• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.6 no.3
• /
• pp.71-86
• /
• 1996

In this paper we propose an explicit rate allocation algorithm for ATM(Asynchronous Transfer Mode) Networks using the available bit rate(ABR) class of service and study the performance of this algorithm. We examine the behavior of ABR traffic with the suggested algorithm, and demonstrate that the algorithm is fair and maintains network efficiency with low cell loss rate. The simulation results show substantial improvements in fairness and efficiency over the existing algorithms.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2020.05a
• /
• pp.63-65
• /
• 2020

과학응용분야의 원활한 협업 지원을 위해서는 원거리간 대용량 연구데이터의 고속 전송이 반드시 요구된다. 이와 관련하여, 본 논문은 기 구축된 대용량 파일 시스템을 다수의 데이터 전송 노드(DTN)에 연동하기 위해 필요한 요구사항들을 정리하고, 이에 기반하여 DTN 클러스터를 설계하고 구축한 사례를 제시한다. 추가적으로, 종단간 왕복지연 시간이 약 130ms에 달하는 원거리 종단 포인트와 대용량 실험데이터를 송수신함으로써 구축된 결과물의 전송 성능을 측정하고 확인한다.

• Journal of Korea Society of Industrial Information Systems
• /
• v.6 no.1
• /
• pp.1-6
• /
• 2001

This paper proposes a method to reduce the timing gap which causes a type of attack to a network-based intrusion detection system. For this, an intrusion defection system is used in order to measure the round trip tin to the destination system, and the measured round trip time is used for estimation of packet's real arrival time to destination. Socket programings are used on the LAN environments to evaluate the performance of the proposed method. The test results show that an estimation method which uses the latest round trip time has the best performance, and the timing gap can be significantly reduced with small overheads.

• Radiation Oncology Journal
• /
• v.22 no.1
• /
• pp.55-63
• /
• 2004

Purpose : To evaluate the reflection of tumor motion according to the planning CT scan time. Material and Methods : A model of N-shape, which moved aiong the longitudinal axis during the ventilation caused by a mechanical ventilator, was produced. The model was scanned by planning CT, while setting the relative CT scan time (T: CT scan time/ventilatory period) to 0.33, 0.50, 0.67, 0.75, 1.00, 1.337, and 1.537. In addition, three patients with non-small cell lung cancer who received stereotactic radiosurgery In the Department of Radiation Oncology, Asan Medical Center from 03/19/2002 to 05/21/2002 were scanned. Slow (10 Premier, Picker, scan time 2.0 seconds per slice) and fast CT scans (Lightspeed, GE Medical Systems, with a scan time of 0.8 second per slice) were peformed for each patient. The magnitude of reflected movement of the N-shaped model was evaluated by measuring the transverse length, which reflected the movement of the declined bar of the model at each slice. For patients' scans, all CT data sets were registered using a stereotactic body frame scale with the gross tumor volumes delineated in one CT image set. The volume and three-dimensional diameter of the gross tumor volume were measured and analyzed between the slow and fast CT scans. Results : The reflection degree of longitudinal movement of the model increased in proportion to the relative CT scan times below 1.00 7, but remained constant above 1.00 T Assuming the mean value of scanned transverse lengths with CT scan time 1.00 T to be $100\%$, CT scans with scan times of 0.33, 0.50, 0.57, and 0.75 T missed the tumor motion by 30, 27, 20, and $7.0\%$ respectively, Slow (scan time 2.0 sec) and Fast (scan time 0.8 sec) CT scans of three patients with longitudinal movement of 3, 5, and 10 mm measured by fluoroscopy revealed the increases in the diameter along the longitudinal axis Increased by 6.3, 17, and $23\%$ in the slow CT scans. Conculsion : As the relative CT scan time increased, the reflection of the respiratory tumor movement on planning CT also Increased, but remained constant with relative CT scan times above 1.00 T When setting the planning CT scan time above one respiration period (>1.00 T), only the set-up margin is needed to delineate the planning target volume. Therefore, therapeutic ratio can be increased by reducing the radiation dose delivered to normal lung tissue.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37 no.7A
• /
• pp.569-580
• /
• 2012

In this paper, an enhanced initial ranging algorithm for large-cell coverage fixed wireless communication system is proposed. In typical wireless communication system such as WiBro, because a round-trip delay between a transmitter and a receiver is within one OFDM (Orthogonal Frequency Division Multiplexing) symbol duration, a frequency-domain differential correlation method is generally used. However, the conventional method cannot be applied due to an increase of a maximum time delay in large-cell system. In case of an accumulative differential method, estimation errors can occur because of frequent sign transitions. In this paper, therefore, we propose an algorithm which can estimate a total timing offset in a ranging channel structure for 15 km cell. The proposed method can improve performance by sign comparison based sign error correction rule between the estimated values and using a weighting scheme based on channel correlation, the number of accumulations, and the noise reduction effect in normalization process. Also, it can estimate the integer timing offset of symbol duration by comparing peak-powers after compensating for the fractional timing offset of symbol duration.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.6D
• /
• pp.801-807
• /
• 2008

This study attempts to evaluate and compare the land consumption efficiencies of various urban transport modes, utilizing the time-area method. With the careful considerations of travel conditions and modal characteristics, equations for the computation of time-area for various different modes are derived. With the appropriate assumed values of parameters, time-area consumptions per person per km for each mode both for peak and off-peak situations are computed and evaluated. The relationships between the time-area consumed and operating speed for each mode are graphically demonstrated and discussed. An example of the time-area consumed for a hypothetical commuter round-trip using various modes are also presented in order to clearly show the consumption of parking requirements by specific modes. It shows that regardless of facilities used, auto users are by far the worst in terms of area efficiency and that transit, especially rail rapid transit, is a superior mode. Pedestrian and bicycle, though consuming more than expected, also demonstrate the advantage in case of a short-distance trip in terms of area efficiency compared with the bus transit modes.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2004.11a
• /
• pp.337-342
• /
• 2004

A construction project of Incheon 2nd bridge, which is connected between the Incheon Song-Do New Town and the Incheon International Airport in Young-Jong-Do, have been proposed by the private capital in 1999. But the optimal span width in the bridge main span have not been decided in spite of the three investigations into the feasibility of ship's safe transit in this planned bridge. In this paper, we study the economic analysis on port operational efficiency according to traffic schemes, me-way or two-way of vessels over 10,000G/T, in the bridge main span of this bridge. In this comparative result, total queueing time due to the one-way in the bridge main span is evaluated 20,362 hours in 2011 and 24,544 hours in 2020. Therefore the demurrage cost and the accumulation cost of freight are evaluated 19.7 billion won in 2011, and 23.3 billion won in 2020, then total accumulated costs during 33 years from 2008 until 2040 are evaluated about 768..9 billion won.

• Journal of KIISE:Information Networking
• /
• v.31 no.1
• /
• pp.91-100
• /
• 2004

This paper presents a receiver-driven TCP flow control mechanism, which is adaptive to the wireless condition, for memory constrained mobile receiver. A receiver-driven TCP flow control is, in general, achieved by adjusting the size of advertised window at the receiver. The proposed method constantly measures at the receiver both the available wireless bandwidth and the packet round-trip time. Depending on the measured values, the receiver adjusts appropriately the size of advertised window. Constrained by the adjusted window which reflects the current state of the wireless network, the sender achieves an improved TCP throughput as well as the reduced round-trip packet delay. Its implementation only affects the protocol stack at the receiver and hence neither the sender nor the router are required to be modified. The mechanism has been implemented in real environments. The experimental results show that in CDMA2000 1x networks the TCP throughput of the proposed method has improved about 5 times over the conventional method when the receiver's buffer size is limited to 2896 bytes. Also, with 64Kbytes of buffer site, the packet round-trip time of the proposed method has been reduced in half, compared the case with the conventional method.

• Journal of Internet of Things and Convergence
• /
• v.6 no.3
• /
• pp.1-6
• /
• 2020

This paper aims to integrate the previous models about mean object transfer latency in one framework and analyze the result through the computational experience. The analytical object transfer latency model assumes the multiple packet losses and the Internet of Things(IoT) environment including multi-hop wireless network, where fast re-transmission is not possible due to small window. The model also considers the initial congestion window size and the multiple packet loss in one congestion window. Performance evaluation shows that the lower and upper bounds of the mean object transfer latency are almost the same when both transfer object size and packet loss rate are small. However, as packet loss rate increases, the size of the initial congestion window and the round-trip time affect the upper and lower bounds of the mean object transfer latency.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.1
• /
• pp.75-81
• /
• 2002

In the re-entry comtrol system, errors apt to induce because the time deriviative of drag acceleration is analytically estimated. Still more, the difficulty of estimation of th exact drag coefficient in hypersonic velocity and the non-reality of the scale height cause a steady-state drag errer. In the Space-Shuttle, a steady-state drag error is reduced by the addition of the integral term of drag acceleation error into the control system. This method, however, induces a difficulties in respect to the modern controller composition due to the multi-poles in a closed-loop system. Thus, this paper proposes the additional method of the disturbance observer. This reduces the steady-state drag error according to the following by the analytic calculation, and then creates the new drag acceleration time derivative using the estimated error. The performance of the re-entry control system is verified about 32 refernce trajectories.