164 research outputs found
GRIDKIT: Pluggable overlay networks for Grid computing
A `second generation' approach to the provision of Grid middleware is now emerging which is built on service-oriented architecture and web services standards and technologies. However, advanced Grid applications have significant demands that are not addressed by present-day web services platforms. As one prime example, current platforms do not support the rich diversity of communication `interaction types' that are demanded by advanced applications (e.g. publish-subscribe, media streaming, peer-to-peer interaction). In the paper we describe the Gridkit middleware which augments the basic service-oriented architecture to address this particular deficiency. We particularly focus on the communications infrastructure support required to support multiple interaction types in a unified, principled and extensible manner-which we present in terms of the novel concept of pluggable overlay networks
QoS monitoring in real-time streaming overlays based on lock-free data structures
AbstractPeer-to-peer streaming is a well-known technology for the large-scale distribution of real-time audio/video contents. Delay requirements are very strict in interactive real-time scenarios (such as synchronous distance learning), where playback lag should be of the order of seconds. Playback continuity is another key aspect in these cases: in presence of peer churning and network congestion, a peer-to-peer overlay should quickly rearrange connections among receiving nodes to avoid freezing phenomena that may compromise audio/video understanding. For this reason, we designed a QoS monitoring algorithm that quickly detects broken or congested links: each receiving node is able to independently decide whether it should switch to a secondary sending node, called "fallback node". The architecture takes advantage of a multithreaded design based on lock-free data structures, which improve the performance by avoiding synchronization among threads. We will show the good responsiveness of the proposed approach on machines with different computational capabilities: measured times prove both departures of nodes and QoS degradations are promptly detected and clients can quickly restore a stream reception. According to PSNR and SSIM, two well-known full-reference video quality metrics, QoE remains acceptable on receiving nodes of our resilient overlay also in presence of swap procedures
Platforms and software systems for an autonomic internet
The current Internet does not enable easy introduction and deployment of new network technologies and services. This paper aims to progress the Future Internet (FI) by introduction of a service composition and execution environment that re-use existing components of access and core networks. This paper presents essential service-centric platforms and software systems that have been developed with the aim to create a flexible environment for an Autonomic Internet.Peer ReviewedPostprint (published version
Development of a system compliant with the Application-Layer Traffic Optimization Protocol
Dissertação de mestrado integrado em Engenharia InformáticaWith the ever-increasing Internet usage that is following the start of the new decade,
the need to optimize this world-scale network of computers becomes a big priority
in the technological sphere that has the number of users rising, as are the Quality of
Service (QoS) demands by applications in domains such as media streaming or virtual
reality.
In the face of rising traffic and stricter application demands, a better understand ing of how Internet Service Providers (ISPs) should manage their assets is needed. An
important concern regards to how applications utilize the underlying network infras tructure over which they reside. Most of these applications act with little regard for
ISP preferences, as exemplified by their lack of care in achieving traffic locality during
their operation, which would be a preferable feature for network administrators, and
that could also improve application performance. However, even a best-effort attempt
by applications to cooperate will hardly succeed if ISP policies aren’t clearly commu nicated to them. Therefore, a system to bridge layer interests has much potential in
helping achieve a mutually beneficial scenario.
The main focus of this thesis is the Application-Layer Traffic Optimization (ALTO) work ing group, which was formed by the Internet Engineering Task Force (IETF) to explore
standardizations for network information retrieval. This group specified a request response protocol where authoritative entities provide resources containing network
status information and administrative preferences. Sharing of infrastructural insight
is done with the intent of enabling a cooperative environment, between the network
overlay and underlay, during application operations, to obtain better infrastructural re sourcefulness and the consequential minimization of the associated operational costs.
This work gives an overview of the historical network tussle between applications
and service providers, presents the ALTO working group’s project as a solution, im plements an extended system built upon their ideas, and finally verifies the developed
system’s efficiency, in a simulation, when compared to classical alternatives.Com o acrescido uso da Internet que acompanha o inĂcio da nova dĂ©cada, a necessidade de otimizar esta rede global de computadores passa a ser uma grande prioridade
na esfera tecnolĂłgica que vĂŞ o seu nĂşmero de utilizadores a aumentar, assim como a
exigência, por parte das aplicações, de novos padrões de Qualidade de Serviço (QoS),
como visto em domĂnios de transmissĂŁo de conteĂşdo multimĂ©dia em tempo real e em
experiĂŞncias de realidade virtual.
Face ao aumento de tráfego e aos padrões de exigência aplicacional mais restritos, é
necessário melhor compreender como os fornecedores de serviços Internet (ISPs) devem
gerir os seus recursos. Um ponto fulcral é como aplicações utilizam os seus recursos
da rede, onde muitas destas não têm consideração pelas preferências dos ISPs, como
exemplificado pela sua falta de esforço em localizar tráfego, onde o contrário seria
preferĂvel por administradores de rede e teria potencial para melhorar o desempenho
aplicacional. Uma tentativa de melhor esforço, por parte das aplicações, em resolver
este problema, não será bem-sucedida se as preferências administrativas não forem
claramente comunicadas. Portanto, um sistema que sirva de ponte de comunicação
entre camadas pode potenciar um cenário mutuamente benéfico.
O foco principal desta tese Ă© o grupo de trabalho Application-Layer Traffic Optimization (ALTO), que foi formado pelo Internet Engineering Task Force (IETF) para explorar
estandardizações para recolha de informação da rede. Este grupo especificou um protocolo onde entidades autoritárias disponibilizam recursos com informação de estado
de rede, e preferĂŞncias administrativas. A partilha de conhecimento infraestrutural
Ă© feita para possibilitar um ambiente cooperativo entre redes overlay e underlay, para
uma mais eficiente utilização de recursos e a consequente minimização de custos operacionais.
É pretendido dar uma visão da histórica disputa entre aplicações e ISPs, assim como
apresentar o projeto do grupo de trabalho ALTO como solução, implementar e melhorar sobre as suas ideias, e finalmente verificar a eficiência do sistema numa simulação,
quando comparado com alternativas clássicas
Incentive-driven QoS in peer-to-peer overlays
A well known problem in peer-to-peer overlays is that no single entity has control over the software,
hardware and configuration of peers. Thus, each peer can selfishly adapt its behaviour to maximise its
benefit from the overlay. This thesis is concerned with the modelling and design of incentive mechanisms
for QoS-overlays: resource allocation protocols that provide strategic peers with participation incentives,
while at the same time optimising the performance of the peer-to-peer distribution overlay.
The contributions of this thesis are as follows. First, we present PledgeRoute, a novel contribution
accounting system that can be used, along with a set of reciprocity policies, as an incentive mechanism
to encourage peers to contribute resources even when users are not actively consuming overlay services.
This mechanism uses a decentralised credit network, is resilient to sybil attacks, and allows peers to
achieve time and space deferred contribution reciprocity. Then, we present a novel, QoS-aware resource
allocation model based on Vickrey auctions that uses PledgeRoute as a substrate. It acts as an incentive
mechanism by providing efficient overlay construction, while at the same time allocating increasing
service quality to those peers that contribute more to the network. The model is then applied to lagsensitive
chunk swarming, and some of its properties are explored for different peer delay distributions.
When considering QoS overlays deployed over the best-effort Internet, the quality received by a
client cannot be adjudicated completely to either its serving peer or the intervening network between
them. By drawing parallels between this situation and well-known hidden action situations in microeconomics,
we propose a novel scheme to ensure adherence to advertised QoS levels. We then apply
it to delay-sensitive chunk distribution overlays and present the optimal contract payments required,
along with a method for QoS contract enforcement through reciprocative strategies. We also present a
probabilistic model for application-layer delay as a function of the prevailing network conditions.
Finally, we address the incentives of managed overlays, and the prediction of their behaviour. We
propose two novel models of multihoming managed overlay incentives in which overlays can freely
allocate their traffic flows between different ISPs. One is obtained by optimising an overlay utility
function with desired properties, while the other is designed for data-driven least-squares fitting of the
cross elasticity of demand. This last model is then used to solve for ISP profit maximisation
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