Browsing by Author "Yen, Li-Hsing"

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A Backbone-Aware Topology Formation (BATF) Scheme for ZigBee Wireless Sensor Networks
(2013-01-01)
Huang, Kuei-Li
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Yen, Li-Hsing
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Wang, Jui-Tang
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Wu, Chao-Nan
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Tseng, Chien-Chao
In a tree-structured ZigBee wireless sensor network, nodes close to the root of the tree (i.e., hot-spot nodes) may exhaust their power earlier than those distant from the root due to heavy loads on packet forwarding. This hot-spot problem is inherent in tree-structured networks and may demand extra energy to recover from failures of hot-spot nodes. In this paper, the backbone-aware topology formation (BATF) scheme is proposed to alleviate the hot-spot problem. BATF utilizes power-rich nodes to form a backbone tree that does not suffer from the hot-spot problem. Each power-rich node independently initiates a ZigBee tree network that attracts associations from ZigBee-compliant devices in order to distribute packet-forwarding loads over a larger set of nodes. Issues of BATF such as the partition of address space and ZigBee-compliant routing are discussed in detail. Simulation results confirm that BATF does alleviate the hot-spot problem as it improves network lifetime as well as data collection capability. Comparisons with native ZigBee protocols show that the improvement comes from our protocol design rather than simply introducing power-rich nodes.
A Cross-Layer Architecture for Service Continuity and Multipath Transmission in Heterogeneous Wireless Networks
(2013)
Chan, Min-Cheng
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Tseng, Chien-Chao
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Yen, Li-Hsing
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資訊工程學系
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Department of Computer Science
Mobile devices equipped with two or more interfaces can roam across heterogeneous networks. This feature enables the devices to maintain service continuity by performing vertical handovers and to increase transmission capability by exploiting multiple physical transmission paths. However, this type of service continuity is not yet commonly provided. Previous approaches toward the provision of service continuity are limited either in their functionalities or in the scope of cross-layer information. In this paper, we analyze how cross-layer architecture provides service continuity from a broader perspective and propose Cooperative Layered Architecture (CoLA) implemented on Android system for service continuity during handover process. CoLA helps comprehensive information gathering from all layers for handover decisions, provides simple interfaces to make applications mobility-sensitive, and achieves efficient multipath transmissions across heterogeneous wireless links. Experimental results show that CoLA achieves its design goal in providing service continuity.
Autonomous Deployment of UAVs as Access Points to Serve Wireless Terminals
(2017-01-01)
Chou, Che-Wei
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Yen, Li-Hsing
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資訊工程學系
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Department of Computer Science
Unmanned aerial vehicle (UAV) nowadays are inexpensive and can serve as a robust communication platform in the sky. Using UAV as access point can be particularly helpful for wireless terminals in areas where terrestrial infrastructure is absent or damaged. The problem is how to deploy a fleet of UAVs to efficiently cover scattered terminals while not wasting too much energy on the deployment process. In this paper, we propose two autonomous service deployment approaches for UAVs based on game theory. In these approaches, UAVs adaptively adjust their locations based on local information rather than instructions from a control station. Experimental results show that the proposed approaches outperform existing approach in terms of average spectral efficiency and UAV travelling distance.
Can: A context-aware NAT traversal scheme
(2013-07-01)
Tseng, Chien-Chao
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Lin, Chia-Liang
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Yen, Li-Hsing
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Liu, Jyun-Yan
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Ho, Cheng-Yuan
Network Address Translation (NAT) is a technique commonly used to share one public IPv4 address among several hosts located behind a NAT device. NAT devices typically block session requests originating from outside, causing NAT traversal problem that prevents the establishment of peer-to-peer (P2P) sessions. There have been many proposals for the NAT traversal problem. However, existing methods induce high connectivity check delay and resource demand when finding a communicating path, calling for a routine that determines the path best suited for a given pair of communicating peers. This study proposes CAN, a Context-Aware NAT traversal scheme which gathers and exchanges network-context information to find the most appropriate path for two communicating peers behind NAT devices. We have implemented CAN and conducted extensive experiments with off-the-shelf NAT devices to compare the performance of CAN with Interactivity Connectivity Establishment (ICE), the most acknowledged approach to creating a session across NATs. Experimental results show that CAN outperforms ICE in terms of direct communication ratio, connectivity check delay and message overload when checking connectivity. (c) 2013 Elsevier Ltd. All rights reserved.
Churn: a Key Effect on Real-World P2P Software
(2013)
Ho, Cheng-Yun
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Chung, Ming-Chen
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Yen, Li-Hsing
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Tseng, Chien-Chao
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資訊工程學系
Churn refers to a large number of arriving and departing participants within a short time in peer-to-peer (P2P) networks. This paper studies the impact of churn on real-world unstructured P2P networks. To this end, we need collecting snapshots of P2P network topology and associated performance metrics. Because P2P topology changes dynamically, the time to take a snapshot must be sufficiently short for the snapshots to be accurate. We propose Third-party-to-servent Crawling with Servent-to-servent Sampling (TCSS) system. TCSS uses a third-party crawling technique to collect network topology information without disturbing the original P2P network under investigation. Furthermore, TCSS adopts distributed and parallel techniques to speed up the crawling process. TCSS also employs a servent-to-servent sampling technique to gather the corresponding performance metrics of the P2P network simultaneously. Empirical results show that TCSS takes around 7 minutes to take a topology snapshot of the P2P network. Besides, we found that churn is indeed a combined effect of peer arrivals/departures and neighbor replacements. As the number of peers increases, the number of very long-lived peers remains nearly constant and the P2P network possesses a small-world property. Moreover, as churn aggravates, the average booting time of peers increases and the variation is proportional to the degree of churn. The response time of the top-rank keyword searches is not affected by the degree of churn.
Crossover Node Discovery for IEEE 802.11s Wireless Mesh Networks
(2013-01-01)
Yen, Li-Hsing
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Su, Jiun-Jang
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Huang, Kuei-Li
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Tseng, Chien-Chao
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Liao, Kuan-Ming
Crossover nodes have been utilized to achieve smooth handoffs for micro mobility management schemes. IEEE 802.11s supports proxy-based frame delivery services for mobile hosts roaming within a wireless mesh network (WMN). Discovering crossover node for mobile hosts in 802.11s WMNs, however, faces several challenges due to intrinsic properties of mesh networks. This paper identifies these challenges and proposes a scheme suitable for crossover node discovery under 802.11s WMNs. This scheme is characterized by source-oriented, MAP-centric, and per-source. It can be performed off-line with the derived results cached for on-line retrievals during handoffs. Simulation results show that the proposed scheme can reduce packet losses due to handoffs, and confirm the necessity of the source-oriented principle.
Decentralized Auctioneerless Combinatorial Auctions for Multi-Unit Resource Allocation
(2019-01-01)
Yen, Li-Hsing
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Sun, Guang-Hong
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資訊工程學系
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Department of Computer Science
Auction has been used to allocate resources or tasks to processes, machines, or other autonomous agents in distributed systems. Among various types of auctions, combinatorial auction (CA) allocates a bundle of items to each agent at once. Finding an optimal auction result for CA that maximizes total winning bid is NP-hard. Many time-efficient approximations to this problem work with a bid ranking function (BRF). However, the existing approximations are mostly for single-unit resource and demand an auctioneer. This paper proposes the first auctioneerless open-bid multi-unit CA (MUCA) scheme. It includes a BRF-based winner determination scheme that enables every agent to locally compute a critical bid value for it to win the MUCA and accordingly take its best response to other agent's bid and win declarations. It also allows each winner to locally compute its payment for a critical-value-based pricing scheme. We analyze stabilization, correctness, and consistency properties of the proposed approach. The simulation results confirm that the proposed approach identifies exactly the same set of winners as the centralized counterpart regardless of initial bid setting, but at the cost of the lower total winning bid and payment.
Designing Self-Stabilizing Systems Using Game Theory
(2016-09)
Yen, Li-Hsing
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Huang, Jean-Yao
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Turau, Volker
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資訊工程學系
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Department of Computer Science
Self-stabilizing systems tolerate transient faults by always returning to a legitimate system state within a finite time. This goal is challenged by several system features such as arbitrary system states after faults, various process execution models, and constrained process communication means. This work designs selfstabilizing distributed algorithms from the perspective of game theory, achieving an intended system goal through private goals of processes. We propose a generic game design for identifying a maximal independent set (MIS) or a maximal weighted independent set (MWIS) among all processes in a distributed system. From the generic game several specific games can be defined which differ in whether and how neighboring players influence each other. Turning the game designs into self-stabilizing algorithms, we obtain the first algorithms for the MWIS problem and also the first self-stabilizingMIS algorithm that considers node degree (including an analysis of its performance ratio). We also show how to handle simultaneous moves of processes in some process execution models. Simulation results indicate that, for various representative network topologies, the new algorithm outperforms existing methods in terms of MIS size and convergence rate. For the MWIS problem, the new algorithms performed only slightly worse than centralized greedy counterparts.
Fast Handover Techniques for ESS-Subnet Topology Mismatch in IEEE 802.11
(2013)
Tseng, Chien-Chao
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Lin, Chia-Liang
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Chang, Yu-Jen
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Yen, Li-Hsing
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資訊工程學系
With the advances in wireless communication technology, mobile applications are gradually being introduced as part of our life. IEEE 802.11 is one of the most popular wireless communication technologies. Prior studies toward layer-2 and layer-3 handoffs assume that Extend Service Set (ESS) exactly matches a dedicated subnet. However, an inter-ESS with intra-subnet handoff and an intra-ESS with inter-subnet handoff may also be possible. Such mismatching ESS-subnet configurations result in performance degradation. This paper proposes FCS, a Further Check Scheme which detects the change of subnet after an intra-ESS handoff and eliminates unnecessary handoff latency after an inter-ESS handoff. The experimental results show that FCS outperforms the conventional implementation of NetworkManager under Linux in terms of handoff latency.
Jitter-Aware Packet Scheduler for Concurrent Multipath Transmission in Heterogeneous Wireless Networks
(2016)
Chan, Min-Cheng
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Tseng, Chien-Chao
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Yen, Li-Hsing
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資訊工程學系
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Department of Computer Science
Mobile devices equipped with multiple network interfaces have the potential to increase transmission throughput by exploiting concurrent multipath transmission (CMT). However, packet scheduling for CMT is challenging since the diversity of latencies among transmission paths can easily yield out-of-order packet receptions and cause receiver buffer blocking if the receiver buffer is not large enough. Previous studies proposed several solutions attempting to eliminate out-of-order receptions and receiver buffer blocking. Delay-Aware Packet scheduling (DAPS) is the only one among them that considers delay diversity at the sender side when scheduling packets. However, DAPS assumes quasi-static path delay and thus does not perform well if path delay changes dynamically. In this paper, we analyze how jitter affects the performance of DAPS. Furthermore, we propose and implement a jitter-aware packet scheduler named JAPS. Performance evaluations show that JAPS outperforms existing algorithms in terms of throughput under different settings of data volume, receiver buffer size, network jitter and bandwidth ratio.
KPAT: A Kernel and Protocol Analysis Tool for Embedded Networking Devices
(2014-01-01)
Wang, Ming-Hung
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Yu, Chia-Ming
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Lin, Chia-Liang
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Tseng, Chien-Chao
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Yen, Li-Hsing
Sniffer tools capture protocol data. Kernel-profiling tools track function calls and events occurring in the kernel. These two types of tools help us observe external and internal behaviors of networking protocols, respectively. We need both types of data for a comprehensive view of protocol behavior. However, none of existing tools performs these two tasks in an integrated way. We developed Kernel and Protocol Analysis Tool (KPAT). KPAT injects software probes into Linux kernel to track interested function calls and event occurrences in the kernel. Probe injection is done systematically and does not require recompiling the kernel. A module in KPAT finds the association between the tracked functions and protocol data captured by an independent sniffer. The result as an integrated log allows users to identify two-way relationship between protocol data and the execution sequence of network functions in the kernel. We successfully used KPAT to identity accurate latency of each handover phase in IEEE 802.11 wireless networks. Experimental results show that KPAT causes light overhead to the patched kernel.
Link-Preserving Channel Assignment Game for Wireless Mesh Networks
(2016-01-01)
Yen, Li-Hsing
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Ye, Bo-Rong
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資訊工程學系
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Department of Computer Science
To deliver user traffic in a wireless mesh network, mesh stations equipped with multiple wireless interfaces communicate with one another utilizing multiple orthogonal channels. Channel assignment in such an environment is to assign one channel to each interface to minimize co-channel interference among wireless links while preserving link connectivity. The interference and connectivity objectives are generally conflicting. This paper proposes a game-theoretic approach that jointly considers the two objectives with a unified payoff function. We prove that the proposed approach is an exact potential game, which guarantees stability in a finite time. We also prove the link-preserving property of the approach. Simulation results show that the proposed approach generally outperforms counterparts in terms of network interference when a moderate number of channels are available.
Link-preserving channel assignment game for wireless mesh networks
(2019-01-01)
Yen, Li-Hsing
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Ye, Bo-Rong
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資訊工程學系
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Department of Computer Science
To deliver user traffic in a wireless mesh network (WMN), mesh stations equipped with multiple interfaces communicate with one another utilising multiple orthogonal channels. Channel assignment is to assign one channel to each interface to minimise co-channel interference among wireless links while preserving link connectivity. The interference and connectivity objectives are generally conflicting. This paper first analyses the probability of link connectivity when channels are randomly assigned to interfaces. We then propose a game-theoretic approach that jointly considers the two objectives with a unified payoff function. We prove that the proposed approach is an exact potential game, which guarantees stability in a finite time. We also prove the link-preserving property of the approach. Simulation results show that the proposed approach generally outperforms counterparts in terms of network interference when a moderate number of channels are available. For fairness of link interference, both the proposed approach and its variant outperform the counterparts.
Mobility Management for Low-Latency Handover in SDN-Based Enterprise Networks
(2016)
Chen, Ce
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Lin, Yu-Ting
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Yen, Li-Hsing
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Chan, Min-Cheng
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Tseng, Chien-Chao
Low-latency handover is crucial to real-time traffic in wireless networks. This paper considers an enterprise network managed by emerging Software Defined Network (SDN) technology. For this networking environment, we propose a mobility management scheme named Mobility SDN (M-SDN) that reduces the traffic pause time caused by a host-initiated layer-2 handover. M-SDN performs handover preparation in parallel with the layer-2 handover that involves N-casting of active flows to every potential handover target. Handover preparation is enabled by efficient address resolution and location tracking. We have implemented a prototype of M-SDN and conducted several experiments to evaluate the performance of M-SDN. Experimental results show that M-SDN effectively reduces the impact of layer-2 handovers without any modification on mobile devices.
OpenNet: A Simulator for Software-Defined Wireless Local Area Network
(2014)
Chan, Min-Cheng
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Chen, Chien
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Huang, Jun-Xian
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Kuo, Ted
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Yen, Li-Hsing
This study is motivated by a plan to install a software-defined wireless local area network (SDWLAN) on campus, which possesses a desired property that both data flow and device behaviors can be software-definable. Because the installation involves hundreds of access points, we must conduct simulations beforehand to verify the design and scalability of the target system. However, existing SDN simulator like Mininet does not support modeling of wireless channel and mobility. On the other hand, common network simulator like ns-3 only has limited support for software-defined controllers and does not fully implement handover process. We thus develop OpenNet, which connects Mininet to ns3 to enjoy both Mininet\'s advantage of controller compatibility and ns-3\'s ability in the wireless/mobility modeling. OpenNet also complements ns-3 by adding probe mechanism, which is missing in the current ns-3 implementation. Our simulation result demonstrates the effectiveness of OpenNet.
Opportunities and Challenges of Joint Edge and Fog Orchestration
(2018-01-01)
Cominardi, Luca
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Abdullaziz, Osamah Ibrahiem
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Antevski, Kiril
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Chundrigar, Shahzoob Bilal
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Gdowski, Robert
Pushing contents, applications, and network functions closer to end users is necessary to cope with the huge data volume and low latency required in future 5G networks. Edge and fog frameworks have emerged recently to address this challenge. Whilst the edge framework was more infrastructure-focused and more mobile operator-oriented, the fog was more pervasive and included any node (stationary or mobile), including terminal devices. This article analyzes the opportunities and challenges to integrate, federate, and jointly orchestrate the edge and fog resources into a unified framework.
PathMon: Path-Specific Traffic Monitoring in OpenFlow-Enabled Networks
(2016)
Wang, Ming-Hung
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Wu, Shao-You
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Yen, Li-Hsing
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Tseng, Chien-Chao
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資訊工程學系
Software-defined networking (SDN) aims to provide open interfaces, such as OpenFlow protocol, that enable programmable flow-based network management. Meanwhile, OpenFlow-enabled switches provide rich statistical information for specific flows, tables, and ports which facilitates various network management tasks. However, current traffic monitoring techniques collecting statistics from existing flow entries do not provide the flexibility of querying path-specific flow statistics at any aggregation levels. In this paper, we proposes PathMon which encodes flow and path information as tags to provide that flexibility and corresponding link-to-link correlations for further anomaly detection or traffic engineering tasks. Our implementation runs on commodity switches which are compliant to OpenFlow 1.3 specification and requires only a few monitoring entries for each switch along monitored paths and un-tag entries for each edge switch.
PIM-Compliant SDN-Enabled IP Multicast Service
(2018-01-01)
Yen, Li-Hsing
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Wang, Ming-Hung
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Wu, Song-Yu
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Tseng, Chien-Chao
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資訊工程學系
Software-defined networking (SDN) has been a promising solution to multicast streaming data due to its scalability and manageability. However, offering a multicast service that spans a large geographical area is still challenging because we still lack a unified multicast scheme that interconnects independent SDN-managed networks and bridges the service between SDN-based networks and the rest of the Internet. This paper proposes a solution that integrates SDN, CORD, and PIM technologies. We provides preliminary performance evaluation results. This work serves as a stepping stone to the ultimate goal of multicast as a service.
Proactive DAD: A fast address-acquisition strategy for mobile IPv6 networks
(2006-11-01)
Tseng, Chien-Chao
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Wong, Yung-Chang
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Yen, Li-Hsing
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Hsu, Kai-Cheng
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資訊工程學系
The increasing number of Wi-Fi-compatible mobile devices highlights various wireless access challenges, including the need for smooth hand offs between Internet attachment points in mobile IPv6 networks. To confirm address uniqueness in a new domain, mobile nodes must run duplicate address detection (DAD), which is a time-consuming process. The Proactive DAD approach uses topology information and layer-2 signals to predict the new network domains prior to or in parallel with layer-3 hand offs. Experimental results show that P-DAD can significantly reduce both hand-off latency and packet loss.
Profit Maximization by Forming Federations of Geo-Distributed MEC Platforms
(2019-01-01)
Yen, Li-Hsing
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Chang, Chi-Han
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Chen, Yi Chia
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資訊工程學系
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Department of Computer Science
Multi-access edge computing (MEC) as an emerging technology which provides cloud service in the edge of multi-radio access networks aims to reduce the service latency experienced by end devices. When individual MEC systems do not have adequate resource capacity to fulfill service requests, forming MEC federations for resource sharing could provide economic incentive to MEC operators. To this end, we need to maximize social welfare in each federation, which involves efficient federation structure generations, federation profit maximization by resource provisioning configuration, and fair profit distribution among participants. We model the problem as a coalition game with difference from prior work in the assumption of latency and locality constraints and also in the consideration of various service policies/demand preferences. Simulation results show that the proposed approach always increases profits. If local requests are served with local resource with priority, federation improves profits without sacrificing request acceptance rates.