These papers are made available as a means to ensure timely dissemination of scholarly and technical work
on a non-commercial basis. Copyright and all rights therein are maintained by the authors or by other copyright holders,
notwithstanding that they have offered their works here electronically. It is understood that all persons copying
this information will adhere to the terms and constraints invoked by each author's copyright. These works may not
be reposted without the explicit permission of the copyright holder.
RConf (PD): Automated resource configuration of complex services in the cloud,
Prasad S Abhinandan, David Koll, Jesus Omana Iglesias, Jordi Arjona Aroca, Volker Hilt, Xiaoming Fu, Future Generation Computer Systems (in press), https://doi.org/10.1016/j.future.2018.02.027,
Elsevier, February 2018.
Optimal deployment of complex services in a virtualized environment is still an open problem. These services typically consist of a set of connected components, and each component may consist of multiple instances. Each instance can in turn be run in different virtual flavors, while the service constructed by the combination of these instances must satisfy a customer Service Level Objective (SLO).
The Good Left Undone: Advances and Challenges in Decentralizing Online Social Networks,
David Koll, Jun Li, Xiaoming Fu, Computer Communications, 108: 36-51,
Elsevier, August 2017.
Billions of users are now inter-connected in Online Social Networks (OSNs) and, as they interact with each other, massive amounts of potentially private data are collected at the OSN providers’ (e.g., Facebook or Twitter) premises. Unfortunately, provider-initiated privacy violations on this data are frequent and there is little chance that the providers will grant users effective data-protection means. To address these issues and to help users regain the control over their data, decentralized OSNs (DOSNs) have lately been introduced as a competitive paradigm to provider-controlled, centralized OSNs. DOSNs are built to function without the participation of a provider and with the intent to prevent any misuse of private user data. However, all proposed DOSNs still lack widespread adoption. While challenging the market-leading OSNs is difficult for many reasons, in this paper, we set out to understand the technical deficiencies behind the absence of a successful DOSN. We focus on the major technical challenge of DOSNs: they need to substitute the datacenter-based infrastructure of centralized OSNs. We first review recent advances in decentralizing OSNs based on how they approach that challenge. In a next step, we analyze the advantages and disadvantages each approach yields, and then derive a series of challenges that a successful DOSN will have to fulfill. Finally, we discuss options of moving forward in designing a new DOSN that could be successful in doing so.
PDF [3939.9 kB]
Gavel: Software-defined Network Control with Graph Databases,
Osamah Barakat, David Koll, Xiaoming Fu, 20th Conference on Innovations in Cloud, Internet and Networks (ICIN 2017), Paris, France,
IEEE, March 2017.
Writing network policies for Software Defined Networks (SDNs) is not a straightforward task. Abstractions play a major role in easing this task, but they are typically provided for a particular use case. As a consequence, emerging applications will require the development and implementation of new abstractions, and combining the policies of different such abstractions becomes difficult. To offer a simpler model, plain data representations of the network and its control infrastructure have been proposed recently to offer programmable ad-hoc abstractions to administrators. However, these representations still induce unnecessary complexity and are additionally inferior to using function-specific abstractions from a performance point-of-view. In this work, we propose Gavel, an SDN controller based on a graph database. By exploiting the native graph support of the database engine, Gavel significantly eases application and policy writing. Additionally, we show by experimental evaluation of several typical applications that Gavel can significantly increase the performance when compared with previous works.
PDF [450.4 kB]
Gavel: Towards a Graph Database Defined Network,
Osamah Barakat, David Koll, Xiaoming Fu, Proceedings of IEEE International Conference on Network Protocols, poster session, Singapore,
IEEE, November 2016.
SOUP: An Online Social Network By The People, For The People,
David Koll, Jun Li, Xiaoming Fu, Proc. of 15th Annual ACM/IFIP/USENIX Middleware Conference (Middleware 2014), Bordeaux, France,
Concomitant with the tremendous growth of online social networking (OSN) platforms are increasing concerns from
users about their privacy and the protection of their data.
As user data management is usually centralized, OSN providers nowadays have the unprecedented privilege to access
every user's private data, which makes large-scale privacy
leakage at a single site possible. One way to address this
issue is to decentralize user data management and replicate
user data at individual end-user machines across the OSN.
However, such an approach must address new challenges.
In particular, it must achieve high availability of the data
of every user with minimal replication overhead and with-
out assuming any permanent online storage. At the same
time, it needs to provide mechanisms for encrypting user
data, controlling access to the data, and synchronizing the
replicas. Moreover, it has to scale with large social networks
and be resilient and adaptive in handling both high churn
of regular participants and attacks from malicious users.
While recent works in this direction only show limited
success, we introduce a new, decentralized OSN called the
Self-Organized Universe of People (SOUP). SOUP employs
a scalable, robust and secure mirror selection design and
can eectively distribute and manage encrypted user data
replicas throughout the OSN. An extensive evaluation by
simulation and a real-world deployment shows that SOUP addresses all aforementioned challenges.
PDF [1009.0 kB]
SOUP: An Online Social Network By The People, For The People,
David Koll, Xiaoming Fu, Jun Li, ACM SIGCOMM 2014, demo session, Chicago, IL,
On the State of OSN-based Sybil Defenses,
David Koll, Jun Li, Joshua Stein, Xiaoming Fu, IFIP Networking 2014, Trondheim, Norway,
IEEE, June 2014.
A Sybil attack can inject many forged identities (called Sybils) to subvert a target system. Because of the severe damage that Sybil attacks can cause to a wide range of networking applications, there has been a proliferation of Sybil defense schemes. Of particular attention are those that explore the online social networks (OSNs) of users in a victim system in different ways. Unfortunately, while effective Sybil defense solutions are urgently needed, it is unclear how effective these OSN-based solutions are under different contexts. For example, all current approaches have focused on a common, classical scenario where it is difficult for an attacker to link Sybils with honest users and create attack edges; however, researchers have found recently that a modern scenario also becomes typical where an attacker can employ simple strategies to obtain many attack edges. In this work we analyze the state of OSN-based Sybil defenses. Our objective is not to design yet another solution, but rather to thoroughly analyze, measure, and compare how well or inadequate the well-known existing OSN-based approaches perform under both the classical scenario and the modern scenario. Although these approaches mostly perform well under the classical scenario, we find that under the modern scenario they are vulnerable to attackers. As shown in our quantitative analysis, very often a Sybil only needs a handful of attack edges to disguise itself as a benign node, and there is only a limited success in tolerating Sybils. Our study further points to capabilities a new solution must posses; in particular, in defense against Sybils under the modern scenario, we anticipate a new approach that enriches the structure of a social graph with more information about the relations between its users can work more effectively.
PDF [466.4 kB]
On the Effectiveness of Sybil Defenses Based on Online Social Networks,
David Koll, Jun Li, Joshua Stein, and Xiaoming Fu, Proceedings of IEEE ICNP 2013 (poster session),
IEEE, October 2013.
GEMSTONE: Empowering Decentralized Social Networking with High Data Availability,
Florian Tegeler, David Koll, and Xiaoming Fu, IEEE GLOBECOM 2011 - Selected Areas in Communications Symposium - Social Networks Track, Houston, TX, USA,
IEEE, December 2011.
Social networking platforms such as Facebook, MySpace, Twitter, and many others have seen an enormous increase in user population and user provided information. However, users are increasingly concerned about identity and data privacy since information is aggregated at single companies. To address this issue researchers have been investigating alternative solutions, where the users’ data such as profile information, comments and messages is stored at user-controlled nodes. Although these solutions provide a plausible means for avoiding privacy leaking in central instances, they raise a new challenge to design a cost-effective storage replica scheme which ensures a high data availability even when some users are offline. In this paper we present Gemstone, a social network platform, where the data replication scheme leverages a learning mechanism based on social relationships, online patterns of peers and user experiences. Our preliminary evaluation shows that compared to related works, it achieves higher data availability while only requiring a smaller number of data replicas.
PDF [434.9 kB]
Development of a Mobile Social Networking Platform supporting Decentralized Data Storage optimized by Social Trust,
David Koll, , master thesis, Center of Computational Sciences, ISSN 1612-6793, No. ZFI-MSC-2010-01, University of Goettingen, Germany,