• 대한공업교육학회지
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• v.33 no.2
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• pp.287-299
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• 2008

HTTP is one of the most widely used protocols of the WWW. Currently it uses TCP as the transport layer protocol to provide reliability. The HTTP uses separate TCP connection for each file request and adds unnecessary head-of-line blocking overhead for the file retrieval. The web application is short sized and affected by the increased handover latency of TCP in wireless environment. SCTP has attractive features such as multi-streaming and multi-homing. SCTP's multi-streaming and multi-homing avoid head-of-line blocking problem of TCP and reduce handover latency of TCP in wired and wireless environment. Mean response time is the important measure in most web application. In this paper, we present the comparison of mean response time between HTTP over SCTP with that of HTTP over TCP in wired and wireless environments using NS-2 simulator. We measured mean response time for varying packet loss rate, bandwidth, RTT, and the number of web objects in wired environment and mean response time and packet loss rate for varying moving speed and region size in wireless environment. Our experimental result shows that SCTP reduces the mean response time of TCP based web traffic.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4A
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• pp.369-379
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• 2011

During the routing process between nodes on the CR(Cognitive Radio) network conducting for efficient use of limited frequency resources, spectrum handover process due to the appearance of the PU occupies most of the routing latency, and also decreases the reliability of the path. In this paper, a cooperative routing protocol in a multi-channel environment is proposed. The source node broadcasts a message with available channel lists and probability of PU appearance during its route guidance. The intermediate nodes re-transmit the message, received from the source node, and update and maintain the information, status table of the path. The destination node determines the optimal path and sends a reply message to the selected path after it receives the messages from the intermediate nodes. The average probability of the PU appearance and the average time of the PU appearance are updated while transferring data. During data transmission the channel with the lowest probability of appearance of the PU is selected dynamically and if a PU appears on the current channel partial repairment is performed. It is examined that reliability of the selected path considerably is improved and the routing cost is reduced significantly compared to traditional routing methods.

• Journal of KIISE:Information Networking
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• v.32 no.2
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• pp.215-219
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• 2005

Generally, the mobile nodes in MANET have the limited power capacity available for actual communications. Thus, the power management is very important for packet routing or forwarding. Although MTPR, MBCR and MMBCR are proposed to treat the problem of power consumption, there have been few researches resolving the link breakdown that is occurred by the power exhaustion during transmission. In this sense, the reliable scheme should be required to ensure the routing connectivity. In this paper, we propose three schemes to enforce the routing connectivity. If the signal strength is dropped below a signal threshold, the candidate route is previously selected to prepare the link breakdown. Also, on multi-channel, we propose the lifetime increment scheme of a node that it manage its available power to the needed power of a new link. The simulation results show the enforcement of the link connectivity and the performance improvements of the delay time through the effective connection management.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5B
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• pp.925-930
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• 2000

The Problem of allocating paths is very significant in order to transmit a large amount of various data on the ATM network. Therefore, selecting an optimal path among available paths between the a source node and a target node has been researched. Alternate paths designed in previous PNNI routing is not considered on the group-occupation so that traffic congestion happens, when errors occur in the network which consists of a hierarchical network architecture extendable to a large network, We propose the Top-Down algorithm considering an average of the occupation among the groups reported from a leader node in each group and minimizing a traffic congestion

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.05a
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• pp.467-470
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• 2012

This paper proposes a technique of sybil attack detection using an ID-based certificate on sensor network. First, it can solve the broadcast storm problem happening when keys are distributed to sensor nodes. Second, it prevents the replay attack by periodically generating and changing the keys of sensor nodes with Key-chain technique. Third, it authenticates sensor node's ID using hash function. So, it maximizes sensor node's memory usage, reduces communication overhead. Finally it detects Sybil attack through ID-based certificate. Therefore, the proposed technique of Sybil attack detection using ID-based certificate consider simultaneously energy efficiency and stability on sensor network environment, and can trust the provided information through sensor network.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.3
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• pp.129-139
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• 1999

This paper presents the operation teclmology and the rerrote rmnitoring system of distribution pole transfonrer. Especially, this system uses cable 1V network as communication m:dia which is located in KEPCO's main distribution line. It has fom major components such as sensor for measuring the secondary voltage and currents of distribution transfonrer, RF modernfor data modulating/de-modulating, connnunication media for sending/receiving of data, and PC server for monitoring the results of sensing or computing information. This paper also describes the configuration of each component'sfunctions with its development process. In addition, the reliability and effectiveness of proposed system was confimed by aoolving this remote monitoring system to Jungbu branch area.h area.

• The Journal of the Korea institute of electronic communication sciences
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• v.2 no.1
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• pp.40-45
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• 2007

The repeaterless system can be designed by applying EDFA technology in receiver, transmitter and optical cable in the case of connecting several hundred km from coast to coast, between continents or islands. Because of no repeater the repeaterless system do not need power system to feed laser diode in repeater for signal amplification and cooper tuber in submarine cable. So we can be configured more reliable and economical compared to repeater system. But lower loss optical fiber must be used to get enough signal amplitude without the amplification of repeater. This report consider long distance optical repeaterless system by reflecting the limitation factor of optical amplification.

• Journal of KIISE:Information Networking
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• v.36 no.2
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• pp.108-117
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• 2009

Data aggregation is one of the well-known techniques to reduce the energy consumption for information transmission over wireless sensor networks (WSN). As the WSNs are deployed in untrusted or even hostile environments, the data aggregation becomes problematic when end-to-end data privacy including data confidentiality and integrity between sensor nodes and base station, is required. Meanwhile, data homomorphic cryptoschemes have been investigated recently and recommended to provide the end-to-end privacy in the hostile environments. In order to assure both data confidentiality and integrity for data aggregation, this paper analyzes the existing homomorphic cryptoschemes and digital signature schemes, proposes possible combinations, and evaluates their performance in terms of CPU overheads and communication costs.

• Journal of Advanced Navigation Technology
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• v.16 no.4
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• pp.641-648
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• 2012

The up-streams of the continuous streaming of data packets with lower importance level in the wireless sink node can cause congestion and delay, they affect on energy efficiency, memory size, buffer size, and throughput. This paper proposes a new wireless sink congestion control mechanism based on tournament scheduling. The proposed method consists of two module parts: stream decision module part and service differentiation module part. The final winner in the tournament controls congestion effectively, minimizes packet loss due to congestion, decreases energy consumption, and improves QoS. The simulation result shows that the proposed method is more effective and has better performance compared with those of congestion descriptor-based control method, reliability-based control method, and best-effort transmission control method.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.4
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• pp.555-560
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• 2017

Currently, railway wireless communication systems adopt several communication schemes depending on the specific region. To increase data rate and achieve high fidelity in railway wireless communication systems, LTE-R scheme has been developed. In this paper, We introduce interoperability technology which converges several railway communication systems including LTE-R. First, we consider two interoperability methods and their standardization. Some empirical test results of interoperability technology are also introduced. It is expected to provide seamless and statable railway communication environments by applying interoperability technologies to railway wireless communication systems.