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MPEG 스트리밍 시스템에서 QoS 제어를 위한 프레임 드롭 필터링 시스템 구현
차호정(Hojung Cha),오재학(Jaehak Oh) 한국정보과학회 1999 정보과학회 컴퓨팅의 실제 논문지 Vol.5 No.5
본 논문은 MPEG 스트리밍 시스템에서 넷트웍 대역폭의 감소에 따른 미디어의 질을 적절히 변화시키는 실시간 미디어 필터링 기법을 설계하고 구현하였다. 구현한 QoS 미디어 필터링 기법은 프레임 드롭 방식으로 코덱 수준의 변환을 하지 않기 때문에 시스템의 부하가 적으며 미디어의 실시간성을 만족시킬 수 있다. 필터 서버는 여러 단계의 모듈로 구성되는데, 실시간 스트리밍이 가능하도록 모듈간의 동기화 및 실시간성을 유지하였다. 특히, 프레임 드롭후의 영상 스트림과 음성 스트림간의 동기화를 MPEG 시스템 스트림 표준에 따라 정확히 구현하였다. 구현한 시스템을 바탕으로, 사용자 QoS를 위한 미디어 대역폭의 조절은 프레임 드롭 필터에 의해 적정화됨들 실험적으로 검증하였다. This paper describes the design and implementation of a media filtering mechanism for MPEG streaming systems by which media quality adapts, in real-time, to reduced network bandwidth. The frame drop mechanism, which is adopted in the implementation for QoS filtering, satisfies the real-time characteristics of streaming systems as it does not translate the media in codec level and therefore saving the processor time. The filter server consists of a sequence of filtering modules Each module is carefully designed to maintain the synchronization characteristics of real-time streaming. A special effort is given to the correct implementation of video(after frame drop) and audio synchronization following the MPEG system standard. Based on the system implemented, the media bandwidth is monitored to be controlled successfully by the frame drop mechanism.
Empirical evaluation of receiver-based TCP delay control in CDMA2000 networks
Kwon, Oh-keun,Cha, Hojung,Han, Seung-jae,Ha, Rhan John Wiley Sons, Ltd. 2007 International journal of communication systems Vol.20 No.8
<P>Wide-area broadband wireless technologies such as CDMA2000 often suffer from variable transfer rate and long latency. In particular, TCP window-based rate control causes excessive buffering at the base station because of the lower transfer rate of the wireless link than that of the wired backhaul link. This performance characteristic of TCP further increases the end-to-end delay, and additional resources are required at the base station. This paper presents a practical mechanism to control the end-to-end TCP delay for CDMA2000 networks (or other similar wireless technologies). The key idea is to reduce and stabilize RTT (round-trip time) by dynamically controlling the TCP advertised window size, based on a runtime measurement of the wireless channel condition at the mobile station. The proposed system has been implemented by modifying the Linux protocol stack. The experiment results, conducted on a commercial CDMA2000 1x network, show that the proposed scheme greatly reduces the TCP delay in non-congested networks, while not sacrificing the TCP throughput in congested networks. Copyright © 2006 John Wiley & Sons, Ltd.</P>