• Journal of KIISE:Information Networking
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• v.31 no.2
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• pp.188-195
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• 2004

We have analyzed the performance of TCP in the CDMA mobile communications systems with the adaptive modulation and coding(AMC). The wireless channel using AMC is characterized with not high error rate but highly varying bandwidth. Due to time-varying bandwidth, timeout events of TCP occurs more frequently, which leads to the throughput degradation. The analysis model is composed of the two parts. In the first part, we divide TCP packet stream into ‘packet groups’and derive the probability distribution of the wireless transmission time of each Packet group that reflects the time varying characteristics of AMC. In the second part, we formulate embedded Markov chain by making use of the results of the first part to model TCP timer mechanism and wireless transmission. Since our system model is characterized by the forward link high speed data transmission using AMC, the results reported in this paper can be used as a guideline for the design and operation of HSDPA, 1xEV-DO, and 1xEV-DV.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.412-414
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• 2001

본 논문은 초고속통신망에서 멀티캐스트 스위칭에서 발생될 수 있는 오버플로우 문제와 블로킹 문제를 보다 효율적으로 해결하고, 공정하게 입력포트에 접근함으로 작은 fanout에 대한 불공정성을 해결하기 위한 멀티캐스트 스위치를 제안하고자 한다. 제안된 스위치는 셀 분할(cell pre-splitting)과 공유된 버퍼, Group Spliiting, 그리고 그룹분할망으로 구성되어지며, 큰 fanout에 대한 작은 fanout을 가진 입력포트에 도착한 패킷의 불공정한 대우를 해결하여 시스템 전체 지연 시간을 줄여 산출량을 극대화할 수 있다.

• Journal of Internet Computing and Services
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• v.5 no.3
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• pp.99-108
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• 2004

We have designed and implemented a Voice Messenger System(VMS) for sending and receiving voice data in order to measure and analyze the performance of a multimedia data transfer system using PDAs(Personal Digital Assistants) in a fast wireless LAN environment. The VMS has been configured as an infrastructure network by integrating a wireless intra-network based on IEEE 802,11 b standard with a wired network based on Ethernet. A sending time, a receiving time and a round-trip time(RTT) have been measured by varying its pecket size from 256 to 6656 bytes, Besides, we have performed the experiments to see which NIC is more stable between CF and PCMCIA type in such a wireless LAN environment, The results of such experiments show that the NIC with PCMClA type is better than that with CF type from the points of both efficiency and stability. The performance of a notebook computer with the attachment of a wireless NIC that is used as a VMS client is almost constant by varying its packet size when transferring voice data. However, with PDA client, in the case of receiving packets from the VMS server, the performance is the best when the pecket size is 6656 bytes, In addition, in the case of sending packets from PDA client to the VMS server, the performance is the best when the packet size is 4096 bytes. Even with the same pecket size, the time of receiving packets from the VMS server to PDA is longer than the time of sending packets from PDA to the VMS Server, Thus, we conclude that when PDA is used as a client by applying different pecket size when sending and receiving packets should be achieved a better performance over a wireless LAN environment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.6
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• pp.513-520
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• 2005

High-speed Portable Internet system provides 1-3 Mbps data transmission speed to terminals moving up to 60 km/sec. Since High-speed Portable Internet system supports services requiring different QoS, it needs an efficient scheduling method based on those different QoSs. This paper shows the performance comparisons of several different packet scheduling schemes for minimizing the mean delay over the downlink of High-speed Portable Internet system to support the packet data service. Simulation results show that proposed scheme superior to other schemes at side throughput and data loss rate.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10c
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• pp.254-256
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• 2000

본 논문에서는 여러 단계의 QoS(Quality of Service)를 지원하면서 빠르고 확장이 용이하며 각종 패킷 폐기(packet drop) 방식을 지원하는 평형 파이프라인 우선순위 아웃풋 큐 구조(balanced pipelined priority output queue architecture)를 제시하고 있다. 본 방안은 기존에 연구된 파이프라인 우선순위 힙(pipelined heap, P-heap)[1]을 기반으로 하고 있다. 파이프라인 우선순휘 힙은 우선순위에 따라 패킷을 전송하는 작업을 파이프라인 방식으로 처리하여 처리 성능을 향상시킨 아웃풋 큐 구조이다. 그러나 P-heap은 평형성(balance) 문제를 전혀 고려하고 있지 않으며, 다양한 패킷 폐기 방안을 제공하고 있지 못하다. 본 논문에서는 이런 측면에서 P-heap을 개선한 Advanced P-heap을 제안하고 있다. Advanced P-heap은 평균적인 상황에서 힙에 평형성을 부여하고, 각종 패킷 폐기 정책을 지원할 수 있는 일반적인 우선순위별 차별 패킷 구조를 제시하고 있다.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.11a
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• pp.455-458
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• 2003

네트워크 사용자의 급속한 증가로 네트워크 내의 부하를 감당하기에는 많은 어려움을 가져왔다. 이와 같은 이유로 기존의 TCP/IP 에서 세션을 통하여 노드들 간의 통신을 연결하는 방식에서 현재는 하나의 채널을 통해 고속의 I/O 가 가능하도록 하는 기술의 많이 연구되고 있다. 그 대표적인 것으로 인피니밴드가 있다. 인피니밴드는 프로세싱 노드와 입출력 장치 사이의 통신, 프로세스간 통신에 대한 산업 표준이 되고 있고 프로세싱 노드와 입출력 장치를 연결하기 위해 스위치 기반의 상호 연결은 전통적인 버스 입출력을 대체하는 새로운 입출력 방식을 사용한다. 또한 인피니밴드는 서버 시스템에서 요구하는 여러 특징 중에서 어플리케이션에게 QoS (Quality of Service)을 보장할 수 있는 메커니즘을 포함하고 있다. 본 논문에서는 어플리케이션에서 요구하는 각 트레픽의 요구 대역폭 크기에 따라 구분하여 효율적인 중재 테이블의 구성을 통해 데이터 전송에 있어 QoS 에 합당하게 출력포트를 통해 나갈 수 있도록 중재 테이블을 관리하는 기법을 제안하고 이를 NS-2 (Network Simulator)을 이용하여 성능 평가를 했다. 특히 기존 인피니밴드에서의 중재 테이블을 이용한 패킷 처리량과 본 논문에서 제안한 중재 테이블 구성 방식을 이용한 패킷 처리량을 비교했으며 성능평가 결과는 기존의 인피니밴드에서의 패킷 처리량에 비해 약 19% 향상된 결과를 나타냈다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.10
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• pp.135-140
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• 2006

In this paper, we present hybrid ARQ techniques to improve the throughput performance in high speed packet transmission such as Internet or multimedia services. In order to evaluate the performance of the three different types of hybrid ARQ schemes, systemized link level simulations based on WWW traffic model are considered. In this paper, we also consider the simulated performance for an average link throughput and a normalized packet delay to compare the hybrid ARQ with link adaptation scheme in GPRS.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.07a
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• pp.415-415
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• 2004

• Journal of KIISE:Information Networking
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• v.29 no.5
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• pp.466-472
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• 2002

We investigate the load sharing problem between the umbrella cell and the overlaid tells in hierarchical cell structure. A load sharing strategy is proposed and its performance is evaluated by simulation when it is used for transmission of the mobile Internet traffic using the High Speed Downlink Packet Access scheme. The results show that, with the proposed strategy, the microcell backs well the overlaid picocells up, especially when a specific picocell cluster suffers unusual heavy load condition. By using the strategy, we can reduce the installation cost, otherwise needed for increasing the system capacity of every picocell cluster to cope with the unusual heavy load.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12C
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• pp.261-267
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• 2001

This paper presents the architecture of multiple-queue manager for input-queued switch, which has arbitration latency, and the design of the chip. The proposed architecture of multiple-queue manager provides wire-speed routing with a pipelined buffer management, and the tolerance of requests and grants data transmission latency between the input queue manager and central arbiter using a new request control method, which is based on a high-speed shifter. The multiple-input-queue manager has been implemented in a field programmable gate array chip, which provides OC-48c port speed. It enhances the maximum throughput of the input queuing switch up to 98.6% with 128-cell shared input buffer in 16$\times$16 switch size.