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The introduction of the space domain in optical communications, collectively referred as space division multiplexing (SDM), have recently gained a lot of research attention motivated by the capacity exhaustion of conventional wavelength division multiplexing (WDM) systems. SDM not only increases the capacity, but also introduces new challenges and opportunities owing to the properties of the spatial channels in the form of fiber cores, modes or a combination of both. One promising application of SDM systems could be in future edge optical networks, where multi-core fibers (MCFs) with low inter-core crosstalk may be used with packet spatial super-channels (pSSCs) and core-joint SDM optical switches in a time-slotted network. We first briefly review the state-of-the-art of SDM transmission systems and other important technologies for edge networks such as burst-mode transmission. Finally, we focus on two recent experimental demonstration of such a switching system, achieving a capacity of 53.3 Tb/s for 7 spatial channels and QPSK modulation formant and an upgraded version with 8 spatial channels and 8PSK modulation format that achieves 83.33 Tb/s.

This paper presents and experimentally demonstrates a novel high-capacity switching system with several types of optical switches, based on time division multiplexing, space division multiplexing, and coherently modulated packet spatial super-channels (pSSCs), suitable for converged inter/intradata center networks. The fundamental subsystem of this network is the core-joint optical switch which enables efficient switching of all the spatial channels of the multicore fibers (MCFs) used for data transmission. Three novel core-joint optical switches, for 7-core MCFs and varying granularities to accommodate different network functions, are developed: 1) an electroabsorption-based, ns-fast joint switch, 2) an acoustooptic modulator-based, $\mu$ s-fast joint switch, and 3) a free-space mirror-based, ms-fast joint switch. We use these three subsystems in a 2 $\times$ 2 switching node that makes use of 64 wavelength channels, 7-core MCFs, and coherently modulated pSSCs to experimentally demonstrate a record switching capacity of 53.3 Tb/s/port and network protection capabilities in less than 10 ms in the event of an MCF failure.

We propose a flow-based adaptive resource allocation in SDM-OPS networks. It attained 24.6% of packet loss probability and 13.8% of the proportion of Degraded Flows compared to baseline methods. Furthermore, its feasibility was verified via functional experiment using real testbed emulated as SDM environment.

We evaluate the requirements for future spatial-division multiplexing networks operating at throughput higher than 1 Pb/s and discuss possible solutions to support ultra-high capacity.

Novel open and disaggregated optical-networking technologies promise to enhance multi-vendor interoperability thanks to their open interfaces in both data-plane and control/management-plane (C/M-plane). From the viewpoint of disaster resilience in optical networks, such interoperability will significantly improve the flexibility in product selection with regard to replacing damaged subsystems with products of different vendors. In this paper, we discuss various approaches for rapid post-disaster recovery in optical networks (including legacy optical networks) employing disaggregated subsystems, namely, the emergency first-aid unit (FAU) with open application programming interfaces and protocols. We address the following problems (and introduce the solutions that we are currently investigating): (1) how to take advantage of the new disaggregated resources and surviving legacy optical resources to achieve early recovery, (2) how to achieve integrated control of FAUs and non-FAU legacy ROADMs, and (3) how to quickly recreate the lost optical performance monitoring (OPM) capability with FAUs and perform a robust telemetry under the restricted bandwidth in the degraded C/M-plane networks.

We discuss how different degrees of slice isolation influence resource allocation in protected optical metro-aggregation networks. The case of slice reliability with dedicated protection at lightpath is modelled and numerically evaluated.

Network connectivity, i.e., the reachability of any network node from all other nodes, is often considered as the default network survivability metric against failures. However, in the case of a large-scale disaster disconnecting multiple network components, network connectivity may not be achievable. On the other hand, with the shifting service paradigm towards the cloud in today’s networks, most services can still be provided as long as at least a content replica is available in all disconnected network partitions. As a result, the concept of content connectivity has been introduced as a new network survivability metric under a large-scale disaster. Content connectivity is defined as the reachability of content from every node in a network under a specific failure scenario. In this work, we investigate how to ensure content connectivity in optical metro networks. We derive necessary and sufficient conditions and develop what we believe to be a novel mathematical formulation to map a virtual network over a physical network such that content connectivity for the virtual network is ensured against multiple link failures in the physical network. In our numerical results, obtained under various network settings, we compare the performance of mapping with content connectivity and network connectivity and show that mapping with content connectivity can guarantee higher survivability, lower network bandwidth utilization, and significant improvement of service availability.

Large-scale disasters affecting both network and datacenter (DC) infrastructures can cause severe disruptions in cloud-based services. During post-disaster recovery, repairs are usually carried out in stages in a progressive manner due to limited repair resource availability. The order in which network elements and DCs are repaired can significantly impact users’ reachability to important contents/services. We investigate joint progressive network and DC recovery in which network recovery and DC recovery are conducted in a coordinated manner such that users have access to the maximum possible amount of contents/services at each repair stage. We first solve the optimization problem of joint progressive recovery to find the optimal sequence of network element and DC repairs with the objective to maximize cumulative weighted content reachability in the network. We then propose a scalable heuristic for scheduling the sequential repair of network nodes/links and DCs. Our model assumes that, at each repair stage, one network node with adjacent links and one DC can be fully repaired; however, full recovery may not be guaranteed due to limited resource availability. Hence, we also propose a “resource-aware” approach (with two resource-allocation strategies, namely “selective allocation” and “adaptive allocation”), which considers both full and partial recovery of elements based on available resources at each stage. We show that, compared to disjoint progressive recovery approach, in which network recovery and DC recovery plans are independent, our joint progressive recovery approach provides significantly higher per-stage content reachability in the network.

Optical network failure management (ONFM) is a promising application of machine learning (ML) to optical networking. Typical ML-based ONFM approaches exploit historical monitored data, retrieved in a specific domain (e.g., a link or a network), to train supervised ML models and learn failure characteristics (a signature) that will be helpful upon future failure occurrence in that domain. Unfortunately, in operational networks, data availability often constitutes a practical limitation to the deployment of ML-based ONFM solutions, due to scarce availability of labeled data comprehensively modeling all possible failure types. One could purposely inject failures to collect training data, but this is time consuming and not desirable by operators. A possible solution is transfer learning (TL), i.e., training ML models on a source domain (SD), e.g., a laboratory testbed, and then deploying trained models on a target domain (TD), e.g., an operator network, possibly fine-tuning the learned models by re-training with few TD data. Moreover, in those cases when TL re-training is not successful (e.g., due to the intrinsic difference in SD and TD), another solution is domain adaptation, which consists of combining unlabeled SD and TD data before model training. We investigate domain adaptation and TL for failure detection and failure-cause identification across different lightpaths leveraging real optical SNR data. We find that for the considered scenarios, up to 20% points of accuracy increase can be obtained with domain adaptation for failure detection, while for failure-cause identification, only combining domain adaptation with model re-training provides significant benefit, reaching 4%–5% points of accuracy increase in the considered cases.

Objectives We examined whether problem-based learning tutorials using patient-simulated videos showing daily life are more practical for clinical learning, compared with traditional paper-based problem-based learning, for the consideration rate of psychosocial issues and the recall rate for experienced learning. Methods Twenty-two groups with 120 fifth-year students were each assigned paper-based problem-based learning and video-based problem-based learning using patient-simulated videos. We compared target achievement rates in questionnaires using the Wilcoxon signed-rank test and discussion contents diversity using the Mann-Whitney U test. A follow-up survey used a chi-square test to measure students’ recall of cases in three categories: video, paper, and non-experienced. Results Video-based problem-based learning displayed significantly higher achievement rates for imagining authentic patients (p=0.001), incorporating a comprehensive approach including psychosocial aspects (p

Telediagnosis (TD), which uses information and communications technology, has recently undergone rapid development. Since no studies have compared the diagnostic precision of TD to that of face-to-face diagnosis (FD), we examined and compared the diagnostic accuracy of these diagnostic approaches among general medicine outpatients.Data of 97 patients (45 men and 52 women with a mean age of 52 years) who underwent initial examinations at a regional hospital were analyzed. Two fully trained general medicine physicians were selected from a group of three physicians to perform FD and TD. Levels of agreement (as κ coefficients) were determined between TD and FD diagnoses as well as between final diagnoses and TD and FD diagnoses.The κ coefficients were 0.75 for TD and FD and 0.81 for both, the final diagnoses and the TD and FD diagnoses, revealing a sufficiently high level of diagnostic agreement.TD can provide the same level of diagnostic accuracy as FD among general medicine outpatients for adults. The help of medical assistants and the utilization of physical examination devices might enable medical staff to provide TD care similar in quality to FD. TD could be a useful diagnostic tool when medical work force is limited (e.g., in remote areas, during natural disasters, and in at-home care).

We propose a method to grasp packet congestion status in downstream of the transit route using Q learning, and to properly offload the packets in each node in optical packet switching networks.

We propose a lightpath provisioning method in coordination with content data placement / cache control in elastic optical networks for content delivery of big data network services and demonstrate 26% improvement of blocking probability.

Network connectivity has been the traditional metric for network survivability against failures. In case of a disaster, network connectivity may not always be guaranteed due to multiple link failures. With the shifting service paradigm towards cloud computing/storage, some network services can still be provided if a content replica is available in all disconnected network segments. As a result, content connectivity has been introduced as an additional metric for network survivability under disasters. Content connectivity is defined as the reachability of content from every node in a logical topology under a given failure scenario. In this work, we investigate the content-connectivity problem in optical metro networks in the case of multiple ( $n$ ) link failures. We consider the problem of mapping a logical topology over an optical metro network such that every node in the logical topology can reach at least one data center hosting the content after $n$ -link failures. We formulate the problem as an integer linear program to minimize total network resource usage. We provide a cost comparison between content connectivity and network connectivity under typical failure scenarios.

Recent progress of computer networks realizes advanced network services such as high-resolution video streaming and Internet of things (IoT) but it requires further huge amount of traffic. To expand transmission capacity, various studies develop time division multiplexing (TDM), wavelength division multiplexing (WDM), and spatial division multiplexing (SDM) technologies. Time-division packet spatial super-channel (pSSC) is expected as one of promising solutions to realize high throughput with low cost. We have developed a switching node system for the pSSC transmissions. The pSSC is suitable for large data transmission. On the other hand, overhead of pSSC is not negligible in the case of small size data transmissions. This paper proposes a fractional pSSC switching system design for both large and small data transmissions. We introduce the spatial super-channel slicing concept and ILP solution for effective data transmission having bimodal distribution of data size. Effect on slice spatial channel was validated through simulation where it is 50% better than no slicing system.

With the development of communication services, backbone networks need to deal with various types of traffic by utilizing appropriate switching systems in a flexible manner. Optical packet and circuit integrated (OPCI) networks offer both optical packet-switching (OPS) and optical circuit-switching (OCS) and have been studied for this purpose. A space division multiplexing-based OPCI network provides significant communication capacity and shares spectrum resources for OPS and OCS traffic demands on the same physical infrastructure to efficiently accommodate future services. For appropriate resource utilization, the ratio of spectrum resources between OPS and OCS must be flexibly managed based on the dynamically changing traffic. One of important issues of OPCI networks is sharing spectrum resources under a dynamic traffic model. In this paper, we propose a dynamic spectrum-sharing method for both OPS and OCS data transmissions to enhance resource utilization. The spectrum-sharing method consists of dynamic resource boundary management and load-balancing by exploiting integer linear programming periodically in operation. We evaluate the proposed method with computer simulation and verify its effectiveness in terms of both OPS loss probability and OCS blocking probability.

We present elasticity and agility in softwarized optical network construction, service continuation, and service update. Programmability among multiple network protocols and multiple classes of transmission and processing speeds is a necessary solution for lower CAPEX and agile network setup. We present beyond 100 Gbps hardware-support programmability in optical edge. Existing services should be kept transient quality against sudden traffic changes and failures. We also show proper optical power management using burst-tolerable EDFAs in network protection for service continuation of in-service paths.

Wireless video delivery using multiple transmission paths has been studied in recent years to improve the received video quality. Hybrid WiFi-VLC is one of the promising multi- path techniques for indoor communications. Hybrid WiFi- VLC uses radio and visible light bands for transmissions. When a sender simply transmits videos over the hybrid path, the received video quality will be low due to two features of the visible light band. First one is the quality of visible light path will be significantly changed depending on the position and angle of devices, unlike the conventional radio communication. The second one is visible light path is typically one-way link. It means the conventional schemes have not been possible to provide video contents of adequate quality for each user. In order to address the above-mentioned issues, this paper proposes a video transmission scheme for hybrid WiFi-VLC environments. The proposed scheme integrates two-dimensional discrete wavelet transform (2D-DWT), digital video coding, and pseudo-analog modulation to provide baseline quality over radio paths and realize graceful quality enhancement according to the quality of visible light paths without the channel state information. Evaluations show that the proposed method improves PSNR performance by 11 dB compared to a simple method of dividing and transmitting video data over the radio and visible light paths across signal-to-noise ratios of 0 to 25 dB.

We experimentally demonstrate a record 83.33 Tb/s switching capacity on a time-division spatial super-channel 2×2 switching node making use of core-joint, ns switching-speed and transparent electro-absorption optical switches.

We compare fractionally and whole spatial super-channel time-slotted switch architecture designs in terms of network-wide performance of its switching granularity and experimentally demonstrate collision avoidance functionality of SDM based transmission.

Real-time multi-view video streaming plays an important role in new interactive and augmented video applications such as telepresence, remote surgery, and entertainment. Multiview video streaming approaches exploit time and inter-camera domain correlations in video frames for compression, thereby obtaining two benefits: video traffic reduction and video quality maintenance. However, excessive video encoding requires long periods of time for encoding/decoding computation in real-time multi-view video streaming and this process is vulnerable to frame loss, both of which may induce stalling and skipping during video playback at the user node. To address these problems, we propose Adaptive Multi-view Video Streaming (AMVS) system for real-time streaming. AMVS employs a greedy algorithm to adaptively select a prediction structure with low encoding/decoding computation based on the available network bandwidth. AMVS encodes and transmits multi-view video by considering the similarity of the user's request and the efficiency of transmission. Evaluations using Joint Multiview Video Coding (JMVC) demonstrated that AMVS achieves low encoding/decoding computation and high video quality while satisfying bandwidth limitations.

We experimentally demonstrate a 7-core 2×2 switching node for time-division spatial superchannels with a record data-rate of 53 Tb/s on SDM networks, full packet-granularity by nanosecond-fast electro-absorption gate array switching and network protection capabilities with 7-core microsecond-fast acousto-optical modulator switches.

Progressive download for multi-view video delivery is one of promising techniques to provide immersive and interactive experiences to users. In conventional multi-view video systems, a user downloads videos of all viewpoints of one content to realize smooth view switching. However, it causes increase of video traffic, and thus low video quality within an available download rate. To download only a desired viewpoint is another approach for reduction on volume of video traffic. However, playback stalls occur after view switching. The stalls induce low user's satisfaction for applications. In this paper, we aim at two objectives: 1) to achieve reduction on video traffic and 2) to achieve reduction on the number of playback stalls. To this end, we propose a new multi-view video delivery scheme for progressive download. The main idea of the proposed scheme is that the user only downloads potential videos, which are potentially played back by the user, to realize both traffic reduction and smooth view switching. In addition, we propose two download scheduling algorithms to prevent playback stalls even in a low download rate. The first algorithm prevents stalls in frequent view switching cases while the other prevents stalls in gazing cases. Evaluations using Joint Multi-view Video Coding (JMVC) encoder and multi-view video sequences show that the proposed method reduces video traffic by 55.1% compared with a simulcast scheme. In addition, the proposed method decreases the number of playback stalls during video playback by 86.0% compared with a request and response scheme.

Optical circuit and packet integrated network is a promising network architecture that can deal with various sizes/types of data efficiently. In this integrated network, paths (routes) for circuit and packet switching are assumed to be calculated and selected independently. However, this approach is insufficient in terms of efficiency and rapidity of total path calculation. Calculating appropriate paths with shorter computation time is necessary. In this paper, we propose and evaluate a high-speed multipath computation method that quickly calculates end-to-end paths for optical circuit switching by making use of the calculation results of next hop information for packet switching.

The multi-view video streaming is one of promising technologies for emerging video services. For those applications of multi-view video streaming, video frames of all viewpoints, i.e., cameras, are needed to be transmitted to viewers because the demands of all the viewers' view-switching are unpredictable. However, existing transmission schemes are highly vulnerable to frame loss. Specifically, the frame loss in one viewpoint induces a collapse of decoding for other viewpoint videos. To improve loss-resilience, we propose a multi-path based multi-view video transmission. Our scheme encodes video frames into multiple descriptions that are mutually independent of each other, by using inter-view prediction. It then transmits each description using multiple transmission paths. Our scheme makes three contributions:1) it reduces video traffic even for a large number of cameras, 2) it prevents an increase in the number of undecoded video frames caused by one frame loss, and 3) it conceals frame loss by using the video frames in the other paths. Our scheme generalizes to an arbitrary number of transmission paths and discusses the detailed performance at the number of the paths of 2. Evaluations show that our proposed scheme improves video quality by 3 dB compared to existing transmission schemes in loss-prone environments.

Various video distribution services have emerged, such as Ultra High Definition (UHD) videos, 3D videos and multi-view videos. Despite the fact that the issue of video distribution in best-effort networks is addressed in vast amount of literatures, little work has been done so far to consider video distribution systems in bandwidth guaranteed networks. In this paper, we propose a P2P-based UHD multi-view video distribution system in order to realize high quality play-back and rapid view switch by distributing UHD multi-view video in best-effort and guaranteed networks cooperatively. Through computer simulations, we demonstrate that the proposed system is suitable for future UHD multi-view video distribution systems.

Simple and flexible RSCA methods in SDM networks are proposed. They introduce Prioritized Area concept, and two kinds of crosstalk-awareness; Strict Constraint and Best-Effort approaches, and extend/compensate their performance by MIMO based approach.

Elastic optical networks (EONs) and spacedivision multiplexing (SDM) are promising technologies for future core optical networks with high transmission capacity. Traditional optical node architectures for SDM-EONs have two important problems: flexibility and power consumption. Architecture on demand (AoD) is a new concept for an optical node architecture, and an optical node based on this concept is called an AoD node. AoD nodes can be dynamically constructed according to the traffic request by interconnecting input/output ports and building modules with optical switches. Although AoD nodes have great flexibility, power consumption is still a serious problem for them. In this paper, we propose an energy-efficient network system that includes a novel energy-efficient AoD node architecture and resource assignment method cooperating with this node architecture. The proposed system solves the power-consumption problem by simplifying the implemented building modules based on spatial multiplicity of SDM-EONs. The proposed on-demand routing and spectrum allocation method efficiently satisfies the restricted spectrum arrangement that is required by energy-efficient AoD nodes. Finally, we evaluate the proposed system of node architecture and resource allocation method through computer simulations. The simulations show that the proposed network system can improve both the power consumption and the blocking probability of path setup requests in the entire network.

Numerous studies have investigated elastic optical networks (EONs) with the aim of expanding the transmission capacities of core networks. To achieve this goal, it is necessary to solve the spectrum resource wastage problem caused by spectrum fragmentation. Moreover, due to the potentially high traffic demands in future networks, it is important to handle requests that need to be reserved immediately (immediate reservation, IR) as well as those that can be reserved in advance (advance reservation, AR). In networks that support the coexistence of IR and AR requests, IR service degradation by AR requests is a challenging issue because AR requests tend to reserve future resources, which causes a lack of current resources to meet IR requests. Therefore, we address the problem of spectrum fragmentation and the service-level control of IR and AR requests by routing and spectrum allocation (RSA). First, we summarize related research into EONs and resource- allocation methods for IR and AR requests. Next, we propose a novel dynamic RSA method to reduce spectrum fragmentation and control the service level of IR and AR requests in terms of bandwidth blocking probability (BBP) in EONs considering the multiplexing effect of spatial channels. Finally, we evaluate the proposed method based on computer simulations and our results demonstrate that the proposed method can improve the BBP for the entire traffic flow by reducing spectrum fragmentation, as well as the service control of AR requests and IR requests under various network conditions.

Elastic optical networks (EONs) are considered to be one of the promising future networks for spectrum flexibility. In conventional wavelength-division multiplexing networks, routing and wavelength assignment is one of the key issues, whereas the routing and spectrum assignment (RSA) problem considerably affects the network performance in EONs. In addition, the data-center traffic and mobile back-haul traffic keeps increasing. To deal with such increasing capacity of applications, space-division multiplexing (SDM) technologies such as multi-core fiber (MCF) and multi-mode fiber (MMF) have been intensively researched. From the network perspective, this paper focuses on the routing, spectrum, and core and/or mode assignment (RSCMA) problem for future SDM-EONs. Introducing MCF or MMF further complicates the RSA problem because the fiber core or mode dimension is newly expanded. In addition, physical impairment caused by MCF or MMF must be considered. In this paper, the target RSCMA problem is first divided into routing and SCMA problems, and a pre-computation method based on the K-shortest path is introduced as the routing solution. Next, we propose SCMA methods with efficiency and flexibility awareness, exploiting prioritized area concept and crosstalk awareness depending on whether MCF or MMF supports intercore/intermode crosstalk. Finally, the paper evaluates and compares the effectiveness of the proposed algorithms with that of representative algorithms.

We develop an SDN-based control for optical-multicast packet transmission and experimentally demonstrate multicast functionality by validating it using an application-layer network service for efficient content duplication in Optical Packet/Circuit Integrated (OPCI) network.