• KSII Transactions on Internet and Information Systems (TIIS)
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• v.3 no.1
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• pp.5-25
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• 2009

In recent years the popularity of multi-hop wireless networks has been growing. Its flexible topology and abundant routing path enables many types of applications. However, the lack of a centralized controller often makes it difficult to design a reliable service in multi-hop wireless networks. While packet routing has been the center of attention for decades, recent research focuses on data discovery such as file sharing in multi-hop wireless networks. Although there are many peer-to-peer lookup (P2P-lookup) schemes for wired networks, they have inherent limitations for multi-hop wireless networks. First, a wired P2P-lookup builds a search structure on the overlay network and disregards the underlying topology. Second, the performance guarantee often relies on specific topology models such as random graphs, which do not apply to multi-hop wireless networks. Past studies on wireless P2P-lookup either combined existing solutions with known routing algorithms or proposed tree-based routing, which is prone to traffic congestion. In this paper, we present two wireless P2P-lookup schemes that strictly build a topology-dependent structure. We first propose the Ring Interval Graph Search (RIGS) that constructs a DHT only through direct connections between the nodes. We then propose the ValleyWalk, a loosely-structured scheme that requires simple local hints for query routing. Packet-level simulations showed that RIGS can find the target with near-shortest search length and ValleyWalk can find the target with near-shortest search length when there is at least 5% object replication. We also provide an analytic bound on the search length of ValleyWalk.

• The Journal of the Korea Contents Association
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• v.8 no.10
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• pp.20-26
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• 2008

The quality of stream remaking is decided the load of a server and Jitter through the traffic of the transmission path between end to end. In order to improve these problems in this paper, I propose tree construction method of low-delay-level-multicast. In this case which the network congestion will be occurred by streaming quality, I also propose the technique which dynamically changes the transmission path. This technique first constructs the overlay structure for relaxing the overload of server. Secondly, in order to decrease Jitter of client, it makes upload bandwidth and low latency balanced. In the evaluation of the performance, this paper showed better enhancement of about $15%{\sim}24%$ than P2CAST[4] in the simulation about node average join count, average bandwidth, service request refusal ratio, RTT measurement of nodes, and node average join count by defect ratio.

• Journal of Positioning, Navigation, and Timing
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• v.5 no.4
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• pp.203-211
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• 2016

A Satellite Based Augmentation System (SBAS) is a system that provides positioning information with high and accurate reliability to users who require ensuring high safety such as airplane taking off and landing. A continuous performance evaluation on navigation safety facilities shall be performed to determine whether developed systems meet the required performance before and after the operation. In this paper, SBAS position domain analysis is discussed in relation to analysis items for performance evaluation. The performance evaluation on the SBAS in the position domain shall conduct analysis on accuracy, integrity, continuity, and availability, which are items in the required navigation performance (RNP). In the paper, position domain analysis was conducted with regard to the Wide Area Augmentation System (WAAS) in the USA and the European Geostationary Navigation Overlay Service (EGNOS), which were developed already and now under operation. The analysis result showed that each of the systems satisfied the APV-I performance requirements recommended by the International Civil Aviation Organization (ICAO) with regard to daily data. It is necessary to verify using long-term data, whether the performance requirements in the RNP items are satisfied for system certification.

• Journal of Korea Multimedia Society
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• v.13 no.12
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• pp.1767-1777
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• 2010

In digital TV broadcasting, such as terrestrial, cable, satellite, and IPTV, the head-end of digital TV broadcasting has a more complicated transmission structure than that of analog TV broadcasting. Furthermore, digital TV broadcasting has a feature that supports multiplex models, such as Multiple Program Transport Stream (MPTS). Therefore, the purpose of our work was to design and examine a more efficient new system of emergency alert message transmission to support the digital TV broadcasting environments. Digital TV broadcasting is the IP generation or RF transmission of 8-VSB, QAM, and QPSK modulated through a multiplexer or re-multiplexer multiplexed stream as a MPEG-2 Transport Stream after content encoding. The new system proposed in this paper transmits an emergency alert message without scrambling after replacing the PID and payload of the -packet with the message prototype in the TS stream from the multiplexer. If we need to transmit an emergency alert message under digital TV broadcasting services, then the receiver first checks the PID of each packet in the TS stream for the emergency alert message. Next, if a packet is determined to be an emergency alert message, then the set-top box displays the message on the TV screen using its function of On Screen Display, or the PC based software displays the message on the monitor screen using its function of overlay with user interface if the packet is found to be an emergency alert message. We have designed an emergency alert message protocol and a system model. By experiments and analysis of the system, we concluded that the system achieved efficiency and the ability to send and receive emergency alert messages using the system under different digital TV broadcasting service environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2B
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• pp.240-249
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• 2004

For the effective IP-based service implementation in the wireless network environment, involvement of IP-related technologies in wireless networks is inevitable and globally unique IPv6 address allocation to the mobile node has become an important issue. In the 3GPP's address allocation mechanism, IPv6 address allocation procedure is performed by the GGSN, which is normally located far from the mobile nodes. This causes IPv6 address allocation time delay and traffics to be longer and increased in the core network, respectively. In this paper, we propose a new IPv6 address allocation mechanism that is performed by Node B located in RAN. The proposed IPv6 address allocation mechanism can provide IPv6 addresses to mobile nodes within a more reduced time than existing 3GPP's IPv6 address allocation mechanism, and co-operates with existing mechanism as an overlay model to improve reliability of wireless networks. And, for implementation of the proposed address allocation mechanism, it needs not to change the structure of current wireless networks except for the some functional addendum of Node B.

• Journal of Bio-Environment Control
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• v.25 no.1
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• pp.1-8
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• 2016

This study was conducted to find the suitability site for the construction of Saemangeum horticulture complex taking into account cost-effective environmental management by analyzing and comparing meteorological conditions. By overlapping the thematic maps, we extracted the regions that scored 50-59 points as suitable sites for the development project. Of these pre-selected sites, we selected the final candidate region for the protected horticulture by overlapping the sites selected for agricultural and living environment construction. The results of this study will contribute to generating added values by minimizing the environmental management costs for horticulture and landscaping. The operation of a large-scale protected horticulture and landscaping in the Saemangeum Complex will enhance the agricultural competitiveness of our country in the global market.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.5
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• pp.217-228
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• 2011

In centralize CDN systems, the content server selection is performed by service node for every user request, and the selected node is notified to the user. In this paper, we present distributed CDN architecture and algorithm in which the request from a user is delivered to the content source by a P2P algorithm utilizing DHT(distributed hash table) through the overlay network and the user selects one of the source nodes based on real-time user-centric criteria. For this purpose, we propose a modified Pastry algorithm for contents registration, search and selection, in addition to the distributed architecture. The proposed architecture has the advantages of load balancing, traffic balancing, scalability, fault-tolerance due to the self-configuration, self-healing attributes of distributed architecture. Various simulation shows the feasibility of the proposed architecture and algorithm, and the performance is compared and discussed for the variations of the proposed scheme.

• The KIPS Transactions:PartC
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• v.12C no.6 s.102
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• pp.817-826
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• 2005

BcN(Broadband convergence Network) is being developed in order to support a variety of network applications, with enhanced capabilities of QoS(Quality of Service) provisioning and security, and IPv6. In a high-speed network environment such as BcN, it if more likely for the network resources to be exposed to various intrusion activities. The propagation speed of intrusion is alto expected to be much faster than in the existing Internet In this paper, we present a multi-domain security management framework which my be used for a global intrusion detection at multiple domains of BcN and describe its characteristics. For the performance evaluation, we first present test results for the security node and compare with other products. Then we design and Implement an OPNET simulator for the proposed framework, and present some simulation results. In the simulation model, we focus on the performance of alert information in the security overlay network.

• Journal of Communications and Networks
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• v.6 no.3
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• pp.216-225
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• 2004

In a cellular network, if there are too many data users in a cell, data may suffer long delay, and system's quality-of-service (QoS) will degrade. Some traditional schemes such as dynamic channel-allocation scheme (DCA) will assign more channels to hot (or overloaded) cells through a central control system (CC) and the throughput increase will be upper bounded by the number of new channels assigned to the cell. In mobile-assisted data forwarding (MADF), we add an ad-hoc overlay to the fixed cellular infrastructure and special channels-called forwarding channels- are used to connect mobile units in a hot cell and its surrounding cold cells without going through the hot cell's base station. Thus, mobile units in a hot cell can forward data to other cold cells to achieve load balancing. Most of the forwarding-channel management work in MADF is done by mobile units themselves in order to relieve the load from the CC. The traffic increase in a certain cell will not be upper bounded by the number of forwarding channels. It can be more if the users in hot cell are significantly far away from one another and these users can use the same forwarding channels to forward data to different cold neighboring cells without interference. We find that, in a system using MADF, under a certain delay requirement, the throughput in a certain cell or for the whole net-work can be greatly improved.

• KIISE Transactions on Computing Practices
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• v.21 no.1
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• pp.1-12
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• 2015

To realize futuristic services with agility, the role of the experimental facility (i.e., testbed) based on integrated resources has become important, so that developers can flexibly utilize the dynamic provisioning power of software-defined networking and cloud computing. Following this trend, an OpenFlow-based SDN testbed environment, denoted as OF@TEIN, connects multiple sites with unique SmartX Racks (i.e., virtualization-enabled converged resources). In this paper, in order to automate the multi-point L2 (i.e., Ethernet) inter-connection of OpenFlow islands, we introduce an automated tool to configure the required Network Virtualization using Generic Routing Encapsulation (NVGRE) tunneling. With the proposed automation tool, the operators can efficiently and quickly manage network inter-connections among multiple OpenFlow sites, while letting developers to control their own traffic flows for service realization experiments.