• Journal of KIISE:Computer Systems and Theory
• /
• v.37 no.3
• /
• pp.172-183
• /
• 2010

Virtual memory systems (VM) reduce disk I/Os caused by page faults using page prefetching, which reads pages together with a desired page at a page fault in a single disk I/O. Operating systems including 4.4BSD attempt to prefetch as many pages as possible at a page fault regardless of page access patterns of applications. However, such an approach increases a disk access time taken to service a page fault when a high portion of the prefetched pages is not referenced. More seriously, the approach can cause the memory pollution, a problem that prefetched pages not to be accessed evict another pages that will be referenced soon. To solve these problems, we propose an adaptive page prefetching control scheme (APC), which periodically monitors access patterns of prefetched pages in a process unit. Such a pattern is represented as the ratio of referenced pages among prefetched ones before they are evicted from memory. Then APC uses the ratio to adjust the number of pages that 4.4BSD VM intends to prefetch at a page fault. Thus APC allows 4.4BSD VM to prefetch a proper number of pages to have a better effect on reducing disk I/Os, though page access patterns of an application vary in runtime. The experiment of our technique implemented in FreeBSD 6.2 shows that APC improves the execution times of SOR, SMM, and FFT benchmarks over 4.4BSD VM by up to 57%.

• Journal of Internet Computing and Services
• /
• v.15 no.5
• /
• pp.83-93
• /
• 2014

Providing personalized services customized to users' needs and preferences becomes highlighted as a key area of user-context computing. It is essential for context-aware technology to be developed more intelligent and meaningful services by being widely applied to a variety of sectors and domains. SDO (Standard Development Organization) such as MPEG and W3C has been actively developed to be standardized services and to improve context-awareness services. Yet current standards related to context-aware technology, such as MPEG-7, MPEG-21, MPEG-V, and emotionML, are not capable enough to support various systems and diverse services. Against this backdrop, the MPEG User Description, referred to also as MPEG-UD Standard, is to ensure interoperability among recommendation services, which take into account user's context when generating recommendations to users. In this light, we introduce standards related to the user context and propose the structure for RD-Engine and the Remote Responsive User Interface(RRUI) system in reference to MPEG-UD. This system collects unit resources matching specific condition according to the user's contexts described by MPEG-UD. In so doing, it improves adaptive user interface considering device features in real-time. By automatically generating adaptive user interfaces tailored to an individual's contexts, the proposed system aims to achieve high-quality user experience for a complex service.

• Journal of Broadcast Engineering
• /
• v.13 no.1
• /
• pp.6-16
• /
• 2008

An instable wireless channel condition causes more packet losses and retransmissions due to interference, fading, station mobility, and so on. Therefore video streaming service over a wireless networks is a challenging task because of the changes in the wireless channel conditions and time-constraints characteristics of the video streaming services. To provide efficient video streaming over a wireless networks, QoS-enhanced MAC protocol, IEEE 802.11e, is standardized recently. Tn this paper, we propose a new network-adaptive H.264 video streaming mechanism in the IEEE 802.11e wireless networks. To improve the quality of video streaming services, video stream has to adapt to the changes in the wireless channel conditions. The wireless channel conditions are estimated by the packet loss probability and informed to the application layer by the cross-layering. According to the wireless channel information, the video streaming application filters out the low-priority data. This adaptation mechanism efficiently uses system resources because it drops the low-priority data in advance. Therefore, our cross-layer design can provide improved video streaming services to the end-user. Through the implementation and performance evaluation, we prove that the proposed mechanism improves the QoS of the video streaming by providing the smoothed playback.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.25 no.3
• /
• pp.117-128
• /
• 2023

Tree dieback in Geumgang pine forest has occurred in Uljin and Bonghwa since the 2010s. In order to identify status of tree dieback and prevent further damages, a monitoring project for tree dieback in Geumgang pine forest had been launched by Southern regional office of forest service in 2020. This study was conducted to understand the characteristics of tree dieback occurrence and assess the high risk areas using the occurrence data in the project. Pine tree dieback occurred frequently in areas with mountain ridges in high elevation, dry south-facing slopes, mature stands, and high temperature rise in winter. Furthermore, the result of risk assessment showed that 6.2 percent(5,294ha) of Geumgang pine forest(85,000 ha) in total study area are at high risk of tree dieback. As the pine trees in the high risk area are prone to experience the dieback due to temperature and drought-related extreme weather events, regular forest management activities are needed to reduce the drought stress of pine trees. Forest health management for the pine forest with high protection priority can be also useful strategy to counter the risk of decline. This results can be used as the basic information for the adaptive forest management to climate change.

• 전자공학회논문지 IE
• /
• v.45 no.1
• /
• pp.15-23
• /
• 2008

In this paper, an algorithm, that provisions absolute differentiation of packet delays is proposed, simulated, and implemented with VHDL on XPC 860 CPU based test board with an objective for enhancing quality of service (QoS) in future packet networks. It features a scheme that compensates the deviation for prediction on the traffic to be arrived continuously. It predicts the traffic to be arrived at the beginning of a time slot and measures the actual arrived traffic at the end of the time slot and derives the difference between them. The deviation is utilized to the delay control operation for the next time slot to offset it. As it compensates the prediction error continuously, it shows superior adaptability to the bursty traffic as well as the exponential traffic. It is demonstrated through both simulation and the real traffic test on the board that the algorithm meets the quantitative delay bounds and shows superiority to the traffic fluctuation in comparison with the conventional non-adaptive mechanism.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.9
• /
• pp.34-41
• /
• 2017

Wireless mesh networks contain multi-hop routing protocols between wireless nodes and are connected to the Internet through a gateway. These networks perform a role as a backbone and are scalable for main applications. We propose the design of QoS supporting mechanisms for wireless mesh networks using software defined networking. Our proposed scheme is cost-effective and features adaptive QoS mechanisms for wireless router's resource constraints. The QoS mechanisms use software defined networking technology with Openflow protocol based on diffserv and intserv models with MPLS mechanism and RSVP respectively. A performance evaluation model is suggested to verify the validity of the proposed scheme using several QoSmetrics of the wireless mesh networks.

• Journal of Satellite, Information and Communications
• /
• v.11 no.1
• /
• pp.6-11
• /
• 2016

In this paper, we have analyzed the effects of co-channel, adjacent-channel, and the human shield(Body Blockage) for wideband WLAN based on the IEEE802.11n 40MHz channel bandwidth required for high speed digital signage service. Simulation results show that wideband WLAN can be operated with 78 interferers over 63m distance in co- channel, 80 interferer over 61m distance in adjacent channel. By applying the mitigation method for reducing the interference, we have confirmed that protection distance is improved to 51m using beamforming, and 40m using cognitive radio in co-channel interference. Also body blockage interference is reduced using adaptive channel bandwidth, C/I ratio, beamforming, power control mitigation methodology.

• The KIPS Transactions:PartC
• /
• v.11C no.6 s.95
• /
• pp.781-786
• /
• 2004

In these days, such services are popularized as E-commerce, E- government, multimedia services, and home networking applications. Most web traffics generated contemporarily basically use the Hyper Text Transfer Protocol(HTTP). Unfortunately, the HTTP is improper for these applications that comprise significant components of the web traffics. In this paper, we introduce a real-time contents compression architecture that maximizes the web service performance as well as reduces the response time. This architecture is built into the linux kernel-based web accelerating module. It guarantees not only the freshness of compressed contents but also the minimum time delay using an server-state adaptive algorithm, which can determine whether the server sends the compressed message considering the consumption of sewer resources when heavy requests reach the web server. Also, We minimize the CPU overhead of the web server by exclusively implementing the compression kernel-thread. The testing results validates that this architecture saves the bandwidth of the web server and that elapsed time improvement is dramatic.

• KIPS Transactions on Computer and Communication Systems
• /
• v.3 no.7
• /
• pp.231-240
• /
• 2014

Video transcoding techniques provide an efficient mechanism to make a video content adaptive to the capabilities of a variety of clients. However, it is hard to provide an appropriate quality-of-service(QoS) to the clients owing to heavy workload on transcoding operations. In light of this fact, this paper presents the dual transcoding method in order to guarantee QoS in streaming services by maximizing resource usage in a transcoding server equipped with both CPU and GPU computing units. The CPU and GPU computing units have different architectural features. The proposed method speculates workload of incoming transcoding requests and then schedules the requests either to the CPU or GPU accordingly. From performance evaluation, the proposed dual transcoding method achieved a speedup of 1.84 compared with traditional transcoding approach.

• Journal of KIISE:Computer Systems and Theory
• /
• v.33 no.7
• /
• pp.440-447
• /
• 2006

Grid computing is the complex deployments of various hardware and software components. The Grid environment should provide a mechanism for real-time monitoring and notification. It is very important to implement a monitoring mechanism in the Grid environment. Most existing monitoring systems only focus on their own requirements. With the development of Grid computing technology, the extensible monitoring systems become more and more feasible and popular. In this paper, we describe our research and development works on M-Mon, a novel framework for the flexible and adaptive Grid monitoring system. M-Mon system focuses on some critical issues like scalability, reusability, runtime extensibility, protocol transparency and uniform data representation. To provide interoperability with other monitoring systems and to reuse legacy facilities with a minimum effort, our monitoring system has been developed using service-oriented architecture.