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Content sharing using personal web pages, blogs, or online social networks is a common means for people to maintain contact with their friends, colleagues, and acquaintances. While such means are essential to overcome distances, using infrastructure services for location-based services may not be desirable. In this paper, we analyze a fully distributed variant of an ephemeral content sharing service,...
Nodes in mobile networks are usually unevenly distributed over space. Several dense clusters of nodes are interconnected by a few nodes in sparsely occupied areas. Removing vital nodes along such bridges would partition the network and severely reduce the overall connectivity. Consequently, detecting and protecting those few vital nodes is crucial for keeping the network operational. In order to achieve...
Peer-to-peer systems provide a scalable content distribution environment where each peer contributes with a share of resources in the distributed system. The efficiency of peer-to-peer networks comes from the file segmentation procedure, allowing peers to redistribute small pieces of the original file as soon as they finish downloading them instead of waiting for the complete file download. Moreover,...
Measurements of real-world peer-to-peer systems have shown that up to 80% of the peers are so-called free-riders; they do not contribute any resources to the system but use resources from other peers. Free-riding is commonly considered a problem, yet no quantitative evaluation about its real effects has been performed. In this paper, we present a quantitative evaluation of the effects of free-riding...
First response communication is tackled by several independent research groups. While there are existing prototypes and simulated results, comparison of first response solutions is hardly possible so far. We have built an universal XML based description format to handle all relevant settings and actions typical for first response scenarios. In addition we implemented a user-friendly movement and environment...
The Distributed Tree Construction (DTC) algorithm is designed for optimally efficient multicast tree construction over structured peer-to-peer networks. It achieves this by creating a spanning tree over the peers in the multicast group, using only information available locally on each peer. Furthermore, we show that the tree depth has the same upper bound as a regular DHT lookup which in turn guarantees...
Efficient communication architectures are vital for handling larger scale first response scenarios, and existing mechanisms have several shortcomings due to the heterogeneity of first response groups. In this paper, we consider using peer-to-peer-based communication architectures for first response scenarios. We evaluated different network overlays in environments found in first response -like scenarios...
Opportunistic communication allows humans equipped with mobile devices to exchange information via a wireless link whenever they are nearby. This work examines the performance of a profile-based data dissemination scheme. We use a 2- step simulation approach which combines realistic user mobility traces with synthetic mobility models. We consider different system configurations and evaluate their...
Efficient communication architectures are vital for handling larger scale disaster management, and existing communication mechanisms have several shortcomings due to the heterogeneity of the first response groups. In this paper, we present requirements leading to FRCS, a sandbox environment for simulating all kinds of communication approaches in a first response scenario. Through extensive telephone...
Several research projects pursuing middleware architectures to support pervasive applications on smart phones reveal the importance of careful resource management, lightweight communication protocols, and asynchronous programming.
The population of mobile devices capable of participating in the Internet has increased dramatically in the last few years. To include this population into the Web service world requires support for the most important features, in particular security at the message level. This paper covers our approach to implement XML security specifications on mobile devices that allows efficient single-pass processing...
A fundamental paradigm in peer-to-peer (P2P) content distribution is that of a large community of intermittently-connected nodes that cooperate to share files. Because nodes are intermittently connected, the P2P community must replicate and replace files as a function of their popularity to achieve satisfactory performance. In this paper, we develop an analytical optimization theory for benchmarking...
In this paper we present the unregister attack, a new kind of a denial of service attack on SIP servers. In this attack, the attacker sends a spoofed "unregister" message to a SIP server and cancels the registration of the victim at that server. This prevents the victim user from receiving any calls. We have tested common implementations of SIP servers and show that the unregister attack...
Peer-to-peer content distribution has become extremely popular, thanks to its highly scalable performance. In this paper, we derive a lower bound on the performance of chunk-based peer-to-peer content distribution systems and develop an algorithm that is within 1 round of the lower bound in special cases, and within 1 + log22 (I) rounds in the general case, where I is the number of peers. We consider...
In the wireless world there has been much interest in alternate serialization formats for XML data, mostly driven by the weak capabilities of both devices and networks. However, an alternate serialization format is not easily made compatible with XML security features such as encryption and signing. We consider here ways to integrate an alternate format with security, and present a solution that we...
In this paper, we present a summary of our experiences with mobile middleware research in the four-year Fuego Core project. The presented work focuses on data communication and synchronization. We present three middleware services for data communication and synchronization, namely the messaging, event, and file synchronizer services, and discuss their development and usage. We conclude with an integrated...
Content distribution on the Web is moving from an architecture where objects are placed on a single, designated server to an architecture where objects are replicated on geographically distributed servers and clients transparently access a nearby copy of an object. In this paper we study how the different redirection schemes used in modern content distribution networks affect the user-perceived performance...
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