Published papers

Connection setup on various computer networks is now achieved by GMPLS. This technology is based on the source-routing approach, which requires the source node to store metric information of the entire network prior to computing a route. Thus all metric information must be distributed to all network nodes and kept up-to-date. However, as metric information become more diverse and generalized, it is hard to update all information due to the huge update overhead. Emerging network services and applications require the network to support diverse metrics for achieving various communication qualities. Increasing the number of metrics supported by the network causes excessive processing of metric update messages. To reduce the number of metric update messages, another scheme is required. This paper proposes a connection setup scheme that uses flooding-based signaling rather than the distribution of metric information. The proposed scheme requires only flooding of signaling messages with requested metric information, no routing protocol is required. Evaluations confirm that the proposed scheme achieves connection establishment without excessive overhead. Our analysis shows that the proposed scheme greatly reduces the number of control messages compared to the conventional scheme, while their blocking probabilities are comparable.

An innovative energy-efficient network design algorithm and a tool to lower the network power consumption are proposed. The goal is an energy efficient network that carries its rated communication load while meeting the QoS requirements by using the minimum set of nodes and links. QoS metrics include hop limit, bandwidth limit reliability and stability. The proposed algorithm addresses the set-covered problem. To discover the optimum network configuration efficiently, we propose a network configuration generation algorithm that utilizes DAPDNA-2, a parallel data flow type reconfigurable processer. The processor automatically produces the node/link set in n-digit binary form where links are modeled as ‘‘1’’ for power on and ‘‘0’’ for power off; it also confirms that the QoS requirements are satisfied. Evaluation results show that DAPDNA-2 is 2-orders faster than the conventional sequential method running on a Pentium-4 processor. Prototype Gigabit Layer-2 switches having remote link power on/off and traffic monitoring functions are developed. Using these switches, we successfully demonstrate an energy efficient IP/Ethernet network. The evaluation results show that network power savings of up to 30% can be realized under the NFSNET topology model. The proposed algorithm and power efficient network architecture can be applied to realize the future green network.

This paper proposes a power efficient optical access network architecture that reduces OLT power consumption. Several PON trees are aggregated thanks to waveguide optical switches with nano second-order switching speed. The proposed network dynamically activates/deactivates OLT according to ONU traffic load, and reduces OLT power use while maintaining transmission fairness.

The power consumption of network devices will continue to increase due to the increase in transmission speed and reach 97 GW by 2020. This paper introduces urgently needed network power reduction methods. First, the paper focuses on the optical access network architectures that use active devices such as high-speed optical switches or variable wavelength lasers to achieve slgnificant energy savings. These new architectures are expected to dramatically reduce the Optical Network Unit (ONU)'s power consumption by introducing an effective sleep mode. Second, this paper introduces an extremely energy efficient future-Internet architecture that uses a large optical aggregation network. It combinesthe centralized Service Cloud with the Cloud Router and application servers and the Optical Aggregation Network. The optical aggregation network can be realized with just simple optical circuit switches, wavelength-Converters,and wavelength-multiplexers/demultiplexers; the complicated layer-3 function is realized only at the center Cloud Router. The optical aggregation network realizes a network structure well suited to today's traffic centralization. According to our evaluation, total network power consumption Can be reduced to Just 1/1000 compare to the electrical based network architecture.

An active optical access network architecture with our newly developed PLZT ((Pb, La) (Zr, Ti)O3) high-speed optical switch is introduced, with a view to realizing the nextgeneration high capacity scalable access network. This system is developed based on the latest IEEE standard of PON (10G-EPON; IEEE802.3av) in consideration of the coordination with future high capacity PON. PLZT high-speed optical switches are able to switch an optical signal at nano-second speed (<5–10 ns). Generally, the merits of using optical switches are increasing the number of subscribers and transmission distance easily, preventing malicious ONUs from interfacing with the communication between OLT and the other ONUs, realizing fast fiber and OLT protection/restoration and providing various services by controlling optical switches dynamically. This paper focuses on two key technologies; a PLZT optical switch and a new discovery process for active optical access network based on MPCP defined at IEEE802.3. A major challenge in designing active optical access network is supporting the discovery process of MPCP because it does not offer broadcast transmission unlike the regular PON. We propose here a new discovery process; it has been tested successfully in an implementation of our proposed system.

This paper proposes a scalable active optical access network using high-speed Plumbum Lanthanum Zirconate Titanate (PLZT) optical switch/splitter. The Active Optical Network, called ActiON, using PLZT switching technology has been presented to increase the number of subscribers and the maximum transmission distance, compared to the Passive Optical Network (PON). ActiON supports the multicast slot allocation realized by running the PLZT switch elements in the splitter mode, which forces the switch to behave as an optical splitter. However, the previous ActiON creates a tradeoff between the network scalability and the power loss experienced by the optical signal to each user. It does not use the optical power efficiently because the optical power is simply divided into 0.5 to 0.5 without considering transmission distance from OLT to each ONU. The proposed network adopts PLZT switch elements in the variable splitter mode, which controls the split ratio of the optical power considering the transmission distance from OLT to each ONU, in addition to PLZT switch elements in existing two modes, the switching mode and the splitter mode. The proposed network introduces the flexible multicast slot allocation according to the transmission distance from OLT to each user and the number of required users using three modes, while keeping the advantages of ActiON, which are to support scalable and secure access services. Numerical results show that the proposed network dramatically reduces the required number of slots and supports high bandwidth efficiency services and extends the coverage of access network, compared to the previous ActiON, and the required computation time for selecting multicast users is less than 30 msec, which is acceptable for on-demand broadcast services.

This paper proposes a new replica placement algorithm that expands the exhaustive search limit with reasonable calculation time. It combines a new type of parallel data-flow processor with an architecture tuned for fast calculation. The replica placement problem is to find a replica-server set satisfying service constraints in a content delivery network (CDN). It is derived from the set cover problem which is known to be NP-hard. It is impractical to use exhaustive search to obtain optimal replica placement in large-scale networks, because calculation time increases with the number of combinations. To reduce calculation time, heuristic algorithms have been proposed, but it is known that no heuristic algorithm is assured of finding the optimal solution. The proposed algorithm suits parallel processing and pipeline execution and is implemented on DAPDNA-2, a dynamically reconfigurable processor. Experiments show that the proposed algorithm expands the exhaustive search limit by the factor of 18.8 compared to the conventional algorithm search limit running on a Neumann-type processor.

ルータの集約及び光スイッチの使用により低消費電力を達成する光アグリゲーションネットワークにおいて，2×2光スイッチを用いた，高信頼性と低光損失性を同時に達成するアーキテクチャを提案した．またその設計手法を示し既存トポロジーとの比較を行った。

Recently, wide area Ethernet, which provides virtual connections between company branches by using Ethernet technology, has become wide spread. Ethernet originally lacked fault recovery mechanisms required in wide area networks (WANs) since it originated as local area network (LAN) technology. Protection mechanism against link or node failure is proposed in Ethernet network, but many frame losses are inevitable during the switch over to the backup path. Therefore, to improve reliability of wide area Ethernet, a fault recovery method with few frame losses is required. This paper proposes a fast fault recovery method for reducing frame losses during the switching over to another route. To achieve fast recovery, a pre-established forwarding table is introduced, which is searched when a fault occurs and frames are forwarded. This paper also proposes a bandwidth control function to guarantee the quality of service of connections that do not use the failed link when a fault occurs. A computer simulation showed that by adding the proposed fault recovery method to the conventional protection method, frame losses can be decreased. The proposed fault recovery method was implemented on a software switch framework to confirm its effectiveness.

近年日本では家庭用ソーラーパネルやマイクロCHPが急速に普及しており, それらの分散化された発電エネルギーの利用法が日本におけるスマートグリッド研究課題の一つである. 効率的な発電エネルギー利用のため消費デバイスとのスケジューリング連携が有効であり, 太陽光発電出力量の短期的な予測が重要となる. 従来の太陽光発電出力予測手法は主に中長期的な規則性を伴う出力変動について議論しており, 気候による不規則な変動の激しい短期的な予測には適さない. また既存の短期的な予測手法についても特別な気象観測機器が必要であるという課題が残る. そこで本論文では, 気象観測情報を用いずに各ソーラーパネルの発電出力情報のみを用いて予測する手法を提案する. 本手法では, ネットワークに接続されたスマートメータから各地点の発電出力情報をサンプリングし, データ補間及びオプティカルフロー推定技術を用いて, 各地点における将来の発電出力量を予測する. その際, 過去のサンプリングデータを仮想的に補間元データとして用いるバーチャルサンプリングにより, 少ないサンプリング数でも高精度な予測を可能とする. コンピュータシミュレーションにより, 本予測手法の有効性及びバーチャルサンプリングによる予測精度の改善を示す.

In order to reduce the energy consumption of transport/data center networks, MiDORi network technology is introduced. This network is based on the concept of aggregating traffic into specific links, and powering off interfaces of routers/switches that do not convey traffic. In this paper, a practical energy-optimal topology calculation method is proposed for the MiDORi PCE. The proposal can adjust the link reduction rate and the calculation time by setting different values for the depth. Moreover, two failure management methods are proposed in order to reduce the risk of traffic aggregation. By computer simulation, it is shown that the proposed method is effective from several perspectives. Lastly, a prototype system of MiDORi network is described to observe the aspect of self organization.

In this paper, Transmission Control Protocol/Intemet Protocol(TCP/IP) over Stream Control Transmission Protocol (SCTP)/IP parallel transmission system is proposed to realize large TCP/IP throughput. The proposed system enables SCTP/IP connection between switches by protocol stacking. The proposed system is implemented on a software switch to evaluate its performance. The evaluation result indicates that proposed system can achieve 90% throughput compared with serial transmission when the delay difference among parallel routes is 20 msec.

スマートネットワークが,原子力依存を減らさざるをえない現状と相侯って,急速に進展することが予想され,その中で,情報,通信技術者から見たビジネスチャンスについて,本論文では概説する.

This paper proposes an on-demand multicast slot allocation scheme for an active optical access network that uses Mach-Zehnder-type high-speed optical switches, which are achieved by the Plumbum Lanthanum Zirconate Titanate (PLZT) switching technology. The Active Optical Network, called ActiON, is based on slot-based switching. Compared to the Passive Optical Network (PON), ActiON quadruples the number of subscribers (128 users) per optical line terminal (OLT) and doubles the maximum transmission distance (40 km) between OLT and optical network units (ONUs). However, as ActiON uses slot-based switching, it needs a large number of slots to deliver multicast contents to the requesting users. This greatly lowers network utilization rates. The proposed multicast slot allocation scheme overcomes this problem to provide on-demand multicast services, while keeping the advantages of ActiON. Multicast delivery is realized by running the Mach-Zehnder-type high-speed optical switch elements in distribution mode, which forces the switch to behave as an optical splitter. The proposed scheme iteratively solves the integer linear programming (ILP) problem to associate multicast users with slots. Numerical results show that the proposed scheme dramatically reduces the required number of slots, compared to non-multicast ActiON and provides comparable the performance of bandwidth efficiency to 10 G-EPON, and the required computation time of the proposed scheme is less than 0.3 sec, which is feasible for on-demand services.

The Internet is an extremely convenient network and has become one of the key infrastructures for daily life. However, it suffers from three serious problems; its structure does not suit traffic centralization, its power consumption is rapidly increasing, and its round-trip time (RTT) and delay jitter are large. This paper proposes an extremely energy efficient layer-3 network architecture for the future Internet. It combines the Service Cloud with the Cloud Router and application servers, with the Optical Aggregation Network realized by optical circuit switches, wavelength-converters, and wavelength-multiplexers/demultiplexers. User IP packets are aggregated and transferred through the Optical Aggregation Network to Cloud transparently. The proposed network scheme realizes a network structure well suited to traffic centralization, reduces the power consumption to 1/20-1/30 compared to the existing Internet, reduces the RTT and delay jitter due to its simplicity, and offers easy migration from the existing Internet.

We evaluated a prototype for 10Gbps Active Optical Access System in which optical switches are used instead of optical splitters in PON. We demonstrate that it achieved optical signal transmission over 40km.

A dynamic deficit round-robin (DDRR) scheduling scheme for a 5-Tb/s switch is proposed. DDRR is a DRR-based packet scheduler and it can satisfy the max-min fair share. However, DRR cannot satisfy both high throughput and delay requirements. DDRR resolves the problem by changing the granularity for deficit counters according to the packet lengths at queue heads. Simulation results showing the efficiency of DDRR are presented and an implementation of DDRR for the switch is also described. © 2002 IEICE.

Many address lookup methods for use on IP routers to improve their packet-forwarding capability have been proposed. However, their performance prediction ability is poor because actual traffic characteristics are not considered in their evaluation processes. The actual traffic must be considered in order to predict router performance more accurately, especially for layer 3 and 4 address lookups, whose performances are more affected by the flow characteristics. We describe a method for predicting IP lookup algorithm performance that is based on statistical analysis of the Internet traffic. We present an example of its application to an existing IP lookup algorithm and show, based on simulation results, that our method can provide accurate performance prediction for IP lookup algorithms. © 2002 IEICE.

This paper describes multi-layer traffic engineering and signaling technologies in photonic-GMPLS-router networks. Multi-layer traffic engineering, which yields the dynamic cooperation of IP and photonic layers for providing IP services cost-effectively, is described. To realize multi-layer traffic engineering, we propose an OSPF extension that advertises both the number of total wavelengths and the number of unused wavelengths, and an RSVP-TE extension that minimizes the number of wavelength conversions needed. In addition, this paper presents a heuristic-based multi-layer topology design scheme that uses IP traffic measurements in a generalized multi-protocol label switch (GMPLS). Our design scheme yields the optical label switch path (OLSP) network topology, i.e. OLSP placement, that minimizes network cost, in response to fluctuations in IP traffic demand. In other words, the OLSP network topology is dynamically reconfigured to match IP traffic demand. Networks are reconfigured by the proposed scheme so as to utilize the network resources in the most cost-effective manner.

A 5-Tb/s asynchronous transfer mode (ATM) switching system called OPTIMA-2 (optically interconnected multi-stage ATM switch architecture ) that uses optical packet-by-packet switched wavelength division multiplexing (WDM) links for the intraswitch interconnections was experimentally described. The design, fabrication, and evaluation of the optical WDM interconnection modules for OPTIMA-2 were discussed. The feasibility of a multi Tb/s switching system was successfully demonstrated.