• Journal of KIISE:Information Networking
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• v.33 no.1
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• pp.38-48
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• 2006

For extending of hot-spot of WLAN, (2) proposes internetworking scheme between wireless LAN (WLAN) and mobile ad-hoc network (MANET), which employ the same layer-2 protocol with different mode. Compared to internetworking schemes between UMTS (Universal Mobile Telecommunications Systems) and WLAN (3-4), the scheme from (2) has relatively low overhead and latencies because WLAN and MANET are physically and logically similar to each other. However, the mode switching algorithm proposed in r2] for internetworking between WLAN and MANET only considers signal strength and determines handoff, and mobile nodes following a zigzag course in pollution area may perform handoff at short intervals. Furthermore, (2) employs mobile IPv6 (MIPv6) at base, which brings still high delay on handoff and overhead due to signal message exchange. In this paper, we present optimized internetworking scheme between WLAN and MANET, modified from (2). To settle ping-pong handoff from (2), we propose adaptive mode switching algorithm. HMIPv6 is employed for IP connectivity and mobility service in WLAN, which solves some shortcomings, such as high handoff overhead and vulnerable security. For routing in MANET, OLSR is employed, which is a proactive Protocol and has optimally reduced signal broadcasting overhead. OLSR operates with current P protocol compatibly with no change or modification. The proposed internetworking scheme based on adaptive mode switching algorithm shows better performance than scheme from (2).

• Journal of KIISE:Information Networking
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• v.33 no.1
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• pp.76-90
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• 2006

Sensor network consists of a large number of sensor nodes that are densely deployed either inside the phenomenon or very close to it. The life time of each node in the sensor network significantly affects the life time of whole sensor network. A node which drained out its battery may incur the partition of whole network in some network topology The life time of each node depends on the battery capacity of each node. Therefore if all sensor nodes in the network live evenly long, the life time of the network will be longer. In this paper, we propose Cluster-Based Power-Efficient Routing (CBPER) Protocol which provides scalable and efficient data delivery to multiple mobile sinks. Previous r(luting protocols, such as Directed Diffusion and TTDD, need to flood many control packets to support multiple mobile sinks and many sources, causing nodes to consume their battery. In CBPER, we use the fact that sensor nodes are stationary and location-aware to construct and maintain the permanent grid structure, which makes nodes live longer by reducing the number of the flooding control packets. We have evaluated CBPER performance with TTDD. Our results show that CBPER is more power-efficient routing protocol than TTDD.

• Journal of KIISE:Information Networking
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• v.33 no.1
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• pp.16-27
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• 2006

The wireless transmission medium inherently broadcasts a signal to all neighbor nodes in the transmission range. Existing asynchronous MAC protocols do not provide a concrete solution for reliable broadcast in link layer. This mainly comes from that an omni-directional broadcasting causes to reduce the network performance due to the explosive collisions and contentions. This paper proposes a reliable broadcast protocol in link taller based on directional antennas, named MDB(MAC protocol for Directional Broadcasting). This protocol makes use of DAST(Directional Antennas Statement Table) information and D-MACA(Directional Multiple Access and Collision Avoidance) scheme through 4-way handshake to resolve the many collision problem wit]1 omni-directional antenna. To analyze its performance, MDB protocol is compared with IEEE 802.11 DCF protocol [9] and the protocol 2 of reference [3], in terms of the success rate of broadcast and the collision rate. As a result of performance analysis through simulation, it was confirmed that the collision rate of the MDB protocol is lower than those of IEEE 802.11 and the protocol 2 of reference [3], and that the completion rate of broadcast of MDB protocol is higher than those of IEEE 802.11 and the protocol 2 of reference [3].

• Journal of KIISE:Information Networking
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• v.36 no.4
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• pp.339-350
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• 2009

In wireless sensor networks, the limited battery resources of sensor nodes have a direct impact on network lifetime. To reduce unnecessary power consumption, it is often the case that only a minimum number of sensor nodes operate in active mode while the others are kept in sleep mode. In such a case, however, the network service can be easily unreliable if any active node is unable to perform its sensing or communication function because of an unexpected failure. Thus, for achieving reliable sensing, it is important to maintain the sensing level even when some sensor nodes fail. In this paper, we propose a new fault-tolerance scheme, called FCP(Fault-tolerant Coverage Preserving), that gives an efficient way to handle the degradation of the sensing level caused by sensor node failures. In the proposed FCP scheme, a set of backup nodes are pre-designated for each active node to be used to replace the active node in case of its failure. Experimental results show that the FCP scheme provides enhanced performance with reduced overhead in terms of sensing coverage preserving, the number of backup nodes and the amount of control messages. On the average, the percentage of coverage preserving is improved by 87.2% while the additional number of backup nodes and the additional amount of control messages are reduced by 57.6% and 99.5%, respectively, compared with previous fault-tolerance schemes.

• Journal of KIISE:Information Networking
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• v.29 no.2
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• pp.117-128
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• 2002

Virtual LAN (VLAN) is an architecture to enable communication between end stations as if they were on the same LAN regardless of their physical locations. VLAN defines a limited broadcast domain to reduce the bandwidth waste. The Newbridge Inc. developed a layer 3 VLAN product called VIVID, which configures a VLAN based on W subnet addresses. In a VIVID system, a single route server is deployed for address resolution, VLAN configuration, and data broadcasting to a VLAN. If the size of the network, over which the VLANS supported by the VIVID system spans, becomes larger, this single route server could become a bottleneck point of the system performance. One possible approach to cope with this problem is to deploy multiple route servers. We propose two architectures, organic and independent, to expand the original VIVID system to deploy multiple route servers. A course of simulations are done to analyze the performance of each architecture that we propose. The simulation results show that the performances of the proposed architectures depend on the lengths of VLAN broadcasting sessions and the number of broadcast data frames generated by a session. It has also been shown that there are tradeoffs between the scalability of the architecture and their efficiency in data transmissions.

• Journal of KIISE:Information Networking
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• v.27 no.3
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• pp.301-314
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• 2000

As the number of World Wide Web (Web) users grows, Web traffic continues to increase at an exponential rate. Currently, Web traffic is one of the major components of Internet traffic. Also, high bandwodth usage due to Web traffic is observed during peak periods while leaving bandwidth usage idle during off-peak periods. One of the solutions to reduce Web traffic and speed up Web access is through the use of Web caching. Unfortunately, Web caching has limitations for reducing network bandwidth usage during peak periods. In this paper, we focus our attention on the use of a prefetching algorithm for reducing bandwidth during peak periods by using off-peak period bandwidth. We propose a statistical, batch, proxy-side prefetching scheme that improves cache hit rate while only requiring a small amount of storage. Web objects that were accessed many times in previous 24 hours but would be expired in the next 24 hours, are selected and prefetched in our scheme. We present simulation results based on Web proxy and show that this prefetching algorithm can reduce peak time bandwidth using off-peak bandwidth.

• Journal of KIISE:Information Networking
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• v.27 no.3
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• pp.348-359
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• 2000

Most of the important real time multimedia applications require multipoint transmissions. To support these applications in ATM based Intermet environments, it is important to provide efficient IP multicast transportations over ATM networks. IETF proposed MARS(Multicast Address Resolution Server) as the service architecture to transport connectionless IP multicast flows over connection oriented ATM VCs. MARS assumes UNI3.0/3.1 signalling. Since UNI3.0/3.1 does not provide any means for receivers to request a join for a multicast ATM VC, MARS provides overlay service to relay join request from IP multicast group members to the sources of the multicast group. Later on, ATM Forum standardized UNI4.0 signalling which is provisioned with a new signalling mechanism called LIJ(Leaf Initiated Join). LIJ enables receivers to directly signal the source of an ATM VC to join. In this paper, we propose a new service architecture providing IP multicast flow transportation over ATM networks deploying UNI4.0 signalling. The proposed architecture is named UNI4MARS. It comprises service components same as those of the MARS. The main functionality provided by the UNI4MARS is to provide source information to the receivers so that the receivers may exploit LIJ to join multicast ATM VCs dynamically. The implementation overhead of UNI4MARS and that of MARS are compared by a course of simulations. The simulation results show that the UNI4MARS supports the dynamic IP multicast group changes more efficiently with respect to processing, memory and bandwidth overhead.

• Journal of the Korean BIBLIA Society for library and Information Science
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• v.22 no.3
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• pp.75-90
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• 2011

This study aimed to investigate, analyze and identify the problems related to SNS usage by publishing companies around Twitter, Facebook and Me2day as well as theoretically investigate SNS, and ultimately to suggest the approaches to improve the outstanding issues identified. In accordance with the analysis, only 0.5%(222 publishing companies) in total publishing companies(41,407) opened SNS[3.7%(1,537) opened the independent website.] Second, in accordance with the investigation on 212 publishing companies in 222 companies opening SNS(71 twitters, 74 facebooks, 67 Me2days), the communication was not significant to the extent that only 50.5%(107) kept the communication with less than 100 readers or potential readers. Furthermore, 77.4%(164 companies) had less than 1,000 postings by publishing companies. The analysis on the postings(500) by users and postings(300) by publishing companies demonstrated that those postings were mostly related to marketing, introduction, recommendation and reading of publications by publishing companies. It means that the postings were mostly positive. However, 86.6% of postings by users in SNS of publishing companies was merely one-time posting. It indicated that continuity was not sufficient.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.1
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• pp.114-123
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• 2007

As a promising technology that enables ubiquitous computing and will lead the information technology industries of the next generation, the new field of sensor networks is one of the most active research topics today. From now on, each node, the network formation, and even the sensor network itself will interact with the generic network and evolve dynamically according to environmental changes, in a process of continual creation and extinction. In this paper, we propose a address-Internetworking scheme for interactive networking between a sensor network and the Internet based on the TCP port-numbers. The proposed scheme enables internetworking between a sensor network address scheme based on Zigbee and the Internet address scheme based on the Internet Protocol version 6 (IPv6). We implement the proposed address-Internetworking scheme using Berkeley TinyOS, Mica Motes, and IP. In addition we verify the proposed scheme by an interconnection experiment, which involves wireless sensor networks and the Internet, using IPv4/IPv6.

• Korean Journal of Social Welfare Studies
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• v.47 no.1
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• pp.233-259
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• 2016

The purpose of this study is to investigate the problems brought about by applying the case management of prostitution in practice, considering its special characteristics. The study is based on the actual experience and understanding of the hands-on workers toward its case management, who are working at the organization for preventing prostitution. To do this, data collected for the research is analyzed by an inductive approache. Participants are selected in the Counseling Centers for Prostitution, General Supporting Facilities, Supporting Centers for Self-help, and Youth Facilities. Three organizations in each type of the centers or facilities are respectively chosen. Twelve participants are composed of six hands-on workers in charge of the case management and six managers supervising it(called the director of the Center in some Centers). According to the analysis, the main issues of their case management experiences are divided into 5 topics and then sub-divided into 12 ones in 3 areas. Each theme of the topics is 'Steady & ordinary, not special tasks', 'Co-existence of a burden & thrilling', 'Sad, but pretending to be serene', 'Know-hows through practical experiences', 'Nevertheless, fill my future with hopes'. On the basis of the result, some policies and instructions necessary to actively revitalize the case management are suggested: expanding professional training centers based on the field, preparing government level customized-services in medical treatments and laws, creating jobs & intensifying job training, setting up various cooperative systems with local organizations via active networking, establishing super-vision systems, and so on.