• The KIPS Transactions:PartC
• /
• v.17C no.1
• /
• pp.1-14
• /
• 2010

IEEE 802.15.4[1] has been standardized for the physical layer and MAC layer of LR-PANs(Low Rate-Wireless Personal Area Networks) as a technology for operations with low power on sensor networks. The standardization is applied to the variety of applications in the shortrange wireless communication with limited output and performance, for example wireless sensor or virtual wire, but it includes vulnerabilities for various attacks because of the lack of security researches. In this paper, we analyze the vulnerabilities against the denial of sleep attacks on the MAC layer of IEEE 802.15.4, and propose a detection mechanism against it. In results, we analyzed the possibilities of denial of sleep attacks by the modification of superframe, the modification of CW(Contention Window), the process of channel scan or PAN association, and so on. Moreover, we comprehended that some of these attacks can mount even though the standardized security services such as encryption or authentication are performed. In addition to, we model for denial of sleep attacks by Beacon/Association Request messages, and propose a detection mechanism against them. This detection mechanism utilizes the management table consisting of the interval and node ID of request messages, and signal strength. In simulation results, we can show the effect of attacks, the detection possibility and performance superiorities of proposed mechanism.

• Journal of the Korean Geographical Society
• /
• v.48 no.5
• /
• pp.686-708
• /
• 2013

The goal of this investigation is to examine the matter as to how various cyberpolitical activities such as on-line civic participation, cyber parties, development and movement of civil society networks are appeared in cyberspace; and how political activities in cyberspace are associated with offline environment. This research was based on in-depth and open-ended interviews centering around 20s (32 interviewees) and the major results are as in the following. First, in terms of on-line civic participation, searching political issues occur in places, where internet users can access information easily relatively, and creating or reconstructing political information is identified in places giving stability or affinity to the public society. Second, even though each party's homepage for the channel of cyber parties has enough capacity as bridgespace, which takes charge of supporting f lows of people, goods, capital, and ideas, most of them don't play a role to establish virtual or real networks. Exceptively, cyber parties contribute to make temporalized places, where nobody takes the responsibility, somewhat. Third, the development and movement of civil society networks is divided into several segments according to political interests and tendency in online; furthermore, such a cyberpolitical activity influences human networks and the decision of major places for political activities in offline.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.46 no.4
• /
• pp.58-66
• /
• 2009

Recently the emerging demands of the light-video encoder promotes lots of research efforts on DVC (Distributed Video Coding). As an appropriate video compression method, DVC has been studied, and Wyner-Ziv (WZ) video compression is its one representative structure. The WZ encoder splits the image into two kinds of frames, one is key frame which is compressed by conventional intra coding, and the other is WZ frame which is encoded by WZ coding. The WZ decoder decodes the key frame first, and estimates the WZ frame using temporal correlation between key frames. Estimated WZ frame (Side Information) cannot be the same as the original WZ frame due to the absence of the WZ frame information at decoder. As a result, the difference between the estimated and original WZ frames are regarded as virtual channel noise. The WZ frame is reconstructed by removing noise in side information. Therefore precise noise estimation produces good performance gain in WZ video compression by improving error correcting capability by channel code. But noise cannot be estimated precisely at WZ decoder unless there is good WZ frame information, and generally it is estimated from the difference of corresponding key frames. Also the estimated noise is limited by comparing with frame level noise to reduce the uncertainty of the estimation method. However these methods cannot provide good noise estimation for every frame or each bit plane. In this paper, we propose a noise nodel selection method which chooses a better noise model for each bit plane after generating candidate noise models. Experimental result shows PSNR gain up to 0.8 dB.

• Journal of Navigation and Port Research
• /
• v.27 no.3
• /
• pp.283-288
• /
• 2003

Recently, the growth of applications and services over high-speed Internet increases, ATM networks as wide area back-bone has been a major solution. As the conventional TCP/IP suite is still the standard protocol used to support upper application on current. Internet, the issues regarding whether TCP/IP will operate efficiently on top of an ATM infrastructure and how to control its QoS still remain for studies. TCP uses a window-based protocol for flow control in the transport layer. When TCP uses the UBR service in ATM layer, the control method is only buffer management. If a cell is discarded in ATM layer, one whole packet of TCP will be lost; this fact occur the most TCP performance degradation. Several dropping strategies, such as Tail Drop, EPD, PPD, SPD, FBA, have been proposed to improve the TCP performance over ATM. In this paper, to improve the TCP performance, we propose a packet dropping scheme that is based on comparison with EPD, SPD and FBA. Our proposed scheme is applied to schemes discussed in the previous technology. Our proposed scheme does not need to know each connection's mean packet size. When the buffer exceeds the given threshold, it is based on comparison between the number of dropped packet and the approved packet. Our results are reported and discussed for comparing these discarding schemes under similar conditions. Although the number of virtual channel (VC) is increased, the simulation results showed that the proposed scheme can allocate more fairly each VC than other scheme.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.1
• /
• pp.466-474
• /
• 2014

This paper presents the line contention avoidance experiments with an optical switch, which was selected based on the comparison analysis and evaluation of the various characteristics. For example, the function, structure, strengths and weaknesses of the optical switches. After considering the nonblocking, modularity, upgrade ability and optical power loss of the several kind of the switch fabrics, a switch was selected. The selected switch fabric by using wavelength converters was controlled to avoid contention of the optical lines. In this experiment shows an example of three cases. As a result of this experiment, optical signal shows a changed peek of optical power in output. By showing a peak it confirms that the contention was avoided. By analyzing of changed optical power according to the channel setting time and release time to control of the switch could be determined. If this analysis applied to the network design, economical and efficient structures can be formed.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.47 no.5
• /
• pp.671-681
• /
• 2014

The distribution and abundance of coastal fish species in Asan Bay, Korea, were estimated from hydroacoustic survey and net catches. Acoustic data were collected with 38 and 200 kHz from July to October of 2012, and converted to the nautical area scattering coefficient (NASC, $m^2/mile^2$) for $0.25n{\cdot}mile$ along ten transects. Japanese anchovy Engraulis japonicus was the dominant specie in the net catches. The virtual echogram technique was used to distinguish E. japonicus from other species based on the differences in the mean volume backscattering strength (${\Delta}MVBS$) at 38 and 200 kHz. Engraulis japonicus and other fishes are mainly distributed in the center channel and outer part of Asan Bay. E. japonicus tends to move from inner to outer Asan Bay in summer and fall. From NASC data, the target strength and length-weight function of E. japonicus and other fishes were used to estimate the E. japonicus stock at 24.1-93.3 tons, and other fish at 40.6-88.4 tons from July to October 2012. The estimated anchovy biomass compared well with the cumulative catch weight from stow net catches. The hydroacoustic method offers an approach to understanding spatial/temporal structure and estimating the biomass of fish aggregations in coastal areas.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.19 no.5
• /
• pp.1097-1103
• /
• 2015

In order to build network infrastructure to implement the aforementioned advantages enabling smart device users to work anywhere, professional support and expensive VPN devices are required. This is a barrier to supplying VPN devices to small and medium-sized institutes. To address this issue, this study aims to implement OpenVPN, OpenSSH and iproute based on the OpenWRT platform which is an embedded OS for open networks in affordable open wired/wireless gateway H/W platforms to support the inter-network VPN. In addition, the network environment can be maintained optimal by applying a "multi-queuing real-time traffic shaping technology" to VPN tunnels, although channel quality changes.

• 한국HCI학회:학술대회논문집
• /
• 2008.02b
• /
• pp.251-256
• /
• 2008

가상 채널을 통한 IPTV 인터렉션 디자인 -멀티미디어 컨텐트 소비를 중심으로 정해진 방송시간에 따라 일 방향적으로 프로그램 매제를 제공하던 TV 는 바야흐로 혁명의 시대를 맞고 있다. 이에 따라 사용자는 오랜 시간 기존의 TV 에서의 사용자 경험을 유지한 채, IPTV 라는 새로운 방식의 시스템을 경험하게 된다. 따라서 기존의 TV 사용자들도 이러한 새로운 형태의 TV를 거부감 없이 적극적으로 사용할 수 있도록 하기 위하여 사용자 중심의 인터렉션에 대한 연구와 인터페이스 개발의 필요성이 높아지고 있다. 본 연구에서는 현재 국내에 상용화된 IPTV 의 서비스들 중에서 주식, 쇼핑, 교통 등과 같은 양방향 서비스를 제외한 실시간 방송과 기존의 VOD 컨텐츠들을 포함한 멀티미디어 컨텐츠 소비에 대한 인터렉션 방법을 연구 범위로 정하였다. 본 연구를 위하여, 기존의 IPTV VOD 컨텐트의 소비 방식에 대해 다양한 사용자 리서치를 실시하였다. 그 결과 피 실험자들은 기존의 TV 에서 경험했던 것과 같이 단순하고 심플한 조작 방식으로 원하는 task 를 수행하여 각 목적에 맞는 결과를 얻는 것을 기대 한다는 것을 알 수 있었다. 그러나 실제 이 과정에서 피실험자들은 인터렉션 상의 여러 가지 문제점을 겪었는데, 특히 VOD 소비 방법의 accessibility 부분에서 해결해야 할 사용자 경험 요소들을 많음을 알 수 있었다. 따라서 본 연구를 통하여 현재 국내에 상용화된 IPTV 의 VOD 컨텐츠 소비 방식과 실시간 방송 컨텐츠를 소비함에 있어서 사용자가 만족하지 못하는 경험적 요소들을 집중적으로 연구하여, 기존의 TV 사용자가 더욱 적극적으로 멀티미디어 컨텐츠를 소비할 수 있는 방안으로 새로운 개념의 가상채널 인터렉션 방법을 제안하고자 한다.

• Journal of Broadcast Engineering
• /
• v.17 no.5
• /
• pp.876-890
• /
• 2012

In this paper, we investigated the performances of the distributed video codec with adaptive Gray code to apply for frame-difference signal. That is, the best cases and the worst cases were analyzed and compared by considering the statistical characteristics of the frame difference signal in view of the Gray code allocation. Through computer simulations, if 9-bit data for frame difference signal is generated for luminance signal with 8-bit definition and so n-bit is allocated to the quantized coefficient, we were able to find the best method to reduce the virtual channel noise by adding $256+2^{9-n-1}$ to the frame difference signal. Through computer simulation with test video sequences, it was shown that the performance difference between the best cases and the worst cases is larger than about 1.5dB at same rate. It is expected that the results in this paper are applicable for the transform-domain scheme as well as the pixel-domain scheme.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.11C
• /
• pp.1152-1157
• /
• 2002

In this paper, a detailed procedure of development for an AAL2 processor widely used in voice gateway application is introduced. The processor supports CPS and SSCS with voice service and framed mode data service. It provides 4 ATM virtual connections, which include 1020 AAL2 channels. The processor has one UTOPIA Level 1 interface for an ATM cell interface and 4 TDM ports for a voice channel interface. The TDM ports carry PCM/ADPCM voice streams. Most AAL2 processors are implemented as software, or hardware and software, so its latency is large. But this processor has very low latency as to CPS and SSCS because all of them are implemented in hardware. Also, it allows not only loopback and switching of CPS packets, but loopback and switching of TDM channels. The key feature is that the internal structure of the CPS and SSCS in this processor seems like as each software function, so they are called whenever they are required. In addition, they are reusable for another design and are scalable for more channels.