• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8B
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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.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.1
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• pp.32-43
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• 2000

In this paper, we investigate the existing medium access control (MAC) protocols to integrate the voice and data services in packet-based CDMA networks and furthermore, propose a new approach to circumvent the operational limits inherent in them. We propose the $P^2R$-CDMA (Prioritized Packet Reservation Code Division Multiple Access) protocol for the uplink in the synchronous multi-code CDMA system, which employs the centralized frame-based slot reservation along with the dynamic slot assignment in the base station using the QoS-oriented dynamic priority of individual terminal. The simulation results show that, as compared with the existing scheme based on the adaptive permission probability control (APC), the proposed approach can significantly improve the system capacity while guaranteeing the real-time requirement of voice service.

• Proceedings of the Korea Society for Simulation Conference
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• 2001.05a
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• pp.133-133
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• 2001

무선 근거리 지역망(Wireless LAN;WLAN) 환경에서 다중 채널을 이용하여 실시간 서비스를 제공하기 위한 매체 접근제어 계층에서의 채널의 사용 구간 할당 방법을 제안하고, 컴퓨터 모의 실험을 통하여 제한된 방식의 실시간 서비스 지원 성능과 채널의 사용 효율을 분석한다. 제안한 채널 사용 구간 할당 방안은 개선된 매체 접근 제어 프로토콜 RICH-DP (Receiver-Initiated Channel-Hopping with Dual Polling)를 바탕으로 한다. 무선 환경에서 RTS-CTS를 사용하는 프로토콜은 SRMA, MACA, MACAW, IEEE 802.11, FAMA 등이 있다. 최근에 단일 채널을 환경에서 RICH(Receiver Initiated Channel-Mopping) 프로토콜이 제안되었다. RICH는 충돌 회피를 위해서 경쟁 구간에서 충돌 감지(carrier sensing)을 사용한다. RICH는 제한된 어플케이션에 국한되는 단절이 있다. 반면에 RICH-DP는 다중 채널 환경에서 충돌 감지와 특별한 코드(spreading code) 할당 없이 일반화된 충돌 회피를 제공한다. 실시간 서비스를 이용하자 차는 단말들로 하여금 RICH-DP를 사용하여 서비스를 제공할 때, 대역폭에 대한 정보를 AP(Access Point)로 전송토록 함으로써 비경쟁 구간에서 뿐 아니라, 경쟁구간에서도 높은 채널 효율이 얻어질 수 있도록 하고 있다. 제한된 방안의 성능 평가를 위한 모의 실험은 OPNET를 이용하여 실시간 서비스 데이터를 7개의 상태 천이를 갖는 VBR 소스로 모델링하고 비동기 트래픽들은 Poisson 소스로 모델링하여 실시간 서비스 단발들의 이용 대역폭과 채널 처리율과 시스템 지연시간을 성능 평가 인자로 하여 수행하였다. 논문에서 제한된 방법을 적용한 개선된 RICH-DP을 모의 실험을 통하여 분석한 결과 기존의 제한된 RICH-DP는 실시간 서비스에 대한 처리율이 낮아지며 서비스 시간이 보장되지 못했다. 따라서 실시간 서비스에 대한 새로운 제안된 기법을 제안하고 성능 평가한 결과 기존의 RICH-DP보다 성능이 향상됨을 확인 할 수 있었다.

• Journal of KIISE:Computing Practices and Letters
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• v.5 no.2
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• pp.157-167
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• 1999

편리한 사용 방법과 멀티미디어 데이터 서비스를 지원하는 웹은 현 인터넷 환경에서 이종 컴퓨터간의 주요한 정보 전달 수단으로 자리잡았다. 그러나 웹이 사용하고 있는 통신 프로토콜 스택만으로는 부상하고 있는 정보 형태인 실시간 멀티미디어 데이터의 서비스를 적절히 지원할수 없었다. 이에 본 논문에서는 실시간 전송 프로토콜인 RTP/RTCP를 웹 통신 프로토콜 스택에 추가하여 실시간 멀티미디어 세션의 서비스를 지원할수 잇도록 그 기능이 확장된 웹 시스템의 구현을 소개한다. 이는 MBone을 통해 실시간으로 멀티캐스트되고 있는 멀티캐스트 되고 있는 멀티미디어 세션의 서비스를 웹에서 지원할수 있도록 한 것으로, 기존의 MBone응용들을 수용한 형태를 가진다. 이를 위하여, MBone상에서 개설된 세션 정보를 수집하여 이를 관리하고 그 정보들을 웹 문서로 제공하는 프로그램인 '웹 SDR'과 MBone을 통해 멀티캐스트되는 실시간 멀티미디어 세션을 웹상에서 시청할수 있도록 웹 브라우저의 기능을 확장한 Windows 95 플랫폼 기반의 '실시간 멀티미디어 웹 플러그인'을 구현하였다 그리고 , 본 연구에서 개발한 수신 위주의 웹 시스템의 서비스 품질을 개선하기 위하여 현 인터넷 환경을 고려한 서비스 품질 제어 기법인 '관측 기반의 수신단 QoS 제어 알고리즘'을 제안하고, 이를 적용하여 실시간세션 서비스 품질이 개선됨을 보였다.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.837-844
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• 2019

In this paper, we propose the AMBM(: Adaptive Multi-channel Backoff Machisum) -Mac protocol to provide high throughput for non-safety applications in VANET(: Vehicular Ad Hoc Networks) environment. The proposed protocol guarantees the quality of service of non-safety packets by dynamically adjusting CW(: Channel Window) of WSA(: WAVE Service Advertisement) to maximize throughput between non-safety packets of different priority. It also shows that allocating a large amount of time for channel coordination and time slot reservation for SC and dynamically adjusting CW and CCI as nodes increase to reduces transmission delay than IEEE 1609.9, C-MAC(: Coordinated multi-channel MAC, and Q-VCI(: QoS Variable CCH Interval) protocols.

• Journal of Korea Multimedia Society
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• v.2 no.3
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• pp.329-338
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• 1999

In this paper we propose a WATM MAC protocol called DTDD/PS (Dynamic Time Division Duplex using Poll/Select scheme). The idea of the DTDD/PS protocol is based that a radio cell is considered as queueing system. The MAC controller in base station is charged in coordinating terminals for the QoS requirement from each terminal. For that reason, terminals send it's own dynamic parameter represented its status, and controller controls the access of terminals and assigns time slots dynamically using received parameters. Therefore this system can satisfy the QoS of real-time service in wireless environments. To evaluate DTDD/PS protocol simulations are executed. In 25Mbps channel capacity, the voice and data coexist traffic situation, as the total number of terminal is increased, the delay of data terminals is increased rapidly. But the case of only increasing data terminals, the number of supported voice terminals is not varying. Therefore we can expect that DTDD/PS protocol can applied to multimedia traffic effectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.3
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• pp.534-541
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• 2018

The number of stations existing in the same wireless channel is increasing due to the spread of the wireless LAN devices. CSMA/CA, a conventional wireless LAN protocol, uses a random backoff method. In the random backoff scheme, collision between stations is frequent in a dense region where the number of stations existing in the same channel is several tens or more, and the performance of the performance degradation of such a protocol, the IEEE 802.11ah standard proposed a Restricted Access Window(RAW) wireless access method. RAW improves performance by limiting the number of concurrent access stations by dividing the stations into several groups. In this paper, we propose a method to improve the performance of channel connection by using new group creation, group removal and group relocation algorithm according to traffic change by improving existing RAW method.

• Journal of KIISE:Computing Practices and Letters
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• v.11 no.4
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• pp.312-333
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• 2005

SIP(Session Initiation Protocol) has been proposed for session control protocol of Internet multimedia communication system like VoIP(Voice over IP). SIP has complicated session control steps to support various kinds of audio and video formats and to assure service quality of real time data communication. Up until now, existing protocol analyzers can not provide such detailed information of SIP based communication system. In this paper, therefore, we propose a new protocol analyzer as a tool that can analyze and diagnose SIP based multimedia communication system throughout the session initiation, data exchange and session change steps. The propose traffic analyzer, which is called STAT(SIP based Traffic Analysis Tool), Is implemented on Winder's environment so that it is generally usable and extensible. Since STAT analyze low level packets captured via Ethernet broadcasting property, it is able to provide session status and real time traffic monitoring information without any affection to the communication system. The STAT which is implemented in this paper. therefore, is expected to be a useful tool for developing and managing of a SIP based multimedia communication system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.1
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• pp.180-186
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• 2017

In this paper we propose a traffic aware Demand Wakeup MAC(TADW-MAC) protocol, in which low data delay and high throughput can be achieved, for wireless sensor networks. With the TADW-MAC protocol, the problem of the DW-MAC protocol, which schedules only one packet to deliver during the Sleep period in a multi-hop transmission is resolved. DW-MAC is not adequate for the applications such as object tracking and fire detection, in which busty data should be transmitted in a limited time when an event occurs [6-8]. When an event occurs, duty cycle can be adjusted in the TADW-MAC protocol to get less energy consumption and low latency. The duty cycle mechanism has been widely used to save energy consumption of sensor node due to idle listening in wireless sensor networks. But additional delay in packet transmission may be increased in the mechanism. Our simulation results show that TADW-MAC outperforms RMAC and DW-MAC in terms of energy efficiency while achieving low latency.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.1
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• pp.129-137
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• 2016

Transmission Control Protocol as a transport layer protocol provides steady data transfer service. There are some serious concerns about the performance of TCP over diverse networks. The vital concern in TCP network environment is congestion which may occur due to quick transmission rates or because of large number of new connections entering the network at the same time. Size of queues in routers grows thus resulting in packet drops. Retransmission of the dropped packets, and reduced throughput can prove costly. Explicit Congestion Notification (ECN) in conjunction with Active Queue Management mechanisms (AQM) such as Random early detection (RED) is used for packet marking rather than dropping. In IP packet header ECN bits can be added as a sign of congestion thus avoiding needless packet drops. The proposed ECN and AQM mechanism can be implemented with help of ns2 simulator and the performance can be tested on different TCP variants.