• Journal of Communications and Networks
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• v.14 no.1
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• pp.51-62
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• 2012

The exponential growth in wireless services has resulted in an overly crowded spectrum. The current state of spectrum allocation indicates that most usable frequencies have already been occupied. This makes one pessimistic about the feasibility of integrating emerging wireless services such as large-scale sensor networks into the existing communication infrastructure. Cognitive radio is an emerging dynamic spectrum access technology that can be used for flexibly and efficiently achieving open spectrum sharing. Cognitive radio is an intelligent wireless communication system that is aware of its radio environment and that is capable of adapting its operation to statistical variations of the radio frequency. In ad hoc cognitive radio networks, a common control channel (CCC) is usually used for supporting transmission coordination and spectrum-related information exchange. Determining a CCC in distributed networks is a challenging research issue because the spectrum availability at each ad hoc node is quite different and dynamic due to the interference between and coexistence of primary users. In this paper, we propose a novel CCC selection protocol that is implemented in a distributed way according to the appearance patterns of primary systems and connectivity among nodes. The proposed protocol minimizes the possibility of CCC disruption by primary user activities and maximizes node connectivity when the control channel is set up. It also facilitates adaptive recovery of the control channel when the primary user is detected on that channel.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.20 no.3
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• pp.105-111
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• 2010

We propose a practical privacy-preserving clustering protocol over horizontally partitioned data. We extend the DBSCAN clustering algorithm into a distributed protocol in which data providers mix real data with fake data to provide privacy. Our privacy-preserving clustering protocol is very efficient whereas the previous privacy-preserving protocols in the distributed environments are not practical to be used in real applications. The efficiency of our privacy-preserving clustering protocol over horizontally partitioned data is comparable with those of privacy-preserving clustering protocols in the non-distributed environments.

• Journal of KIISE:Computer Systems and Theory
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• v.29 no.5
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• pp.257-264
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• 2002

In this paper, we give a detailed description of KDSM(KAIST Distributed Shared Memory) system. KDSM is implemented as a user-level library running on Linux 2.2.13, and TCP/IP is used for communication. KDSM uses page-based invalidation protocol, multiple-writer protocol, and supports HLRC(Home-based Lazy Release Consistency) memory consistency model. To evaluate performance of KDSM, we executed 4 scientific applications and compared the result to JLAJLA. The results showed that performance of KDSM almost equal to JIAJIA for 2 applications and performance of KDSM is better than JIAJIA for 2 applications.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.2131-2136
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• 2003

Since the number of user-requests increases dramatically on the Internet, the servers and networks can be swamped unexpectedly without any prior notice. Therefore, the end-users are waiting or refused for the responses of the contents from the originating servers. To solve this problem, it has been considered that a distributed web caching system efficiently utilizes structural elements of the network. Because a distributed web caching system uses the caches that are close to end-users on the network, it transmits the contents to users faster than the original network system. This paper proposes a simple client-based distributed web caching system(2HRCS) that client can directly perform object allocation and load balancing without an additional DNS for load balancing in CARP (Cache Array Routing Protocol) and GHS (Global Hosting System) that are the recent distributed web caching system protocol. The proposed system reduces the cost of setup and operation by removing DNS that needs to balance the load in the existing system. The system has clients with consistent hashing method, so it extends its environment to other distributed web caching system that has caches of different capacity. A distributed web caching system is composed and tested to evaluate the performance. As a result, it shows superior performance to consistent hashing system. Because this system can keep performance of the existing system and reduce costs, it has the advantage of constructing medium or small scale CDN (Contents Delivery Network).

• Journal of Korea Multimedia Society
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• v.19 no.3
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• pp.567-572
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• 2016

N-screen is an emerging technology to support multimedia multicasting, content sharing and content mobility. N-screen service providers should obtain the technology that provides the highest quality content seamlessly. Distributed nature of WiMedia distributed-MAC protocol can provide full mobility support, and achieves seamless medium access method in contrast to IEEE 802.15.3. So, in this paper, WiMedia distributed-MAC protocol is adopted and an asynchronous multicast transmission (AMT) technology is proposed to enhance performance of seamless N-screen wireless service based on distributed-MAC. The ACK frame transmissions are not required for multicast transmissions. By using this property in AMT, if a device is a multicast receiver, its reserved time slots can be reserved by the other devices with 1-hop distance. Furthermore, each N-screen device broadcasts and shares the information including an order in asynchronous traffic reservations to reduce conflicts in determining the transmission order of asynchronous N-screen packets. Therefore, AMT scheme expands the number of time slots available and throughputs for multicast and asynchronous traffic reservations when comparing with the distributed-MAC standard system. N-screen communications based on distributed-MAC with the proposed AMT shows a new framework for realizing N-screen wireless service with the full content mobility.

• Journal of Korea Multimedia Society
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• v.19 no.11
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• pp.1871-1877
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• 2016

In this paper, a Wireless USB (WUSB) protocol is adopted for development of ASMD (Adaptive Source Multi Device) N-screen wireless services. WUSB is the USB technology merged with WiMedia PHY and Distributed-MAC (D-MAC). However, the current WUSB protocol can't provide seamless N-screen streaming services to moving WUSB devices in home network environment. Therefore, to provide the ASMD N-screen services through WUSB based on D-MAC protocol, a channel management scheme is proposed to support seamless mobility between adjacent ASMD groups for wireless IPTV N-screen services. In simulation results, proposed ASMD channel management (ACM) scheme is compared with conventional WUSB channel management scheme in view points of throughput, average path interference and energy consumption according to various numbers of nodes and elapsed simulation times. Through simulation results, it is explained that proposed ASMD channel management (ACM) scheme should be adopted in the WUSB protocol to realize ASMD N-screen wireless services.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.795-798
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• 1999

To transmit multimedia information efficiently and use it in realtime, it needs a private multimedia terminal for service type. But multimedia information terminal was developped for of offered service type in case by case. Accordingly, general multimedia terminal have not been developed yet. Multimedia database structure and standard communication protocol must be designed first to develop the general multimedia terminal. Multimedia database structure needs to store the various multimedia information consistently and, standard communication protocol access the database transparently. In this paper, we design a multimedia database structure and communication protocol that are able to access the multimedia information on distributed database servers in the network.

• Proceedings of the KIEE Conference
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• 2002.07d
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• pp.2212-2215
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• 2002

This dissertation suggests and implements a middle level network which is called PICNET-NP (Plant Implementation and Control Network for Nuclear Power Plant). PICNET-NP is based partly on IEEE 802.4 token-passing bus access method and partly on IEEE 802.3 physical layer. For this purpose a new interface a physical layer service translator, is introduced. A control network using this method is implemented and applied to a distributed real-time system. To verify the performance of proposed protocol experimental were carried out, and the following results are obtained. 1) proper initialization of the protocol. 2) normal receiving and transmission of data. 3) proper switching of transmission media in case of a fault condition on the one of transmission media. The proposed protocol exhibits the excellent performance in the experimental system. From the test results in the experimental system, the proposed protocol, PICNET-NP, can be used for the upgrading of a nuclear power plant and the distributed control system in the next generation of nuclear power plant.

• Journal of Advanced Information Technology and Convergence
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• v.10 no.2
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• pp.83-90
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• 2020

A protocol HMNR, was proposed to utilize control information of every other process piggybacked on each sent message for minimizing the number of forced checkpoints. Then, an improved protocol, called Lazy-HMNR, was presented to lower the possibility of taking forced checkpoints incurred by the asymmetry between checkpointing frequencies of processes. Despite these two different minimization techniques, if the high message interaction traffic occurs, Lazy-HMNR may considerably lower the probability of knowing whether there occurs no Z-cycle due to its shortcomings. Also, we recognize that no previous work has smart procedures to be able to utilize network infrastructures for highly decreasing the number of forced checkpoints with dependency information carried on every application message. We introduce a novel Lazy-HMNR protocol for group communication-based distributed computing systems to cut back the number of forced checkpoints in a more effective manner. Our simulation outcomes showed that the proposed protocol may highly lessen the frequency of forced checkpoints by comparison to Lazy-HMNR.

• Journal of KIISE:Information Networking
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• v.35 no.1
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• pp.91-97
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• 2008

In order to get a desired service in such environments, we need a service discovery method for discovering a device providing that service. In this paper, we propose a service discovery protocol which is based on DHTs (Distributed Hash Tables) to solve these problems. Our protocol is scalable since it does not require a central lookup server and does not rely on multicast or flooding. Simulation results show that our protocol is scalable and outperforms existing service discovery protocols.