• Journal of KIISE:Computing Practices and Letters
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• v.9 no.4
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• pp.369-380
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• 2003

With the proliferation of a wireless support and the advances of mobile devices, there is a growing need of making it available for a wireless network as well. Low bandwidth of a wireless network is one of the major issues that should be considered for extending a synchronous collaboration system developed for a wired network to supuort a wireless network. We propose a priority-based view synchronization scheme, exploiting the relaxed synchronization. The proposed scheme leverages the fact that mobile users need not have the exactly same view as the users in a wired network since they usually have a limited screen size and thus focus only on part of a whole document. We evaluate the performance of a simple group editor with the propose scheme using ns -2. The performance results show that the proposed scheme keeps the message transmission delay low so that mobile users can have synchronous colloboration with wired users without signification delay. The proposed scheme is designed and implemented as a framework to support various kinds of realtime groupware applications, exploiting the existing groupware framework, Habanero. As a client program, we implemented a simple group text editor.

• KIISE Transactions on Computing Practices
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• v.20 no.11
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• pp.598-603
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• 2014

In wireless sensor networks, two methods have been generally used to track continuously moving object: a user query-based method and a periodic report-based method. Although the former method generates more overhead as a result of the user queries, the former one is also an energy-efficient method that does not transfer unnecessary information. For the user query-based method, a virtual tree that consist of sensor nodes is used to perform the user query and the sensor reporting. The tree stores the information of the mobile objects, and the stored information triggers a report b the user query. However, in case of a fast-moving object, the tracking accuracy decreases as a result of the time delay of the end-to-end repeated query. In order to solve this problem, we propose a query-relay method that reduces the time delay for mobile object tracking. In the proposed method, the nodes in the tree relay the query to adjacent nodes according to the movement of mobile object that is tracked. When the query messages are relayed. The end-to-end querying time delay is reduced. and a simulation shows that our method is superior to existing ones in terms of tracking accuracy.

• Journal of KIISE:Information Networking
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• v.30 no.5
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• pp.631-640
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• 2003

Because of multi-hop wireless communication, P2P applications in ad hoc networks suffer poor performance. We Propose neighbor caching strategy to overcome this shortcoming and show it is more efficient than self caching that nodes store data in theirs own cache individually. A node can extend its caching storage instantaneously with neighbor caching by borrowing the storage from idle neighbors, so overcome multi-hop wireless communications with data source long distance away from itself. We also present the ranking based prediction that selects the most appropriate neighbor which data can be stored in. The node that uses the ranking based prediction can select the neighbor that has high possibility to keep data for a long time and avoid caching the low ranked data. Therefore the ranking based prediction improves the throughput of neighbor caching. In the simulation results, we observe that neighbor caching has better performance, as large as network size, as long as idle time, and as small as cache size. We also show the ranking based prediction is an adaptive algorithm that adjusts times of data movement into the neighbor, so makes neighbor caching flexible according to the idleness of nodes

• Journal of KIISE:Information Networking
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• v.29 no.4
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• pp.428-436
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• 2002

Providing a mobile host with its required QoS is highly influenced by its mobility. The resource ReSerVation Protocol(RSVP) establishes and maintains a reservation state to ensure a given QoS level along the path from the sender to the receiver. However, RSVP is designed for use in fixed networks and thus it is inadequate in the mobile networking environment where a host changes its point of attachment. In this paper, we propose a new resource reservation protocol, RSVP-RA(RSVP by RSVP Agent) for mobile hosts. Our protocol assumes IETF Mobile IP as a mobility support mechanism. The proposed protocol introduce a new protocol entity - RSVP agent - to manage reservations in a mobile host's current visiting network. RSVP Agent is located in a local network and makes resource reservations in neighboring cells that the mobile host is expected to visit in the future. Thus, the proposed Protocol can provide a seamless QoS to the mobile host and significantly improve the scalability problem of RSVP by reducing the end-to-end signalling messages acrossing the backbone networks. The proposed protocols reduce packet delay, bandwidth overhead and the number of RSVP messages to maintain reservation states. We compared the performance of our proposed protocol with other proposed protocols in terms of signalling overhead, packet delay by simulation.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.9
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• pp.626-636
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• 2009

In Mobile IP-enabled wireless LAN (WLAN), packet flows are corrupted due to the handoff of a mobile node (MN) at the link and network layers, which results in burst packet losses and can cause temporary buffer underflow in a streaming client at the MN. This transient behavior hurts time-sensitive streaming media applications severely. Among many suggestions to address this handoff problem, few studies are concerned with empirical issues regarding the practical validation of handoff options on the time-sensitive streaming media applications. In this paper, targeting seamless streaming over Mobile IP-enabled WLAN, we introduce a seamless media streaming framework that estimates accurate pre-buffering level to compensate the handoff latency. In addition, we propose a link-layer (L2) assisted seamless media streaming system as a preliminary version of this framework. The proposed system is designed to reduce the handoff latency and to overcome the playback disruption from an implementation viewpoint. A packet buffering and forwarding mechanism with L2 trigger is implemented to reduce the handoff latency and to eliminate burst packet losses generated during the handoff. A pre-buffering adjustment is also performed to compensate the handoff latency. The experimental results show that the proposed approach eliminates packet losses during the handoff and thus verify the feasibility of seamless media streaming over Mobile IP-enabled WLAN.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.4
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• pp.244-254
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• 2009

This paper describes a remote system to monitor the circadian behavioral patterns of elders who live alone. The proposed system was designed and implemented to provide more conveniently and reliably the required functionalities of a remote monitoring system for elders based on the development of first phase prototype[2]. The developed system is composed of an in-house sensing system and a server system. The in-house sensing system is a set of wireless sensor nodes which have pyroelectric infrared (PIR) sensor to detect a motion of elder. Each sensing node sends its detection signal to a home gateway via wireless link. The home gateway stores the received signals into a remote database. The server system is composed of a database server and a web server, which provides web-based monitoring system to caregivers (friends, family and social workers) for more cost effective intelligent care service. The improved second phase system can provide 'automatic diagnosis', 'going out detection', and enhanced user interface functionalities. We have evaluated the first and second phase monitoring systems from real field experiments of 3/4 months continuous operation with installation of 9/15 elders' houses, respectively. The experimental results show the promising possibilities to estimate the behavioral patterns and the current status of elder even though the simplicity of sensing capability.

• Information Systems Review
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• v.15 no.3
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• pp.111-128
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• 2013

Conventions play important roles as tools for effective marketing. It will be able to understand the changes of particular industry's market, develop a new market and potential clients, and get a chance such as strategic network constructing. To support effective viewing of visitors, conventions have introduced a variety of ubiquitous computing technologies. This study introduces a case of applying the Utility Tag-based convention service system at the Cosmetics & Beauty Expo, Osong Korea 2013. The Utility Tag-based convention service system is constructed total three systems: (1) NFC Tag Management System; allowing effective access and management of NFC tags in various locations and objects, (2) Information Provide System; allowing participating vendors to manage information they want to provide information to visitors, and (3) Utility Tags; providing a variety of service to visitors for effective viewing in exhibition/convention space. This study first explores literature review and applying case related to ubiquitous computing in this field and introduces Applying an Utility Tag-based convention service system. In addition, we analyze visitors' behaviors and association rules by take advantage of collected touch data, present various possible for applications of the Utility Tag-based convention service system.

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.1_2
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• pp.80-89
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• 2001

The development in the mobile computing systems have arisen new and previously unforeseen problems, such as problems in information management of mobile host, disconnection of mobile host and low bandwidths of wireless communications. Especially, location information management strategy of mobile host results in an increased overhead in mobile computing systems. Due to the mobility of the mobiles host, the changes in the mobile host's address depends on the mobile host's location, and is maintained by mapping physical address on virtual address, Since previously suggested several strategies for mapping method between physical address and virtual address did not tackle the increase of mobile host and distribution of location information, it was not able to support the scalability in mobile computing systems. Thus, to distribute the location inrormation, we propose an advanced n-depth LiST (Location information Search Tree) and the parallel location search and update strategy based on the advanced n-depth LiST. The advanced n-depth LiST is logically a hierarchical structure that clusters the location information server by ring structure and reduces the location information search and update cost by parallel seatch and updated method. The experiment shows that even though the distance of two MHs that communicate with each other is large, due to the strnctural distribution of location information, advanced n-depth LiST results in good performance. Moreover, despite the reduction in the location information search cost, there was no increase in the location information update cost.

• Journal of Korea Spatial Information System Society
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• v.8 no.2 s.17
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• pp.75-89
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• 2006

LBS (Location-Based Service) systems have become a serious subject for research and development since recent rapid advances in wireless communication technologies and position measurement technologies such as global positioning system. The architecture named the GALIS (Gracefully Aging Location Information System) has been suggested which is a cluster-based distributed computing system architecture to overcome performance losses and to efficiently handle a large volume of data, at least millions. The GALIS consists of SLDS and LLDS. The SLDS manages current location information of moving objects and the LLDS manages past location information of moving objects. In this thesis, we implement a monitoring technique for the GALIS prototype, to allow dynamic load balancing among multiple computing nodes by keeping track of the load of each node in real-time during the location data management and spatio-temporal query processing. We also propose a buffering technique which efficiently manages the query results having overlapped query regions to improve query processing performance of the GALIS. The proposed scheme reduces query processing time by eliminating unnecessary query execution on the overlapped regions with the previous queries.

• The KIPS Transactions:PartD
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• v.13D no.6 s.109
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• pp.839-846
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• 2006

Context-aware adaptive service for overcoming the limitations of wireless devices and maintaining adequate service levels in changing environments is becoming an important issue. However, most existing studies concentrate on an adaptation module on the client, proxy, or server. These existing studies thus suffer from the problem of having the workload concentrated on a single system when the number of users increases md, and as a result, increases the response time to a user's request. Therefore, in this paper the adaptation module is dispersed and arranged over the client, proxy, and server. The module monitors the contort of the system and creates a proposition as to the dispersed adaptation system in which the most adequate system for conducting operations. Through this method faster adaptation work will be made possible even when the numbers of users increase, and more stable system operation is made possible as the workload is divided. In order to evaluate the proposed system, a prototype is constructed and dispersed operations are tested using multimedia based learning content, simulating server overload and compared the response times and system stability with the existing server based adaptation method. The effectiveness of the system is confirmed through this results.