• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.9A
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• pp.1535-1541
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• 2001

TCP is the most widely-used transport layer protocol in current Internet, while ATM technology is used to increase the data communication speed at data link layer and network layer. In the TCP-over-ATM architecture, the most significant problems are (i) the partial packet discarding problem, and (ii) the TCP window timeout problem. Several approaches have been proposed to solve the partial packet discard problem and the timeout problem individually, but none of them considered the two problems together. In this paper, we propose an enhanced UBR+ scheme which supports fairness among the TCP connections using UBR+ scheme, and provides protection of damaged VC from the multiple packet losses in the same TCP sliding window. To analyze its performance, we simulate the proposed scheme using OPNET. The simulation results show that the proposed scheme supports fairness, and also increases the throughput by reducing the probability of multiple cell losses in the same TCP window.

• Proceedings of the Korea Information Processing Society Conference
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• 2019.05a
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• pp.328-330
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• 2019

RTT(Round Trip Time)가 큰 위성링크에서는 TCP의 정상적인 동작이 어렵다. PEP(Performance Enhanced Proxy)은 위성과 지상 통신간의 성능 향상을 위해 개발되었으나. PEP의 위성링크 구간에 적용되는 TCP Cubic, TCP Hybla등 기존의 Enhanced TCP는 충분한 윈도우사이즈를 확보하는데 시간이 걸리는 문제점이 있다. 본 논문에서는 Cubic의 초기 윈도우 값을 높게 설정해 위성 대역폭을 보다 빨리 점유할 수 있는 수정된 혼잡제어 알고리즘을 제안한다. 제안한 방법은 기존 혼잡제어 알고리즘보다 전송률이 약 26% 향상되었다.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.7
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• pp.794-798
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• 2010

Assuming that a wireless link is mostly used at the network edge and the wireless NIC driver keeps monitoring the error rate of its link, this paper proposes an enhanced TCP congestion control, TCP-L (TCP Link-Aware). TCP-L predicts true congestion losses occurred inside the wired link area by utilizing the wireless link error rate. As a result, it mitigates performance degradation caused from TCP congestion control actions when segments losses occur in a wireless link. Experimental results show that TCP-L provides better performance and fairness in lossy wireless links than existing TCP congestion control schemes. Our approach utilizing the characteristic of the link at TCP could be well adapted to new wireless environments such as Cognitive Radio and ACK-less IEEE 802.11, where a frame may be delivered with a very long delay or lost in the link.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.1
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• pp.24-51
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• 2011

When supporting both voice and TCP in a wireless multihop network, there are two conflicting goals: to protect the VoIP traffic, and to completely utilize the remaining capacity for TCP. We investigate the interaction between these two popular categories of traffic and find that conventional solution approaches, such as enhanced TCP variants, priority queues, bandwidth limitation, and traffic shaping do not always achieve the goals. TCP and VoIP traffic do not easily coexist because of TCP aggressiveness and data burstiness, and the (self-) interference nature of multihop traffic. We found that enhanced TCP variants fail to coexist with VoIP in the wireless multihop scenarios. Surprisingly, even priority schemes, including those built into the MAC such as RTS/CTS or 802.11e generally cannot protect voice, as they do not account for the interference outside communication range. We present VAGP (Voice Adaptive Gateway Pacer) - an adaptive bandwidth control algorithm at the access gateway that dynamically paces wired-to-wireless TCP data flows based on VoIP traffic status. VAGP continuously monitors the quality of VoIP flows at the gateway and controls the bandwidth used by TCP flows before entering the wireless multihop. To also maintain utilization and TCP performance, VAGP employs TCP specific mechanisms that suppress certain retransmissions across the wireless multihop. Compared to previous proposals for improving TCP over wireless multihop, we show that VAGP retains the end-to-end semantics of TCP, does not require modifications of endpoints, and works in a variety of conditions: different TCP variants, multiple flows, and internet delays, different patterns of interference, different multihop topologies, and different traffic patterns.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.9
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• pp.2323-2340
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• 2012

Recent advances in cognitive radio technology have drawn immense attention to higher layer protocols above medium access control, such as transmission control protocol (TCP). Most proposals to improve the TCP performance in cognitive radio (CR) networks have assumed that either all nodes are in CR networks or the TCP sender side is in CR links. In those proposals, lower layer information such as the CR link status could be easily exploited to adjust the congestion window and improve throughput. In this paper, we consider a TCP network in which the TCP sender is located remotely over the Internet while the TCP receiver is connected by a CR link. This topology is more realistic than the earlier proposals, but the lower layer information cannot be exploited. Under this assumption, we propose an enhanced TCP protocol for CR networks called TCP for cognitive radio (TCP-CR) to improve the existing TCP by (1) detection of primary user (PU) interference by a remote sender without support from lower layers, (2) delayed congestion control (DCC) based on PU detection when the retransmission timeout (RTO) expires, and (3) exploitation of two separate scales of the congestion window adapted for PU activity. Performance evaluation demonstrated that the proposed TCP-CR achieves up to 255% improvement of the end-to-end throughput. Furthermore, we verified that the proposed TCP does not deteriorate the fairness of existing TCP flows and does not cause congestions.

• Journal of Internet Computing and Services
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• v.9 no.6
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• pp.179-188
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• 2008

Even though a lot of researches to improve the performance of TCP over wireless networks have been performed, the performance of TCP cannot satisfy users under high packet loss rate of wireless networks. This paper addresses the problem of TCP Westwood under high packet loss rate and reveals the reasons through the extensive simulation analysis. The ABE(Available Bandwidth Estimation) of TCP westwood becomes incorrect due to TCP dynamics of loss recovery. Based on this observation, we propose two algorithms for enhancing the correctness of ABE. We have evaluated the effects of the proposed algorithms through simulation. The proposed algorithms have achieved more correct ABE under the packet loss rate less than 1%.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.131-140
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• 2017

Multipath TCP (MPTCP) is a transport layer protocol that simultaneously transmits data using multiple interfaces. MPTCP is superior to existing TCP in network environment with homogeneous subflows, but it shows worse performance compared to existing TCP in network environment with bufferbloat. If a bufferbloat occurs in one of the MPTCP multipaths, the packet will not arrive at the MPTCP receive buffer due to a sudden increase in delay time, resulting in a HoL blocking phenomenon. It makes the receive window of the other path to be zero. In this paper, we apply Adaptive Random Early Detection (ARED), Controlled Delay (CoDel) and Proportional Integral Controller Enhanced (PIE) among the proposed Active Queue Management (AQM) to limit the delay of bufferbloat path. Experiments were conducted to improve the performance of MPTCP in heterogeneous networks. In order to carry out the experiment, we constructed a Linux-based testbed and compared the MPTCP performance with that of the existing droptail.

• Journal of information and communication convergence engineering
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• v.4 no.2
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• pp.71-74
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• 2006

A basic access method about IEEE 802.11 MAC layer protocol using IEEE 802.11 wireless LANs is the DCF thatis based on the CSMA/CA. But, cause of IEEE 802.11 MAC layer uses original backoff algorithm (exponential backoff method), when collision occurred, the size of contention windows increases the double size Also, a time of packet transmission delay increases and efficienty is decreased by original backoff scheme. In this paper, we have analyzed TCP packet transmission time of IEEE 802.11 MAC DCF protocol for wireless LANs a proposed enhanced backoff algorithm. It is considered the transmission time of transmission control protocol (TCP) packet on the orthogonal frequency division multiplexing (OFDM) in additive white gaussian noise (A WGN) and Rician fading channel. From the results, a proposed enhanced backoff algorithm produces a better performance improvement than an original backoff in wireless LAN environment. Also, in OFDM/quadrature phase shift keying channel (QPSK), we can achieve that the transmission time in wireless channel decreases as the TCP packet size increases and based on the data collected, we can infer the correlation between packet size and the transmission time, allowing for an inference of the optimal packet size in the TCP layer.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.530-533
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• 2006

Recently, a basic access method about IEEE 802.11 MAC layer protocol using IEEE 802.11 wireless LANs is the DCF thatis based on the CSMA/CA. But, cause of IEEE 802.11 MAC layer uses original backoff algorithm (exponential backoff method), when collision occurred, the size of contention windows increases the double size. Also, a time of packet transmission delay increases and efficiency is decreased by original backoff scheme. In this paper, we have analyzed TCP packet transmission time of IEEE 802.11 MAC DCF protocol for wireless LANs a proposed enhanced backoff algorithm. It is considered the transmission time of transmission control protocol (TCP) packet on the orthogonal frequency division multiplexing (OFDM) in additive white gaussian noise (AWGN) and Rician fading channel. From the results, a proposed enhanced backoff algorithm produces a better performance improvement than an original backoff in wireless LAN environment. Also, in OFDM/quadrature phase shift keying channel (QPSK), we can achieve that the transmission time in wireless channel decreases as the TCP packet size increases and based on the data collected, we can infer the correlation between packet size and the transmission time, allowing for an inference of the optimal packet size in the TCP layer.