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Edge computing provides computing capability at close-user proximity to reduce service latency for end users. To improve the efficiency of edge computing infrastructures, geographically-distributed edge datacenters can co-work with each other and with cloud datacenters, forming a new paradigm referred to as cooperative edge-cloud computing. In this context, applications typically run on a virtual machine (VM) that can be replicated at multiple sites, and thus user traffic can be served at all the sites where corresponding VMs reside. For the performance of many applications, latency is a critical parameter. In this work, taking applications latencies as the primary constraint, we model the problem of VM placement and workload assignment as a mixed integer linear program and develop heuristic algorithms accordingly. The goal is to minimize the consumption of information technology (IT) infrastructures for placing VMs in cooperative edge-cloud computing, while meeting the heterogeneous latency demands of different applications. Some preliminary results indicate that edge datacenters resource efficiency can be optimized by proper cross-site VM placement and workload re-direction.

Efficient real-time disparity estimation is critical for the application of stereo vision systems in various areas. Recently, stereo network based on coarse-to-fine method has largely relieved the memory constraints and speed limitations of large-scale network models. Nevertheless, all of the previous coarse-to-fine designs employ constant offsets and three or more stages to progressively refine the coarse disparity map, still resulting in unsatisfactory computation accuracy and inference time when deployed on mobile devices. This paper claims that the coarse matching errors can be corrected efficiently with fewer stages as long as more accurate disparity candidates can be provided. Therefore, we propose a dynamic offset prediction module to meet different correction requirements of diverse objects and design an efficient two-stage framework. In addition, a disparity-independent convolution is proposed to regularize the compact cost volume efficiently and further improve the overall performance. The disparity quality and efficiency of various stereo networks are evaluated on multiple datasets and platforms. Evaluation results demonstrate that, the disparity error rate of the proposed network achieves 2.66% and 2.71% on KITTI 2012 and 2015 test sets respectively, where the computation speed is 2× faster than the state-of-the-art lightweight models on high-end and source-constrained GPUs.

This letter first reports a digital coherent quantum noise stream cipher (QNSC) experiment over 300km fiber without intermediate amplifiers. With the help of Raman fiber amplifiers, ultra-low loss fiber, and the optimized fuzzy C-means clustering algorithm, the results show the system can carry 10.2 Tbit/ $\text{s}\cdot $ km data, which is significantly improved in the single polarization and single wavelength digital coherent context without intermediate amplifiers. We further analyze the transmission and security performances under the 16 quadrature amplitude modulation (QAM) scenario in detail. The number of masked signals of 16 QAM/QNSC is 3843.2.

Quantum key distribution (QKD) has demonstrated a great potential to provide future-proofed security, especially for 5G and beyond communications. As the critical infrastructure for 5G and beyond communications, optical networks can offer a cost-effective solution to QKD deployment utilizing the existing fiber resources. In particular, measurement-device-independent QKD shows its ability to extend the secure distance with the aid of an untrusted relay. Compared to the trusted relay, the untrusted relay has obviously better security, since it does not rely on any assumption on measurement and even allows to be accessed by an eavesdropper. However, it cannot extend QKD to an arbitrary distance like the trusted relay, such that it is expected to be combined with the trusted relay for large-scale QKD deployment. In this work, we study the hybrid trusted/untrusted relay based QKD deployment over optical backbone networks and focus on cost optimization during the deployment phase. A new network architecture of hybrid trusted/untrusted relay based QKD over optical backbone networks is described, where the node structures of the trusted relay and untrusted relay are elaborated. The corresponding network, cost, and security models are formulated. To optimize the deployment cost, an integer linear programming model and a heuristic algorithm are designed. Numerical simulations verify that the cost-optimized design can significantly outperform the benchmark algorithm in terms of deployment cost and security level. Up to 25% cost saving can be achieved by deploying QKD with the hybrid trusted/untrusted relay scheme while keeping much higher security level relative to the conventional point-to-point QKD protocols that are only with the trusted relays.

In the era of the fifth-generation fixed network (F5G), optical networks must be developed to support large bandwidth, low latency, high reliability, and intelligent management. Studies have shown that software-defined optical networks (SDON) and artificial intelligence can help improve the performance and management capabilities of optical networks. Inside a large-scale optical network, many types of alarms are reported that indicate network anomalies. Relationships between the alarms are complicated, making it difficult to accurately locate the source of the fault(s). In this work, we propose a knowledge-guided fault localization method, using network alarm knowledge to analyze network abnormalities. Our method introduces knowledge graphs (KGs) into the alarm analysis process. We also propose a reasoning model based on graph neural network (GNN), to perform relational reasoning on alarm KGs and locate the network faults. We develop an ONOS-based SDON platform for experimental verification, which includes a set of processes for the construction and application of alarm KGs. The experimental results show the proposed method has high accuracy and provide motivation for the industry-scale use of KGs for alarm analysis and fault localization.

Due to the development of broadband access technologies including FTTx and 5G, the traffic in metro and core networks is forecasted to be more dynamic. To support this dynamicity, flex-grid elastic optical networks (EONs) have started to become prolific over the past few years. During the migration from the legacy fixed-grid wavelength division multiplexing optical networks to flex-grid EONs, a transition technology called the fixed/flex-grid optical network has become popular. In such fixed/flex-grid networks, the energy consumption caused by serious capacity mismatch between variable IP traffic and the different optical channel capacities is significantly high to be ignored. In fact, energy-efficient traffic grooming (i.e., to aggregate multiple fine-grained IP flows and map them onto a lightpath) is a challenge in IP-over-fixed/flex-grid optical networks because co-existing fixed-grid and flex-grid nodes have different traffic grooming ability and energy consumption models. To overcome the challenge, we propose an auxiliary-graph-based energy-efficient traffic-grooming ( EETG ) algorithm in IP-over-fixed/flex-grid optical networks for the first time. The construction of an auxiliary graph (AG) model for each connection request is one of the core steps. The well-designed weight-assignment scheme of the AG establishes the relationships between traffic grooming operations and specific energy consumption models. The final traffic grooming operations are undertaken based on the calculated weight-minimized path. The simulation results show that the EETG algorithm achieves 1) the least energy consumption compared with the state-of-the-art traffic grooming algorithms under the non-blocking scenario; and 2) achieves the tradeoff between energy consumption and blocking probability under the blocking scenario.

The emergence of edge computing provides an effective solution to execute distributed model training (DMT). The deployment of training data among edge nodes affects the training efficiency and network resource usage. This letter aims for the efficient provisioning of DMT services by optimizing the partition and distribution of training data in edge computing-enabled optical networks. An integer linear programming (ILP) model and a data parallelism deployment algorithm (DPDA) are proposed to solve this problem. The performance of the proposed approaches is evaluated through simulation. Simulation results show that the proposed algorithm can deploy more DMT services compared with benchmark.

Time-Wavelength Division Multiplexing Passive Optical Network (TWDM-PON) is considered as a promising solution of next generation PON (NG-PON). The integration of Edge Computing (EC) and TWDM-PON can satisfy the QoS requirements of delay-sensitive applications by providing storage, processing and caching capabilities at the network edge. However, with limited resource capacity, edge nodes in TWDM-PON are vulnerable to network attacks, e.g., Distributed Denial of Service (DDoS) attacks. Resource exhaustion in the attacked nodes easily leads to QoS degradation and even service blocking. This paper investigates how to effectively schedule traffic to mitigate the DDoS attack in EC-enabled TWDM-PON. Based on the collaboration of edge nodes, an adaptive traffic scheduling algorithm is designed to minimize the impact of DDoS attacks on delay sensitive services. The performance of the proposed algorithm is evaluated in simulation, where direct and indirect DDoS attacks are simulated. Besides, the attack duration and the number of attacked nodes are considered in the evaluation. Simulation results show that the proposed algorithm can effectively mitigate DDoS attacks in terms of reducing the QoS degradation rate and blocking rate of delay-sensitive services.

Quantum-key-distribution (QKD) enabled optical networks can provide secure keys for different kinds of applications to ensure the high security of communication processes. As the number of wavelength channels in a single-core fiber is limited, space division multiplexing (SDM) has been considered to be a valuable technique to provide more wavelength resources, which solves the problem of insufficient channel capacity. Due to the rapid expansion of data volume, the SDM-based QKD network has been regarded as an important paradigm. At the same time, resource allocation in multi-core optical networks is a problem worthy of studying. In this work, four routing, core, and wavelength allocation (RCWA) algorithms are proposed in the multi-core optical network for quantum service requests and classical service requests, which are referred to as RCWA without perception (RCWA-WP), RCWA with crosstalk perception (RCWA-XTP), RCWA with spectrum perception (RCWA-SP), and RCWA with core perception (RCWA-CP). Simulations are carried out to evaluate the network performance in terms of blocking probability, key utilization, and average crosstalk intensity. The comparative results indicate that the RCWA-SP algorithm can improve network performance and reduce the blocking probability, while the RCWA-XTP algorithm can reduce inter-core crosstalk during transmission.

Traffic flows are often processed by a chain of Service Functions (SFs) (known as Service Function Chaining (SFC)) to satisfy service requirements. The deployed path for a SFC is called Service Function Path (SFP). SFs can be virtualized and migrated to datacenters, thanks to the evolution of Software Defined Network (SDN) and Network Function Virtualization (NFV). In such a scenario, provisioning of paths (i.e., SFPs) between virtualized network functions is an important problem. SFP provisioning becomes more complex in a multi-domain network topology. ‘Topology aggregation’ helps to create a single-domain view of such a network by abstracting multi-domain networks. However, traditional ‘topology aggregation’ methods are unable to abstract SF resources properly, which is required for SFP provisioning. In this paper, we propose an SFC-Oriented Topology Aggregation (SOTA) method to enable abstraction for SFs in multi-domain optical networks. This study explores the node and the link aggregation degree to evaluate information compression during the ‘Topology aggregation’ process. Additionally, we also propose a new data structure named wheel matrix and related operations to store routing information in the aggregated topology. Based on SOTA, we propose two cross-domain SFP provisioning algorithms named Ordered Anchor Selection (OAS) and ${k}$ -paths OAS (K-OAS), and a benchmark named Global OAS (GOAS). Simulation results show that SOTA could aggregate large-scale multi-domain optical networks into a small network that contains only 6.9% of the nodes and 10.1% of the links. Both OAS and K-OAS can calculate SFPs efficiently and reduce blocking probability up to 52.10% compared to the benchmark.

The introduction of functional splits in C-RANs brings a tradeoff between radio performance and transport capacity. Higher-layer splits relax transport capacity requirements, whereas radio performance is not guaranteed. Lower-layer splits are beneficial for the radio performance, but they may require a more expensive and high capacity transport network. Facing the challenge of how to deploy 5G RANs in the short-term future, network operators need to find the best functional split options able to accommodate radio performance requirements without incurring excessive transport network costs. This article presents an architecture referred to as F-RAN able to choose the most appropriate split option while considering time-varying radio performance and the availability of transport resources. F-RAN can accommodate these needs by means of an SDNbased orchestration layer and a programmable optical transport network. The performance of F-RAN is benchmarked against a conventional C-RAN architecture in terms of the number of wavelengths and transponders to be deployed. Simulation results confirm the overall benefits of F-RAN in terms of better utilization of transport resources.

Quantum key distribution (QKD) networks are potential to be widely deployed in the immediate future to provide long-term security for data communications. Given the high price and complexity, multi-tenancy has become a cost-effective pattern for QKD network operations. In this work, we concentrate on addressing the online multi-tenant provisioning (On-MTP) problem for QKD networks, where multiple tenant requests (TRs) arrive dynamically. On-MTP involves scheduling multiple TRs and assigning non-reusable secret keys derived from a QKD network to multiple TRs, where each TR can be regarded as a high-security-demand organization with the dedicated secret-key demand. The quantum key pools (QKPs) are constructed over QKD network infrastructure to improve management efficiency for secret keys. We model the secret-key resources for QKPs and the secret-key demands of TRs using distinct images. To realize efficient On-MTP, we perform a comparative study of heuristics and reinforcement learning (RL) based On-MTP solutions, where three heuristics (i.e., random, fit, and best-fit based On-MTP algorithms) are presented and a RL framework is introduced to realize automatic training of an On-MTP algorithm. The comparative results indicate that with sufficient training iterations the RL-based On-MTP algorithm significantly outperforms the presented heuristics in terms of tenant-request blocking probability and secret-key resource utilization.

The problem of communication, computation, caching, and cryptographic (4C) resource allocation is first solved in quantum-key-distribution-secured datacenter networks with cloud-edge collaboration. Simulation shows great performances of the proposed solution considering blocking rate and key consumption.

The fast and diversified development of Internet services leads to numerous services with differentiated delay tolerance of optical connections set-up are converging in the optical network. Consequently, the average set-up delay of optical connection is increased, which will inevitably bring pressures to optical networks. To solve this problem, a delay aware routing spectrum assignment (RSA) algorithm based on services scheduling in priority queues with dynamic virtual topology construction (QVT-RSA) is proposed. First, the QVT-RSA algorithm reasonably identifies various different services and arranges them in order according to their priority, waiting time and delay tolerance requirements. Then, software defined networks (SDN) controller with multi-threads technology is adopted to innovatively parallel serve the ordered service requests to reduce the average set-up delay of optical connections, which also offset the induced delay caused by services scheduling. The network resource is accurately shared among multi-threads using the proposed mutual exclusive resource utilization model realized by dynamic virtual topology construction. The continuously coloring and usable virtual topology linkage reconfiguration can provide topology resources for service requests and adapt the dynamic transformation among serving, waiting and new arriving service requests. The shortest-path routing and first fit spectrum assignment (SPFF-RSA) algorithm is used as the baseline algorithm. Furthermore, by combining the SPFF-RSA algorithm and partial strategy of our strategy, the QSPFF-RSA and V-RSA algorithms are proposed as baseline algorithms as described in V-B. The simulation experiment results demonstrate that the average optical connections set-up delay of QVT-RSA algorithm is reduced compared with SPFF-RSA and QSPFF-RSA algorithms, and the blocking probability of QVT-RSA algorithm is reduced compared with SPFF-RSA, QSPFF-RSA and VRSA algorithms. The optical connections set-up success probability within delay tolerance about high, medium and low priority services of QVT-RSA algorithm is higher than that of the SPFF-RSA, QSPFF-RSA and VRSA algorithms.

With the increasing bandwidth requirements for people and the development of urbanization, the movement of the population in the city (especially the supercity) has an increasing influence on the traffic distribution in both space and time dimensions. The imbalanced distribution results in the regional blocking of different areas in different time periods and reduces the spectrum resource utilization in elastic optical networks. To resolve this problem, this paper proposes a tidal traffic model to formulate a kind of tidal traffic phenomenon firstly. Based on the analysis for this model, the area-aware routing and spectrum allocation algorithm that focuses on the traffic adjustment in specific functional areas is proposed. And two benchmark algorithms named min-hop k-shortest path routing algorithm and occupied-slots-as-weight k-shortest path routing algorithm are introduced. The evaluation results show that, compared to the benchmark algorithms, the proposed area-aware algorithm could reduce the blocking probability efficiently from 2% to 47% with low time complexity.

Physical layer authentication is an important way to ensure the security of optical communication network. We hereby propose a scheme to realize it by measuring the variation of the bit error rate (BER) on both sides of communication. In this scheme, the legitimacy of the receiver is identified by analyzing the BER variation of the optical fiber loop based on the short-term correlation of the channels. We then simulate a 16 PSK optical transmission system with intensity modulation direct detection-orthogonal frequency division multiplexing (IMDD-OFDM). The authentication effect is analyzed in the case of disturbance and beam split, as well as replacement of optical fiber channels caused by eavesdropper (Eve). The results show that this scheme is sensitive to the three kinds of attacks. A high probability of detection (PD) and a low false alarm rate (FAR) can be obtained. The experimental results show that with the increase of the frequency test, PD and FAR tend to be stable, and the authentication effect is better with the accuracy rate 100%.

As an important bearer network of the fifth generation (5G) mobile communication technology, the optical transport network (OTN) needs to have high-quality network performance and management capabilities. Proof by facts, the combination of artificial intelligence (AI) technology and software-defined networking (SDN) can improve significant optimization effects and management for optical transport networks. However, how to properly deploy AI in optical networks is still an open issue. The training process of AI models depends on a large amount of computing resources and training data, which undoubtedly increases the carrying burden and operating costs of the centralized network controller. With the continuous upgrading of functions and performance, small AI-based chips can be used in optical networks as on-board AI. The emergence of edge computing technology can effectively relieve the computation load of network controllers and provide high-quality AI-based networks optimization functions. In this paper, we describe an architecture called self-optimizing optical network (SOON) with cloud-edge collaboration, which introduces control-layer AI and on-board AI to achieve intelligent network management. In addition, this paper introduces several cloud-edge collaborative strategies and reviews some AI-based network optimization applications to improve the overall network performance.

Elastic optical network (EON) is a promising technology for the next generation of optical transport network. Routing, modulation and spectrum assignment is one of the key issues in EON. In the problem, the constraints of spectrum continuity and contiguity must be satisfied. In this paper, we propose a spectrum assignment policy named minimizing sum of weighted resource reductions ( $\boldsymbol {\min \Sigma w\Delta R}$ ) algorithm. The algorithm includes three contributions: 1) The concept of resource reduction ( $\boldsymbol {\Delta R}$ ) is defined to measure variation of idle resources in a path when a spectrum block is assigned to a connection request, which is combination of changes of continuity and contiguity in the path. 2) When a spectrum block in a path is used, resource reductions in all associated paths rather than only the current path are taken into account. 3) A function of path's hop is used as a weight to adjust the path's impact. Simulations were carried out based on the national science foundation network (NSF-Net) and the pan-European Cost239 network (Cost239) to investigate the performance of the algorithm, by comparing with three well-performed benchmarks. Simulation results show that, when the parameters of the metric are set to appropriate values, the proposed algorithm can significantly decrease blocking probability in both two topologies.

In the Internet Age, optical networks are vulnerable to numerous cyberattacks, and conventional key distribution methods suffer from the increased computational power. QKD can distribute information-theoretically secure secret keys between two parties based on the principles of quantum mechanics. Integrating QKD into optical networks can leverage existing fiber infrastructures with wavelength division multiplexing for the practical deployment of secret keys, and accordingly employ the secret keys for optical-layer security enhancement. Then, how to efficiently deploy and employ secret keys over QKD-integrated optical networks are emerging as two challenges. This article proposes a framework of key as a service (KaaS, i.e., providing secret keys as a service in a timely and accurate manner to satisfy the security requirements) to jointly overcome these two challenges. To enable the typical functions (i.e., secret-key deployment and employment) in KaaS, two secret-key virtualization steps, that is, key pool (KP) assembly and virtual key pool (VKP) assembly, are introduced. Also, we illustrate a new QKD-integrated optical network architecture from a holistic view, where the control layer is implemented by software defined networking for efficient network management. A time-shared KP assembly strategy and an on-demand VKP assembly strategy are presented for KaaS implementation. The success probabilities of KP assembly and VKP assembly are defined to evaluate the benefits of KaaS for efficiently deploying and employing secret keys as well as for security enhancement over QKD-integrated optical networks.

As a concept to enhance and extend cloud-computing capabilities, edge computing aims to provide Internet-based services in the close proximity to users by placing IT infrastructures at the network edge in forms of tiny datacenters. Taking advantage of the close distance to end user and access networks, edge datacenters can provide low-latency and context-aware services and further improve users' quality of experience. As the network edge is a geographically spread concept, the edge datacenters are usually highly distributed so that they can provide nearby storage and processing capabilities to most of the end users. Furthermore, edge datacenters also co-work with centralized cloud datacenters for service orchestration. Such decentralization and collaboration are expected to introduce significant transformations to both infrastructures and applications. To provide an overview of how edge can be integrated with cloud-computing and how edge computing can benefit applications, this paper studies the infrastructure and application issues of edge computing and networking in several sub-aspects, including related concepts, infrastructures, resource management and virtualization, performance, and applications.

Quantum key distribution (QKD) networking over wavelength-division multiplexing (WDM) network infrastructure provides a new paradigm for secure communications across the networks. With limited wavelength resources in existing WDM networks, how to efficiently schedule QKD to provision sufficient secret keys over WDM networks becomes a new challenge. This study proposes a new time-scheduled scheme in combination with quantum key pool (QKP) technique to overcome this challenge. A new architecture of QKD-over-WDM networks is presented, in which QKPs are constructed to decouple secret-key resources from the underlying infrastructure for timely secret-key provisioning. In the time-scheduled scheme, routing, wavelength, and time-slot allocation (RWTA) problem is proposed for efficient QKP construction (QKPC) over WDM networks, in which three sub-problems (i.e., secret-key consumption, time-slot allocation, and time-slot continuity) are discussed, respectively. An integer linear programming (ILP) model and a novel joint path-and-link-based RWTA (JPL-RWTA) heuristic algorithm are designed to solve the RWTA problem, in which the three sub-problems are addressed together. Simulation results indicate that the ILP model and JPL-RWTA algorithm are effective approaches to obtain the positive balance between resource utilization of QKPC and successful probability of QKPC (SPQKPC). Moreover, the SPQKPC can be increased at the cost of reducing the flexibility of secret-key consumption, the uniformity of time-slot allocation, and the proportion of time-slot continuous QKPC to time-slot discrete QKPC requests.

Optical network security is attracting increasing research attention, as loss of confidentiality of data transferred through an optical network could impact a huge number of users and services. Data encryption is an effective way to enhance optical network security. In particular, QKD is being investigated as a secure mechanism to provide keys for data encryption at the endpoints of an optical network. In a QKD-enabled optical network, apart from TDChs, two additional channels, called QSChs and PIChs, are required to support secure key synchronization. How to allocate network resources to QSChs, PIChs, and TDChs is emerging as a novel problem for the design of a security-guaranteed optical network. This article addresses the resource allocation problem in optical networks secured by QKD. We first discuss a possible architecture for a QKD-enabled optical network, where an SDN controller is in charge of allocating the three types of channels (TDCh, QSCh, and PICh) over different wavelengths exploiting WDM. To save wavelength resources, we propose to adopt OTDM to allocate multiple QSChs and PIChs over the same wavelength. An RWTA algorithm is designed to allocate wavelength and time slot resources for the three types of channels. Different security levels are included in the RWTA algorithm by considering different key updating periods (i.e., the period after which the secure key between two endpoints has to be updated). Illustrative simulation results show the effects of different security-level configuration schemes on resource allocation.

Achievable capacity of optical fiber is approaching its physical limitation in frequency domain. Space division multiplexing (SDM) technology can scale the network capacity using multi-core fiber and multi-mode fiber. In order to provide high-speed transmission services with fine granularities, SDM enabled elastic optical networks (SDM-EONs) become a promising candidate of future optical transport networks. However, since the spectrum status in SDM-EONs becomes more complex with the introduction of spatial dimension, the issue of spectrum fragmentation will be more serious in SDM-EONs compared in simple EONs. To remedy the issue of spectrum fragmentation in SDM-EONs, we propose a crosstalk-aware spectrum defragmentation (CASD) algorithm based on a metric, i.e., spectrum compactness (SC), which we define to measure the spectrum status in the SDM-EONs. Simulation results show that the proposed CASD algorithm can achieve better performance than a benchmark algorithm in terms of blocking probability and spectrum utilization. We also compare CASD algorithm with different SC thresholds in bandwidth blocking probability and spectrum utilization. Among them, CASD algorithm with SC threshold of 50 performs the best. It can achieve low spectrum moving times as well as low defragmentation latency.

We are pleased to provide readers with the newest and important technologies presented in Asia Communications and Photonics Conference (ACP) and International Conference on Information Photonics and Optical Communications (IPOC) 2020 (ACP/IPOC 2020), through this Special Issue published by the IEEE Photonics Technology Letters (PTL) journal. Technologies of photonics and optical communications (POCs) have developed rapidly in the last decades and have evolved to become a key-enabling component for the applications of high-speed telecommunications, advanced microwave signal generation and processing, astronomy observations, and even for quantum information processing and computing. The field of POC continues attracting a great deal of attention and keeps progressing in several important directions. Based on the nowadays matured exploration methods, current research is mainly directed towards implementations in integrated formats, such as high-speed optical transmission, big-capacity optical switching, automated optical-network/system evolution, and so on. In addition, intensive research is being conducted toward the utilization of POC across the abovementioned practical application areas and others.

Spatial division multiplexing enabled elastic optical networks (SDM-EONs) are the potential implementation form of future optical transport networks, because it can curve the physical limitation of achievable transmission capacity in single-mode fiber and single-core fiber. However, spectrum fragmentation issue becomes more serious in SDM-EONs compared with simple elastic optical networks (EONs) with single mode fiber or single core fiber. In this paper, multi-core virtual concatenation (MCVC) scheme is first proposed considering inter-core crosstalk to solve the spectrum fragmentation issue in SDM-EONs. Simulation results show that the proposed MCVC scheme can achieve better performance compared with the baseline scheme, i.e., single-core virtual concatenation (SCVC) scheme, in terms of blocking probability and spectrum utilization.

This paper presents a comprehensive and detailed investigation on the bend-induced characteristics of the most advanced few-mode fibers (FMFs) that allow one to multiply the capacity of single-mode fiber transmissions by a high factor (≥12), suitable for dense mode-division multiplexing (MDM) systems. To be specific, we numerically demonstrate how bend can affects the normalized propagation constant, modal field distribution, bend loss, and effective area of all supported spatial LP modes, for both the weakly coupled step-index (SI) 7-LP-mode fiber (adapted to weakly coupled MDM systems with a modal multiplicity factor of 12) and the trench-assisted graded-index (GI) low-differential-mode-group-delay 9-LP-mode fiber (adapted to strongly coupled MDM systems with a modal multiplicity factor of 15). Also presented are the empirical relations of normalized spatial density for the above two FMFs at different bend radii. Finally, for weakly coupled SI FMFs and GI low-DMGD FMFs, we reexamine their design strategy and scalability depicted in [4] , from a unique perspective of bend performance.

Compared with fixed-grid optical network, flexible-grid optical network (FON) enabling technologies could provide higher spectrum efficiency and thus more capacity. With more data capacity, physical network failure (i.e., link or node) will lead to more communication disruptions, especially for multiple failures. In previous research, the protection strategies against multiple failures is mainly single-path provisioning (SPP). They require multiple diverse routes and allocate protection resource separately, which are resource consuming. With the advantages of partial protection and lower resources consumption, the multipath provisioning (MPP) scheme has been considered in traditional wavelength-division multiplexing network, where traffic is split into multiple lower-rate streams and each stream is separately routed. In MPP, the number of required paths and the amount of resource allocated for each path are the two important parameters to be determined and will have great impact on the spectrum efficiency. In light of the above discussion, a spectrum-efficient shared-protection MPP (S-MPP) scheme against multiple failures in FONs is proposed. It is formulated as an Integer Linear Programming (ILP) model and a heuristic algorithm is also developed. Also, the determination of the number of paths and the resource requirement of each path in FON is analyzed in this paper. Furthermore, with MPP, the shared protection in FON is different from that with SPP, because the paths are equal in MPP (no primary path or backup path) and sharing partial path is available. Therefore, we discuss the partial sharing scheme and analyze the amount of shared spectrum resource on each path. Finally, the simulation results show that the proposed S-MPP scheme in FON achieves a significant gain on spectrum efficiency with enough protection against multiple failures. Moreover, the performance of the proposed heuristic algorithm is very close to the optimal solution achieved by solving ILP.

Inter-datacenter services such as data replication and virtual machine migration contribute significantly to the underlying network traffic. These bulk-data transfer services can tolerate certain delay if the completion time is guaranteed with a pre-defined deadline. In this paper, we propose joint frequency- and time-domain optimization algorithms of static routing and spectrum assignment (RSA) for these deadline-driven bulk-data transfer requests in elastic optical networks. We formulate the problem as an integer linear program (ILP) and then propose six scheduling schemes, which combine three request ordering strategies with two RSA algorithms. Simulation results show that compared with ILP, our schemes can achieve the same performance in terms of spectrum utilization with efficient time complexity. Furthermore, based on the numerical results and computational efficiency, we provide a guideline on choosing scheduling schemes.

Due to the accelerated evolution of application services, optical network virtualization simplifies optical-layer resource management and provides flexibility in spectrum resource allocation. However, the energy consumption is one of the great challenges in the virtual optical networks (VONs). This paper focuses on the energy efficiency problem in survivable VONs with the sliceable multi-flow transponders and the elastic regenerators. For each VON, all virtual links provide the dedicated-path protection in the flexible bandwidth optical networks. An integer linear program (ILP) and a minimum unit-energy submatrix (MinEnSub) VON mapping approach are developed to improve the energy efficiency, minimize the power consumption, and reduce the spectrum usage under different line rates. For comparison, a baseline VON mapping approach is introduced. Simulation results show that the ILP model and the proposed MinEnSub VON mapping approach can save power consumption, improve the energy efficiency, and reduce the spectrum usage compared with the baseline VON mapping approach in a 6-node network. As expected, in a 14-node network, simulation results also validate that our proposed MinEnSub VON mapping approach can achieve better performance in terms of power consumption, energy efficiency, number of frequencies, and the number of regenerators.

This paper addresses the minimum network cost problem for survivable virtual optical network mapping in flexible bandwidth optical networks. For each virtual link, we provide dedicated-path protection, i.e., primary path and backup path, to guarantee high survivability on the physical network. To simplify the virtual links mapping, an extended auxiliary graph is constructed by coordinating the virtual optical network and the physical network. We develop an integer linear program (ILP) model, the LBSD (the largest bandwidth requirement (LB) of virtual links versus the shortest distance (SD)) mapping approach, the LCSD (the largest computing (LC) resources requirement versus the shortest distance) mapping approach to minimize the network cost for a given set of VONs. For comparison, we also introduce one baseline mapping approach, named LCLC (the largest computing resources requirement versus the largest computing resources (LC) provisioning), and the lower bound. Simulation results show that, comparing to the LCLC mapping approach, the ILP model, the LBSD and LCSD mapping approaches not only solve the problem of minimizing the total network cost but also guarantee that the spectrum usage and the number of regenerators are minimum. The ILP model and the LBSD mapping approach are greatly close to a lower bound of network cost and perform the same results as a lower bound of spectrum usage in both the 6-node network and the 14-node network. As a result, our proposed LBSD mapping approach can efficiently reduce the network cost, spectrum usage, and the number of regenerators, which is near the optimal solutions of the ILP model.

Due to the fact that network connectivity has a fixed value for a given network, only using network connectivity to improve the survivability of data center networks will reach bottleneck. The content connectivity, which is defined as the reachability of content from any point of a network becomes research focus. In this letter, the definition of $k$ -node (edge) content connectivity is given. Theoretical analysis shows that achieving $k$ -node (edge) content connectivity is equivalent to searching $k$ independent end-to-content paths. Designing $k$ -node (edge) content connected optical data center networks is formulated as an integer liner program (ILP) with objective of minimizing the total wavelengths consumption. Numerical results show that, to achieve dual-node (edge) content connectivity, leveraging content distributed deployment can reduce about 30% wavelengths consumption with NSFNet and about 25% with COST239, than merely relying on network connectivity. Furthermore, about 30% wavelengths consumption could be saved in COST239 to achieve three-node (edge) content connectivity. Data center’s storage capacity and location have significant impact on the total wavelengths consumption.

Based on the virtualization technique in optical networks, virtual transport network services (VTNS) has been introduced as a new kind of service in transport networks. With VTNS, transport providers are able to provide their customers entire virtual topologies instead of traditional end-to-end connections. This letter analyzes the new characteristics (i.e., multiple operators, diversified services) aiming at the survivability problem in virtualized optical transport networks, and proposes three novel protection schemes for VTNS against the new features. For the first time, VTNS with the proposed protection schemes are demonstrated on the flexi-grid optical networks testbed with commercial optical transport equipments. Additionally, the performances of the proposed protection schemes have been evaluated via simulations.

Ubiquitous data center optical interconnection is a promising scenario to meet the high burstiness and high-bandwidth requirements of services in terms of the user-access-oriented interconnection between user and data center, inter-data- center, and intra-data-center interconnection. However, in the current mode of operation, the control of the data center and optical network is separately deployed. Enabling even limited interworking among these separated control systems does not provide a mechanism to exchange resource information and enhance the high-level performance requirement of applications. Our previous work implemented cross-stratum optimization of optical network and application strata resources inter-data-center, which allows the accommodation of data center services. In view of this, this study extends to the ubiquitous data center optical interconnection scenario. This article presents a novel SUDOI architecture aimed at extensive user access from the perspective of heterogeneous cross-stratum and multi-layer networking modes. SUDOI can enable cross-stratum optimization of application and optical network stratum resources, and enhance multiple- layer resource integration in the ubiquitous data center optical interconnection. The functional modules of SUDOI architecture, including the core elements of various controllers, are described in detail. The cooperation procedure in user-access-oriented interconnection, multiple- layer resource integration inter-data-center, and intra-data-center service modes is investigated. The feasibility and efficiency of the proposed architecture are also experimentally demonstrated on our OaaS testbed with OpenFlow-enabled optical nodes, and compared to the CSO scheme in terms of blocking probability and resource occupation rate. Numerical results are given and analyzed based on the testbed. Some future discussion and exploration issues are presented in the conclusion.

Data center interconnection with elastic optical networks is a promising scenario to meet the high burstiness and high-bandwidth requirements of services. Many data center services require lower delay and higher availability with end-to-end guaranteed QoS, which involves both application and transport network resources. However, in the current mode of operation, the control of elastic optical networks and data centers is separately deployed. Enabling even limited interworking among these separated control systems requires the adoption of complex and inelastic interfaces among the various networks, and this solution is not efficient enough to provide the required QoS. In this article, we present a novel cross stratum optimization (CSO) architecture in elastic data center optical interconnection. The proposed architecture can allow global optimization and control across elastic optical transport network and data center application stratum heterogeneous resources to meet the QoS requirement with the objective of optical as a service (OaaS). The functional modules of CSO architecture, including the core elements of application and transport controllers, are described in detail. The cooperation procedure in CSO-based service provisioning and cross stratum service resilience modes is investigated. The overall feasibility and efficiency of the proposed architecture is also experimentally demonstrated on our OaaS testbed with four OpenFlow-enabled elastic optical nodes, and compared to MFA, ALB, and CSO-DGLB service provisioning schemes in terms of path setup/release/adjustment latency, blocking probability, and resource occupation rate. Numerical results are given and analyzed based on the testbed. Some future discussion and exploration issues are presented in the conclusion.

Due to the emergence of cloud computing and various cloud services which are remote and geographically distributed, datacenters interconnected by optical networks have attracted much attention of network operators and service providers. With the purpose of supporting cloud services more effectively and efficiently, IT resources and interconnected network resources provisioning could be considered in an orchestrated way. In this paper, we present a datacenter resources integrated provisioning (DRIP) architecture utilizing coordinated virtualization of distributed datacenters and operator's multi-domain software defined optical networks. The DRIP architecture aims to accomplish IT resources and optical network resources integrated allocation. In order to investigate the feasibility and efficiency of the proposed architecture, two IT resources allocation strategies and two virtual network composition strategies are evaluated on our testbed. We perform experimental demonstration to evaluate the strategies’ performance in terms of three metrics, i.e., CPU utilization ratio of physical hosts, virtual network failure rate, and average latency.

This letter focuses on the protection method for all dual-link failures in optical mesh networks. We first state the problem and discuss the possible scenarios of dual-link failures. We then present our proposed preconfigured ball (p-Ball) protection method that provides protection against dual-link failures using fewer backup links than preconfigured cycles (p-Cycles). We propose integer linear programming to formulate the p-Ball protection method. We also propose a heuristic algorithm to find backup paths in p-Ball. Simulation results show that p-Ball is better than p-Cycle in both construction cost metrics (such as backup link number, resource redundancy, etc.) and operation cost metrics (such as average hop, protection resource utilization ratio, etc.).

This paper proposes k-regular and k-connected (k&k) structure against multi-faults in ultra-high capacity optical networks. Theoretical results show that pre-configured k&k structure can reach the lower bound on logical redundancy. The switching time of k&k protection structure is as quickly as ring-based protection in SDH network. It is the optimal protection structure in ultra-high capacity optical networks against multi-faults. We develop the linear programming model for k&k structure and propose a construction method for k&k structure design. Simulations are conducted for spare spectrum resources efficiency of the pre-configured k&k structure under multi-faults on representative COST239 and NSFnet topologies. Numerical results show that the spare spectrum resources efficiency of k&k structure can reach the lower bound on logical redundancy in static networks. And it can largely improve spare spectrum resources efficiency compared with p-cycles based protection structure without reducing protection efficiency under dynamic traffics.

Optical WDM backbone networks based on fixed spectrum grid have limitations such as low spectrum utilization and rigidity in provisioning for heterogeneous rates. Flexible-grid technologies can alleviate these limitations for on-demand provisioning. These technologies represent promising candidates for future optical networks supporting beyond-100-Gb/s signals. However, a one-time green-field deployment of flexible-grid technologies may not be practical, as the already-made investment in existing fixed-grid WDM networks needs to be preserved, and interruptions to ongoing services need to be minimized. Therefore, we envision that fixed-and flexible-grid technologies will coexist, which will bring the challenge of interoperating fixed-and flexible-grid equipment. It is also important to design the optimum migration strategy to maximize cost effectiveness and minimize service interruption. In this article, we discuss the key aspects of network architectures supporting coexistence of fixed and flexible grid technologies, and outline the challenges of network operations. We also propose and evaluate different migration strategies from fixed grid to flexible grid under different network scenarios.

Novel advance reservation (AR) requests, such as user data replication and grid computing, which are different from immediate reservation requests, allow certain initial-delay during setting up, as long as the resources are allocated before a preset deadline. Empowered by the optical orthogonal frequency-division multiplexing (O-OFDM) technology, the elastic optical networks (EON) support channels operating at heterogeneous line rates by allocating spectral resources in a flexible and dynamic manner. However, in a dynamic traffic scenario, dynamic path setup and teardown operation will inevitably lead to spectral fragmentation. In this paper, to effectively allocate the spectrum in a suitable duration along a better route, we introduce a notion of available time-spectrum consecutiveness (TSC) to describe the spectrum fragmentations along frequency axis and time axis. Based on TSC, three time-aware routing and spectrum assignment (RSA) algorithms are proposed. The novel algorithms retain the TSC as much as possible when establishing a lightpath and reduce the spectrum fragmentation. Simulation results indicate three proposed algorithms achieve lower blocking probability and higher spectrum efficiency.

This paper addresses the problem of spectrum-aware survivable strategies with failure probability constraints under static traffic in flexible bandwidth optical networks. The joint failure probability between primary and backup paths must be below the maximum tolerable joint failure probability for each traffic demand. We develop integer linear program (ILP) models for dedicated-path protection and shared-path protection in order to minimize the total number of frequency slots consumed, and we also propose a spectrum-aware dedicated protection (SADP) algorithm and a spectrum-aware shared protection (SASP) algorithm. Simulation results show that the ILP model solutions consume minimum number of frequency slots, but lead to higher average joint failure probability compared to the SADP and SASP algorithms. Moreover, both the SADP and SASP algorithms achieve a better performance in terms of total number of frequency slots consumed as compared to a conventional dedicated-path protection algorithm and a conventional shared-path protection algorithm, respectively, but lead to higher average joint failure probability.

We propose a novel global resources integrated resilience (GRIR) algorithm for a software defined data center interconnection architecture based on IP over elastic optical network (EON). The proposed algorithm provides resilience using the multiple stratums resources and enhances the data center service resilience responsiveness to the dynamic end-to-end recovery demands in case of the converged optical node failure. Our simulation results indicate that GRIR achieves significant improvements in terms of path blocking probability, resilience latency and resource occupation rate, compared with other resilience algorithms.

The key current challenges for the industrial application of all optical switching networks are energy consumption, transmission rate, spectrum efficiency, and switching throughput. The energy consumption problem is mainly researched in this paper. From the perspective of components and modules, node equipment, and network levels, different enabling technologies are proposed to overcome this problem, which are also evaluated through different experimental demonstrations. First, high-sampling-rate digital-to-analog converters (DACs) and WSS-based ROADM modules are demonstrated as components and modules for energy-efficient all optical switching networks. Then, an all optical transport network test-bed consisting of 10 Pbit/s level all optical switching nodes based on multi-level and multi-planar switching architecture is experimentally demonstrated for the first time, which can reduce power consumption by 43%. A control architecture for energy-efficient all optical switching networks is built with OpenFlow based software defined networking (SDN), and experimental results are given to verify the performance of this control architecture. Finally, we describe an All Optical Networks Innovation (AONI) project in China, which aims to explore transmission, switching, and networking technologies in all optical switching networks, and then two application scenarios are forecast based on the technical breakthroughs of this project.