• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1542-1550
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• 2015

Delayed ACK is an algorithm implemented to decrease the number of ACK transmissions by delaying an ACK transmission and by waiting for additional ACK instead of transmitting the ACK immediately. By using Delayed ACK in TCP, the congestion of network and the overhead of handling ACKs can be reduced. Waiting time of Delayed ACK is defined as the Delayed ACK timeout, and it is fixed in Window OS basically. However, the fixed value of Delayed ACK timeout is not suitable for dynamic network circumstance, and it may cause unnecessary delay. This paper proposes a regulating Delayed ACK timeout algorithm to reduce the aforementioned unnecessary delay caused by the lengthy default value of the Delayed ACK timeout. We confirm that TCP transmission performance in dynamic network circumstance can be improved using the proposed algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.9A
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• pp.790-795
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• 2011

The need for broadband wireless data networks such as IEEE 802.16e WiMAX systems increases as a variety of wireless information devices like smart phones are adopted rapidly in everyday life. Since most of mobile applications employ TCP as their transport layer protocol, the performance improvement of TCP in WiMAX systems is crucial. This paper proposes an efficient method to transmit uplink piggyback ACK packets by exploiting the uplink packet buffering which happens because of the resource allocation scheme of the WiMAX systems. The proposed method can support not only the ACK filtering but also the merging of the piggyback ACK packets. As a result, the bandwidth reduction in the piggyback ACK packet transmission leads to the improvement of the downlink throughput. The simulation results show that the bandwidth for the ACK packets reduces more than 90%, and the downlink throughput increases at least 30%.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.6
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• pp.1194-1201
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• 2003

Measurements of network traffic have shown that self-similarity is a ubiquitous phenomenon spanning across diverse network environments. We have advance the framework of multiple time scale congestion control and show its effectiveness at enhancing performance for fast TCP prototype control. In this paper, we extend the fast TCP prototype control framework to window-based congestion control, in particular, TCP. This is performed by interfacing TCP with a large time scale control module which adjusts the aggressiveness of bandwidth consumption behavior exhibited by TCP as a function of "large time scale" network state. i.e., conformation that exceeds the horizon of the feedback loop as determined by RTT. Performance evaluation of fast TCP prototype is facilitated by a simulation bench-mark environment which is based on physical modeling of self-similar traffic. We explicate out methodology for discerning and evaluating the impact of changes in transport protocols in the protocol stack under self-similar traffic conditions. We discuss issues arising in comparative performance evaluation under heavy-tailed workload. workload.

• IEMEK Journal of Embedded Systems and Applications
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• v.1 no.2
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• pp.64-72
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• 2006

The long propagation delay over satellite internet causes degradation of TCP performance in slow start phase. Especially, web traffic performance is greatly reduced by low throughput in slow start phase. To improve web traffic performance, we propose the Dynamic ACK Generation Scheme which generates ACKs and considers sender RTO in PEP (Performance Enhancing Proxy). The Normal ACK generation mechanism improves TCP throughput, and also decreases sender RTO. if PEP stops generating ACKs, TCP performance will be reduced by frequent RTO expiration. To solve this problem, our scheme adjusts RTO using ACK generation interval. And it supports retransmission mechanism for loss recovery in PEP. The results of the performance analysis provide a good evidence to demonstrate the efficiency of our mechanisms over satellite internet.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6B
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• pp.396-405
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• 2005

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. In this paper, we propose Enhanced Snoop(E-Snoop) protocol to solve this problem of Snoop protocol. With E-Snoop protocol, packet losses can be noticed by receiving new ACK packets as well as by receiving duplicate ACK packets or local retransmission timeout. Therefore, TCP throughput can be enhanced by fast recognition of bursty packet losses and fast local retransmissions. From the simulation results, E-Snoop protocol can improve TCP throughput more efficiently than Snoop protocol and can yield more TCP improvement especially in the channel with high packet loss rates.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.392-401
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• 2007

Wireless network has high BER characteristic because of path loss, fading, noise and interference. Many packet losses occur without any congestion in wireless network. Therefore, many wireless TCP algorithms have been proposed. SNOOP, one of wireless TCP algorithms, hides packet losses for Fixed Host and retransmits lost packets in wireless network. However, SNOOP has a weakness for bust errors in wireless network. This paper proposes the SACK-SNOOP to improve TCP performance based on SNOOP and Freeze-TCP that use ZWA messages in wireless network. This message makes FH stop sending packets to MH. BS could retransmit error packets to MH for this time. SACK-SNOOP use improved Selective ACK, thereby reducing the number of packet sequences according to error environment. This method reduces the processing time for generation, transmission, analysis of ACK. This time gain is enough to retransmit local burst errors in wireless link. Furthermore, SACK-SNOOP can manage the retransmitted error by extending delay time to FH. The simulation shows that our proposed protocol is more effective for packet losses in wireless networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.10
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• pp.1309-1316
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• 2016

This paper suggests adjusting TCP for smartphones that often have small size data transmission tendency. Usage of smartphones has been risen dramatically in recent years, including frequent usage of real-time map search, public transportation search, online games, and SNS. Because the small size data transmission ends before the phase of the TCP congestion avoidance, this paper suggests an algorithm that increases the transmission speed ahead of the traffic congestion event. The algorithm reduces unnecessary delay by data size-driven adjustment of the Linux Quick ACK and Nagle's algorithm. Therefore, TCP is improved to maintain a high transmission rate steadily in small data transmission.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.679-681
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• 2001

인터넷 화상 전화와 같이 비디오 데이터를 압축하여 실시간 전송하는 응용 프로그램의 사용 시 일어날 수 있는 비디오 데이터 오류 전파를 방지하기 위한 대표적인 기법으로 FEC를 향상시킨 Periodic FEC가 있다. 본 논문에서는 ACK 메시지를 기반으로 연속적인 패킷 손실을 예측하여 PFEC의 중복 정보(redundant information)외 전송량 조절이 가능한ACK기반 중복 정보 제어 기법을 제안한다. 또한 대용량의 멀티미디어 데이터 전송 시 발생할 수 있는 congestion을 제어하기 위해 TCP와 공정하게 대역폭을 공유하는 TCP-friendly rate control 기법을 고려하여 PFEC의 중복 정보의 양을 네트워크 상태에 적응적으로 조절하는 기법을 제안한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.1 no.2
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• pp.102-109
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• 2006

In this paper, we improve 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. For example, 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 congestion avoidance as a function of aggressiveness threshold for three levels of background traffic 2.5Mbps, 5Mbps and 7.5Mbps.

• Journal of KIISE:Information Networking
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• v.30 no.2
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• pp.233-243
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• 2003

With the original Transmission Control Protocol(TCP) design, which is particularly targeted at the wired networks, a packet loss is assumed to be caused by the network congestion. In the wireless environment where the chances to lose packets due to transmission bit errors are not negligible, though, this assumption may result in unnecessary TCP performance degradation. In this paper, we propose three schemes that improve the ability to conceal the packet losses in the wireless network while limiting the degree of violating TCP end-to-end semantics to a temporary incidents. If there happens a packet loss at the wireless link and there is a chance that the loss is noticed by the sending TCP, the proposed schemes send an indirect acknowledgement. Each of the proposed schemes uses different criteria to decide whether there is a chance that the packet loss occurred in the wireless part is noticed by the sender. In order to limit the buffer overhead in the base, the indirect acknowledgements are issued only when the length of buffer is less than a certain threshold. We use simulation to compare the overhead and the performance of the proposed schemes, and to show that the proposed schemes improve the TCP performance compared to Snoop with a limited amount of buffer at the base station.