Content Replication in Mobile Networks

2010

This paper proposes CADRE (Collaborative Allocation and Deallocation of Replicas with Efficiency), which is a dynamic replication scheme for improving the typically low data availability in dedicated and cooperative mobile ad-hoc peer-to-peer (M-P2P) networks. In particular, replica allocation and deallocation are collaboratively performed in tandem to facilitate effective replication. Such collaboration is facilitated by a hybrid super-peer architecture in which some of the mobile hosts act as the 'gateway nodes' (GNs) in a given region. GNs facilitate both search and replication. The main contributions of CADRE are as follows. First, it facilitates the prevention of 'thrashing' conditions due to its collaborative replica allocation and deallocation mechanism. Second, it considers the replication of images at different resolutions to optimize the usage of the generally limited memory space of the mobile hosts (MHs). Third, it addresses fair replica allocation across the MHs. Fourth, it facilitates the optimization of the limited energy resources of MHs during replication. Our performance evaluation demonstrates that CADRE is indeed effective in improving data availability in M-P2P networks with significant reduction in query response times and low communication traffic during replication as compared to a recent existing scheme as well as a baseline approach, which does not consider any replication.

Proceedings of the 7th …, 2004

Mobile networks are becoming increasingly popular as a means for distributing information to a large number of users. In comparison to wired networks, mobile networks are distinguished by a potentially much higher variability in client demand due to user mobility. Most previous content distribution techniques assume a static client demand distribution and, thus, may not perform well in mobile networks.

A Mobile Ad-hoc Network (MANET) is a self-configured infrastructure-less network. It consists of autonomous mobile nodes that communicate over bandwidth-constrained wireless links. Nodes in a MANET are free to move randomly and organize themselves arbitrarily. They can join the network or quit the network in an unpredictable way, such rapid and untimely disconnections may cause network partitioning. In such a case, the network faces multiple difficulties, which in turn can dramatically impact the applications deployed on top of it. One major problem is data availability. Replicating data on multiple nodes can improve availability and response time. Determining " when " and " where " to replicate data in order to meet performance goals with many users and files, and dynamic network characteristics are difficult. We identify the issue of power consumption and propose an efficient method to replicate data in appropriate nodes in the network.

Computer Networks, 2013

Wireless Mesh Networks (WMNs) extend Internet access in areas where the wired infrastructure is not available. A problem that arises is the congestion around gateways, delayed access latency and low throughput. Therefore, object replication and placement is essential for multi-hop wireless networks. Many replication schemes are proposed for the Internet, but they are designed for CDNs that have both high bandwidth and high server capacity, which makes them unsuitable for the wireless environment. Object replication has received comparatively less attention from the research community when it comes to WMNs. In this paper, we propose an object replication and placement scheme for WMNs. In our scheme, each mesh router acts as a replica server in a peer-to-peer fashion. The scheme exploits graph partitioning to build a hierarchy from fine-grained to coarse-grained partitions. The challenge is to replicate content as close as possible to the requesting clients and thus reduce the access latency per object, while minimizing the number of replicas. Using simulation tests, we demonstrate that our scheme is scalable, performing well with respect to the number of replica servers and the number of objects. The simulation results show that our proposed scheme has better performance compared to other replication schemes.

IEEE Journal on Selected Areas in Communications, 2000

Mobile networks are becoming increasingly popular in enterprise environments as a means for distributing information to a large community of highly dynamic users. In comparison to traditional wired networks, mobile networks are distinguished by a potentially much higher variability in users demand due to user mobility. Most previous content distribution techniques assume a static user demand distribution and, thus, may not perform well in mobile networks. This paper proposes and analyzes a mobile dynamic content distribution network model, which takes demand variations into account to decide whether to replicate a content and whether to remove previously created replicas in order to minimize total network traffic. We develop two solutions to our model: an offline optimal solution, which provides an ideal lower bound on the total traffic, and a practical heuristic online algorithm, which uses demand forecasting to make replication decisions. We provide a thorough evaluation of our solutions, comparing them against ACDN, the only previous dynamic content placement algorithm targeting bandwidth minimization that we are aware of. Our results show that our online algorithm significantly outperforms ACDN, reducing total network traffic by up to 85% in a number of experiments covering a large system design space.

2010 10th IEEE/ACM International Conference on Cluster, Cloud and Grid Computing, 2010

In a publish/subscribe (pub/sub) network, message delivery is guaranteed for all connected subscribers at publish time. However, in a dynamic mobile scenario where users join and leave the network, it is important that content published at the time they are disconnected is still delivered when they reconnect from a different point. In this paper, we enhance the caching mechanisms in pub/sub networks to support client mobility. We build our mobility support with minor changes in the caching scheme while preserving the main principles of loose coupled and asynchronous communication of the pub/sub communication model. We also present a new proactive mechanism to reduce the overhead of duplicate responses. The evaluation of our proposed scheme is performed via simulations and testbed measurements and insights are given for future work.

An important challenge to database researchers in mobile computing environments is to provide a data replication solution that maintains the consistency and improves the availability of replicated data. This paper addresses this problem for large scale mobile environments. Our solution represents a new binary hybrid replication strategy in terms of its components and approach. The new strategy encompasses two components: replication architecture to provide a solid infrastructure for improving data availability and a multi-agent based replication method to propagate recent updates between the components of the replication architecture in a manner that improves availability of last updates and achieves the consistency of data. The new strategy is a hybrid of both pessimistic and optimistic replication approaches in order to exploit the features of each. These features are supporting higher availability of recent updates and lower rate of inconsistencies as well as supporting the mobility of users. To model and analyze the stochastic behavior of the replicated system using our strategy, the research developed Stochastic Petri net (SPN) model. Then the Continuous Time Markov Chain (CTMC) is derived from the developed SPN and the Markov chain theory is used to obtain the steady state probabilities.

International Journal of Information Technology, …, 2009

Transaction management in wireless environment poses challenging issues in preserving data consistency and fault tolerance. As the mobile databases are prone to frequent disconnections, bandwidth limitations, mobility, etc. efficient execution of the transaction may not always be guaranteed. Replicating data at several sites is a powerful mechanism which not only increases performance but also provides fault tolerance for demanding database applications. However the major concern is to keep the replicated copies always consistent. In this paper various replication techniques and their applicability in the mobile environments are presented. Based on the requirements of the services provider and the type of execution model used, one of the replication strategies may be implemented.

International Journal of Interactive Multimedia and Artificial Intelligence, 2014

The most frequent challenge faced by mobile user is stay connected with online data, while disconnected or poorly connected store the replica of critical data. Nomadic users require replication to store copies of critical data on their mobile machines. Existing replication services do not provide all classes of mobile users with the capabilities they require, which include: the ability for direct synchronization between any two replicas, support for large numbers of replicas, and detailed control over what files reside on their local (mobile) replica. Existing peer-topeer solutions would enable direct communication, but suffers from dramatic scaling problems in the number of replicas, limiting the number of overall users and impacting performance. Roam is a replication system designed to satisfy the requirements of the mobile user. Roam is based on the Ward Model, replication architecture for mobile environments. Using the Ward Model and new distributed algorithms, Roam provides a scalable replication solution for the mobile user. We describe the motivation, design, and implementation of Roam and report its performance. Replication is extremely important in mobile environments because nomadic users require local copies of important data.

The need for mobile access to large databases leads to problems with mobile computers connectivity. Mobile computers often suffer from limited connectivity or lack of network access. Existing replicated databases are not well suited for mobile scenarios as well as algorithms used for data replication. Distributed database systems and distributed database management systems have been developed in response to trend of distributed computation. In distributed models of computations several sites are interconnected via a communications network. The advantages of data distribution involve increased availability, distributed access to data and improved performance of parallel processing. Disadvantages, on the other hand, are given by increased overhead and complexity in the system design and implementation. In the following paper we introduce algorithm for adaptive data replication including mobile computers.

2008

Distributed database systems and distributed database management systems have been developed in response to trend of distributed computation. In distributed models of computations several sites are connected via a communications network. However, the need for mobile access to large databases leads to problems with mobile computers connectivity. Mobile computers often suffer from limited connectivity or lack of network access. Existing replicated databases are not well suited for mobile scenarios as well as algorithms used for data replication, in spite of fact that it is the most desirable environment. In the following paper we introduce algorithm for adaptive data replication including mobile computers connected by wireless network based on IEEE 802.11. K e y w o r d s: distributed database systems, distributed database management systems, wireless networks, data replication

In mobile environments, mobile device users access and transfer a great deal of data through the online servers. In order to enhance users’ access speed in a wireless network, decentralizing replicated servers appropriately in the network is required. Previous work regarding this issue had focused on the placement of replicated servers along with the moving paths of the users to maximize the hit ratio. When a miss occurs, they simply ignored the file request. Therefore, we suggest a solution to take care of such a miss by sending a file request to a replicated server nearby in the network. This paper is to propose new cost-effective wireless access algorithms incorporating a present replicated server allocation algorithm with more keen analysis of the moving patterns of mobile device users. We propose four different algorithms that allocate available replicated servers in the network so as to minimize the communication costs. The experimental results show that, among the proposed algorithms, the replicated server clustering algorithm allocated replicated servers with near optimal communication costs.

Mobile Networks and Applications, 2009

This study investigates replication strategies for reducing latency to desired content in a vehicular peer-to-peer network. We provide a general constrained optimization formulation for efficient replication and study it via analysis and simulations employing a discrete random walk mobility model for the vehicles. Our solution space comprises of a family of popularity based replication schemes each characterized by an exponent n. We find that the optimal replication exponent depends significantly on factors such as the total system storage, data item size, and vehicle trip duration. With small data items and long client trip durations, n ∼ 0.5 i.e., a square-root replication scheme provides the lowest aggregate latency across all data item requests. However, for short trip durations, n moves toward 1, making a linear replication scheme more favorable. For larger data items and long client trip durations, we find that the optimal replication exponent is below 0.5. Finally, for these larger data items, if the client trip duration is short, the optimal replication exponent is found to be a function of the total storage in the system. Subsequently, the above observations are validated with two real data sets: one based on a city map with freeway traffic information and the other employing encounter traces from a bus network.