• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12B
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• pp.800-808
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• 2007

With the development of wireless data communication technology, all IP-based network will become compositions of wired and wireless networks. TCP is a connection-oriented, reliable transport protocol and has been used as de facto standard in most wired networks. Because TCP's congestion control algorithm could not distinguish congestion from BER, link failure and frequent route changes, TCP shows a poor performance over mobile ad-hoc networks. In this paper, the theoretical feature of TCP was studied and the performance of TCP over mobile ad-hoc networks was analyzed with ns2.

• Journal of Digital Contents Society
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• v.15 no.2
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• pp.147-154
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• 2014

There have been company researches for TCP-Westwood algorithms in wireless TCP environment with high packet loss rate. Because the TCP-Westwood algorithm adjusts the congestion window according to the ABE(Available Bandwidth Estimation), the algorithm has a problem which the accuracy of ABE decreases as the error rate increases. To solve such a problem, the proposed scheme in this paper adopts the existing packet pattern based algorithm that the ABE is ignored when the arriving interval time of ACK is longer than a given interval time and uses new algorithm that the ABE is reallocated to a given allowable ABE when the ABE is over the allowable range. The proposed scheme shows the simulation result that the ABE is closest to the setting bandwidth for simulation compared to the existing algorithms.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.7
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• pp.1599-1609
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• 2014

TCP does not ensure the bandwidth and delay bound required for multimedia streaming services in broadband wireless network environments. In this paper, we propose a new congestion control scheme for efficient multimedia transmission, called COLO TCP (Concave Increase Slow Start Logarithmic Increase Congestion Avoidance TCP). The COLO TCP prevents the burst packet loss by applying the concave increase algorithm in slow start phase. In the congestion avoidance phase, COLO TCP uses the logarithmic increase algorithm that quickly recovers congestion window after packet loss. To highly utilize network bandwidth and reduce packet loss ratio, COLO TCP uses additive increase algorithm and adaptive decrease algorithm. Through simulation results, we prove that our COLO TCP is more robust for random loss. It is also possible for efficient multimedia transmission.

• The KIPS Transactions:PartC
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• v.17C no.6
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• pp.451-458
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• 2010

To detect and recover packet losses over wireless links is very important in terms of reliability in packet transmission. Most wireless communication systems adopt an automatic repeat request (ARQ) protocol operating at link layer. However, it has been constantly addressed that the interaction not harmonized sufficiently between ARQ and TCP rather degrades TCP performance. In this paper, therefore, we propose an improved scheme from the aspect of the interaction with TCP loss recovery mechanism that can be applied to selective repeat ARQ (SR-ARQ) protocol and prove that the proposed scheme improves TCP performance significantly by OPNET simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.107-109
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• 2016

In this paper, we address the TCP-over-WLAN performance problem that occurs during periodic active background scanning with which mobile devices discover available APs in the vicinity. We measure the impact of the scanning period on the TCP throughput and observe a significant performance degradation when the scan operation period is shortened. Our experimental analysis has identified the main cause of the problem, that is, the associated AP continues to send packets to the mobile device even when the device is not able to receive due to the scanning operation.

• Proceedings of the Korea Information Processing Society Conference
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• 2015.10a
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• pp.319-321
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• 2015

인지무선네트워크 (Cognitive Radio Networks) 환경에서 스펙트럼의 원소유주인 1차사용자가 전송을 개시하는 경우, 같은 채널을 사용하는 2차사용자의 TCP (Transmission Control Protocol) 는 전송 불능 상태가 되어 심각한 성능저하가 발생한다. 이러한 성능저하는 1차사용자의 등장으로 인해 채널이 사용 불가능 해지는 상태를 패킷 손실로 판단하여 재전송 타임아웃이 발생하기 때문에 발생된다. 우리는 이 문제를 링크 또는 물리 계층 (하위계층) 과 TCP간의 크로스레이어링을 통하여 해결하고자 한다. 하위 계층은 1차사용자의 전송이 감지되면, 이를 TCP에게 시그널링하고, TCP는 이를 통해 재전송 타이머와 혼잡 윈도우를 고정시키고, 패킷 전송을 중단하도록 한다. 또, 하위계층이 가용 채널을 감지하게 되면, 재차 TCP에게 시그널링을 함으로써, 전송이 신속하게 재개되도록 한다. 제안하는 방법은 실제 USRP(Universal Software Radio Peripheral)에 구현하여 성능의 향상을 검증한다.

• Journal of KIISE:Information Networking
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• v.29 no.4
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• pp.447-458
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• 2002

In this paper, we design and implement Wireless Transaction Protocol(WTP) and evaluate it for wireless transaction processing in mobile computing environments. The design and implementation of WTP are based on the coroutine model that might be suitable for light-weight portable devices. We test the compatibility between our product and the other products such as Nokia, Kannel and WinWAP For the evaluation of WTP, we use an Internet simulator that can arbitrary generate random wireless errors based on the Gilbert model. In our experiment, the performance of WTP is measured and compared to those of Transmission Control Protocol(TCP) and TCP for Transactions. The experiment shows that WTP outperforms the other two protocols for wireless transaction processing in terms of throughput and delay. Especially, WTP shows much higher performance In ease of high error rate and high probability of burst errors. This comes from the fact that WTP uses a small number of packets to process a transaction compared to the other two protocols and introduces a fixed time interval for retransmission instead of the exponential backoff algorithm. The experiment also shows that the WTP performance is optimized when the retransmission counter is set to 5 or 6 in case of high burst error rate.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.11
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• pp.2553-2562
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• 2013

It is difficult for TCP congestion control algorithm to ensure the bandwidth and delay bound required for media streaming services in broadband wireless network environments. In this paper, we propose the COIN TCP (COncave INcrease TCP) scheme for providing a high-quality media streaming services. The COIN TCP concavely increases the congestion window size by adjusting the increment rate of congestion window, that is inversely proportional to the amount of data accumulated in the router queue. As a result, our scheme can quickly occupy the available bandwidth and prevent the heavy congestion. It also improves the link utilization by adjusting the decrement rate of congestion window according to the packet loss rate with the random loss. Through the simulation results, we prove that our scheme improves the total throughput in broadband wireless network.

• Journal of KIISE:Information Networking
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• v.30 no.6
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• pp.743-754
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• 2003

TFRC(TCP-Friendly Rate Control) is proposed to satisfy the demands of multimedia applications while being reasonably fair when competing for bandwidth with TCP flows[1-3]. However, TFRC has a shortcoming that the fairness and throughput are degraded when the mobile host using TFRC experiences handoffs. This paper proposes a new control mechanism based on TFRC, which deals with the congestion caused by handoffs as well as the losses caused during the handoffs. The simulation results show that our mechanism achieves better throughput and fairness compared to TFRC for repeated handoffs.