She-Hwa Yen

Sleep Mode for Energy Saving PONs: Advantages and Drawbacks

A common approach to reduce energy consumption in communication networks is to allow network elements to switch to sleep mode. While this technique has been widely utilized in wireless networks, recent studies have proposed to exploit sleep mode in wired networks to conserve energy as well. This paper focuses on some feasible implementations of sleep mode in passive optical networks (PONs). In particular, ONU sleep mode is considered. The paper first outlines the ONU wake-up process using current time division multiplexing (TDM) PON protocols. Current and novel optical network unit (ONU) architectures that selectively switch-off some elements are then described. Their advantages in terms of energy savings are analytically computed under different traffic scenarios. Using the proposed architectures, analytical results show more than 50% energy saving under realistic TDM traffic. Finally, possible drawbacks in terms of new scheduling challenges are also discussed and potential solutions are presented.

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.

Photonic components for future fiber access networks

Fiber based access networks are recognized as promising technologies for solving broadband bandwidth bottlenecks. TDM-PONs, which are passive and non-reconfigurable, are the most widely deployed type of fiber access networks today. However, due to their passive nature, TDM-PONs encounter several issues such as inflexible coverage, lack of intelligence for control, and inability to counter security attacks. Based on current issues in optical access networks, we propose a novel non-volatile, reconfiguration node. The proposed remote node can reconfigure the network to adapt to varying degrees of deployment conditions and/or network attacks. Moreover, the proposed remote node incorporates a novel quasi-passive device that reconfigures using remotely supplied energy from CO. This quasi-passive device technology does not consume any energy once it reconfigures into a new latching states. Therefore, the proposed remote node has very low energy consumption and does not require local power supply to preserve the passivity of the passive distribution network. In particular, the proposed quasi-passive device technology is implemented using a novel tri-state Micro- Electro-Mechanical System (MEMS) actuator structure and the device demonstrates very small energy consumption requirement to enable energy be remotely supplied from CO. Also, the MEMS structure is shown to demonstrate acceptable insertion losses to makes it suitable for flexible energy distribution. Simulation study shows the proposed reconfigurable device would outperform traditional passive splitter in terms of maximum number of supportable users under realistic deployment conditions.

Reconfigurable Optical Backhaul and Integrated Routing Algorithm for Load Balancing in Hybrid Optical-Wireless Access Networks

Various wireless and optical access technologies have been developed to address different issues in access networks. By combining the complementary characteristics of wireless and optical networks, a hybrid optical-wireless access network will enable broadband, ubiquitous, and cost-effective last-mile service to the users. In this paper, a reconfigurable optical backhaul leveraging both the standard Time Division Multiplexing Passive Optical Network (TDM-PON) technology and wavelength division multiplexed (WDM) ring is proposed to achieve a higher bandwidth efficiency than simply using point-to-point backhaul links. Furthermore, an integrated routing algorithm which can adapt to the change of overall demand among different service districts by taking advantage of the proposed optical backhaul is also proposed. An experimental testbed is implemented to evaluate the reconfigurable scheme and its feasibility. Also, simulation results show that the proposed integrated routing with load balancing can improve the performance in hybrid optical and wireless networks.

European and American research toward next-generation optical access networks

Next-generation optical access networks will deliver substantial benefits to consumers including a dedicated high-QoS access to bit rates of hundreds of Megabits per second. They must also deliver significant benefits to network owners/operators to justify the needed infrastructure investment expected to reach billions of Euros. Benefits to network owners/operators are expected to include reduced total cost of ownership, due to higher reliability, lower energy consumption, better flexibility and efficiency, and a smaller number of sites needed to support network operations. This paper will describe recent progress toward that goal including R&D efforts in Europe under the FP7 projects ALPHA and OASE and in the US at Stanford University under the SUCCESS and DAN projects.

Long reach passive optical networks with adaptive power equalization using semiconductor optical amplifiers

A new scheme for adaptive optical power equalization in passive optical networks is proposed based on dynamic gain control of semiconductor optical amplifiers. Because of this new scheme, continuous-mode receiver front-end can be used for upstream burst-mode transmission. Experimental testbed is demonstrated with -31dBm receiver sensitivity and >34dB dynamic range using continuous-mode receiver front-end.

A Novel Technique for Denial of Service Identification in Optical Access Networks

We discuss the limitations of current optical access networks in providing protection against physical layer attacks like denial of service and present a scheme for identifying intruders causing this attack.

Photonic devices for next-generation broadband fiber access networks

Next-generation optical access networks will deliver substantial benefits to consumers including a dedicated high-QoS access to bit rates of hundreds of Megabits per second. They must include the following features such as: reduced total cost of ownership, higher reliability, lower energy consumption, better flexibility and efficiency. This paper will describe recent progress and technology toward that goal using novel photonic devices