• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9A
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• pp.685-696
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• 2009

The requirements of the NGA are to provide broader bandwidth, higher splitting ratio, and longer reach than those of the current FTTH. In the TDMA PON accounting for large percentage in the total FTTH, the increase in distance between the OLT and the ONU leads to the increase in propagation delay and in packet delay three times more than the propagation delay. It is because a packet arrived in the ONU is handled through bandwidth request, grant, and transmission. To reduce the increased packet delay, the OLT have to reduce the cycle time. However, it will cause increased overhead and reduced link efficiency. In this paper, we investigate several problems in TDMA PON when the subscriber access network extended to 60 or 100 Km reach as a NGA goal and provide a method that determines an optimal cycle time to satisfy QoS for delay sensitive traffics. In particular, we suggest a variable equalized round trip delay method and a variable cycle time method. It is shown that the former reduces the packet delay and the latter increase the link efficiency.

• Journal of Information Technology Services
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• v.20 no.6
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• pp.83-95
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• 2021

In this study, various usage patterns were analyzed after establishing a data mart for micro mobility analysis based on the rental history of public bicycles in Seoul. Rental history data is origin-destination data that includes the rental location and time, and the return location and time. About 1500 rental locations were classified according to the characteristics of the location to create a 'station type' dimension. We also created a 'path type' dimension that displays whether the rental location and return location are the same. In addition, a derived variable called speed, which is obtained by dividing the distance used by the time used, is added, and through this, the characteristics of the riding area and the reason for the rental can be estimated. Meanwhile, administrative district link, administrative neighborhood link, and station type link were created to apply network analysis. Through this analysis, the roles and proportions of administrative districts, public facilities, and private facilities engaged in micro-mobility services were visualized. 49.9% of rentals occur at rental offices near transportation facilities, and half of them occur at rental offices near subway stations. The number of rentals during the evening rush hour is more than double that of the morning rush hour. When the path type is unidirectional, there is a fixed destination, so the distance and time used are short, and the movement speed tends to be high. In the case of round-trip, the purpose of use is exercise or leisure, so the distance and time used are long, and the movement speed is slow. It is expected that the results of the analysis can be used as reference materials for selecting new rental locations, providing convenient services for users, and developing user-specialized products.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2B
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• pp.44-52
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• 2005

This paper proposes a neural network prediction model to improve the valid packet transmission rate for the QoS(Quality of Service) of multimedia transmission. The Round Trip Time(RTT) and Packet Loss Rate(PLR) are predicted using a neural network and then the transmission rate is decided based on the predicted RTT and the PLR. The suggested method will improve the transmission rate since it uses the rate control factors corresponding to time of data is being transmitted, while the conventional one uses the transmission rate determined based on the past informations. An experimental set-up has been established using a Linux PC system, and the multimedia data are transmitted using UDP protocol in real time. The valid transmitted packets are about 5% higher than the one in the conventional TCP-Friendly congestion control method when the suggested algorithm was applied.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.5C
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• pp.454-464
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• 2002

In the ATM-PON (Asynchronous Transfer Mode-Passive Optical Network), the downstream cell transmitted by an OLT is broadcast to all ONUs. The ONU receives selectively its own cells by VP filtering. On the other hand, the upstream cell can be transmitted by ONU in the case of receiving a grant from the OLT. After providing the grant to an ONU, the OLT expects the arrival of a cell after an elapse of the equalized round trip delay. ITU-T G.983.1 recommends that one bit error is allowed between the expected arrival time and the actual arrival time at the OLT. Because the ONU processes the different delay to each type of grant (ranging, user cell, and mimi-slot grant), it is not simple to design the transmission part of ONU. In this paper, we implement a grant processor which provides the delay accurately in the ONU TC chip with the FPGA. For the given equalized delay, it deals with the delay for the cell, the byte, and the bit unit by using the shift register, the byte counter, and the D flip-flop, respectively. We verify the operation of the grant processor by the time simulation and the measurement of the optical board output.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.2
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• pp.295-303
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• 2004

In this Paper, we discuss an active TCP link of unsynchronized transmission mode network in two-way traffic and the Improvement of its traffic patron thorough the network pathway of protocol is shown. This is because the traffic pattern is performed on the basis of existing windows which are distributing information in several periods of time in the way of interfacing LTS control module, which is controlling by an information of exceeding the time limit of feedback loop determined by RTP, with TCP. The simulation to utilize this efficiently is performed with the circumstance of bench mark based on physical modeling of the self-similarity traffic in the performance of TCP. In this paper, we use a methodology to understand and evaluate the effect of change of transmitting protocol in sticks under the condition of the self-similar traffic in two-way network and it is shown that an improvement of congestion control by self-similarity under a heavy condition.

• Journal of Korea Society of Industrial Information Systems
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• v.10 no.3
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• pp.48-56
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• 2005

This paper proposes a dynamic end-to-end flow control algorithm that is more effective than previous methods considering either the Rate of Packet Loss (RPL) or Round Trip Time (RTT). When the RPL is under normal conditions, the current network status will be in one of three defined states by using the RTT and this makes bandwidth control precise before serious packet loss occurs. If the RPL exceeds a critical level, then the network is considered to be in a fourth state. Suitable transmission rates are determined depending on the network status and are controlled by adjusting not only the number of transmitted frames but also the quality of the frames. In this paper, we present some experimental results of the proposed algorithm. According to our quantitative analysis, the proposed method performs 1.6 to 6 times better than the previous method in terms of the RPL. At the same time, the total number of transmitted packets is increased, which indicates that the proposed method can provide greater bandwidth capacity than previous methods.

• The Korean Journal of Community Living Science
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• v.15 no.1
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• pp.35-47
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• 2004

This study investigated the health and eating habits of college students who commute long distances to and from their schools. Among ninety-eight commuters, 61.2% were females while 38.8% were males. The mean round-trip commuting time was 4.60 hours and the mean number of days of commuting was 3.68. The proportion of underweight females (26.7%) was significantly greater than that of underweight males (5.3%). Conversely, the proportion of overweight males was 34.2% while only 1.6% of the females were overweight, and the difference was statistically significant. The mean number of health-related problems was 1.47 for males and 1.90 for females. Commuting affected the eating habits (90.8%) and health status more noticeably among females. Physical discomfort such as fatigue, stomach discomfort, constipation, weight change, and insomnia appeared after commuting. Irregular meal times, skipping breakfast, frequent overeating and insufficient time to eat were the most prevalent problems indicated. The scores for dietary attitude and eating habits were 20.1/30 and 27.6145, for males and females respectively. Although self-perceived nutrition knowledge was significantly related to dietary attitude and satisfaction with meals, a correlation was not found between self-perceived nutrition knowledge or dietary attitude and the eating habits score. The more concerned the parents were about student's eating habits, the higher the score relating to eating habits. The parents' concerns about students' meals and the food expenses were significantly correlated, but no correlation was found between the food expenses and the eating habits score. Consistent parental concern and encouraging students to maintain good eating habits are recommended. University administrators should also be aware of the needs of commuters and provide a proper and adequate food-related environment for the students.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.101-104
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• 2000

Nowadays, the issue of congestion control in high-speed communication networks becomes critical in view of the bandwidth-delay products for efficient data flow. In particular, the fact that the congestion is often accompanied by the data flow from the high-speed link to low-speed link is important with respect to the stability of closed-loop congestion control. The Virtual-Connection Network (VCN) in Gigabit Ethernet networks is a packet-switching based network capable of implementing cell- based connection, link-by-link flow-controlled connection, and single- or multi-destination virtual connections. VCN described herein differ from the virtual channel in ATM literature in that VCN have link-by-link flow control and can be of multi-destination. VCNs support both connection-oriented and connectionless data link layer traffic. Therefore, the worst collision scenario in Ethernet CSMA/CD with virtual collision brings about end-to-end delay. Gigabit Ethernet networks based on CSMA/CD results in non-deterministic behavior because its media access rules are based on random probability. Hence, it is difficult to obtain any sound mathematical formulation for congestion control without employing random processes or fluid-flow models. In this paper, an analytical method for the design of a congestion control scheme is proposed based on Smith＇s principle to overcome instability accompanied with the increase of end-to-end delays as well as to avoid cell losses. To this end, mathematical analysis is provided such that the proposed control scheme guarantees the performance improvement with respect to bandwidth and latency for selected network links with different propagation delays. In addition, guaranteed bandwidth is to be implemented by allowing individual stations to burst several frames at a time without intervening round-trip idle time.

• Journal of Internet of Things and Convergence
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• v.1 no.1
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• pp.1-4
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• 2015

This paper aims to present the mathematical model to find the mean web object transfer latency in the slow-start phase of TCP congestion control mechanism, which is one of the main control techniques of Internet. Mean latency is an important service quality measure of end-user in the network. The application area of the proposed latency model is the narrowband environment including multi-hop wireless network and Internet of Things(IoT), where packet loss occurs in the slow-start phase only due to small window. The model finds the latency considering initial window size and the packet loss rate. Our model shows that for a given packet loss rate, round trip time and initial window size mainly affect the mean web object transfer latency. The proposed model can be applied to estimate the mean response time that end user requires in the IoT service applications.

• Journal of KIISE:Information Networking
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• v.30 no.6
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• pp.755-763
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• 2003

To improve performance over noisy wireless channels, mobile wireless networks employ forward error correction(FEC) techniques. The performance of static FEC algorithms, however, degrades by poorly matching the overhead of their correction code to the degree of the fluctuating underlying channel error. This paper proposes an adaptive FEC technique called FECA(FEC-level Adaptation), which dynamically tunes FEC strength to the currently estimated channel error rate at the data link layer. FECA is suitable for wireless networks whose error rate is high and slowly changing compared to the round-trip time between two communicating nodes. One such example network would be a sensor network in which the average bit error rate is higher than $10^{-6}$ and the detected error rate at one time lasts a few hundred milliseconds on average. Our experiments show that FECA performs 15% in simulations with theoretically modeled wireless channels and in trace-driven simulations based on the data collected from real sensor networks better than any other static FEC algorithms.