• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.8
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• pp.674-680
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• 2014

In this paper, as one of the fusion of IT and ocean technology, we propose a scheme to support NEMO in a harbor area network to provide network mobility for passengers, distribution as well as give a connection to an MN from an outside network. In a harbor area under PMIPv6 with NEMO support, a problem could be occurred due to overlapping HA/LMA tunnels and duplicate BCE fields. To Solve these problems, we consider the existing mobility option and add an optional field in the PBU message, which can notify the LMA and HA for either an initial connection or handover request. This procedure can reduce some overlapped steps of binding procedure. Hence, our proposed scheme could reduce an amount of delay and save the processing resource in the harbor area under PMIPv6 with NEMO support.

• Journal of KIISE:Computing Practices and Letters
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• v.10 no.2
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• pp.134-145
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• 2004

With rapid growth in the amount of data transferred on the Internet, traditional storage systems have reached the limits of their capacity and performance. SAN (Storage Area Network), which connects hosts to disk with the Fibre Channel switches, provides one of the powerful solutions to scale the data storage and servers. In this environment, the maintenance of data consistency among hosts is an important issue because multiple hosts share the files on disks attached to the SAN. To preserve data consistency, each host can execute the disk I/O whenever disk read and write operations are requested. However, frequent disk I/O requests cause the deterioration of the overall performance of a SAN cluster. In this paper, we introduce a SANtopia global buffer manager to improve the performance of a SAN cluster reducing the number of disk I/Os. We describe the design and algorithms of the SANtopia global buffer manager, which provides a buffer cache sharing mechanism among the hosts in the SAN cluster. Micro-benchmark results to measure the performance of block I/O operations show that the global buffer manager achieves speed-up by the factor of 1.8-12.8 compared with the existing method using disk I/O operations. Also, File system micro-benchmark results show that SANtopia file system with the global buffer manager improves performance by the factor of 1.06 in case of directories and 1.14 in case of files compared with the file system without a global buffer manager.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.10
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• pp.2430-2447
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• 2013

In recent years, HTTP adaptive streaming (HAS) has attracted considerable attention as the state-of-the-art technology for video transport. HAS dynamically adjusts the quality of video streaming according to the network bandwidth and device capability of users. Content-Centric Networking (CCN) has also emerged as a future Internet architecture, which is a novel communication paradigm that integrates content delivery as a native network primitive. These trends have led to the new research issue of harmonizing HAS with the in-network caching provided by CCN routers. Previous research has shown that the performance of HAS can be improved by using the H.264/SVC(scalable video codec) in the in-network caching environments. However, the previous study did not address the misbehavior that causes video freeze when overestimating the available network bandwidth, which is attributable to the high cache hit rate. Thus, we propose a new SVC-based adaptation algorithm that utilizes a drop timer. Our approach aims to stop the downloading of additional enhancement layers that are not cached in the local CCN routers in a timely manner, thereby preventing excessive consumption of the video buffer. We implemented our algorithm in the SVC-HAS client and deployed a testbed that could run Smooth-Streaming, which is one of the most popular HAS solutions, over CCNx, which is the reference implementation of CCN. Our experimental results showed that the proposed scheme (SLA) could avoid video freeze in an effective manner, but without reducing the high hit rate on the CCN routers or affecting the high video quality on the SVC-HAS client.

• Journal of Broadcast Engineering
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• v.23 no.1
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• pp.26-35
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• 2018

The recent development of overlay network technology enables distributed sharing of various types of contents. Although overlay network has great advantages as a huge content repository, it is practically difficult to directly provide such Internet service as streaming of contents. On the other hand, the media server, which is specialized in content services, has excellent service capabilities, but it suffers from the huge contents that are constantly created and requires large expansion of severs and storages, and thus requires much effort for efficient management of the huge repository. Hence, the association of an overlay network of huge storage with a media server of high performance content service will show a great synergy effect. In this paper, a location-aware scheme of constructing overlay networks and associating it with media server is proposed, and then cache-based contents management and service policy are proposed for efficient content service. The performance is analysed for one of the content services, streaming service.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.2B
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• pp.129-137
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• 2003

Multimedia streams, like MPEG continuously retrieve multimedia data because of their incessant playback. While these streams need an efficient support of kernel, the current buffer cache mechanism of Linux kernel such as Unix operating system was designed apt for small files, which is aperiodically requested as well as time uncritical. But, in case of continuous media, the CPU must enormously copy memory from kernel address space to user address space. This must lead to a large CPU overhead. This overhead both degrades system throughput and cannot guarantee QOS. In this paper, we have designed and implemented two memory copy reduction schemes in Linux kernel, direct I/O and one copy. The direct I/O skips the buffer cache layer of Linux kernel and results in dramatic reduction of CPU memory copy overhead. And, the one copy provides a fast disk-to-network data path without copying to user address space. The experimental results show considerable reduction of CPU overhead and throughput improvements.

• The KIPS Transactions:PartD
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• v.10D no.3
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• pp.359-366
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• 2003

Although the reuse of the cached data for scrolling the map reduces the amount of passed data between client and server, it needs the conversions of data coordinates, selective deletion of objects, cache compaction and object structuring step in the clients. The conversion is a time- intensive operation due to limited resources of mobile phones such as low computing power, small memory. Therefore, in order to control the map efficiently in the vector map service based mobile phones, it is necessary to study the methods which reuse cached objects for reducing wireless network bandwidth and overwhelming the limited resources of mobile phones as well. This paper proposes the methods of reusing pre-received spatial objects for map control in the mobile vector map service system based on client-server architecture. The experiments conducted on the Web GIS systems with real data show that the proposed method is appropriate to map services for mobile phone. We also analyze the advantages and drawbacks between the reuse of cached data and transmission of raw data respectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.8
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• pp.1847-1854
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• 2005

This paper proposes a approach to configure efficient video-on-demand system by introducing Multicast and Cache Video-on-Demand (MCVoD) system. As a key element or the MCVoD system, interchange agent provides this system with multicasting and switching functions. With the multicasting, the MCVoD system is able to reduce the load on the network as well as VoD servers by transmitting only one video request instead of sending multiple requests on a same video stream. The switching enables clients to receive the lust stream of requested video streams instantly without waiting time and also allows avoiding undesirable duplication of video streams in the system. With various experiment results through simulation about waiting tine and cache hit ratio, we show that the MCVoD system employing the interchange agent provides better performance than current uni-proxy based system.

• Journal of KIISE:Databases
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• v.28 no.3
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• pp.458-467
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• 2001

Optimistic Two-Phase Locking(O2PL) performs as well as or better than the other approaches because it exploits client caching well and also has relatively lower network bandwidth requirements. However, O2PL leads to unnecessary waits, because, it can not be commit a transaction until the transaction obtains all requested locks. In addition, Optimistic Concurrency Control(OCC) tends to make needless aborts. This paper suggests an efficient optimistic cache consistency protocol that overcomes such shortcomings. Our scheme decides whether to commit or abort a transaction without wait and it adopts transaction re-ordering in order to minimize the abort rate. Our scheme needs only one version for each data item in spite of the re-ordering mechanism used. Finally, this paper presents a simulation-based analysis that shows superiority in performance of out scheme to O2PL and OCC.

• The KIPS Transactions:PartA
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• v.8A no.4
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• pp.419-428
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• 2001

Advances in circuit and integration technology are continuously boosting the speed of processors. One of the main challenges presented by such developments is the effective use of powerful processors in shared memory multiprocessor system. We believe that the interconnection problem is not solved even for small scale shared memory multiprocessor, since the speed of shared buses is unlikely to keep up with the bandwidth requirements of new powerful processors. In the past few years, point-to-point unidirectional connection have emerged as a very promising interconnection technology. The single slotted ring is the simplest form point-to-point interconnection. The main limitation of the single slotted ring architecture is that latency of access increase linearly with the number of the processors in the ring. Because of this, we proposed the dual slotted ring as an alternative to single slotted ring for cache-based multiprocessor system. In this paper, we analyze the proposed dual slotted ring architecture using new snooping protocol and enforce simulation to compare it with single slotted ring.

• Journal of the Korea Society of Computer and Information
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• v.26 no.1
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• pp.111-118
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• 2021

This paper proposes a novel method of caching contents that can be encoded into multiple quality levels in device-to-device (D2D)-assisted caching networks. Different from the existing caching schemes, the author allows caching fractions of an individual file and considers the self cache hit event, which the user can find the desired content in its device. The author analyzes the tradeoff between the quality of cached contents and the cache hit rate, and proposes the device caching method maximizing the expected quality that the user can enjoy. Depending on the parameter of the relationship between the quality and the file size, the optimal caching method can be obtained by solving the convex optimization problem and the DC programming problem. If the file size increases faster than the quality, the cached fractions of the contents continuously increase as the popularity grows. Meanwhile, if the file size increases slower than the quality, some of the high-popularity files are entirely cached but others are not cached at all.