2 P2P or Not 2 P2P?

In the hope of stimulating discussion, we present a heuristic decision tree that designers can use to judge the likely suitability of a P2P architecture for their applications. It is based on the characteristics of a wide range of P2P systems from the literature, both proposed and deployed.Comment: 6 pages, 1 figur

Self-Healing Protocols for Connectivity Maintenance in Unstructured Overlays

In this paper, we discuss on the use of self-organizing protocols to improve the reliability of dynamic Peer-to-Peer (P2P) overlay networks. Two similar approaches are studied, which are based on local knowledge of the nodes' 2nd neighborhood. The first scheme is a simple protocol requiring interactions among nodes and their direct neighbors. The second scheme adds a check on the Edge Clustering Coefficient (ECC), a local measure that allows determining edges connecting different clusters in the network. The performed simulation assessment evaluates these protocols over uniform networks, clustered networks and scale-free networks. Different failure modes are considered. Results demonstrate the effectiveness of the proposal.Comment: The paper has been accepted to the journal Peer-to-Peer Networking and Applications. The final publication is available at Springer via http://dx.doi.org/10.1007/s12083-015-0384-

A Highly Robust P2P-CDN Under Large-Scale and Dynamic Participation

International audienceBy building a P2P Content Distribution Network (CDN), peers collaborate to distribute the content of under-provisioned websites and to serve queries for larger audiences on behalf of the websites. This can reveal very challenging, given the highly dynamic and autonomous participation of peers. Indeed, the P2P-CDN should adapt to increasing numbers of participants and provide robust algorithms under churn because these issues have a key impact on performance. Also, the distribution of tasks and content over peers should take into account their interests in order to give them proper incentives to cooperate. Finally, the routing of queries should aim peers close in locality and serve content from close-by providers to reduce network overload and achieve scalability. We have previously proposed a locality and interest-aware P2P-CDN, Flower-CDN, that lacks efficient management of robustness and scalability. In this paper, we focus on these crucial shortcomings and propose PetalUp-CDN. The performance evaluation with respect to scalability and churn shows highly significant gains

Leveraging P2P overlays for Large-scale and Highly Robust Content Distribution and Search

International audienceIn the last decade, there has been a tendency of shifting content distribution towards peer-to-peer (P2P) technology. The reason behind this is the self-scalability of P2P systems provided by the principles of communal collaboration and resource sharing in P2P systems. By building a P2P Content Distribution Network}(CDN), peers collaborate to distribute the content of under-provisioned websites and to serve queries for large audiences on behalf of the websites. When designing a P2P CDN, the main challenge is to actually maintain an acceptable level of performance in terms of client-perceived latency and hit ratio while minimizing the incurred overhead. This is not a straightforward endeavor given that the P2P CDN relies on autonomous and dynamic peers rather than a dedicated infrastructure. Indeed, the distribution of duties and content over peers should take into account their interests in order to give them proper incentives to cooperate. Moreover, the P2P-CDN should adapt to increasing numbers of participants and provide robust algorithms under high levels of churn because these issues have a key impact on performance. Finally, the routing of queries should aim peers close in locality and serve content from close-by providers to achieve short latencies. This paper gives an overview of our contributions in designing and maintaining a P2P CDN that tackles the issues identified above. First, we present Flower-CDN, a P2P content distribution network (CDN) that tackles some of these issues. Peers store only content of websites they are interested in and serve them to others. Furthermore, peers can find close-by content providers by a locality aware P2P directory structure. Secondly, we present a highly scalable approach of Flower-CDN called PetalUp-CDN which dynamically adjusts the directory structure in order to avoid overload situations and to keep the index information any peer must maintain at an acceptable level. Thirdly, we discuss maintenance protocols for Flower-CDN and PetalUp-CDN to cope with the worst scenarios of churn. The performance evaluation wrt. scalability and churn management shows that our generic approach enhances hit ratio by 40% and reduces response time by a factor of 12, compared to a well-known P2P-CDN

APRE: A Replication Method for Unstructured P2P Networks

We present APRE, a replication method for structureless Peer-to-Peer overlays. The goal of our method is to achieve real-time replication of even the most sparsely located content relative to demand. APRE adaptively expands or contracts the replica set of an object in order to improve the sharing process and achieve a low load distribution among the providers. To achieve that, it utilizes search knowledge to identify possible replication targets inside query-intensive areas of the overlay. We present detailed simulation results where APRE exhibits both efficiency and robustness relative to the number of requesters and the respective request rates. The scheme proves particularly useful in the event of flash crowds, managing to quickly adapt to sudden surges in load

DotSlash: A Scalable and Efficient Rescue System for Handling Web Hotspots

This paper describes DotSlash, a scalable and efficient rescue system for handling web hotspots. DotSlash allows different web sites to form a mutual-aid community, and use spare capacity in the community to relieve web hotspots experienced by any individual site. As a rescue system, DotSlash intervenes when a web site becomes heavily loaded, and is phased out once the workload returns to normal. It aims to complement existing web server infrastructure such as CDNs to handle short-term load spikes effectively, but is not intended to support a request load constantly higher than a web site's planned capacity. DotSlash is scalable, cost-effective, easy to use, self-configuring, and transparent to clients. It targets small web sites, although large web site can also benefit from it. We have implemented a prototype of DotSlash on top of Apache. Experiments show that DotSlash can provide an order of magnitude improvement for a web server in terms of the request rate supported and the data rate delivered to clients even if only HTTP redirect is used. Parts of this work may be applicable to other services such as the Grid computational services and media streaming

Hajautettu sisällönjakelu videonjakopalvelussa

Ihmisten käyttäytyminen internetissä voi määräytyä hyvin sattumanvaraisesti. Esimerkiksi sosiaalisen median kautta uudet ja kiinnostavat asiat voivat levitä hyvinkin nopeasti usealle eri ihmiselle. Jos sisällönjakaja ei ole varautunut, tai pystynyt varautumaan esimerkiksi rahallisista syistä, piikkeihin kysynnässä, niin odottamaton kiinnostus voi vaikuttaa palvelun laatuun tai jopa estää palvelun kokonaan. Esimerkkinä tilanteesta, jossa sisällön jakaja ei pysty täysin varautumaan äkkinäiseen resurssitarpeeseen, otetaan pieni videonjakopalvelu. Palvelua käyttää pieni vakiokäyttäjien joukko, jonka palveluun tarvittavan resurssimäärän yksittäinen palvelin pystyy hyvin tarjoamaan. Jos tällaisessa tilanteessa yksittäinen video menee viraaliksi sosiaalisessa mediassa ja käyttäjäkunta nousee hetkellisesti siihenastisesta maksimaalisesta ruuhkahuipusta 10-1000 -kertaiseksi, voi palvelin kaatua kokonaan tai ainakaan se ei pysty tarjoamaan ainoallekaan käyttäjälle palvelua. Jopa perinteinen sisällönjakeluverkko (CDN, content distribution network) auttaa huonosti tilanteeseen, jossa syntynyt salamajoukko (flash crowd) on vahvasti paikkaan sidottu ilmiö. Sisällönjakeluverkossa tieto jakaantuu kyllä suuremmalle maantieteelliselle alueelle kuin vain yksittäiseen keskuskoneeseen, mutta kun tarvitaan paljon kapasiteettia pienemmässä, vahvasti lokaalissa, paikallisessa osassa ei sisällönjakeluverkko olekaan enää paras ratkaisu ongelmaan. Tässä pro gradu -tutkielmassa keskitytään tutkimaan miten hyvin rajatuilla resursseilla varustettu palveluntarjoaja pystyisi rakentamaan suorituskykyisen videonjakopalvelun hajautetulla sisällönjakelulla. Samalla varmistetaan, että mahdollisen salamajoukon aiheuttaman käyttäjäpiikin aiheuttama ongelma ei johda palvelun kaatumiseen. Ratkaisuvaihtoehdoissa keskitytään käyttäjille hajautettuun ratkaisuun, koska palvelinkapasiteettia nimenomaan ei haluta lisätä. Jos pienemmillä resursseilla varustetut yksityishenkilöt voisivat ylläpitää omia palveluitaan halvalla ratkaisulla, saavutettaisiin monia etuja. Näitä etuja ovat muun muassa mahdollisen sensuurin väheneminen, yksityisyyden suoja, kilpailun mahdollistaminen, sopeutumiskyky ja virheiden sietokyky