Unstructured Overlay Networks Research Articles

Social Characteristic-Based Propagation-Efficient PBFT Protocol to Broadcast in Unstructured Overlay Networks

Blockchain allows for secure management of a shared ledger by agreement protocols, where transactions are validated over network without central authorities. Although the agreement protocol has been thoroughly conducted of propagation and consensus researches, mobility of nodes in unstructured overlay networks has not received much attention. Besides, current dynamic propagation schemes waste travel hops and are low of delivery ratio. In this article, we propose a social characteristic-based propagation-efficient protocol NefSBFT to agree on system state plus consensus mechanisms in public blockchains. We devise a propagation technique (travel hops of at least <inline-formula><tex-math notation="LaTeX">$\frac{1}{3}$</tex-math></inline-formula> savings, delivery ratio above 0.93, etc.) for message multicasting when exploiting real nodes’ social characteristics of intermittent connectivity and frequent partitions. This propagation technique is executed in the improved FastBFT to achieve transaction ordering and block verification, thus, no controllable mobility is required during the whole system’s execution. NefSBFT achieves fast propagation, small message complexity and few resource consumption of travel hops and running nodes for complete protocol execution. We analyze NefSBFT’s security against DDOS attack of non-primary failure. The experiments show the performance tradeoff under different parameters, compare the propagation efficiency with Erlay and Flooding, and clarify NefSBFT’s impact on the whole system performance through comparison.

Wide-Scale Internet Disconnection: Impact and Recovery on Social-Based P2P Overlays

In the recent years, there have been situations where wide-scale network fraction of Internet users have been disconnected from the rest of the network, due to natural hazards or national censorships (e.g., a government cuts connectivity to the outside world as a mechanism for suppression of uprisings). Peer-to-peer systems are known to be resilient in the presence of churn and uncorrelated failures. However, their behavior in extreme scenarios, where massive correlated failures occur, is not well-studied. In this paper, we consider nodes within a relatively small geographical region of the network (2.5 percent or fewer Internet users), and study whether users can communicate with their ( $n$ -hop away) social neighbors in a peer-to-peer fashion after network partitions. The contribution of our work is twofold: 1) we study the effect of such partitions on topology and routing of structured and social-based unstructured P2P overlays, including a newly proposed Social-aware overlay; 2) for the overlay with better routability observed from the first step, we propose and evaluate a social-based bootstrapping method for nodes to join the overlay, under the constraints imposed by firewalls and NATs. In our analysis, we consider both real and synthetic datasets of online social networks. The results of our evaluation show that structured P2P overlay routability is severely hampered by wide-scale partition events. In addition, the proposed social-based unstructured overlay network provides improved routability while maintaining a smaller number of links. Furthermore, in the evaluation of bootstrapping, by varying several input parameters, from 90 to 97 percent of nodes in Social-aware overlay could bootstrap and reach their direct-neighbors.

Context-aware RAON middleware for opportunistic network

Application development and deployment on Mobile Ad Hoc Networks (MANET) is a major challenge in the widespread use of MANET. The increasing D2D communication in 5G networks has renewed interest in an effective middleware design for MANET where application developers face various challenges such as unstable connectivity, high error rate, mobility induced disruption and disconnection, and limited battery power. We find that unstructured overlay network provides a good abstraction to facilitate application development and deployment on MANET. In this paper, we present the design of a middleware that builds a Resource-Aware Overlay Network (RAON), which is an unstructured overlay network of nodes engaged in the application that employs a query–reply mechanism for resource discovery. RAON is enhanced with features such as proactive neighbor replacement, congestion-aware data download and cooperative caching. Simulation results show that these features are effective in reducing query delay, improving data availability, and balancing node power consumption with protocol performance. We also present the middleware software design that offers the API based on node and path abstractions to applications. The middleware implements a generic context framework for acquiring device and user context. We discuss the implementation of application-level multicast and credit-based file-sharing applications using the middleware API. The middleware is implemented in Java J2ME on Android, which is tested in an ad hoc network of Nexus 7 devices running OLSR.

A Routing Technique for Query Scheduling and Forwarding in Unstructured Overlay Topology Networks

A Routing Technique for Query Scheduling and Forwarding in Unstructured Overlay Topology Networks

An Approach to Continuous Queries in Unstructured Overlays (Coquos)

The current peer-to-peer (P2P) content distribution systems are running by their simple on-demand content discovery mechanism. The utility of these systems can be improved by incorporating two capabilities, first a mechanism through which peers can register their long term interests with the network so that they can be continuously notified of new data items, and second one is the peers to advertise their contents. Although researchers have proposed a few unstructured overlay-based publish-subscribe systems that provide the above capabilities, most of these systems require complex indexing and routing schemes, which not only make them highly complex but also gives less flexible on propagate the queries around transient peers. This paper argues that for many P2P applications, implementing full-fledged publish-subscribe systems is an complex task. For these applications, we study the alternate continuous query paradigm, which is a best-effort service providing the above two capabilities. we present a scalable and effective middleware, called CoQUOS stands for Continious queries in Unstructured Overlays for supporting continuous queries in unstructured overlay networks. Besides being independent of the overlay topology, CoQUOS preserves the simplicity and flexibility of the unstructured P2P network. Index Terms: Peer-to-peer networks, Continuous queries, Publish-subscribe systems, Random walk. I. Introduction: UNSTRUCTURED peer-to-peer (P2P)-based content/resource sharing platforms such as Gnutella and Kazaa have experienced excellent growths in the past days. The popularity of unstructured P2P networks can be based on the simplicity of their designs and their flexibility towards transient node population. Searching in these networks is essentially performed by circulating query messages in an ad-hoc manner and probing individual peer nodes. The current unstructured P2P content distribution systems suffer from certain serious limitations. One such limitation is their simple-on demand mechanism for content discovery. Peers in these systems discover data items by circulating queries within the overlay network. A peer receiving a query responds back to the initiating node if it has any matching content. Upon processing a query, the recipient node removes it from its local buffers1. Thus, a query expires after it completes its circulation within the network. In other words, the network forgets the queries once they have completed their circulation. For clarity purpose called this as a ad hock query model , and we refer to the queries as ad hoc queries. The ad hoc query model suffers from two main short comings First, an ad hoc query is only capable of searching and retrieving content that exists in the P2P network at the time the query was issued. In this scenario, the only way for a peer to discover newly added data items would be to repeatedly issue the same query. This is not desirable, since it creates unnecessary traffic within the network. Second, P2P systems that are purely based on the ad hoc query -model provide no support for peers to advertise or announce the data items they own to other interested peers. Advertisements are important for P2P applications where peers advertise their content. The above are shortcomings render the ad hoc query model .The many advanced P2P applications suffered from above two drawbacks. For handling the above situation we use a naive approach for tackling this problem would be to send advertisements to large subsets of peers through Flooding. However, this approach is unviable. When heavy messaging overheads, this scheme could gives the peers with unwanted advertisements. To address the above limitations we use well-studied paradigm of publish-subscribe (pub-sub) Systems is a possible approach to address the above limitations. The pub-sub involves intricate indexing and routing mechanisms . To overcome the above problem we present a scalable and effective middleware, called CoQUOS stands for Continious queries in Unstructured Overlays for supporting continuous queries in unstructured overlay. 1.1.) Paper Contributions: The diffculties in implementing pub-sub systems on top of unstructured overlays can be attributed to the inherent mismatch between the design requirements of pub-sub systems and the very nature of unstructured P2P systems. The pub-sub model provides weaker guarantees and individual implementations of may not provide and notification guarantees are weaker due to system failures or churn.

The CoQUOS Approach to Continuous Queries in Unstructured Overlays

The current peer-to-peer (P2P) content distribution systems are constricted by their simple on-demand content discovery mechanism. The utility of these systems can be greatly enhanced by incorporating two capabilities, namely a mechanism through which peers can register their long term interests with the network so that they can be continuously notified of new data items, and a means for the peers to advertise their contents. Although researchers have proposed a few unstructured overlay-based publish-subscribe systems that provide the above capabilities, most of these systems require intricate indexing and routing schemes, which not only make them highly complex but also render the overlay network less flexible toward transient peers. This paper argues that for many P2P applications, implementing full-fledged publish-subscribe systems is an overkill. For these applications, we study the alternate continuous query paradigm, which is a best-effort service providing the above two capabilities. We present a scalable and effective middleware, called CoQUOS, for supporting continuous queries in unstructured overlay networks. Besides being independent of the overlay topology, CoQUOS preserves the simplicity and flexibility of the unstructured P2P network. Our design of the CoQUOS system is characterized by two novel techniques, namely cluster-resilient random walk algorithm for propagating the queries to various regions of the network and dynamic probability-based query registration scheme to ensure that the registrations are well distributed in the overlay. Further, we also develop effective and efficient schemes for providing resilience to the churn of the P2P network and for ensuring a fair distribution of the notification load among the peers. This paper studies the properties of our algorithms through theoretical analysis. We also report series of experiments evaluating the effectiveness and the costs of the proposed schemes.

HASH-BASED OVERLAY PARTITIONING IN UNSTRUCTURED PEER-TO-PEER SYSTEMS

Unstructured peer-to-peer (P2P) networks suffer from the increased volume of traffic produced by flooding. Methods such as random walks or dynamic querying managed to limit the traffic at the cost of reduced network coverage. In this paper, we propose a partitioning method of the unstructured overlay network into a relative small number of distinct subnetworks. The partitioning is driven by the categorization of keywords based on a uniform hash function. The method proposed in this paper is easy to implement and results in significant benefit for the blind flood method. Each search is restricted to a certain partition of the initial overlay network and as a result it is much more targeted. Last but not least, the search accuracy is not sacrificed to the least since all related content is searched. The benefit of the proposed method is demonstrated with extensive simulation results, which show that the overhead for the implementation and maintenance of this system is minimal compared to the resulted benefit in traffic reduction.

Assisted interest-based method for searching shared files in P2P network

Having studied the advantages and disadvantages of some traditional searching methods in structured and unstructured P2P networks, an assisted interest-based searching method was proposed to enhance the search in unstructured P2P overlay networks by registering interests of nodes in structured P2P overlay networks. Experimental results show that this method achieves good performance in success rate and search latency.

Distributed Construction Protocols of Probabilistic Degree-Weighted Peer-to-Peer Overlays

Unstructured overlay networks are widely adopted in large-scale and heterogeneous peer-to-peer (P2P) systems for their scalability and flexibility. A distinct feature of such systems is that they randomly route messages e.g., by flooding or random walk. In such systems, the number of messages and tasks carrying by those messages each peer receives is greatly affected by the number of the peer's incoming links. The objective of this paper is to build controllable degree-weighted networks in which the expected number of incoming links of each peer is proportional to its weight which is a local parameter. In such a network, a peer can control the number of those randomly disseminated messages and tasks it receives by adjust it weight. In addition, in order to bound the construction overhead for highly biased networks, we restrict all peers to have the same number of outgoing links. The objective network is constructed by local topology transformations that peers periodically exchange outgoing links with each other. A framework, which includes 81 different protocols by combination of exchange rules, is presented and evaluated by simulation. The simulation result shows that two of them can generate the networks having similar properties with the objective network. This work first achieves the weight-proportional degree control under the out-regular network model.

Improving the Performance of P2P Content Distribution Systems by Choosing Proper Content Providers

Searching mechanisms employed in unstructured overlay networks typically hit multiple peers for the desired content. We propose the use of a simple method that raises the hit rates of unpopular contents and balances the loads by choosing the peer holding the least contents as the provider when multiple candidates exist.

Reverse-query diffusion over unstructured overlay network for content delivery

When a P2P client requests content it is difficult to diffuse its broadcast without causing a query explosion. By applying percolation theory to diffuse newly defined reverse-query messages over the unstructured P2P network, we propose a novel information delivery network architecture built over the existing unstructured P2P network. We analysed our algorithm and examine the validity of our model, which will cover more than 80% of all the clients, by relaying reverse-query messages under a probability as low as 10%. It is proven to be effective in reducing the total traffic generated by query propagation drastically. This architecture can be applied to building content sharing networks over the unstructured overlay network.

Peer-to-peer applications beyond file sharing: overlay network requirements and solutions

In this paper we analyze the functional and non-functional requirements of peer-to-peer (P2P) systems that go beyond the needs of the well explored file-sharing P2P systems. Four basic subcategories are suggested to classify the non-functional requirements: adaptability, efficiency, validity and trust. Similarly, the functional requirements are divided into user-triggered and system-triggered functions. Then, we present and discuss several existing solutions following different design approaches in order to reveal their suitability for different types of P2P applications. More particularly, we capture the characteristics of structured and unstructured overlay networks. For the structured solutions, we investigate distributed hash tables and lexicographic graph based solutions. For the unstructured approaches, we discuss both hierarchical and non-hierarchical overlay networks and emphasize on small-world and power-law networks. Finally, we provide a set of demanding application classes such as voice over IP and massive multiplayer online games that may be benefited by utilizing the P2P technology.

Structuring topologically aware overlay networks using domain names

Overlay networks are application layer systems which facilitate users in performing distributed functions such as searches over the contents of other users. An important problem in such networks is that the connections among peers are arbitrary, leading in that way to a topology structure, which does not match the underlying physical topology. This topology mismatch leads to large user experienced delays, degraded performance and excessive resource consumption in Wide Area Networks. In this work we propose and evaluate the Distributed Domain Name Order (DDNO) technique, which makes unstructured overlay networks topologically aware. In DDNO, a node devotes half of its connections to nodes that share the same domain-name and the remaining half connections to random nodes. The former connections achieve good performance, because the bulk of the overlay traffic is kept within the same domain, while the latter connections ensure that the topology structure remains connected. Discovery of nodes in the same domain is achieved through on-demand lookup messages, which are guided by local ZoneCaches. Our technique is entirely decentralized making it appropriate for use in Wide Area Networks. Our simulation results, which are based on a real dataset of Internet latencies, indicate that DDNO outperforms other proposed techniques and that it optimizes many desirable properties such as end-to-end delays, connectivity and diameter.

Consistency maintenance in dynamic peer-to-peer overlay networks

In this paper, we present techniques to maintain temporal consistency of replicated objects in data-centric peer-to-peer overlay applications. We consider both structured and unstructured overlay networks, represented by Chord and Gnutella, respectively, and present techniques for maintaining consistency of replicated data objects in the presence of dynamic joins and leaves. We present extensions to the Chord and Gnutella protocol to incorporate our consistency techniques and implement our extensions to Gnutella into a Gtk-Gnutella prototype. An experimental evaluation of our techniques shows that: (i) a push-based approach achieves near-perfect fidelity in a stable overlay network, (ii) a hybrid approach based on push and pull achieves high fidelity in highly dynamic overlay networks and (iii) the run-time overheads of our techniques are small, making them a practical choice for overlay networks.