Shin’ichi Arakawa

Gradually reconfiguring virtual network topologies based on estimated traffic matrices

Traffic matrix is essential to traffic engineering (TE) methods. Because it is difficult to monitor traffic matrices directly, several methods for estimating them from link loads have been proposed. However, estimated traffic matrix includes estimation errors which degrade the performance of TE significantly. In this paper, we propose a method that reduces estimation errors while reconfiguring the virtual network topology (VNT) by cooperating with the VNT reconfiguration. In our method, the VNT reconfiguration is divided into multiple stages instead of reconfiguring the suitable VNT at once. By dividing the VNT reconfiguration into multiple stages, our traffic matrix estimation method calibrates and reduces the estimation errors in each stage by using information monitored in prior stages. We also investigate the effectiveness of our proposal using simulations. The results show that our method can improve the accuracy of the traffic matrix estimation and achieve an adequate VNT as is the case with the reconfiguration using the actual traffic matrices.

Adaptive Virtual Network Topology Control Based on Attractor Selection

One approach to accommodating traffic on a wavelength-routed optical network is to construct a virtual network topology (VNT) by establishing a set of lightpaths between nodes. To accommodate fluctuating traffic on a VNT, we propose an adaptive VNT control method, which reconfigures VNTs according to traffic conditions on VNTs, in IP over wavelength-routed wavelength-division-multiplexing networks. To achieve adaptability in the VNT control method, we focus on attractor selection, which models behaviors where biological systems adapt to unknown changes in their surrounding environments and recover their conditions. The biological system driven by attractor selection adapts to environmental changes by selecting attractors at which the system condition is preferable. Our VNT control method uses deterministic and stochastic behaviors and controls these two appropriately by simple feedback of the conditions of an IP network. By utilizing stochastic behavior, our new approach adapts to various changes in traffic demand with selecting suitable attractors, which correspond to VNTs in our method, for the current traffic demand. Moreover, to define feedback of the conditions on the IP network, our proposed scheme only uses load information on links, which is easily and directly retrieved and thus achieves quick responses to changes in traffic demand. The simulation results indicate that our VNT control method based on attractor selection quickly and adaptively responds to various changes in traffic demand, and our method adapts to at most twice larger changes in traffic demand than existing heuristic approaches.

Parallel reservation protocols for achieving fairness in optical burst switching

Optical burst switching (OBS) is one promising method for data transfer in photonic networks based on a WDM (wavelength division multiplexing) technology. In the OBS scheme, the wavelength is exclusively reserved along the source and destination nodes, when the burst data is generated at the source. Then, efficient data transfer is expected. However, its performance is heavily dependent on the number of links that the lightpath goes through, We propose a new protocol for OBS networks, where the lightpath for the burst transmission is set up by parallel wavelength reservations. Through simulation results, we show that our protocol makes data transfer efficiently and improves the fairness among the connections with different number of hop counts.

Stability of virtual network topology control for overlay routing services

Overlay networks achieve new functionality and enhance network performance by enabling control of routing at the application layer. However, this approach results in degradations of underlying networks due to the selfish behavior of overlay networks. We discuss the stability of virtual network topology (VNT) control under overlay networks that perform dynamic routing updates. We find that the dynamics of routing on overlay networks cause a high fluctuation in the traffic demand matrix, which leads to significant VNT control instability. To overcome this instability, we introduce three extensions, hysteresis, two-state utilization hysteresis, and filtering, to VNT control. Simulation results show that the hysteresis mechanism improves network stability, but cannot always improve network performance. We therefore extend the hysteresis mechanism and show that it improves both network stability and performance. However, this extension requires a lot of time for the VNT to converge to a stable state. To achieve fast convergence, we use a filtering method for VNT control. Through simulations, we prove that our methods achieve stability against overlay routing without loss of adaptability for changes in traffic demand.

Design Method of Logical Topologies with Quality of Reliability in WDM Networks

As the bandwidth capacity of WDM networks continues to grow rapidly,traffic loss caused by a failure of network components is becoming unacceptable. To prevent such traffic loss and thus enhance network reliability, a protection method that prepares backup lightpaths for each working path is now being developed. In this paper, we first introduce the concept of QoR (quality of reliability), which is a realization of QoS with respect to the reliability needed in a WDM network. We define QoR in terms of the recovery time from when a failure occurs to when traffic on the affected primary lightpath is switched to the backup lightpath. After that, we propose a heuristic algorithm that can be used to design a logical topology that satisfies the QoR requirement for every node pair. The objective is to minimize the number of wavelengths needed for a fiber in the logical topology to carry the traffic with the required QoR. We compare this algorithm with two existing algorithms and show that it enables more effective use of wavelength resources; with the proposed algorithm, up to 25% fewer wavelengths are needed than with the other algorithms.

Re-optimization strategies to maximize traffic-carrying readiness in WDM survivable mesh networks

We propose and compare four re-optimization strategies for mesh survivable networks. We show how these strategies improve the networks ability to carry future random-arrival traffic.

Gradually Reconfiguring Virtual Network Topologies Based on Estimated Traffic Matrices

In this paper, we present a practical VNT (virtual network topology) reconfiguration method for large-scale IP and optical networks with traffic matrix estimation considerations. We newly introduce a partial VNT reconfiguration algorithm with multiple transition stages. By dividing the whole VNT transition sequence into multiple transitions, estimation errors are calibrated at each stage by using network state information of prior stages. Because estimation errors are mainly due to the fewer information in the estimated traffic matrix calculation, our approach tries to increase the constraint conditions for traffic matrix estimation by introducing partial reconfiguration, and to relax the impact of estimation errors by limiting the number of optical-paths reconfigured at each stage. We also investigate the effectiveness of our proposal through simulations and clarify the robustness against estimation errors by using partial reconfiguration.

Analyzing and Modeling Router---Level Internet Topology

Measurement studies on the Internet topology show that connectivities of nodes exhibit power---law attribute, but it is apparent that only the degree distribution does not determine the network structure, and especially true when we study the network---related control like routing control. In this paper, we first reveal structures of the router---level topologies using the working ISP networks, which clearly indicates ISP topologies are highly clustered; a node connects two or more nodes that also connected each other, while not in the existing modeling approaches. Based on this observation, we develop a new realistic modeling method for generating router---level topologies. In our method, when a new node joins the network, the node likely connects to the nearest nodes. In addition, we add the new links based on the node utilization in the topology, which corresponds to an enhancement of network equipments in ISP networks. With appropriate parameters, important metrics, such as the a cluster coefficient and the number of node-pairs that pass through nodes, exhibit the similar value of the actual ISP topology while keeping the degree distribution of resulting topology to follow power---law.

Application of attractor selection to adaptive virtual network topology control

The growth of the Internet and emerging application layer technologies causes numerous changes in network environments. Therefore, it becomes important to achieve adaptive methods of controlling networks in addition to optimizing their performance. To achieve an adaptive network control method, we focus on attractor selection, which models behaviors where biological systems adapt to unknown changes in their surrounding environments and recover their conditions. In this paper, we show the applicability of the attractor selection to the adaptive virtual network topology (VNT) control in IP over wavelength-routed WDM networks. The simulation results indicate that our VNT control method based on attractor selection quickly and adaptively responds to various changes in traffic demand.

Distributed clustering method for large-scaled wavelength routed networks

The scalability of routing protocol has been considered as a key issue in large-scaled wavelength routed networks. Hierarchical routing scales well by yielding enormous reductions in routing table length, but it also increases path length. This increased path length in wavelength-routed networks leads to increased blocking probability because longer paths tend to have less free wavelength channels. However, if the routes assigned to longer paths have greater wavelength resources, we can expect that the blocking probability does not increase. In this paper, we propose a distributed node-clustering method that maximizes the number of lightpaths between nodes. The key idea behind our method is to construct node-clusters that have much greater wavelength resources from the ingress border nodes to the egress border nodes, which increases the wavelength resources on the routes of lightpaths between nodes. We evaluate the blocking probability for lightpath requests and the maximum table length in simulation experiments. We find that the method we propose significantly reduces the table length, while the blocking probability is almost the same as that without clustering.