• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.3
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• pp.173-176
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• 2020

This study focuses on a pillar in which is implanted a P-type maneuver under a P base. This structure is called a super junction structure. By inserting the pillar, the electric field concentrated on the P base is shared by the pillar, so the columns can be dispersed while maintaining a high breakdown voltage. Ten pillars were generated during the multi epitaxial process. The interval between pillars is varied to optimize the electric field to be concentrated on the pillar at a threshold voltage of 6 V, a yield voltage of 4,500 V, and an on-state voltage drop of 3.8 V. The density of the filler gradually decreased when the interval was extended by implanting a filler with the same density. The results confirmed that the size of the depletion layer between the filler and the N-epitaxy layer was reduced, and the current flowing along the N-epitaxy layer was increased. As the interval between the fillers decreased, the cost of the epitaxial process also decreased. However, it is possible to confirm the trade-off relationship that deteriorated the electrical characteristics and efficiency.

• Journal of the Korea Computer Graphics Society
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• v.4 no.1
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• pp.89-100
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• 1998

A multi-user virtual reality system supports shared environments for concurrent accesses by multiple users. The performance of these systems depends heavily on the network environments. This paper experiments an effective network model for shared virtual environments. This model has a middle layer called groups placed between the server and its clients, and the tasks of server are distributed to these groups. Using groups solves some of the problems of existing systems such as lack of scalability, message overheads, and latency due to message passing among locally communicating entities in the virtual environment. Some experiments show lower overhead than existing distributed virtual environment systems in WAN as well as LAN environments. This model also supports a method that can be used to construct application specific network environments using message handler which allows user-defined message formats.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3747-3765
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• 2017

Existing authentication mechanisms in cellular mobile communication networks are realized in the upper layer by employing cryptographic techniques. Authentication data are broadcasted over the air in plaintext, enabling attackers to completely eavesdrop on the authentication and get some information about the shared secret key between legitimate nodes. Therefore, reusing the same secret key to authenticate several times results in the secret key's information leakage and high attacking rate. In this paper, we consider the most representative authentication mechanism, Authentication and Key Agreement (AKA), in cellular communication networks and propose an enhanced AKA scheme based on Physical Layer Authentication (AKA-PLA). Authentication responses generated by AKA are no longer transmitted in plaintext but masked by wireless channel characteristics, which are not available to adversaries, to generate physical layer authentication responses by a fault-tolerant hash method. The authenticator sets the threshold according to the authentication requirement and channel condition, further verifies the identity of the requester based on the matching result of the physical layer authentication responses. The performance analyses show that the proposed scheme can achieve lower false alarm rate and missing rate, which are a pair of contradictions, than traditional AKA. Besides, it is well compatible with AKA.

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.4
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• pp.226-238
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• 2010

OpenSSL is an open-source library implementing SSL that is a secure communication protocol. However, the library has a severe vulnerability that its security information can be easily exposed to malicious software when the library is used in a form of shared library on Linux and UNIX operating systems. We propose a scheme to attack the vulnerability of the OpenSSL library. The scheme injects codes into a running client program to execute the following attacks on the vulnerability in a SSL handshake. First, when a client sends a server a list of cryptographic algorithms that the client is willing to support, our scheme replaces all algorithms in the list with a specific algorithm. Such a replacement causes the server to select the specific algorithm. Second, the scheme steals a key for data encryption and decryption when the key is generated. Then the key is sent to an outside attacker. After that, the outside attacker decrypts encrypted data that has been transmitted between the client and the server, using the specified algorithm and the key. To show that our scheme is realizable, we perform an experiment of collecting encrypted login data that an ftp client using the OpenSSL shared library sends its server and then decrypting the login data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4B
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• pp.269-277
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• 2012

The future battlefield environment has changed platform centric warfare into a network centric warfare. The NCO is a operational concept to improve combat power through information sharing, shared situational awareness, decision making and synchronized action based on powerful network grid. In addition, these operational environment is composed of physical, information, cognitive and social domains. The platform environment system is associated with the OSI 7 layer. However, OSI 7 layer is limited to express NCW environment including cognitive and social domains. Therefore, we requires a new model for expressing cognitive and social domains. After we developed a new model, this model applied to the NCW architecture taxonomy.

• Journal of computational fluids engineering
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• v.16 no.1
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• pp.30-35
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• 2011

In this paper, our effort to apply 3-D Virtual Reality system for stereoscopic visualization of mesh data on the web is briefly described. This study is an extension of our previous and on-going research efforts to develop an automatic grid generation program specialized for wing mesh, named as eGWing. The program is developed by using JAVA programming language, and it can be used either as an application program on a local computer or as an applet in the network environment. In this research advancing layer method(ALM) augmented by elliptic smoothing method is used for the structured grid generation. And to achieve a stereoscopic viewing capability, two graphic windows are used to render its own viewing image for the left and right eye respectively. These two windows are merged into one image using 3D monitor and the viewers can see the mesh data visualization results with stereoscopic depth effects by using polarizing glasses. In this paper three dimensional mesh data visualization with stereoscopic technique combined with 3D monitor is demonstrated, and the current achievement would be a good start-up for further development of low-cost high-quality stereoscopic mesh data visualization system which can be shared by many users through the web.

• Journal of the Korea Society for Simulation
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• v.12 no.4
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• pp.73-81
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• 2003

An Ad Hoc network is a dynamic multi-hop wireless network that is established by a group of mobile hosts on a shared wireless channel by virtue of their proximity to each other. Since wireless transmissions are locally broadcast in the region of the transmitting host, hosts that are in close proximity can hear each other and are said to be neighbors. The transitive closure of the neighborhood of all the hosts in the set of mobile hosts under consideration forms an Ad Hoc network. Thus, each host is potentially a router and it is possible to dynamically establish routes by chaining together a sequence of neighboring hosts from a source to a destination in the Ad Hoc network. In a network, various real-time services require the network to guarantee the Quality of Services provided to the receiver. End-to-end QoS can be provided most efficiently when each layer of the protocol stack translates the requirements of the application into layer classified requirements and satisfies them. In this study, a mechanism to guarantee the QoS in Ad Hoc networks with buffer nodes is proposed. They effectively prevent traffic congestion and yield better transmission rate. In this way QoS is enhanced.

• Journal of Communications and Networks
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• v.12 no.3
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• pp.275-284
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• 2010

The current multihome-aware protocols (like stream control transmission protocol (SCTP) or parallel TCP for concurrent multipath data transfer (CMT) are not designed for high-capacity and large-latency networks; they often have performance problems transferring large data files over shared long-distance wide area networks. It has been shown that SCTP-CMT is more sensitive to receive buffer (rbuf) constraints, and this rbuf-blocking problem causes considerable throughput loss when multiple paths are used simultaneously. In this research paper, we demonstrate the weakness of SCTP-CMT rbuf constraints, and we then identify that rbuf-blocking problem in SCTP multihoming is mostly due to its loss-based nature for detecting network congestion. We present a simulation-based performance comparison of FAST TCP versus SCTP in high-speed networks for solving a number of throughput issues. This work proposes an end-to-end transport layer protocol (i.e., FAST TCP multihoming as a reliable, delaybased, multihome-aware, and selective ACK-based transport protocol), which can transfer data between a multihomed source and destination hosts through multiple paths simultaneously. Through extensive ns-2 simulations, we show that FAST TCP multihoming achieves the desired goals under a variety of network conditions. The experimental results and survey presented in this research also provide an insight on design decisions for the future high-speed multihomed transport layer protocols.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1998.11a
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• pp.450-455
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• 1998

This paper proposes an enhanced transport protocol for multipeer communications. It is assumed that there exists a transport connection owner that takes the roles of the establishment, management and termination of a transport connection. The proposed protocol classifies the data transfer type into simplex, duplex and N-plex multicasts and provides several transport services to support various requirements in group communications. The general operations and reliability controls of each transfer type are different from one another and carried out by a shared control tree. The QoS negotiation is performed during the creation phase. The notification of negotiated values is followed by an acknowledgment procedure for confirmation. The four-way handshake is introduced. After negotiation, such a resource reservation protocol as RSVP can reserve system and network resources according to the arbitrated values. This paper suggests a conceptual model of the transport layer and its protocol behaviors over the IP multicast and RSVP network.

• Journal of Communications and Networks
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• v.14 no.4
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• pp.385-395
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• 2012

This paper tackles the problem of generating shared secret keys based on the physical characteristics of the wireless channel. We propose intelligent quantization mechanisms for key generation, achieving high secret bits generation rate. Moreover, some practical issues affecting the performance of the key generation mechanism are deeply investigated. Mainly, we investigate the effects of delay and mobility on the performance and we enhance the key generation mechanism accordingly. As a result, this paper presents a framework towards robust key generation from multipath wireless channels.