• Journal of KIISE:Information Networking
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• v.27 no.1
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• pp.30-38
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• 2000

In distributed HLR environment, the pointer forwarding with distributed HLR(Pointer Forwarding Scheme) has been proposed for eliminating the cost of updating multiple HLRs. In Pointer Forwarding Scheme, the find cost can be changed according to from which HLR a call originates. If a user changes PCS registration areas frequently, but receives calls relatively infrequently, and call for such a user originates from any other HLRs than the recently updated HLR, many VLRs should be traversed in order to find that user. In this paper, location tracking with jumping pointer in distributed HLR(Jumping Pointer Scheme) is proposed. The jumping pointer can be connected between the recently updated VLR and the VLR in which the mobile host currently resides. In case of call delivery, the mobile host can be found sooner by using the jumping pointer. In terms of 'find' cost, Jumping Pointer scheme improves about 17% over Forwarding Pointer scheme. Otherwise, Jumping Pointer scheme takes additional update charge in order to manage the jumping pointer. However the total costs of 'find' cost and 'update' cost for Jumping Pointer scheme are cheaper than them for Forwarding Pointer scheme when call-to-mobility ratio is smaller.

• Journal of KIISE:Information Networking
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• v.32 no.1
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• pp.12-19
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• 2005

Reliable transport protocols such as TCP are tuned to Perform well in traditional networks where packet losses occur mainly because of congestion. In a wireless network, however, packet losses will occur more often due to reasons such as the high bit error rate and the handoff rather than due to congestion. When using TCP over wireless network, TCP responds to losses due to the high bit error rate and the handoff by invoking congestion control and avoidance algorithms, resulting in the degraded end-to-end performance in the wireless network. There have been several schemes for improving TCP performance over wireless links. Among them, SNOOP Is a very promising scheme because of the localized retransmission. In this thesis, an efficient scheme is proposed by modifying SNOOP scheme. The invocation of congestion control mechanism is now minimized by knowing the cause of packet loss.

• Journal of KIISE:Computing Practices and Letters
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• v.6 no.2
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• pp.206-215
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• 2000

This paper is concerned with the development of PCS(Platform for Collaborative System), which is a platform for development of remote collaborative experiment systems. Platform does not aim at the development of special-domain applications. This system implies the common development environments which can develop all-domain applications. PCS consists of collaborative experimental objects such as communication, session, user, application, media, message object and management objects that have management functions. Management objects are made up of collaborative experimental objects and operations which manipulate control information and data. It also supports application sharing for making single user interface of experimental applications to multi-user interface. Application sharing also supports instruments control on the remote site. PCS platform supports total environments for remote collaborative experiment and can be used as infrastructure to all kinds of collaboratory systems.

• Journal of KIISE:Computing Practices and Letters
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• v.13 no.6
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• pp.388-396
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• 2007

In this paper, a ubiquitous parking management system(UPMS) using sensor network is proposed. Ubiquitous parking management system provides information on free space in the parking lot through PDA or cellular phone connected to wireless LAN. For the implementation of UPMS, we have developed sensor node, sensor application and web server application. The proposed system periodically updates parking space data and monitors in real-time according to the user's request from the personal internet device. Collected parking data are stored onto the database for further analysis. The implemented UPMS system was installed on campus parking lot using 10 sensor nodes and we successfully demonstrated its feasibility by accessing the web server from out of the campus.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.9
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• pp.608-614
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• 2006

The popularization of high-speed networks and the innovation of high-performance hardware/servers have enlarged the role of large-scale, highly distributed IT infrastructure. Though many criteria on the assessment of IT infrastructure can be considered, the survivability assessment is treated as the most important one due to the essential role as an infrastructure. While assessing the survivability of some given IT infrastructures, we can not only choose the best one among them but also improve their survivability by modifying their structure and security policies. In this paper, we propose a DMKB-based assessment system on the survivability of IT infrastructures, where DMKB is a kind of database which provides the known vulnerabilities and defense mechanism for many system components.

• Journal of KIISE:Computing Practices and Letters
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• v.11 no.1
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• pp.69-80
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• 2005

Recent popularity of web-ready mobile devices such as PDA and cellphone has made mobile Internet access very popular. However, most of existing Web contents and services are optimized for desktop computing environment and not well suited for mobile devices. Considering different system features of mobile devices such as small display and limited input capability, an alternative scheme to access the Web efficiently is required. On the other hand, personalization plays an important role in the tailored access to the Web contents and services. In this paper, we propose a proxy- based personalization scheme of Web service pages for mobile users. For that purpose, in addition to log data. service related features of Web pages are considered for the correct identification of popular services. It automatically provides mobile users with the tailored list of Web services well suited for diverse mobile devices. Consequently, mobile users can utilize customized Web services with minimum navigation on the mobile devices with limited capability. In order to show its effectiveness, we have performed several experiments on the prototype system and reported some of the results.

• Journal of KIISE:Information Networking
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• v.29 no.3
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• pp.314-323
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• 2002

The routing protocols designed for wired networks can hardly be used for mobile ad-hoc networks due to limited bandwidth of wireless transmission and unpredictable topological change. Recently, several routing protocols for mobile ad-hoc networks have been Proposed. However, when theme protocols are applied to support real time services like multimedia transmission, they still have problems in ad-hoc networks, where the topology changes drastically. In this paper, we propose a new route selection algorithm which selects the most reliable route that is impervious to route failures by topological changes by mobile hoots. For reliable route selection, the concept of virtual zone (stable zone and caution zone) is proposed. The zone is located in a mobile node'transmission range and determined by mobile node's mobility information received by Global Positioning System (GPS). The proposed algorithm is applied to the route discovery procedure of the existing on-demand routing protocol, AODV, and evaluated by simulation in various traffic conditions and mobility patterns.

• Journal of KIISE:Computing Practices and Letters
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• v.8 no.6
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• pp.765-777
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• 2002

For the battlefield analysis, it is required to get correct information about the identification and moving status of target enemy units. However, it is difficult for us to collect all of the information perfectly, because of the technology of communications, jamming, and tactics. Therefore, we need a reasoning function that predicts and analyzes future moving status for target units by using collected moving information and domain knowledge. Especially. since the moving units have characteristics of moving objects, which change their position and shape over time, they require functions to manage and predict locations of moving objects. Therefore, in this paper, we propose a location prediction system of moving units for battlefield analysis. The proposed system not only predicts unknown units, unidentified units, and main strike directions to application domain for battlefield analysis, but also estimates the past or future locations of moving objects not stored in a database.

• Journal of KIISE:Information Networking
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• v.29 no.3
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• pp.205-215
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• 2002

In this paper the Dynamic Minislot Reservation Protocol(DMRP) in which the control channel is divided into contention-less and contention minislots in order to reduce re-transmission probability in multicasting is proposed. In the network, earth node has two pairs of transceivers. A transceiver consisting of a fixed transmitter and a fixed receiver is used to control packet registration and the other transceiver is used to transmit data. Two types f transceivers for data transmission are considered : one is FT-TR(Fixed Transmitter-Tunable Receiver) and the other is TT-TR(Tunable Transmitter-Tunable Receiver). In the analysis, FT-TR and TT-TR single-hop passive star networks are compared. As results, we conclude that the DMRP protocol with dynamically divided control channel has improved the system performance such as throughput and system delay regardless of traffic type or network structure.

• Journal of KIISE:Information Networking
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• v.33 no.5
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• pp.343-354
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• 2006

There has been much research efforts trying to integrate mobile IP that has been proposed to guarantee the mobility of mobile nodes on MANET (Mobile Ad Hoc Networks) and wired integrated networks. To support the mobility service of nodes in MIPMANET, this paper proposes MAAM(Mobility Agent Advertisement Mechanism) and AMAAM protocols. In MAAM, the mobility agent of the mobile IP can maintain the information of ad hoc networks by broadcasting advertisement messages periodically. AMAAM(Aggregation based Mobility Agent Advertisement Mechanism) is an enhancement of MAAM for reducing the number of transmission of advertisement messages by aggregating them. The proposed schemes are applied in MIPMANET for agent advertisement mechanism. For the performance evaluation of both protocols, we simulated them by NS2. We evaluate the protocols by ns2 with such performance metrics as packet delivery ratio, transmission throughput, and energy consumption.