• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.12C
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• pp.1238-1244
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• 2002

In this paper, H.235-based security mechanism for H.323 multimedia applications was implemented. H.235 covers authentication using HMAC, Diffie-Hellman key exchange, session key management for voice channel, and encryption functions such as DES, 3DES, RC2. Extra encryption algorithms such as SEED, and AES were also included for possible use in the future. And, we also analyzed the quality of service (QoS), the requirement of implementation, and interoperability to the result in this study. The results could be applied to secure simple IP phone terminals, gateways, or gatekeepers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.6
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• pp.1480-1489
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• 1996

In ATM networks there are two methods in traffic control as schemes advancing the quality of service. One is reactive control after congestion and the other which is generally recommended, is preventive control before congestion, including connection admission control on call leel and usage parameter control, network parameter control, priority control and congestion control on cell level. In particular, usage parameter control is required for restricting the peak cell rate of bursy tracffic to the parameter negotiated at call set-up phase since the peak cell rate significantly influences the network quality of service. The scheme for progressing quality of service by usage parameter control is themethod using VSA(Virtual Scheduling Algorlithm) recommended ITU-T. The method using VSSA(Virtual Scheduling Suggested Algorlithm) in this paper is suggested by considering cell delay variation and token rate of leaky bucket, compared VSA and VSANT(Virtual Scheduling Algolithm with No Tolerance) with VSSA which polices violated cell probability of conformed peak cell rate and intentionally excessive peak cell rate. VSSA method using IPP(Interruped Poisson Process) model of input traffic source showed more quality of service than VSA and VSANT methods as usage parameter control because the suggested method reduced the violated cell probability of contformed peak cell rate and intentionally excessive peak cell rate.

• Journal of electromagnetic engineering and science
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• v.16 no.1
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• pp.35-43
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• 2016

A compact ultra-wide band antenna with a quadruple band-notched characteristic is proposed. The proposed antenna consists of a slotted trapezoid patch radiator, an inverted U-shaped band stop filter, a pair of C-shaped band stop filters, and a rectangular ground plane. To realize the quadruple notch-band characteristic, a U-shaped slot, a complementary split ring resonator, an inverted U-shaped band stop filter, and two C-shaped band stop filters are utilized in this antenna. The antenna satisfies the -10 dB reflection coefficient bandwidth requirement in the frequency band of 2.88-12.67 GHz, with a band-rejection characteristic in the WiMAX (3.43-3.85 GHz), WLAN (5.26-6.01 GHz), X-band satellite communication (7.05-7.68 GHz), and ITU 8 GHz (8.08-8.87 GHz) signal bands. In addition, the proposed antenna has a compact volume of $30mm{\times}33.5mm{\times}0.8mm$ while maintaining omnidirectional patterns in the H-plane. The experimental and simulated results of the proposed antenna are shown to be in good agreement.

• ETRI Journal
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• v.23 no.3
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• pp.111-120
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• 2001

For scalable multicast transport, one of the promising approaches is to employ a control tree known as acknowledgement (ACK) tree which can be used to convey information on reliability and session status from receivers to a root sender. The existing tree configuration has focused on a 'bottom-up' scheme in which ACK trees grow from leaf receivers toward a root sender. This paper proposes an alternative 'top-down' configuration where an ACK tree begins at the root sender and gradually expands by including non-tree nodes into the tree in a stepwise manner. The proposed scheme is simple and practical to implement along with multicast transport protocols. It is also employed as a tree configuration in the Enhanced Communications Transport Protocol, which has been standardized in the ITU-T and ISO/IEC JTC1. From experimental simulations, we see that the top-down scheme provides advantages over the existing bottom-up one in terms of the number of control messages required for tree configuration and the number of tree levels.

• ETRI Journal
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• v.35 no.2
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• pp.245-252
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• 2013

In this work, we study the physical layer solutions for 10-gigabit-capable passive optical networks (PONs), particularly for an optical link terminal (OLT) including a 10-Gbit/s electroabsorption modulated laser (EML) and a 2.5-Gbit/s burst mode receiver (BM-Rx) in a novel bidirectional optical subassembly (BOSA). As unique features, a bidirectional mini-flat package and a 9-pin TO package are developed for a 10-gigabit-capable PON OLT BOSA composed of a 1,577-nm EML and a 1,270-nm avalanche photodiode BM-Rx, including a single-chip burst mode integrated circuit that is integrated with a transimpedance and limiting amplifier. In the developed prototype, the 10-Gbit/s transmitter and 2.5-Gbit/s receiver characteristics are evaluated and compared with the physical media dependent (PMD) specifications in ITU-T G.987.2 for XG-PON1. By conducting the 10-Gbit/s downstream and 2.5-Gbit/s upstream transmission experiments, we verify that the developed 10-gigabitcapable PON PMD prototype can operate for extended network coverage of up to a 40-km fiber reach.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.327-330
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• 2002

컴퓨터를 통한 커뮤니케이션의 수단을 보다 인간 중심으로 바꾸고 있는 VoIP 관련 기술들은 최근들어 신속하게 시장의 뜨거운 흐름을 타고 있다. 초창기 인터넷 텔레포니 서비스들은 ITU-T의 H.323을 기반으로 제공 되었으나, 여러 가지 문제점들로 인하여 IETF의 SIP를 이용한 서비스 모델로 변화하고 있는 추세이다. SIP 프로토콜은 인터넷 텔레포니 서비스를 제공하기 위해, 통신하고자 하는 상대방의 위치를 찾아 단말간의 호 설정, 호 정보 수정, 호 해지 등의 기능을 제공하는 응용계층의 호 제어 프로토콜이다. SIP 프로토콜에서 개인의 이동성을 보장하기 위해서는 사용자들의 위치가 변경될 때마다 현재 위치를 Registrar에게 등록 시켜야 하며, 이러한 등록 정보들은 이후 Proxy 서버나 Redirect 서버를 위한 Location Service 제공을 위해 사용된다. Registrar에서는 사용자의 위치정보에 대한 등록, 수정, 삭제, 조회에 대한 요청 메시지 수신 시, SIP URI 비교 API가 요구된다. 본 논문에서는 RFC3261 기반의 SIP Registrar의 기본 동작을 간단히 소개하며, SIP URI 비교 시 요구 되는 기능들을 분석하고, API를 설계한다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.11a
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• pp.310-312
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• 2018

In this paper, We stduy addtional consideration and method to treat carrier frquency offset on defined system parameter & requirements in IALA G1139, previous studied consecutively. We studied the method to treat carrier frequency offset by extending length of training symbol and by differential modulation. This study will publish and argue in IALA ENAV22. We will decide a method to treat carrier frequency offset from result of IALA ENAV22.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.1B
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• pp.18-26
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• 2003

Earlier efforts on optical access concentrated on the design of PONs for the collection and distribution portion of the access network PON architecture is very simple but it requires MAC protocol for control of upstream traffic This paper proposes a Request-Counter MAC protocol for a broadband access network using an ATM Passive Optical Network supporting CBR/rtVBR, nrtVBR, UBR and ABR traffic For the proposed MAC scheme, we present Grant Field format, Minislot format, and bandwidth allocation algorithm From the simulation result, we have confirmed that our proposed scheme can reduce the average cell delay in comparison to that of conventional MAC schemes.

• Information and Communications Magazine
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• v.29 no.6
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• pp.14-21
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• 2012

지식 정보화 사회로의 진입 이후로 IT 기술은 눈부실 정도로 빠르게 발전하고 있다. 이로 인해서 IT 분야의 전력 소비량도 급증하고 있으며, 전체 전력량의 약 2%를 차지하고 있다. 지구 온난화를 해결하기 위해서 IT 분야 자체의 에너지 절감은 물론 IT 기술을 활용한 가정 및 산업 분야의 에너지를 절감하려는 노력이 전세계적으로 진행되고 있다. 데이터센터는 IT 분야의 총아로 불리며 정보 제공 및 데이터웨어 하우스 기능을 수행한다. 데이터센터와 관련하여 더욱 주목해야할 것은 데이터센터가 전기먹는 하마처럼 엄청난 양의 전력을 소비한다는 것이다. 데이터센터는 그 용량 뿐만 아니라 그 수도 급증하고 있어 에너지 절감은 데이터센터의 미래를 결정짓는 핵심적이면서 필수적인 요소가 되었다. 본고에서는 에너지 효율적인 데이터센터, 즉 그린 IDC(Internet Data Center) 분야의 표준화 동향 및 전망에 대해서 기술하고 있다. 먼저 1장에서는 그린 IDC 연구에 대한 필요성과 국내외 유관 표준화 기구의 현황을 소개한다. 2장에서는 그린 IDC의 정의와 그린 IDC관련 표준화 동향을 살펴본다. 특히 ISO, ITU-T를 비롯한 국제 표준화 기구의 동향과 산업체 표준을 살펴본다. 한다. 3장은 2장에서 살펴본 국제 표준화 기구 및 산업체 표준을 바탕으로 향후 그린 IDC 표준화 추진을 위한 국제 및 국내표준화 추진 방향을 전망해본다.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.3166-3168
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• 2000

This paper proposed variable threshold dual rate ADPCM coding method which is modified from the standard ADPCM of ITU G.726 for speech quality improvement. The speech quality of variable threshold dual rate ADPCM is better than single rate ADPCM at noisy environment without increasing the complexity by using ZCR(Zero Crossing Rate). In this case, ZCR is used to divide input signal samples into two categories(noisy & speech). The samples with higher ZCR is categorized as the noisy region and the samples with lower ZCR is categorized as the speech region. Noisy region uses higher threshold value to be compressed by 16Kbps for reduced bit rates and the speech region uses lower threshold value to be compressed by 40Kbps for improved speech quality. Comparing with the conventional ADPCM, which adapts the fixed coding rate. the proposed variable threshold dual rate ADPCM coding method improves noise character without increasing the bit rate. For real time applications, ZCR calculation was considered as a simple method to obtain the background noise information for preprocess of speech analysis such as FFT and the experiment showed that the simple calculation of ZCR can be used without complexity increase. Dual rate ADPCM can decrease the amount of transferred data efficiently without increasing complexity nor reducing speech quality. Therefore result of this paper can be applied for real-time speech application such as the internet phone or VoIP.