• Electronics and Telecommunications Trends
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• v.26 no.5
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• pp.112-122
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• 2011

CPS(Cyber-Physical Systems)는 고수준의 신뢰성을 기반으로 네트워크를 통해 물리 시스템을 실시간 제어하기 위한 임베디드 시스템이며 무인 주차, 항공, 스마트 그리드와 같이 다양한 의료, 군사, 교통, 로봇제어 분야에 활용 가능한 기술이다. 이러한 환경에서 시스템들 간의 실시간적이고 신뢰성 높은 데이터 통신을 제공하기 위하여 발행/구독 모델에 기반한 실시간 데이터 통신 미들웨어 표준인 DDS(Data Distribution Service)를 사용한다. 그러나, DDS는 임베디드 기기 또는 모바일 기기들이 동적으로 구성된 네트워크에 자유로운 참여, 탈퇴가 가능한 상황에서 실시간 데이터 통신에는 적합하지만 전송되는 데이터 도청, 재전송 등과 같은 다양한 네트워크 공격에는 취약하다. 따라서, 본 고에서는 DDS 보안상의 취약점과 보안강화를 위한 접근 방법에 대해 기술하고, 이후에 DDS 통신채널 보호를 위한 상용제품의 접근법과 안전 통신채널 제공을 위한 멀티캐스트 인증, 암호화에 관련된 접근방법에 대해 기술한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.8B
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• pp.1003-1011
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• 2011

In this paper, a real-time multi-source sensor data management system based on wireless sensor network is proposed and implemented. The proposed management system is designed to transmit the wireless data to the server in order to monitor and control the multi-source target's status efficiently by analyzing them. The proposed system is implemented to make it possible to control and transmit the wireless sensor data by classifying them, of which data are issued from the clustered sources composed of a number of the remote multiple sensors. In order to evaluate the performance of the proposed system, we measure and analyze both the transmission delay time according to the distance and the data loss rate issued from multiple data sources. From these results, it is verified that the proposed system has a good performance.

• Journal of Korea Multimedia Society
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• v.2 no.1
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• pp.59-68
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• 1999

Multimedia applications have an ability to transmit a lot of data in real time. In mobile circumstances the replay of continuous multimedia data in real time causes frequent replay breaks and poor service quality because of low transmission speed and new transmission path settings in hand-off. To avoid these unfavorable side effects, we need a new mechanism which can transmit data efficiently between base station and mobile hosts, to control the buffers of mobile hosts, and to switch to a new transmission path rapidly in hand-off. The study is to propose how to give good service to mobile hosts during hand-off and the mechanism which can increase the number of mobile hosts in the cell unit.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10e
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• pp.562-564
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• 2002

본 논문에서는 멀티미디어 데이터와 실시간 특성을 가진 데이터의 end-to-end 전달기능과 QoS 감시기능 등을 지원하기 위해 개발된 RTP를 분석하고 개선방안을 제시한다. 기존의 RTP 구현 모듈은 실시간 전달기능은 지원하나, 상세한 QoS 파라미터 보장측면에서는 해결해야할 사항이 존재한다. 따라서 본 논문에서는 이러한 문제점을 해결하기 위해 송신측에서 보낸 데이터에 대한 전송 정보를 수신측으로부터 제공받아, 이를 토대로 네트워크의 상태를 3단계로 분류하여 네트워크에의 QoS를 보장할 수 있는 방안을 제안하고 성능 검증을 수행한다.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10a
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• pp.674-676
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• 1998

본 논문에서는 H.263 비디오 코덱을 사용한 인터넷 스트리잉 서버와 클라이언트의 구현을 기술한다. 서버와 클라이언트간의 데이터 전송은 RTP 실시간 프로토콜을 사용하여 이루러진다. 스트리밍 서버는 저장된 H.263 파일 또는 입력 받은 비디오를 실시간으로 H.263으로 엔코딩하여 멀티캐스팅하고, 클라이언트는 멀티캐스트 세션에 접속하여 서버가 전송한 H.263 데이터를 받아 실시간으로 디코딩한다.

• Journal of Korea Society of Industrial Information Systems
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• v.15 no.5
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• pp.19-27
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• 2010

In this paper, we propose a scheme for real-time data retransmission in LR-WPAN to support the required QoS even in the severe channel error environments. In IEEE 802.15.4a, as the user data rate is supported up to 850Kbps, the real-time streaming data can be transferred more easily. In this research, we study the beacon-enabled mode in IEEE 802.15.4 LR-WPAN standard. In the proposed scheme, special slots are dynamical1y assigned for retransmission of the packet that fails during a real-time data service, and in the severe channel error environments a time diversity is acquired. Analytical results show that the proposed scheme is more robust and achieves a much higher throughput than the previous protocol in LR-WPAN.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.5
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• pp.424-434
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• 2017

In industrial wireless sensor networks, many applications require integrated QoS supporting. This paper proposes a reliable protocol for real-time monitoring in industrial wireless sensor networks. Retransmission is well-known to recover the transmission failure, however, this might cause the time delay to violate the real-time requirement. The proposed protocol exploits broadcasting feature of wireless networks and the temporal opportunity concept. The opportunities to relay the data packets are shared by the broadcasting feature and the temporal opportunity concept maximize the number of candidates in communication. Simulation results show that the proposed protocol is superior to the existing real-time protocols in term of real-time service and reliability.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.229-232
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• 2005

기존 E-mail 프로그램은 비싼 통신요금과 저속의 위성통신 환경에서 최대한 통신비용을 줄이기 위한 목적으로 개발되었고, 그 결과 프로그램의 유연성이 떨어져 새로운 기능의 추가나 업그레이드가 용이하지 않았다. 또한 기존 프로그램의 경우는, E-mail 전용 프로그램으로서 다양한 육상과 해상간의 업무용 프로그램과 연동시키는 데에 어려움이 많았으며, 개발자 입장에서도 무선 위성통신의 특성상 개발이 쉽지 않았다. 따라서 본 논문에서는 기존 프로그램과는 달리 데이터를 패킷으로 분리하여 전송함으로써 프로토콜에 유연성을 주고, 실시간으로 여러 종류의 데이터를 전송할 수 있게 하여 동시에 E-mail뿐만 아니라, 모니터링 데이터, SMS, PMS를 위한 데이터베이스 등의 다양한 데이터를 전송할 수 있도록 설계 및 구현하였다. 또한 프로그램 개발자들이 까다로운 위성통신 환경을 몰라도 쉽게 개발할 수 있게 하고자, 컴포넌트를 윈도우즈 서비스 프로그램화 하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.1
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• pp.146-154
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• 2007

In this paper, we have presented a real-time transfer mechanism for the delay-sensitive data in WSNs (Wireless Sensor Networks). The existing methods for real-time data transfer select a path whose latency is shortest or the number of hops is least. Although the approaches of these methods are acceptable, they do not always work as efficiently as they can because they had no consideration for the link error rates. In the case of transmission failures on links, they can not guarantee the end-to-end real-time transfer due to retransmissions. Therefore, we have proposed an algorithm to select a real-time transfer path in consideration of the link error rates. Our mechanism estimates the 1-hop delay based on the link error rate between two neighboring nodes, which in turn enables the calculation of the expected end-to-end delay. A source node comes to choose a path with the shortest end-to-end delay as a real-time route, and sends data along the path chosen. We performed various experiments changing the link error rates and discovered that this proposed mechanism improves the speed of event-to-sink data transfer and reduces delay jitter. We also found that this mechanism prevents additional energy consumption and prolongs network lifetime, resulting from the elative reduction of transmission failures and retransmissions.

• Journal of KIISE:Information Networking
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• v.28 no.3
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• pp.389-405
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• 2001

In these days, we have increasing demands on the real-time services, especially for the multimedia data transmission in both of wired and wireless environments and thus efficient and stable ways of transmitting realtime data are needs. Although RTP is widely used for internet-based realtime applications, it cannot avoid packet losses, due to the use of UDP stack and its underlying layers. In the case of mobile computing applications, the packet losses are more frequent and consecutive because of the limited bandwidth. In this paper, we first statistically analyze the characteristics of packet losses in the wired and wireless communications, based on Gilbert model, and a new packet recovery scheme for realtime data transmission is presented. To reflect the transmission characteristics of the present network environment, our scheme makes the sender to dynamically adjust the amount of redundant information, using the current packet loss characteristic parameters reported by the receiver. Additionally, we use relatively large and discontinuous offset values, which enables us to recover from both of the random and consecutive packet losses. Due to these characteristics, our scheme is suitable for the mobile computing environment where packet loss rates are relatively high and varies rapidly in a wide range. Since our scheme is based on the analytic model form statistics, it can also be used for other network environments. We have implemented the scheme with Mobile IP and RTP/RTCP protocols to experimentally verify its efficiency.