• The Journal of Korean Institute of Next Generation Computing
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• v.14 no.6
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• pp.75-86
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• 2018

The DDS (Data Distribution Service) specification defines a discovery method for finding participants and endpoints in a DDS network. The standard discovery mechanism uses the multicast protocol and finds all the endpoints in the network. Because of using multicasting, discovery may fail in a network with different segments. Other problems include that memory space wastes due to storing information of all the endpoints. The Topic Name Service (TNS) solves these problems by unicasting only the endpoints, which are required for communication. However, an extra delay time is inevitable in components of TNS, i.e, a front-end server, topic name servers, and a terminal server. In this paper, we analyze the performance of TNS. Delay times in the servers of TNS and time required to receive endpoint information are measured. Time to finish discovery and number of receiving endpoints compare with the standard discovery method.

• Journal of The Korean Association of Information Education
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• v.3 no.2
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• pp.113-119
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• 2000

I studied a distance education model for English learning on the Internet. Basic WWW files, that contain courseware, are constructed with HTML, and functions, which are required in learning, are implemented with Java. Students and educators can access the preferred unit composed of the appropriate text, voice and image data by using a WWW browser at any time. The education system supports the automatic generation facility of English problems to practice reading and writing by making good use of the courseware data or various English text resources located on the Internet. Our system has functions to manage and control the flow of distance learning and to offer interaction between students and the system in a distributed environment. Educators can manage students' learning and can immediately be aware of who is attending and who is quitting the lesson in virtual space. Also, students and educators in different places can communicate and discuss a topic through the server. I implemented these functions, which are required in a client/server environment of distance education, with the use of Java. The URL for this system is "http://park.taegu-e.ac.kr" in the name of GAIA.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.4
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• pp.27-36
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• 2018

In this paper, we design and implement a real time IoT messaging system that can collect location information of moving vehicles and pedestrians in real time using MQTT protocol and provides location based information service in administrative area. We implemented MQTT based IoT device for vehicle location information collection and communication and MQTT based smartphone application for pedestrian location information service. IoT clients can send messages to the server in administrative units by using the MQTT Topic which is equal to administrative names. The SLIMS (Seoul Location based IoT Messaging System) implemented in this study is able to analyze the real time traffic volume of pedestrians and vehicles by tracking clients. It also can deliver messages to clients based on coordinate range. SLIMS can be used as a real-time location-based information service for large-scale IoT devices such as real-time flow population and vehicle traffic analysis and location-based message delivery.