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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.

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.

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.

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.

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.

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.