The multifaceted utilization of mobile computing devices, including smart phones, PDAs, tablet computers with increasing functionalities and the advances in wireless technologies, has fueled the utilization of collaborative computing (peer-to-peer) technique in mobile environment. Mobile collaborative computing, known as mobile peer-to-peer (MP2P), can provide an economic way of data access among users of diversified applications in our daily life (exchanging traffic condition in a busy high way, sharing price-sensitive financial information, getting the most-recent news), in national security (exchanging information and collaborating to uproot a terror network, communicating in a hostile battle field) and in natural catastrophe (seamless rescue operation in a collapsed and disaster torn area). Nonetheless, data/content dissemination among the mobile devices is the fundamental building block for all the applications in this paradigm. The objective of this research is to propose a data dissemination scheme for mobile distributed systems using an MP2P technique, which maximizes the number of required objects distributed among users and minimizes to object acquisition time. In specific, we introduce a new paradigm of information dissemination in MP2P networks. To accommodate mobility and bandwidth constraints, objects are segmented into smaller pieces for efficient information exchange. Since it is difficult for a node to know the content of every other node in the network, we propose a novel Spatial-Popularity based Information Diffusion (SPID) scheme that determines urgency of contents based on the spatial demand of mobile users and disseminates content accordingly. The segmentation policy and the dissemination scheme can reduce content acquisition time for each node. Further, to facilitate efficient scheduling of information transmission from every node in the wireless mobile networks, we modify and apply the distributed maximal independent set (MIS) algorithm. We also consider neighbor overlap for closely located mobile stations to reduce duplicate transmission to common neighbors. Different parameters in the system such as node density, scheduling among neighboring nodes, mobility pattern, and node speed have a tremendous impact on data diffusion in an MP2P environment. We have developed analytical models for our proposed scheme for object diffusion time/delay in a wireless mobile network to apprehend the interrelationship among these different parameters. In specific, we present the analytical model of object propagation in mobile networks as a function of node densities, radio range, and node speed. In the analysis, we calculate the probabilities of transmitting a single object from one node to multiple nodes using the epidemic model of spread of disease. We also incorporate the impact of node mobility, radio range, and node density in the networks into the analysis. Utilizing these transition probabilities, we construct an analytical model based on the Markov process to estimate the expected delay for diffusing an object to the entire network both for single object and multiple object scenarios. We then calculate the transmission probabilities of multiple objects among the nodes in wireless mobile networks considering network dynamics. Through extensive simulations, we demonstrate that the proposed scheme is efficient for data diffusion in mobile networks.

In this paper, we propose two schemes for layer allocations to adjust the number of layers of SVC (Scalable Video Coding) segments according to the bandwidth variation in P2P video streaming networks. The first scheme is Periodical Layer Allocation (PLA) that can adjust the number of layers to fully satisfy the available bandwidth measured periodically. However, when the available bandwidth is changed abruptly, two major drawbacks may be occurred by PLA algorithm; first, the quality of video frames may become unsmooth so that users would feel uncomfortable about the picture quality, and second, the cost is increased due to the periodical measurement of the available bandwidth. Therefore, we propose Dynamic Layer Allocation (DLA), to dynamically change the time interval for adjusting SVC layers. When freeze-up occurred or when there was not enough buffer space to store the video segments during the interval, the interval would be reduced. When the interval for adjusting SVC layers was expired, available bandwidth can be determined by the number of video segments waiting in the buffer. Compared with PLA, DLA adjusts the SVC layers gracefully so that the quality of picture becomes smoother and users feel more comfortable while watching the film. We built a simulator written in C++ under two scenarios: the available bandwidth is changed abruptly and the one changed gradually. Simulation results show that the performance of PLA is quite similar to DLA when the available bandwidth is changed gradually. However, when the available bandwidth is changed abruptly, DLA can not only obtain the smoother video film but also decrease the freeze-up time significantly.

Despite recommender systems being useful, for some applications it is hard to accumulate all the required information needed for the recommendation. In today‟s ubiquitous environment, mobile devices with different characteristics are widely available. Our work focuses on the recommendation service built on mobile environment to support tourists‟ traveling need. When tourists visit a new attraction, their recommender systems can exchange data with the attraction system to help obtain rating information of people with similar tastes. Such asynchronous rating exchange mechanisms allow a tourist to receive ratings from other people even though they may not collocate at the same time. We proposed four data exchange methods between a user and an attraction system. Our recommendation mechanism incorporates other users‟ opinions to provide recommendations once the user has collected enough ratings. Every method is compared under four conditions which attraction systems carry different amount of existing data. Then we compare these methods under different amount of existing rating data and shed the light on their advantages and disadvantages. Finally, we compare our proposed asynchronous methods with other synchronous data exchange methods proposed previously.

In recent years, digital watermarking technique has become the most useful method for protecting the ownership of a user's digital content, and it can be used to verify ownership by embedding a user's digital watermark into that digital content. By showing the watermark, someone can prove legal ownership of the intelligent property on the digital content. Because of the maturity of e-commerce on the Internet, users can purchase digital content through buyer-seller watermarking protocols, and these protocols can help users to embed their watermarks into their digital content. After the transaction is terminated, users can also obtain their own digital content with the desired watermark embedded. However, when users attempt to exchange their digital content with each other over a network, it is important that a secure and efficient method be used. If users directly execute one of the above buyer-seller watermarking protocols, they will find that it cannot achieve significant transfers of digital content. On the other hand, they cannot be guaranteed that the transaction will be fair and efficient. Besides, when users are located on different networks, it is important to understand how they can obtain a protocol that is fair and efficient. To address these problems, we propose efficient and fair digital content exchange protocols for different networks such as Ethernets, P2P networks and cloud networks. Our proposed protocols can achieve identity authentication before performing the digital content exchange protocol, and can also maintain fair transactions between users. Finally, we also provide the formal security proofs for the proposed protocols and properties comparisons with other related schemes. Moreover, our protocols also offer solutions that are suitable for users who are located on different networks, and guarantee that digital content exchange transactions will be performed fairly and efficiently.

In the future, more data intensive applications, such as P2P auction networks, P2P job--search networks, P2P multi--player games, will require the capability to respond to more complex queries such as the nearest neighbor queries involving numerous data types. For the problem of answering nearest neighbor queries (NN query) for spatial region data in the P2P environment, a quadtree-based structure probably is a good choice. However, the quadtree stores the data in the leaf nodes, resulting in the load unbalance and expensive cost of any query. The MX--CIF quadtree can solve this problem. The MX--CIF quadtree has three properties: controlling efficiently the height of the tree, reducing load unbalance, and reducing the NNquery scope with controlling the value of the radius. Although the P2P MX--CIF quadtree can do the NN query efficiently, it still has some problems as follows: low accuracy of the nearest neighbor query, the expensive cost of the tree construction, the high search cost of the NN query, and load unbalance. In fact, the index structures for the region data can also work for the point data which can be considered as the degenerated case of the region data. Therefore, the KDB--tree which is a well-known algorithm for the point data can be used to reduce load unbalance, but it has the same problem as the quadtree. The data is stored only in the leaf nodes of the KDB--tree. In this thesis, we propose an Adjustable KDB--tree (AKDB--tree) to improve this situation for the P2P system. The AKDB--tree has five properties: reducing load unbalance, low cost of the tree construction, storing the data in the internal nodes and leaf nodes, high accuracy and low search cost of the NN query. The Chord system is a well--known structured P2P system in which the data search is performed by a hash function, instead of flooding used in most of the unstructured P2P system. Since the Chord system is a hash approach, it is easy to deal with peers joining/exiting. Besides, in order to combine AKDB--tree with the Chord system, we design the IDs of the nodes in the AKDB--tree. Each node is hashed to the Chord system by the ID. The IDs can be used to differentiate the edge node in the AKDB-tree is a vertical edge or a horizontal edge and the relative position of two nodes in the 2D space. And, we can calculate the related edge of a region in the 2D space according to the ID of the region. As discussed above, we make use of the property of IDs to reduce the search cost of the NN query by a wide margin. In our simulation study, we compare our method with the P2P MX--CIF quadtree by considering five performance measures under four different situations of the P2P MX--CIF quadtree. From our simulation results, for the NN query, our AKDB-tree can provide the higher accuracy and lower search cost than the P2P MX--CIF quadtree. For the problem of load, our AKDB-tree is more balance than the P2P MX--CIF quadtree. For the time of the tree construction, our AKDB-tree needs shorter time than the P2P MX--CIF quadtree.

¡@¡@Recommendation techniques are developed to uncover users¡¥ real needs among large volume of information. Recommender systems help us filter information and present those similar to our tastes. As wireless technology develops and mobile devices become more and more powerful, new recommender systems appear to adapt to new implementation environment. We focus on travel recommender systems implemented in a mobile P2P environment using collaborative filtering recommendation algorithms which intend to provide real-time suggestions to travelers when they are on the move. Using the concept of incorporating other travelers¡¥ suggestions to the next attraction, we let users exchange their ratings toward visited attractions and use these ratings as a basis of recommendation. ¡@¡@We proposed six data exchange algorithms for travelers to exchange their ratings. The proposed methods were experimented in the homogeneous and heterogeneous environment. The experimental results show that the proposed data exchange methods have better recommendation hit ratio than content-based recommendation methods and better performance compared with other methods only using ratings of users when they meet face-to-face. Finally, all methods are compared and evaluated. An optimal method should be able to strike a balance between algorithm performance and the amount of data communication.

<p>Existing VoD solutions often rely on unicast to distribute content, which leads to a higher load on the VoD server as more nodes become interested in the content. In such case, P2P is an alternative way of distributing content since it makes better use of available resources in the network. In this report, several P2P structures are evaluated from an operators point of view. We believe BitTorrent is the most adequate protocol for a P2P solution in IPTV environments. Two BitTorrent clients have been implemented on an IP-STB as proof of concept to find out whether P2P is suited for IPTV environments. Several tests were conducted to evaluate the performance of both clients and to see if they were able to reach a sufficient throughput on the IP-STB. Based upon the tests and the overall impressions, we are convinced that this particular P2P protocol is well suited for IPTV environments. Hopefully, a client developed from scratch for the IP-STB will offer even greater characteristics.</p><p>Further, we have studied how to share recorded content among IP-STBs. Such a design would probably have many similarities to BitTorrent since a central node needs to keep track of content; the IP-STBs take care of the rest.</p><p>The report also brings up whether BitTorrent is suitable for streaming. We believe that the necessary changes required to obtain such functionality will disrupt the strengths of BitTorrent. Some alternative solutions are presented where BitTorrent has been extended with additional modules, such as a server.</p>

<p>In the environment of the 3:rd generation Internet based on peer-to-peer architecture, well-trusted methods must exist to establish a secure environment. One main issue is the possibility to verify that a node actually is who it claims to be (authentication). Establishment of authentication between nodes in a peer-to-peer environment where nodes are exchanging information directly with each other requires more planning than in a typical client-server environment where the authentication methods are server-based. The peer-to-peer applications described in this report use authentication methods based on central authorities as well as solutions without central authorities. </p><p>Lack of standards in the way peer-to-peer systems should communicate and apply security lead to a variety of “local” communication and security solutions. These local solutions make different applications incompatible with each other, meaning that a peer using one application will not be able to communicate and exchange information with other peers using some other application.</p>

Thanks to their increasing sophistication and popularity, mobile devices, in the form of smartphones and tablets, have become the fastest growing contributors to Internet traffic. Indeed, smartphones are projected to account for 50% of global Internet traffic by 2017, with the share of mobile video increasing to about 40% of total Internet traffic. As users embrace Internet streaming of video, several studies have found that a small decrease in video quality leads to a substantial increase in viewer abandonment and disengagement rates. To handle the explosive growth in video traffic, Adaptive HTTP streaming, which exploits the prevalence of commodity web servers and content distribution networks, has emerged as the key technology for delivering video to end users. Although a number of systems have been proposed for HTTP video streaming in traditional environments and for fixed clients, existing platforms for video streaming on mobile devices are still in their infancy and do not address the additional challenges often experienced by mobile clients: high fluctuations in network conditions, heterogeneous networking interfaces, multiple form-factors, and limited battery life. In this dissertation, we propose a number of solutions for improving the Quality of Experience of HTTP video streaming on mobile devices. We begin by evaluating the performance of several existing video quality adaptation schemes when deployed on mobile platforms. Through experiments with smartphones in wide-area environments, we assemble several key findings. First, we show that the high fluctuations in network throughput on cellular and Wi-Fi networks impose significant challenges for efficiently architecting the video adaptation scheme. Second, we find significant differences between the performance of the current state-of-the-art schemes in controlled experimental settings and their performance in mobile settings on key quality metrics such as inefficiency, instability, rebuffering ratio, and startup latency. We also find noticeable differences in the behavior of the schemes under Wi-Fi and cellular network access, with most of the schemes performing worse when the network access is cellular. Given these observations, we hypothesize on the possible causes of these inefficiencies. We also identify the best practices of existing schemes and key insights from experimental results that can serve as foundations for addressing many of the limitations. Armed with these measurement-driven insights, we propose a novel video quality adaptation scheme, called MASS, which is more robust to the vagaries of the wireless networking conditions. We implement and evaluate our solution on commodity Android smartphones, and demonstrate significant performance gains over existing schemes. To further improve the streaming experience, we introduce an extension to HTTP video streaming that leverages the synergy between social network participation and video streaming to optimize end-user Quality of Experience. Our system, called SDASH, integrates and applies well-known concepts such as cooperative caching, prefetching, and P2P streaming for reducing bitrate fluctuations and optimizing the viewing experience. Finally, we develop a general infrastructure for constructing temporally and spatially localized P2P communities of mobile devices sharing similar interests. The platform enables on-demand cooperation among mobile clients based on device context and client preferences. We use a concrete implementation of the mobile P2P infrastructure for evaluating the performance of SDASH. This dissertation addresses the challenges facing Adaptive HTTP Streaming under mobile networking conditions. Through experimentation with commodity mobile devices, we show that the proposed techniques for bitrate adaptation and cooperative streaming can significantly improve the video viewing experience.

Current estimates are that more than nine million PCs in the U.S. are part of peer-to-peer (P2P) file sharing overlay networks on the Internet. These P2P hosts generate about 20% of the traffic on the Internet and consume about 7.8 TWh/yr equal to $630 million per year. File search in a P2P network is based on a wasteful paradigm of broadcasting query messages. Reducing P2P overhead traffic to reduce bandwidth waste and enabling power management to reduce electricity usage are clearly of great interest. In this dissertation, two new search paradigms with reduced overhead traffic are investigated. The new Targeted Search method uses statistics from previous searches to target future searches. Targeted Search is shown to reduce query overhead traffic when compared to broadcast-based search used by Gnutella. The new Broadcast Updates with Local Look-up Search (BULLS) protocol enables new capabilities including power management and reduces overhead traffic by enabling a local look-up of shared files. BULLS hosts periodically broadcast changes in their list of files shared and build a table of shared files by all other hosts. Power management in P2P networks is studied as an application of the minimum set cover problem. A reduction in overall energy consumption is achieved by powering down hosts that have all of their shared files fully shared (or covered) by other hosts. A new set cover heuristic -- called the Random Map Out (RMO) algorithm --is introduced and compared to the well-known Greedy heuristic. The algorithms are evaluated for minimum set cover size and computational complexity (number of comparisons). The RMO algorithm requires significantly less comparisons than Greedy and still achieves a set cover size within a few percent of that of Greedy. Additionally, the RMO algorithm can be distributed and independently executed by each host with reduced complexity per host where the Greedy heuristic does not reduce in complexity by being distributed. With RMO there is a non-zero probability of a given file being "lost" (not in set cover). The probability of this event is modeled and numerical results show that the probability of a file being lost is practically insignificant.