Kazuyuki Tajima

Asymmetric ATM-PON interface compliant to ITU-T/FSAN standard for global optical access systems

This paper presents a first optical access implementation prototype of asymmetric 622 Mbps/156 Mbps ATM-PON interface compliant to ITU-T/FSAN standard, with a dynamic bandwidth allocation mechanism for efficient IP traffic accommodation.

Hub site oriented traffic grooming for mesh OTN/WDM networks

We have proposed a novel traffic grooming method with a relaxed ILP model considering hub site locations. This method showed more than 80% of computation time reduction with maintaining the grooming performance.

Iteration-free node-disjoint paths search in WDM networks with asymmetric nodes

Provisioning of a pair of disjoint paths is very important in WDM network planning and management to provide fault tolerant services. However, known node-disjoint paths search methods do not efficiently work in networks with asymmetric nodes which have restrictions on the internal connection between outer links. In this paper, we present a novel node-disjoint paths search method for networks with asymmetric nodes. The proposed approach handles the internal connections properly. In simulation results, the proposed approach efficiently solves the problems. In addition, the proposed method can result in valid disjoint paths with low computation cost.

Wavelength defragmentation for seamless service migration

Emerging applications require future elastic optical networks to provide dynamic and reconfigurable services while maintaining efficient usage of wavelength resources. In this paper, we propose integer linear programming (ILP)-based wavelength defragmentation solutions with minimal optical path disruptions during the migration process. The new approaches achieve up to 20% resource efficiency improvement with less than a quarter of disruptions compared to a conventional approach in the sample networks. In addition, we enhance our approach to shorten the computation time and evaluate it under a computation time limitation of 10 min. The enhanced approach also achieves a resource efficiency improvement of more than 20% with no optical path disruption in the realistic networks, compared with the case where defragmentation is not supported.

Cost-efficient multi-layer network design employing traffic re-aggregation and shared protection across layers

Shared protection/restoration is a promising solution for reducing protection resources and is supported at each layer of the current multi-layer networks. Software-defined networking is expected to reduce equipment cost as well as operational cost by orchestrating these shared protection functionalities. However, although protection resource sharing improves link utilization, it sometimes increases the required equipment. Meanwhile, traffic re-aggregation at each layer is an important technique for low volume traffic to utilize the underlying link capacity more efficiently, but re-aggregation also makes it difficult to share protection resources with traffic at lower layers. In this paper, we present multi-layer network design strategy and method that reduce equipment cost by means of both traffic re-aggregation at each layer and protection resource sharing among multiple service traffic at different layers. The strategy first prioritizes traffic re-aggregation at each layer, and then maximally delegates shared protection to lower layers as long as it does not increase the required capacity at the lower layer. Evaluation results from the example three-layer networks confirm that the proposed method can effectively reduce equipment cost compared to the conventional design method. Cost reduction is achieved by leveraging shared protection functions at multiple layers.

An Evaluation Technique Using Network Voronoi Diagram for Balanced Optical Network Design

An optical network with wavelength-division multiplexing technology enables us to communicate with a large capacity. To minimize capital expenditure, cost-effective network architecture is urgently required. Network evaluation has been conducted using quantitative indices such as equipment cost and optical signal degradation. In fact, experts use a subjective equipment allocation balance when they evaluate the final network design. But it is still difficult to establish an objective criterion and an evaluation method. This study focuses on the communications equipment distribution balance as an evaluation criterion and proposes an evaluation technique using the Network Voronoi diagram.

Towards seamless service migration in network re-optimization for optically interconnected datacenters

Emerging applications require datacenter networks to provide dynamic and reconfigurable services in order to adapt to the dynamicity of cloud traffic, as well as to maintain the optimality of resource utilization. In this paper, we demonstrate novel re-optimization design techniques for realizing agile and seamless service. Our main contribution is a novel integer linear programming (ILP) based approach which can minimize connection disruption, while optimizing resource utilization in a re-optimization process. We propose an ILP-based approach that integrates resource assignment and resource dependency digraph construction. We also propose a method to determine migration order. We compare the proposed ILP-based approach with a heuristic approach in terms of the number of connection disruptions and the migration process. Simulation results demonstrate the effectiveness of our approach.

Wavelength defragmentation with minimum optical path disruptions for seamless service migration

We propose wavelength defragmentation solutions with minimum optical path disruptions. The new approaches achieve up to 20% resource efficiency improvement with less than one fourth of disruptions compared to the conventional approach.

Cost-Efficient Traffic Aggregation Employing Cross-Layer Shared Protection

Shared protection/restoration is a promising solution for reducing protection resources and is supported at each layer of the current multi-layer networks. Software-defined networking is expected to reduce equipment cost as well as operational cost by orchestrating these shared protection functionalities. However, although protection resource sharing improves link utilization, it sometimes increases the required equipment. Meanwhile, traffic re-aggregation at each layer is an important technique for low volume traffic to utilize the underlying link capacity more efficiently, but re-aggregation also makes it difficult to share protection resources with traffic at lower layers. In this paper, we present multi-layer network design strategy and method that reduce equipment cost by means of both traffic re-aggregation at each layer and protection resource sharing among multiple service traffic at different layers. The strategy first prioritizes traffic re-aggregation at each layer, and then maximally delegates shared protection to lower layers as long as it does not increase the required capacity at the lower layer. Evaluation results from the example three-layer networks confirm that the proposed method can effectively reduce equipment cost compared to the conventional design method. Cost reduction is achieved by leveraging shared protection functions at multiple layers.

Evaluation of wavelength defragmentation effectiveness in elastic optical networks

We demonstrate more than threefold increase of “effective capacity” by defragmentation in a realistic elastic network. Through diversified analysis, we also confirm that two simple indices, High-slot-Mark and Utilization-Entropy, represent wavelength fragmentation conditions well.