Takashi Miyamura

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.

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.

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.

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.

Minimum Backup Configuration-Creation Method for IP Fast Reroute

IP Fast Reroute techniques have been proposed for achieving fast failure recovery in just a few milliseconds. The basic idea of IP Fast Reroute is to reduce recovery time after failure by precomputing backup routes. A multiple routing configurations (MRC) algorithm has been proposed for obtaining IP Fast Reroute. MRC prepares backup configurations, which are used for finding a detour route after failure. On the other hand, requiring too many backup configurations consumes more network resources. It is necessary to recover more traffic flows with fewer backup configurations to ensure scalability. We propose a new backup configuration-creation algorithm for maximizing traffic flows which are fast recovered as much as possible under a limited number of backup configurations. The basic idea is to construct a spanning tree excluding failure links with higher link-loads in each backup configuration. We show that our algorithm has more robust on actual large IP networks.

Enhancing Bandwidth on Demand Service Based on Virtual Network Topology Control

This paper presents multilayer IP optical traffic engineering technologies based on VNT (virtual network topology) control and studies their application to BoD (bandwidth on demand) services to improve flexibility and efficiency. Multilayer TE (traffic engineering) optimizes network-resource utilization considering all layers, rather than performing optimization independently for each layer, by performing traffic control in cooperation with IP routes and optical cross-connects (OXCs) in multilayer IP optical networks. Hence, we can accommodate unexpected traffic- demand fluctuations and network failures by dynamically reconfiguring VNT so that it consists of several optical paths among IP routers. The key to achieving multilayer TE lies in the optimal design of VNT based on measured traffic demand. Thus, by introducing multilayer TE into a BoD service, we can enhance flexibility of the service regarding unexpected traffic- demand changes without adding operational overhead that affects customers of the service.

On the stability of virtual network topology control for overlay routing services

Overlay networks achieve new functionality and enhance network performance by allowing routing to be controlled at the application layer. However, these approaches result in degradations of underlying networks due to the selfish behavior of overlay networks. In this paper, we investigate the stability of virtual network topology (VNT) control under the overlay networks that perform dynamic routing updates. We reveal that the dynamics of routing on overlay networks causes a high fluctuation in the traffic demand matrix, which leads to significant instability of VNT control. To overcome the instability induced by the overlay routing, we introduce hysteresis to the VNT control. Simulation results indicate that the hysteresis mechanism improves the network stability, but cannot always improve the network performance. We therefore extend the hysteresis mechanism and show that the proposed method improves both the network stability and the performance when the amount of traffic for overlay network is not large.

A disjoint path selection scheme based on enhanced shared risk link group management for multi-reliability service

We consider a mechanism for providing a multi-reliability service in multilayer GMPLS networks. By introducing GMPLS restoration techniques and shared risk link group management, we can provide a highly reliable protected connection service. However, there is a trade-off between reliability and efficiency of network resource usage. In addition, reliability requirements differ depending on the type of service (e.g., Internet access or leased line). Thus, we propose a mechanism for calculating an efficient route for a protected connection that can satisfy specific reliability conditions requested by customers. We also present simulation results that indicate our schemes are remarkably effective for achieving a better balance between end-to-end reliability and efficiency. We also demonstrate the quantitative relationship between availability of service and resource efficiency through simulation experiments

Dispersing Hotspot Traffic in Backup Topology for IP Fast Reroute

A backup topology design algorithm for avoiding congestion in IP fast reroute is presented. In IP fast reroute techniques, detour routes are computed by using backup topologies. Reducing the number of backup topologies is the main problem, but some links will become overloaded if the number of backup topologies is reduced. The proposed backup topology design algorithm splits the traffic on high load links to other links by considering network conditions, such as the traffic matrix or topology. The key idea of the algorithm is a new concept called the special node, which has a higher node degree in a backup topology, to handle the backup topology design problem. The effectiveness of the algorithm in terms of maximum link load reduction is quantitatively shown.