316 research outputs found
Robust streaming in delay tolerant networks
Delay Tolerant Networks (DTN) do not provide any end to end connectivity guarantee. Thus, transporting data over such networks is a tough challenge as most of Internet applications assume a form of persistent end to end connection. While research in DTN has mainly addressed the problem of routing in various mobility contexts with the aim to improve bundle delay delivery and data delivery ratio, little attention has been paid to applications. This paper investigates the support of streaming-like applications over DTN. We identify how DTN characteristics impact on the overall performances of these applications and present Tetrys, a transport layer mechanism, which enables robust streaming over DTN. Tetrys is based on an
on the fly coding mechanism able to ensure full reliability without retransmission and fast in-order bundle delivery in comparison to classical erasure coding schemes. We evaluate our Tetrys prototype on real DTN connectivity traces captured from the Rollerblading tour in Paris. Simulations show that on average, Tetrys clearly outperforms all other reliability schemes in terms of bundles delivery service
A packet error recovery scheme for vertical handovers mobility management protocols
Mobile devices are connecting to the Internet through an increasingly heterogeneous network environment. This connectivity via multiple types of wireless networks allows the mobile devices to take advantage of the high speed and the low cost of wireless local area networks and the large coverage of wireless wide area networks. In this context, we propose a new handoff framework for switching seamlessly between the different network technologies by taking advantage of the temporary availability of both the old and the new network technology through the use of an "on the fly" erasure coding method. The goal is to demonstrate that our framework, based on a real implementation of such coding scheme, 1) allows the application to achieve higher goodput rate compared to existing bicasting proposals and other erasure coding schemes;
2) is easy to configure and as a result 3) is a perfect candidate to ensure the reliability of vertical handovers mobility management protocols. In this paper, we present the implementation of such framework and show that our proposal allows to maintain the TCP goodput(with a negligible transmission overhead) while providing in a timely manner a full reliability in challenged conditions
On-the-Fly Coding for Real-Time Applications
Although ironically it does not offer any real-time guarantee, Internet is a popular solution to support multimedia time-constrained applications (e.g. VoIP, Video Conferencing, ...). Following this trend, this paper focuses on the performance of these applications by studying the benefit of using a novel reliability concept which aims at signifi- cantly improving the performance of these time constrained applications over lossy best-effort networks. This reliability mechanism emerged from several recent works from both network and coding theories. Its principle is to integrate feedbacks in an on-the fly coding scheme in order to optimize the trade-off ”packet decoding delay” vs ”throughput”. We present the first evaluations of this mechanism for VoIP and video-conferencing applications for various erasure channels. Compared to classic block-based erasure codes, the results show significant gains in terms of quality observed by the user for both applications
eCMT-SCTP: Improving Performance of Multipath SCTP with Erasure Coding Over Lossy Links
Performance of transport protocols on lossy links is a well-researched topic, however there are only a few proposals making use of the opportunities of erasure coding within the multipath transport protocol context. In this paper, we investigate performance improvements of multipath CMT-SCTP with the novel integration of the on-the-fly erasure code within congestion control and reliability mechanisms. Our contributions include: integration of transport protocol and erasure codes with regards to congestion control; proposal for a variable retransmission delay parameter (aRTX) adjustment; performance evaluation of CMT-SCTP with erasure coding with simulations. We have implemented the explicit congestion notification (ECN) and erasure coding schemes in NS-2, evaluated and demonstrated results of improvement both for application goodput and decline of spurious retransmission. Our results show that we can achieve from 10% to 80% improvements in goodput under lossy network conditions without a significant penalty and minimal overhead due to the encoding-decoding process
A packet error recovery scheme for vertical handovers mobility management protocols
Mobile devices are connecting to the Internet through an increasingly heterogeneous network environment. This connectivity via multiple types of wireless networks allows the mobile devices to take advantage of the high speed and the low cost of wireless local area networks and the large coverage of wireless wide area networks. In this context, we propose a new handoff framework for switching seamlessly between the different network technologies by taking advantage of the temporary availability of both the old and the new network technology through the use of an “on the fly” erasure coding method. The goal is to demonstrate that our framework, based on a real implementation of such coding scheme, 1) allows the application to achieve higher goodput rate compared to existing bicasting proposals and other erasure coding schemes; 2) is easy to configure and as a result 3) is a perfect candidate to ensure the reliability of vertical handovers mobility management protocols. In this paper, we present the implementation of such framework and show that our proposal allows to maintain the TCP goodput (with a negligible transmission overhead) while providing in a timely manner a full reliability in challenged conditions
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Recommendation on the Historic Urban Landscape, the New Urban Agenda and Cultural Landscapes. Looking at concepts and vocabulary
The Recommendation on the Historic Urban Landscape (HUL), adopted in 2011, updates UNESCO\u27s international instruments by emphasizing the links between conservation and sustainable development. It was developed following the boom in conservation issues in urban World Heritage properties or in properties in urban contexts from the 2000s, particularly in historic centers. Its principle is to pursue the proposals made in the 1976 Nairobi Recommendation and other normative instruments concerning heritage conservation by extending it to the concept of territory and landscape while emphasizing the importance of taking people into account and the concept of quality of life. Its originality also lies in the idea of doing away with the opposition between conservation and development and of promoting an integrated approach. HUL is in line with the ideas of the Sustainable Development Goals, which give culture and heritage a crucial transversal role.
The term landscape is to be understood in the geographical sense of the term, as a territory taking into account the interaction of humans with their cultural and natural environment and not only as an aesthetic landscape, even if the concept of visual urban landscape or symbolic landscape is important.
Developed in response to a specific time and context centered on urban conservation issues, HUL does not seem to integrate cultural landscapes. However, by taking into account the notion of a wider setting it can be said that HUL considers cultural landscapes. This is all the more true as over the years, reflection at the international level on the implementation of the HUL approach increasingly takes into account the hinterland, the peri-urban territory of cities and the city and its wider landscape relationship.
Français:
La Recommandation concernant le paysage urbain historique (PUH), adoptée en 2011 vient mettre à jour les instruments internationaux de l’UNESCO en mettant l’accent sur les liens entre conservation et développement durable. Elle a été élaborée suite au boom des problèmes de conservation dans les biens du patrimoine mondial urbains ou dans des biens dans des contextes urbains à partir des années 2000, en particuliers dans les centres historiques
Son principe est de poursuivre les propositions élaborées dans la Recommandation dite de Nairobi de 1976 et autres instruments normatifs concernant la conservation du patrimoine en l’élargissant à la notion de territoire et de paysage tout en accentuant l’importance de la prise en compte des populations et de la notion de qualité de vie. Sont originalité tient aussi dans l’idée d’en finir avec l’opposition entre conservation et développement et de promouvoir une démarche intégrée. PUH s’inscrit dans les idées des Objectifs du Développement Durable qui donne à la culture et au patrimoine un rôle transversal crucial.
Le terme de paysage est à comprendre au sens géographique du terme, comme territoire prenant en compte l’interaction de l’humain avec son environnement culturel et naturel et non pas seulement comme un paysage esthétique, quand bien même la notion de paysage urbain visuel ou symbolique est importante.
Elaborée en réponse à un moment et un contexte précis centrée sur des enjeux de conservation urbaine, PUH semble ne pas intégrer les paysages culturels. Or dans l’esprit de la prise en compte de la notion de territoire élargi on peut affirmer que HUL considère les paysages culturels. Ceci est d’autant plus vrai qu’au fil des ans, la réflexion au niveau internationale, sur la mise en œuvre de l’approche PUH prend en compte de plus en plus le hinterland, le territoire périurbain des villes et la relation ville/territoire.
Español:
La Recomendación sobre el Paisaje Urbano Histórico (PUH), adoptada en 2011, actualiza los instrumentos internacionales de la UNESCO al enfatizar los vínculos entre la conservación y el desarrollo sostenible. Se desarrolló tras el auge de las cuestiones de conservación en los bienes del Patrimonio Mundial urbano o en los bienes en contextos urbanos a partir de la década de 2000, particularmente en los centros históricos. Su principio es dar seguimiento a las propuestas formuladas en la denominada Recomendación de Nairobi del 1976 y otros instrumentos normativos sobre conservación del patrimonio extendiéndolo al concepto de territorio y paisaje al tiempo que enfatiza la importancia de tener en cuenta a las poblaciones. Y el concepto de calidad de vida. Su originalidad radica también en la idea de eliminar la oposición entre conservación y desarrollo y promover un enfoque integrado. PUH está en línea con las ideas de los Objetivos de Desarrollo Sostenible que otorgan a la cultura y el patrimonio un papel transversal crucial.
El término paisaje debe entenderse en el sentido geográfico del término, como un territorio que tiene en cuenta la interacción del ser humano con su entorno cultural y natural y no solo como un paisaje estético, incluso si el concepto de paisaje urbano visual o simbólico es importante. Desarrollado en respuesta a un tiempo y contexto específicos centrados en temas de conservación urbana, PUH no parece integrar paisajes culturales. Sin embargo, con el ánimo de tener en cuenta la noción de territorio ampliado, se puede decir que HUL considera paisajes culturales. Esto es tanto más cierto cuanto que a lo largo de los años, la reflexión a nivel internacional sobre la implementación del enfoque PUH tiene cada vez más en cuenta el hinterland, el territorio periurbano de las ciudades y la relación ciudad / territorio
On the Limit of Fountain MDC Codes for Video Peer-To-Peer Networks
Video streaming for heterogeneous types of devices, where nodes have different devices characteristics in terms of computational capacity and display, is usually handled by encoding the video with different qualities. This is not well suited for Peer-To-Peer (P2P) systems, as a single peer group can only share content of the same quality, thus limiting the peer group size and efficiency. To address this problem, several existing works propose the use of Multiple Descriptions Coding (MDC). The concept of this type of video codec is to split a video in a number of descriptions which can be used on their own, or aggregated to improve the global quality of the video. Unfortunately existing MDC codes are not flexible, as the video is split in a defined number of descriptions. In this paper, we focus on the practical feasibility of using a Fountain MDC code with properties similar to existing Fountain erasure codes, including the ability to create any number of descriptions when needed (on the fly). We perform simulations using selected pictures to assess the feasibility of using these codes, knowing that they should improve the availability of the video pieces in a P2P system and hence the video streaming quality. We observe that, although this idea seems promising, the evaluated benefits, demonstrated by the PSNR values, are limited when used in a real P2P video streaming system
Tetrys : Un mécanisme de fiabilisation polyvalent
Actuellement, une succession d’erreurs qui ne peut être masquée par le mécanisme de fiabilisation (code à effacement) doit attendre au minimum un RTT pour être corrigée, ce qui n’est souvent pas satisfaisant pour les application temps-réel. Les concepts apportés par la théorie du codage réseau (Network Coding) permettent aujourd’hui de combler le fossé entre fiabilisation et fiabilité totale en s'abstrayant du concept d’ARQ. Cet article présente un mécanisme innovant nommé Tetrys dont l’une des caractéristiques est de pouvoir reconstruire les pertes dans un temps paramétrable et indépendant du RTT. A notre meilleure connaissance, c'est la première fois que les propriétés temps réel d'un tel mécanisme sont énoncées et étudiées. Intuitivement, les applications ciblées sont celles nécessitant une fiabilité totale avec contrainte de délai. Il s’avère qu’à taux de redondance égal, des applications telles que la VoIP et la vidéo-conférence sont bien plus performantes lorsque les flux sont protégés par le mécanisme Tetrys que par les mécanismes FEC ou H-ARQ classiques. Après un rapide rappel des points clés relatifs à FEC et H-ARQ, nous décrivons le principe de Tetrys et montrons son possible déploiement. Nous comparons les performances de FEC, H-ARQ et Tetrys du point de vue applicatif à l'aide d’un prototype et suivant des métriques de délai et dans le cadre de la VoIP, de qualité de la transmission (MOS)
When on-the-fly erasure code makes late video decoding happen
In this paper, we proposed the late decoding solution based on Tetrys (called LD-Tetrys) to deal with delay constrained applications. Our analysis showed that LD-Tetrys fits well to the requirements for late video decoding while the other schemes (e.g., FEC, HARQ) do not. We also developed an evaluation framework which is independent of video codec and network topology. Simulation results acknowledge that LD-Tetrys' performance is better than the normal decoding with Tetrys, the original Tetrys. Furthermore, LD-Tetrys consistently outperforms the traditional block based erasure codes such as AL-FEC in terms of video quality. For future work, we are working on the theoretical modeling and analysis. We also expect to perform extensive experiments to obtain a complete evaluation
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