the experiment revealed that utilizing shared virtual memory for performing asynchronous communication was in general slightly slower than- or comparable to using explicitly transferred memory. In some cases, where the memory access pattern was right, utilization of shared virtual memory lead to a 50% reduction in execution time compared to explicitly transferred memory. Conclusions A conclusion that shared virtual memory can be utilized for performing asynchronous communication was reached. It was also concluded that by utilizing shared virtual memory a performance increase can be achieved over explicitly transferred memory. In addition it was concluded that careful consideration of data size and access pattern is required to utilize the performance increasing properties of shared virtual memory.

This thesis explores the use of the World Wide Web asinfrastructure for collaboration among small or middle sizedgroups. A collection of Web-based tools has been developed,whose main characteristic is that they allow users to makeannotations to shared documents. These Web annotations form adialogue that is persistent and immediately accessible to theusers. Special interest has been devoted to observing howcollaborators make use of a common space where Web-documents aswell as Web-annotations are organized and stored. This commonspace has been called a domain. We have also tried a novel method for the design ofcollaborative Web-based systems, called“designing frominside”. It is based on communication between the usersand the designer in the form of a dialogue, which is generatedand presented“inside”the system that is beingdeveloped. In this way, users can make comments about theirexperience using the tool while in the appropriate context.Comments by the users as well as the designer's replies areshared with other users. In this way the users become involvedunobtrusively in the design process of the tool. One of the tools, DHS, has been used in longitudinal studieswithin courses where students also met regularly in theclassroom. In one contextthe students used the DHS as adiscussion or annotation tool for documents that they hadwritten. Within this framework, we also explored how secondlanguage students collaboratively made use of the tool toaccomplish a task that is normally done individually (readingcomprehension). Col·lecció is the latest version of the DHS. Themost important change in this tool is that users can add theWeb-documents to the domain themselves. This gives a newperspective to the tools because it can work as a collectivebookmark system. This system has been used in three casestudies in which a distributed and co-located group discussed acollection of Web-documents. Another system in the family is Col·laboració,which is oriented to supporting collaborative writing tasks. Itfocuses primarily on the communication needs co-authors mighthave around a shared document that is being produced. Thesystem also allows for on-line revision and for generatingversions of the document. This system has been used in 8 casestudies, where we have observed the users’interaction andexplored the possibilities that the Web offers to collaborativewriting. For example, co-authors can use the commenting spaceas a“window to the Web”, as the Web provides a hugeamount of information that can be relevant during the writingprocess. One of the characteristics of all these tools is that theypresent the comments in chronological order. No threadingmechanism is used, although several users have requested athreaded presentation of the comments. This design choice isbased on the belief that with threading of comments, the focusof the discussion could drastically divert from its originaltopic, the document. In our observations, a dual discoursecontext is often found in the comments referring both to aprevious comment and to the shared document. To facilitateorientation in the discussions, we have also developed avisualization tool called Domain Interactivity Diagram (DID),designed to work together with the other systems. The studies show that the Web offers a suitableinfrastructure for text-based discussions in which the documentcan be given a prime role. It also emerged that the integrationof email was appreciated by users mainly because it wasconsidered as a reminder of the task. In educational settings,students valued the possibility to go through many exampleswritten by other students in comparison with the traditionalway. Also the dialogue formed by the comments was astraightforward way to promote collaboration amongstudents. WWW, discussion, annotation, design, writing, collaborativework, asynchronous communication, text-based communication.

<p>This thesis explores the use of the World Wide Web asinfrastructure for collaboration among small or middle sizedgroups. A collection of Web-based tools has been developed,whose main characteristic is that they allow users to makeannotations to shared documents. These Web annotations form adialogue that is persistent and immediately accessible to theusers. Special interest has been devoted to observing howcollaborators make use of a common space where Web-documents aswell as Web-annotations are organized and stored. This commonspace has been called a domain.</p><p>We have also tried a novel method for the design ofcollaborative Web-based systems, called“designing frominside”. It is based on communication between the usersand the designer in the form of a dialogue, which is generatedand presented“inside”the system that is beingdeveloped. In this way, users can make comments about theirexperience using the tool while in the appropriate context.Comments by the users as well as the designer's replies areshared with other users. In this way the users become involvedunobtrusively in the design process of the tool.</p><p>One of the tools, DHS, has been used in longitudinal studieswithin courses where students also met regularly in theclassroom. In one contextthe students used the DHS as adiscussion or annotation tool for documents that they hadwritten. Within this framework, we also explored how secondlanguage students collaboratively made use of the tool toaccomplish a task that is normally done individually (readingcomprehension).</p><p>Col·lecció is the latest version of the DHS. Themost important change in this tool is that users can add theWeb-documents to the domain themselves. This gives a newperspective to the tools because it can work as a collectivebookmark system. This system has been used in three casestudies in which a distributed and co-located group discussed acollection of Web-documents.</p><p>Another system in the family is Col·laboració,which is oriented to supporting collaborative writing tasks. Itfocuses primarily on the communication needs co-authors mighthave around a shared document that is being produced. Thesystem also allows for on-line revision and for generatingversions of the document. This system has been used in 8 casestudies, where we have observed the users’interaction andexplored the possibilities that the Web offers to collaborativewriting. For example, co-authors can use the commenting spaceas a“window to the Web”, as the Web provides a hugeamount of information that can be relevant during the writingprocess.</p><p>One of the characteristics of all these tools is that theypresent the comments in chronological order. No threadingmechanism is used, although several users have requested athreaded presentation of the comments. This design choice isbased on the belief that with threading of comments, the focusof the discussion could drastically divert from its originaltopic, the document. In our observations, a dual discoursecontext is often found in the comments referring both to aprevious comment and to the shared document. To facilitateorientation in the discussions, we have also developed avisualization tool called Domain Interactivity Diagram (DID),designed to work together with the other systems.</p><p>The studies show that the Web offers a suitableinfrastructure for text-based discussions in which the documentcan be given a prime role. It also emerged that the integrationof email was appreciated by users mainly because it wasconsidered as a reminder of the task. In educational settings,students valued the possibility to go through many exampleswritten by other students in comparison with the traditionalway. Also the dialogue formed by the comments was astraightforward way to promote collaboration amongstudents.</p><p>WWW, discussion, annotation, design, writing, collaborativework, asynchronous communication, text-based communication.</p>

In this study, the participants&rsquo / perceptions about Information Technologies Certificate Program which was based on synchronous and asynchronous communication methods over the Internet offered by cooperation of Middle East Technical University, Computer Engineering Department and Continuing Education Center were examined. This online certificate program started in May 1998. The program includes eight fundamental courses of Computer Engineering Department and comprised of four semesters lasting nine months. The courses in the program are given by instructors of Computer Engineering Department. In the study, participants&rsquo / perceptions about Information Technologies Certificate Program in regard to four major items which were preferences, course effectiveness, learner support and computer mediated communication were examined and the study included the 3rd, 4th and 5th programs&rsquo / participants who attended the certificate programs. The data were collected by using online survey at the end of the each term of programs and analyzed by using descriptive statistical analyzing methods. The results showed that there was a parallelism between participants&rsquo / perceptions and aims of Information Technologies Certificate Program. It was revealed that the courses in the program were effective in general and majority of the participants found learner support satisfied. The results showed that the participants were satisfied with computer mediated communication provided in program, however, the chat sessions were not beneficial enough. In addition to these, participants made important suggestions to improve the program.

Cooperative diversity exploits the broadcast nature of wireless channels and uses relays to improve link reliability. Most cooperative communication protocols are assumed to be synchronous in nature, which is not always possible in wireless communication. Also the relay nodes are assumed to be half duplex which in turn reduces the spectral efficiency. In this thesis, we first present a novel asynchronous cooperative communication protocol exploiting polarization diversity, which does not require synchronization at the relay node. Dual polarized antennas are employed at the relay node to achieve full duplex amplify-and-forward (ANF) communication. Hence the transmission duration is reduced which results into an increased throughput rate. Capacity analysis of the proposed scheme ascertains the high data rate as compared to conventional ANF. Bit error rate (BER) simulation also shows that the proposed scheme significantly outperforms both the non-cooperative single-input single-output and the conventional ANF schemes. Considering channel path loss, the proposed scheme consume less total transmission energy as compared to ANF and non-cooperative scheme in more practical distance range. Thus the proposed scheme is suitable for high rate and energy efficient relay-enabled communication. In addition to that, we also present a novel power allocation scheme for multiple relay nodes that results in efficient cooperative multiple-input multiple-output (MIMO) communication. Considering channel path loss, the total transmission energy is distributed between the source and the relay nodes. The energy distribution ratio between the relay and direct link is optimized such that the quality of received signal is maintained with minimum total transmission energy consumption. We calculate the energy distribution ratio analytically and verified it through computer simulation. With the new power allocation scheme, the system also obtains an increased channel capacity as compared to cooperative scheme with conventional equal power allocation and non-cooperative scheme. Optimal relay positioning with proposed energy allocation scheme is also explored to maximize the capacity.

The Generative Communication (GC) paradigm was introduced in the early 1980s in the form of the Linda coordination and communication language (Gelernter & Bernstein, 1982). The goal of the language was to provide an elegant, intuitive alternative to the state-of-the-art in parallel and distributed processing languages at that time, namely remote procedure calls; message passing systems; and shared memory systems (Gelernter, 1985). Despite the longevity of the Linda coordination language and the GC paradigm, in general, the literature is devoid of meaningful research into the construction and manipulation of dynamic, pointer-based data structures within the context of the GC paradigm. This document motivates the need for such data structures in GC. In addition, this document explores the reasons for the lack literature regarding dynamic pointer-based data structures in GC. Finally, we develop solutions to address the lack of support, within the GC paradigm, for such data structures. / Ph. D.

Répondre à des requêtes de routage requiert que les entités du réseau, nommées routeurs, aient une connaissance à jour sur la topologie de celui-ci, cette connaissance est appelée table de routage. Le réseau est modélisé par un graphe dans lequel les noeuds représentent les routeurs, et les arêtes les liens de communication entre ceux ci.Cette thèse s’intéresse au calcul des tables de routage dans un modèle distribué.Dans ce modèle, les calculs sont effectués par un ensemble de processus placés sur les noeuds. Chaque processus a pour objectif de calculer la table de routage du noeud sur lequel il se trouve. Pour effectuer ce calcul les processus doivent communiquer entre eux. Dans des réseaux de grande taille, et dans le cadre d’un calcul distribué, le maintien à jour des tables de routage peut être coûteux en terme de communication. L’un des thèmes principaux abordés et celui de la réduction des coûts de communication lors de ce calcul. L’une des solutions apportées consisteà réduire la taille des tables de routage, permettant ainsi de réduire les coûts de communication. Cette stratégie classique dans le modèle centralisé est connue sous le nom de routage compact. Cette thèse présente notamment un algorithme de routage compact distribué permettant de réduire significativement les coûts de communication dans les réseaux tels que le réseau internet, i.e. le réseau des systèmes autonomes ainsi que dans des réseaux sans-échelle. Ce document contient également une étude expérimentale de différents algorithmes de routage compact distribués.Enfin, les problèmes liés à la dynamique du réseau sont également abordés. Plusprécisément le reste de l’étude porte sur un algorithme auto-stabilisant de calcul d’arbre de plus court chemin, ainsi que sur l’impact de la suppression de noeuds ou d’arêtes sur les tables de routage stockées aux routeurs. / In order to respond to routing queries, the entities of the network, nammedrouters, require to have a knowledge concerning the topology of the network, thisknowledge is called routing table. The network is modeled by a graph in whichnodes represent routers and edges represent communication links between nodes.This thesis focuses on routing tables computation in a distributed model. In thismodel, computations are done by a set of process placed on nodes. Every processhas for objective to compute the routing table of the node on which he is placed.To perform this computation, processes have to communicate with each other. Inlarge scale network, in the case of a distributed computation, maintaining routingtables up to date can be costly in terms of communication. This thesis focuses mainlyon the problem of communication cost reduction. One of the solution we proposeis to reduce routing tables size which allow to reduce communication cost. In thecentralised model this strategy is well known under the name of compact routing.This thesis presents in particular a distributed compact routing algorithm that allowsto reduce significantly the communication costs in networks like Internet, i.e. theautonomous systems network and others networks that present scale-free properties.This thesis also contains an experimental study of several distributed compact routingalgorithms. Finally, some problems linked to network dynamicity are addressed.More precisely, the problem of network deconnexion during a shortest path treecomputation with auto-stabilisation guaranties, together with a study of the impactof several edges or nodes deletion on the state of the routing tables.

Cette thèse présente un nouveau modèle temporisé appelé timed-pNets pour la modélisation et la vérification des comportements des systèmes distribués hétérogènes. Un défi essentiel de ces systèmes est de spécifier correctement les contraintes de temps du système, dans la mesure où les nœuds dans les systèmes distribués n'ont pas l'horloge physique commune. Timed-pNets utilise un modèle de temps basé sur des horloges logiques, de manière à ce que les mesures de temps dans ce modèle ne reposent pas sur une horloge physique commune. Les timed-pNets ont une structure hiérarchique en arbre: les feuilles de cet arbre sont des Systèmes de Transition Étiquetés paramétrés temporisés (timed-LTSs), et les autres nœuds sont des dispositifs de synchronisation qui permettent de composer les comportements de leurs sous-réseaux. A chaque nœud d'un timed-pNet peut être associée une spécification temporisée, qui consiste en un ensemble d’horloges logiques et de relations sur ces horloges. Les spécifications temporisées sont utilisées pour spécifier les comportements du système, y compris les communications synchrones et asynchrones. Grâce à la spécification temporisée, les timed-pNets peuvent modéliser des systèmes de manière flexible. Les analyses des limites de temps, de la sûreté et de la latence sont discutées par l'étude des conflits de relations entre les horloges logiques du système. Nous utilisons un scénario d'insertion de voitures dans les systèmes de transport intelligents (ITS) comme un exemple pour illustrer l'utilisation de notre modèle timed-pNets. Finalement, l'outil TimeSquare est utilisé pour effectuer une simulation logique et vérifier la validité de notre modèle. / This thesis presents a novel timed model called timed-pNets for modeling and verifying the communication behaviours of heterogeneous distributed systems. Since the nodes in distributed systems have no common physical clock, it brings the challenges of correctly specifying the system time constraints. Timed-pNets build the time model on top of logical clocks such that the time of this model does not rely on a common physical clock. Timed-pNets are tree style hierarchical structures. Each node is associated with a timed specification which consists of a set of logical clocks and some relations on these clocks. The leaves are represented by timed Parametrized Label Transition Systems (timed-pLTSs). Non-leaf nodes (called timed-pNets nodes) are synchronisation devices that synchronize the behaviours of subnets (these subnets can be leaves or non-leaf nodes). Both timed-pLTSs and timed-pNets nodes can be translated to timed specifications. Timed specifications are designed to specify the system behaviours including synchronous and asynchronous communications. Thanks to the timed specification, timed-pNets are able to model systems in a flexible way. Time bound analysis, safety and latency properties are discussed by investigating the relations conflicts between system logical clocks. We take a simple case of car insertion from the area of Intelligent Transportation Systems (ITS) as an example to demonstrate the use of the timed-pNets model. In the end, the TimeSquare tool is used to perform a logical simulation and check the validity of our model.