• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.3
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• pp.303-308
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• 2016

Recently, as the rapid development of network technology and the increase of services required high bandwidth such as multimedia service, the network traffic dramatically increases. This massive increase of network traffic causes some problems such as the degradation of QoS and the lack of network resources and, to solve these problems, various research to guarantee QoS have been performing. Currently, The most representative method to guarantee the QoS is the DiffServ(: Differentiated Service). The DiffServ defines the AF(: Assured Forwarding) PHB(: Per Hop Behavior) and statistically ensures the throughput over the certain level of data rate. However, the TCP congestion control method that make up the majority of the Internet traffic is not fundamentally suitable to the DiffServ that guarantees the throughput without managing the individual flow. Therefore, in this paper, we present this mismatch through the simulation as an example and propose the solution by controlling the TCP of the terminal in the network. The proposed scheme utilizes the information of the reception window size included in the ACK frame and does not require any modification of the TCP algorithms currently in use.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.11b
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• pp.939-942
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• 2003

TCP Westwood[1]는 송신측에 수신된 ACK를 통해서 대역폭을 계산하여 데이터를 전송하는 기법이다. 위성망 같이 손실률이 매우 높은 환경을 위해 TCP Westwood에서는 기존의 Bu]k Retransmission[2] 기법을 보안 하였다. 하지만 Bulk 재 전송 기법은 불필요한 데이터도 함께 재전송하기 때문에 성능이 저하되게 된다. 이 논문에서는 재 전송 패킷의 수를 적절히 조절하는 Adaptive Bulk Retransmission 기법을 제안하고자 한다.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10c
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• pp.211-213
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• 2003

무선 랜을 사용하는 애드 혹 네트워크에서는 경쟁 기반의 전송을 하는 링크 계층의 동작으로 인해 기존의 TCP의 정책들이 불리하게 작용하는 점이 있다. 특히, 이러한 환경에서는 패킷 전송을 위한 채널 경쟁이 큰 요소로 작용하게 된다. 본 논문에서는 무선 랜을 사용하는 애드 혹 네트워크에서 TCP의 ACK 기법을 조절하여, 경쟁으로 인한 오버헤드를 줄임으로써. 전송 효율을 높일 수 있는 방식을 제시한다.

• Proceedings of the Korean Information Science Society Conference
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• 2008.06d
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• pp.418-423
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• 2008

802.11 에서 유니캐스트 통신을 할 때 수신 호스트는 ACK 프레임을 전송하여 데이터의 수신을 확인한다. 그러나 프레임 오류율이 낮은 상황에서 ACK 프레임을 전송하는 것은 에너지 측면에서 낭비가 될 수 있다. 본 논문에서는 상위 계층의 유비캐스트 통신을 상위 계층에는 투명하게 ACK가 없는 802.11 멀티 캐스팅을 이용하여 통신을 하는 기법을 제안하고 실제 환경에서 이를 구현 및 실험하였다. 실험결과, TCP와 같이 상위 계층에서 오류제어를 하는 경우 정상적인 통신이 항상 가능하며, 무선 전송 오류가 낮 은 경우는 에너지는 물론 처리량도 증가하는 것을 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.153-156
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• 2017

In this paper, we propose a novel uplink congestion control scheme, which enhances downlink TCP throughput by improving response time of TCP acknowledgements without TCP modification. Through the experimental results, it is manifested that the proposed scheme is able to achieve better downlink TCP throughput.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.4
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• pp.369-377
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• 2008

Today, Ethernet technology is rapidly developing to have a bandwidth of 10Gbps beyond 1Gbps. In such high-speed networks, the existing method that host CPU processes TCP/IP in the operating system causes numerous overheads. As a result of the overheads, user applications cannot get the enough computing power from the host CPU. To solve this problem, the TCP/IP Offload Engine(TOE) technology was emerged. TOE is a specialized NIC which processes the TCP/IP instead of the host CPU. In this paper, we implemented a high-performance, lightweight TCP/IP(HL-TCP) for the TOE and applied it to an embedded system. The HL-TCP supports existing fundamental TCP/IP functions; flow control, congestion control, retransmission, delayed ACK, processing out-of-order packets. And it was implemented to utilize Ethernet MAC's hardware features such as TCP segmentation offload(TSO), checksum offload(CSO) and interrupt coalescing. Also we eliminated the copy overhead from the host memory to the NIC memory when sending data and we implemented an efficient DMA mechanism for the TCP retransmission. The TOE using the HL-TCP has the CPU utilization of less than 6% and the bandwidth of 453Mbps.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10e
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• pp.532-534
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• 2002

본 논문에서는 UDP／IP기반 SAN의 구현을 소개하였고 TCP／IP기반 SAN 및 로컬디스크와의 성능 비교를 통해 UDP／IP기반 SAN이 클러스터 웹서버에서 사용될 수 있는 가능성을 보였다. 실험결과 UDP／IP기반 SAN은 TCP／IP기반 SAN의 경우보다 약 20%정도 성능이 우수함을 볼 수 있다. 이는 UDP의 경우 TCP의 프로토콜 오버헤드가 없고 slow start의 영향을 받지 않으며 ACK를 기다릴 필요가 없기 때문이다.

• Journal of KIISE:Information Networking
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• v.34 no.6
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• pp.435-445
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• 2007

Snoop protocol is one of the efficient schemes to compensate TCP packet loss and enhance TCP throughput in wired-cum-wireless networks. However, Snoop protocol has a problem: it cannot perform local retransmission efficiently under the bursty-error prone wireless link. To solve this problem, SACK-Aware-Snoop and SNACK mechanism have been proposed. These approaches improve the performance by using SACK option field between base station and mobile host. However in the wireless channel with high packet loss rate, SACK-Aware-Snoop and SNACK mechanism do not work well because of two reason: (a) end-to-end performance is degraded because duplicate ACKs themself can be lost in the presence of bursty error, (b) energy of mobile device and bandwidth utilization in the wireless link are wasted unnecessarily because of SACK option field in the wireless link. In this paper, we propose a new local retransmission scheme based on Cross-layer approach, called Cross-layer Snoop(C-Snoop) protocol, to solve the limitation of previous localized link layer schemes. C-Snoop protocol includes caching lost TCP data and performing local retransmission based on a few policies dealing with MAC-layer's timeout and local retransmission timeout. From the simulation result, we could see more improved TCP throughput and energy efficiency than previous mechanisms.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.1
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• pp.45-57
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• 2005

In this paper, we extend the performance of bidirectional TCP connection over end-to-end network that uses transfer rate-based flow and congestion control. The sharing of a common buffer by TCP packets and acknowledgement has been known to result in an effect called ack compression, where acks of a connection arrive at the source bunched together, resulting in unfairness and degraded throughput. The degradation in throughput due to bidirectional traffic can be significant. Even in the simple case of symmetrical connections with adequate window size, the connection efficiency is improved about 20% for three levels of background traffic 2.5Mbps, 5.0Mbps and 7.5Mbps. Otherwise, the throughput of jitter is reduced about 50% because round trip delay time is smaller between source node and destination node. Also, we show that throughput curve is improved with connection rate algorithm which is proposed for TCP congetion avoidance as a function of aggressiveness threshold for three levels of background traffic 2.5Mbps, 5Mbps and 7.5Mbps. By analyzing the periodic bursty behavior of the source IP queue, we derive estimated for the maximum queue size and arrive at a simple predictor for the degraded throughput, applicable for relatively general situations.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.4
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• pp.63-70
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• 2010

In IEEE 802.11e system providing differentiated services, there exist some problems as follows; collision probability increase due to the increase in the number of nodes by employing CSMA/CA transmission mode, transmission speed declining tendency towards the worst of it, which is caused by different transmission mode and decrease of TCP transmission rate as the result of the link occupancy by UDP when TCP shares the link with UDP by the TCP’s flow control characteristic. In this thesis, the initial minimum and maximum CW are set differently according to the number of connected nodes in the network to avoid collisions and TXOP is adjusted according to the channel state, in which ACs with low priority but better channel state will get gradually more chances to transmit leading to optimal channel capacity. Also, by allowing higher priority for ACK frames which control the TCP transmission, the flow control becomes better because that reduces the channel occupancy by UDP flow, and by this, fair transmission is obtained from the result of the more fair transmission and active resource allocation.