Yoshihiko Uematsu

Multi-staged network restoration from massive failures considering transition risks

In a scenario of restoration from massive failures, a network is repaired through multiple restoration stages because availability of repair resources is limited. In a practical case, a network operator should assure the reachability of important traffic in transient stages, even as risks and/or operational overheads caused by stage transitions are suppressed. We discuss the novel problem of optimizing both traffic recovery ratio and transition risks caused by paths switching operation. We formulate our problem as linear programming, and show that it obtains Pareto-optimal solutions of traffic recovery versus transition risks. We also propose a heuristic algorithm for applying networks consisting of a few hundred nodes, and it could produce sub-optimal solutions within 4% difference from optimal solutions.

Forward Error Correction for Visual Communication Systems Using VBR Codec

Packet loss and delay cause degradation in the quality of real-time, interactive applications such as video conferencing. Forward error correction (FEC) schemes have been proposed to make the applications more resilient to packet loss, because the time required to recover the lost packets is shorter than that required to retransmit the lost packets. On the other hand, the codec generally used in real-time applications like MPEG4 has the feature that the sending bit rate and the packet size of the traffic vary significantly according to the motion of an object in a video. If the traditional FEC coding, which is calculated on the basis of a fixed-size block, is applied to such applications, a waste of bandwidth and a delay variation are caused and the quality is degraded. In this paper, we propose suitable FEC schemes for visual communication systems using variable bit-rate (VBR) codec and evaluate the effectiveness of these schemes using our prototype implementation and experimental network.

Experiments on Multi-layer Network Virtualization towards the Software Defined Transport Network

This paper proposes a novel architecture which enables software defined networking not only at the routing layer but also at the transport layer. Proposed architecture provides multiple SDTNs with wide range of controllability level, in spite that the SDTNs coexist upon a shared multilayered network infrastructure. We have conducted a nationwide experiment where we have provided SDTNs to practical users such as broadcasting studios. Through the experiments, we have successfully verified the resource management mechanism and network control functionalities.

End-node-based congestion-aware network load balancing

Streaming services and visual communication services delivered over the Internet have become popular in recent years. In the future, broadband services using MPEG2/4 will become the dominant type. These services require transport protocols that provide high quality and high throughput from end to end of the system. We propose a new transfer method that allows the network load to be adaptively balanced according to the networks state. We also estimated the effectiveness of the proposed scheme by computer simulation.

Resolution of network topology using fast graph mining

We propose algorithms that uses fast graph mining for resolving the network topology to a locally regulated area defined as a component of network topology. Though the IP backbone network should be reconfigured periodically in accordance with environmental changes, reconfiguration results in heavy workload, such as routing re-designs or testing these re-designs for network operators. If a network can be reconfigured within the component, however, we can drastically reduce the operation workload for network reconfiguration. For finding the components from the network topology, we should solve the subgraph isomorphism problem, which is NP-hard. We propose the heuristic graph mining algorithm that reduces the size of search space by considering network operating conditions. We visualize the results of components analysis, and show that the computation finishes within the practical time.

OSPF and BGP State Migration for Resource-Portable IP Router

This paper proposes an Internet protocol (IP) state migration method for developing resource-portable IP routers that are not virtual-machine based but commercial based. Resource-portable IP routers have the potential for achieving a sustainable network by functioning as a shared backup router. While previous studies relied on a virtualized technology (e.g., a virtual machine-based router on commodity hardware), current commercial routers was not virtualized but implemented as a proprietary hardware and software. We achieved IP state migration for a proprietary router with control packet sniffing of the open shortest path first (OSPF) protocol and border gateway protocol (BGP) peer masquerade using a software-defined network controller. We implemented our method and verified the accuracy of the state migration of routing tables generated using OSPF and BGP.

Role of ATM transport system and implementation of ATM cross-connect system

This paper describes the role of the ATM transport system in a multi-service network. The ATM transport system based on virtual paths is an economical and flexible infrastructure. This paper describes the role and features of the ATM transport system in the IP era. This paper also introduces the requirements of an ATM cross-connect system for a multi-service network.

High-quality clock distribution method with fast-restoration for synchronous ring networks

In synchronous networks, the reference timing signal of the primary reference clock is distributed to each clock supply module (CSM), which provides clocks to the communication equipment in each node. This paper proposes a high-quality clock distribution method for synchronous ring networks. Since the reference is directly fed into each CSM in the ring without going through the CSMs in the intermediate nodes, each CSM receives the reference with a small amount of wander. The restoration procedure of the proposed clock distribution path is performed only within the node nearest to the failure and does nor require communication between nodes. Therefore, it has a short restoration delay.