• The KIPS Transactions:PartC
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• v.13C no.5 s.108
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• pp.621-626
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• 2006

A mobile ad hoc network (MANET) is an infrastructureless network that supports multi-hop communication. For the MANET nodes wishing to communicate with nodes in the wired Internet, the global Internet connectivity is required and this functionality can be achieved with the help of the Internet gateway. For the support of reliability and flexibility, multiple Internet gateways can be provisioned for a MANET. In this case, load-balancing becomes one of the important issues since the network performance such as the network throughput can be improved if the loads of the gateways are well-balanced. In this paper, we categorize the load-balancing mechanisms and propose a new metric for load-balancing. Simulation results show that our proposed mechanism using the hop distance and the number of routing table entries as a load-balancing metric enhances the overall network throughput.

• Journal of KIISE:Information Networking
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• v.27 no.2
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• pp.187-196
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• 2000

Failures in ATM networks can occur at virtual path (VP) links, virtual path switches, and virtual channel (VC) switches. Restoration schemes have been proposed for VP link and VP switch failures, however, none for VC switch failures. In general, VC switches are used for edge nodes in protection domains. Since even only one VC switch failure can cause a critical problem, new restoration schemes for VC switch failures are highly required. Restoration schemes at the VP level proposed so far can be categorized into those using the flooding algorithm and those using the backup virtual path (BVP) concept. Even though the latter cannot handle unpredictable failures, it has some advantages such as fast restoration and low spare capacity requirement. In this paper, we propose new restoration schemes using a new type of BVPs to handle VC switch failures. The simulation results show that the proposed schemes can restore virtual connection failures due to VC switch failures without degrading restorability for VP failures.

• Journal of KIISE:Information Networking
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• v.35 no.1
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• pp.34-45
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• 2008

In dynamic wireless sensor networks where sources and sinks are moving or are created/died, control overheads for route establishment are increased and thus become one of the major factors for energy consumption. This study introduces prefetching and pruning for Directed Diffusion to remove redundant control messages. Prefetching collects path information for each event with "AnyEvent" in advance and gives quick responses without further flooding of requests. Pruning accumulates history information from previous requests and replies, and then stops forwarding a request towards where the event does not exist. Simulation results with ns show that it is possible to build implicit and soft infrastructures within a Directed Diffusion system through these active collection and passive accumulation and they improve energy consumption more as control overhead goes higher.

• Journal of KIISE:Information Networking
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• v.37 no.1
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• pp.35-41
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• 2010

Since the ad-hoc network allow nodes to communicate each other without infrastructure system and predefined configuration, it comes into the spotlight that is suitable to ubiquitous society. In ad-hoc network, route recovery mechanism is considered important. Normally route recovery is needed to solve the link failure problem because there is no route maintaining system like a router in ad-hoc networks. In this paper we propose BS-AODV(Bidirectional Searching-AODV) route recovery method. The proposed method is a local repair method that can be applied in all of the network area. Unlike a limited local repair method in AODV. the proposed method adopts the bidirectional searching method where the upstream/downstream nodes can send the route maintenance messages. Restricting the flooding of route request messages, the proposed scheme attempts to minimize the costs of local repair, the performance of the proposed scheme is evaluated through the simulations. In two scenarios which variate the node numbers and node speed, the comparison among the proposed scheme, AODV and AOMDV is shown in terms of the control traffic and data delivery ratio.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11B
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• pp.1297-1304
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• 2011

SIP(Session Initiation Protocol) has some security vulnerability because it works on the Internet. Therefore, the proxy server can be affected by the flooding attack such as DoS and service interruption. However, traditional schemes to corresponding Denial of Service attacks have some limitation. These schemes have high complexity and cannot protect to the variety of Denial of Service attack. In this paper, we newly define the normal user who makes a normal session observed by verifier module. Our method provides continuous service to the normal users in the various situations of Denial of Service attack as constructing a whitelist using normal user information. Various types of attack/normal traffic are modeled by using OPNET simulator to verify our scheme. The simulation results show that our proposed scheme can prevent DoS attack and achieve a low false rate and fast searching time.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.9
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• pp.8-15
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• 2009

Although traditional single-hop cellular networks had been serving well in past years, they are no longer economically feasible in supporting high data-rate, multimedia services of $4^{th}$Generation (4G) communications due to the requirement of high transmission power By contrast, multi-hop cellular networks (MCN) are capable of dramatically saving the transmission power by overlaying the capability of ad hoc networking among mobile terminals on the cellular network infrastructure. To achieve this performance gain as well as enable 4G services, an efficient routing protocol needs to be designed for MCN. In this paper, we propose a reactive route discovery protocol for MCN that uses directional information to the base station in the route discovery process. Our analysis/simulation results have demonstrated that the proposed protocol significantly reduces flooding overheads. In addition, we consider issues for 4G services in MCN and applications of the proposed protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.11A
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• pp.1173-1181
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• 2007

A number of routing algorithms have been studied for wireless mobile ad-hoc network. Among them, the AODV routing algorithm with on-demand method periodically transmits hello message and monitors link state during data transmission in order to maintain routing paths. When a path is disconnected, a node that senses it transmits a RERR packet to the transmitting node or transmits a RREQ locally so that the path could be repaired. With that, the control packet such as a RREQ is broadcast, which causes the consumption of bandwidth and incurs data latency. This paper proposes a LRRLBP algorithm that locally repairs a path by predicting link state before disconnecting the path based on the AODV routing protocol for solving such problems. Intensive simulations with the results using NS-2 simulator are shown for verifying the proposed protocol.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.8 s.350
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• pp.1-14
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• 2006

Multi-constraint QoS routing has been seen as crucial network property in the next generation optical Internet based on DWDM Networks. This paper proposes a new QoS routing algorithm based on flooding method, called bounded flooding routing (BFR) algorithm which can meet multi-constraint QoS requirements. Primarily, the BFR algorithm tries to reduce network overhead by accomplishing bounded-flooding to meet QoS requirements, and improve blocking probability and wavelength utilization. Also, as one effort to improve routing performance, we introduce a new concept, ripple count, which does not need any link-state information and computational process. For extensive analysis and simulation study, as a critical concern, in DWDM-based networks we deploy limited wavelength conversion capability within DWDM nodes. And the simulation results demonstrate that the BFR algorithm is superior to other predominant routing algorithms (both original flooding method and source-directed methods) in terms of blocking probability, wavelength channels required and overhead.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.2
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• pp.29-34
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• 2008

In this paper, we proposed a system protocol for detecting injurious insect to support energy saving transmission in wireless bio sensor networks. The main ideas and features of the system are as follows. First, the route establishment method which is based on the energy efficiency and stability by using time-division tree structure. Second, multi-hop direction-based data gatering structure. In this structure, the selected fading method is used to transmit packet via the established tree structure for supporting power saving and route lifetime efficiently. Finally, we can get the node power saving and reduce transmission delay, thus network lifetime and efficiency are improved. The performance evaluation of the proposed protocol is via OPNET(Optimized Network Engineering Tool).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.8
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• pp.1038-1045
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• 2000

An experimental study was carried out to delineate the flow characteristics in a closed countescurrent two-phase thermo syphon with concentric tubes. This is to be installed in the HANARO research reactor as a part of a Cold Neutron Source(CNS). In the present investigation, experiments ata room temperature with Freon-II3 as a moderator were performed. Results show that, based on the magnitude of pressure fluctuation, the flow regimes could be divided into 4 distinct ones in the ($V_f,\;Q_i$) plane, where $V_f$ represents the volume of the charged liquid and $Q_i$ the heat load: a stable flow regime, an oscillatory flow regime, a restablized flow regime and a dryout flow regime. For $V_f$>2.5l, the flow is stable at low $Q_i$. However, as $Q_i$ increases, the flow becomes oscillatory and finally restablizes As $V_f$ increases, the oscillation amplitude decreases, reaching to the restablized flow region at low $Q_i$, and the liquid level in the moderator cell remains high. In the oscillatory flow regimes, for a fixed VI; the oscillating period of time varies with $Q_i$, having a minimum value at a certain value of $Q_i$. The heat load, where the oscillating period of time is minimum, decreases as $V_f$ increases.