Dung Pham Van

Energy efficiency in passive optical networks: where, when, and how?

This article provides an overview of current efforts in reducing energy consumption in passive optical access networks. Both ITU-T and IEEE standardized PONs are considered. The current solutions proposed by standardization authorities, industry, and academia are classified based on the layer they address in the standardized architectures: physical layer, data link layer, and hybrid. Then, the article provides answers to major questions, such as where, when, and how to reduce PON energy consumption in TDM PONs by means of a quantitative evaluation. Results show that to reduce energy consumption, ONUs must be provided with physical devices that are not only power-efficient but also provide improved services (e.g., fast synchronization) to upper layers. For this latter purpose, novel physical ONU architectures are proposed to speed up the synchronization process and enable effective data link layer solutions. Finally, the feasibility of switching ONUs to low power mode in idle slots is assessed through a testbed implementation.

The tactile internet: vision, recent progress, and open challenges

The advent of commercially available remote-presence robots may be the precursor of an age of technological convergence, where important tasks of our everyday life will be increasingly done by robots. A very low roundtrip latency in conjunction with ultra-high reliability and essentially guaranteed availability for control communications has the potential to move todays mobile broadband experience into the new world of the Tactile Internet for a race with (rather than against) machines. To facilitate a better understanding of the Tactile Internet, this article first elaborates on the commonalities and subtle differences between the Tactile Internet and the Internet of Things and 5G vision. After briefly reviewing its anticipated impact on society and infrastructure requirements, we then provide an up-to-date survey of recent progress and enabling technologies proposed for the Tactile Internet. Given that scaling up research in the area of future wired and wireless access networks will be essential for the Tactile Internet, we pay particular attention to the latency and reliability performance gains of fiber-wireless (FiWi) enhanced LTE-Advanced heterogeneous networks and their role for emerging cloudlets, mobile-edge computing, and cloud robotics. Finally, we conclude by outlining remaining open challenges for the Tactile Internet.

Experimental evaluation of a sleep-aware dynamic bandwidth allocation in a multi-ONU 10G-EPON testbed

In this paper, a sleep-aware dynamic bandwidth allocation (SDBA) algorithm and the supporting protocol are proposed for maximizing energy efficiency while satisfying the end-user QoS constraints on downstream (DS) and upstream (US) transmissions in 10G-EPONs. The SDBA maximizes the Optical Network Unit (ONU) polling cycle to increase the time for which each ONU sleeps outside the allocated timeslot. The polling cycle, however, is computed by considering QoS constraints (i.e., frame delay and loss rate) of all the transmissions given their finite data buffers to provide the users with the requested QoS. Moreover, based on the observed traffic conditions, the SDBA can allow an ONU to sleep for the whole or for a part of the allocated timeslot by assigning just enough bandwidth to transmit both DS and US traffic accumulated during ONU sleep time. FGPA-based design and evaluation of 10G-EPON systems featuring the proposed SDBA are thoroughly described. Experimental results show that the SDBA maximizes ONU energy saving while guaranteeing the strictest end-user QoS requirements for any considered data rate scenario.

Mobile Edge Computing Empowered Fiber-Wireless Access Networks in the 5G Era

The expected stringent requirements of future 5G networks such as ultra-low latency, user experience continuity, and high reliability will drive the need for highly localized services within RANs in close proximity to mobile subscribers. In light of this, the mobile edge computing (MEC) concept has emerged, which aims to unite telco, IT, and cloud computing to deliver cloud services directly from the network edge. To facilitate better understanding of MEC, this article first discusses its potential service scenarios and identifies design challenges of MEC-enabled networks. Given the importance of scaling up research in the area of network integration and convergence in support of MEC toward 5G, the article explores the possibilities of empowering integrated fiber-wireless (FiWi) access networks to offer MEC capabilities. More specifically, envisioned design scenarios of MEC over FiWi networks for typical RAN technologies (i.e., WLAN, 4G LTE, LTE-A HetNets) are investigated, accounting for both network architecture and enhanced resource management. The performance of MEC over Ethernet-based FiWi networks in terms of delay, response time efficiency, and battery life of edge devices is then analyzed. The obtained results demonstrate the feasibility and effectiveness of the proposed MEC over FiWi concept.

Energy-efficient framework for time and wavelength division multiplexed passive optical networks

For the first time, to the best of our knowledge, an energy-efficient framework that optimizes the number of active wavelengths and uses sleep/doze mode to improve the energy savings of a delay-constrained time and wavelength division multiplexed passive optical network is presented in this work. In the proposed framework, the optical network units (ONUs) operate under the maximum polling cycle time that satisfies a given delay constraint to achieve maximum possible energy savings at the ONUs. When the average bandwidth requested by an ONU exceeds the maximumallowable bandwidth, a new wavelength is introduced to the network to satisfy delay constraints. Conversely, when the bandwidth requested by an ONU is small, idle wavelengths are switched off to increase energy savings at the optical line terminal (OLT). The proposed framework is analyzed using online and offline just-in-time dynamic wavelength and bandwidth allocation (DWBA) algorithms. The performance of both algorithms, under the proposed framework, is evaluated in terms of average delay, percentage of energy savings at the ONU, and percentage of energy savings at the OLT. Our analytical and simulation results indicate that under the proposed framework, the average delay of the network remains below a specified maximum allowable delay, in both algorithms. The online DWBA algorithm, however, results in improved energy savings, both at the OLT and at the ONUs, compared to the offline DWBA algorithm.

Mobile-edge computing vs. centralized cloud computing in fiber-wireless access networks

The advent of Internet of Things and 5G applications renders the need for integration of both centralized cloud computing and emerging mobile-edge computing (MEC) with existing network infrastructures to enhance storage, processing, and caching capabilities in not only centralized but also distributed fashions for supporting both delay-tolerant and mission-critical applications. This paper investigates performance gains of centralized cloud and MEC enabled integrated fiber-wireless (FiWi) access networks. A novel resource management scheme incorporating both centralized cloud and MEC offloading activities into the underlying FiWi dynamic bandwidth allocation process is proposed. An analytical framework is developed to model packet delay, response time efficiency, and gain-offload overhead ratio for both cloud and conventional broadband access traffic. The obtained results demonstrate the feasibility of implementing conventional cloud and MEC in FiWi access networks, while not affecting network performance of broadband access traffic.

Energy-saving framework for passive optical networks with ONU sleep/doze mode

This paper proposes an energy-saving passive optical network framework (ESPON) that aims to incorporate optical network unit (ONU) sleep/doze mode into dynamic bandwidth allocation (DBA) algorithms to reduce ONU energy consumption. In the ESPON, the optical line terminal (OLT) schedules both downstream (DS) and upstream (US) transmissions in the same slot in an online and dynamic fashion whereas the ONU enters sleep mode outside the slot. The ONU sleep time is maximized based on both DS and US traffic. Moreover, during the slot, the ONU might enter doze mode when only its transmitter is idle to further improve energy efficiency. The scheduling order of data transmission, control message exchange, sleep period, and doze period defines an energy-efficient scheme under the ESPON. Three schemes are designed and evaluated in an extensive FPGA-based evaluation. Results show that whilst all the schemes significantly save ONU energy for different evaluation scenarios, the scheduling order has great impact on their performance. In addition, the ESPON allows for a scheduling order that saves ONU energy independently of the network reach.

Machine-to-machine communications over FiWi enhanced LTE networks : A power-saving framework and end-to-end performance

To cope with the unprecedented acceleration of machine-to-machine (M2M) services over cellular networks, this paper envisions a highly converged network architecture based on the integration of high-capacity and reliable Ethernet fiber-wireless (FiWi) access networks with flexible and cost-effective 4G long term evolution (LTE) technology to support M2M connectivity in an end-to-end fashion, i.e., from air interface to transport (backhaul) network. In such emerging architecture, energy efficiency must be addressed in a comprehensive way, in which both wireless front-end and optical backhaul segments are considered at the same time to maximize the battery life of battery-constrained M2M devices as well as reduce operational expenditures for network operators, while maintaining acceptable network performance. Toward this end, an end-to-end power-saving framework is introduced in this paper that devises a timeout driven discontinuous reception (DRX) mechanism for LTE-enabled M2M devices and a polling-based power-saving mechanism for optical network units (ONUs) to improve the overall energy efficiency. End-to-end performance in terms of energy saving and packet delay is analytically modeled based on a semi-Markov process for the front-end and an M/G/1 queue for the backhaul. The obtained results indicate that the device battery life is significantly prolonged by extending the DRX cycle, whereas the backhaul energy consumption is minimized by incorporating the ONU power-saving modes into the dynamic bandwidth allocation process of the optical backhaul.

Trading energy savings and network performance in reconfigurable TWDM-PONS

In time and wavelength division multiplexed (TWDM) passive optical networks (PONs), energy savings at the optical line termination (OLT) are achievable by dynamically allocating the number of active wavelengths in the network and by turning off unutilized OLT transceivers. However, optical network unit (ONU) and PON parameters might impact network performance. This paper evaluates the impact of ONU parameters (e.g., transceiver tuning time) and other PON parameters (e.g., reconfiguration period) on OLT energy savings and average frame delay when dynamic wavelength allocation is performed periodically. Results show that the average frame delay is mainly affected by tuning time and reconfiguration period with lower absolute values if only one ONU buffers traffic during tuning. Increased tuning time trades increased delay with increased energy savings while increased reconfiguration period trades decreased delay with decreased energy savings.

Introducing cognition in TDM PONs with cooperative cyclic sleep through runtime sleep time determination

In this paper cognition is exploited to maximize energy efficiency while guaranteeing quality of service (QoS) constraints in TDM PONs with time-variable network conditions. In the proposed solution the previously introduced cooperative cyclic sleep scheme exploits runtime computation and adaptation to network conditions of the sleep time. Simulation results show the potentials of the proposed approach in maximizing energy savings while guaranteeing average delay constraints when applied to limited buffer ONUs.