Browsing by Author "Chan, YC"

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A TCP-friendly stateless AQM scheme for fair bandwidth allocation
(2005)
Ho, CY
;
Chan, YC
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
Queue management, bandwidth share, and congestion control are very important to both robustness and fairness of the Internet. In this article, we investigate the problem of providing a fair bandwidth allocation to those flows that share congested link in a router A new TCP-friendly router-based AQM (active queue management) scheme, termed WARD, is proposed to approximate the fair queueing policy. WARD is a simple packet dropping algorithm with a random mechanism, and discriminates against the flows which transmit more packets than allowed. By doing this, it not only protects TCP connections from UDP flows, but also solves the problem of competing bandwidth among different TCP versions such as TCP Vegas and Reno. In addition, WARD works quite well for TCP flow isolation even with different round trip times. In other words, WARD improves the unfair bandwidth allocation properties. Furthermore, it is stateless and easy to implement, so WARD controls unresponsive or misbehaving flows with a minimum overhead.
An aided congestion avoidance mechanism for TCP Vegas
(2005-01-01)
Ho, CY
;
Shih, CH
;
Chen, YC
;
Chan, YC
;
資訊工程學系
TCP Vegas detects network congestion in the early stage and successfully prevents periodic packet loss that usually occurs in TCP Reno. It has been demonstrated that TCP Vegas achieves much higher performance than TCP Reno in many aspects. However, TCP Vegas cannot prevent unnecessary throughput degradation when congestion occurs in the backward path, it passes through multiple congested links, or it reroutes through a path with longer round-trip time (RTT). In this paper, we propose an aided congestion avoidance mechanism for TCP Vegas, called Aid-Vegas, which uses the relative one-way delay of each packet along the forward path to distinguish whether congestion occurs or not. Through the results of simulation, we demonstrate that Aid-Vegas can solve the problems of rerouting and backward congestion, enhance the fairness among the competitive connections, and improve the throughput when multiple congested links are encountered.
An aided congestion avoidance mechanism for TCP Vegas
(2005-01-01)
Ho, CY
;
Shih, CH
;
Chen, YC
;
Chan, YC
;
交大名義發表
TCP Vegas detects network congestion in the early stage and successfully prevents periodic packet loss that usually occurs in TCP Reno. It has been demonstrated that TCP Vegas achieves much higher performance than TCP Reno in many aspects. However, TCP Vegas cannot prevent unnecessary throughput degradation when congestion occurs in the backward path, it passes through multiple congested links, or it reroutes through a path with longer round-trip time (RTT). In this paper, we propose an aided congestion avoidance mechanism for TCP Vegas, called Aid-Vegas, which uses the relative one-way delay of each packet along the forward path to distinguish whether congestion occurs or not. Through the results of simulation, we demonstrate that Aid-Vegas can solve the problems of rerouting and backward congestion, enhance the fairness among the competitive connections, and improve the throughput when multiple congested links are encountered.
An efficient mechanism of TCP-Vegas on mobile IP networks
(2005)
Ho, CY
;
Chan, YC
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
Mobile IP network provides hosts the connectivity to the Internet while changing locations. However, when using TCP Vegas over a mobile network, it may respond to a handoff by invoking a congestion control algorithm, thereby resulting in performance degradation, because TCP Vegas is sensitive to the change of RTT (Round-Trip Time) and it may recognize the increased RTT as a result of network congestion. Since TCP Vegas could not differentiate whether the increased RTT is due to route change or network congestion. This work investigates how to improve the performance of Vegas after a Mobile IP handoff and proposes a variation of TCP Vegas, so-called Demo-Vegas, which is able to detect the movement of two end-hosts of a connection, and re-measure the BaseRTT (Minimum Round-Trip Time) if necessary. The proposed mechanism maintains end-to-end semantics, and operates under the existing network infrastructure. Demo-Vegas presents a simple modification in the two end sides of a connection and uses one reserved bit in TCP header. Simulation results demonstrate that Demo-Vegas features higher performance than Vegas in Mobile IP networks.
An enhanced congestion avoidance mechanism for TCP vegas
(2003-07-01)
Chan, YC
;
Chan, CT
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
TCP Vegas detects network congestion in the early stage and successfully prevents periodic packet loss that usually occurs in traditional schemes. It has been demonstrated that TCP Vegas achieves much higher throughput than TCP Reno. However, TCP Vegas cannot prevent unnecessary throughput degradation when congestion occurs in the backward path. In this letter, we propose an enhanced congestion avoidance mechanism for TCP Vegas. By distinguishing whether congestion occurs in the forward path or not, it significantly improves the connection throughput when the backward path is congested.
An enhanced slow-start mechanism for TCP Vegas
(2005)
Ho, CY
;
Chan, YC
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
In this article, we present a new slow-start variant, which improves the throughput of TCP Vegas, we call this new mechanism Gallop-Vegas which quickly ramps up to the available bandwidth and reduces the burstiness during the slow-start phase. Since TCP (Transmission Control Protocol) is known to send bursts of packets during its slow-start phase due to the fast increase of window size and the ACK-clock based transmission. This phenomenon causes TCP Vegas to change from slow-start phase to congestion-avoidance phase too early in the large BDP (bandwidth-delay product) links. Therefore, in Gallop-Vegas, we increase the congestion window size with a rate between exponential growth and linear growth during slow-start phase. Our extensive simulation results show that GallopVegas significantly improves the performance during the slow-start phase. Furthermore, it is implementation feasible because only sending part needs to be modified.
Design and performance evaluation of an improved TCP congestion avoidance scheme
(2004-02-01)
Chan, YC
;
Chan, CT
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
TCP Vegas detects network congestion in its early stage and successfully prevents the periodic packet loss that usually occurs in traditional schemes. It has been demonstrated that TCP Vegas achieves a much higher throughput than TCP Reno. However, TCP Vegas cannot prevent unnecessary throughput degradation when congestion occurs on the backward path. A router-based congestion avoidance scheme for TCP Vegas is proposed. By distinguishing whether or not congestion occurs in the forward path, it significantly improves the connection throughput when the backward path is congested.
Direct oxidation of Si1-xGex layers using Vacuum-Ultra-Violet light radiation in oxygen
(1998-02-01)
Chen, LP
;
Chan, YC
;
Chang, SJ
;
Huang, GW
;
Chang, CY
Oxidation of Si1-xGex films has been carried out by direct photo chemical Vapor deposition (direct photo-CVD) directly with activated O-2 induced by Vacuum-Ultra-Violet (VUV) light radiation, The Auger electron spectroscopy profiles show that no Ge-pileup layer at the oxide/Si1-xGex interface is observed after VUV-induced Si1-xGex oxidation process. The X-ray photoelectron spectroscopy analysis of the samples reveals that Si and Ge are oxidized simultaneously in oxidation process and a mixed oxide layer consisting both SiO2 and GeO2 is formed, This might be the reason that Cc pileup effect is eliminated in this study.
Direct oxidation of Si1-xGex layers using Vacuum-Ultra-Violet light radiation in oxygen
(1998-02-01)
Chen, LP
;
Chan, YC
;
Chang, SJ
;
Huang, GW
;
Chang, CY
Oxidation of Si1-xGex films has been carried out by direct photo chemical Vapor deposition (direct photo-CVD) directly with activated O-2 induced by Vacuum-Ultra-Violet (VUV) light radiation, The Auger electron spectroscopy profiles show that no Ge-pileup layer at the oxide/Si1-xGex interface is observed after VUV-induced Si1-xGex oxidation process. The X-ray photoelectron spectroscopy analysis of the samples reveals that Si and Ge are oxidized simultaneously in oxidation process and a mixed oxide layer consisting both SiO2 and GeO2 is formed, This might be the reason that Cc pileup effect is eliminated in this study.
Intermediate inhibition in the heterogeneous UV-catalysis using a TiO2 suspension system
(2001-10-01)
Chan, YC
;
Chen, JN
;
Lu, MC
;
環境工程研究所
;
Institute of Environmental Engineering
Langmuir-Hinshelwood (L-H) kinetic expression was used to develop a basic mathematical model, which could describe the inhibition of intermediates in the photocatalysis of 2-chlorophenol (2-CP) in a suspended TiO2 system. Results showed that the photocatalytic oxidation of 2-chlorophenol followed the L-H type behavior and the reaction by-products displayed an inhibiting effect on the degradation rate. The inhibition was estimated by comparing to observed and estimated half-lives. The higher the initial concentration of 2-chlorophenol, the higher the inhibition of photocatalytic reaction. The L-H kinetic has been modified slightly in this study to rationalize the contrast of inhibited behavior and to improve in favor of a surface reaction. The concentrations of 2-chlorophenol were investigated ranging from 7.78 x 10(-5) to 7.78 x 10(-4) mol l(-1). The degradation of 2-chlorophenol in this reaction condition approximates a first-order kinetics to near-complete degradation. Calculated kinetic profiles are in an excellent agreement with the experimental observation. The results of the theoretical analysis can be used to estimate reaction rates in different initial concentrations of target compound. (C) 2001 Elsevier Science Ltd. All rights reserved.
Large earthquake-triggered landslides and mountain belt erosion: The Tsaoling case, Taiwan
(2005-09-01)
Chen, RF
;
Chan, YC
;
Angelier, J
;
Hu, JC
;
Huang, C
The 1999 Chi-Chi earthquake triggered the catastrophic Tsaoling landslide in central Taiwan. We mapped the landslide area and estimated the landslide volume, using high-resolution digital elevation model from airborne LiDAR (Light Detection and Ranging), satellite images, aerial photographs and topographic maps. The comparison between cut and fill volumes, about 0.126 and 0.150 km(3), respectively, suggests a volume increase of 19% due to decompaction during landsliding. In April 2002, the cut and fill volumes were about 0.137 and 0.116 km(3), respectively. These estimates suggest that 2.5 years after the event, the volume of landslide debris removed by river erosion was nearly 0.045 km(3). Such a large value highlights the importance of landslide processes for erosion and long-term denudation in the Taiwan mountain belt.
MBR/RO/ozone processes for TFT-LCD industrial wastewater treatment and recycling
(2005)
Chen, TK
;
Ni, CH
;
Chan, YC
;
Lu, MC
;
環境工程研究所
This research is mainly to explore the treatment capacity for TFT-LCD industrial wastewater recycling by the processes combined with membrane bioreactor (MBR), reverse osmosis (RO) and ozone(03). The organic wastewater from the TFT-LCD industry was selected as the target. MBR, RO and ozone plants were established for evaluation. An MBR plant consisted of a 2-stage anoxic/aerobic bioreactor and an immersed UF membrane unit was employed. The effluent of MBR was conducted into the RO system then into the ozone system. The RO system consisted of a spiral membrane in the vessel. One bubble column, 75 cm high and diameter 5 cm, were used as the ozonation reactor. On the bottom of ozonation reactor is a porous diffuser for releasing gas, with an aperture of 100 mu m (0.1 cm). Over the whole experimental period, the MBR process achieved a satisfactory organic removal. The COD could be removed with an average of over 98.5%. For the TOC item, the average removal efficiency was 97.4%. The stable effluent quality and satisfactory removal performance were ensured by the efficient interception performance of an immersed UF membrane device incorporated with the biological reactor. Moreover, the MBR effluent did not contain any suspended solids and the SDI value was under 3. After the treatment of RO, excellent water quality was found. The water quality of permeate was under 5 mg/l, 2 mg/l and 50 mu s/cm for COD, TOC and conductivity respectively. The treated water can be recycled and reused for the cooling tower make-up water or other purposes. After the treatment of ozone, the treated water quality was under 5 mg/l and 0.852 mg/l for COD and TOC respectively. The test results of MBR, MBR/RO and MBR/RO/ozone processes were compared as possible appropriate treatment technologies applied in TFT-LCD industrial wastewater reuse and recycling.
Performance improvement of congestion avoidance mechanism for TCP vegas
(2004)
Chan, YC
;
Chan, CT
;
Chen, YC
;
Ho, CY
;
資訊工程學系
In this paper we propose a router-based congestion avoidance mechanism (RoVegas) for TCP Vegas. TCP Vegas detects network congestion in the early stage and successfully prevents periodic packet loss that usually occurs in TCP Reno. It has been demonstrated that TCP Vegas outperforms TCP Reno in many aspects. However TCP Vegas suffers several problems that inhere in its congestion avoidance mechanism, these include issues of rerouting, persistent congestion, fairness, and network asymmetry. By performing the proposed scheme in routers along the round-trip path, RoVegas can solve the problems of rerouting and persistent congestion, enhance the fairness among the competitive connections, and improve the throughput when congestion occurs on the backward path. Through the results of both analysis and simulation, we demonstrate the effectiveness of RoVegas.
Performance improvement of TCP Vegas over heterogeneous networks
(2004)
Chan, YC
;
Chan, CT
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
Current IP network has become the dominant paradigm for all networking environments. The significant cause of packet losses in such heterogenous networks is no longer limited to network congestion. Traditional TCP interprets every packet loss as caused by congestion which may be not the case in the current Internet. Misinterpretation of wireless random loss as an indication of network congestion results in TCP slowing down its sending rate unnecessarily. In this paper we propose a new variant of TCP Vegas named RedVegas. By using the innate nature of Vegas and congestion indications marked by routers, RedVegas may detect random packet losses precisely. Through the packet loss differentiation, RedVegas reacts appropriately to the losses, and therefore the throughput of connection over heterogeneous networks can be significantly, improved.
Photocatalytic oxidation of chlorophenols in the presence of manganese ions
(1999)
Chen, JN
;
Chan, YC
;
Lu, MC
;
環境工程研究所
;
Institute of Environmental Engineering
The decomposition of chlorophenols in aqueous solution with UV-illuminated TiO2 suspensions in the presence of manganese ions was studied. It was found that the removal rare of chlorophenols would be the highest at pH 3 in the presence of 1.18x10(-4) M manganese ion. The effect of ionic strength on the 2-CP decomposition can be ignored in the range from 0.1 to 0.005 M for NaClO4. This study is also to explore the relationship between the adsorption rate and reaction rate. Results showed that the more the adsorption rate the more the decomposition rate for the three chlorophenols. Manganese ions can increase the photocatalytic oxidation of 2-chlorophenol in terms of DOC. The relationship between temperature and reaction rate for 2-CP is k = 0.0043 T - 1.2146. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.
RedVegas: Performance improvement of TCP Vegas over heterogeneous networks
(2004-07-01)
Chan, YC
;
Chan, CT
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
Current IP network has become the dominant paradigm for all networking environments. The significant cause of packet losses in such heterogenous networks is no longer limited to network congestion. Traditional TCP interprets every packet loss as caused by congestion which may be not the case in the current Internet. Misinterpretation of wireless random loss as an indication of network congestion results in TCP slowing down its sending rate unnecessarily. In this paper, we propose a new variant of TCP Vegas named RedVegas. By using the innate nature of Vegas and congestion indications marked by routers, RedVegas may detect random packet losses precisely. Through the packet loss differentiation, RedVegas reacts appropriately to the losses, and therefore the throughput of connection over heterogeneous networks can be significantly improved.
RoVegas: a router-based congestion avoidance mechanism for TCP Vegas
(2004-10-15)
Chan, YC
;
Chan, CT
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
Transmission control protocol (TCP) Vegas detects network congestion in the early stage and successfully prevents periodic packet loss that usually occurs in TCP Reno. It has been demonstrated that TCP Vegas outperforms TCP Reno in many aspects. However, TCP Vegas suffers several problems that inhere in its congestion avoidance mechanism, these include issues of rerouting, persistent congestion, fairness, and network asymmetry. In this paper, we propose a router-based congestion avoidance mechanism (RoVegas) for TCP Vegas. By performing the proposed scheme in routers along the round-trip path, RoVegas can solve the problems of rerouting and persistent congestion, enhance the fairness among the competitive connections, and improve the throughput when congestion occurs on the backward path. Through the results of both analysis and simulation, we demonstrate the elfectiveness of RoVegas. (C) 2004 Elsevier B.V. All rights reserved.
Smart window adjustment for XCP's congestion management
(2006)
Yang, YR
;
Chan, CT
;
Chen, YC
;
Chan, YC
;
資訊工程學系
In the large bandwidth-delay product (BDP) networks, it has been demonstrated that the eXplicit Control Protocol, XCP, outperforms TCP and remains efficient, fair, and stable. However, once a packet drop is detected, an XCP's congestion management should follow TCP's Van Jacobson congestion control. In other words, congestion window should be halved and the fast retransmission/fast recovery, congestion avoidance algorithms should be applied. In the mean time, congestion window should be reduced by the value of the negative feedback. In this article, we present a smart window adjustment scheme for XCP's congestion management to shorten the response time and improve network performance.