• 한국정보통신학회논문지
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• 제11권5호
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• pp.897-905
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• 2007

본 논문에서는 TMO 실시간 객체 모델을 이용하여 실시간 통신 메시지 서비스를 효과적으로 지원하기 위해 새로운 프레임워크 및 동기화 메카니즘을 나타내었다. 또한 분산된 네트워크 시스템에서 TMO 구조를 이용하여 DHS(Distributed High-Precision Simulation) 응용 환경 에 적용함으로서 실시간 메시지 서 비스를 보장하였다. 분산된 다중 노드 시스템에서 TMO의 시간 구동 및 메시지 구동 구조는 실시간 통신 서비스 능력을 적시에 보장하기 위한 설계자의 노력을 충분히 줄일 수 있었으며, 제안된 프레임워크는 분산된 객체 구성요소들 사이의 데드라인 시간을 보다 쉽게 보장하기 위해 일관된 구조 및 구성을 제공하였다. 프로그래머의 데드라인 설계 시간을 처음 객체부터 적용하여 보장함으로서 형성될 수 있다. TMO 객체 모델을 기반으로 한 실시간 시뮬레이션에서 몇 가지의 TMO 구조의 장점을 가지고 있으며, TMO 객체 모델은 요구 명세서와 설계 사이의 강력한 연관성을 가지고 있다.

• ETRI Journal
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• 제32권6호
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• pp.854-862
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• 2010

One-way delay variation (OWDV) has become increasingly of interest to researchers as a way to evaluate network state and service quality, especially for real-time and streaming services such as voice-over-Internet-protocol (VoIP) and video. Many schemes for OWDV measurement require clock synchronization through the global-positioning system (GPS) or network time protocol. In clock-synchronized approaches, the accuracy of OWDV measurement depends on the accuracy of the clock synchronization. GPS provides highly accurate clock synchronization. However, the deployment of GPS on legacy network equipment might be slow and costly. This paper proposes a method for measuring OWDV that dispenses with clock synchronization. The clock synchronization problem is mainly caused by clock skew. The proposed approach is based on the measurement of inter-packet delay and accumulated OWDV. This paper shows the performance of the proposed scheme via simulations and through experiments in a VoIP network. The presented simulation and measurement results indicate that clock skew can be efficiently measured and removed and that OWDV can be measured without requiring clock synchronization.

• 한국멀티미디어학회논문지
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• 제8권10호
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• pp.1403-1410
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• 2005

멀티미디어, 특히 실시간 통신에서 동기화 문제는 서비스 품질과 직결된다고 할 수 있다. 본 연구에서는 MPEG-2의 시스템계층의 표준 디코더가 고정 지연요소의 경우만 고려하여 설계되어 엔코더와 디코더간의 동기화가 되지 못함을 알게 되었다. 이를 해결하기 위해 MPEG-2에 적용할 수 있는 Extended-SRTS (extended-synchronous residual-time stamp)기법을 제안했다. 이 알고리즘은 MPEG-2의 STC(system time clock)를 서비스클럭(27MHz)으로 사용하여 전송스트림과 동기 시킨다. 그 결과 주파수 드리프트, 시변망 지터 및 패킹지터 등의 영향을 개선시킬 수 있다. 또한 망 클럭의 의존도를 낮출 수 있어 종단 간에 동기화를 쉽게 하고 투명한 연결을 할 수 있어, 실시간 멀티미디어 통신 분야에 폭넓게 적용할 수 있으리라 기대한다.

• International journal of advanced smart convergence
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• 제9권1호
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• pp.109-112
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• 2020

Many devices are connected on the internet to give functionalities for interconnected services. In 2020', The number of devices connected to the internet will be reached 5.8 billion. Moreover, many connected service provider such as Google and Amazon, suggests edge computing and mesh networks to cope with this situation which the many devices completely connected on their networks. This paper introduces the current state of the introduction of the wireless mesh network and edge cloud in order to efficiently manage a large number of nodes in the exploding Internet of Things (IoT) network and introduces the existing Network Time Protocol (NTP). On the basis of this, we propose a relatively accurate time synchronization method, especially in heterogeneous mesh networks. Using this NTP, multiple time coordinators can be placed in a mesh network to find the delay error using the average delay time and the delay time of the time coordinator. Therefore, accurate time can be synchronized when implementing IoT, remote metering, and real-time media streaming using IoT mesh network.

• ETRI Journal
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• 제28권1호
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• pp.31-44
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• 2006

In a packet switching network, congestion is unavoidable and affects the quality of real-time traffic with such problems as delay and packet loss. Packet fair queuing (PFQ) algorithms are well-known solutions for quality-of-service (QoS) guarantee by packet scheduling. Our approach is different from previous algorithms in that it uses hardware time achieved by sampling a counter triggered by a periodic clock signal. This clock signal can be provided to all the modules of a routing system to get synchronization. In this architecture, a variant of the PFQ algorithm, called digitized delay queuing (DDQ), can be distributed on many line interface modules. We derive the delay bounds in a single processor system and in a distributed architecture. The definition of traffic contribution improves the simplicity of the mathematical models. The effect of different time between modules in a distributed architecture is the key idea for understanding the delay behavior of a routing system. The number of bins required for the DDQ algorithm is also derived to make the system configuration clear. The analytical models developed in this paper form the basis of improvement and application to a combined input and output queuing (CIOQ) router architecture for a higher speed QoS network.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제3권4호
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• pp.344-365
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• 2009

The performance of a tracking system is greatly increased if multiple types of sensors are combined to achieve the objective of the tracking instead of relying on single type of sensor. To conduct the multi-modal tracking, we have previously developed a multi-modal sensor-based tracking model where acoustic sensors mainly track the objects and visual sensors compensate the tracking errors [1]. In this paper, we find a network synchronization problem appearing in the developed tracking system. The problem is caused by the different location and traffic characteristics of multi-modal sensors and non-synchronized arrival of the captured sensor data at a processing server. To effectively deliver the sensor data, we propose a time-based packet aggregation algorithm where the acoustic sensor data are aggregated based on the sampling time and sent to the server. The delivered acoustic sensor data is then compensated by visual images to correct the tracking errors and such a compensation process improves the tracking accuracy in ideal case. However, in real situations, the tracking improvement from visual compensation can be severely degraded due to the aforementioned network synchronization problem, the impact of which is analyzed by simulations in this paper. To resolve the network synchronization problem, we differentiate the service level of sensor traffic based on Weight Round Robin (WRR) scheduling at the routers. The weighting factor allocated to each queue is calculated by a proposed Delay-based Weight Allocation (DWA) algorithm. From the simulations, we show the traffic differentiation model can mitigate the non-synchronization of sensor data. Finally, we analyze expected traffic behaviors of the tracking system in terms of acoustic sampling interval and visual image size.

• 방송공학회논문지
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• 제17권4호
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• pp.596-610
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• 2012

본 논문은 모바일 방송망에서 고화질의 3D 방송 서비스를 제공하는 방법을 제안한다. 제안방법에서는 제한된 방송망의 대역폭을 극복하는 방법으로 오디오와 비디오를 방송망과 이동통신망으로 구성된 이종망을 통해 전달한다. 특히 서로 다른 망을 통해 각각 전송되는 스테레오스코픽 좌/우 영상을 동기화하는 방법을 제안한다. 본 논문에서의 동기화 방법은 RTP(Real Time Protocol)의 초기 타임스탬프(Timestamp)로부터의 옵셋을 이용하여 영상의 프레임(Frame) 순서를 구별하고 동일한 시점에 재생되어야 하는 좌/우 영상의 쌍을 찾는다. 마지막으로 3D 방송 서비스를 구별하고 타임스탬프를 얻기 위한 시그널링(Signaling)방법을 제시한다.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2007년도 학술대회
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• pp.136-141
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• 2007

The frequency accuracy and phase alignment is necessary for ensuring the quality of service (QoS) for applications such as voice, real-time video, wireless hand-off, and data over a converged access medium at the telecom network. As telecom networks evolve from circuit to packet switching, proper synchronization algorithm should be meditated for IP networks to achieve performance quality comparable to that of legacy circuit-switched networks. The Time of Packet (ToP) specified in IEEE 1588 is able to synchronize distributed clocks with an accuracy of less than one microsecond in packet networks. But, The ToP can be affected by impairments of a network such as packet delay variation. This paper proposes the efficient method to minimize the expectable delay variation when ToP synchronizes the distributed clocks. The simulation results are presented to demonstrate the improved performance case when the efficient ToP transmit algorithm is applied.

• 한국재난정보학회 논문집
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• 제19권2호
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• pp.432-438
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• 2023

연구목적: 생활안전 예방서비스 앱에서 신고되는 이미지를 AI를 사용하여 실시간으로 위험 카테고리를 자동으로 분류하여 사용자에게 편리한 위험신고를 가능하게 하는 것을 목적으로 한다. 연구방법: 인터넷으로 상호연결되는 생활안전 예방서비스 플랫폼, 생활안전 예방서비스 앱, AI 모델 서빙 서버와 sftp 서버로 구성되는 시스템을 통하여 신고된 생활안전 이미지를 실시간으로 자동분류하며, 이때 사용되는 AI모델 생성을 위한 AI 학습 알고리즘도 개발하였다. 연구결과: 이미지를 실시간으로 AI 처리하여 자동으로 분류할 수 있게 되어, 신고자가 생활안전 관련 사항을 보다 편리하게 신고할 수 있게 되었다. 결론: 본 논문에서 제시하는 AI 이미지 자동분류 시스템은 90% 이상의 분류 정확도로 신고 이미지를 실시간으로 자동분류하여 신고자가 간편하게 생활안전 관련 이미지를 신고할 수 있게 되었으며 향후 생활안전 예방서비스 앱의 사용자의 증가에 따라 더욱 빠르고 정확한 AI 모델 개발 및 시스템 처리용량 향상이 필요하다.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2009년도 정보통신설비 학술대회
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• pp.275-280
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• 2009

Femtocells are viewed as a promising option for mobile operators to improve coverage and provide high-data-rate services in a cost-effective manner Femtocells can be used to serve indoor users, resulting in a powerful solution for ubiquitous indoor and outdoor coverage. TThe frequency accuracy and phase alignment is necessary for ensuring the quality of service (QoS) forapplications such as voice, real-time video, wireless hand-off, and data over a converged access medium at the femtocell. But, the GPS has some problem to be used at the femtocell, because it is difficult to set-up, depends on the satellite condition, and very expensive. The IEEE 1588 specification provides a low-cost means for clock synchronisation over a broadband Internet connection. The Time of Packet (ToP) specified in IEEE 1588 is able to synchronize distributed clocks with an accuracy of less than one microsecond in packet networks. However, the timing synchronization over packet switched networks is a difficult task because packet networks introduce large and highly variable packet delays. This paper proposes an enhanced filter algorithm to reduce ths packet delay variation effects and maintain ToP slave clock synchronization performance. The results are presented to demonstrate in the intra-networks and show the improved performance case when the efficient ToP filter algorithm is applied.