• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.4
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• pp.394-401
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• 2013

Recently there have been much interest in the performance improvement of maritime communication system. In the maritime communication system, the wireless channel is likely to be time-invariant and the retransmission scheme is not proper because it does not provide time diversity. For the improvement of reliability, we consider MIMO ARQ scheme using Alamouti-type signal which can provide space and time diversity. In this paper, we also propose the criterion of optimal retransmission order and provide its performance of error probability and packet throughput. The proposed MIMO ARQ scheme with optimal retransmission order has performance gain over random ordered MIMO ARQ and conventional Chase combining method. Therefore we expect that it can be adapted to the next generation maritime communication system.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10c
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• pp.514-516
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• 2000

현재 가장 널리 쓰이는 수송계층 프로토콜인 TCP는 패킷 손실의 원인을 망의 혼잡 때문에 일어난다고 가정하고 있으므로 기존의 유선망과 고정 호스트로 이루어진 전통적인 네트워크에 적합하다. 그러나 무선 링크에서의 패킷 손실은 대부분 혼잡에 의해서가 아니라 높은 에러율과 핸드오프에 의해 발생하게 되므로 기존의 TCP를 그대로 사용하면 불필요한 혼잡제어 메커니즘의 호출로 성능의 저하를 가져온다. 현재까지 무선환경에 적합한 TCP를 위한 많은 방안이 제시되고 있지만 근본적인 해결책을 제시하지 못하고 있다. 본 논문에서 제안하는 기법은 패킷손실이 유선링크에서 일어나는 것인지, 무선링크에서 일어나는 것인지를 판별하여 패킷손실이 유선링크에서 일어난 경우는 기존의 혼잡제어 메커니즘을 호출하여 재전송하고, 무선링크에서 일어난 경우는 혼잡제어 메커니즘을 호출하지 않고 재전송 하여 성능을 개선한다.

• Journal of Digital Contents Society
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• v.10 no.2
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• pp.279-289
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• 2009

As the TCP is the protocol designed for the wired network that packet loss probability is very low, because TCP transmitter takes it for granted that the packet loss by the wireless network characteristics is occurred by the network congestion and lowers the transmitter's transmission rate, the performance is degraded. In this article, we suggest the newly improved algorithm using two parameters, the local retransmission time value and the local retransmission critical value to the BS based on the Snoop. This technique adjusts the base stations local retransmission timer effectively according to the wireless link status to recover the wireless packet loss rapidly. We checked that as a result of the suggested algorithm through various simulations, A-Snoop protocol improve more the wireless TCP transmission rate by recovering the packet loss effectively in the wireless link that the continuous packet loss occur than the Snoop protocol.

• Proceedings of the Korean Information Science Society Conference
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• 2008.06d
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• pp.165-169
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• 2008

본 논문에서는 IEEE 802.16 시스템에서 ARQ(Automatic Repeat reQuest)의 동작이 TCP 성능에 끼치는 영향을 분석한다. IEEE 802.16 표준에서는 MAC 계층에서 패킷 전송의 성공 혹은 실패를 확인하여, 실패 시 패킷을 재전송하는 ARQ 기법을 포함하고 있다. 이러한 무선 링크상의 재전송은 TCP와 맞물려 동작할 때, 적절한 ARQ 재전송 타임아웃(timeout)이 보장되지 않으면 심각한 TCP 성능 저하를 초래할 수 있다. 이에 대하여 IEEE 802.16 시스템의 ARQ는 총 4가지의 타이머(timer)들이 존재하지만 그 구체적인 값들은 표준에서 다루고 있지 않다. 본 연구는 이러한 ARQ 타이머들의 값에 따라 TCP 성능이 어떻게 변하는지를 시뮬레이션을 통해 분석하고 적절한 값을 제시한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.5
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• pp.1196-1207
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• 1998

The link sublayer segmentizes a use data into several frames and transmits it through a wireless channel. In this case, the packet error probability and link throughput are affected by the frame size. And a portion of pure user data in a packet affects a link throughput. In this paper we analyze and simulate the retransmission scheme of the Wireless Local Loop(WLL) system and study the link throughput according to the payload size.

• The KIPS Transactions:PartC
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• v.13C no.5 s.108
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• pp.635-640
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• 2006

The Snoop in the BS (Base Station) performs a local retransmission over wired-wireless networks to recover packet loss quickly. However, when the MH (Mobile Host) leaves the reception range of the signal, the local retransmission causes performance to degrade. In this paper, we minimize the packet loss and local retransmission caused by the unreachability from BS to MH to improve network performance. To do this, we suggest to add RSS(Received Signal Strengths) flag bit in ACK packet of MH. By using this flag bit, the BS decides whether it retransmits or not to minimize packet loss. The result of the simulation by ns-2 shows a big improvement of performance in the networks.

• Journal of KIISE:Information Networking
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• v.32 no.4
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• pp.443-451
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• 2005

Stateful inspection devices must maintain flow information. These devices create the flow information also for network attack packets, and it can fatally inflate the dynamic memory allocation on stateful inspection devices under network attacks. The memory inflation leads to memory overflow and subsequent performance degradation. In this paper, we present a guideline to set the flow entry timeout for a stateful inspection device to remove harmful embryonic entries created by network attacks. Considering Transmission Control Protocol (TCP) if utilized by most of these attacks as well as legitimate traffic, we propose a parsimonious memory management guideline based on the design of the TCP and the analysis of real-life Internet traces. In particular, we demonstrate that for all practical purposes one should not reserve memory for an embryonic TCP connection with more than (R+T) seconds of inactivity where R=0, 3, 9 and $1\leqq{T}\leqq{2}$ depending on the load level.

• Journal of KIISE:Information Networking
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• v.27 no.3
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• pp.315-322
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• 2000

네트워크에서 QoS를 보장하기 위해 최근에 제안되는 패킷 스케줄링 알고리즘은 대부분 우선 순위에 입각한 패킷 전송 서비스를 한다. 이러한 우선 순위를 유지하기 위한 큐의 관리에는 많은 비용이 들므로 QoS를 보장하는 네트워크에서 우선 순위 큐의 관리 비용을 줄이는 노력이 필요하다. 패킷 스케줄링 알고리즘 중 RPO+(Rotate Priority Queue)는 우선 순위 FIFO(First in first out)큐를 사용하여 주기 적으로 재명명되는 패킷 스케줄링 알고리즘이다. FIFO 큐에 패킷들을 근사 정렬하여 패킷의 우선 순위를 유지하므로 계산 복잡도를 줄이지만, 패킷 우선 순위를 유지하기 위해 2배(2P)의 큐를 필요로 한다.[1] 본 논문에서는 필요한 큐의 개수를 P개의 큐로 제한하여 큐에 대한 관리 비용을 줄였으며 엔터프라이즈 환경에서 애플리케이션이 요구하는 서비스 특성에 따라 클래스로 구분하여 적합한 패킷 스케줄링 서비스를 제공하는 알고리즘을 제시한다. 본 기법은 추가적인 오버플로우 큐를 관리하고 패킷 어드미션 컨트롤러를 통해 패킷 전송 지연 시간을 제한함으로 다양한 애플리케이션의 네트워크 QoS 요구를 보장하고 패킷 전손 효율을 높였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8A
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• pp.787-793
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• 2008

3GPP evolved packet system (EPS) is an all-IP based system that supports various access networks such LTE, HSPA/HSPA+, and non-3GPP networks. Recently, the support of IP flows with packet level QoS profiles was added to the requirements of the EPS. This paper proposes an adaptive modulation and coding (AMC) scheme that supports the QoS of such IP flows in the 3G LTE access network of the EPS. Defining the retransmission as a critical factor for QoS, the proposed scheme applies different maximum packet error probability $P_{max}$ to each packet when selecting the AMC transmission mode. In determining $P_{max}$, the QoS constraints and NACK-to-ACK error as well as channel condition are considered, balancing two objectives: the satisfaction of the QoS and the maximization of spectral efficiency. The simulation results show that it is able to reduce both delay violation and status report by 10%, while improving the throughput 10% in comparison with an existing scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.8
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• pp.950-953
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• 2016

A packet loss caused TCP segment drop and retransmission. This makes the energy useless, which is consumed to deliver the whole packets of the dropped segment over many hops. In this paper, end-to-end TCP retramission will be analyzed for the effect to energy consumed for delivering data. Especially, this paper will compare and analyze the legacy TCP method and Store-and-Forward method, and the method of computing the energy efficiency to transmission loss. This paper expects that the proposed method can contribute to new energy saving decision or algorithm on diverse data transmission situation.