Social Relations to Improve Network Resiliency against Failures and Censorships

During the last decade, the Internet have penetrated our life. An increasing number of people relies on the Internet and its applications. Many client/server based Internet services, such as e-commerce (e.g., Amazon) and social networking (e.g., Facebook), are carefully provisioned and managed to deliver high availability. However, in the recent years, there have been situations where country-scale network fraction of Internet users have been disconnected from the rest of the network. In particular, because of national censorships, natural hazards, misconfiguration or DDoS attacks on links, the network is splitted into two or more areas, and consequently, web services/applications may become unavailable to users. This severely undermine the ability of people to communicate and organize, since many of the services used to discover and relay messages to other users (e.g., Twitter, Facebook) were unavailable. For example, because of a censorship, people in the censored area were not able to use microblogging service (i.e., Twitter). However, owing to the news media property of microblogging, under this situation (i.e., governments performing censorship), people are more willing to rely on this service, in order to spread information. Therefore, these web services/applications, need to be carefully provisioned to maintain high availability, against network failures or censorships. This dissertation focuses on improving the network resiliency against the network failures/partitions. More precisely, the contribution of this thesis is twofold: (i) we present our design of a social-aware P2P overlay that is able to provide better connectivity comparing with existing structured P2P overlays, and introduce a bootstrapping method for the proposed overlay; and (ii) based on social-aware overlay, we present two applications that are able to work in different network partition scenario. In particular, we present a decentralized microblogging system, named SAND and a decentralized censorship circumvention system, named SeND. In the first part of this thesis, we focus on solutions to recover the connectivity within a partitioned area. In particular, we present a social aware overlay where users have private communication channels to their social friends, enabling virtual private network communication among social peers (even through NATs and firewalls). We compared the connectivity of social-aware overlay with other structured P2P overlays (i.e., Chord and SPROUT).We carried our an extensive simulation that shows the structured P2P overlays routability is severely hampered by country-scale partition events. The proposed social-based unstructured overlay network provides improved routability while maintaining a smaller number of links. Moreover, we present a bootstrapping method for the proposed social-aware overlay. In particular, our bootstrap method allows nodes to easily join the overlay network, by leveraging close neighbors with public IP addresses. In the second part of this thesis, we present two representative applications based on social-aware overlay. First, we present SAND, a socialaware, network-failure resilient, and decentralized microblogging system. Compared with other decentralized microblogging systems, SAND has the following advantages: (i) SAND is designed for (and hence is able to handle) scenarios where massive correlated failures occur; (ii) the delivery rates of SAND is significantly high (i.e., with SAND-SN, a variant of SAND, peers are able to effectively follow each others updates with 100% delivery rate); and (iii) we evaluated SAND on partitioned networks based on a ground-truth dataset with a real publisher-subscriber distribution. Then, we present SeND, a social network friendship enhanced decentralized system to circumvent censorships. In order to be resilient to current censorship techniques, such as IP address blocking and active probing attacks, with SEnD, users in an uncensored area can act as proxy servers for their social friends in a censored area, allowing them to bypass the censorship. We assessed the effectiveness of SEnD through extensive simulations based on a synthetic dataset, as well as through experiments based on a prototype implementation. We built our synthetic dataset based on parameters obtained from questionnaires administered both inside and outside China (we consider China as a case study of censored area).

Durante l'ultimo decennio, Internet ha penetrato la nostra vita. Un numero crescente di persone che si basa su Internet e le sue applicazioni. Molti servizi internet basati su client / server, come l'e-commerce (ad esempio, Amazon) e il social networking (ad esempio, Facebook), sono accuratamente provisioning e sono riusciti a fornire alta disponibilità. Tuttavia, negli ultimi anni, ci sono state situazioni in cui frazione rete paese scala degli utenti di Internet sono stati scollegati dal resto della rete. In particolare, a causa delle censure nazionali, rischi naturali, errata configurazione o attacchi DDoS sul link, la rete è divisa in due o più aree, e, di conseguenza, i servizi web / applicazioni potrebbe non essere disponibile per gli utenti. Questo potrebbe gravemente compromettere la capacità delle persone di comunicare e organizzare, dal momento che molti dei servizi utilizzati per scoprire e trasmettere messaggi ad altri utenti (ad esempio, Twitter, Facebook) non erano disponibili. Ad esempio, a causa di una censura, persone nella zona censurata non erano in grado di utilizzare il servizio di microblogging (vale a dire, Twitter). Tuttavia, a causa della proprietà notizie dei media di microblogging, nell'ambito di questa situazione (cioè, i governi che svolgono la censura), le persone sono più disposti a fare affidamento su questo servizio, al fine di diffondere informazioni. Pertanto, questi servizi web / applicazioni, devono essere attentamente provisioning per mantenere l'alta disponibilità, contro i guasti di rete o censure. Questa tesi si concentra sul miglioramento della resilienza della rete contro i guasti di rete / partizioni. Più precisamente, il contributo di questa tesi è duplice: (i) Vi presentiamo il nostro progetto di una sovrapposizione socio-consapevoli P2P che è in grado di fornire una migliore connettività a confronto con esistenti strutturato sovrapposizioni P2P, e introdurre un metodo bootstrap per la sovrapposizione proposto; e (ii) basato su overlay sociale consapevole, presentiamo due applicazioni che sono in grado di lavorare in differenti scenari partizione della rete. In particolare, vi presentiamo un sistema di microblogging decentrato, denominato di sabbia e un sistema di censura elusione decentrato, denominato inviare.