Takafumi Tanaka

Distance-adaptive spectrum resource allocation in spectrum-sliced elastic optical path network [Topics in Optical Communications]

The rigid nature of current wavelength-routed optical networks brings limitations on network utilization efficiency. One limitation originates from mismatch of granularities between the client layer and the wavelength layer. The recently proposed spectrum-sliced elastic optical path network (SLICE) is expected to mitigate this problem by adaptively allocating spectral resources according to client traffic demands. This article discusses another limitation of the current optical networks associated with worst case design in terms of transmission performance. In order to address this problem, we present a concept of a novel adaptation scheme in SLICE called distance-adaptive spectrum resource allocation. In the presented scheme the minimum necessary spectral resource is adaptively allocated according to the end-to-end physical condition of an optical path. Modulation format and optical filter width are used as parameters to determine the necessary spectral resources to be allocated for an optical path. Evaluation of network utilization efficiency shows that distance-adaptive SLICE can save more than 45 percent of required spectrum resources for a 12-node ring network. Finally, we introduce the concept of a frequency slot to extend the current frequency grid standard, and discuss possible spectral resource designation schemes.

Algorithms for maximizing spectrum efficiency in elastic optical path networks that adopt distance adaptive modulation

We propose optical path routing and frequency slot assignment algorithms that suit elastic optical paths and the distance adaptive modulation scheme. The algorithms are proven to yield high spectrum efficiency for the distant-adaptive frequency allocation scheme.

Distance-adaptive super-wavelength routing in elastic optical path network (SLICE) with optical OFDM

We propose a spectrally-efficient super-wavelength-path routing in SLICE by selecting a set of subcarrier numbers and modulation levels according to path distances. We demonstrate 420 Gb/s path routing using short-reach 14-subcarrier 8-APSK and long-reach 21-subcarrier QPSK.

Advantages of IP over elastic optical networks using multi-flow transponders from cost and equipment count aspects

To evaluate the cost efficiency of IP over elastic optical network architectures, we use a multi-layer network design scheme that covers network to node equipment level. An evaluation in a static traffic environment shows that the multi-flow optical transponder-based elastic optical network reduces total cost as well as equipment counts compared to other elastic network models based on fixed-rate, mixed-line-rate and bandwidth-variable transponders.

Impact of Transponder Architecture on the Scalability of Optical Nodes in Elastic Optical Networks

The elastic optical network has proven to be a promising network architecture for handling the rapid growth in IP traffic in the optical layer in a spectrum-efficient manner. This study reveals the optical node requirements in elastic optical networks by comparing multiple network architectures using an integrated resource allocation scheme that considers both network and node parameters. Evaluations show that the multi-flow (MF) transponder-based elastic optical network architecture is superior to two other architectures in terms of scalability of optical nodes and network costs.

A novel elastic optical path network that utilizes bitrate-specific anchored frequency slot arrangement

We propose a novel elastic optical path network where each specific bitrate signal uses its own dedicated fixed grid and one edge of its frequency grid is anchored at a specific frequency. Numerical evaluations using various bitrate signal patterns and network topologies show that the network proposal can almost match the performance of conventional flexible grid networks, while greatly mitigating the hardware requirements: it allows the use of the tunable filters for the fixed grid systems.

Multiperiod IP-over-elastic network reconfiguration with adaptive bandwidth resizing and modulation

Elastic optical networks (EONs) represent a promising network architecture that accommodates a wide variety of traffic demands in the optical layer. Thanks to the functionality of bandwidth flexibility of elastic optical paths, we can now accommodate IP traffic directly into the optical layer by configuring, for example, the modulation format and subcarrier counts to client demands (optical path demands). At the same time, to accommodate temporally and geographically changing IP traffic demands efficiently in optical networks, cooperation between the IP and optical layers is essential. This paper proposes a multilayer network reconfiguration algorithm that supports periodically changing IP traffic patterns. We incorporate two schemes, which make IP over EONs more flexible, into the heuristic iterative multilayer network reconfiguration algorithm (IMNR). The first scheme involves bandwidth resizing achieved through subcarrier expansion and reduction, and the second employs energy-efficient adaptive modulation according to the data rate and distance of the client demands. We evaluated the impact of the following on energy efficiency: the IMNR algorithm, the proposed adaptive bandwidth resizing and modulation schemes, and some multicarrier-based transponder architectures including bandwidth-variable transponder (BVT) and sliceable BVT (SBVT). The evaluation results show that the IMNR algorithm with the proposed schemes significantly reduces the energy consumption compared with traditional network planning schemes and equipment.

Flexible and robust optical network technologies for SDN and network virtualization

This paper reviews the progress of flexible and robust technologies for a reliable optical network infrastructure that can be used for software defined networking (SDN) and network virtualization. We focus on the elastic optical network (EON), which will play an important role in achieving both flexibility and robustness, and introduce our current works on fault tolerance.

Demonstration of Single-Mode Multicore Fiber Transport Network With Crosstalk-Aware In-Service Optical Path Control

Multicore fiber (MCF) transmission is considered as one of the promising technologies for breaking the capacity limit of traditional single mode fibers. Managing the crosstalk (XT) and configuring optical paths adaptively based on the XT as well as achieving longer distance and larger capacity transmission are important, because intercore XT could be the main limiting factor for MCF transmission. In a real MCF network, the intercore XT in a particular core is likely to change continuously as the optical paths in the adjacent cores are dynamically assigned to match the dynamic nature of the data traffic. If we configure the optical paths while ignoring the intercore XT value, the Q-factors may become excessive. Therefore, monitoring the intercore XT value continuously and configuring optical path parameters adaptively and flexibly are essential. To address these challenges, we develop an MCF transport network testbed and demonstrate an XT-aware traffic engineering scenario. With the help of a software-defined network controller, the modulation format and optical path route are adaptively changed based on the monitored XT values by using programmable devices such as a real-time transponder and a reconfigurable optical add–drop multiplexer.

Path accommodation design and reconfiguration for different reliability classes in virtualized multi-layer transport network

We propose differenced accommodation design and reconfiguration in virtualized multi-layer transport networks. Numerical evaluation shows that when the number of classes allowing reconfiguration is dominant, the number of transponders is reduced up to 12 %.