• 한국경영과학회지
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• 제21권2호
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• pp.111-124
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• 1996

The main purpose of this study is to develop an algorithm to solve the scheduling problems of FMS using Petri-net is well suited to model the dynamics of FMS and Petri-net is an ideal tool to formulate scheduling problems with routing flexibility and shared resources. By using the marking of Petri-net, We can model features of discrete even system, such as concurrency, asynchronous, conflict and non-determinism. The proposed algorithm in this paper can handle back-tracking using the marking of Petri-net. The results of the experiment show that marking is one of the best ways that describe exactly movement of the discrete event system. To show the effectiveness of the algorithm suggested here, we compare it with L1 algorithm using the Petri-net through the test on randomly generated test problems.

• Journal of Communications and Networks
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• 제15권3호
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• pp.321-328
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• 2013

In this paper, we present a technique for obtaining conflict-free schedules for real-time automation protocol for industrial Ethernet (RAPIEnet) switches. Mathematical model of the switch is obtained using graph theory. Initially network traffic entry and exit parts in a single RAPIEnet switch are identified, so that a bipartite conflict graph can be constructed. The obtained conflict graph is transformed to three kinds of matrices to be used as inputs for our simulation model, and selection of any of the matrix forms is application-specific. A greedy edge-coloring algorithm is used to schedule the network traffic and to solve the minimum coloring problem. After scheduling, empty slots are identified for forwarding the non real-time traffic of asynchronous devices. Finally, an algorithm for synchronizing the schedules of adjacent switches is proposed using edge-contraction and minors. All simulations were carried out using Matlab.

• 대한전자공학회논문지TC
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• 제42권6호
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• pp.41-52
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• 2005

무선 환경에서는 유선과 달리 다중 경로 페이딩, 간섭, 신호의 감쇠 등으로 발생되는 에러가 존재하고 있으며, 이러한 무선 채널 에러는 네트워크의 성능을 감소시킨다. 특히, ISM 대역에서 동작하는 IEEE 802.15.3은 무선 채널에러에 많이 노출되어 있다. 본 논문은 네트워크의 성능을 감소시키는 채널에러 환경에서 효율적인 비동기 트래픽의 스케줄링 알고리즘을 제안한다. 제안한 알고리즘은 디바이스가 요구하는 시간에 비례하여 채널시간(Channel Time Allocation, CTA)를 할당한다. 또한 디바이스간의 채널에러 상황을 인식하여 에러 상황인 디바이스에게 할당되는 CTA를 회수하여 에러를 겪지 않는 다른 디바이스들에게 CTA를 할당함으로써 네트워크의 전송효율을 높인다. 채널에러 상황에서 복구된 디바이스는 디바이스들 간의 공평성을 유지하기 위해 완전보상 또는 점진적 보상을 통해 CTA를 보상 받는다. 시뮬레이션 결과 제안한 알고리즘은 무선 채널에러 환경에서 기존의 SRPT(Shortest Remain Processing Time) 나 RR(Round Robin)방식에서 제공할 수 없었던 디바이스들의 비례적 공평성을 제공할 수 있으며, 네트워크의 높은 전송 효율을 유지한다.

• 인터넷정보학회논문지
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• 제10권2호
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• pp.171-177
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• 2009

광 패킷 스위칭 기술은 대용량 인터넷 트래픽을 패킷레벨에서 보다 유동적인 대역폭으로 전송해 줄 수 있으며, WDM 계층과 I P 계층을 유연하게 통합 해 줄 수 있기 때문에 차세대 광 인터넷을 위한 가장 강력한 스위칭 기술 중 하나이다. 광 패킷 스위칭 기술의 연구는 동기식 망 안에서의 연구와 비동기식 망 안에서의 연구로 나뉘며 본 논문에서는 인터넷 트래픽과 같은 비동기 가변길이 패킷들을 위한 광 패킷 스위치 내부에 경합해결 이슈에 초점이 맞추어져 있다. 하이브리드 버퍼는 광 지연 선로 버퍼와 전자 버퍼로 구성 되어 비동기 가변길이 패킷들의 경합 해결을 위한 하나의 대체 버퍼로서 패킷 손실 확률을 감소시키기 위해 소개된바 있다. 그런데 스위치 내부의 자원 중 튜닝 가능한 파장 변환기의 개수와 내부 파장 개수를 고려한 광 패킷 스위치의 디자인은 스위치 비용과 자원 이용 효율을 결정짓는 매우 중대한 이슈이다. 따라서 본 논문에서는 한정된 수의 튜닝 가능한 파장 변환기와 내부 파장 개수를 고려한 하이브리드 버퍼 구조형 광 패킷 스위치를 설계하고 그것의 스케쥴링 알고리즘을 소개하고자 한다. 제안한 스케쥴링 알고리즘은 광 지연 선로 버퍼만을 갖는 기존의 LAUC-VF 알고리즘과 비교하여 더 나은 패킷 손실 확률을 제공해 줄 수 있었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1986년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 17-18 Oct. 1986
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• pp.158-163
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• 1986

This article surveys techniques and issues related to real time process control system developed for industrial control applications. It covers the system architecture and software engineering issues such as the design of data structures, scheduling of asynchronous task activities, management of shared resources, handling of interrupt and implementing an user friendly man-machine interface. Also problems associated with implementing a real-time system that supports dynamic configuration of data base is addressed.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(1)
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• pp.275-278
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• 2000

Recently ATM(Asynchronous Transfer Mode) technology is facing challenges from Integrated Service IP(Internet Protocol), IP router, Gigabit Ethernet. Although ATM is approved by ITU-T as the standard technology in B-ISDN, its survival is still in question. In the ATM networks, the Guaranteed Frame Rate(GFR) service has been designed to accommodate non-real-time applications, such as TCP(Transmission Control Protocol)/IP based traffic. The GFR service not only guarantees a minimum throughput at the frame level, but also supports a fairshare of available resources. We have studied different discarding and scheduling schemes, and compared their throughput and fairness when TCP/IP Traffic is carried. Through simulations, we know that only per-VC queueing with weighted Round Robin(WRR) can guarantee Minimum Cell Rate Among all the Schemes that have been experimented, we recommend DT-EPD(Dynamic Threshold-Early Packet Discard) integrated with MCRplus(Minimum Cell Rate) to support the GFR service.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(1)
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• pp.129-132
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• 2001

Broadband Integrated Services Digital Network(B-lSDN) supports multimedia information in real time. This can be accomplished by using Asynchronous Transfer Mode(ATM) technology. In addition, ATM networks can provide not only bandwidth reservation, but also Quality of Service(QoS) guarantees. In this paper, we propose a efficient cell scheduling algorithm considering ABR service in ATM networks. The proposed algorithm can support ABR service more efficiently than existing fixed cell slot allocation method and priority cell slot allocation method algorithm. proposed algorithm dynamically schedules cells in a real time by considering the current traffic buffer conditions. Throughout the computer simulation, evaluates the performance of the proposed algorithm.

• 한국통신학회논문지
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• 제21권6호
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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.

• 제어로봇시스템학회논문지
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• 제6권7호
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• pp.602-610
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• 2000

In communication networks used in safety-critical systems such as control systems in nuclear power plants there exist three types of data traffic : urgent or asynchronous hard real-time data hard real-time periodic data and soft real-time periodic data. it is necessary to allocate a suitable bandwidth to each data traffic in order to meet their real-time constraints. This paper proposes a method to meet the real-time constraints for the three types of data traffic simultaneously under a timer-controlled token bus protocol or the IEEE 802.4 token bus protocol and verifies the validity of the presented method by an example. This paper derives the proper region of the high priority token hold time and the target token rotation time for each station within which the real-time constraints for the three types of data traffic are met, Since the scheduling of the data traffic may reduce the possibility of the abrupt increase of the network load this paper proposes a brief heuristic method to make a scheduling table to satisfy their real-time constraints.

• Journal of Communications and Networks
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• 제7권2호
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• pp.144-156
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• 2005

Video streaming over wireless networks is challenging due to node mobility and high channel error rate. In this paper, we propose a multi-source video streaming (MUVIS) system to support high quality video streaming service over IEEE 802.1l-based wireless networks. We begin by collocating a streaming proxy with the wireless access point to help leverage both the media server and peers in the WLAN. By tracking the peer mobility patterns and performing content discovery among peers, we construct a multi-source sender group and stream video using a rate-distortion optimized scheme. We formulate such a multi-source streaming scenario as a combinatorial packet scheduling problem and introduce the concept of asynchronous clocks to decouple the problem into three steps. First, we decide the membership of the multisource sender group based on the mobility pattern tracking, available video content in each peer and the bandwidth each peer allocates to the multi-source streaming service. Then, we select one sender from the sender group in each optimization instance using asynchronous clocks. Finally, we apply the point-to-point rate-distortion optimization framework between the selected sender-receiver pair. In addition, we implement two different caching strategies, simple caching simple fetching (SCSF) and distortion minimized smart caching (DMSC), in the proxy to investigate the effect of caching on the streaming performance. To design more realistic simulation models, we use the empirical results from corporate wireless networks to generate node mobility. Simulation results show that our proposed multi-source streaming scheme has better performance than the traditional server-only streaming scheme and that proxy-based caching can potentially improve video streaming performance.