Browsing by Author "Lin, TH"

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An efficient load balancing strategy for scalable WAP gateways
(2002)
Lin, TH
;
Wang, KC
;
資訊工程學系
;
Department of Computer Science
In this paper we propose a load balancing strategy that has the following features: (1)estimating the potential load of real gateways with low computation and no communication overhead, (2) asynchronous alarm sent when the utilization of a real gateway exceeds a critical threshold, and (3) WAP-awareness. We also propose a scalable WAP gateway (SWG) that consists of a WAP dispatcher and a cluster of real gateways. The WAP dispatcher is a front-end distributor with our load balancing strategy. To prevent the WAP dispatcher from becoming a bottleneck, the WAP dispatcher distributes mobile clients' requests in kernel space and does not process outgoing gateway-to-client responses. Experimental results show that our SWG has better load balancing performance, throughput, and delay compared to the LVS and the Kannel gateway. Although WAP services are not so popular as expected, our load balancing strategy can be easily adapted to other distributed services.
An efficient load balancing strategy for scalable WAP gateways
(2005-06-02)
Lin, TH
;
Wang, KC
;
Liu, AY
;
資訊工程學系
;
Department of Computer Science
Clustering provides a promising way to build a scalable, reliable, and high-performance WAP gateway architecture. However, this requires an efficient load balancing mechanism for assigning a request to a suitable gateway in the cluster, that can offer the best service. In addition, unpredictable connection time and nonuniformity of incoming load from different mobile clients are big obstacles to load balancing among real gateways. In this paper, we propose a load balancing strategy that has the following features: (1) estimating the potential load of real gateways with small computation time and no communication overhead, (2) asynchronous alarm sent when the utilization of a real gateway exceeds a critical threshold, and (3) WAP-awareness. We also propose a scalable WAP gateway (SWG) architecture that consists of a WAP dispatcher and a cluster of real gateways. The WAP dispatcher is a front-end distributor with our load balancing strategy. To prevent the WAP dispatcher from becoming a bottleneck, the WAP dispatcher distributes mobile clients' requests in kernel space and does not process outgoing gateway-to-client responses. Experiment results show that our SWG has better load balancing performance, throughput, and delay compared to the LVS and the Kannel gateway. (C) 2004 Elsevier B.V. All rights reserved.
An examination of the wind-driven effect on the drift of precipitation particles using the Chung-Li VHF radar
(1997-05-01)
Chu, YH
;
Chen, TY
;
Lin, TH
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
One of the essential assumptions made in estimating the terminal velocity and the drop-size distribution of hydrometeor from the precipitation Doppler spectrum observed by VHF/UHF radar (or wind profiler) is that all of the precipitation particles are moving together at the same velocity as the ambient wind. However, this may not be the case. In this paper, taking advantage of the capability of simultaneously measuring the motions of precipitation particles and the clear-air turbulence with a VHF radar, we develop a method to examine the wind-driven effect on the drift of precipitation particles using the Chung-Li VHF radar. By appropriately setting the radar parameters and steering the radar beams, experimental results show that the drift velocity of the precipitation particles in response to the drag force exerted by the background atmosphere is not the same as the ambient wind velocity, approximately 83% of the latter in this case. This feature indicates that the precipitation particles are not moving with the background wind, causing inaccurate estimations of the terminal velocity and the drop-size distribution of hydrometeor if this effect is not taken into account.
An examination of the wind-driven effect on the drift of precipitation particles using the Chung-Li VHF radar
(1997-05-01)
Chu, YH
;
Chen, TY
;
Lin, TH
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
One of the essential assumptions made in estimating the terminal velocity and the drop-size distribution of hydrometeor from the precipitation Doppler spectrum observed by VHF/UHF radar (or wind profiler) is that all of the precipitation particles are moving together at the same velocity as the ambient wind. However, this may not be the case. In this paper, taking advantage of the capability of simultaneously measuring the motions of precipitation particles and the clear-air turbulence with a VHF radar, we develop a method to examine the wind-driven effect on the drift of precipitation particles using the Chung-Li VHF radar. By appropriately setting the radar parameters and steering the radar beams, experimental results show that the drift velocity of the precipitation particles in response to the drag force exerted by the background atmosphere is not the same as the ambient wind velocity, approximately 83% of the latter in this case. This feature indicates that the precipitation particles are not moving with the background wind, causing inaccurate estimations of the terminal velocity and the drop-size distribution of hydrometeor if this effect is not taken into account.
Influence of two-dimensional gas phase radiation on downward flame spread
(1999)
Lin, TH
;
Chen, CH
;
機械工程學系
;
Department of Mechanical Engineering
This work investigates how radiation heat transfer influences downward flame spread by presenting a gas phase radiation model, described by a two dimensional P-1 approximation method, to incorporate with the combustion model of Duh and Chen (1991). The parametric study is based on the variation of gravity, which changes the Damkohler number (Da) and radiation to conduction parameter (1/N-infinity) simultaneously. Comparing the results with the previous studies of Duh and Chen (1991) and Chen and Cheng (1994), which only considered the radiation effect in cross stream direction, the role of stream-wise radiation was identified. The stream-wise radiation contributes to reinforce the forward heat transfer rate subsequently increasing the flame spread rate. However, this model also provides more directional radiation loss than that of Chen and Cheng (1994) and, in doing so, draws more energy out from the flame to further reduce its strength. The results indicates that the effect of heat loss is greater than that of enhancing the upstream heat transfer since the flame spread rate in the present model is always lower than the one predicted by Duh and Chen (1991). Finally, a contour of the Planck mean absorption coefficient distribution is illustrated to demonstrate the effectiveness of gas radiation distribution. It reveals that the strongest radiation occurs near the pyrolyzing surface and the other significant one is in the plume region. A comparisons with available experimental data also given to evaluate the ability of predict in the present combustion model.