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Leveraging Social Networks for P2P Content-Based File Sharing in Disconnected MANETs

Current peer-to-peer (P2P) file sharing methods in mobile ad hoc networks (MANETs) can be classified into three groups: flooding-based, advertisement-based, and social contact-based. The first two groups of methods can easily have high overhead and low scalability. They are mainly developed for connected MANETs, in which end-to-end connectivity among nodes is ensured. The third group of methods adapts to the opportunistic nature of disconnected MANETs but fails to consider the social interests (i.e., contents) of mobile nodes, which can be exploited to improve the file searching efficiency.

In this paper, we propose a P2P content-based file sharing system, namely SPOON, for disconnected MANETs. The system uses an interest extraction algorithm to derive a node’s interests from its files for content-based file searching. For efficient file searching, SPOON groups common-interest nodes that frequently meet with each other as communities. It takes advantage of node mobility by designating stable nodes, which have the most frequent contact with community members, as community coordinators for intracommunity searching, and highly mobile nodes that visit other communities frequently as community ambassadors for intercommunity searching.

Our proposed for high file searching efficiency. Additional strategies for file prefetching, querying-completion, and loop-prevention, and node churn consideration are discussed to further enhance the file searching efficiency. We first tested our system on the GENI Orbit testbed with a real trace and then conducted event-driven experiment with two real traces and NS2 simulation with simulated disconnected and connected MANET scenarios. The test results show that our system significantly lowers transmission cost and improves file searching success rate compared to current methods.


IN the past few years, personal mobile devices such as laptops, PDAs, and smartphones have been more and more popular. Indeed, the number of smartphone users increased by 118 million across the world in 2007, and is expected to reach around 300 million by 2013. The incredibly rapid growth of mobile users is leading to a promising future, in which they can freely share files

between each other whenever and wherever. Click for more info The number of mobile searching users (through smartphones, feature phones, tablets, etc.) is estimated to reach 901.1 million in 2013. Currently, mobile users interact with each other and share files via an infrastructure formed by geographically distributed base stations. However, users may find themselves in an area without wireless service (e.g., mountain areas and rural areas). Moreover, users may hope to reduce the cost on the expensive infrastructure network data.

The P2P file sharing model makes large-scale networks a blessing instead of a curse, in which nodes share files directly with each other without a centralized server. Wired P2P file sharing systems have already become a popular and successful paradigm for file sharing among millions of users. The successful deployment of P2P file sharing systems and the aforementioned impediments to file sharing in MANETs make the P2P file sharing over MANETs (P2P MANETs in short) a promising complement to current infrastructure model to realize pervasive file sharing for mobile users. As the mobile digital devices are carried by people that usually belong to certain social relationships, in this paper, we focus on the P2P file sharing in a disconnected MANET community consisting of mobile users with social network properties. In such a file sharing system, nodes meet and exchange requests and files in the format of text, short videos, and voice clips in different interest categories. A typical scenario is a course material (e.g., course slides, review sheets, assignments) sharing system in a school campus. Such a scenario ensures for the most that nodes sharing the same interests (i.e., math), carry corresponding files (i.e., math files), and meet regularly (i.e., attending math classes).

In MANETs consisting of digital devices, nodes are constantly moving, forming disconnected MANETs with opportunistic node encountering. Such transient network connections have posed a challenge for the development of P2P MANETs. Traditional methods supporting P2P MANETs are either flooding-based or advertisement-based. The former methods rely on flooding for file searching. However, they lead to high overhead in broadcast. In the latter methods, nodes advertise their available files, build content tables, and forward files according to these tables. But they have low search efficiency because of expired routes in the content tables caused by transient network connections. Continue Reading Also, advertising can lead to high overhead.

Some researchers further proposed to utilize cache/replication to enhance data dissemination/access efficiency in disconnected MANETs. However, nodes in these methods passively wait for contents that they are interested in rather than actively search files, which may lead to a high search delay.

Recently, social networks are exploited to facilitate content dissemination/publishing in disconnected MANETs. These methods exploit below property to improve the efficiency of message forwarding:

  • (P1) nodes (i.e., people) usually exhibit certain movement patterns (e.g., local gathering, diverse centralities, and skewed visiting preferences).

However, these methods are only for the dissemination of information to subscribers. They are not specifically designed for file searching. Also, they fail to take into account other properties of social networks revealed by recent studies to facilitate content sharing:

  • (P2) Users usually have a few file interests that they visit frequently and a user’s file visit pattern follows a power-law distribution.
  • (P3) Users with common interests tend to meet with each other more often than with others. By leveraging these properties of social networks, we propose social network-based P2P cOntent-based file sharing in disconnected mObile ad hoc Networks (SPOON) with four components.

1. Based on P2, we propose an interest extraction algorithm to derive a node’s interests from its files. The interest facilitates queries in content-based file sharing and other components of SPOON.

2. We refer to a collective of nodes that share common interests and meet frequently as a community. Get more projects ideas from the industry experts According to P3, a node has high probability to find interested files in its community. If this fails, based on P1, the node can rely on nodes that frequently travel to other communities for file searching. Thus, we propose the community construction algorithm to build communities to enable efficient file retrieval.

3. According to P1, we propose a node role assignment algorithm that takes advantage of node mobility for efficient file searching. The algorithm designates a stable node that has the tightest connections with others in its community as the community coordinator to guide intracommunity searching. For each known foreign community, a node that frequently travels to it is designated as the community ambassador for intercommunity searching.

4. We propose an interest-oriented file searching and retrieval scheme that utilizes an interest-oriented routing algorithm (IRA) and above three components. Based on P3, IRA selects forwarding node by considering the probability of meeting interest keywords rather than nodes. The file searching scheme has two phases: Intra- and intercommunity searching. In the former, a node first queries nearby nodes, then relies on coordinator to search the entire home community. If it fails, the intercommunity searching uses an ambassador to send the query to a matched foreign community. A discovered file is sent back through the search path or the IRA if the path breaks.

SPOON is novel in that it leverages social network properties of both node interest and movement pattern. First, it classifies common-interest and frequently encountered nodes into social communities. Second, it considers the frequency at which a node meets different interests rather than different nodes in file searching. Third, it chooses stable nodes in a community as coordinators and highly mobile nodes that travel frequently to foreign communities as ambassadors. Such a structure ensures that a query can be forwarded to the community of the queried file quickly. SPOON also incorporates additional strategies for file prefetching, querying-completion and loop-prevention, and node churn consideration to further enhance file searching efficiency.



PUBLICATION:Y. Huang, Y. Gao, K. Nahrstedt, and W. He, Proc. IEEE 29th Int’l Conf. Distributed Computing Systems (ICDCS ’09), 2009.

In WiFi-based content distribution community infrastructure (CDCI), file servers are deployed in diverse locations around cities, caching popular files interesting to a community. They serve file download requests from mobile users in proximity via WiFi. In this paper, we study the optimal caching strategy for file servers in CDCI so that file retrieval probability within deadline is maximized, subject to storage constraint of each file server. The optimal caching strategy depends on many factors, such as users’ mobility patterns, access point topology, file popularity, etc. We have formalized this content management problem as a mixed integer optimization problem. Because of N P-hardness and a large variable space of this optimization problem, we propose a heuristic algorithm MobaSsign to allocate file blocks. Extensive experiments show that our heuristic caching strategy considering mobility patterns improves the file retrieval probability within deadline


PUBLICATION: W. Gao, G. Cao, A. Iyengar, and M. Srivatsa, Proc. 31st Int’l Conf. Distributed Computing Systems (ICDCS ’11), 2011.

Disruption Tolerant Networks (DTNs) are characterized by the low node density, unpredictable node mobility and lack of global network information. Most of current research efforts in DTNs focus on data forwarding, but only limited work has been done on providing effective data access to mobile users. In this paper, we propose a novel approach to support cooperative caching in DTNs, which enables the sharing and coordination of cached data among multiple nodes and reduces data access delay.

Our basic idea is to intentionally cache data at a set of Network Central Locations (NCLs), which can be easily accessed by other nodes in the network. We propose an effective scheme which ensures appropriate NCL selection based on a probabilistic selection metric, and coordinate multiple caching nodes to optimize trade off between data accessibility and caching overhead. Extensive trace-driven simulations show that our scheme significantly improves data access performance compared to existing schemes.


PUBLICATION: J. Reich and A. Chaintreau, Proc. Fifth Int’l Conf. Emerging Networking Experiments and Technologies (CoNEXT ’09), 2009.

Multimedia content dissemination in mobile settings requires significant bandwidth. Centralized infrastructure is often either inadequate or overly expensive to fill the demand. Here, we study an alternative P2P content dissemination scheme for mobile devices (e.g., smart-phones), which leverages local dedicated caches on these devices to opportunistically fulfill user requests. In our model, the allocation of content in the global distributed cache comprising the union of all local caches, determines the pattern of demand fulfillment. By selectively replicating local content at node meetings, the global cache can be driven towards a more efficient allocation.

However, the allocation’s efficiency itself is determined by a previously overlooked factor – the impatience of content requesters. By describing user impatience in the form of any monotonically decreasing delay-utility functions, we show that an optimal allocation can be efficient computed or approximated. As users become increasingly impatient, the optimal allocation varies steadily between uniform and highly-skewed towards popular content. Moreover, in opportunistic environments, the global cache state may be difficult or impossible to obtain, requiring that replication decisions be made using only local knowledge.

We develop a reactive distributed algorithm, Query Counting Replication (QCR) that for any delay-utility function drives the global cache towards the optimal allocation – without use of any explicit estimators or control channel information. We validate our techniques on real-world contact traces, demonstrating the robustness of our analytic results in the face of heterogeneous meeting rates and bursty contacts. We find QCR compares favorably to a variety of heuristic perfect control-channel competitors.