13-02-2013, 09:32 PM
i need the ns2 coding for this topic .
i am having doubts about how to start replicate data.
before applying otoo,Rn schems , the nodes have data or empty
ie detail about system model before replicating data
13-02-2013, 09:32 PM
i need the ns2 coding for this topic . i am having doubts about how to start replicate data. before applying otoo,Rn schems , the nodes have data or empty ie detail about system model before replicating data
27-06-2013, 01:00 PM
Balancing the Tradeoffs between Query Delay and Data Availability in MANETs
Balancing the Tradeoffs.pdf (Size: 441.12 KB / Downloads: 18) Abstract In mobile ad hoc networks (MANETs), nodes move freely and link/node failures are common, which leads to frequent network partitions. When a network partition occurs, mobile nodes in one partition are not able to access data hosted by nodes in other partitions, and hence significantly degrade the performance of data access. To deal with this problem, we apply data replication techniques. Existing data replication solutions in both wired or wireless networks aim at either reducing the query delay or improving the data availability, but not both. As both metrics are important for mobile nodes, we propose schemes to balance the tradeoffs between data availability and query delay under different system settings and requirements. Extensive simulation results show that the proposed schemes can achieve a balance between these two metrics and provide satisfying system performance. INTRODUCTION In mobile ad hoc networks (MANETs), since mobile nodes move freely, network partition may occur, where nodes in one partition cannot access data held by nodes in other partitions. Thus, data availability (i.e., the number of successful data accesses over the total number of data accesses) in MANETs is lower than that in conventional wired networks. Data replication has been widely used to improve data availability in distributed systems, and we will apply this technique to MANETs [1]. By replicating data at mobile nodes which are not the owners of the original data, data availability can be improved because there are multiple replicas in the network and the probability of finding one copy of the data is higher. Also, data replication can reduce the query delay since mobile nodes can obtain the data from some nearby replicas. However, most mobile nodes only have limited storage space, bandwidth and power, and hence it is impossible for one node to collect and hold all the data considering these constraints. By taking these issues into consideration, we expect that mobile nodes should not be able (or willing) to replicate all data items in the network (more discussions in Appendix A.) DATA REPLICATION Data replication has been extensively studied in the Web environment and distributed database systems (See Appendix B in the supplemental material for detailed literature review). However, most of them either do not consider the storage constraint or ignore the link failure issue. Before addressing these issues by proposing new data replication schemes, we first introduce our system model. In a MANET, mobile nodes collaboratively share data. Multiple nodes exist in the network and they send query requests to other nodes for some specified data items. Each node creates replicas of the data items and maintains the replicas in its memory (or disk) space. During data replication, there is no central server that determines the allocation of replicas, and mobile nodes determine the data allocation in a distributed manner. Reliable Grouping (RG) Scheme OTOO only considers one neighboring node when making data replication decisions. RN further considers all one-hop neighbors. However, the cooperations in both OTOO and RN are not fully exploited. To further increase the degree of cooperation, we propose the reliable grouping (RG) scheme which shares replicas in large and reliable groups of nodes, whereas OTOO and RN only share replicas among neighboring nodes. The basic idea of the RG scheme is that it always picks the most suitable data items to replicate on the most suitable nodes in the group to maximize the data availability and minimize the data access delay within the group. Simulation Results Experiments were run using different workloads and system settings. The performance analysis presented here is designed to compare the effects of different workload parameters such as Zipf parameter, network size, radio range, memory size and node mobility (due to the space limitation, the effects of different mobility models are provided in Appendix G). For each workload parameter (e.g., the mean update arrival time or the mean query generate time), the mean value of the measured data is obtained by collecting a large number of samples such that the confidence interval is reasonably small. In most cases, the 95% confidence interval for the measured data is less than 10% of the sample mean. CONCLUSIONS In MANETs, due to link failure, network partitions are common. As a result, data saved at other nodes may not be accessible. One way to improve data availability is through data replication. In this paper, we proposed several data replication schemes to improve the data availability and reduce the query delay. The basic idea is to replicate the most frequently accessed data locally and only rely on neighbor’s memory when the communication link to them is reliable. |
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