Peer-to-Peer Networks and Computation: Current Trends and Future Perspectives

This research papers examines the state-of-the-art in the area of P2P networks/computation. It attempts to identify the challenges that confront the community of P2P researchers and developers, which need to be addressed before the potential of P2P-based systems, can be effectively realized beyond content distribution and file-sharing applications to build real-world, intelligent and commercial software systems. Future perspectives and some thoughts on the evolution of P2P-based systems are also provided

Optimal Caching Policy of Stochastic Updating Information in Delay Tolerant Networks

To increase the speed of information retrieval, one message may have multiple replicas in Delay Tolerant Networks (DTN). In this paper, we adopt a discrete time model and focus on the caching policy of stochastic updating information. In particular, the source creates new version in every time slot with certain probability. New version is usually more useful than the older one. We use a utility function to denote the availability of different versions. To constrain the number of replicas, we propose a probabilistic management policy and nodes to discard information with certain probability determined by the version of the information. Our objective is to find the best value of the probability to maximize the total utility value. Because new version is created with certain probability, nodes other than the source may not know whether the information stored in them is the latest version. Therefore, they can make decisions only according to the local state and decisions based on the local state can be seen as local-policy. We also explore the global-policy, that is, nodes understand the real state. We prove that the optimal policies in both cases conform to the threshold form. Simulations based on both synthetic and real motion traces show the accuracy of our theoretical model. Surprisingly, numerical results show that local-policy is better than the global-policy in some cases

Data availability in challenging networking environments in presence of failures

This Doctoral thesis presents research on improving data availability in challenging networking environments where failures frequently occur. The thesis discusses the data retrieval and transfer mechanisms in challenging networks such as the Grid and the delay-tolerant networking (DTN). The Grid concept has gained adaptation as a solution to high-performance computing challenges that are faced in international research collaborations. Challenging networking is a novel research area in communications. The first part of the thesis introduces the challenges of data availability in environment where resources are scarce. The focus is especially on the challenges faced in the Grid and in the challenging networking scenarios. A literature overview is given to explain the most important research findings and the state of the standardization work in the field. The experimental part of the thesis consists of eight scientific publications and explains how they contribute to research in the field. Focus in on explaining how data transfer mechanisms have been improved from the application and networking layer points of views. Experimental methods for the Grid scenarios comprise of running a newly developed storage application on the existing research infrastructure. A network simulator is extended for the experimentation with challenging networking mechanisms in a network formed by mobile users. The simulator enables to investigate network behavior with a large number of nodes, and with conditions that are difficult to re-instantiate. As a result, recommendations are given for data retrieval and transfer design for the Grid and mobile networks. These recommendations can guide both system architects and application developers in their work. In the case of the Grid research, the results give first indications on the applicability of the erasure correcting codes for data storage and retrieval with the existing Grid data storage tools. In the case of the challenging networks, the results show how an application-aware communication approach can be used to improve data retrieval and communications. Recommendations are presented to enable efficient transfer and management of data items that are large compared to available resources

Towards Efficient File Sharing and Packet Routing in Mobile Opportunistic Networks

With the increasing popularity of portable digital devices (e.g., smartphones, laptops, and tablets), mobile opportunistic networks (MONs) [40, 90] consisting of portable devices have attracted much attention recently. MONs are also known as pocket switched networks (PSNs) [52]. MONs can be regarded as a special form of mobile ad hoc networks (MANETs) [7] or delay tolerant networks (DTNs) [35, 56]. In such networks, mobile nodes (devices) move continuously and meet opportunistically. Two mobile nodes can communicate with each other only when they are within the communication range of each other in a peer-to-peer (P2P) manner (i.e., without the need of infrastructures). Therefore, such a network structure can potentially provide file sharing or packet routing services among portable devices without the support of network infrastructures. On the other hand, mobile opportunistic networks often experience frequent network partition, and no end-to-end contemporaneous path can be ensured in the network. These distinctive properties make traditional file sharing or packet routing algorithms in Internet or mobile networks a formidable challenge in MONs. In summary, it is essential and important to achieve efficient file sharing and packet routing algorithms in MONs, which are the key for providing practical and novel services and applications over such networks. In this Dissertation, we develop several methods to resolve the aforementioned challenges. Firstly, we propose two methods to enhance file sharing efficiency in MONs by creating replicas and by leveraging social network properties, respectively. In the first method, we investigate how to create file replicas to optimize file availability for file sharing in MONs. We introduce a new concept of resource for file replication, which considers both node storage and meeting frequency with other nodes. We theoretically study the influence of resource allocation on the average file access delay and derive a resource allocation rule to minimize the average file access delay. We also propose a distributed file replication protocol to realize the deduced optimal file replication rule. In the second method, we leverage social network properties to improve the file searching efficiency in MONs. This method groups common-interest nodes that frequently meet with each other into a community. It takes advantage of node mobility by designating stable nodes, which have the most frequent contact with community members, as community coordinators for intra-community file request forwarding, and highly-mobile nodes that visit other communities frequently as community ambassadors for inter-community file request forwarding. Based on such a community structure, an interest-oriented file searching scheme is proposed to first search local community and then search the community that is most likely to contain the requested file, leading to highly efficient file sharing in MONs. Secondly, we propose two methods to realize efficient packet routing among mobile nodes and among different landmarks in MONs, respectively. The first method utilizes distributed social map to route packets to mobile nodes efficiently with a low-cost in MONs. Each node builds its own social map consisting of nodes it has met and their frequently encountered nodes in a distributed manner. Based on both encountering frequency and social closeness of two linked nodes in the social map, we decide the weight of each link to reflect the packet delivery ability between the two nodes. The social map enables more accurate forwarder selection through a broader view and reduces the cost on information exchange. The second method realizes high-throughput packet routing among different landmarks in MONs. It selects popular places that nodes visit frequently as landmarks and divides the entire MON area into sub-areas represented by landmarks. Nodes transiting between two landmarks relay packets between the two landmarks. The frequency of node transits between two landmarks is measured to represent the forwarding capacity between them, based on which routing tables are built on each landmark to guide packet routing. Finally, packets are routed landmark by landmark to reach their destination landmarks. Extensive analysis and real-trace based experiments are conducted to support the designs in this Dissertation and demonstrate the effectiveness of the proposed methods in comparison with the state-of-art methods. In the future, we plan to further enhance the file sharing and packet routing efficiency by considering more realistic scenarios or including more useful information. We will also investigate the security and privacy issues in the proposed methods

Optimal Content Placement in ICN Vehicular Networks

Information Centric Networking (ICN) is a networking framework for content distribution. The communication is based on a request/response model where the attention is centered on the content. The user sends interest messages naming the content it desires and the network chooses the best node from which delivers the content. This way for retrieving contents naturally fits a context where users continuously change their location. One of the main problems of user mobility is the intermittent connectivity that causes loss of packets. This work shows how in a Vehicle-to-Infrastructure scenario, the network can exploit the ICN architecture with content pre-distribution to maximize the probability that the user retrieves the desired content. We give an ILP formulation of the problem of optimally distributing the contents in the network nodes and discuss how the system assumptions impact the success probability. Moreover, we validate our model by means of simulations with ndnSIM