• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.152-155
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• 2018

Over the past years, Link Flooding Attacks (LFAs) have been introduced as new network threats. LFAs are indirect DDoS attacks that selectively flood intermediate core links, while legacy DDoS attacks directly targets end points. Flooding bandwidth in the core links results in that a wide target area is affected by the attack. In the traditional network, mitigating LFAs is a challenge since an attacker can easily construct a link map that contains entire network topology via traceroute. Security researchers have proposed many solutions, however, they focused on reactive countermeasures that respond to LFAs when attacks occurred. We argue that this reactive approach is limited in that core links are already exposed to an attacker. In this paper, we present SDHoneyNet that prelocates vulnerable links by computing static and dynamic property on Software-defined Networks (SDN). SDHoneyNet deploys Honey Topology, which is obfuscated topology, on the nearby links. Using this approach, core links can be hidden from attacker's sight, which leads to effectively building proactive method for mitigating LFAs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.9
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• pp.772-779
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• 2012

In the current MANET, DOS or DDOS attacks are increasing, but as MANET has limited bandwidth, computational resources and battery power, the existing traceback mechanisms can not be applied to it. Therefore, in case of traceback techniques being applied to MANET, the resource of each node must be used efficiently. However, in the traceback techniques applied to an existing ad hoc network, as a cluster head which represents all nodes in the cluster area manages the traceback, the overhead of the cluster head shortens each node's life. In addition, in case of multi-hop clustering, as one Cluster head manages more node than one, its problem is getting even worse. This paper proposes TNA(Traceback against Network Attacks) based on multihop clustering using the depth of tree structure in order to reduce the overhead of distributed information management.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4C
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• pp.338-346
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• 2012

Wireless sensor network (WSN) technology provides a variety of medical and healthcare solutions to assist detection and communication of body conditions. However, data reliability inside WSN might be influenced to healthcare routing protocol due to limited hardware resources of computer, storage, and communication bandwidth. For this reason, we have conducted various wireless communication experiments between nodes using parameters such as RF strength, battery status, and deployment status to get a optimal performance of mobile healthcare routing protocol. This experiment may also extend the life time of the nodes. Performance analysis is done to obtain some important parameters in terms of distance and reception rate between the nodes. Our experiment results show optimal distance between nodes according to battery status and RF strength, or deployment status and RF strength. The packet reception rate according to deployment status and RF strength of nodes was also checked. Based on this performance evaluation, the optimized sensor node battery and deployment in the developed our mobile healthcare routing protocol were proposed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5C
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• pp.548-554
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• 2009

OFDM systems are very sensitive to the frequency offset. Therefore, frequency offset estimation is one of the most important procedures in OFDM systems. Ren's periodogram-based frequency offset estimation scheme consists of three steps which estimates the frequency offset accurately. However, there are the drawbacks of the limited frequency offset estimation ranges in the second and third estimation steps of the Ren's scheme. This ranges are insufficient compared with the overall signal bandwidth, making the high complexity of the first estimation step. In this paper, we propose a novel lower complexity frequency offset estimation scheme for OFDM systems which extends the frequency offset estimation range. The simulation results show that the proposed scheme has a wider frequency offset estimation range and lower complexity than those of the Ren's scheme.

• The KIPS Transactions:PartC
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• v.16C no.1
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• pp.57-64
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• 2009

In order to efficiently provide IP based Wireless Broadband services in Mobile WiMAX, schemes for more efficiently utilizing a limited bandwidth in radio links are needed. Robust Header Compression (ROHC), a standard header compression scheme proposed by IETF, Bi-directional Optimistic (O) mode provides higher compression efficiency and robustness compared with Payload Header Suppression (PHS) which is an optional header compression scheme for mobile WiMAX [1, 2]. However, if consecutive packet losses occur because of a Shadow Region of Mobile WiMAX or bit errors, header decompression failure rate of the ROHC O mode increases due to inconsistency of the compression information between the Compressor and the Decompressor. Therefore, a complementary mechanism is needed. In this paper, we propose an approach for the dynamic adjustment of an optimistic parameter, which has an effect on both the compression efficiency and the robustness, for improving the performance of ROHC O mode. We also analyze the performance of the proposed approach using an OPNET simulator.

• Journal of the Korea Society of Computer and Information
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• v.10 no.4 s.36
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• pp.93-102
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• 2005

Excessive traffic of P2P applications in the limited communication environment is considered as a network bandwidth problem. Moreover, Though P2P systems search a resource in the phase of search using weakly connected systems(peers' connection to P2P overlay network is very weakly connected), it is not guaranteed to download the very peer's resource in the phase of download. In previous P2P search algorithm (1), we had adopted the heuristic peer selection method based on Random Walks to resolve this problems. In this paper, we suggested an adaptive P2P search algorithm based on the previous algorithm(1) to reform the node distribution rate which is affected in unit peer ability. Also, we have adapted the discriminative replication method based on a query ratio to reduce traffic amount additionally. In the performance estimation result of this suggested system, our system works on a appropriate point of compromise in due consideration of the direction of searching and distribution of traffic occurrence.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.2
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• pp.104-109
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• 2020

In this paper, we proposed a miniaturized folded inverted F antenna with ISM-band (center frequency : 447 MHz) for mounting in intelligent parking sensor. First, to mount the antenna in the intelligent parking sensor module (72 mm × 70 mm) with limited size, a folded inverted F antenna was designed at low frequency 447 MHz (wavelength λ : 670 mm) of the ISM-band. As a result, it resonates in the ISM band and obtains suitable characteristic with a -10 dB bandwidth of 13 MHz (2.9%). In addition, the H-plane pattern by the vertical and horizontal elements represents the omni-directional patterns from which the null point is removed, and the E-plane has directivity in a specific direction. Finally, it is suitable as and antenna for vehicle management in parking lots.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.4
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• pp.39-45
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• 2009

With the rapid growth of recent wireless mobile computing application technology and handheld mobile terminal device development technology, one of the big issue in these fields is to design online games in wireless mobile ad hoc network environment. Online games in mobile computing environment have lots of constraints for developing online games because mobile terminals have many limitations such as low performance of processor, limited memory space, small bandwidth of wireless communication, and confined life of battery power. Therefore, most of mobile games are restrictive in the function of online and multi-play up to date. In this paper, the online MMORPG game, capable of multi-play with many other mobile users using mobile terminals in wireless mobile computing environment, is designed and implemented. Proposed mobile online game uses bluetooth to construct temporary wireless mobile ad hoc network with other mobile clients, and designed to carry out online MMORPG game with these clients. It also supports multi-play among them.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.7
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• pp.9-19
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• 2004

WLAN (Wireless Local Area Networks) needs error recovery and flow control schemes to support reliable multicast protocol. Limited wireless bandwidth, as well as queuing losses caused by the asymmetric wired/wireless interactions, demands more effective approaches for reducing packet losses. Moreover, since the wireless channel is a shared broadcast medium, if sender receives feedback information simultaneously from several receivers, the feedback delays data frame transmission of forward direction by introducing channel congestion and burden at the sender. Therefore, it is important to minimize the amount of feedback information from receivers. In this paper, we propose an ARS(Adaptive Redundancy Scheme) that combines FEC(Forward Error Correction) using channel state estimation and ARQ(Automatic Repeat Request) both to reduce the amount of feedback information and the number of retransmissions and to guarantee high data reliability in a WLAN multicast environment. Performance of the proposed scheme is evaluated by means of analysis and simulations in AWGN and Rayleigh fading channels. The results show that the proposed scheme reduces the amount of feedback information and the number of retransmissions and guarantees high data reliability, while keeping throughput efficiency similarly with the conventional FEC and ARQ scheme.

• Journal of the Korea Society for Simulation
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• v.20 no.4
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• pp.157-166
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• 2011

As underwater environment monitoring system's interest has increased, the research is proceeding about underwater acoustic sensor network. Underwater sensor network can be applicable to many fields, such as underwater environment monitoring, underwater resource exploration, oceanic data collection, military purposes, etc. It is essential to define the PHY-MAC protocol for revitalization of the underwater acoustic sensor network which is available utilization in a variety of fields. However, underwater acoustic sensor network has to implement by consideration of underwater environmental characteristics, such as limited bandwidth, multi-path, fading, long propagation delay caused by low acoustic speed. In this paper, we define frequency of adjusted PHY protocol, network topology, MAC protocol, PHY-MAC interface, data frame format by consideration of underwater environmental characteristics. We also present system configuration of our implementation and evaluate performance based on our implementation with test in real underwater field.