Browsing by Author "Wang, Chih-Chiang"

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CDNPatch: a cost-effective failover mechanism for hybrid CDN-P2P live streaming systems
(2016-11-25)
Wang, Chih-Chiang
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Lin, Ying-Dar
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資訊工程學系
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Department of Computer Science
Among the most well-established live media distribution technologies is content delivery network (CDN), which improves user-perceived quality of service by delivering content from proxy servers deployed at the Internet\'s edge. In recent years, CDN providers started to tap into their subscribers\' peer-to-peer (P2P) capacity to alleviate their server costs. Under the inherent peer dynamics, a major challenge of these hybrid CDN-P2P systems is to provide efficient failure recovery with good quality of service guarantees at a reduced server cost. In this work we propose a cost-effective failover solution named CDNPatch to address the aforementioned problem. CDNPatch enables peers to periodically precompute a few backup content suppliers by efficient information exchange and maintenance algorithms, and leverages auxiliary CDN servers and an economic server provisioning algorithm to reduce the chance of playback interruption occurring to peers. Our simulation results show that CDNPatch can mask the impact of peer dynamics of 3 real P2P systems, namely, SOPCast, PPStream, and PPTV, with 100% failure recovery success rate and a failure recovery time less than 1 second at a cost of small P2P communication overhead of less than 1 kilobits per second, while using only 10%, 21%, and 51%, respectively, of the pure CDN scheme\'s server consumption.
Cost minimization in placing service chains for virtualized network functions
(2020-03-01)
Wang, Chien Ting
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Lin, Ying-Dar
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Wang, Chih-Chiang
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Lai, Yuan-Cheng
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交大名義發表
Network function virtualization (NFV) places network functions onto the virtual machines (VMs) of physical machines (PMs) located in data centers. In practice, a data flow may pass through multiple network functions, which collectively form a service chain across multiple VMs residing on the same or different PMs. Given a set of service chains, network operators have two options for placing them: (a) minimizing the number of VMs and PMs so as to reduce the server rental cost or (b) placing VMs running network functions belonging to the same service chain on the same or nearby PMs so as to reduce the network delay. In determining the optimal service chain placement, operators face the problem of minimizing the server cost while still satisfying the end-to-end delay constraint. The present study proposes an optimization model to solve this problem using a nonlinear programming (NLP) approach. The proposed model is used to explore various operational problems in the service chain placement field. The results suggest that the optimal cost ratio for PMs with high, hybrid, and low capacity, respectively, is equal to 4:2:1. Meanwhile, the maximum operating utilization rate should be limited to 55% in order to minimize the rental cost. Regarding quality of service (QoS) relaxation, the server cost reduces by 20%, 30%, and 32% as the end-to-end delay constraint is relaxed from 40 to 60, 80, and 100 ms, respectively. For the server location, the cost decreases by 25% when the high-capacity PMs are decentralized rather than centralized. Finally, the cost reduces by 40% as the repetition rate in the service chain increases from 0 to 2. A heuristic algorithm, designated as common sub chain placement first (CPF), is proposed to solve the service chain placement problem for large-scale problems (eg, 256 PMs). It is shown that the proposed algorithm reduces the solution time by up to 86% compared with the NLP optimization model, with an accuracy reduction of just 8%.
Hierarchical CORD for NFV Datacenters: Resource Allocation with Cost-Latency Tradeoff
(2018-09-01)
Lin, Ying-Dar
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Wang, Chih-Chiang
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Huang, Chien-Ying
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Lai, Yuan-Cheng
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交大名義發表
Network Function Virtualization (NFV) allows datacenters to consolidate network appliance functions onto commodity servers and devices. Currently telecommunication carriers are re-architecting their central offices as NFV datacenters that, along with SDN, help network service providers to speed deployment and reduce cost. However, it is still unclear how a carrier network shall organize its NFV datacenter resources into a coherent service architecture to support global network functional demands. This work proposes a hierarchical NFV/SDN-integrated architecture in which datacenters are organized into a multi-tree overlay network to collaboratively process user traffic flows. The proposed architecture steers traffic to a nearby datacenter to optimize user-perceived service response time. Our experimental results reveal that the 3-tier architecture is favored over others as it strikes a good balance between centralized processing and edge computing, and the resource allocation should be decided based on traffic's source-destination attributes. Our results indicate that when most traffic flows within the same edge datacenter, the strategy whereby resources are concentrated at the carrier's bottom-tier datacenters is preferred, but when most traffic flows across a carrier network or across different carrier networks, a uniform distribution over the datacenters or over the tiers, respectively, stands out from others.
Modeling the well-edge proximity effect in highly scaled MOSFETs
(2006-11-01)
Sheu, Yi-Ming
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Su, Ke-Wei
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Tian, Shiyang
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Yang, Sheng-Jier
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Wang, Chih-Chiang
The well-edge proximity effect caused by ion scattering during implantation in highly scaled CMOS technology is explored from a physics and process perspective. Technology computer-aided design (TCAD) simulations together with silicon wafer experiments have been conducted to investigate the impact of this effect. The ion scattering model and TCAD simulations provided a physical understanding of how the internal changes of the MOSFETs are formed. A new compact model for SPICE is proposed using physics-based understanding and has been calibrated using experimental silicon test sets.
Reproducing subthreshold characteristics of metal-oxide-semiconductor field effect transistors under shallow trench isolation mechanical stress using a stress-dependent diffusion model
(2006-08-01)
Sheu, Yi-Ming
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Yang, Sheng-Jier
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Wang, Chih-Chiang
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Chang, Chih-Sheng
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Chen, Ming-Jer
N-channel metal-oxide-semiconductor field effect transistors (MOSFETs) with a lightly doped well exhibit subthreshold current versus voltage (I-V) characteristics that are sensitive to shallow trench isolation (STI) mechanical stress. Such striking dependencies offer the opportunity to validate a proposed two-dimensional (2D) process model that relates the impurity diffusion to the mechanical stress throughout the substrate. With the assistance of sophisticated process/device simulations, the model appears to satisfactorily reproduce subthreshold I-V characteristics for different active area lengths and different substrate biases. The stress-dependent point defect equilibrium concentration and diffusion model are also implemented to evaluate the stress effect on transient enhanced diffusion.
Toward Optimal Resource Allocation of Virtualized Network Functions for Hierarchical Datacenters
(2018-12-01)
Wang, Chih-Chiang
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Lin, Ying-Dar
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Wu, Jang-Jiin
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Lin, Po-Ching
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Hwang, Ren-Hung
Telecommunications service providers (TSPs) previously provided network functions to end users with dedicated hardware, but they are resorting to virtualized infrastructure for reducing costs and increasing flexibility in resource allocation. A representative case is the Central Office Re-architected as Datacenter (CORD) project from AT&T, which aims to deploy virtualized network functions (VNFs) to over 4000 central offices (COs) across the U.S. However, there is a wide spectrum of options for deploying VNFs over the COs, varying from highly distributed to highly centralized manners. The former benefits end users with short response time but has its inherent limitation on utilizing geographically dispersed resources, while the latter allows resources to be better utilized at a cost of longer response time. In this work, we model the TSP's virtualized infrastructure as hierarchical datacenters, namely hierarchical CORD, and provide a resource allocation solution to strike the optimal balance between the two extreme options. Our evaluations reveal that in general, the 3-tier architecture incurs the least cost in case of deploying VNFs under moderate or loose delay constraints. Furthermore, the margin of improvement on the resource allocation cost increases inversely with the overall system utilization rate. Our results also suggest that as heavy request load overwhelms the network infrastructure, the relevant VNFs shall be migrated to lower-tier edge datacenters or to some nearby datacenters with superior network capacity. The evaluations also demonstrate that the proposed model allows highly adaptive VNF deployment in the hierarchical architecture under various conditions.
Two-tier project and job scheduling for SaaS cloud service providers
(2015-06-01)
Lin, Ying-Dar
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Thai, Minh-Tuan
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Wang, Chih-Chiang
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Lai, Yuan-Cheng
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資訊工程學系
This study addresses a two-tier job scheduling problem for SaaS cloud Service providers which rely on resources leased from laaS cloud providers to achieve elasticity to computational power. In our model, a project represents a user request which consists of multiple jobs; the SaaS is obligated to complete projects using multiple resources leased from IaaS or PaaS providers. The goals are to reduce the project turn-around time and to support priority scheduling by employing suitable scheduling algorithms. We propose a set of two-tier backfilling algorithms which extend the well-known conservative backfilling algorithm with project slack-time and priority concepts. Among the proposed algorithms, Two-Tier Strict Backfilling (2TSB) does not allow preemption in job waiting queues. On the other hand, preemption is allowable in Two-tier Flexible Backfilling which has two versions: 2TFB and 2TFB-SF (slack factor). In 2TFB, a new incoming project can preempt waiting jobs but not waiting projects, while 2TFB-SF permits preemption in both job and project waiting queues. Two-Tier Priority Backfilling (2TPB) algorithm takes priority into account such that only high-priority projects can preempt the low-priority ones. The experimental results indicate that, compared with 2TSB, 2TPB could reduce the mean turn-around time of high-priority projects by more than 25%. (C) 2015 Elsevier Ltd. All rights reserved.