Motoyoshi Sekiya

Spectrally and spatially flexible optical network planning and operations

The advent of spectrally flexible (a.k.a. elastic) optical networking is widely identified as the next generation optical network solution that permits varying bandwidth demands to be dynamically assigned over flexible spectral containers, targeting optimum use of the available network resources. Additionally, the adoption of the space dimension is identified as a promising solution for the capacity expansion of future networks, while novel spatial-spectral switching solutions show that the flexible networking concept can be further expanded over both the spatial and spectral dimensions. This article provides an overview of the latest developments and possible approaches with respect to flexible optical networking and the emerging benefits that spatially flexible networking approaches can offer. The focus is on the network planning and resource optimization functions, the main network operations related to fragmentation and IP/optical layer integration, and the control plane solutions.

Survivable virtual optical network mapping in flexible-grid optical networks

In this paper, we study the problem of survivable impairment-aware virtual optical network mapping in flexible-grid optical networks (SIA-VONM). The objective is to minimize the total cost of transponders, regenerators, and shared infrastructure for a given set of virtual optical networks, which can survive single link failures. We first provide the problem definition of SIA-VONM, and then formulate the problem as an integer linear program (ILP). We also develop a novel heuristic algorithm together with a baseline algorithm and a lower bound. Numerical results show that our proposed heuristic achieves results that are very close to those of the ILP for small scale problems, and that our proposed heuristic can solve large scale problems very well.

Survivable impairment-aware traffic grooming and regenerator placement with connection-level protection

In this paper, we address the problem of survivable traffic grooming and regenerator placement in optical wavelength division multiplexing (WDM) networks with impairment constraints. The working connections are protected end to end by provisioning bandwidth along a sequence of lightpaths through either a dedicated or a shared connection-level protection scheme. We propose an auxiliary-graph-based approach to address the placement of regenerators and grooming equipment for both working and backup connections in the network in order to minimize the total equipment cost. Simulation results show that the proposed algorithms outperform lightpath-level protection algorithms, in which each lightpath is protected separately. We also show the performance of connection-level protection under both dedicated and shared protection schemes in terms of the network cost, along with the effect of different cost models on equipment placement and performance for networks with different line rates. The restoration time of dedicated and shared connection-level protection is also investigated.

Reliable resource allocation for optically interconnected distributed clouds

In this paper, we study the reliable resource allocation (RRA) problem of allocating virtual machines (VMs) from multiple optically interconnected data centers (DCs) with the objective of minimizing the total failure probability based on the information obtained from the optical network virtulization. We first describe the framework of resource allocation, formulate the RRA problem, and prove that RRA is NP-complete. We provide an algorithm, named Minimum Failure Cover (MFC), to obtain optimal solutions for small scale problems. We then provide a greedy algorithm, named VM-over-Reliability (VOR), to solve large scale problems. Numerical results show that VOR achieves results close to optimal solutions gained by MFC for small scale problems. Numerical results also show that VOR outperforms the resource allocation through random DC selection (RDS).

Holding-time-aware scheduling for immediate and advance reservation in elastic optical networks

In this paper, we consider the problem of routing, modulation, and spectrum assignment (RMSA) for immediate and advance reservation requests in elastic optical networks. We design a two-dimensional resource model for maintaining resource state information in both spectrum and time domains. For the purpose of minimizing the blocking probability and increasing spectrum utilization, we develop a two phase RMSA algorithm that attempts to decrease spectrum resource fragmentation by scheduling the requests in a manner that takes into account the holding time of each request. We design a simulation to evaluate the performance of the proposed algorithm, and the experiment results show that our proposed two phase RMSA algorithm can greatly reduce blocking probability and obtain high spectrum utilization.

Virtual network provisioning over distance-adaptive flexible-grid optical networks [Invited]

In software-defined optical networks (SDONs), network services are provided in terms of virtual optical networks (VONs). VON provisioning requires additional considerations regarding their optical characteristics and constraints compared to virtual networks offered in the electrical domain. In this paper, we present a new VON provisioning procedure that is specifically designed for distance-adaptive flexible-grid optical networks. Simulations show up to three times increase in network capacity by leveraging the combined effect of flexible node mapping and distance-adaptive modulation.

Systematic analysis of intra-superchannel nonlinear crosstalk in flexible grid networks

Intra-superchannel nonlinear crosstalk affects center subcarriers of multi-carrier superchannels more than the edge subcarriers; its impact on center subcarriers significantly increases with increase of the number of subcarriers. Power pre-emphasis of subcarriers effectively equalizes performance and extends reach by 20%.

Phase noise mitigation of QPSK signal utilizing phase-locked multiplexing of signal harmonics and amplitude saturation.

We demonstrate an all-optical phase noise mitigation scheme based on the generation, delay, and coherent summation of higher order signal harmonics. The signal, its third-order harmonic, and their corresponding delayed variant conjugates create a staircase phase-transfer function that quantizes the phase of quadrature-phase-shift-keying (QPSK) signal to mitigate phase noise. The signal and the harmonics are automatically phase-locked multiplexed, avoiding the need for phase-based feedback loop and injection locking to maintain coherency. The residual phase noise converts to amplitude noise in the quantizer stage, which is suppressed by parametric amplification in the saturation regime. Phase noise reduction of ∼40% and OSNR-gain of ∼3  dB at BER 10(-3) are experimentally demonstrated for 20- and 30-Gbaud QPSK input signals.

Survivable impairment-constrained virtual optical network mapping in flexible-grid optical networks

In this paper, we study the problem of survivable impairment-constrained virtual optical network mapping in flexible-grid optical networks (SIC-VONM). The objective is to minimize the total cost of working and backup resources, including transponders, regenerators, and shared infrastructure, for a given set of virtual optical networks, which can survive single link failures. We first provide the problem definition of SIC-VONM, and then formulate the problem as an integer linear program (ILP). We also develop a novel heuristic algorithm, together with a baseline algorithm and a lower bound for comparison. Numerical results show that our proposed heuristic achieves results that are very close to those of the ILP for small-scale problems and that our proposed heuristic can solve large-scale problems very well.

Survivable path computation in PCE-based multi-domain networks

We propose an optimal scheme for finding end-to-end shortest disjoint paths with a given sequence of domains in path computation element-based multi-domain networks. We compute the shortest path over multiple domains in the forward direction and compute the disjoint path in the backward direction. The scheme has lower time and message complexity compared to contemporary schemes for finding optimal survivable paths across domains. We prove the optimality of the proposed scheme. To further simplify the implementations in practical scenarios, we also provide heuristic algorithms. Simulation results exhibit superior performance of the proposed optimal and heuristic algorithms compared to existing approaches.