• The Journal of Korean Institute of Communications and Information Sciences
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• 제33권8B호
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• pp.646-656
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• 2008

In this paper, we design and verify the MAC chip of the two-stage AWG-based WDM-PON which considers 128 ONUs and 32 wavelengths. Each wavelength with the capacity of 1Gbps is allocated to ONU for downstream transmission but each wavelength for upstream transmission can be shared by four ONUs. Therefore, MAC protocol is required to avoid the collision and use the network resource efficiently among ONUs which are sharing the same wavelength. To design a request/permit-based MAC protocol, we define a unit-chip module called sub-MAC. The WDM-PON with 128 ONUs can be implemented by using 32 sub-MAC modules. The sub-MAC consists of one control unit, one receipt unit and four transmission units. The state transition diagram of the module is described by the internal/external control signals among the functional units. The function of the sub-MAC module is verified through logic simulation using ModelSIM.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제32권6A호
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• pp.617-623
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• 2007

A novel c-DSDV routing protocol is proposed in clustered mobile ad hoc networks. Clusterheads that manage members in their own cluster construct a higher layer backbone to which the DSDV concept is applied. Each clusterhead maintains its own global routing table by exchanging Update Request (UREQ) messages with its neighboring clusterheads. A number of entries in the table is as small as a number of clusterheads unlike a number of nodes in DSDV Since a UREQ message travels from one clusterhead to all its neighboring clusterheads that are at most 3 hops away, the topology convergence range by each UREQ message is at least 9 times as wide as that of DSDV and CGSR, greatly improving accuracy of routing information. However, overhead in c-DSDV is similar to that of DSDV because only clusterheads initiate UREQ messages. Delivery ratio increases by about 32$\sim$50%.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제40권10호
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• pp.1994-2005
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• 2015

Voice over IP (VoIP) is a technology for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks. Instead of being transmitted over a circuit-switched network, however, the digital information is packetized, and transmission occurs in the form of IP packets over a packet-switched network which consist of several layers of computers. VoIP Service that used the various techniques has many advantages such as a voice Service, multimedia and additional service with cheap cost and so on. But the various frauds arises using VoIP because VoIP has the existing vulnerabilities at the Internet and based on complex technologies, which in turn, involve different components, protocols, and interfaces. According to research results, during in 2012, 46 % of fraud calls being made in VoIP. The revenue loss is considerable by fraud call. Among we will analyze for Toll Bypass Fraud by the SIM Box that occurs mainly on the international call, and propose the measures that can detect. Typically, proposed solutions to detect Toll Bypass fraud used DPI(Deep Packet Inspection) based on a variety of detection methods that using the Signature or statistical information, but Fraudster has used a number of countermeasures to avoid it as well. Particularly a Fraudster used countermeasure that encrypt VoIP Call Setup/Termination of SIP Signal or voice and both. This paper proposes the solution that is identifying equipment of Toll Bypass fraud using those countermeasures. Through feature of Voice traffic analysis, to detect involved equipment, and those behavior analysis to identifying SIM Box or Service Sever of VoIP Service Providers.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제18권8호
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• pp.964-969
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• 2007

A regulated low phase noise differential colpitts VCO(Voltage Controlled Oscillator) for mobile RFID system is presented. The differential colpitts VCO meets the dense reader environment specifications. The VCO use a $0.35{\mu}m$ technology and achieves tuning range $1.55{sim}2.053 GHz$. Measuring 910 MHz frequency divider output, phase noise performance is -106 dBcMz and -135dBc/Hz at 40 kHz and 1MHz offset, respectively. 5-bit digital coarse-tuning and accumulation type MOS varactors allow for 28.2% tuning range, which is required to cover the LO frequency range of a UHF Mobile RFID system, Optimum design techniques ensure low VCO gain(<45 MHz/V) for good interoperability with the frequency synthesizer. To the author' knowledge, this differential colpitts VCO achieves a figure of merit(FOM) of 1.93dB at 2-GHz band.

• Journal of Chest Surgery
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• 제49권6호
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• pp.427-434
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• 2016

Background: Recent studies have demonstrated the benefits of off-pump coronary bypass grafting over the on-pump technique in patients with chronic kidney disease (CKD). To further reduce the risk of acute kidney injury and the need for renal replacement therapy, even in patients undergoing off-pump coronary artery bypass grafting, we adopted protocol-based perioperative management for patients with CKD. Methods: From December 2012 to March 2015, 265 patients underwent isolated off-pump coronary artery bypass grafting. To analyze renal function in a stable condition, we excluded 12 dialysis-dependent end stage renal failure and 10 emergency or urgent cases. Among the remaining 243 patients, 208 patients had normal kidney function (normal group), and 35 patients had CKD (CKD group). Minimizing contrast exposure, ensuring adequate hydration, using strict drug dosage adjustment, and optimizing hemodynamic status were key elements of the protocol for the CKD group. Results: The risk of acute kidney injury was about ${\times}3$ higher in the CKD group than in the normal group (p=0.01). Estimated glomerular filtration rates and serum creatinine levels deteriorated until the third postoperative day in the CKD group. However, by adopting protocol-based perioperative management, this transient renal dysfunction recovered to preoperative levels by the fifth postoperative day without requiring renal replacement therapy in all cases. Conclusion: Off-pump coronary bypass surgery combined with this protocol-based perioperative management strategy in patients with non-dialysis-dependent CKD could mostly be performed without renal replacement therapy.

• The KIPS Transactions:PartC
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• 제9C권3호
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• pp.343-350
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• 2002

This paper describes the implementation of H.235 protocol for authentication and media stream encryption of multimedia conference systems. H.235 protocol is recommended by ITU-T for H.323 multimedia conference security protocol to prevent from being eavesdropped and modified by an illegal attacker. The implementation in this paper has used password-based with symmetric encryption authentication. Media streams are encrypted using the Diffie-Hellman key exchange algorithm and symmetric encryption algorithms such as RC2, DES and Triple-DES. Also, 128-bit Advanced Encryption Standard and 128-bit Korean standard SEED algorithms are implemented for the future extension. The implemented authentication and media stream encryption has shown that it is possible to identify terminal users without exposing personal information on networks and to preserve security of multimedia conference. Also, encryption delay time and used memory are not increased even though supporting media stream encryption/decryption, thus the performance of multimedia conference system has not deteriorated.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권2호
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• pp.542-558
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• 2016

Vehicular Ad Hoc Networks (VANETs) are self-configuring networks where the nodes are vehicles equipped with wireless communication technologies. In such networks, limitation of signal coverage and fast topology changes impose difficulties to the proper functioning of the routing protocols. Traditional Mobile Ad Hoc Networks (MANET) routing protocols lose their performance, when communicating between vehicles, compromising information exchange. Obviously, most applications critically rely on routing protocols. Thus, in this work, we propose a methodology for investigating the performance of well-established protocols for MANETs in the VANET arena and, at the same time, we introduce a routing protocol, called Genetic Network Protocol (G-NET). It is based in part on Dynamic Source Routing Protocol (DSR) and on the use of Genetic Algorithms (GAs) for maintenance and route optimization. As G-NET update routes periodically, this work investigates its performance compared to DSR and Ad Hoc on demand Distance Vector (AODV). For more realistic simulation of vehicle movement in urban environments, an analysis was performed by using the VanetMobiSim mobility generator and the Network Simulator (NS-3). Experiments were conducted with different number of vehicles and the results show that, despite the increased routing overhead with respect to DSR, G-NET is better than AODV and provides comparable data delivery rate to the other protocols in the analyzed scenarios.

• Proceedings of the IEEK Conference
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.1169-1172
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• 2005

In this paper, we propose an improved anti-collision algorithm for multi tag interrogation in ubiquitous sensor network(USN) and show the result of simulation for multi tag interrogation in RFID systems. We have analyzed an EPC(Electronic Product Code) protocol which specifies the physical and logical requirements for a passive-backscatter Reader-Talk-First(RTF) RFID(Radio Frequency Identification) system operating in the $860MHz{\sim}960MHz$ frequency range. We have also designed and implemented the simulator of the RFID system based on the EPC protocol. Finally, we find that proposed algorithm works better than an existing algorithm.

• Journal of Sensor Science and Technology
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• 제16권4호
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• pp.247-253
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• 2007

Low power consumption sensor network platform (sensor node) for sensor networking with IEEE 802.15.4 protocol was fabricated. The sensor node used ceramic bar type antenna for increasing RF signal performance and decreasing PCB size occupied by antenna. The communication range of the fabricated sensor node was about $20{\sim}30$ m in open environment with 915 MHz frequency bandwidth and well supported by Tiny OS. The sensor node have good connectivity with various external devices by RS-232, I2C, analogue and digital expansion board, hence, this sensor node can be applied to various applications in wireless sensor network and ubiquitous sensor network.

• Proceedings of the Korea Information Processing Society Conference
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• 한국정보처리학회 2002년도 추계학술발표논문집 (상)
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• pp.77-80
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• 2002

최근 동영상 데이터를 활용한 교육 프로그램, 오락, 인터넷 방송 등의 서비스는 활성화되고 있으나, 중앙 집중형의 서버로 운영을 할 경우 서버의 고용량화, 고성능화가 요구되어 지며, 또한 여러 관련 기관들의 유대관계로 서로 공유할 수 있는 동영상 자료가 요구되어 지므로 이를 분산화 시켜 통합 관리하는 시스템이 필요하다. 이에 디렉토리 서비스의 표준 프로토콜인 LDAP(Light weight Directory Access Protocol)을 이용하여 네트워크 안에 있는 동영상의 자원을 마치 하나의 사이트에 있는 자원처럼 관리하며, 액세스가 가능하도록 하였다. 구현된 시스템은 실시간 전송 프로토콜인 RTO(Real-time Transport Protocol)를 이용하여 클라이언트에게 분산 되어있는 동영상과 동영상 관련 정보를 적절히 서비스하기 위한 시스템 이다.