Analysis of generic discrete-time buffer models with irregular packet arrival patterns

De kwaliteit van de multimediadiensten die worden aangeboden over de huidige breedband-communicatienetwerken, wordt in hoge mate bepaald door de performantie van de buffers die zich in de diverse netwerkele-menten (zoals schakelknooppunten, routers, modems, toegangsmultiplexers, netwerkinter- faces, ...) bevinden. In dit proefschrift bestuderen we de performantie van een dergelijke buffer met behulp van een geschikt stochastisch discrete-tijd wachtlijnmodel, waarbij we het geval van meerdere uitgangskanalen en (niet noodzakelijk identieke) pakketbronnen beschouwen, en de pakkettransmissietijden in eerste instantie één slot bedragen. De grillige, of gecorreleerde, aard van een pakketstroom die door een bron wordt gegenereerd, wordt gekarakteriseerd aan de hand van een algemeen D-BMAP (discrete-batch Markovian arrival process), wat een generiek kader creëert voor het beschrijven van een superpositie van dergelijke informatiestromen. In een later stadium breiden we onze studie uit tot het geval van transmissietijden met een algemene verdeling, waarbij we ons beperken tot een buffer met één enkel uitgangskanaal. De analyse van deze wachtlijnmodellen gebeurt hoofdzakelijk aan de hand van een particuliere wiskundig-analytische aanpak waarbij uitvoerig gebruik gemaakt wordt van probabiliteitsgenererende functies, die er toe leidt dat de diverse performantiematen (min of meer expliciet) kunnen worden uitgedrukt als functie van de systeemparameters. Dit resul-teert op zijn beurt in efficiënte en accurate berekeningsalgoritmen voor deze grootheden, die op relatief eenvoudige wijze geïmplementeerd kunnen worden

Efficient computer-aided verification of parallel and distributed software systems

The society is becoming increasingly dependent on applications of distributed software systems, such as controller systems and wireless telecommunications. It is very difficult to guarantee the correct operation of this kind of systems with traditional software quality assurance methods, such as code reviews and testing. Formal methods, which are based on mathematical theories, have been suggested as a solution. Unfortunately, the vast complexity of the systems and the lack of competent personnel have prevented the adoption of sophisticated methods, such as theorem proving. Computerised tools for verifying finite state asynchronous systems exist, and they been successful on locating errors in relatively small software systems. However, a direct translation of software to low-level formal models may lead to unmanageably large models or complex behaviour. Abstract models and algorithms that operate on compact high-level designs are needed to analyse larger systems. This work introduces modelling formalisms and verification methods of distributed systems, presents efficient algorithms for verifying high-level models of large software systems, including an automated method for abstracting unneeded details from systems consisting of loosely connected components, and shows how the methods can be applied in the software development industry.reviewe

Modelling and evaluation of load and performance control mechanisms of B-ISDN/ATM switching systems

Behandelt wird die Problematik der Last- und Leistungsregelung im Kontext der ATM-basierten Breitband-Vermittlungstechnik.Objective of this thesis are load control and performance control concepts for broadband switching systems. Focus is the services integrating network technology B-ISDN using ATM as transfer mode. The studied mechanisms and concepts are principally of generic nature. Specifically they are designed within the envisaged context of B-ISDN, due to its extensive vision with respect to service integration, Quality of Service (QoS) support and ATM bearer capabilities. Area of application is implicitly the network control plane, but interactions between user and control plane have to be considered, too. The prime scope are switching nodes between access and core network domain, i.e., B-ISDN switches which have to provide user-to-network and network-to-network signalling protocol functions. Thus, beside service distinction call type differentiation is also covered due to the considered network positioning

Älykäs tunnistauminen ja käyttöoikeuksien hallinta monimuotoisessa verkotetussa maailmassa

Our living environments are full of various connected computing devices. These environments in homes, offices, public spaces, transportation etc. are gaining abilities to acquire and apply knowledge about the environment and its users in order to improve users' experience in that environment. However, before smart adaptive solutions can be deployed in critical applications, authentication and authorization mechanisms are needed to provide protection against various security threats. These mechanisms must be able to interoperate and share information with different devices. The thesis focuses to questions on how to facilitate the interoperability of authentication and authorization solutions and how to enable adaptability and smartness of these solutions. To address questions, this thesis explores existing authentication and authorizations solutions. Then the thesis builds new reusable, interoperable, and adaptive security solutions. The smart space concept, based on semantic web technologies and publish-and-subscribe architecture, is recognized as a prominent approach for interoperability. We contribute by proposing solutions, which facilitate implementation of smart access control applications. An essential enabler for smart spaces is a secure platform for information sharing. This platform can be based on various security protocols and frameworks, providing diverse security levels. We survey security-levels and feasibility of some key establishment protocols and solutions for authentication and authorization. We also study ecosystem and adaptation issues as well as design and implement a fine-grained and context-based reusable security model, which enables development of self-configuring and adaptive authorization solutions.Ympäristöt, joissa elämme, ovat täynnä erilaisia verkkolaitteita. Nämä koteihin, toimistoihin, julkisiin tiloihin ja ajoneuvoihin muodostuvat ympäristöt ovat oppimassa hyödyntämään ympäriltä saatavilla olevaa tietoa ja sopeuttamaan toimintaansa parantaakseen käyttäjän kokemusta näistä ympäristössä. Älykkäiden ja sopeutuvien tilojen käyttöönotto kriittisissä sovelluksissa vaatii kuitenkin tunnistautumis- ja käyttöoikeuksien hallintamenetelmiä tietoturvauhkien torjumiseksi. Näiden menetelmien pitää pystyä yhteistoimintaan ja mahdollistaa tiedonvaihto erilaisten laitteiden kanssa. Tämä lisensiaatin tutkimus keskittyy kysymyksiin, kuinka helpottaa tunnistautumis- ja käyttöoikeusratkaisujen yhteensopivuutta ja kuinka mahdollistaa näiden ratkaisujen sopeutumiskyky ja älykäs toiminta. Tutkimuksessa tarkastellaan olemassa olevia menetelmiä. Tämän jälkeen kuvataan toteutuksia uusista tietoturvaratkaisuista, jotka ovat uudelleenkäytettäviä, eri laitteiden kanssa yhteensopivia ja eri vaatimuksiin mukautuvia. Älytilat, jotka perustuvat semanttisten web teknologioiden ja julkaise-ja-tilaa arkkitehtuurin hyödyntämiseen, tunnistetaan työssä lupaavaksi yhteensopivuuden tuovaksi ratkaisuksi. Tutkimus esittää ratkaisuja, jotka helpottavat älykkäiden tunnistautumis- ja käyttöoikeuksien hallintaratkaisujen kehitystä. Oleellinen yhteensopivuuden mahdollistaja on tietoturvallinen yhteensopivuusalusta. Tämä alusta voi perustua erilaisiin avaintenhallinta ja tunnistautumisprotokolliin sekä käyttöoikeuksien hallintakehyksiin. Tutkimuksessa arvioidaan joidenkin olemassa olevien ratkaisujen käytettävyyttä ja tietoturvatasoa. Tutkimuksessa myös tutkitaan ekosysteemi- ja sopeutumiskysymyksiä sekä toteutetaan hienojakoinen ja kontekstiin perustuva uudelleen käytettävä tietoturvamalli, joka mahdollistaa itsesääntyvien ja mukautuvien käyttöoikeuksien hallinta sovellusten toteuttamisen

Proceedings of the Third Symposium on Programming Languages and Software Tools : Kääriku, Estonia, August 23-24 1993

http://www.ester.ee/record=b1064507*es

Middleware for Mobile Sensing Applications in Urban Environments

Sensor networks represent an attractive tool to observe the physical world. Networks of tiny sensors can be used to detect a fire in a forest, to monitor the level of pollution in a river, or to check on the structural integrity of a bridge. Application-specific deployments of static-sensor networks have been widely investigated. Commonly, these networks involve a centralized data-collection point and no sharing of data outside the organization that owns it. Although this approach can accommodate many application scenarios, it significantly deviates from the pervasive computing vision of ubiquitous sensing where user applications seamlessly access anytime, anywhere data produced by sensors embedded in the surroundings. With the ubiquity and ever-increasing capabilities of mobile devices, urban environments can help give substance to the ubiquitous sensing vision through Urbanets, spontaneously created urban networks. Urbanets consist of mobile multi-sensor devices, such as smart phones and vehicular systems, public sensor networks deployed by municipalities, and individual sensors incorporated in buildings, roads, or daily artifacts. My thesis is that "multi-sensor mobile devices can be successfully programmed to become the underpinning elements of an open, infrastructure-less, distributed sensing platform that can bring sensor data out of their traditional close-loop networks into everyday urban applications". Urbanets can support a variety of services ranging from emergency and surveillance to tourist guidance and entertainment. For instance, cars can be used to provide traffic information services to alert drivers to upcoming traffic jams, and phones to provide shopping recommender services to inform users of special offers at the mall. Urbanets cannot be programmed using traditional distributed computing models, which assume underlying networks with functionally homogeneous nodes, stable configurations, and known delays. Conversely, Urbanets have functionally heterogeneous nodes, volatile configurations, and unknown delays. Instead, solutions developed for sensor networks and mobile ad hoc networks can be leveraged to provide novel architectures that address Urbanet-specific requirements, while providing useful abstractions that hide the network complexity from the programmer. This dissertation presents two middleware architectures that can support mobile sensing applications in Urbanets. Contory offers a declarative programming model that views Urbanets as a distributed sensor database and exposes an SQL-like interface to developers. Context-aware Migratory Services provides a client-server paradigm, where services are capable of migrating to different nodes in the network in order to maintain a continuous and semantically correct interaction with clients. Compared to previous approaches to supporting mobile sensing urban applications, our architectures are entirely distributed and do not assume constant availability of Internet connectivity. In addition, they allow on-demand collection of sensor data with the accuracy and at the frequency required by every application. These architectures have been implemented in Java and tested on smart phones. They have proved successful in supporting several prototype applications and experimental results obtained in ad hoc networks of phones have demonstrated their feasibility with reasonable performance in terms of latency, memory, and energy consumption.Deploying a network of sensors to monitor an environment is a common practice. For example, cameras in museums, supermarkets, or buildings are installed for surveillance purposes. However, while a decade ago, most deployed sensor networks involved a limited number of sensors, wired to a central processing unit, nowadays, the focus is on wireless, distributed, sensing nodes. Sensor technology has greatly advanced in terms of size, power consumption, processing capabilities, and low cost, thus fostering deployments of self-organizing wireless sensor networks over large geographical areas. For example, sensor networks have been used to detect a fire in a forest, to monitor the level of pollution in a river, or to check on the structural integrity of a bridge. Yet, sensor networks are usually perceived as ``something'' remote in the forest or on the battlefield, and regular users do not yet benefit from them. With the ubiquity and ever-increasing capabilities of mobile devices, such as smart phones and computers embedded in cars, urban environments offer the elements necessary to create people-centric mobile sensor networks and support a large variety of so-called sensing applications ranging from emergency and surveillance to tourist guidance and entertainment. For example, near-ubiquitous smart phones with audio and video sensing capabilities and more sensors in the near future can be used to provide shopping recommender services to inform users of special offers at the mall. Sensor-equipped cars can be used to provide traffic information services to alert drivers to upcoming traffic jams. However, urban mobile sensor networks are challenging programming environments due to the dynamism of mobile devices, the resource constraints of battery-powered devices, the software and hardware heterogeneity, and the large number of concurrent applications that they need to support. These requirements hinder the direct adoption of traditional distributed computing platforms developed for static resource-rich networks. This dissertation presents two architectures that can support the development of mobile sensing applications in urban environments. Contory offers a declarative programming model that views the urban network as a distributed sensor database. Context-aware Migratory Services provides a client-server paradigm, where services are capable of migrating to different nodes in the network in order to maintain a continuous interaction with clients. Compared to previous approaches to supporting mobile sensing urban applications, our architectures are entirely distributed and do not assume constant availability of Internet connectivity. These architectures have been implemented in Java and tested on smart phones. They have proved successful in supporting several prototype applications and experimental results obtained in networks of phones have demonstrated their feasibility with reasonable performance in terms of latency, memory, and energy consumption. The proposed architectures offer many opportunities to flexibly and quickly establish customized services that can greatly enhance the users' urban experience. Further steps to fully accomplish people-centric mobile sensing applications will have to address more technical issues as well as social and legal concerns