• Journal of the Korea Society of Computer and Information
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• v.13 no.1
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• pp.175-183
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• 2008

QoS-support technology in networks is based on measuring QoS metrics which reflect a magnitude of stability and performance. The one-way delay measurement of the QoS metrics especially requires a guarantee of clock synchronization between end-to-end hosts. However, the hosts in networks have a relative or absolute difference in clock time by reason of clock offsets. flock skews and clock adjustments. In this paper, we present a theorem, methods and simulation results of one-way delay and clock offset estimations between end-to-end hosts. The proposed theorem is a relationship between one-way delay, one-way delay variation and round-trip time And we show that the estimation error is mathematically smaller than a quarter of round-trip time.

• Journal of KIISE:Information Networking
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• v.32 no.3
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• pp.359-369
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• 2005

Delay estimation is a difficult Problem in computer networks. Accurate one-way delay estimation is crucial because it serves a very important role in network performance and thus application design. RTT(Round Trip Time) is often used as an approximation of the delay, but because it is a sum of the forward and reverse delays, the actual one-way delay cannot be estimated accurately from RTT. To estimate one-way delay accurately, this paper proposes a new scheme that analytically derives one-way delay, forward and reverse delay respectively. We show that the performance of TCP can improve dramatically in asymmetric networks using our scheme. A key contribution of this paper is that our one-way deiay estimation is much more accurate than RTT estimation so that TCP can quickly find the network capacity in the slow start phase. Since RTT is the sum of the forward and reverse delays, our scheme can be applied to any protocol that is based on RTT.

• ETRI Journal
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• v.32 no.6
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• pp.854-862
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• 2010

One-way delay variation (OWDV) has become increasingly of interest to researchers as a way to evaluate network state and service quality, especially for real-time and streaming services such as voice-over-Internet-protocol (VoIP) and video. Many schemes for OWDV measurement require clock synchronization through the global-positioning system (GPS) or network time protocol. In clock-synchronized approaches, the accuracy of OWDV measurement depends on the accuracy of the clock synchronization. GPS provides highly accurate clock synchronization. However, the deployment of GPS on legacy network equipment might be slow and costly. This paper proposes a method for measuring OWDV that dispenses with clock synchronization. The clock synchronization problem is mainly caused by clock skew. The proposed approach is based on the measurement of inter-packet delay and accumulated OWDV. This paper shows the performance of the proposed scheme via simulations and through experiments in a VoIP network. The presented simulation and measurement results indicate that clock skew can be efficiently measured and removed and that OWDV can be measured without requiring clock synchronization.

• Journal of KIISE:Information Networking
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• v.34 no.2
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• pp.100-109
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• 2007

Streaming protocol with the Available Bandwidth measurement scheme has problems that are to measure a Available Bandwidth uncorrectly and slowly. In this basis, in order to overcome limitations of the previous streaming protocols, we propose the NABO that is a New Available Bandwidth measurement scheme used by OWD(One-Way Delay). Proposed NABO(New Available Bandwidth measurement based on OWD) measures the constant transmission delay occurred by bottleneck link capacity and the variable delay. Competing traffic contribute to the variable delay. Through the measurement of the constant transmission delay and the competing traffic, a NABO can measure the Available Bandwidth correctly and fast in network. The simulation result proves that the proposed NABO has a performance that satisfies both accuracy viewpoint and measurement speed viewpoint.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.5
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• pp.16-24
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• 2007

Wireless mesh network extends the limited coverage of conventional wireless service from one-hop access point to wider area. It is recognized as an important issue to provide seamless handoff in the wide coverage of wireless mesh network. A long handoff delay may cause high packet loss and disconnection of service, degrading the network performance. The handoff delay is mainly introduced from the channel scanning process obtaining information to make handoff decision and the unnecessary handoffs due to inaccurate handoff decision. In this paper, we propose the handoff algorithm based on one-way trip time (OTT) to expedite the handoff procedure. As compared to the handoff algorithm based on the receiving signal power, the proposed algorithm takes advantage of OTT to obtain the necessary handoff information in a relatively shorter time and reduce the unnecessary handoffs. The performance of proposed algorithm is evaluated through the simulations. It is verified that the proposed handoff algorithm can effectively enhance the handoff accuracy, and therefore reduce the handoff delay and unnecessary handoffs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11B
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• pp.969-978
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• 2006

Recently, there has been explosive growth in Internet service contents, and we have witnessed the emergence of many real-time applications on the Internet. These types of applications require special support from the underlying network such as reliability, timeless, and guaranteed delivery, as well as different levels of service quality. Estimation network status and transcoding data rate are researching for QoS of multimedia service by using the RTP/RTCP. We propose two schemes that the way to calculate the one-way delay by expanding the structure of RTP/RTCP in Internet that provides us 'best effort' service and to estimate the network condition by using this in this paper. And we propose the dynamic RTCP mechanism based on one-way delay to deal with rapidly changed network situation immediately. In simulation, proposed monitoring schemes using the one-way delay has similar in performance to monitoring schemes using the GPS, proposed dynamic RTCP scheme obtain the desired result of decreased packet loss rate by sending RTCP RR packet lower than other schemes.

• Journal of Communications and Networks
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• v.15 no.4
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• pp.430-438
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• 2013

This paper addresses the issue of throughput-delay of one-to-many wireless multi-hop flows based on random linear network coding (RLNC). Existing research results have been focusing on the single-hop model which is not suitable for wireless multi-hop networks. In addition, the conditions of related system model are too idealistic. To address these limitations, we herein investigate the performance of a wireless multi-hop network, focusing on the one-to-many flows. Firstly, a system model with multi-hop delay was constructed; secondly, the transmission schemes of system model were gradually improved in terms of practical conditions such as limited queue length and asynchronous forwarding way; thirdly, the mean delay and the mean throughput were quantified in terms of coding window size K and number of destination nodes N for the wireless multi-hop transmission. Our findings show a clear relationship between the multi-hop transmission performance and the network coding parameters. This study results will contribute significantly to the evaluation and the optimization of network coding method.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.502-504
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• 2005

TFRC는 전송률 산출을 위해 Loss Rate와 RTT정보를 TCP-equation에 적용한다. 그러나 무선망과 같이 지연 변화가 큰 환경의 경우 RTT 값이 정확한 망상황을 표현한다고 할 수 없다. 모바일 단말의 경우 움직임에 따라 지연정보는 계속 변화하게 되며 순방향, 역방향 지연정보간의 차이도 발생하게 된다. 본 논문에서는 지연 변화가 큰 환경에 맞는 지연정보인 One-way Delay를 사용하여 TFRC의 전송률 예측방법을 개선한다. One-way Delay 정보를 이용하여 Average Weighting을 거쳐 TCP-equation에 적용하여 전송률을 산출함으로써 정확한 Bandwidth의 예측이 가능함을 시뮬레이션을 통해 나타낸다.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.10 no.2
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• pp.74-79
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• 2011

The goal of this research is to reduce dynamic and static power consumption for a low power cache system. The proposed cache can achieve a low power consumption by using a drowsy and a way prediction mechanism. For reducing the static power, the drowsy technique is used at 4-way set associative cache. And for reducing the dynamic energy, one among four ways is selectively accessed on the basis of information in the Way-Line Prediction Unit (WLPU). This prediction mechanism does not introduce any additional delay though prediction misses are occurred. The WLPU can effectively reduce the performance overhead of the conventional drowsy caching by waking only a drowsy cache line and one way in advance. Our results show that the proposed cache can reduce the power consumption by about 40% compared with the 4-way drowsy cache.

• International Journal of Highway Engineering
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• v.18 no.3
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• pp.95-107
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• 2016

PURPOSES : This study compared two measures of traffic flow effectiveness on roads with roundabouts and signalized intersections and determined the more appropriate measure. METHODS : In addition to average delay time, the conventionally used measure, average travel time was introduced to measure traffic flow effectiveness because it is able to be obtained through field survey and reflect different travel distances and speed limits of roundabouts and signalized intersections. Using the two measures, roundabouts and signalized intersections were compared through simulations in terms of traffic flow effectiveness. RESULTS : For one-way single-lane roads, the two measures indicated consistent results that roundabouts were more effective than were signalized intersections when the traffic volume was less than 300 vphpl but vice versa when it exceeded 450 vphpl; however, the measures yielded inconsistent results when the volume was 350~400 vphpl. For one-way double-lane roads, the two measures indicated consistent results that roundabouts were more effective than were signalized intersections when the volume was less than 200 vphpl but vice versa when it exceeded 400 vphpl; however, the measures yielded inconsistent results when the volume was 250~350 vphpl. The results obtained using the two measures differed substantially for double-lane roads because behaviors such as weaving and lane changing at roundabouts are more common in double-lane roads than in single-lane roads. CONCLUSIONS : The average delay time would be lower on roads with roundabouts, but average travel time would be lower on roads with signalized intersections. Thus, evaluating the relative effectiveness of roads with roundabouts and signalized intersections by using average delay time alone would be inappropriate, whereas using average travel time as the evaluation index would yield fairer results.