To achieve the ultra-low latency required by Beyond 5G, realizing direct wavelength connections between users is necessary. Metro networks will also need to accommodate massive multiple wavelengths, several tens of times greater than current wavelength-division multiplexing technology. In this paper, we propose a metro network architecture that achieves multi-band massive multiple wavelengths by using newly developed programmable wavelength selective switches (WSSs). The proposed network introduces a new paradigm of network design and control using Digital Twins. Furthermore, we investigate the impact of remotely located transceivers on the performance of metro networks with programmable WSSs for user direct wavelength connections. We quantify the resource efficiency of the remotely located transceiver model to demonstrate the feasibility of user direct wavelength connection.

The Keio Future Photonic Network Open Laboratory was opened in Apr. 2023 as a testing field for future Beyond 5G networking technology. This paper presents a proof-of-concept system for the new multi-access edge computing technology "AMec" using OpenLab’s networking equipment, and actual application verification experiments using newly installed Hollow-Core optical fiber cables at OpenLab.

This paper proposes a priority-aware guaranteed hardware resource allocation in virtual packet optical nodes (VPONs) and describes experimental evidence of service provisioning with the proposed method on testbed. A network based on the VPON brings solution of service diversification and traffic explosion because it provides multiple services by hardware level separated virtual networks such as IP/Ethernet/ Multi-Protocol Label Switching. The VPON has reconfigurable hardware which is dedicatedly allocated for each service and service-specific logical functions are implemented respectively. However, a previous hardware resource allocation method is not efficient. In previous work, the hardware resources once allocated to a service are not reallocated until the service terminated whenever the hardware is not optimally used. In recent years, hardware reconfiguration time has become shorter and it has enabled to apply for service demand change by releasing hardware from services with low demand and reallocating it to other services with high demand. Thus, this paper proposes preemptive dynamic hardware resource reallocation algorithm for VPON and a priority-aware guaranteed hardware resource reallocation method to realize efficient resource usage and high service capacity. Results of the computer simulation show improving service capability. Furthermore, to demonstrate the feasibility of service provisioning with the proposed method, emulators of the virtual packet optical node were constructed and performed resource reallocation. Results of the experiment show that the virtual packet optical node can configure function chains for providing services based on calculation results of the proposed resource reallocation method.

Recently, the energy consumption in data centers is increasing. Introducing optical circuit to the inter-rack communication is considered as an effective solution. The authors are working on the research and development of the High-speed Optical Layer 1 Switch system for Time slot switching based optical data center networks (HOLST). We focused on Plomb Lanthanum Zirconate Titanate (PLZT) optical switch that performs nano seconds switching time. In this paper, several ideas on how to connect PLZT optical switches and Micro Electro Mechanical Systems (MEMS) optical switches, the composing modules of the HOLST, are proposed to design network architecture and evaluated in order to compare and consider power saving effect. The result of the numerical simulation shows that the proposal architecture achieves 50% energy consumption reduction than the conventional architecture.

In a high-speed backbone network, the failure of a network link may cause large data losses, so it is necessary to reserve spare network resources for faster recovery. The conventional protection methods to reserve backup routes do not consider the failure probability of each network link, so the same amount of network resources for the backup route are needed regardless of the failure probability of network links. This leads a decrease in the number of connections that can be accepted into the network. This paper proposes a routing and capacity allocation method that guarantees the expected value of allocated capacity. We formulate a mixed integer liner programming model for the proposed method. We conduct simulations to study the advantage of the expected capacity guaranteed routing over the conventional routing method in terms of bandwidth blocking probability. The results show that the proposed method reduces the bandwidth blocking probability to about 1/3 as compared to that of the conventional path protection method.

A flexible orthogonal frequency-division multiplexing optical network enables to change bandwidth flexibly by changing the number of sub-carriers. We consider that users request to dynamically change the number of sub-carriers. In this context, the network resources can be used more efficiently. The dynamic bandwidth change needs a certain time. Service centric resource allocation must be considered in terms of waiting time to change the number of sub-carriers. If the user demands drastically increase such as a disaster priority telephone service, a waiting time for bandwidth changes is not tolerated because emergency is time-critical. This is caused by a chain-change of bandwidth such as a multiple-car pileup. This paper proposes a grouped elastic spectrum allocation scheme to satisfy the tolerable waiting time of the service in an optical fiber link. Spectrums are grouped to restrict a waiting time in the proposed scheme. In addition, the proposed scheme determines a margin bandwidth with neighbor spectrums to prevent frequent reallocation by estimating real traffic behavior. Numerical results show that a required bandwidth can be saved with satisfying waiting time constraints. Additionally measurement granularity is discussed.

This paper proposes a source-based high-speed wavelength-path protection scheme configuring a tree-shaped backup path in WDM networks. In the proposed scheme, a failure-detecting node on a primary path starts protection by sending a failure notification to a source node of the primary path through the tree-shaped backup path. Intermediate nodes on the backup path and the source node which receive the failure notification switch to the backup path autonomously. Therefore, the proposed scheme provides high-speed protection. The simulation results revealed that the proposed scheme reduces the failure-recovery time compared with the conventional protection schemes.

This paper aims to design a Hadoop system and evaluates the performance of a task allocation scheme. The task allocation scheme splits each job into tasks using an appropriate splitting ratio, and assigns tasks to slave servers based on server processing performance and network resource availability. We experimentally evaluate the performance of the scale out of the task allocation scheme with five machines. We focus on the configuration of jobtracker and tasktracker in Hadoop. In cases with heterogeneous Hadoop clusters, we distribute task blocks to high-capability slaves with proportionally larger-sized tasks than to low-capability slaves. We create an environment in which high-capability slaves perform more work than low-capability slaves. The experimental testbed results indicate that the task allocation scheme is effective.

Software switches offer flexibility to service providers but potentially suffer from low performance. A software switch called Lagopus was implemented using Intel's Data Plane Development Kit (DPDK), which offers libraries for high-performance packet handling. Prior work on software switches focused on characterizing packet forwarding throughput. In this work, we evaluated the impact of certain parameters and settings in Lagopus on application performance and studied packet drop rates. The importance of receive-thread packet classification for load balancing and to send delay-sensitive flows to a different worker thread from high-throughput flows was first demonstrated. Next, we showed that a loop-count variable used to control packet batching should be kept small in case link utilization is low. Finally, we showed that packet drop rate could be non-zero when the OpenFlow table size is large and packet arrival rate is high, and interestingly, the packet drop rate was higher with four worker threads than with a single worker thread. This implies a need for careful calibration and planning of the parameters of parallelization.

Smart Open Shortest Path First (S-OSPF), which is an extended scheme of OSPF, was previously presented to avoid network congestion. However, it is difficult to achieve S-OSPF implementation, since the S-OSPF architecture is different from the conventional OSPF network architecture. A conventional network requires an autonomous distributed routing architecture, but S-OSPF partly requires a centralized routing architecture while keeping the feature of the conventional network. We employ software-defined networking (SDN) technology to support S-OSPF. Edge routers in the S-OSPF network must have both traffic distribution function, which is a feature of S-OSPF, and OSPF-based forwarding function, which is used in case that the edge router behaves as a transit router as is in the original OSPF network. A conflict occurs on the common forwarding table, which is accessed by SDN and OSPF, in the edge router when we try to utilize existing software modules. To solve this issue, this paper proposes an implementation method by introducing a hybrid router with virtualization technique. A hybrid router by the proposed method achieves the traffic distributing function of S-OSPF as well as the OSPF behavior while minimizing the modification of existing routing software modules. We develop a prototype of the hybrid router, confirm that the traffic distributing function of S-OSPF and OSPF functions work correctly, and observe that the congestion is avoided in our experimental network.

This paper proposes a new two-wavelength design for large-enterprise access links. The goal of this design is to lower power consumption and equipment costs without having a significant impact on performance. In our design, one wavelength is used as part of a lower-rate static circuit for general-purpose IP traffic, while the second wavelength is dynamically configured into a high-rate circuit for large dataset transfers whenever needed. A few provider-router ports are shared among a larger number of customers given that large dataset transfers are relatively infrequent. This leads to potential start-time delays, but results in significant power and cost savings. Using analytical models, we provide a quantitative power-and-cost comparison of our dynamic solution with the static always- on high-rate single-circuit solution used currently. The number of shared provider-router ports is kept large enough based on the number of customers to ensure that the probability of start-time delay exceeding a threshold is less than 1%.

Information-Centric Networking (ICN) employs communication based on location independent data identifiers (IDs) that enables efficient data dissemination. However, some important challenges still remains in the conventional ICN schemes when they are applied to a highly mobile and distributed environment, such as growth in amount of route information or increased transaction load of name resolution services. To accommodate this, we propose a new ICN scheme where routes are aggregated at aggregation nodes and optimized routes are established during data registration transactions to mitigate the amount of route information, delay, and transaction load. We evaluate the proposed scheme using a nation-wide test bed of 37 intermediate nodes and 336 mobile terminals. We show that the proposed scheme enables efficient data dissemination where the mobile terminals register and retrieve data in widely distributed manner.

This article proposes a network control method that realizes on-demand service providing in Elastic Lambda Aggregation Network (EλAN). EλAN is a next-generation access/aggregation network that provides various network services having different protocols and QoS requirements. EλAN also achieves the reduction of total network power consumption by sharing access network equipment by multiple network services. In the proposed method, fixed optical trees are introduced to EλAN to exchange control messages in the same manner as today's FTTH systems. Discovery process and optical path/tree aggregation using the optical trees are explained in this article. We also discuss the energy-saving effect of the optical path/tree aggregation in EλAN.

This paper presents a concept of the Energy Efficient and Enhanced-type Data-centric Network (E3-DCN). For future network technology, the Contents-centric Network (CCN) is widely studied. DCN is an extended version of CCN. M2M communication and mobility of the data are supported. In the enhanced-type DCN, a user requests data name or identifier to the network. If the exactly matched requested data are not found in the network, the network constructs the requested data. E3-DCN provides an energy efficient contents delivery network on the network virtualization platform.

We propose a new efficient singlecast / multicast method for active optical access network using PLZT 10 nsec high-speed optical switches. The Active Optical Network, called ActiON, has been proposed using slot type switched optical network. Compared with Passive Optical Network (PON), ActiON can quadruplicate the number of subscribers (128 users) per OLT and double the maximum transmission distance (40 km) between OLT and ONUs. However, ActiON uses slot based switching method, so it is difficult to realize the multicast delivery. In this paper, we propose the efficient singlecast / multicast method for ActiON by using PLZT optical switch elements which are controlled as “distribution mode” like an optical splitter by applying mid-control voltage. In addition, a new efficient multicast slot allocation method is proposed and formulated as a linear programming problem. This formula develops the maximum number of users which is able to be connected by multicast and the minimum number of slots is used for multicast users.

This paper proposes a fast fault recovery method for the wide area Ethernet. To achieve fast recovery, a pre-established forwarding table is introduced. The pre-established table is looked up when a fault occurs, and frames are forwarded without frame loss. Ethernet lacks of fault recovery features required in Wide Area Network (WAN) since it is originated as Local Area Network (LAN) technology. Protection or restoration is a typical method for fault recovery, but a lot of frame losses are inevitable. Our proposal can decrease frame losses since frames are forwarded without waiting for path switching to be completed to use the pre-preparation table. In addition, the proposed method can be operated with the legacy forwarding method seamlessly. The simulation results show that frame loss decreases to 40% or less with our proposed method.

This paper proposes a distributed virtual network topology (VNT) reconfiguration method for Internet Protocol over a wavelength-division-multiplexing network under dynamic traffic demand. We have developed a simple heuristic algorithm for calculating the VNT for distributed control. A generalized multiprotocol label switching (GMPLS)-based routing protocol has been developed. The VNT is quickly reconfigured by setting up and/or tearing down lightpaths using a GMPLS signaling protocol. Traffic demand is measured at the ingress node and advertised by the extended GMPLS routing protocol. Performance of the proposed method is investigated using variable traffic model.

Multiple fiber ring (MFR) networks employing the optical path (OP) concept are discussed to realize robust networks. The architecture is superior to that discussed in several testbeds, with respect to fault recoverability. Both the OP based and non-OP based MFRs can develop several architectures, each of which provides different performance regarding network resource utilization. The required node system scale can be a good measure in determining the network performance. Network design simulations, varying path distribution patterns, have been performed and they elucidated the criteria for selecting the most suitable architecture in terms of resource utilization.

To realize a large scale and robust photonic transport network, this paper proposes a network protection strategy and maintenance signaling flow for WDM optical path transport networks. The network protection strategy is applicable for mesh-type WDM optical path transport networks, and the OA&M flow that is required for the network to recover from failures are clarified. The proposed OA&M flow does not rely on the OP-AIS (optical path alarm indication signal) generation method. This signaling method can also be applied to the all-optical type network.

In order to realize a large-scale and robust photonic transport network, a network protection strategy and operation, administration, and management (OA&M) realization scheme in wavelength division multiplexing optical path (WDM OP) transport networks has been developed. This paper discusses the networking (restoration/protection) concepts in each optical layer and proposes the most suitable networking strategy. To develop the OA&M technique, the characteristic information format of each optical layer must be discerned. A network node interface (NNI) structure for the WDM OP transport network is proposed. The proposed NNI is defined as the optical transport module (OTM). An OP signal format is defined as the optical transport unit (OTU). Overhead information and schemes to transmit it are also discussed.

This paper proposes a new layered transport network architecture on which the WDM optical path network can be effectively created. The optical path network will play a key role in the development of the transport network that will realize the bandwidth-abundant B-ISDN. This paper extends the layered transport network architecture described in ITU-T Recommendation G.803 which is applied in existing SDH networks. First, we elucidate an application example of WDM optical path networks. Next, we propose a new layered architecture for WDM-based transport networks that retains maximum commonality with the layered architectures developed for existing B-ISDN networks. The proposed architecture is composed of circuit layer networks, electrical path layer networks, optical layer networks, and physical media (fiber) networks. The optical layer is divided into an optical path layer and an optical section layer. The optical path layer accommodates electrical paths. Optical section layer networks are divided into optical multiplex section (OMS) layer networks and optical repeater section (ORS) layer networks. The OMS layer network is concerned with the end-to-end transfer of information between locations transferring or terminating optical paths, whereas the ORS layer is concerned with the transfer of information between individual optical repeaters. Finally, a detailed functional block model of WDM optical path networks, the function allocation of each layer, and an optical transport module (OTM) are developed.

This paper proposes optical path accommodation design algorithms for both the wavelength path (WP) and virtual wavelength path (VWP) schemes with or without failure restoration. The optical path (OP) employs WDM/FDM (wavelength/frequency division multiplexing) and wavelength routing in the path layer of the transport network. The proposed algorithms adopt some heuristic approaches to the algorithmic complexity caused by the NP-completeness of the wavelength assignment problem. The objective function is taken as minimizing the average total number optical path cross-connect (OPXC) ports, in other words, OPXC system scale. Utilizing the developed algorithms, extensive simulations quantitatively evaluate the OPXC system scale requirements of a large scale network whose physical topology and path demand distribution pattern are arbitrary. The simulations reveal the basic difference between the WP and VWP schemes.

This paper proposes a layered network architecture for optical transport networks and the concept of optical path network management. First, the WDM (wavelength division multiplex) based optical path network concept and realization techniques such as the WP (wavelength path) and the VWP (virtual WP) are presented. Second, a new layered architecture for WDM based transport networks is proposed. The proposed network architecture retains maximum commonality with existing B-ISDN networks. Finally, optical transport network management functions such as configuration, performance and fault management, are discussed.

The optical path (OP) technology, which employs both wavelength-division multiplexing and wavelength routing, will be the key to enhanced network integrity and an ubiquitous broadband integrated services digital network (B-ISDN) in the future. To construct the OP network, path accommodation design that can solve simultaneously the problems of path routing and wavelength assignment must be established. Since optical wavelengths are scarce resources, even with state-of-the-art technologies, the available number of wavelengths that can be multiplexed into a fiber is restricted to a relatively small number. This entails space division multiplexing with multiple fibers in the link in order to accommodate the large number of paths within a link. This paper proposes novel OP accommodation design algorithms that can heuristically establish wavelength paths (WPs) or virtual wavelength paths (VWPs) in the network, where each link is composed of multiple fibers. These algorithms minimize the average number of fibers (in other words, cross-connect ports) handled at the WP/VWP cross-connect nodes and enable us to obtain the required OP cross-connect (OPXC) system scale at each node in WP/VWP networks. Algorithms that consider failure restoration are also proposed. Some WP/VWP accommodation designs over a polygrid network are simulated using the proposed algorithms. The difference between the WP and VWP schemes in terms of the required OPXC system scale with and without considering failure restoration is quantitatively evaluated for the first time.

Path layer technologies will play a key role in the development of a powerful and failure resilient B-ISDN. So far, they have been based on electrical technologies. This paper highlights WDM/FDM techniques and demonstrates that optical paths can greatly enhance the path layer capability and, therefore, the network performance. It is also shown that effective network failure restoration can be achieved with optical paths. The applicability of the wavelength path (WP) technique to global area networks is revealed by comparing different optical path realization techniques. WPs are applied to the national backbone network example to evaluate the required number of wavelengths, and to identify optical cross-connect node requirements. It then proposes a new optical path concept: the virtual wavelength path (VWP). In the VWP scheme, wavelengths are assigned on a link-by-link basis. In other words, the wavelength assigned to a wavelength path has only local significance. Significant benefits of the VWP such as the simplified path accommodation design within a transmission facility network and the reduced number of wavelengths needed, are elucidated. An optical cross-connect node architecture that enables the VWPs is also proposed. The architecture allows the VWP concept to be realized with commercially available optical technologies. The optical path layer concept proposed exploits and consolidates the layered transport network architecture and optical technologies, and will open up new opportunities for creating a B-ISDN that is bandwidth abundant and has a high degree of integrity.>