• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.3
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• pp.310-317
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• 1993

This paper presents a mechanism for improving performance of the IEEE 802.6 MAN(Metropolitan Area Network), a dual-bus structured high-speed communication network, by a more efficient use of bandwidth. The MAN protocol is able to handle various traffic and offers better transmission speed than the conventional LAN, but the unidirectional bus structure and propagation delay of request bits results in unfairness since higher nodes use more bandwidth. As the number of stations and the distances between them are increased, the problem becomes mere serious. As a solution, this paper presents a method that every station enables to identify the used slots, and that a specified class denoted 'erasure station' has with the functions of destination release, slot reuse. As a result, it is export to improve network bandwidth values of each station and the throughput and delay time was analytically analyzed, and it is shown that according to computer simulation results, this mechanism improves the network performance.

• Journal of Internet Computing and Services
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• v.9 no.2
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• pp.43-50
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• 2008

In IEEE 802.11b wireless LAN, stations keep synchronization by receiving beacons being periodically sent by the AP (access point) when they run in low power mode. Beacon transmission is delayed if wireless channel is busy at a scheduled TBTT (target beacon transmission time), and stations must be awake until they receive the delayed beacon. In this paper, we propose a scheme that stations get their transmission delayed if they have little time for successful data transmission by the next TBTT. Beacon transmission without delay is guaranteed at every TBTT with this method so that the awake time of low power stations to receive beacon can be reduced. The proposed method is simulated and its characteristics ore described with the analysis of the results. The measured results in terms of beacon delay show some enhancement in energy consumption.

• Annual Conference of KIPS
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• 2009.11a
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• pp.427-428
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• 2009

무선 네트워크 환경에서 합법적인 AP(Access Point)의 MAC 주소, SSID(Service Set Identifier), 채널등의 정보를 이용하여 복제된 AP(Cloned Access Point)를 만들 수 있다. 복제된 AP는 합법적인 AP와 연결되어 있는 무선 스테이션들의 연결 설정을 끊고 자신과 연결 설정을 하게 한다. 무선 스테이션들이 복제된 AP와 통신을 하게 되면서 많은 공격으로부터 노출되게 된다. 본 연구에서는 복제된 AP가 설치되었을 때 무선 스테이션들이 합법적이 AP의 비콘 프레임과 복제된 AP 비콘 프레임의 시퀀스 번호를 이용하여 복제된 AP을 판별하였다. 시뮬레이터 NS-2를 이용하여 실험한 결과 본 논문에서 제안하는 메커니즘을 통해 무선 스테이션들이 복제된 AP의 등장을 판별할 수 있게 되어 보다 안전한 무선랜 환경을 구축할 수 있게 되었다.

• Journal of KIISE:Computing Practices and Letters
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• v.10 no.1
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• pp.49-56
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• 2004

Load imbalance is a serious impediment to achieving good performance in parallel processing. Global load balancing schemes cannot adequately manage to balance parallel tasks generated from a single application. Dynamic loop scheduling methods are known to be useful in balancing parallel loops on shared-memory multiprocessor machines. However, their centralized nature causes a bottleneck for the relatively small number of processors in a network of workstations because of order-of-magniture differences in communication overheads. Moreover, improvements of basis loops scheduling methods have not effectively dealt with irregularly distributed workloads in parallel loops, which commonly occur in applications for a network of workstation. In this paper, we present a new reconfigurable and decentralized balancing method for parallel loops on a network of workstations. Since our method supplements performance balancing with those tranditional load balancing methods, it minimizes the overall execution time.

• Journal of KIISE
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• v.43 no.11
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• pp.1223-1232
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• 2016

A virtual network technology can provide a network reflecting the requirements of various services. The virtual network can distribute resources of the physical network to each virtual slice. An efficient resource distribution technique is needed to reflect the requirements of various services. Existing bandwidth distribution techniques can only control downlink traffic without taking traffic conditions on the network into account. Downlink and uplink share the same resources in a wireless network. The existing bandwidth distribution techniques assumed that all stations generate saturated traffic. Therefore, the existing bandwidth distribution technique cannot make traffic isolation in a virtual wireless network. In this paper, we proposed a traffic-based bandwidth control techniques to solve these problems. We applied Software-Defined Networking(SDN) to the virtual wireless network, monitored the traffic at each station, and searched for stations that generated unsaturated traffic. We also controlled both uplink and downlink traffics dynamically based on monitoring information. Our system can be implemented with legasy 802.11 clients and SDN-enabled APs. After the actual test bed configuration, it was compared to existing techniques. As a result, the distribution performance of the proposed technique was improved by 14% in maximum.

• Journal of KIISE:Computing Practices and Letters
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• v.6 no.4
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• pp.421-429
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• 2000

In present, ATM integrated switching system has been developed to a mixed modules that complexed switching system including maintenance, operation based on B-ISDN/LAN service and plug-in module, , which runs on workstation computer system. Meanwhile, workstation has HMI operation system feature including file system management, time management, graphic processing, TMN agent function. The workstation has communicated with between ATM switching module and clients. This computer system architecture has much burden messages communication among processes or processor. These messages communication consume system resources which are socket, message queue, IO device files, regular files, and so on. Therefore, in this paper we proposed new performance modeling with this system architecture. We will analyze the system bottleneck and improve system performance. In addition, in the future, the system has many additional features should be migrated to workstation system, we need previously to evaluate system bottleneck and redesign it. In performance model, we use queueing network model and the simulation package is used PDQ and C-program.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6B
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• pp.553-558
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• 2009

There have been various research efforts to support the fairness between uplink and downlink of TCP streams in IEEE 802.11 networks. Existing methods, which have been effective for the fairness, however could not provide the solution for the unfairness caused by the situation in which a station which is having multiple TCP uplink streams monopolizes the uplink bandwidth. This paper proposes a method that AP allocates token buckets for each uplink TCP station. The proposed method is also able to support the fairness between the uplink and downlink. To remedy the underutilization which may happen under token bucket-based schemes, it allows the movement of redundant tokens among the token buckets. By controlling the token movements, it can balance the fairness and the utilization. Simulation results show that the proposed method is able to support the fairness of the TCP uplink stations, as well as the fairness between the uplink and downlink.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1992.06a
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• pp.94-97
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• 1992

• The Bulletin of The Korean Astronomical Society
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• v.20
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• pp.23.2-23.2
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• 1995

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12A
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• pp.1303-1310
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• 2007

In IEEE 802.11b wireless network, stations synchronize themselves to the beacons periodically sent by the access point (AP) when they are running in low power mode. Stations stay awake for enough time to receive beacon because it is delayed in AP if the wireless channel has been being used by other traffic at each scheduled instant. In this paper, we propose a method that measures the delay of received beacons and calculates wake-up interval of station to receive the next one. Beacon transmission delay at the AP is analyzed. The proposed method is simulated and its characteristics are described in the analysis. The result measured in terms of station's wake-up interval shows some enhancement in energy consumption.