Browsing by Author "Chang, Je-Wei"

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CROP: Community-Relevance-Based Opportunistic Routing in Delay Tolerant Networks
(2014-09-01)
Chang, Je-Wei
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Chen, Chien
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交大名義發表
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資訊工程學系
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資訊技術服務中心
Researchers have developed several social-based routing protocols for delay tolerant networks (DTNs) over the past few years. Two main routing metrics to support social-based routing in DTNs are centrality and similarity metrics. These two metrics help packets decide how to travel through the network to achieve short delay or low drop rate. This study presents a new routing scheme called Community-Relevance based Opportunistic routing (CROP). CROP uses a different message forwarding approach in DTNs by combining community structure with a new centrality metric called community relevance. One fundamental change in this approach is that community relevance values do not represent the importance of communities themselves. Instead, they are computed for each community-community relationship individually, which means that the level of importance of one community depends on the packet\'s destination community. The study also compares CROP with other routing algorithms such as BubbleRap and SimBet. Simulation results show that CROP achieves an average delivery ratio improvement of at least 30% and can distribute packets more fairly within the network.
CROP: Community-Relevance-Based Opportunistic Routing in Delay Tolerant Networks
(2013)
Chang, Je-Wei
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Chen, Chien
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資訊工程學系
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Department of Computer Science
Researchers have developed several social-based routing protocols for delay tolerant networks (DTNs) over the past few years. Two main routing metrics to support a social-based routing in DTNs are centrality and similarity metrics. These two metrics help packets decide how to travel through the network to achieve a low delay or low drop rate. This study presents a new routing scheme called Community-Relevance based OPportunistic routing (CROP). CROP uses a different message forwarding approach in DTNs by combining community structure with a new centrality metric called community relevance. One fundamental change in this approach is that community relevance values do not represent the importance of communities themselves. Instead, they are computed for each community-community relationship individually which means that the level of importance of one community varies depending on the packet's destination community. This study compares CROP with other routing algorithms such as BubbleRap and SimBet. Simulation results show that CROP achieves an average delivery ratio improvement of at least 30% and can distribute packets more fairly within the network.
Distortion-based Video Streaming over Vehicular Ad Hoc Networks in Highway
(2014-01-01)
Chang, Je-Wei
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Sun, Kuan-Yu
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Chen, Chien
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Jeng, Andy An-Kai
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資訊工程學系
There are already many routing protocols tailored for Vehicular Ad Hoc Networks (VANET). However, few of them are suitable for real-time video streaming delivery. The network partition nature and dynamic changing network topology of VANET make it hard for existing protocols to satisfy the stringent delay requirements of video streaming or other multimedia applications. To address this issue, this study first develops a rate distortion model based on a shadowing model and 802.11 DCF with RTS/CTS scheme over a highway road segment. Based on the proposed rate distortion model and traffic statistic information (vehicle density over a road), we can decide the best next-hop forwarding distance. Since a vehicle may not have a neighbor vehicle at the best forwarding distance, this study proposes a cell based packet forwarding scheme based on the derived best forwarding distance to prioritize the neighboring vehicles of a sender We set up the simulations using NS2 to validate the performance of the proposed protocol. The results show that the proposed protocol can yield a 30% PSNR improvement.
Elephant Flow Detection in Datacenters Using OpenFlow-based Hierarchical Statistics Pulling
(2014)
Lin, Chun-Yu
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Chen, Chien
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Chang, Je-Wei
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Chu, Yu Huang
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資訊工程學系
This paper proposes an effective elephant flow detection in datacenters. Equal Cost MultiPath (ECMP) is a popular routing mechanism to achieve load balancing in datacenter networks. However, ECMP only considers equally distributing the flows over equal-length paths, but does not take the size of the flows into account. Previous studies show that detecting and rerouting elephant flows (flows that transfer significant amount of data) effectively can lead to a 113% improvement in aggregate throughput compared with the simple use of ECMP. A naive way to detect the elephant flows is to pull statistics from each flow independently. Since "the elephant and mouse phenomenon" suggests that there are only very few elephant flows in a datacenter network, it\'s not efficient to collect information from each flow. Therefore, we propose a Hierarchical Statistics Pulling (HSP) mechanism using OpenFlow protocol to save bandwidth consumption and processing time. In order to further improve the performance of HSP, two supplement functions called elephant store and range splitting are developed. Our approaches can detect elephant flows with only a small amount of network bandwidth consumption. We use Mininet emulator and mathematical analysis to verify our methods. Both of them confirm the benefits of our approaches.
Maximum Multicommodity Flow of Small-World Networks
(2008)
Chang, Je-Wei
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Chen, Chien
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Jan, Rong-Hong
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資訊工程學系
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Department of Computer Science
This study investigates the capacity of small-world networks that are formulated as acquiring the Maximum Multicommodity Flows (MMF). The minimum multicut provides the upper bound of the MMF. Therefore, a heuristic algorithm, named Ring Lattice Min Multicut (RLMM) algorithm, is first designed to compare the capacity of Regular Ring Lattice Networks (RRLNs) and Small-world Ring Lattice Networks (SRLNs) constructed by rewiring the edges of the RRLNs with a certain probability. The rewired edges are considered shortcuts. Then, the asymptotic analysis is adopted to predict the capacity of SRLNs. Finally, the simulation results show that the MMF of the SRLNs has a capacity that is 10-50% greater than that of the RRLNs, and the capacity on the shortcut affects the MMF dramatically.
Network-aware Service Function Chaining Placement in a Data Center
(2016)
Hsieh, Cheng-Husan
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Chang, Je-Wei
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Chen, Chien
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Lug, Ssu-Hsuan
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資訊工程學系
Network function virtualization (NFV) has drawn much attention in recent years, where some network functions that used to be deployed on specific hardware have become virtualized instances on general servers to achieve more scalability and flexibility. In a data center, service function chaining (SFC) makes a workflow traverse different network functions in a specific order to provide different levels of service for its customer. Because the distance between any adjacent network functions in a service chain will decide the total bandwidth consumption for that chain, the placement of the virtualized network functions in a data center becomes an important problem. In this study, this placement problem is treated as a multi-layer bin packing problem. Two greedy algorithms are proposed for the treelike network topology: Multi-layer Worst-Fit (MWF) and Multi-layer Best Fit (MBF). Furthermore, the placement problem is formulated as an integer linear programming. The experimental results show that MWF can reduce bandwidth consumption by 15% while only increasing the number of used servers by 1% compared to the traditional Best-fit algorithm.
Shortest Path Routing with Reliability Requirement in Delay Tolerant Networks
(2009)
Lian, Huai-En
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Chen, Chien
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Chang, Je-Wei
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Shen, Chien-Chung
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Jan, Rong-Hong
The topology of a delay tolerant network (DTN) over time has been modeled by a space-time graph. However, the mobility of nodes, such as buses, may not be completely predictable due to factors such as traffic load, road condition, the number of passengers getting on and off the buses, and the operations of traffic lights. In this paper, we adapt the space-time graph by augmenting each horizontal edge with a direct contact probability to model the uncertainty of connectivity. With such an augmented space-time graph, our goal is to compute a shortest routing path satisfying a given end-to-end delivery reliability in a DTN. To facilitate such computation, we adapt the Floyd-Warshall algorithm to compute the maximum contact probability matrix at each time interval. By using an iterative matrix multiplication scheme on a maximum contact matrix, we can compute the shortest path satisfying the reliability constraint. Simulation results validate the performance of our solution which achieves a good balance between delay and reliability.
Wafer Scale Phase-Engineered 1T-and 2H-MoSe2/Mo Core-Shell 3D-Hierarchical Nanostructures toward Efficient Electrocatalytic Hydrogen Evolution Reaction
(2016-11-23)
Qu, Yindong
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Medina, Henry
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Wang, Sheng-Wen
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Wang, Yi-Chung
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Chen, Chia-Wei
The necessity for new sources for greener and cleaner energy production to replace the existing ones has been increasingly growing in recent years. Of those new sources, the hydrogen evolution reaction has a large potential. In this work, for the first time, MoSe2/Mo core-shell 3D-hierarchical nanostructures are created, which are derived from the Mo 3D-hierarchical nanostructures through a low-temperature plasma-assisted selenization process with controlled shapes grown by a glancing angle deposition system.