• Proceedings of the Korea Society for Simulation Conference
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• 2002.11a
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• pp.9-16
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• 2002

Mobile IP는 단순히 이동성을 지원하는 것만을 목표로 제안되었기 때문에, 새로운 네트워크로의 연결만을 보장할 뿐, 핸드오프 후의 QoS는 보장하지 못한다. mobile IP에서 QoS는 이동 환경에서 멀티미디어 서비스나 실시간 서비스 제공 시 매우 중요시되는 문제로, 핸드오프에 의한 지연과 밀접히 연관되어있다. 본 논문에서는 이러한 핸드오프 지연 문제를 해결하기 위해, SNMP 정보 기반 라우팅을 이용하여 핸드오프 지연을 최소화하는 QoS 향상 기법을 제시한다. 이후 제시한 기법과 기존 핸드오프방법에서 필요한 요소를 모델링한 후 NS-2를 사용하여 시뮬레이션 한다. 시뮬레이션 결과는 제시한 기법이 핸드오프 지연을 감소시켜 결과적으로 QoS가 향상되는 것을 입증한다.

• Convergence Security Journal
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• v.6 no.2
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• pp.61-69
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• 2006

For the efficient business, the telecommunication providers should have an attention for the minimization of the basic setup cost to implement the network infrastructure. Furthermore, the provision of the quality of service (QoS) to the service users is crucial for the service providers and vendors. In this paper, we propose the new algorithm to provide the user's QoS under the various traffic in the broadband convergence network. Using the NS-2 network simulator, we evaluate the QoS for the proposed algorithm, and compare those with the results of the previous differentiated service network.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.11a
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• pp.311-314
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• 2007

AODV 프로토콜은 최단경로 라우팅 기법, 에너지 효율, 빠른 지역 경로 복구 등을 위한 많은 알고리즘이 연구되어 왔다. AODV 프로토콜의 성능평가는 대부분 NS2 시뮬레이터를 통해 이루어지고 있으며, AODV의 성능개선을 위한 알고리즘의 적용은 NS2의 AODV 소스파일 변경을 통해 이루어진다. AODV 소스파일의 AODV 클래스가 아주 많은 역할을 하는 구조로 작성되어 있어 알고리즘의 적용이 쉽지 않고, 이로 인해 성능평가를 위한 시뮬레이션에 시간과 노력이 많이 들게 된다. 이를 위해 기존 소프트웨어를 재사용하고 유연성을 높일 수 있도록 소프트웨어의 리팩토링을 해주어야 한다. 리팩토링은 소프트웨어를 효율적이고 유지보수가 쉽도록 전환하는 과정이며, 소프트웨어의 재사용성을 높여주고 유연성을 제공해 줄 수 있다. 본 연구에서는 AODV의 성능 개선을 위한 알고리즘 적용이 보다 유연해지도록 AODV 관련 클래스들에 대해 리팩토링을 수행한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.4
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• pp.741-746
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• 2012

Transmission control protocol(TCP) widely used as a transport protocol in the Internet includes a loss recovery function that detects and recovers packet losses by retransmissions. The loss recovery function consists of the two algorithms; fast retransmit and fast recovery. There have been researches to avoid nonnecessary retransmission timeouts (RTOs), which leads to selective acknowledgement (SACK) option and limited transmit scheme that are standardized by IETF (Internet Engineering Task Force). Recently, a method that covers the case in which a retransmitted packet is lost again has been propsed. The method, however, is not proved in terms of the additive increase multiplicative decrease (AIMD) principle of TCP congestion control. In this paper, therefore, we analyzed the method in terms of the principle by ns-simulations.

• Korea Information Processing Society Review
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• v.14 no.6
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• pp.96-103
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• 2007

• The KIPS Transactions:PartC
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• v.16C no.3
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• pp.393-406
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• 2009

This paper introduces two functions added to the current version of ns-2 simulator for better accuracy of IEEE 802.15.4 network simulations. The first one is to automatically place hidden nodes over the ring topology in which the coordinator is centered, when the number of hidden nodes and total number of nodes is given. Collisions of signals can be distinguished into the trace file according to the ways of participation of hidden nodes. The second one is the CCA deferment algorithm described in IEEE 802.15.4-2006 standard which is not implemented in the current version of ns-2. Owing to these additional functions, we can carry out the precise analysis of the performance effects of hidden nodes and CCA deferment algorithm on 802.15.4 networks. Simulation results present at least 66% of performance degradation in throughput and drastic increase of collision probability up to 90% from 65% by just a single hidden node. Besides, 2006 standard for CCA deferment algorithm gives 19% lower collision probability and 38% higher performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7A
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• pp.666-673
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• 2006

In this paper, we evaluated the performance of 4 types of ARQ algorithms that have been adopted to offer reliable transmission between MAC layers. First of all, we implemented IEEE 802.16 ARQ algorithms with NS-2 network simulator and then evaluated the performances in various channel states. We used two performance measures to evaluate those performances. First, we used the total number of ARQ block in bytes that have been received without error. Second, we used ACK_Efficiency that is newly defined in this paper. From the results of simulation, we could be aware that each ARQ algorithm has different performance in a various channel states. For improving the transmission data rate in a specific channel state, we have to choose the right ACK interval as well as a suitable ARQ algorithm.

• The KIPS Transactions:PartA
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• v.18A no.6
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• pp.281-292
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• 2011

In this paper, a simulator adapted in AMI network environment with NS-2 was designed and implemented. The limited AMI operation environment such as processing times of data, network protocol and system performance can be simulated to find out the optimal AMI formations. Consequently, it is simulated under conditions that are closely analogous to the actual networks and each device. In future, the result of simulation would be applied to AMI network, mitigated the waste of resources and much contributed towards the real optimal AMI deployments in utilities.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.1
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• pp.88-97
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• 2000

We have proposed and analysed a novel Lookup Algorithm which had a short switching speed and tiny memory size for IP router. This algorithm could simply be implemeted by a hardware with SRAM because of simple structure. This Lookup scheme needs 1${\sim}$3 memory access times. When we simulated with 40,000 routing record obtained from IPMA Website, the maximum memory size of this algorithm was 316KB(the offset threshold for compression algorithm was 8). When we simulated by HDL using ALTERA EPM7256 series and 100MHz clock and SRAM of 10ns access time, the total lookup time was 45ns for two memory access, 175ns for three memory access.

• Proceedings of the Korea Society for Simulation Conference
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• 2003.11a
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• pp.139-144
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• 2003

Mobile Node has to maintain communication as they move form place to place, so it doesn't guarantee Quality of Service(QoS). Fast Handoff is important to provide multimedia and real-time applications services in mobile, and it is closely related to handoff delay. Therefore, handoff delay problem is actively studied to quarantee QoS as a main issue in mobile IP research area. Next generation Mobile IPv6 resolve this problem somewhat, triangle problem for first packet and handoff delay still remain. In this paper, we suggest SNMP Information-based routing that adds keyword management method to Information-based routing in active network in order to resolve such a problem, and then suggest QoS controlled handoff based on SNMP Information-Based routing. After modeling of suggested method and existing handoff method, simulations are carried out with NS-2 for performance evaluation. The results of simulations show the some improvement on handoff delay, and therefore on QoS improvement.