• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.286-288
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• 2005

최근 기지국(Base Station)의 도움 없이 이동 단말기 간의 다중 무선 홉을 사용하여 송,수신자 간의 데이터 전송을 가능하게 하는 Ad-hoc 통신망에 관한 연구가 활발히 진행되고 있다. 유선망과 달리 Ad-hoc 통신망은 무선 전송 매체를 사용하기 때문에 신호의 페이딩(Fading), 간섭(Interference), 잡음(Noise) 등에 의해 높은 BER(Bit Error Rate)이 발생하는 특징을 가지고 있다. 하지만, 현재 인터넷 상에서 광범위하게 사용되고 있는 전송 규약인 TCP(Transmission Control Protocol)는 유선망의 신뢰적인 전송 매체를 고려하여 개발된 프로토콜이기 때문에 TCP를 수정 없이 Ad-hoc 통신망에 적용할 경우 전송 성능이 저하되는 문제를 가지고 있다. 전송 성능이 저하되는 문제는 기존 TCP가 에러 발생의 원인을 혼잡에 의한 것으로 인식하고 불필요한 혼잡 제어를 하기 때문이다. 본 논문에서는 송신자가 에러 발생 원인을 구별하고, 그에 따라 전송률을 조절함으로써 Ad-hoc 망에서의 TCP성능 향상을 위한 방법을 제시하였다. 또한 ns-2 시뮬레이터를 이용한 실험을 통해 TCP의 성능이 제안된 알고리즘에 의해 향상되었음을 확인하였다

• Journal of Computing Science and Engineering
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• v.1 no.1
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• pp.31-55
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• 2007

Contemporary end-servers and network-routers rely on traffic shaping to deal with server overload and network congestion. Although such traffic shaping provides a means to mitigate the effects of server overload and network congestion, the lack of cooperation between end-servers and network-routers results in waste of network resources. To remedy this problem, we design, implement, and evaluate NetDraino, a novel mechanism that extends the existing queue-management schemes at routers to exploit the link congestion information at downstream end-servers. Specifically, NetDraino distributes the servers' traffic-shaping rules to the congested routers. The routers can then selectively discard those packets-as early as possible-that overloaded downstream servers will eventually drop, thus saving network resources for forwarding in-transit packets destined for non-overloaded servers. The functionality necessary for servers to distribute these filtering rules to routers is implemented within the Linux iptables and iproute2 architectures. Both of our simulation and experimentation results show that NetDraino significantly improves the overall network throughput with minimal overhead.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3B
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• pp.130-137
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• 2005

Wireless communication environment is changing rapidly as we use new wireless communication technology such as WiBro to access high speed Internet. As a result, reliable data transmission using TCP is also expected to increase. Since TCP assumes that it is used in wired network, TCP suffers significant performance degradation over wireless network where packet losses are related to non-congestion loss. Especially RTO imposes a great performance degradation of TCP. In this paper, we analyze the loss recovery probabilities based on previous researches, and use simulation results of our algorithm to show that it prevents performance degradation by quickly detecting and recovery losses without RTO during fast recovery.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7B
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• pp.650-659
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• 2004

Domestic wireless network environment is changing rapidly while adapting to meet service requirements of users and growth of market. As a result, reliable data transmission using TCP is also expected to increase. Since TCP assumes that it is used in wired networt TCP suffers significant performance degradation over wireless network where packet losses are not always result of network congestion. Especially RTO imposes a great performance degradation of TCP. In this paper, we propose DAC$^{＋}$ and EFR in order to prevent performance degradation by quickly detecting and recovering loss without RTO during fast recovery. Compared with TCP NewReno, proposed scheme shows improvements in steady-state in terms of higher fast recovery Probability and reduced response time.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8B
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• pp.699-706
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• 2008

This paper compares throughput performance of TCP and SCTP in a variety of network environments. For experiments, we construct a Linux-based testbed and consider a set of performance metrics such as MSS(Maximum Segment Size), transmission delay, and packet loss rate. In addition, we analyze the effect of SCTP multi-streaming on throughput. From the experimental results, we can see that SCTP provides throughput gain of approximately $20%{\sim}50%$ over TCP. This performance gain comes from the distinctive features of SCTP such as chunk bundling, initial congestion window of 2 MTU and SACK(Selective ACK) based error control. In the lossy networks, we can see that SCTP multi-streaming transmissions can effectively overcome the so-called HoLB(Head-of-Line Blocking) phenomenon of TCP.

• Journal of Digital Convergence
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• v.12 no.12
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• pp.323-328
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• 2014

D-MAC protocol is used convergence network, which is designed to connect wireless link between things. This protocol is supported to local data exchange and aggregation among neighbor nodes, and distributed control packet from sink to sensor node. In this paper, we analysis about efficiency of power consumption according to whether or not security authentication of D-MAC in convergence network. If authentication scheme is applied to MAC communication, it is related to power consumption of preamble whether or not with and without authentication process. It is reduced to energy consumption against denial attack of service, when it is applied to authentication. Future work will take the effort to deal with security authentication scheme.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.6 no.3
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• pp.138-152
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• 2007

A communication system based on DATEX-ASN, an international communication protocol for use in COSMOS, a real-time traffic responsive signal system of Seoul, was developed in this study. Through laboratory experiments, it was identified that some additional rules were necessary for its successful application to COSMOS and thus proper complementary rules were devised. Laboratory experiments were to measure error-rates of monitoring information packet, EOC duration and operating cycle-length errors at different data transmission rates and the results of each experiment were compared each other. The results show that the DATEX-ASN protocol requires a transmission rate of at least 9,600bps which is higher than a transmission rate of 4,800bps required by NTCIP.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.5
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• pp.293-298
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• 2010

The key of USN(Ubiquitous Sensor Network) technology is low power wireless communication technology and proper resource allocation technology for efficient routing. The distinguished resource allocation method is needed for efficient routing in sensor network. To solve this problems, we propose an algorithm that can be adopted in USN with making up for weak points of PQ and WRR in this paper. The proposed algorithm produces the control discipline by the fuzzy theory to dynamically assign the weight of WRR scheduler with checking the Queue status of each class in sensor network. From simulation results, the proposed algorithm improves the packet loss rate of the EF class traffic to 6.5% by comparison with WRR scheduling method and that of the AF4 class traffic to 45% by comparison with PQ scheduling method.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.289-293
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• 2011

In our previous research, we proposed a MOST GATEWAY system for organically connected to the network MOST150 and MOST 25 and we proposed a simulation design method for performance analysis of Scheduling Algorithm in MOST GATEWAY system. Therefore in this paper, after comparing the performance among the existing scheduling algorithm methods in MOST25 and MOST150 Networks, we use NS-2 simulator in order to analyze the performance. Finally, we present an improvement scheme of the efficiency and scalability.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.294-306
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• 2005

Group oriented multicast applications are becoming increasingly popular in mobile ad hoc networks (MANETs). Due to dynamic topology of MANETs, stateless multicast protocols are finding increased acceptance since they do not require maintenance of state information at intermediate nodes. Recently, several multicast schemes have been proposed which scale better' with the number of multicast sessions than traditional multicast strategies. These schemes are also known as explicit multicast (Xcast; explicit list of destinations in the packet header) or small group multicast (SGM). In this paper, we propose a new scheme for small group' multicast in MANETs named extended explicit multicast (E2M), which is implemented on top of Xcast and introduces mechanisms to make it scalable with number of group members for a given multicast session. Unlike other schemes, E2M does not make any assumptions related to network topology or node location. It is based on the novel concept of dynamic selection of Xcast forwarders (XFs) between a source and its potential destinations. The XF selection is based on group membership and the processing overhead involved in supporting the Xcast protocol at a given node. If the number of members in a given session is small, E2M behaves just like the basic Xcast scheme with no intermediate XFs. As group membership increases, nodes may dynamically decide to become an XF. This scheme, which can work with few E2M aware nodes in the network, provides transparency of stateless multicast, reduces header processing overhead, minimizes Xcast control traffic, and makes Xcast scalable with the number of group members.