• 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.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.11a
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• pp.1019-1022
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• 2010

네트워크 기술의 발전으로 이용할 수 있는 대역폭이 증가하고 있다. 그에 따라 증가한 대역폭을 효율적으로 사용하기 위한 전송 기술이 요구되고 있다. TCP Vegas는 RTT(Round Trip Time)를 이용해 혼잡을 미리 예측하여 윈도우 크기를 조절하는 혼잡 제어 알고리즘을 사용한다. UDT는 높은 대역폭과 큰 RTT 환경에서 대용량 데이터를 전송하기 위해 제공된 응용 기반의 전송 프로토콜이다. 본 논문에서는 UDT에 혼잡예측 알고리즘을 적용한 새로운 UDT의 혼잡제어 알고리즘을 제안한다. 혼잡예측을 통해 혼잡한 구간, 혼잡하지 않은 구간을 나누어 혼잡윈도우를 갱신한다. 혼잡하지 않은 구간에서 혼잡윈도우를 증가시키고 혼잡한 구간에서 혼잡윈도우를 감소시킴으로써 기존의 UDT보다 성능이 개선되었음을 확인 할 수 있다.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.04a
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• pp.717-720
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• 2011

고속 네트워크 환경에서 AR UDT(Adaptive Rate control UDT)는 표준 전송 프로토콜인 TCP에 비해 뛰어난 성능을 보인다. UDT(UDP-based Data Transfer)를 기반으로 하는 AR UDT의 혼잡제어는 네트워크 상태를 예측하여 패킷 간 전송시간을 변화시킴으로써 기존 UDT보다 향상된 성능을 보인다. 그러나 AR UDT는 네트워크 상태 예측의 오차가 클 뿐만 아니라 rate control만을 공격적으로 조절하기 때문에 수신 버퍼의 초과로 인해 안정적인 성능을 기대하기 어렵다. 본 논문에서는 AR UDT환경에서 네트워크 상태에 따라 적응적으로 혼잡제어를 하는 기법을 제안한다. RTT(Round Trip Time)의 변화량에 따라 네트워크 상태를 예측하여 flow control과 rate control을 적응적으로 조절한다. 네트워크 시뮬레이션 결과를 통하여 AR UDT에 비해 전송속도와 안정성이 향상되었음을 보였다.

• The KIPS Transactions:PartC
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• v.9C no.4
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• pp.489-496
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• 2002

This study proposes a new polling algorithm allowing dynamic change in polling period based on line utilization prediction. Polling is the most important function in network monitoring, but excessive polling data causes rather serious congestion conditions of network when network is In congestion. Therefore, existing multiple polling algorithms decided network congestion or load of agent with previously performed polling Round Trip Time or line utilization, chanced polling period, and controlled polling traffic. But, this algorithm is to change the polling period based on the previous polling and does not reflect network conditions in the current time to be polled. A algorithm proposed in this study is to predict whether polling traffic exceeds threshold of line utilization on polling path based on the past data and to change the polling period with the prediction. In this study, utilization of each line configuring network was predicted with AR model and violation of threshold was presented in probability. In addition, suitability was evaluated by applying the proposed dynamic polling algorithm based on line utilization prediction to the actual network, reasonable level of threshold for line utilization and the violation probability of threshold were decided by experiment. Performance of this algorithm was maximized with these processes.

• The Transactions of the Korea Information Processing Society
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• v.6 no.1
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• pp.148-158
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• 1999

ABR traffic form ATM LAN is controlled through RM cell, and the interface function to public ATM network is necessary to provide ABR service efficiently. This paper presnets new interface architecture, which is based on "Projected Node" [6]. using AIPU(ABR Interface Proxy Unit) to support ABR traffic streams incoming from ATM LAN in the public ATM network. For the efficient interworking, the AIPU has designed for interworking functions with ERICA switch mechanism. Conventional ERICA switch mechanism specified in TM 4.0 is basically used for short distance comparative to public network, however AIPU adopts the novel control mechanism to cover logng roud trip time (RTT). To improve the problems and to provide a dynamic range of UCI(Update Count Interval), this paper proposes, a novel control scheme, DUCI ( Dynamic Update Count Interval. And the paper shows inefficiencies of ERICA mechanism with fixed UCI through the simulation results, and represents the performance enhancement of DUCI mechanism developed to adjust the update count interval dynamically.

• Journal of Korea Multimedia Society
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• v.19 no.12
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• pp.2014-2023
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• 2016

Web presence is one of the key issues for extensive deployment of Internet-of-Things (IoT). An obstacle to overcome for Web presence is relatively low computing power of IoT devices. In this paper, we present implementation of an IoT platform based on Constrained Application Protocol (CoAP) which is a web transfer protocol proposed by Internet Engineering Task Force (IETF) for the low performance IoT devices such as Wireless Sensor Network (WSN) nodes and micro-controllers. To qualify the performance of CoAP-based IoT system for such an application as smart grid, we designed a test platform consisting of Raspberry Pi2, Kmote WSN node and a desktop PC. Using open source softwares, CoAP was implemented on top of the platform. Leveraging the GET command defined at CoAP specification, performance of the system was measured in terms of round-trip time (RTT) from web application to the Kmote sensor node. To investigate abnormal cases among the test results, hop-by-hop delays were measured to analyze resulting data. The average response time of CoAP-based communication except the abnormal data was reduced by 23% smaller than the previous research result.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.649-652
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• 2015

Previous marking policy for the AF service of TCP traffic in the Diffserv network have no sufficient consideration on the effect of RTT and target rate. In this paper, in order to improve fairness Index by the effect RTT difference of TCP traffic, we propose the modified TSW3CDM(Time Sliding Window Three Color Dynamic Marker) based on average transfer rate estimation and the flow state. The proposed algorithm is dynamic marking policy that do allocate band width in proportion to transmission rate. To evaluate the performance of the proposed algorithm, We accomplished a computer simulation using NS-2. From simulation results, the proposed TSW3CDM algorithm improves fairness index by comparison with TSW3CM.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1674-1683
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• 2003

The performance of a packet data multiplexer with stop­and­wait ARQ protocols under Markovian interruption is considered in this work It is assumed that the input process, into the system is Poisson process, and that the output channel is divided into a series of time slots and a data packet can be transmitted in a slot time. In this system the round­trip propagation delay is defined to be the frame time. It is modeled that the output channel can be blocked by some Markevian interruption, whose state change between the blocking and non­-blocking states is given by Markov process. The overall system has been analyzed by constructing a relationship, taking the Markovian interruption into account, about the buffer behavior between the successive frames of slots. The validity of this analytical results has been verified by computer simulation.

• The Journal of the Korea Contents Association
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• v.9 no.8
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• pp.73-83
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• 2009

TCP(Transmission Control Protocol) is currently used connection-oriented protocol as a typical transport layer protocol in the Internet. However, it has deficiency not be able to communicate with other TCP entities when any link included in the path is down because of single-homing on single path. SCTP(Stream Control Transmission Protocol) suggested as the new transport layer protocol supports multi-homing feature, which provides several paths between source and destination. It can communicate with other SCTP entities using alternate path even when any link on the primary path is down. This paper aims to measure and analyze the multi-homing effect of SCTP over TCP in case of link-down using NS-2 simulator. We classify SCTP into $SCTP_{single-homing}$ and $SCTP_{multi-homing}$ because SCTP with single-homing can also be used like TCP. We measured throughput and bandwidth utilization varying link-down duration, bandwidth, and RTT(round trip time), Simulation results show that throughput of $SCTP_{multi-homing}$ is more than that of TCP by 18 % on average. It is also shown that $SCTP_{multi-homing}$ on varying RTT and bandwidth increases the throughput of TCP by 'l7% and 9% on average, respectively in the link-down environment. In above cases, more or less difference between $SCTP_{single-homing}$ and TCP on throughput and bandwidth utilization was found To summarize, multi-homing effect of SCTP over TCP on throughput is about 18 % on average in the link-down environment This experimental result can be used as the benchmark in order to estimate the multi-homing effect of SCTP over TCP when the link-down happens in the real Internet.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.11 no.2
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• pp.1-9
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• 2012

This study proposed a method to determine the number and location of bus information terminals (BIT), which is a device to provide passengers with bus arrival time at bus stops in a Bus Information System (BIS). In low-density area, it is not efficient to survey bus demands such as the number of passengers at all bus stops due to time and cost. This kind of a survey would, however, competently cover all bus stops if performed inside the bus. The number of riding-on and -off passengers is observed for every bus stop, and this data collection is repeated over all day. Data obtained from the survey are aggregated each bus stop. This study defines Utility Index (UI), an aggregate each bus stop. Bus stops are ranked according to UI and determined for a BIT within budget limitation. As a case study, a bus line in Jeju island, Korea, was dealt with. This case showed that the more aggregate the better data quality. This study is expected to contribute to solving a location problem of BITs in a BIS.