Pagrindinis šio darbo tikslas buvo suprasti kas yra vaizdo konferencijos, kokios yra naudojamos technologijos interaktyviam bendravimui, išsiaiškinti kokios yra didžiausios kompanijos vaizdo konferencijų sprendimų rinkoje ir kokius produktus jie siūlo, suvokti kokie protokolai ir standartai yra naudojami vaizdo konferencijų transliavimui, pristatyti kaip skirtingos vaizdo konferencijų sistemos iš skirtingų gamintojų gali komunikuoti viena su kita. Šio vaizdo konferencijų naudojimo galimybių tyrimo pabaigoje galima rasti vaizdo konferencijų infrastruktūros rekomendacijas skirtingoms vartotojų grupėms (namų vartotojai, mokyklos, nuotolinio mokymo klasės, nuotolinio mokymo centrai), kurios buvo suskirstytos pagal savo dydį ir poreikius. Taip pat gale yra pateikiamos darbo išvados. / The main goal of this paper was to understand what is video conference, what technologies are used for interactive communications, to find out which companies are the biggest players in videoconferencing solutions market and what products they are offering, to realize what protocols and standards are used in videoconferencing, to introduce how videoconferencing systems from different vendors can communicate with each other. In the in the end of this research of opportunities of using video conferences you can find recommendations for video conference infrastructure for different users groups (home users, schools, distance learning class, distance learning center) which were distributed by their size and needs. Also you can find conclusions in the end of this research.

Noting how organizations today are increasingly dependent on IT for a broad range of organizational activities, the thesis starts from the observation that many IT-related endeavors nevertheless fail. In tracing part of the problem to the inability of many organizations to cope with changes in the surrounding material and social context, the emphasis is put on the processes by which IT-artifacts are adapted and re-adapted, after they have been put into daily use. Assuming human sensemaking as a good basis for coping with the changes, qualitative data from two organizations — a Swedish social services department and a software firm — provides an empirical context for assessing how sensemaking processes affect IT-adaptation. Conceptually, the thesis draws on Karl Weick's thinking, introducing the "double interact" and the "response repertoire" as sensitizing concepts with which to understand the mechanisms generating adaptation of IT-artifacts. Methodologically, the interpretive case study is employed, using the "hermeneutic circle" as the guiding principle for the research process. The thesis draws some specific implications concerning how IT-adaptation can be understood in organizations. The generic IT-adaptation process can be divided into two elementar}- phases, exploration and exploitation. During the exploration phase, several individual interpretations of a particular IT-artifact co-exist, occasioning ambiguity about its meaning in organizational daily activity. During the exploitation phase, the IT-artifact itself is in the background of matters of attention, providing organizational actors, who pursue individual goals and desires, the opportunity to exploit the shared and taken-for-granted meaning they see in the artifact. While the exploitation phase is important for organizational efficacy, there is nevertheless a risk that the meaning exploited becomes outdated by surrounding socio-material changes over time. Among other proposals, the thesis therefore suggests that triggering sensemaking processes can be important for meaningful IT-adaptation. In addition, it suggests the activity of searching for the interlacing areas of professional identity of actor groups, as a means to make IT-artifacts meaningful in organizing endeavors. / <p>[8] s., s. 1-64: sammanfattning, s. 65-168: 6 uppsatser</p> / digitalisering@umu

Les applications en temps réel, telles que les systèmes de conférence multi-utilisateurs, ont des exigences de qualité de service élevées pour garantir une qualité d'expérience décente. De nos jours, la plupart de ces conférences sont effectuées sur des appareils sans fil. Ainsi, les appareils mobiles hétérogènes et la dynamique du réseau doivent être correctement gérés pour fournir une bonne qualité d’expérience. Dans cette thèse, nous proposons deux algorithmes pour construire et gérer des sessions de conférence basées sur un réseau défini par logiciel qui utilise à la fois la distribution multicast et l’adaptation de flux. Le premier algorithme configure la conférence téléphonique en créant des arborescences de multidiffusion pour chaque participant. Ensuite, il place de manière optimale les emplacements et les règles d’adaptation des flux sur le réseau afin de minimiser la consommation de bande passante. Nous avons créé deux versions de cet algorithme: le premier, basé sur les arborescences les plus courtes, minimise la latence, tandis que le second, basé sur les arborescences, minimise la consommation de bande passante. Le deuxième algorithme adapte les arborescences de multidiffusion en fonction des modifications du réseau qui se produisent pendant un appel. Il ne recalcule pas les arbres, mais ne déplace que les emplacements et les règles d’adaptation des flux. Cela nécessite un calcul très faible au niveau du contrôleur, ce qui rend notre proposition rapide et hautement réactive. Des résultats de simulation étendus confirment l'efficacité de notre solution en termes de temps de traitement et d'économies de bande passante par rapport aux systèmes de conférence existants basés sur une unité de contrôle multipoint et une multidiffusion de couche d'application. / Real-time applications, such as Multi-party conferencing systems, have strong Quality of Service requirements for ensuring a decent Quality of Experience. Nowadays, most of these conferences are performed on wireless devices. Thus, heterogeneous mobile devices and network dynamics must be properly managed to provide a good quality of experience. In this thesis, we propose two algorithms for building and maintaining conference sessions based on Software-Defined Network that uses both multicast distribution and streams adaptation. The first algorithm set up the conference call by building multicast trees for each participant. Then, it optimally places the stream adaptation locations and rules inside the network in order to minimize the bandwidth consumption. We have created two versions of this algorithm: the first one, based on the shortest path trees is minimizing the latency, while the second one, based on spanning trees is minimizing the bandwidth consumption. The second algorithm adapts the multicast trees according to the network changes occurring during a call. It does not recompute the trees, but only relocates the locations and rules of stream adaptation. It requires very low computation at the controller, thus making our proposal fast and highly reactive. Extensive simulation results confirm the efficiency of our solution in terms of processing time and bandwidth savings compared to existing conferencing systems based on a Multipoint Control Unit and Application Layer Multicast.