Myong-Soon Park

Outlier detection and countermeasure for hierarchical wireless sensor networks

Outliers in wireless sensor networks (WSNs) are sensor nodes that issue attacks by abnormal behaviours and fake message dissemination. However, existing cryptographic techniques are hard to detect these inside attacks, which cause outlier recognition a critical and challenging issue for reliable and secure data dissemination in WSNs. To efficiently identify and isolate outliers, this study presents a novel outlier detection and countermeasure scheme (ODCS), which consists of three mechanisms: (i) abnormal event observation mechanism for network surveillance; (ii) exceptional message supervision mechanism for distinguishing fake messages by exploiting spatiotemporal correlation and consistency and (iii) abnormal behaviour supervision mechanism for the evaluation of node behaviour. The ODCS provides a heuristic methodology and does not need the knowledge about normal or malicious sensors in advance. This property makes the ODCS not only to distinguish and deal with various dynamic attacks automatically without advance learning, but also to reduce the requirement of capability for constrained nodes. In the ODCS, the communication is limited in a local range, such as one-hop or a cluster, which can reduce the communication frequency and circumscribe the session range further. Moreover, the ODCS provides countermeasures for different types of attacks, such as the rerouting scheme and the rekey security scheme, which can separate outliers from normal sensors and enhance the robustness of network, even when some nodes are compromised by adversary. Simulation results indicate that our approach can effectively detect and defend the outlier attack.

Processor reordering algorithms toward efficient GEN_BLOCK redistribution

The use of data redistribution represents a performance tradeoff between the expected higher efficiency of a new distribution for subsequent computation and the communication cost of redistributing the data among processor memories. This paper focuses on reducing the communication cost in GEN_BLOCK redistribution using a logical processor reordering method. We propose three algorithms; Number_Oriented, Size_Oriented and Numsize_Oriented. According to experiments on CRAY T3E, the algorithms show good performance comparing typical GEN_BLOCK redistribution, which does not reorder logical processor numbers.

Scheduling GEN_BLOCK Array Redistribution

This article is devoted to the redistribution of arrays that are distributed in a GEN_BLOCK fashion over a processor grid. While GEN_BLOCK redistribution is essential for load balancing, prior research about redistribution has been focused on block-cyclic redistribution. The proposed scheduling algorithm exploits a spatial locality in message passing from a seemingly irregular array redistribution. The algorithm attempts to obtain near optimal scheduling by trying to minimize communication step size and the number of steps. According to experiments on CRAY T3E and IBM SP2, the algorithm shows good performance in typical distributed memory machines.

PRODUCE: A Probability-Driven Unequal Clustering Mechanism for Wireless Sensor Networks

There has been proliferation of research on seeking for distributing the energy consumption among nodes in each cluster and between cluster heads to extend the network lifetime. However, they hardly consider the hot spots problem caused by heavy relay traffic forwarded. In this paper, we propose a distributed and randomized clustering algorithm that consists of unequal sized clusters. The cluster heads closer to the base station may focus more on inter-cluster communication while distant cluster heads concentrate more on intra-cluster communication. As a result, it nearly guarantees no communication in the network gets excessively long communication distance that significantly attenuates signal strength. Simulation results show that our algorithm achieves abundant improvement in terms of the coverage time and network lifetime, especially when the density of distributed nodes is high.

TASL: A Traffic-Adapted Sleep/Listening MAC Protocol for Wireless Sensor Network

In this paper, we proposed TASL-MAC, a medium-access control (MAC) protocol for wireless sensor networks. In wireless sensor networks, sensor nodes are usually deployed in a special environment, are assigned with long-term work, and are supported by a limited battery. As such, reducing the energy consumption becomes the primary concern with regard to wireless sensor networks. At the same time, reducing the latency in multi-hop data transmission is also very important. In the existing research, sensor nodes are expected to be switched to the sleep mode in order to reduce energy consumption. However, the existing proposals tended to assign the sensors with a fixed Sleep/Listening schedule, which causes unnecessary idle listening problems and conspicuous transmission latency due to the diversity of the traffic-load in the network. TASL-MAC is designed to dynamically adjust the duty listening time based on traffic load. This protocol enables the node with a proper data transfer rate to satisfy the application`s requirements. Meanwhile, it can lead to much greater power efficiency by prolonging the nodes` sleeping time when the traffic. We evaluate our implementation of TASL-MAC in NS-2. The evaluation result indicates that our proposal could explicitly reduce packet delivery latency, and that it could also significantly prolong the lifetime of the entire network when traffic is low.

Multicast-based Distributed LVS (MD-LVS) for improving scalability and availability

Clustering with a single-system image view is the most commonly used approach to increase throughput of a Web site. There are two types of clustering architecture: centralized IP cluster and distributed IP cluster. In the centralized IP cluster the load balancer distributes incoming requests of clients to an appropriate real server based on load characteristics. However the availability and scalability of the cluster system is low, since this kind of solution creates a single-point-of-failure and the total throughput of the cluster is limited by the performance of the load balancer. We propose the Multicast-based Distributed LVS (MD-LVS), which combines the centralized IP cluster and the distributed IP cluster. There are multiple load balancers, and each of the load balancers has an individual and independent cluster group, which consists of several real servers. This mechanism efficiently can improve scalability and availability of the cluster system, since it is easy to expand the cluster system and may avoid the entire system failure.

An authentication protocol for hierarchy-based wireless sensor networks

Hierarchy-based wireless sensor networks (WSNs) achieve excellent performance with reserving energy consumption and decreasing system delay. However, distinguished hierarchy-based research such as LEACH (low-energy adaptive clustering hierarchy) does not consider a security issue for ensuring the protection of the network. Due to the peculiar character of LEACH such as round base operation and header centrality topology, adopting security in LEACH is a complicated task. In this paper, we present an authentication protocol for hierarchy-based WSNs to protect network from inside attackers. This protocol uses pre-distribution unique symmetric key with authentication management database (AMDB) and live message to monitor the network to detect the entrance of compromise node using illegal keys.

Reducing cache conflicts in data cache prefetching

As processor speed has increased dramatically in recent years, the gap between processor and memory speeds becomes the main cause of degrading processor utilization. A cache memory is a well-known hardware mechanism used to reduce this gap. Caches, however, show poor performance on some programs such as scientific and engineering applications due to their high cache miss ratio. Data prefetching[1,3,4,5,6,8,9,10,1 1,12,15] is one of the effective solutions to this problem. This technique reduces cache miss penalty by generating prefetch requests to bring data before actually being used. The prefetched data are stored in the data cache or in the prefetch buffer. Cache prefetching[3,4,5,6] suffers from cache conflicts(called cache pollution) because the current and the future working sets coexist on the cache at the same time. These two working sets conflict with each other and cause cache misses. The prefetch buffer[4,5,6,10] can remove cache conflicts, but it needs complex hardware and sacrifices chip area that could otherwise be used for a normal cache. Therefore, if we could reduce cache conflicts, cache prefetching would be the better choice. In this paper, we discuss the effect of the cache size on the cache conflicts and the methods to reduce cache conflicts. Figure 1 shows the three possible results of cache prefetching, where two data A and A conflict with each other on the cache. All other cases can be explained by these. Ca}e 1 is the very case that we want. Two cache misses occur in Case 2 due to cache conflicts. The prefetch instructions for the data, which are already in the cache, can be discarded. In this case, a cache miss occurs as Case 3. Case 2 and 3 must be avoided. If we can predict cache conflicts among data and make them not conflict, we can prevent Case 2 and 3.

A Compensation-Based Reliable Data Delivery for Instant Wireless Sensor Network

Instant wireless sensor network (IWSN) is a type of WSN deployed for a class of special applications which have the common requirement on instantly responding for collecting and transmitting sensory data, e.g., volcanic eruption monitoring or nuclear leakage detection. In this paper, having a cluster- based WSN, we present a compensation-based reliable data delivery protocol (CRDD) to collect and transmit sensory data timely, reliably, and energy-efficiently. The CRDD consists of three important parts: 1) reliability calculating mechanism, 2) information classifying mechanism, and 3) intelligent balancing mechanism. By using these three mechanisms, the CRDD can reduce redundant messages for enhancing the transmission performance and compensate the deficient messages for reliability. The simulation results show that CRDD can outperform both LEACH and ECDG and significantly improve sensory data collection speed and system dependability.

Optimizing iSCSI Parameters for Improving the Performance of iSCSI based Mobile Appliance in Wireless Network

Mobile appliances are going to be used in more area as the time goes by. The devices should be small, thus they can not have enough storage capacity. To alleviate these problems, we developed MobileStor, a iSCSI based remote storage system, for providing the allocation of a mass storage space to each mobile client through networks. The iSCSI protocol enables a clients block-level access to the data on remote storage over an existing IP infrastructure. However, the performance of the system for mobile appliances was dropped in wireless networks, since the protocol was originally developed for wired networks. Especially when we use default parameters values suggested in standard, the performance is decreased. This paper presents a remote storage system named MobileStor. Our experiments which are performed to investigate the best performance values of iSCSI parameters for iSCSI based remote storage system are taken out in CDMA networks in order to realize the access to a remote storage system anytime and anywhere. And after the experiment, we suggest the optimal value of parameters. The experiment results from several test cases show us the best values are not the default values specified in the iSCSI standard.