• Journal of the Korean Physical Society
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• 제73권10호
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• pp.1589-1595
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• 2018

Similarity index measures the topological proximity of node pairs in a complex network. Numerous similarity indices have been defined and investigated, but the dependency of structure on the performance of similarity indices has not been sufficiently investigated. In this study, we investigated the relationship between the performance of similarity indices and structural properties of a network by employing a two-state random network. A node in a two-state network has binary types that are initially given, and a connection probability is determined from the state of the node pair. The performances of similarity indices are affected by the number of links and the ratio of intra-connections to inter-connections. Similarity indices have different characteristics depending on their type. Local indices perform well in small-size networks and do not depend on whether the structure is intra-dominant or inter-dominant. In contrast, global indices perform better in large-size networks, and some such indices do not perform well in an inter-dominant structure. We also found that link prediction performance and the performance of similarity are correlated in both model networks and empirical networks. This relationship implies that link prediction performance can be used as an approximation for the performance of the similarity index when information about node type is unavailable. This relationship may help to find the appropriate index for given networks.

• Journal of Communications and Networks
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• 제6권1호
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• pp.46-59
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• 2004

In this paper, we present two algorithms for efficiently aggregating link state information needed for quality-of-service (QoS) routing. In these algorithms, each edge node in a group is mapped onto a node of a shufflenet or a node of a de Bruijn graph. By this mapping, the number of links for which state information is maintained becomes aN (a is an integer, N is the number of edge nodes) which is significantly smaller than N2 in the full-mesh approach. Our algorithms also can support asymmetric link state parameters which are common in practice, while many previous algorithms such as the spanning tree approach can be applied only to networks with symmetric link state parameters. Experimental results show that the performance of our shufflenet algorithm is close to that of the full-mesh approach in terms of the accuracy of bandwidth and delay information, with only a much smaller amount of information. On the other hand, although it is not as good as the shufflenet approach, the de Bruijn algorithm also performs far better than the star approach which is one of the most widely accepted schemes. The de Bruijn algorithm needs smaller computational complexity than most previous algorithms for asymmetric networks, including the shufflenet algorithm.

• 전자공학회논문지
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• 제53권4호
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• pp.79-86
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• 2016

물리계층보안은 신호의 물리적 특성을 이용하여 정보를 보호하는 보안 기법이다. 현재 이에 대한 연구가 활발히 진행 중이지만 해결해야할 다음과 같은 문제점들이 존재한다. 도청자는 자신의 존재를 숨기기 위해서 자신의 채널상태정보를 다른 합법적인 노드와 공유하지는 않는다. 그리고 노드가 신호를 전송할 때 하드웨어 왜곡이 발생하지만 많은 연구들은 노드 모델들이 이상적인 것으로 가정을 하고, 하드웨어 왜곡문제를 고려하지 않고 있다. 이와 같은 문제점들을 해결하기 위한 본 논문의 주요한 특징 및 기여도는 다음과 같다. 첫째, 도청자의 채널상태정보를 얻기 위해서 조력자노드를 합법적인 노드주변에 설치하고, 조력자노드의 채널상태정보를 이용하여 노드모델에서 하드웨어 왜곡을 고려한다. 둘째, 제안된 시스템 모델의 인터셉트 확률에 대한 Closed-Form Expression을 제시한다. 제안된 시스템의 성능평가를 위해서 다양한 시뮬레이션를 통하여 제안된 시스템 모델의 물리계층보안에 미치는 영향을 알아본 결과, 불완전한 채널상태정보는 인터셉트 확률에는 영향을 미치지 못한 반면에, 불완전한 노드모델의 경우, 인터셉트 확률, 에르고딕 시크리스 용량과 보안채널용량에 영향을 준다는 것을 보여준다.

• Journal of Gastric Cancer
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• 제17권4호
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• pp.306-318
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• 2017

Purpose: Guidelines in Western countries recommend retrieving ${\geq}15$ lymph nodes (LNs) during gastric cancer resection. This study sought to determine whether the number of examined lymph nodes (eLNs), a proxy for lymphadenectomy, effects survival in node-negative disease. Materials and Methods: The US National Cancer Database (2003-2011) was reviewed for node-negative gastric adenocarcinoma. Treatment was categorized by neoadjuvant therapy (NAT) vs. initial resection, and further stratified by eLN. Kaplan-Meier and Weibull models were used to analyze overall survival. Results: Of the 1,036 patients who received NAT, 40.5% had ${\leq}10eLN$, and most underwent proximal gastrectomy (67.8%). In multivariate analysis, greater eLN was associated with improved survival (eLN 16-20: HR, 0.71; P=0.039, eLN 21-30: HR, 0.55; P=0.001). Of the 2,795 patients who underwent initial surgery, 42.5% had ${\leq}10eLN$, and the majority underwent proximal gastrectomy (57.2%). In multivariate analysis, greater eLN was associated with improved survival (eLN 11-15: HR, 0.81; P=0.021, eLN 16-20: HR, 0.73; P=0.004, eLN 21-30: HR, 0.62; P<0.001, and eLN >30: HR, 0.58; P<0.001). Conclusions: In the United States, the majority of node-negative gastrectomies include suboptimal eLN. In node-negative gastric cancer, greater LN retrieval appears to have therapeutic and prognostic value, irrespective of initial treatment, suggesting a survival benefit to meticulous lymphadenectomy.

• 대한전자공학회논문지
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• 제26권9호
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• pp.1395-1401
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• 1989

An efficient file allocation algorithm and a new method which calculate appraisal value of candidate computer site for distributed computer systems are proposed. The file allocation problem size is reduced by using the preassignment condition. The appraisal value of candidate node is calcualted as the user state array and node state array are varied according to control variables. As the selection criteria is applied to the candidates, the reasonable node is selected and assign state is determined. The proposed algorithm is heuriatic polynomial time algorithm. By performing algorithm for sample problems. It is shown that the proposed algorithm is superior to conventional method in terms of deviation from optimal solution.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권8호
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• pp.2875-2893
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• 2015

Existing coding aware routing algorithms focused on novel routing metric design that captures the characteristics of network coding. However, in packet coding algorithm, they use opportunistic coding scheme which didn't consider the queue state of the coding node and are equivalent to the conventional store-and-forward method in light traffic load condition because they never delay packets and there are no packets in the output queue of coding node, which results in no coding opportunity. In addition, most of the existing algorithms assume that all flows participating in the network have equal rate. This is unrealistic since multi-rate environments are often appeared. To overcome above problem and expand network coding to light traffic load scenarios, we present an enhanced coding-aware routing algorithm based on queue state and local topology (OQMCAR), which consider the queue state of coding node in packet coding algorithm where the control policy is of threshold-type. OQMCAR is a unified framework to merge single rate case and multiple rate case, including the light traffic load scenarios. Simulations results show that our scheme can achieve higher throughput and lower end-to-end delay than the current mechanisms using COPE-type opportunistic coding policy in different cases.

• 융합보안논문지
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• 제8권2호
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• pp.57-62
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• 2008

본 논문은 RPR 망에서 외부의 공격으로 인해 새로운 노드의 추가, 제거 혹은 링크의 단절과 같은 상황이 발생하였을 때, 보다 신속하게 망을 복원할 수 있도록 새로운 방안을 제안한다. 망 복원에 소요되는 시간은 크게 문제를 감지하는데 소요되는 시간과 이를 복원하는데 소요되는 시간으로 나눌 수 있다. 본 논문에서는 이러한 시간들을 각각 단축함으로써 신속한 망 복원을 가능하게 하는 방법을 제안한다. 기존의 복구 방식에서는 망 복원용으로 사용되는 프로텍션 메시지의 전송으로 링크 또는 노드의 상태를 지속적으로 보고하며, 이러한 프로텍션 메시지의 전송 간격은 지수증가 한다. 프로텍션 메시지의 전송 간격이 지수증가 함으로써 야기되는 문제점은, 프로텍션 메시지의 전송 실패로 인해, 링크 또는 노드의 상태 보고가 지연될 수 있다는 것이다. 이를 해결하기 위해서 본 논문에서는 노드간의 자동 대역조절을 위하여 1ms주기로 전송되는 b형 공평메시지에 링크 또는 노드의 상태 정보를 실어서 전송하는 방법을 제안한다. 또한, 기존의 링크의 단절을 보다 신속히 감지하기 위한 방법도 제안한다.

• Journal of Computing Science and Engineering
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• 제9권4호
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• pp.163-176
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• 2015

Self-organization of distributed wireless sensor nodes is a critical issue in wireless sensor networks (WSNs), since each sensor node has limited energy, bandwidth, and scalability. These issues prevent sensor nodes from actively collaborating with the other types of sensor nodes deployed in a typical heterogeneous and somewhat hostile environment. The automated self-organization of a WSN becomes more challenging as the number of sensor nodes increases in the network. In this paper, we propose a dynamic self-organized architecture that combines tree topology with a drawn-grid algorithm to automate the self-organization process for WSNs. In order to make our proposed architecture scalable, we assume that all participating active sensor nodes are unaware of their primary locations. In particular, this paper presents two algorithms called active-tree and drawn-grid. The proposed active-tree algorithm uses a tree topology to assign node IDs and define different roles to each participating sensor node. On the other hand, the drawn-grid algorithm divides the sensor nodes into cells with respect to the radio coverage area and the specific roles assigned by the active-tree algorithm. Thus, both proposed algorithms collaborate with each other to automate the self-organizing process for WSNs. The numerical and simulation results demonstrate that the proposed dynamic architecture performs much better than a static architecture in terms of the self-organization of wireless sensor nodes and energy consumption.

• 한국ITS학회 논문지
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• 제8권6호
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• pp.73-81
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• 2009

무선 매체로의 전송은 유선 매체로의 전송에 비해 낮은 신뢰성과 전송의 안정성이라는 단점을 갖는다. 이를 위한 하나의 대안으로 협업 통신의 다이버시티 효과와 채널 코딩 방법을 통한 오류 정정 효과를 사용하고자 한다. 본 문에서는 전송의 신뢰성 향상을 위해 RCPC codes와 Hybrid-ARQ type-2 전송 방식을 사용한 협업 통신 시스템을 제안하고 그에 대한 시뮬레이션을 실시하였다. 그 결과로 기존의 전송에 비해 제안한 시스템이 낮은 BER값을 가져옴을 보였다. 또한 릴레이 노드와 목적지 노드 사이의 채널 상태보다 소스 노드와 릴레이 노드 사이의 채널 상태가 시스템 성능에 더 중요하다는 사실을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제2권1호
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• pp.5-21
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• 2008

In order to securely transmit multicast data packets in a mobile environment where frequent join/leave events are a characteristic of the environment, there is a need for a new secure and efficient group key management solution. We propose a secure group key generation/distribution solution providing scalability and reliability. Using this solution, when a mobile node, which is in a multicast session, enters a new domain, the agent of the domain joins the multicast session and coordinates its data packets with the mobile node. The agent encrypts and transmits subsequent data packets to the mobile node, using a local one-time pad key. This key is generated with FI sequences, enabling the mobile node to regenerate the same data packet, based on the information sent by the agent. Our performance analysis demonstrates that the proposed solution can significantly reduce the number of key generations and distributions, when it is applied to the hierarchical mobile IPv6 network.