• Journal of Korea Multimedia Society
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• v.11 no.10
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• pp.1446-1459
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• 2008

In an infrastructure-based wireless network, an access point is used for all communications among mobile devices. However, when a mobile device moves into a dead Bone, a connectivity disruption between the mobile device and the access point occurs. Such connectivity disruption consequently leads to another connectivity disruption between the mobile device moving toward the dead zone and other wireless-enabled devices located within the area of the infrastructure-based wireless network. To cope with the connectivity disruption in the infrastructure-based wireless network the ad hoc network that dynamically forms a network without any preexisting communication infrastructure needs to be set up to provide seamless connections among mobile devices. In this paper, we propose the DNSQ-MAC (Dynamic Network State aware QoS-Medium Access Control) technique that meets the deadlines of MAC frames forwarded over hop-by-hop multipaths and guarantees the QoS performance of an ad hoc-based wireless network. Mobile devices incorporating the DNSQ-MAC technique are capable of adjusting to the new dynamic network status in order to enhance the QoS performance in the ad hoc-based wireless network. A case study which exploits the Qualnet simulator shows that the proposed DNSQ-MAC technique can guarantee the deadlines of MAC frames forwarded over hop-by-hop multipaths and enhance the QoS performance of various routing protocols and packet schedulers running on the network layer above the MAC layer.

• Journal of Korea Multimedia Society
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• v.11 no.10
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• pp.1409-1419
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• 2008

Inauthentic resources can be easily spread by P2P (Peer-to-Peer) participants due to the openness and anonymity of P2P networks. A possible way to restrict the distribution of inauthentic resources and prevent malicious peers from joining P2P networks is to exploit peers' reputation which reflect their past behaviors and are also helpful to predict peers' future behaviors. There is a possibility that some peers intentionally plays along with other peers in order to increase/decrease its reputation through false feedback exchanges. Therefore, we propose a new reputation management scheme, called TrustRRep (Trustable Resource sharing service using Reputation) scheme, which improves the trustworthiness and efficiency of P2P networks by identifying peers who give false feedback. The TrustRRep scheme is also capable of providing peers with the trustworthiness of shared resources by discriminating resources distributed by malicious peers. We implement the proposed TrustRRep scheme on the NS-2 simulator for evaluating its performance compared to the recent reputation management work available in literature. A case study on simulations shows that the proposed reputation management scheme yields efficient performance in terms of the minimal download ratio and dissemination of inauthentic resources, the efficient identification of peers who give false feedback, and the provisioning of the trustworthiness of peers' reputation. It also shows that the proposed TrustRRep scheme imposes the restrictions of participating P2P networks on a malicious peers by diminishing its trust value.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7B
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• pp.608-618
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• 2006

The increasing popularity of multimedia streaming services introduces new challenges in content distribution. Especially, it is important to provide the QoS guarantees as they are increasingly expected to support the multimedia applications. The service providers can improve the performance of multimedia streaming by caching the initial segment (prefix) of the popular streams at proxies near the requesting clients. The proxy can initiate transmission to the client while requesting the remainder of the stream from the server. In this paper, in order to apply the prefix caching service based on IETF's RTSP environment to the wireless networks, we propose the effective RTSP handling scheme that can adapt to the radio situation in wireless network and reduce the cutting phenomenon. Also, we propose the traffic based caching algorithm (TSLRU) to improve the performance of caching proxy. TSLRU classifies the traffic into three types, and improve the performance of caching proxy by reflecting the several elements such as traffic types, recency, frequency, object size when performing the replacement decision. In simulation, TSLRU and RTSP handling scheme performs better than the existing schemes in terms of byte hit rate, hit rate, startup latency, and throughput.

• Journal of the Korea Society of Computer and Information
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• v.18 no.7
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• pp.11-21
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• 2013

Recently operating a large scale computing resource like a data center becomes easier because of the virtualization technology that virtualize servers and enable flexible resource provision. The most of public cloud services provides automatic scaling in the form of scale-in or scale-out and these scaling approaches works well to satisfy the service level agreement (SLA) of users. However, a novel scaling approach is required to operate private clouds that has smaller amount of computing resources than vast resources of public clouds. In this paper, we propose a hybrid server scaling architecture and related algorithms using both scale-in and scale-out to achieve higher resource utilization rate for private clouds. We uses dynamic resource allocation and live migration to run our proposed algorithm. Our propose system aims to provide a fine-grain resource scaling by steps. Thus private cloud systems are able to keep stable service and to reduce server management cost by optimizing server utilization. The experiment results show that our proposed approach performs better in resource utilization than the scale-out approach based on the number of users.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.8
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• pp.51-61
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• 2007

For provisioning reliable data transmission, the 3GPP RLC specification adopted a selective-repeat ARQ scheme assisted by a window-based admission control scheme. In the 3GPP ARQ, which is a member of the selective-repeat ARQ clan, inheres the reordering problem A long and irregular reordering time results in the degradation of throughput and delay performance, and may incur the overflow of the reordering buffer. Furthermore, the reordering time must be regulated to meet the requirements of some services which are loss-sensitive and delay-sensitive as well. Perceiving the reordering hazard, we propose an alternative, identified as snowball scheme, to the original admission control scheme of the 3GPP ARQ with aiming at deflating the occupancy of the reordering buffer. A unique feature of the snowball scheme is to reject a new DATA PDU if it is non-adjacent to any DATA PDU sojourning at the reordering buffer. Such an intentional rejection apparently reduces the occupancy of the reordering buffer while it may deteriorate the throughput and delay performance. Developing an analytical approximation method, we investigate the effect of snowball scheme on the saturated occupancy and throughput. Also, we, using a simulation method, evaluate the peak occupancy, normalized throughput and average delay in the practical environment. From the simulation results, we reveal that the snowball scheme is able to enhance occupancy performance as well as throughput performance compared with the original admission control scheme of the 3GPP ARQ.

• Journal of the Korean Institute of Landscape Architecture
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• v.42 no.3
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• pp.76-89
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• 2014

The functions of urban park including health related benefit and climate adaptation and mitigation are expanding. However, in-depth research and discourse on the equitable distribution of expanded park function has been limited so far. Following research suggests Green Welfare concept to reflect distributive equity and multifunctionality in the process of urban park policy development and execution. This study developed park welfare indices to analyze disparities of neighborhood urban park(NUP) distribution viewed from green welfare by literature review. The findings analyzed through the Correlation Analysis and Cluster Analysis by SPSS 18.0. The results of the study are as follows. First, green welfare is defined as "to receive equitable benefits and participate in the delivery process of green services which are promoting health and securing safety from climate change risks for every citizen by life cycle regardless of socioeconomic status". Second, NUP per person in Seoul indicate meaningful differences by socioeconomic and environmental status of Seoul administrative districts. Park welfare indices correlated to NUP per person were shown population density(negative), percentage of individuals $aged{\geq}65$(positive), percentage of self-reliance of local finance(positive), flood and air pollution vulnerability by climate change(negative). Third, the cluster analysis identifies three significant clusters that indicate differences of park welfare level. Thus, it was found that NUP in Seoul from a green welfare perspective was provided disproportionately. Future urban park policy in Seoul was required equitable distribution of multifunctionality of park beyond quantitative expansion, and priority consideration should be given to park service consumer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12B
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• pp.1450-1458
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• 2011

The HPcN (Hybrid & high Performance Convergence Network) in research networks means environment which can provide both computing resource such as supercomputer, cluster and network resource to application researchers in the field of medical, bio, aerospace and e-science. The most representative research network in Korea, KREONET has been developing following technologies through the HERO (Hybrid Networking project for research oriented infrastructure) from 200S. First, we have constructed and deployed a control plane technology which can provide a connection oriented network dynamically. Second, the integrated resource management system technology has been developing for reservation and allocation of both computing and network resources, whenever users want to utilize them. In this paper, a testbed network is presented, which is possible to reserve and allocate network resource using the integrated resource management system. We reserve network resource through GNSI (Grid Network Service Interface) messages between GRS (Global Resource Scheduler) and NRM (Network Resource Manager) and allocate network resource through GUNI (Grid User Network Interface) messages between the NRM (network resource manager) and routers, based on reservation information provided from a user on the web portal. It is confirmed that GUNI interface messages are delivered from the NRM to each router at the starting of reservation time and traffic is transmitted through LSP allocated by the NRM.

• The Journal of the Korea Contents Association
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• v.15 no.5
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• pp.570-581
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• 2015

In recent years, many institutions predict that cloud services and big data will be popular IT trends in the near future. A number of leading IT vendors are focusing on practical solutions and services for cloud and big data. In addition, cloud has the advantage of unrestricted in selecting resources for business model based on a variety of internet-based technologies which is the reason that provisioning and virtualization technologies for active resource expansion has been attracting attention as a leading technology above all the other technologies. Big data took data prediction model to another level by providing the base for the analysis of unstructured data that could not have been analyzed in the past. Since what cloud services and big data have in common is the services and analysis based on mass amount of data, efficient operation and designing of mass data has become a critical issue from the early stage of development. Thus, in this paper, I would like to establish data processing architecture based on technological requirements of mass data for cloud and big data services. Particularly, I would like to introduce requirements that must be met in order for distributed file system to engage in cloud computing, and efficient compression technology requirements of mass data for big data and cloud computing in terms of cost-saving, as well as technological requirements of open-source-based system such as Hadoop eco system distributed file system and memory database that are available in cloud computing.

• Journal of Internet of Things and Convergence
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• v.6 no.2
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• pp.45-50
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• 2020

In this paper, we propose a QoS-based handover management scheme in SDN. Even though there have been lots of recent services such as IoT, the conventional networks provide a monolitic handover method without considerations on flow-specific QoS features. For example, the conventional Internet provides a handover method which only considers IP continuity. On the other hand, 4G and 5G networks use a strict handover method for all kinds of flows with resource reservations. This means that it is difficult to guarantee the QoS requirements for the flow with a strict QoS requirement in Internet and the inefficient resource utilization can occur in the 4G and 5G because of the strict QoS-based handover management. The proposed scheme proposes the flow handover management scheme based on QoS requirements according to the SDN controller's management. From the network operators' perspective, the proposed scheme can provide the efficient resource utilization as well as QoS provisioning.

• Journal of the Korea Society for Simulation
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• v.15 no.1
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• pp.77-85
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• 2006

The cost of downloading content from the Internet may be costly for mobile device users using its 3G connection, because the 3G connection cost to download data from the Internet is a function of the amount of data downloaded. This paper introduces an approach in which mobile devices, called peers, form an ad hoc network and share their downloaded content with others. As an example, spectators may want to collect/share information about players and game records in a stadium. In an art gallery, visitors may want to retrieve some background information about the displayed work from the nearby ad hoc network. In an outdoor class, a teacher may download today's topic files from the Internet, and all students may share the content with minimal or no cost paid. This is possible if mobile device has both a 3G interface and a wireless LAN interface. If the peers want to improve privacy md discourage traffic analysis when sharing content, this paper describes a low-delay anonymous connection between the sending peer and the receiving peer using two additional peers. Simulation results show that the transmission time overhead of the anonymous connection may increase 50% or less as the number of peers increase or the peers are scattered over the larger area.