• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.5
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• pp.1929-1950
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• 2020

Reliable and secure data transmission in the application environment assisted by the wireless sensor network is one of the major challenges. Problem like blind forwarding and data inaccessibility affect the efficiency of overall infrastructure performance. This paper proposes routing protocol for forwarding and error recovery during packet loss. The same is achieved by energy and hops distance-based formulation of the routing mechanism. The reachability of the intermediate node to the source node is the major factor that helps in improving the lifetime of the network. On the other hand, intelligent hop selection increases the reliability over continuous data transmission. The number of hop count is factor of hop weight and available energy of the node. The comparison over the previous state of the art using QualNet-7.4 network simulator shows the effectiveness of proposed work in terms of overall energy conservation of network and reliable data delivery. The simulation results also show the elimination of blind forwarding and data inaccessibility.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.4
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• pp.39-48
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• 2009

Asynchronous sequential machines, or clockless logic circuits, have several advantages over synchronous machines such as fast operation speed, low power consumption, etc. In this paper, we propose a novel robust controller for input/output asynchronous sequential machines with uncertain state transitions. Due to model uncertainties or inner failures, the state transition function of the considered asynchronous machine is not completely known. In this study, we present a formulation to model this kind of asynchronous machines ana using generalized reachability matrices, we address the condition for the existence of an appropriate controller such that the closed-loop behavior matches that of a prescribed model. Based on the previous research results, we sketch design procedure of the proposed controller and analyze the stable-state operation of the closed-loop system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.6
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• pp.2180-2200
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• 2015

This paper considers mobility control to improve packet delivery in delay-tolerant networks (DTNs) under group mobility. Based on the group structure in group mobility, we propose two mobility control techniques; group formation enforcement and group purposeful movement. Both techniques can be used to increase the contact opportunities between groups by extending the group's reachability. In addition, they can be easily integrated into some existing DTN routing schemes under group mobility to effectively expedite the packet delivery. This paper is divided into 2 parts. First, we study how our proposed mobility control schemes reduce the packet delivery delay in DTNs by integrating them into one simple routing scheme called group-epidemic routing (G-ER). For each scheme, we analytically derive the cumulative density function of the packet delivery delay to show how it can effectively reduce the packet delivery delay. Then, based on our second proposed technique, the group purposeful movement, we design a new DTN routing scheme, called purposeful movement assisted routing (PMAR), to further reduce the packet delay. Extensive simulations in NS2 have been conducted to show the significant improvement of PMAR over G-ER under different practical network conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.15 no.6
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• pp.516-525
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• 1990

This paper proposes a hierarchical control algorithm for an efficient network management of a loosely-coupled system which consists of functional division and duplicating structure with a LAN to enhance reliability and availability. The algorithm is modeled using the Perti-net and verified with the reachability tree. Here, the proposed algorithm is compared with the purely centralized control algorithm and distributed control algorithm in terms of message traffic for the network management. The result shows that the message traffic related to system performance is as low as centralized control algorithm and the system availability is independent of a specific processor failure.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.3
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• pp.490-508
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• 2013

One of the most important scalability issues facing the current Internet is the rapidly increasing rate of BGP updates (BGP churn), to which route flap and path exploration are the two major contributors. Current countermeasures would either cause severe reachability loss or delay BGP convergence, and are becoming less attractive for the rising concern about routing convergence as the prevalence of Internet-based real time applications. Based on the observation that highly active prefixes usually repeatedly explore very few as-paths during path exploration, we propose a router-level mechanism, Path Exploration Aggregation (PEA), to scale BGP without either causing prefix unreachable or slowing routing convergence. PEA performs aggregation on the transient paths explored by a highly active prefix, and propagates the aggregated path instead to reduce the updates caused by as-path changes. Moreover, in order to avoid the use of unstable routes, PEA purposely prolongs the aggregated path via as-path prepending to make it less preferred in the perspective of downstream routers. With the BGP traces obtained from RouteViews and RIPE-RIS projects, PEA can reduce BGP updates by up to 63.1%, shorten path exploration duration by up to 53.3%, and accelerate the convergence 7.39 seconds on average per routing event.

• Journal of Korea Society of Digital Industry and Information Management
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• v.16 no.1
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• pp.79-92
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• 2020

As the number of systems increases and the network size increases, automated attack prediction systems are urgently needed to respond to cyber attacks. In this study, we developed four types of information gathering sensors for collecting asset and vulnerability information, and developed technology to automatically generate attack graphs and predict attack targets. To improve performance, the attack graph generation method is divided into the reachability calculation process and the vulnerability assignment process. It always keeps up to date by starting calculations whenever asset and vulnerability information changes. In order to improve the accuracy of the attack target prediction, the degree of asset risk and the degree of asset reference are reflected. We refer to CVSS(Common Vulnerability Scoring System) for asset risk, and Google's PageRank algorithm for asset reference. The results of attack target prediction is displayed on the web screen and CyCOP(Cyber Common Operation Picture) to help both analysts and decision makers.

• International Journal of Aeronautical and Space Sciences
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• v.4 no.1
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• pp.1-8
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• 2003

In this paper, a reconfigurable flight control system is designed by applying the sliding mode control scheme. The sliding mode control method is a nonlinear control method which has been widely used because of its merits such as robustness and flexibility. In the sliding mode controller design, the signum function is usually included, but it causes the undesirable chattering problem. The chattering phenomenon can be avoided by using the saturation function instead of signum function. However, the boundary layer of the sliding surface should be carefully treated because of the use of the saturation function. In contrast to the conventional approaches, the thickness of the boundary layer of our approach does not need to be small. The reachability to the boundary layer is guaranteed by the sliding mode controller. The fault detection and isolation process is operated based on a sliding mode observer. To evaluate the reconfiguration performance, a numerical simulation using six degree-of-freedom aircraft dynamics is performed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.4
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• pp.1630-1642
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• 2016

Inter-domain routing is the most critical function of the Internet. The routing system is a logical network relying on the physical infrastructure with geographical characteristics. Nature disasters or disruptive accidents such as earthquakes, cable cuts and power outages could cause regional failures which fail down geographically co-located network nodes and links, therefore, affect the resilience of inter-domain routing system. This paper presents a model for regional failures in inter-domain routing system called REFER for the first time. Based on REFER, the resilience of the inter-domain routing system could be evaluated on a finer level of the Internet, considering different routing policies of intra-domain and inter-domain routing systems. Under this model, we perform simulations on an empirical topology of the Internet with geographical characteristics to simulate a regional failure locating at a city with important IXP (Internet eXchange Point). Results indicate that the Internet is robust under a city-level regional failure. The reachability is almost the same after the failure, and the reroutings occur at the edge of the Internet, hardly affecting the core of inter-domain routing system.

• Journal of the Korea Safety Management & Science
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• v.13 no.3
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• pp.1-8
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• 2011

The overall goal of a safety based railroad system is either to eliminate hazards in designing or to minimize the possibility of it. In order to indicate system safety or low risk although it may not be possible to achieve zero risk conditions, first, it shall ensure that any disasters would occur due to system operation because the prescribed specifications are properly fulfilled and there are no failures of any kind. Second, the risk of faults or failures leading to a mishap must be eliminated or minimized by using fault-tolerance or fail-safe procedures. This paper will attempt to summarize the personal and social risk criterion at widely scattered points, presently used as a safety approach in all over EU, in order to establish the step by step procedures of the detailed standard for railway facilities. In addition, we present the new safety analysis method using the SIL-based evaluation standard and the Reachability Graph of the Petri Net.

• Journal of the Korean Institute of Intelligent Systems
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• v.25 no.2
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• pp.139-146
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• 2015

This paper presents the solution to model matching of switched asynchronous sequential machines by corrective control. We propose a model of switched asynchronous sequential machines, in which the system can have different dynamics of asynchronous machines governed by a pre-determined sequence of switching. The control objective is to derive a corrective control law so that the stable state behavior of the closed-loop system can match that of a prescribed model. A new skeleton matrix is defined to represent the reachability of the switched asynchronous machine, and a novel control scheme is presented that interweaves the switching signal and the corrective control procedure. A design algorithm for the proposed controller is illustrated in a case study.