• The KIPS Transactions:PartC
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• v.14C no.1 s.111
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• pp.45-54
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• 2007

As one of the most threatening attacks, DDoS attack makes distributed multiple agents consume some critical resources at the target within the short time, thus the extent and scope of damage is serious. Against the problems, the existing defenses focus on detection, traceback (identification), and filtering. Especially, in the hierarchical networks, the traffic congestion of a specific node could incur the normal traffic congestion of overall lower nodes, and also block the control traffic for notifying the attack detection and identifying the attack agents. In this paper, we introduce a DDoS attack tolerant network structure using a hierarchical overlay for hierarchical networks, which can convey the control traffic for defense such as the notification for attack detection and identification, and detour the normal traffic before getting rid of attack agents. Lastly, we analyze the overhead of overlay construction, the possibility of speedy detection notification, and the extent of normal traffic transmission in the attack case through simulation.

• Journal of Digital Contents Society
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• v.18 no.1
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• pp.133-139
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• 2017

To address the problems caused by such high installation and maintenance cost in the conventional server-based cloud systems, researches on P2P cloud storages have been conducted recently. In this paper, we propose a hierachical overlay structure that can improve the playback quality in P2P cloud storage systems for video transmission. In this structure, after we make groups by clustering the participating peers based on their similarities, we construct subgroups by geographically dividing the peers belonging to a specific group considering the physical proximities among them. Therefore, when a request for video playback is issued, we can minimize the transmission delay by selecting the source peers depending on their locality. By simulations, we show that our proposed hierarchical overlay structure considering the peers' locality outperforms the structure where source peers are selected randomly.

• Communications of the Korean Institute of Information Scientists and Engineers
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• v.25 no.1 s.212
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• pp.59-68
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• 2007

홈 네트워크가 다양하고 풍부한 콘텐츠를 보유하는 엔터테인먼트 네트워크로 발전함에 따라 향후에는 사용자들이 UCC(user created contents) P2P(peer-to-peer) 파일공유 응용의 사례와 유사하게 자신들의 관심 정보에 기초하여 콘텐츠를 홈 네트워크들 간의 커뮤니티를 예상하면서 이를 디지털 홈 커뮤니티(DHC: digital home community)로 명명한다. DHC 환경하에서 효율적으로 콘텐츠를 공유하려면 계층적인 P2P 기반 오버레이(overlay) 네트워킹에 의한 연결성 및 검색 기법, QoS 및 보안을 안정적으로 지원하는 P2P기반 콘텐츠 분배 기법, 그리고 이에 수반되는 각종 미디어지원 홈 네트워크기기들의 자원 관리 및 구성 기법 등의 다양한 사항들이 만족되어야 한다. 따라서 본 논문에서는 DHC 환경에 적합한 특성을 지니는 오버레이 기반 콘텐츠 검색 및 전송 기법들에 대한 고찰을 시도해 본다.

• The KIPS Transactions:PartC
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• v.13C no.5 s.108
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• pp.627-634
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• 2006

Overlay network eliminates the need to change the application-layer tree when the underlying network changes and enables the overlay network to survive in environments where nonmember nodes do not support multicast functionality. An overlay protocol monitors group dynamics, while underlying unicast protocols track network dynamics, resulting in more stable protocol operation and low control overhead even in a highly dynamic environment. But, if overlay multicast protocols does not know the location information of node, this makes it very difficult to build an efficient multicasting tree. So, we propose a Hierarchical Overlay Multicast Architecture (HOMA) with the location information. Because proposed architecture makes static region-based dynamic group by multicast members, it is 2-tired overlay multicasts of application layer that higher layer forms overlay multicast network between members that represent group, and support multicast between multicast members belonging to region at lower layer. This use GPS, take advantage of geographical region, and realizes a region-sensitive higher layer overlay multicast tree which is impervious to the movements of nodes. The simulation results show that our approach solves the efficiency problem effectively.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.05a
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• pp.1339-1342
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• 2005

이기종 네트워크들이 계층적인 구조로 결합되어 있는 오버레이 네트워크 환경에서 이동 단말(Mobile Terminal:MT)의 끊김없는 이동성 지원을 위해서는, 패킷 손실 및 호 단절 현상을 최소화할 수 있는 최적의 핸드오버 시점을 결정할 수 있어야 한다. 기존의 수직적 핸드오버 기법은, 단순히 MT의 위치 정보를 바탕으로 핸드오버 수행을 예측하고 결정하였다. 하지만 이 기법은, MT의 위치와 관계없이 네트워크의 과부하로 인한 패킷 손실 및 호 단절 현상이 발생할 수 있기 때문에, 네트워크의 과부하에 따른 핸드오버 시점을 간과하는 문제점을 노출하였다. 하루가 다르게 인터넷 트래픽이 급증하는 현실에서, 네트워크의 과부하를 고려하는 핸드오버 기법이 필요한 때이다. 따라서 본 논문에서는 MT의 위치와 네트워크의 부하를 모두 고려하여 핸드오버 시점을 결정할 수 있는 핸드오버 맵(Handover-Map:H-Map)의 개념을 제안한다. 그리고 핸드오버 동기화 현상을 최소화하기 위해 향상된 H-Map을 기반으로 차별화된 핸드오버 시점을 부여하는 VAH(Vertical handover on Advanced H-Map) 기법을 소개하고, 이의 성능을 기존기법과 비교한다.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.7
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• pp.743-747
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• 2008

Hierarchical overlay of heterogeneous wireless cells is considered as a promising architecture for next-generation wireless networks. This paper considers a special form of such architecture, WWAN/WLAN two-hop wireless relay networks. We first describe an undesirable scheduling phenomenon that the conventional proportional fair algorithm can cause in such networks. We, then, propose an enhanced proportional fair scheduling to remedy this problem. We demonstrate the performance of the proposed scheme via a simulation of UMTS/WLAN networks using NS-2.

• Journal of KIISE:Information Networking
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• v.34 no.2
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• pp.88-99
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• 2007

P2P systems are distributed data sharing systems, and each node in them plays the role of client as well as server. There are several studies using Distributed Hash Table, such as Chord, CAN, Tapestry, Pastry, but these systems don't consider the physical latency, therefore they have a weakness of difficulty to guarantee stable performance. To improve this problem, we present the TP2P system. This system is a self-organizing hierarchical overlay system and it uses Chord routing mechanism for lookup data. This system is organized by several subnets, each subnet is organized by physically close nodes, and global network organized by all nodes. In each subnet, one node finds a data, it saves in a node in the subnet, therefore it has higher probability to reduce physical lookup latency than Chord system. And each node has global information of some nodes in its subnet, and it is used to lookup data, therefore the number of hops decrease about 25% as well as the physical lookup latecy are reduced.

• The KIPS Transactions:PartA
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• v.14A no.6
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• pp.333-340
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• 2007

In multi agent systems, various inter agent communication models have been proposed, and, especially, there are several group communication schemes proposed so far, where some schemes guarantees transparent communication among the agents. However, in mobile agent environments, we require new group communication schemes that consider topology changes caused by mobile agent migrations. Also, these group communication schemes should be secure in order for them to be practical. In this paper, we propose a secure group communication scheme using the hierarchical overlay ring structure of mobile agents. The proposed scheme uses the ring channel in order to cope adaptively with the change of ring topology. The ring channel has basic information for construction of the ring and is managed only by the mobile agent platforms. Therefore, each mobile agent need not directly handle the ring channel and it can perform group communication without any consideration on the change of the ring topology.

• Journal of Internet Computing and Services
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• v.7 no.5
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• pp.43-57
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• 2006

Next-generation mobile communication systems evolve in the form of high speed data transmission along with integration of wired-wireless network. Therefore, it needs researches on integrating service to heterogeneous networks to offer high speed data transmission and various services while supporting user mobility. In existing studies, heterogeneous networks are linked to single core network separatively, Since vertical handoff between heterogeneous networks leads to some delay, packets may be lost during vertical handoff. To solve this problem, this paper proposes an hierarchically integrated network architecture considering the characteristics of CDMA2000, WiBro, and WLAN. The hierarchically integrated networks are overlaid according to coverage of each network. Therefore, the proposed architecture can minimize handoff delay and packet loss. In addition, this paper proposes an integrated framework for next generation mobile communication networks.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.5
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• pp.457-461
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• 2008

Previous studies on overlay ad hoc multi-casting are mainly divided into two categories: hierarchical structure-based multicast schemes and non-hierarchical structure-based multicast schemes. They do not reflect their real-time location information for routing updates. This can be a cause of low performance on energy consumption, throughput, and latency. For improving the problems, we propose an implicit cluster based overlay ad hoc multicast scheme with analysis of related work, and then we evaluate performance through computer simulation.