2021

1. IEEE IoT J

   Fast Consensus-Based Time Synchronization Protocol Using Virtual Topology for Wireless Sensor Networks

   Linh-An Phan, and Taehong Kim

   IEEE Internet of Things Journal 2021

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   Slow convergence is a major drawback of average-based consensus time synchronization protocols, particularly in large or sparse wireless sensor networks. The convergence speed can be increased by adding more nodes or increasing the transmission range of nodes, because the network becomes strongly connected. However, these solutions are not always feasible owing to hardware constraints. In this article, a virtual topology-based time synchronization protocol (VTSP) is proposed to address the aforementioned drawback of consensus-based protocols. Notably, VTSP performs the consensus process on a virtual topology that has a stronger algebraic connectivity than a physical one. Therefore, VTSP can significantly accelerate convergence speed without modifying the physical structure of the network. The virtual topology is formed by creating virtual links between each node and its two-hop neighbors. Moreover, two optimization techniques are suggested for reducing data redundancy, which is caused during the creation of the virtual links, in timing messages and for speeding up the convergence by excluding edge nodes from the consensus process. Simulation results demonstrate that VTSP can achieve convergence three times faster than the gradient time synchronization protocol, a well-known consensus-based time synchronization protocol, in various topologies while preserving the same level of accuracy.

2. FGCS

   Dynamic fog-to-fog offloading in SDN-based fog computing systems

   Linh-An Phan, Duc-Thang Nguyen, Meonghun Lee, Dae-Heon Park, and Taehong Kim

   Future Generation Computer Systems 2021

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   Fog computing is a promising paradigm aimed at reducing latency and network traffic between end devices and cloud servers. In fog computing systems, a fog node can be overloaded by an increased number of requests from end devices. In this situation, an efficient offloading mechanism among fog nodes is necessary to meet the requirements of fog computing. Software Defined Networking (SDN) has become the de facto standard for future network infrastructures, including fog computing systems. In this paper, we propose a dynamic offloading service among fog nodes for an SDN-based fog computing system that aims at selecting an optimal offloading node and assisting the offloading path by providing an end-to-end bandwidth guarantee based on SDN technology. The proposed solution outperforms traditional approaches without SDN technology in terms of both throughput and request response time by selecting the appropriate offloading node using current computational and network resource information and providing a reliable end-to-end path.

3. IEEE IoT J

   Robust Neighbor-Aware Time Synchronization Protocol for Wireless Sensor Network in Dynamic and Hostile Environments

   Linh-An Phan, Taejoon Kim, and Taehong Kim

   IEEE Internet of Things Journal 2021

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   Average-based consensus time synchronization protocols have been widely used in wireless sensor networks owing to their robustness against a single point of failures. In these types of distributed protocols, each node is designed to have the same role as other nodes in the network. However, because of this design, these protocols are limited in that any unsynchronized node can negatively affect other nodes in the system. Since the presence of unsynchronized nodes, such as newly joined nodes or malicious nodes is unavoidable, average-based consensus time synchronization protocols are vulnerable in dynamic or hostile environments. In this article, we propose a new protocol named neighbor-aware time synchronization protocol (NTSP) that incorporates the neighbor-aware concept to overcome the aforementioned limitation and improve the robustness of the average-based consensus time synchronization protocol in both dynamic and hostile environments. In particular, by being aware of each neighbor’s status (e.g., synchronized, new, or unsynchronized neighbor), each node can decide whether to include a neighbor in the calculation of the consensus process. As a result, NTSP can prevent adverse effects from unsynchronized nodes. The simulation results demonstrate that NTSP has a relatively faster recovery time than gradient time synchronization protocol and Average TimeSynch when new nodes join and can protect the synchronization of the network from attacks by a malicious node.

2020

1. IEEE Access

   ElasticFog: Elastic Resource Provisioning in Container-Based Fog Computing

   Nguyen Dinh Nguyen, Linh-An Phan, Dae-Heon Park, Sehan Kim, and Taehong Kim

   IEEE Access 2020

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   The recent increase in the number of Internet of Things (IoT) devices has led to the generation of a large amount of data. These data are generally processed by cloud servers because of their high scalability and ability to provide resources on demand. However, processing large amounts of data in the cloud is an impractical solution for the strict requirements of IoT services, such as low latency and high bandwidth. Fog computing, which brings computational resources closer to the IoT devices, has emerged as a suitable solution to mitigate these problems. Resource provisioning and application orchestration are two of the key challenges when running IoT applications in a Fog computing environment. In this article, we present ElasticFog, which runs on top of the Kubernetes platform and enables real-time elastic resource provisioning for containerized applications in Fog computing. Specifically, ElasticFog collects network traffic information in real time and allocates computational resources proportionally to the distribution of network traffic. The experimental results prove that ElasticFog achieves a significant improvement in terms of throughput and network latency compared with the default mechanism in Kubernetes.

2. Sensors

   Breaking Down the Compatibility Problem in Smart Homes: A Dynamically Updatable Gateway Platform

   Linh-An Phan, and Taehong Kim

   Sensors 2020

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   Smart home is one of the most promising applications of the Internet of Things. Although there have been studies about this technology in recent years, the adoption rate of smart homes is still low. One of the largest barriers is technological fragmentation within the smart home ecosystem. Currently, there are many protocols used in a connected home, increasing the confusion of consumers when choosing a product for their house. One possible solution for this fragmentation is to make a gateway to handle the diverse protocols as a central hub in the home. However, this solution brings about another issue for manufacturers: compatibility. Because of the various smart devices on the market, supporting all possible devices in one gateway is also an enormous challenge. In this paper, we propose a software architecture for a gateway in a smart home system to solve the compatibility problem. By creating a mechanism to dynamically download and update a device profile from a server, the gateway can easily handle new devices. Moreover, the proposed gateway also supports unified control over heterogeneous networks. We implemented a prototype to prove the feasibility of the proposed gateway architecture and evaluated its performance from the viewpoint of message execution time over heterogeneous networks, as well as the latency for device profile downloads and updates, and the overhead needed for handling unknown commands.

2019

1. Sensors

   Performance analysis of time synchronization protocols in wireless sensor networks

   Linh-An Phan, Taejoon Kim, Taehong Kim, JaeSeang Lee, and Jae-Hyun Ham

   Sensors 2019

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   The time synchronization protocol is indispensable in various applications of wireless sensor networks, such as scheduling, monitoring, and tracking. Numerous protocols and algorithms have been proposed in recent decades, and many of them provide micro-scale resolutions. However, designing and implementing a time synchronization protocol in a practical wireless network is very challenging compared to implementation in a wired network; this is because its performance can be deteriorated significantly by many factors, including hardware quality, message delay jitter, ambient environment, and network topology. In this study, we measure the performance of the Flooding Time Synchronization Protocol (FTSP) and Gradient Time Synchronization Protocol (GTSP) in terms of practical network conditions, such as message delay jitter, synchronization period, network topology, and packet loss. This study provides insights into the operation and optimization of time synchronization protocols. In addition, the performance evaluation identifies that FTSP is highly affected by message delay jitter due to error accumulation over multi-hops. We demonstrate that the proposed extended version of the FTSP (E-FTSP) alleviates the effect of message delay jitter and enhances the overall performance of FTSP in terms of error, time, and other factors.

2019

1. ICCCN

   Distributed TDMA Scheduling Using Topological Ordering in Wireless Sensor Networks

   Thanh-Tung Nguyen, Linh-An Phan, Taejoon Kim, Taehong Kim, JaeSeang Lee, and JaeHyun Ham

   In 28th International Conference on Computer Communication and Networks (ICCCN) 2019
2. ICCCN

   A Study of the Z-Wave Protocol: Implementing Your Own Smart Home Gateway

   Yong Jeong Kim, Linh-An Phan, Taejoon Kim, Taehong Kim, JaeSeang Lee, and Jae-Hyun Ham

   In 28th International Conference on Computer Communication and Networks (ICCCN) 2019
3. INFOCOM

   A Fast Consensus-Based Time Synchronization Protocol with Virtual Links in WSNs

   Linh-An Phan, Taejoon Kim, Taehong Kim, JaeSeang Lee, and Jae-Hyun Ham

   In IEEE INFOCOM 2019 - IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS) 2019

2018

1. ICCCS

   A Study of the Z-Wave Protocol: Implementing Your Own Smart Home Gateway

   Linh-An Phan, and Taejoon Kim

   In 3rd International Conference on Computer and Communication Systems (ICCCS) 2018