• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.6
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• pp.1689-1706
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• 2012

The preservation of temporal dependencies among a group of processes that exchange continuous media at runtime is a key issue for emerging mobile distributed systems (MDS), such as monitoring of biosignals and interactive multiuser games. Although several works are oriented to satisfy temporal dependencies, most of them are not suitable for MDSs. In general, an MDS is characterized by the absence of global references (e.g. shared memory and wall clock), host mobility, limited processing and storage capabilities in mobile hosts, and limited bandwidth on wireless communication channels. This paper proposes an asymmetric synchronization protocol to be used at runtime in an MDS without using a common reference. One main aspect of our synchronization protocol is that it translates temporal constraints to causal dependencies of the continuous media data as seen by the mobile hosts. We simulate the protocol by considering a cellular network environment and by using MPEG-4 encoders. The simulation results show that our protocol is effective in reducing the synchronization error. In addition, the protocol is efficient in terms of processing and storage costs at the mobile devices, as well as in the overhead attached per message across the wired and wireless channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.1A
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• pp.46-54
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• 2005

This paper presents an effcient mobile multicast method using the user pattern. We exploit the repetitive movement pattern of mobile node to reduce the total number of experience of graft and join procedure. We defined the locality scope by a movement pattern. While the network is included in the locality scope, the network should maintain a multicast tree even when the mobile node moves to the other network. In this way, the mobile host can receive a multicast service without a delay when it moves to the network in the locality scope later. We compare our scheme with existing schemes under the total signaling cost and the service delay time by using a discrete analytical model for cost analysis. Analytical results demonstrated that the total signaling cost and service delay time was significantly reduced through our proposed scheme.

• Journal of KIISE:Computer Systems and Theory
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• v.26 no.10
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• pp.1217-1224
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• 1999

이동 호스트들의 위치 정보를 관리하는 것은 이동 컴퓨터 시스템에서 중요한 문제이다. 이동 호스트가 이동할 때 위치 수정과 위치 탐색간에는 상반관계가 존재한다. 본 논문에서는 위치 서버를 이용한 간단한 quorum 기반 분산 동적 위치 관리 방법을 제안한다. 이 방법에서는 이동 호스트들의 위치 정보가 모든 위치 레지스터가 아닌 위치 레지스터들의 부분집합에서 효율적으로 관리되기 때문에 위치 수정 비용과 위치 탐색 비용이 감소된다. 그리고 위치 레지스터들의 부분집합은 동적으로 변하고, 각 위치 서버의 부하는 이동 호스트에 대한 질의율을 고려하므로 균등해진다. 제안된 알고리즘의 성능은 위치 수정비용과 위치 탐색비용의 전체비용으로 평가되었고, Prakash의 알고리즘과 비교되었다.Abstract Managing location information of mobile hosts is an important issue in mobile computing systems. There is a trade-off between location update and search, when a mobile host moves. This paper proposes a simple quorum-based distributed dynamic location management method using location registers. The cost of location updates and searches is reduced by our method because the location information of mobile hosts is managed efficiently in a subset of location registers instead of in all location registers. In our method, the subset of location registers is dynamically changed, and the load of each location register is balanced by considering query rate for mobile hosts. The performance of proposed algorithm is evaluated in terms of the total cost of a location update and a location search, and is compared with Prakash's algorithm.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.8
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• pp.1365-1373
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• 2002

In this paper, we present two types of vision algorithm that mobile robot has CCD camera. for obstacle avoidance. This is simple algorithm that compare with grey level from input images. Also, The mobile robot depend on image processing and move command from PC host. we has been studied self controlled mobile robot system with CCD camera. This system consists of digital signal processor, step motor, RF module and CCD camera. we used wireless RF module for movable command transmitting between robot and host PC. This robot go straight until recognize obstacle from input image that preprocessed by edge detection, converting, thresholding. And it could avoid the obstacle when recognize obstacle by line histogram intensity. Host PC measurement wave from various line histogram each 20 pixel. This histogram is (x, y) value of pixel. For example, first line histogram intensity wave from (0, 0) to (0, 197) and last wave from (280, 0) to (2n, 197. So we find uniform wave region and nonuniform wave region. The period of uniform wave is obstacle region. we guess that algorithm is very useful about moving robot for obstacle avoidance.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.3
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• pp.93-99
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• 2009

The Internet Engineering Task Force (lETF)proposed the Mobile IPv6 protocol to provide host mobility in IPv6-based network and to offer a standardized technology. However, Mobile IPv6 (MIPv6) is not applied in actual network because of long handover latency and packet loss problems. Therefore, to compensate these drawbacks, many studies are in progress and FMIPv6 (Fast handover for Mobile IPv6) is one of the studies that has been proposed to supplement the shortcomings of MIPv6. But there are problems occurred in using router tunneling which causes packet loss and out of sequence problems. In this paper, we propose an Advanced Mobile IPv6 (AMIPv6) protocol to minimize the handover latency when Mobile Node frequently moves in each subnet. We compared the performance analysis of AMIPv6 handover latency with MIPv6 handover latency in the same network environment to prove that AMIPv6 is more efficient.

• Journal of Internet Computing and Services
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• v.3 no.1
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• pp.61-69
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• 2002

Big-bang growth of Internet and World Wide Web is supplying much information and resources to network. However, use of internet resources is receiving many limitations by bandwidth for most users. But, through Applet way, can solve degradation problem that follow on static side and bandwidth of CGI that HTML has. Mobile Agent starts in user's computer to accomplish user's specification purpose and achieves work rooving network. Because code that can perform so is transmitted, and is achieved in network through network, important problem happens to mobile code's security naturally. In computing environment that this research uses this Mobile Agent way that can protect host and agent groping report, describe problem that happen composing Mobile Agent relationship concept and Mobile Agent, and do so that may present method that is studying to solve these problem, and use method that application is possible actually among presented method and design transfer agent's security system.

• Journal of the Korea Society of Computer and Information
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• v.11 no.2 s.40
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• pp.131-143
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• 2006

The rapid growth of mobile communication technology has provided the expansion of mobile internet services, particularly mobile realtime transaction takes much weight among mobile fields. Current mobile transaction service has serious problems which check its development, such as low bandwidths, hand over, expensive charge system, and low response time. but, There is an increasing demand for various mobile applications to process transactions in a mobile computing fields. In mobile computing environments. A mobile host computing system demands for new concurrency control method to use the bandwidth efficiently, to improve the bottleneck and the response time of transactions. This study suggests about an efficient concurrency control in a mobile computing environment. Concurrency control method in existing method uses two phases locking method. In this method, Many clients can't use the same segment simultaneously, and so useless waiting time increases. The characteristic of this proposed method unlike existing one, Enable the transaction approaching different data in the same segment to minimize the useless waiting time by permitting segments, and therefore improves the coexistence of system. Also, It shows the algorithm of the proposed concurrence control method.

• The Transactions of the Korea Information Processing Society
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• v.4 no.4
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• pp.973-981
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• 1997

This paper identifies the main features and problems which have to be considerde when providing multicast services for mobile hosts.We also present a schme for solving these problems.To do this,we intreduce the ieda of the group view with a host status and present a multicast algorithm based on the group view concept.This paper mainly fouces on the exactly-once semantic for multicast delivery.It will provide basis for build-ing multicast servies for mobile hosts.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.571-574
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• 2002

In a recent wireless network environments, dynamic host configuration protocol (BHCP) service is used to assign IP addresses to mobile terminals. In IPv6 networks, it is necessary to introduce the concept of handoff to support a seamless service to mobile terminals. In a general soft handoff technique used by code-division multiple acces (CDMA) communication systems, the powers received to base station are simply compared to determine which base station will handle the signal to and from each mobile termins. However, in IPv6 network, to transmit data-oriented services, it is necessary to support an enhanced soft handoff technique with more security and quality of service. In this paper, we propose a scheme to reduce a signaling process of handoff in IPv6 network. Also, we propose a technique to reduce wasted reservation resources and to guarantee quality of service (QoS) using DHCP.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1094-1097
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• 2002

Realtime applications like VoIP(Voice over IP) in All-IP networks need smooth handoffs in order to minimize or eliminate packet loss as a Mobile Host(MH) transitions between network links. In this paper, we design a new dynamic buffering(DB) mechanism for IPv6 by which an MH can request that the router on its current subnet buffers packets on its behalf while the MH completes registration procedures with the router of a new subnet. Performance results show that our proposed buffering scheme with a dynamic buffer space allocation is quite appropriate for mobile Internet, or the All-IP environment in terms of the datagram loss rate.