• Journal of KIISE:Databases
• /
• v.33 no.3
• /
• pp.271-281
• /
• 2006

Recently the need for Location-Based Service (LBS) has increased due to the development and widespread use of the mobile devices (e.g., PDAs, cellular phones, labtop computers, GPS, and RFID etc). The core technology of LBS is a moving-objects database that stores and manages the positions of moving objects. To search for information quickly, the database needs to contain an index that supports both real-time position tracking and management of large numbers of updates. As a result, the index requires a structure operating in the main memory for real-time processing and requires a technique to migrate part of the index from the main memory to disk storage (or from disk storage to the main memory) to manage large volumes of data. To satisfy these requirements, this paper suggests a unified index scheme unifying the main memory and the disk as well as migration policies for migrating part of the index from the memory to the disk during a restriction in memory space. Migration policy determines a group of nodes, called the migration subtree, and migrates the group as a unit to reduce disk I/O. This method takes advantage of bulk operations and dynamic clustering. The unified index is created by applying various migration policies. This paper measures and compares the performance of the migration policies using experimental evaluation.

• KIISE Transactions on Computing Practices
• /
• v.22 no.1
• /
• pp.44-49
• /
• 2016

Recently, data has been growing dramatically along with the growth of social media and digital devices. A distributed memory processing system has been used to efficiently process large amounts of data. However, if a load is concentrated in a certain node in distributed environments, a node performance significantly degrades. In this paper, we propose a load balancing scheme to distribute load in a distributed memory environment. The proposed scheme replicates hot data to multiple nodes for managing a node's load and migrates the data by considering the load of the nodes when nodes are added or removed. The client reduces the number of accesses to the central server by directly accessing the data node through the metadata information of the hot data. In order to show the superiority of the proposed scheme, we compare it with the existing load balancing scheme through performance evaluation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.1C
• /
• pp.25-34
• /
• 2004

In mobile agent environments, cascaded delegations among places occur frequently due to the mobility of agents. Cascaded delegation in mobile agent environments can be defined as the process whereby the delegated place delegates the rights of the delegating place further. The representative study for delegation in mobile agent environments is Berkovits et al.'s study. Their study only defines the messages that is sent between the place executing the agent and the place where the agent migrates. Because their study considers only the delegation between two places which participate in migration of an agent, it is inadequate in the situation that the cascaded delegation is necessary. In other words, the relationships among the messages sent from and to places is necessary. However, their study does not exist the relationships. In this paper, we propose a delegation scheme that provides agents with secure cascaded delegation. The proposed scheme achieves the goal by nesting each delegation token within the signed part of the next immediate delegation token. We prove that the proposed scheme is secure against the attack of replaying a message and of substituting a delegation token.

• Journal of the Korean Institute of Rural Architecture
• /
• v.4 no.1
• /
• pp.9-18
• /
• 2002

Keumsan-gun is the area where there are many mobile populations as the place to be adjacent to Daejon. There is the tendency that the empty houses at Keumsan area are increasing as 1,115 houses every year as of 2001. So, this researcher examined and analyzed the actual state by grasping the present situation of empty houses centering around Keumsan-gun. And, this researcher could obtain the following conclusion as the result that this researcher progressed the study so as to present the application scheme of empty houses. As for Keumsan-gun, farming populations are more than other city and gun at Choongcheong Southern Proince Area as the area formed with mountain groups topographically. Thus, it is forecast that the appearance of empty houses will increase, as the population decrease and the residents to have migration plan will appear higher than other city and gun in the future also. Therefore, as for the superannuated empty houses that use is impossible, to service by removing will be helpful to the image uplifting of village. In addition, as for the empty houses that use is possible, the establishment of system to connect buyers by rebuilding them as garden houses and weekend houses etc. through purchase and sale and long-term lease etc. is necessary.

• IEMEK Journal of Embedded Systems and Applications
• /
• v.11 no.2
• /
• pp.125-134
• /
• 2016

NAND flash memory has unique characteristics like as 'out-place-update' and limited lifetime compared with traditional storage systems. According to out-of-place update scheme, a number of invalid (or called dead) pages can be generated. In this case, garbage collection is needed to reclaim invalid pages. Because garbage collection results in not only erase operations but also copy operations of valid (or called live) pages to other blocks, many garbage collection techniques have proposed to reduce the overhead and to increase the lifetime of NAND Flash systems. This techniques sometimes select victim blocks including cold data for the wear leveling. However, most of them overlook the cost of selecting victim blocks including cold data. In this paper, we propose a garbage collection technique named CAPi (Cost Age with Proportion of invalid pages). Considering the additional overhead of what to select victim blocks including cold data, CAPi improves the response time in garbage collection and increase the lifetime in memory systems. Additionally, the proposed scheme also improves the efficiency of garbage collection by separating cold data from hot data in valid pages. In experimental evaluation, we showed that CAPi yields up to, at maximum, 73% improvement in lifetime compared with existing garbage collections.

• Journal of Advanced Marine Engineering and Technology
• /
• v.21 no.4
• /
• pp.430-436
• /
• 1997

Time-dependent Flow characteristics of a two-dimensional lid-driven square cavity flow of six high Reynolds numbers, $10^4 2{\times}lO^4., 3{\times}l0^4, 5{\times}lO^4, 7.5{\times}lO^4$ and $10^5$ were investigated. A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy was adopted on irregular grid formation. Irregular grid number is $80{\times}80$ and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that at Re= $10^4$, periodic migration of small eddies appearing in corner separation region and its temporal sinusoidal fluctuation are represented. And another critical Reynolds number which shows the commencement of flow randomness emerging from the periodic fluctuation is assumed to be around Re= $1.5{\times}10$. At five higher Reynolds numbers ($2{\times}lO^4., 3{\times}l0^4, 5{\times}lO^4, 7.5{\times}lO^4$ and $10^5$), an organizing structure of four consecutive vortices similar to a Moffat vortex at two lower corners is revealed from time-mean flow patterns.

• Geophysics and Geophysical Exploration
• /
• v.22 no.4
• /
• pp.225-238
• /
• 2019

Migration velocity analysis (MVA) for creating optimum depth-domain velocities in seismic imaging was applied to marine long-offset multi-channel data, and the effectiveness of the MVA approach was demonstrated by the combinations of conventional data processing procedures. The time-domain images generated by conventional time-processing scheme has been considered to be sufficient so far for the seismic stratigraphic interpretation. However, when the purpose of the seismic imaging moves to the hydrocarbon exploration, especially in the geologic modeling of the oil and gas play or lead area, drilling prognosis, in-place hydrocarbon volume estimation, the seismic images should be converted into depth domain or depth processing should be applied in the processing phase. CMP-based velocity analysis, which is mainly based on several approximations in the data domain, inherently contains errors and thus has high uncertainties. On the other hand, the MVA provides efficient and somewhat real-scale (in depth) images even if there are no logging data available. In this study, marine long-offset multi-channel seismic data were optimally processed in time domain to establish the most qualified dataset for the usage of the iterative MVA. Then, the depth-domain velocity profile was updated several times and the final velocity-in-depth was used for generating depth images (CRP gather and stack) and compared with the images obtained from the velocity-in-time. From the results, we were able to confirm the depth-domain results are more reasonable than the time-domain results. The spurious local minima, which can be occurred during the implementation of full waveform inversion, can be reduced when the result of MVA is used as an initial velocity model.

• The KIPS Transactions:PartA
• /
• v.11A no.4
• /
• pp.257-266
• /
• 2004

Mobile agents are defined as processes which can be autonomously delegated or transferred among the hosts in a network in order to perform some computations on behalf of the user and co-operate with other agents. Currently, mobile agents are used in various fields, such as electronic commerce, mobile communication, parallel processing, search of information, recovery, and so on. In pure P2P network environment, if mobile agents that require computing resources rashly migrate to another peers without consideration on the peer's capacity of resources, the peer may have a problem that the performance of the peer is degraded due to lack of resources. To solve this problem, we propose resource reservation based load balancing scheme of using RMA(Resource Management Agent) that monitors workload information of the peers and that decides migrating agents and destination peers. In mobile agent migrating procedure, if the resource of specific peer is already reserved, our resource reservation scheme prevents other mobile agents from allocating the resource.

• International Journal of Contents
• /
• v.13 no.2
• /
• pp.29-34
• /
• 2017

Cloud computing is becoming an effective and efficient way of computing resources and computing service integration. Through centralized management of resources and services, cloud computing delivers hosted services over the internet, such that access to shared hardware, software, applications, information, and all resources is elastically provided to the consumer on-demand. The main enabling technology for cloud computing is virtualization. Virtualization software creates a temporarily simulated or extended version of computing and network resources. The objectives of virtualization are as follows: first, to fully utilize the shared resources by applying partitioning and time-sharing; second, to centralize resource management; third, to enhance cloud data center agility and provide the required scalability and elasticity for on-demand capabilities; fourth, to improve testing and running software diagnostics on different operating platforms; and fifth, to improve the portability of applications and workload migration capabilities. One of the key features of cloud computing is elasticity. It enables users to create and remove virtual computing resources dynamically according to the changing demand, but it is not easy to make a decision regarding the right amount of resources. Indeed, proper provisioning of the resources to applications is an important issue in IaaS cloud computing. Most web applications encounter large and fluctuating task requests. In predictable situations, the resources can be provisioned in advance through capacity planning techniques. But in case of unplanned and spike requests, it would be desirable to automatically scale the resources, called auto-scaling, which adjusts the resources allocated to applications based on its need at any given time. This would free the user from the burden of deciding how many resources are necessary each time. In this work, we propose an analytical and efficient VM-level scaling scheme by modeling each VM in a data center as an M/M/1 processor sharing queue. Our proposed VM-level scaling scheme is validated via a numerical experiment.

• The Transactions of the Korea Information Processing Society
• /
• v.4 no.8
• /
• pp.2092-2105
• /
• 1997

In this paper, we propose a load sharing scheme in distributed systems. In the proposed scheme, the state of each host is classified as a server or a source by its current load and, to prevent excessive state changes of each host, we used three threshold values for identifying the current state of each host. Based on the threshold values, some hosts, called brokers, manage the servers registered to them. The brokers, whose number is determined by the system utilization factor and the total number of hosts, support task migration processes from overloaded sources to lightly loaded servers. Also they can hand over the broker's role to another host when it is overloaded. Simulation studies were performed for examining the sensitivity of each system parameters such as threshold values, utilization factor, the number of hosts, and the number of brokers to the system performance indices including mean response time, mean queue length.