Recent years have seen several earnest initiatives from both academic researchers as well as open source communities to implement and deploy decentralized online social networks (DOSNs). The primary motivations for DOSNs are privacy and autonomy from big brotherly service providers. The promise of decentralization is complete freedom for end-users from any service providers both in terms of keeping privacy about content and communication, and also from any form of censorship. However decentralization introduces many challenges. One of the principal problems is to guarantee availability of data even when the data owner is not online, so that others can access the said data even when a node is offline or down. In this paper, we argue that a pragmatic design needs to explicitly allow for and leverage on system heterogeneity, and provide incentives for the resource rich participants in the system to contribute such resources. To that end we introduce SuperNova - a super-peer based DOSN architecture. While proposing the SuperNova architecture, we envision a dynamic system driven by incentives and reputation, however, investigation of such incentives and reputation, and its effect on determining peer behaviors is a subject for our future study. In this paper we instead investigate the efficacy of a super-peer based system at any time point (a snap-shot of the envisioned dynamic system), that is to say, we try to quantify the performance of SuperNova system given any (fixed) mix of peer population and strategies.
Work on peer-to-peer storage systems date back to the OceanStore @cite_4 initiative to achieve archival storage using end-user resources. More than a decade of P2P storage related research later, we have several hybrid or peer-to-peer storage and backup cloud like services in actual deployment, e.g., Wuala www.wuala.com , where storage task is centrally coordinated, or as academic prototypes such as FriendStore @cite_0 , where storage is carried out at nodes' friends. While allowing for options for sharing and socializing, the original design of such systems is not social networking. At a very high level, other instances of hybrid (central coordination assisted) peer-to-peer virtual community networks include internet telephony service like Skype @cite_19 , P2P massively multiplayer online games and virtual worlds @cite_15 and social peer-to-peer file sharing systems like Tribler @cite_16 . The need and challenges of realizing DOSNs were formalized recently @cite_1 , and since then, there has been a flurry of academic initiatives to realize both complete systems, as well as to surmount individual challenges. A more exhaustive survey of existing DOSN specific research covering various aspects of DOSN designs can be found in @cite_18 .
@cite_18 @cite_4 @cite_1 @cite_0 @cite_19 @cite_15 @cite_16
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Current Online social networks (OSN) are web services run on logically centralized infrastructure. Large OSN sites use content distribution networks and thus distribute some of the load by caching for performance reasons, nevertheless there is a central repository for user and application data. This centralized nature of OSNs has several drawbacks including scalability, privacy, dependence on a provider, need for being online for every transaction, and a lack of locality. There have thus been several efforts toward decentralizing OSNs while retaining the functionalities offered by centralized OSNs. A decentralized online social network (DOSN) is a distributed system for social networking with no or limited dependency on any dedicated central infrastructure. In this chapter we explore the various motivations of a decentralized approach to online social networking, discuss several concrete proposals and types of DOSN as well as challenges and opportunities associated with decentralization. OceanStore is a utility infrastructure designed to span the globe and provide continuous access to persistent information. Since this infrastructure is comprised of untrusted servers, data is protected through redundancy and cryptographic techniques. To improve performance, data is allowed to be cached anywhere, anytime. Additionally, monitoring of usage patterns allows adaptation to regional outages and denial of service attacks; monitoring also enhances performance through pro-active movement of data. A prototype implementation is currently under development. Online Social Networks like Facebook, MySpace, Xing, etc. have become extremely popular. Yet they have some limitations that we want to overcome for a next generation of social networks: privacy concerns and requirements of Internet connectivity, both of which are due to web-based applications on a central site whose owner has access to all data. To overcome these limitations, we envision a paradigm shift from client-server to a peer-to-peer infrastructure coupled with encryption so that users keep control of their data and can use the social network also locally, without Internet access. This shift gives rise to many research questions intersecting networking, security, distributed systems and social network analysis, leading to a better understanding of how technology can support social interactions. This paper is an attempt to identify the core functionalities necessary to build social networking applications and services, and the research challenges in realizing them in a decentralized setting. In the tradition of research-path defining papers in the peer-to-peer community [5, 14], we highlight some challenges and opportunities for peer-to-peer in the era of social networks. We also present our own approach at realizing peer-to-peer social networks. Today, it is common for users to own more than tens of gigabytes of digital pictures, videos, experimental traces, etc. Although many users already back up such data on a cheap second disk, it is desirable to also seek off-site redundancies so that important data can survive threats such as natural disasters and operator mistakes. Commercial online backup service is expensive [1, 11]. An alternative solution is to use a peer-to-peer storage system. However, existing cooperative backup systems are plagued by two long-standing problems [3, 4, 9, 19, 27]: enforcing minimal availability from participating nodes, and ensuring that nodes storing others' backup data will not deny restore service in times of need. We present an approach to support massively multiplayer games on peer-to-peer overlays. Our approach exploits the fact that players in MMGs display locality of interest, and therefore can form self-organizing groups based on their locations in the virtual world. To this end, we have designed scalable mechanisms to distribute the game state to the participating players and to maintain consistency in the face of node failures. The resulting system dynamically scales with the number of online players. It is more flexible and has a lower deployment cost than centralized games servers. We have implemented a simple game we call SimMud, and experimented with up to 4000 players to demonstrate the applicability of this approach. Most current peer-to-peer (P2P) file-sharing systems treat their users as anonymous, unrelated entities, and completely disregard any social relationships between them. However, social phenomena such as friendship and the existence of communities of users with similar tastes or interests may well be exploited in such systems in order to increase their usability and performance. In this paper we present a novel social-based P2P file-sharing paradigm that exploits social phenomena by maintaining social networks and using these in content discovery, content recommendation, and downloading. Based on this paradigm's main concepts such as taste buddies and friends, we have designed and implemented the TRIBLER P2P file-sharing system as a set of extensions to BitTorrent. We present and discuss the design of TRIBLER, and we show evidence that TRIBLER enables fast content discovery and recommendation at a low additional overhead, and a significant improvement in download performance. Copyright © 2007 John Wiley & Sons, Ltd.