• Journal of KIISE:Information Networking
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• v.36 no.5
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• pp.383-388
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• 2009

In this paper, we focus on the retransmission following transmission failure in impulse radio ultra wideband (IR-UWB). The reasons of transmission failure are classified and a new 'selfish' retransmission protocol is proposed because time hopping can support multiple transmissions at the same time. Selfish retransmission protocol retransmits packets immediately without any kind of timeout or channel observation. Simulation results show that the proposed protocol improves throughput up to 50% and decreases retransmission delay also up to 70%, compared to a conventional retransmission system in IR-UWB.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.04a
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• pp.597-600
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• 2011

멀티패스 전송은 단대 노드간 다중 경로를 동시에 사용함으로써 효과적인 대용량 전송을 실현하는 미래 인터넷 설계의 한 부분이다. 이에 따라 draft-‘TCP Extensions for Multipath Operation with Multiple Addresses'에서 MPTCP 가 언급되었으며 기존 TCP 를 활용한 다중 전송에서 발생할 수 있는 다양한 오픈 이슈가 나오게 되었다. 본 논문에서는 위 논의로부터 나온 다양한 오픈 이슈 중 수신측에서 발생 할 수 있는 패킷의 재조합(packet reordering)을 줄이는데 초점을 둔다. 패킷의 재조합은 불필요한 에너지 소비와 빈번한 패킷 재전송(packet retransmission) 문제를 초래하며, 특히 에너지 효율이 중요한 모바일기기에 있어 반드시 해결되어야 문제라 할 수 있다. 이를 해결하기 위해 본 논문에서는 전송 경로들의 RTT 값을 비교하여 패킷의 스케줄링 하는 기법을 제안하였으며 시뮬레이션을 통해 성능을 검증하였다.

• The KIPS Transactions:PartC
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• v.11C no.7 s.96
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• pp.931-936
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• 2004

We need to have an adaptive TCP protocol that can be tolerable on wireless network environement. TCP Westwood for use in the environe-ment that have a very high loss rate like a sattelite was proposed by modifying the existing bulk retransmission protocol. Bulk retransmission mechanism shows a highly enhanced performance on networks that have a very high loss rate but are prone to bursty loss networks. Also, it can exprience less performance on low late transmission environement. This paper proposes Adaptive Bulk Retransmission Mechanism that adjusts the number of bulk retransmitted packets based on the network conditions. The proposed mechanism was evaluated by using NS-2.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.4B
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• pp.170-177
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• 2005

Due to the redundant rebroadcast packets, network-wide broadcasting is a costly operation in wireless mobile ad hoc networks. To reduce this redundancy, most of previous approaches implicitly or explicitly require periodic refreshing of neighborhood information which continuously imposes additional broadcast overheads. In this paper, we propose a practical broadcast pruning scheme based on the local prediction of a remained coverage area. As the proposed scheme uses only information available in the on-going broadcast process, it can minimize the overheads prevalent in previous approaches.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10c
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• pp.88-90
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• 2000

컴퓨터에 있어서 네트워킹이 중요한 요소로 부각되면서 운영체제는 네트워킹을 보다 효율적으로 지원할 수 있어야 한다. 데이터가 송신자에서 수신자로 전송될 때, 데이터는 이동경로상의 라우터들을 경유하게 된다. 그러나 경유하는 중간회선과 라우터의 처리능력이 서로 다르며, 처리 가능한 크기보다 큰 패킷을 받을 경우는 적절한 크기로 분할되게 된다. 수신측에서는 분할된 패킷을 다시 재조합하여 원래의 데이터로 복원시켜야 한다. 이러한 패킷 재조합은 운영체제의 커널에서 수행된다. 본 논문에서는 리눅스 커널에서의 분할패킷 재조합 과정을 개선함으로써 노드간 데이터 전송률을 향상시킬 수 있는 방안을 제시한다.

• Journal of the Korea Convergence Society
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• v.7 no.4
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• pp.25-32
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• 2016

When using reliable multicast protocol over air links, the multicast packets lost in the air link cause the initiation of retransmission request packets and the implosion of retransmission packets, which deteriorate multicast session performance. This paper proposes on the efficient reliable multicast mechanism in wireless networks utilizing the Agents. In this paper we show the design of a retransmission agent which improves the performance of reliable multicast sessions in wireless network. The main idea is to cache reliable multicast packets at the base station and perform local retransmissions across the wireless link. MATLAB has been used to simulate and to get performance results for signaling overhead and processing delay through the comparison of the proposed agent model to the Multicast File Transfer Protocol. It has been proven from the simulation results that the proxy module make pass trials shorter in Multicast File Transfer Protocol.

• Journal of the Korea Society of Computer and Information
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• v.13 no.4
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• pp.161-167
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• 2008

A method to compute the size of packet and the optimal way to transmit the packets are proposed in this work for the VoIP communication using the MIL-STD-188-220C, military wireless Ad-hoc protocol which is used for the amicable communications of both speeches and data between several radiotelegraph. The expected time of data transmission is estimated beforehand, and then the size of package and transmission method are decided in the consideration of VoIP speech quality for the users as well as the data transmission quality of radiotelegraph.

• Journal of KIISE:Information Networking
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• v.32 no.3
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• pp.382-390
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• 2005

As today's networks evolve towards an If-based integrated network, the role of transmission control protocol(TCP) has been increasing as well. As a well-known issue, the performance of TCP is affected by its loss recovery mechanism that is comprised of two algorithms; fast retransmit and fast recovery. Although retransmission timeout(RTO) caused by multiple packet losses can be avoided by using selective acknowledgement(SACK) option, RTO cannot be avoided if a retransmitted packet is lost. Therefore, we propose a simple modification to make it possible for a TCP sender using SACK option to detect a lost retransmission. In order to evaluate the proposed algorithm, simulations have been performed for two scenarios where packet losses are random and correlated. Simulation results show that the proposed algorithm can improve TCP performance significantly.

• 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.

• Proceedings of the Korean Information Science Society Conference
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• 2001.04a
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• pp.379-381
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• 2001

라우터나 스위치 같은 네트워크상의 접근 포인트에서 트래픽들에 대한 불공정 큐잉은 서비스의 성능을 저하시킬 뿐만 아니라 불필요한 병목을 일으킬 우려가 많기 때문에 트래픽들에 대한 공정한 패킷 스케줄링 기법들이 많이 연구되고 있다[2]. 그 중에서 서비스 할당량 SQ(Service Quantum)와 결손 계측자 DC(Deficit Counter)를 사용하는 DRR 기법은 다른 것들에 비해 작업 복잡도가 낮고 보다 정확한 공정성을 보장하는 패킷 스케줄링 기법이다. 그러나 이 기법은 TCP 프로토콜의 재전송 타이머에 의해 검출된 전송이 실패된 패킷을 고려하지 않고 있다. 본 논문에서는 TCP 프로토콜의 재전송 타이머에 의해 검출된 전송이 실패된 TCP 패킷을 관리하기 위한 추가적인 큐를 두어 기존의 DRR 보다 정확한 공정성을 보장하는 기법을 제안한다.