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## Über dieses Buch

This book constitutes the refereed proceedings of the 23rd International IFIP conference on Optical Network Design and Modeling, ONDM 2019, held in Athens, Greece, in May 2019. The 39 revised full papers were carefully reviewed and selected from 87 submissions. The papers focus on cutting-edge research in established areas of optical networking as well as their adoption in support of a wide variety of new services and applications. This involves the most recent trends in networking including 5G and beyond, big data and network data analytics, cloud/edge computing, autonomic networking, artificial intelligence assisted networks, secure and resilient networks, that drive the need for increased capacity, efficiency, exibility and adaptability in the functions that the network can perform. In this context new disaggregated optical network architectures were discussed, exploiting and integrating novel multidimensional photonic technology solutions as well as adopting open hardware and software platforms relying on software defined networking (SDN), and network function virtualization (NFV) to allow support of new business models and opportunities.

## Inhaltsverzeichnis

### Hybrid Backup Resource Optimization for VNF Placement Over Optical Transport Networks

The concept of edge computing is vital in the 5G ecosystem, as a means of introducing application awareness in the network and enabling constructs such as slicing to be effectively implemented. In this scope, an efficient infrastructure dimensioning requires visibility of both network and data-center resources. While this joint optimization is becoming increasingly common even at the optical layer, some aspects of the dimensioning remain siloed between the network/IT worlds. Survivability mechanisms are one such example, where protection for lightpaths and/or virtual network functions (VNFs) is typically provisioned independently, potentially incurring in resource overprovisioning. This paper investigates the merits of exploiting a hybrid strategy where backup resources are selectively distributed between the IT and optical layers in metro ring scenarios, according to specific service requirements such as latency and bandwidth. Critically, this analysis incorporates, through an integer linear programming (ILP) model, the effect of optical path performance on the cost efficiency of protection mechanisms, which is shown to greatly influence the optimal resource distribution in each deployment scenario.

João Pedro, António Eira

### Software-Defined Reconfigurability, White Boxes, and Abstraction

Next generation networks – spanning from wide area networks to intra-datacenters – are expected to encompass devices and sub-devices from different vendors. Inter operability and vendor neutrality are now key topics for researchers and companies as a way to reduce costs avoiding to be tied to a single vendor. Also the management system is expected to be disaggregated from the hardware and possibly developed by a different company. An example is the white box, which disaggregates the software from the hardware and can be composed of modules from different vendors. Currently, NETCONF – based on YANG – is the protocol considered for the (re)configuration of white boxes. Discussions are being carried on to identify commonly agreed information models to guarantee vendor-neutral configuration and management of next generation networks.In addition, emerging services (e.g., 5G) will impose the involvement of a variety of technologies (e.g., networks, datacenters) and resources (e.g., compute, storage, radio). Such heterogeneity will imply the cooperation of several business actors to bring services to the users. In such a scenario, the management of resources will require their abstraction in order to satisfy confidentiality as well as to increase scalability and, again, to provide information that is neutral with respect to the related vendor and technology.In this paper, we propose to use NETCONF also for the exchange of resource information among different business actors considering the several network segments (wide area network, data centers, radio segment) involved in a 5G vertical. To this purpose, resource abstraction is proposed based on a YANG data model. An experiment will involve the (re)configuration of a wide area network composed of white boxes. Moreover, resource information (virtual links) will be exchanged through NETCONF with the objective of orchestrating resources.

Nicola Sambo, Alessio Giorgetti, Andrea Sgambelluri, Piero Castoldi, Luca Valcarenghi

### Embedding Virtual Networks in Flexible Optical Networks with Sliceable Transponders

Emerging inter-datacenter applications involving data transferred, processed, and analyzed at multiple data centers, such as virtual machine migrations, real-time data backup, remote desktop, and virtual data centers, can be modeled as virtual network requests that share computing and spectrum resources of a common substrate physical inter-datacenter network. Recent advances make flexible optical networks an ideal candidate for meeting the dynamic and heterogeneous connection demands between datacenters. In this paper, we address the static (offline) version of the virtual network embedding problem in flexible optical networks equipped with sliceable bandwidth variable transponders (SBVTs). The objective is to minimize the total number of required SBVTs in the network. An Integer Linear Programming (ILP) formulation is presented, lower bounds are derived, and four heuristics are proposed and compared. Simulation results are presented to show the effectiveness of the proposed approaches.

Juzi Zhao, Suresh Subramaniam

### Virtualized Controller Placement for Multi-domain Optical Transport Networks

Optical multi-domain transport networks are often controlled by a hierarchical distributed architecture of controllers. Optimal placement of these controllers is very important for their efficient management and control. Traditional SDN controller placement methods focus mostly on controller placement in datacenter networks. But the problem of virtualized controller placement for multi-domain transport networks needs to be solved in the context of geographically-distributed heterogeneous multi-domain networks. In this context, Edge Datacenters have enabled network operators to place virtualized controller instances closer to users, besides providing more candidate locations for controller placement. In this study, we propose a dynamic controller placement method for optical transport networks that considers the heterogeneity of optical controllers, resource limitations at edge hosting locations, latency requirements, and costs. Simulation studies considering practical scenarios show significant cost savings and delay reductions compared to standard placement approaches.

Sabidur Rahman, Tanjila Ahmed, Sifat Ferdousi, Partha Bhaumik, Pulak Chowdhury, Massimo Tornatore, Goutam Das, Biswanath Mukherjee

### End-to-End Network Slicing in Support of Latency-Sensitive 5G Services

Network slicing has been taking a major role in upcoming 5G network implementations. However, in order to provision and maintain end-to-end slices, the management and orchestration among different network segments is required. As a result, techniques and components have risen to fulfil these tasks. In this work, we present latency-aware slicing, which is enabled by the provisioning of network slices equipped with an end-to-end latency sensor. This sensor is added to the service chain, allowing for real time monitoring and eventually actuation upon latency requirements violations. Moreover, we introduce an architecture capable of handling the deployment of such sensors while also coordinating the provisioning of the slice across optically interconnected DCs. To experimentally demonstrate the deployment of a slice with latency sensing we set up a multi-segment testbed connecting client VMs. The presented results demonstrate the behavior of the latency sensor and how it enables latency optimization through path reconfiguration.

Rafael Montero, Fernando Agraz, Albert Pagès, Salvatore Spadaro

### The Impact of the Optical Network on 5G – The Metro-Haul Project

An overview of the current status of the EU Metro-Haul project and its impact on 5G End to End KPIs together with a summary of the use cases and demonstrations intended to illustrate the technology being developed.

Andrew Lord, Albert Rafel, Michael Parker, Adrian Farrel

### Availability-Guaranteed Slice Provisioning in Wireless-Optical Broadband Access Networks Supporting Mobile Edge Computing

A wireless-optical broadband access network (WOBAN) shows promise as potential 5G access infrastructure. Since network slicing allows efficient sharing of physical network resources, we consider the provisioning of availability-guaranteed slices in a WOBAN supporting mobile edge computing (MEC). A new definition for the availability of a slice is proposed accounting for a slice that functions only partially because of the failure of a fiber link, a microwave link, a base station (BS) node, and/or an optical line terminal (OLT). An integer linear programming (ILP) model and a simple but effective heuristic algorithm that balances the network traffic load and maximizes the slice availability are developed to maximally provision availability-guaranteed slices. Simulation results show the efficiency of the proposed approaches.

Ke Chen, Gangxiang Shen, Shuiping Jie, Boping Jiang, Sanjay K. Bose

### DU/CU Placement for C-RAN over Optical Metro-Aggregation Networks

To meet emerging mobile traffic requirements, Centralized Radio Access Network (C-RAN) has been proposed to split the base station (BS) into two functional entities: the baseband units (BBU) and the remote radio heads (RRH). In C-RAN, by centralizing BBUs into BBU pools and leaving the RRHs in the cell sites, significant cost and energy savings and improved radio coordination can be achieved. However, C-RAN requires a costly high-capacity and low-latency access/aggregation network to support fronthaul traffic (i.e., digitized baseband signal). Hence, more recently, a new C-RAN architecture has been proposed (i.e., by 3GPP, IEEE 1914 WG), that defines three baseband function entities (or “splits”): central unit (CU), distributed unit (DU) and remote unit (RU). These three entities are expected to be interconnected by two external interfaces, called F1 and Fx. By transforming the RAN into a 3-layer (CU-DU-RU) architecture, more flexible deployment of the baseband functions can be achieved that better adapts to the heterogeneous characteristics of incoming 5G service requirements. It is also expected that, by properly placing CUs and DUs in the metro/aggregation network, higher benefits in terms of cost and power consumption can be achieved with respect to the previous 2-layer (BBU-RRH) architecture. In this paper, we investigate the optimal CU/DU placement problem in a 3-layer RAN architecture and formalize it by integer linear programming. We evaluate the benefits of the 3-layer architecture compared to the 2-layer architecture, showing that the consolidation degree of baseband processing depends heavily on fronthaul traffic latency, transport network capacity and processing capacity.

Hao Yu, Francesco Musumeci, Jiawei Zhang, Yuming Xiao, Massimo Tornatore, Yuefeng Ji

### Adaptive Function Chaining for Efficient Design of 5G Xhaul

Next generation fronthaul interface has been recently proposed to support different functional splits in 5G access networks. Each split option is characterized by different requirements in terms of latency and bandwidth. The mapping of different functional splits on the nodes of 5G access network introduces several degrees of freedom in relation to the variation of the traffic during the day. This paper proposes a novel function location algorithm, which adopts dynamic function chaining in relation to the evolution of the traffic estimate. The obtained results show remarkable improvement in terms of bandwidth saving and multiplexing gain with respect to conventional C-RAN fronthaul and suggest design criteria for the emerging 5G access network.

Bahare M. Khorsandi, Didier Colle, Wouter Tavernier, Carla Raffaelli

### Dynamic Softwarised RAN Function Placement in Optical Data Centre Networks

The ability to assign functions that comprise the BBU processing in centralized softwarised Radio Access Networks into different servers the, have been proven to be beneficial, in terms of energy efficiency. This paper proposes a heuristic suitable for BBU functions allocation and evaluates the impact of dynamic resource management in these environments facilitated through Virtual Machine (VM) live migration. The benefits associated with VM migration are quantified through a series of experiments. Our results show notable improvement in terms of resource and energy efficiency.

Nikolaos Gkatzios, Markos Anastasopoulos, Anna Tzanakaki, Dimitra Simeonidou

### Techno-Economic Aspects of 5G Transport Network Deployments

5G networks will comprise multiple, versatile infrastructures at finest granularity consisting of multiple disaggregated pools of network, compute and storage resources. To support the 5G network architectures and satisfy the access network demanding performance requirements, transport networks consisting of various converging technologies shall provide mechanisms to support deployment flexibility and scalability. The deployment of the complementary or alternative transport network technologies in real network deployments shall take into account various factors such as area specifics, technologies’ deployment feasibility, traffic/usage forecasts considering long-term services roadmaps and certainly, the implicated costs. Thus, transport network planning and dimensioning shall be tightly accompanied by the techno-economic analysis of the various deployment alternatives. This paper provides insights on the techno-economic aspects of 5G transport network technologies and its applicability on the architectural concepts of 5G-XHaul and 5G-PICTURE 5G-PPP projects.

I. Mesogiti, E. Theodoropoulou, G. Lyberopoulos, F. Setaki, K. Filis, A. Di Giglio, A. Percelsi, Anna Tzanakaki

### RHODA Topology Configuration Using Bayesian Optimization

The rapid growth of data center traffic requires data center networks (DCNs) to be scalable, energy-efficient, and provide low latencies. Optical Wavelength Division Multiplexing (WDM) is a promising technique to build data centers comprising millions of servers. In [24], a WDM-based Reconfigurable Hierarchical Optical DCN Architecture (RHODA) was presented, which can accommodate up to 10+ million of servers and a variety of traffic patterns. RHODA also saves tremendous amounts of power and cost through its extensive use of passive optical devices, and minimal use of power-hungry and costly devices. RHODA achieves high throughput through reconfigurable clustering of racks of servers. In this paper, we focus on the design of the cluster topology (also called inter-cluster network). Given the pair-wise cluster traffic, our objective for the cluster topology is to minimize the average hop length. In [24], a simple variant of the Hungarian algorithm that maximizes the one-hop or direct traffic among clusters was used. In this paper, we leverage the Bayesian Optimization (BO) framework and propose a fast algorithm to minimize the average number of hops in the inter-cluster network of RHODA. To the best of our knowledge, this is the first paper that employs BO to optimize optical DCN performance. We present our design decisions and modifications to BO based on the network constraints. Results show that BO can achieve optimal or near-optimal results, and outperforms a well-known regular topology (Gemnet) and the Hungarian-based method by up to $$13\%$$ and $$58\%$$, respectively.

Maotong Xu, Min Tian, Eytan Modiano, Suresh Subramaniam

### Dynamic Abstraction of Optical Networks with Machine Learning Technologies

The emerging 5G network will bring a huge amount of network traffic with big variations to optical transport networks. Software-defined optical networks and network function virtualization contribute to the vision for future programmable, disaggregated, and dynamic optical networks. Future optical networks will be more dynamic in network functions and network services, with high-frequency network re-configurations. Optical connections will last shorter than that of the static optical networks. It’s straightforward that Programmable optical hardware will require a reduced link margin to improve the hardware utilization. To configure network dynamically, real-time network abstractions are required for both current links and available-for-deploy links. The former abstraction guarantees the established links not be interfered by the newly established link while the latter abstraction provides information for intelligent network planning. In this talk, we use machine-learning technologies to process the collected monitoring data in a field-trial testbed to abstract performances of multiple optical channels. Based on the abstract information, a new channel can be established with maximum performance and minimized interference on the current signals. We demonstrated the dynamic network abstraction over a 563.4-km field-trial testbed for 8 dynamic optical channels with 32 Gbaud Nyquist PM-16QAM signals. The work can be further extended to support complex optical networks.

Shuangyi Yan, Zhengguang Gao, Rui Wang, Alex Mavromatis, Reza Nejabati, Dimitra Simeonidou

### Novel P-Cycle Selection Algorithms for Elastic Optical Networks

Elastic optical networks (EONs) promise to provide high spectrum utilization efficiency due to flexibility in resource allocation. Survivability is regarded as an important aspect of EONs. P-cycle protection is very attractive for EONs due to fast restoration and high protection efficiency. P-cycles have been extensively studied for conventional fixed-grid WDM networks; however, p-cycle design and selection for EONs has received much less attention. In this paper, we consider the design and selection of p-cycles for EONs with distance-dependent modulation. We propose two novel link-based p-cycle evaluation methods: individual p-cycle selection and p-cycle set selection for EONs. Based on these methods, two p-cycle design algorithms, namely, Traffic Independent P-cycle Selection (TIPS) and Traffic-Oriented P-cycle Selection (TOPS), are proposed to find the best set of p-cycles that is able to provide 100% failure-dependent protection against single link failures. We evaluate our algorithms using both static and dynamic traffic models. Simulation results indicate that the proposed algorithms have better performance than commonly used baseline algorithms.

Rujia Zou, Suresh Subramaniam

### How to Survive Targeted Fiber Cuts: A Game Theoretic Approach for Resilient SDON Control Plane Design

Software-defined optical networking (SDON) paradigm enables programmable, adaptive and application-aware backbone networks via centralized network control and management. Aside from the manifold advantages, the control plane (CP) of an SDON is exposed to diverse security threats. As the CP usually shares the underlying optical infrastructure with the data plane (DP), an attacker can launch physical-layer attacks to cause severe disruption of the CP.This paper studies the problem of resilient CP design under targeted fiber cut attacks, whose effectiveness depends on both the CP designer’s and the attacker’s strategies. Therefore, we model the problem as a non-cooperative game between the designer and the attacker, where the designer tries to set up the CP to minimize the attack effectiveness, while the attacker aims at maximizing the effectiveness by cutting the most critical links. We define the game strategies and utility functions, conduct theoretical analysis to obtain the Nash Equilibrium (NE) as the solution of the game. Extensive simulations confirm the effectiveness of our proposal in improving the CP resilience to targeted fiber cuts.

Jing Zhu, Marija Furdek, Carlos Natalino, Lena Wosinska, Zuqing Zhu

### Joint Fronthaul Optimization and SDN Controller Placement in Dynamic 5G Networks

To address the limitations of current Radio Access Networks (RANs), centralized-RANs adopting the concept of flexible splits of the BBU functions between Radio Units (RUs) and the central unit (CU) have been proposed. This concept can be implemented combining both the Mobile Edge Computing model and relatively large-scale centralized Data Centers. This architecture requires high bandwidth/low latency optical transport networks interconnecting RUs and compute resources adopting SDN control. This paper proposes a novel mathematical model based on Evolutionary Game Theory that allows to dynamically identify the optimal split option with the objective to unilaterally minimize the infrastructure operational costs in terms of power consumption. Optimal placement of the SDN controllers is determined by a heuristic algorithm in such a way that guarantees the stability of the whole system.

Victoria-Maria Alevizaki, Markos Anastasopoulos, Anna Tzanakaki, Dimitra Simeonidou

### 3-Stage Hierarchical Quality of Service for Multi-tenant Passive Optical Networks

Passive Optical Networks (PONs) are an economically efficient means of providing high bandwidth services to end users because end-points can share the cost and the benefit of fibre optic connection. There is a growing interest in the use of PONs as a bearer for services such as Long Term Evolution (LTE), however work remains to be done to ensure stable, low latency and low packet loss for full duplex Transmission. In this paper we are mostly concerned with the characteristics of the downstream channel so as to further the case for PON sharing. We review typical downstream schedulers used in the industry and propose a three-stage downstream scheduler that assures quality of service, accurately, across Virtual Network Operators (VNOs) in multi-tenant PONs environment. We benchmark our scheduler against other algorithms, obtaining almost ideal scheduling performance.

Frank Slyne, Bruno Cornaglia, Marco Boselli, Marco Ruffini

### Machine Learning Assisted Optical Network Resource Scheduling in Data Center Networks

Parallel computing allows us to process incredible amounts of data in a timely manner by distributing the workload across multiple nodes and executing computation simultaneously. However, the performance of this parallelism usually suffers from network bottleneck. In optical switching enabled data center networks (DCNs), to satisfy the complex and time-varying bandwidth demands from the parallel computing, it is critical to fully exploit the flexibility of optical networks and meanwhile reasonably schedule the optical resources. Considering that the traffic flows generated by different applications in DCNs usually exhibit different statistical or correlative features, it is promising to schedule the optical resources with the assistance of machine learning. In this paper, we introduce a framework called intelligent optical resources scheduling system, and discuss how this framework can assist resource scheduling based on machine learning approaches. We also present our recent simulation results to verify the performance of the framework.

Hongxiang Guo, Cen Wang, Yinan Tang, Yong Zhu, Jian Wu, Yong Zuo

### Machine Learning Assisted Quality of Transmission Estimation and Planning with Reduced Margins

In optical transport networks, the Quality of Transmission (QoT) using a physical layer model (PLM) is estimated before establishing new or reconfiguring established optical connections. Traditionally, high margins are added to account for the model’s inaccuracy and the uncertainty in the current and evolving physical layer conditions, targeting uninterrupted operation for several years, until the end-of-life (EOL). Reducing the margins increases network efficiency but requires accurate QoT estimation. We present two machine learning (ML) assisted QoT estimators that leverage monitoring data of existing connections to understand the actual physical layer conditions and achieve high estimation accuracy. We then quantify the benefits of planning/upgrading a network over multiple periods with accurate QoT estimation as opposed to planning with EOL margins.

Konstantinos Christodoulopoulos, Ippokratis Sartzetakis, Polizois Soumplis, Emmanouel (Manos) Varvarigos

### Network Programmability and Automation in Optical Networks

During last years, novel protocols and data models are arising to control and monitor optical network equipment. These protocols enable network programmability and automation by fulfilling the vision introduced by Software Defined Networking (SDN).This paper offers an overview and hands-on experience on programming the necessary tools to control and monitor the network equipment. These tools introduce the necessary network programmability that will enable its automation, following current Zero-Touch service control and management. Data modelling languages are firstly explored. Later, protocols for control and monitoring are presented. Moreover, common standards data models are discussed. Finally, an evaluation of the different presented protocols and data models is provided, which includes recommendations for their selection and deployment.

Ricard Vilalta, Ramon Casellas, Ricardo Martí­nez, Raul Muñoz

### Fragmentation Metrics in Spectrally-Spatially Flexible Optical Networks

Spectrally-spatially flexible optical networks (SS-FONs) are proposed as a solution for future traffic requirements in optical backbone networks. As SS-FONs operate within flex-grid, the provisioning of lightpaths spanning multiple frequency slots results in spectrum fragmentation, especially in presence of dynamic traffic. Fragmentation, in turn, may lead to blocking of dynamic requests due to the lack of sufficiently-large free spectral windows. In this paper, to reach a better understanding of fragmentation in SS-FON, we extend several metrics used in (single-core) elastic optical networks to measure the fragmentation in SS-FONs. Next, we apply these metrics to a dynamic-routing algorithm with the goal of minimizing bandwidth blocking. Finally, we analyze the impact of spatial continuity constraint (SCC) on the network fragmentation. Simulations run on two representative network topologies show that the root mean square factor metric yields the best performance in terms of blocking when compared to other analyzed metrics.

Piotr Lechowicz, Massimo Tornatore, Adam Włodarczyk, Krzysztof Walkowiak

### Intrinsically Resilient Optical Backbones: An Efficient Ring-Based Interconnection Paradigm

Physical topologies are evolving from elementary survivable rings into complex mesh networks. Nevertheless, no topology model is known to provide an economic, systematic, and flexible interconnection paradigm for ensuring that those meshes bear resilience features. This paper argues that intrinsic resilience can be brought by twin graph topologies, as they satisfy equal length disjoint path property with minimal number of physical links. An exhaustive investigation is performed across twin graph families composing networks from 4 to 17 nodes, whereas diverse real-world topologies and ring networks are used as benchmarks. First, we illustrate the growing process, and discuss the topology diversity of twin graphs. We analyze the impact of single cable cuts between neighbouring nodes, then we stress topologies with 2, 3, and 4 simultaneous cable cuts. Improved resiliency is seen for neighbor nodes and also reduction of cut sets able to disconnect the twin topologies in comparison with real-world networks. Finally, we present as a use case the redesign of CESNET into a resilient network.

Marcia H. M. Paiva, Gilles Caporossi, Moises R. N. Ribeiro, Marcelo E. V. Segatto

### Experimental Evaluation of Dynamic Resource Orchestration in Multi-layer (Packet over Flexi-Grid Optical) Networks

In future 5G infrastructures, network services will be deployed through sets of Virtual Network Functions (VNFs) leveraging the advantages of both Software Defined Networking (SDN) and Network Function Virtualization (NFV). A network service is composed of an ordered sequence of VNFs, i.e., VNF Forwarding Graph (VNFFG), deployed across distributed data centers (DCs). Herein, we present a Cloud/Network Orchestrator which dynamically processes and accommodates VNFFG requests over a pool of DCs interconnected by a multi-layer (packet/flexi-grid optical) transport network infrastructure. We propose two different cloud and network resource allocation algorithms aiming at: (i) minimizing the distance between the selected DCs, and (ii) minimizing the load (i.e., consumed cloud resources) of the chosen DCs. Both algorithms run on a Cloud/Network Orchestrator and are experimentally validated and benchmarked on the CTTC ADRENALINE testbed.

Silvia Fichera, Barbara Martini, Ricardo Martínez, Ramon Casellas, Ricard Vilalta, Raul Muñoz, Piero Castoldi

### Optics for Disaggregating Data Centers and Disintegrating Computing

We present a review of photonic Network-on-Chip (pNoC) architectures and experimental demonstrations, concluding to the main obstacles that still impede the materialization of these concepts. We also propose the employment of optics in chip-to-chip (C2C) computing architectures rather than on-chip layouts towards reaping their benefits while avoiding technology limitations on the way to many-core set-ups. We identify multisocket boards as the most prominent application area and present recent advances in optically enabled multisocket boards, revealing successful 40 Gb/s transceiver and routing capabilities via integrated photonics. These results indicate the potential to bring energy consumption down by more than 60% compared to current QuickPath Interconnect (QPI) protocol, while turning multisocket architectures into a single-hop low-latency setup for even more than 4 interconnected sockets, which form currently the electronic baseline.

Nikos Terzenidis, Miltiadis Moralis-Pegios, Stelios Pitris, Charoula Mitsolidou, George Mourgias-Alexandris, Apostolis Tsakyridis, Christos Vagionas, Konstantinos Vyrsokinos, Theoni Alexoudi, Nikos Pleros

### Simplifying Optical DCN Fabrics with Blocking Space Switching and Wavelength-Constrained WDM

The introduction of all-optical switching in data center interconnection networks (DCN) is key to addressing some of the shortcomings of state-of-the-art electronic switched solutions. Limitations in the port count, reconfiguration speed and cost of optical switches, however, require novel optical switching and DCN designs. We present the concept of a simplified DCN fabric that relies on a lean optical switch design of limited but scalable functionality that offers high reconfiguration speeds, real-time scheduling, efficient control and low equipment cost. To achieve these objectives, the proposed architecture relaxes the usual non-blocking switching requirements but opts for switching modules that are constrained in terms of the achievable space and wavelength input-output configurations. We analytically compare the functionality and complexity of the simplified fabric with those of a non-blocking switch. We evaluate the throughput performance of the simplified DCN fabric and compare it to that of other fabrics with a different level of functionality and centralized control.

Konstantinos Kontodimas, Kostas Christodoulopoulos, Emmanouel Varvarigos

### Dual-Layer Locality-Aware Optical Interconnection Architecture for Latency-Critical Resource Disaggregation Environments

Significant research efforts, both industrial and academic, have been committed in the direction of Rack-scale computing through resource disaggregation, that aims to increase resource utilization at a reduced energy and cost envelope. However, the realization of resource disaggregation necessitates an underlying network infrastructure that can compete with a challenging set of requirements including low-latency performance and high-port count connectivity, as well as high data-rate operation. At the same time, it is crucial for the interconnection architecture to be able to accommodate efficient delivery of traffic with different locality characteristics. We propose a dual-layer locality-aware optical interconnection architecture for disaggregated Data Centers by combining the STREAMS silicon-based on-board communication paradigm with the disaggregation-oriented Hipoλaos high-port count switch. Simulation evaluation of a 256-node disaggregated system, comprising 32 optically-interconnected 8-socket boards, revealed up to 100% throughput and mean, p99 latencies not higher than 335 nsec and 610 nsec, respectively, when a 50:50 ratio between on- and off-board traffic is employed. Evaluation of the same layout with 75:25 on-/off-board traffic yields even lower mean and p99 latency at 210 ns and 553 ns, respectively.

Nikos Terzenidis, Miltiadis Moralis-Pegios, Theoni Alexoudi, Stelios Pitris, Konstantinos Vyrsokinos, Nikos Pleros

### Network-Wide Localization of Optical-Layer Attacks

Optical networks are vulnerable to a range of attacks targeting service disruption at the physical layer, such as the insertion of harmful signals that can propagate through the network and affect co-propagating channels. Detection of such attacks and localization of their source, a prerequisite for secure network operation, is a challenging task due to the limitations in optical performance monitoring, as well as the scalability and cost issues. In this paper, we propose an approach for localizing the source of a jamming attack by modeling the worst-case scope of each connection as a potential carrier of a harmful signal. We define binary words called attack syndromes to model the health of each connection at the receiver which, when unique, unambiguously identify the harmful connection. To ensure attack syndrome uniqueness, we propose an optimization approach to design attack monitoring trails such that their number and length is minimal. This allows us to use the optical network as a sensor for physical-layer attacks. Numerical simulation results indicate that our approach obtains network-wide attack source localization at only 5.8% average resource overhead for the attack monitoring trails.

Marija Furdek, Vincent W. S. Chan, Carlos Natalino, Lena Wosinska

### Analytical Modeling of Survivable Anycast Communication in Optical Networks

Network resources are imperfect and vulnerable to failure from a wide variety of sources. Survivability is a well-researched field that focuses on strategies to prevent or reduce the harm inflicted when network elements fail. Solutions tend to either provision resources, such as backup paths, proactively so that traffic can be switched to the alternative route after a failure, or quickly find new resources to provision after failure event occurs. Current survivability solutions guarantee protection against these failures, but there is no mathematical model to calculate the network blocking probability for survivability solutions of anycast communication. In this paper, we developed new analytical models to calculate network-wide blocking performance for anycast survivability approaches. Performance results show that our models are accurate and are verified by extensive simulation results.

Yan Cui, Vinod M. Vokkarane

### Network Coding for Security Against Eavesdropping Attacks in Elastic Optical Networks

In this work, routing and spectrum allocation (RSA) algorithms together with network coding (NC) are proposed for elastic optical networks. NC has been used in optical networks for protection against link failures and also in multicasting to improve spectral efficiency. In this work, NC is used to protect confidential connections against eavesdropping attacks. The confidential signals are XOR-ed with other signals at different nodes in their path while transmitted through the network. These signals can be combined either at the source node and/or at intermediate nodes. To implement NC for confidential connections, a set of constraints for the NC problem in addition to the constraints of the RSA problem are incorporated to the algorithms. The combination of signals through network coding significantly increases the security of confidential connections, since an eavesdropper will receive a combination of signals from different connections, making it extremely difficult for the confidential signal to be decrypted. A number of RSA strategies are examined in terms of confidentiality, spectrum utilization, and blocking probability. Performance results demonstrate that network coding provides an additional layer of security for confidential connections with only a small increase in the spectrum usage.

Giannis Savva, Konstantinos Manousakis, Georgios Ellinas

### Resilient Cloud-RANs Adopting Network Coding

This study focuses on the provisioning of resilient Cloud Radio Access Network (C-RAN) services employing optical transport networks. In response to the high bandwidth requirements necessary for the protection of the C-RAN architecture from optical transport network and/or BBU failures, a novel approach based on Network Coding (NC) is proposed. A novel architectural and hardware framework to enable NC are also provided and a suitable implementation addressing the problem of fast NC-related operations processing at the edge is demonstrated. A global time stamping solution that can be used to address the strict synchronization requirements of FH flows arriving at the BBUs, keeping buffering at the edge as low as possible, has been developed. The performance of the proposed solution has been experimentally evaluated demonstrating negligible penalties. Network level modeling results demonstrate a reduction of the total optical network capacity required for this type of applications by 33%.

Arash Farhadi Beldachi, Markos Anastasopoulos, Alexandros Manolopoulos, Anna Tzanakaki, Reza Nejabati, Dimitra Simeondou

### A Novel Carrier-Cooperation Scheme with an Incentive for Offering Emergency Lightpath Support in Disaster Recovery

To achieve the fast recovery of optical transport networks following a disaster, we investigate a novel scheme to enable cooperation between carriers. Carriers can take advantage of their surviving or recovered optical resources to aid one another with emergency lightpath support to reduce efficiently the burden of recovery, which is heavy immediately after disasters. These lightpaths can be employed exclusively by the counterpart carriers to satisfy their highest priority traffic demands, such as safety confirmation and victim relief. In addition, we introduce an incentive to carriers to prompt cooperation. The carrier cooperation-planning problem is decomposed into eight tasks, and distributed to individual carriers and a third-party organization. During cooperation, the carriers’ confidential information can be strictly protected by employing a carrier optical network abstraction mechanism. The evaluation results reveal that our proposal can significantly reduce the burden on recovery and the corresponding cost for carriers, resulting in fast and efficient disaster recovery.

Sugang Xu, Noboru Yoshikane, Naoki Miyata, Masaki Shiraiwa, Takehiro Tsuritani, Xiaocheng Zhang, Yoshinari Awaji, Naoya Wada

### State-of-the-Art and Future of Submarine Cable System Technology

The FASTER cable system has been developed as the first trans-pacific optical submarine cable system designed for digital-coherent transmission at the initial state. With this significant change for submarine cables, the design capacity is continuously being upgraded following the improvement of the state-of-the-art modulation format to maximize spectral efficiency even at the limited optical signal-to-noise ratio (OSNR). For the next generation, the novel technologies are expected to increase the capacity per cable under the conditions of limited feeding power and space in a cable. This report reviews some technologies from the current to the promising future submarine cable systems such as the introduction of space-division-multiplexing (SDM) technologies.

Hidenori Takahashi

### Modeling Long-Haul Optical Networks with Quasi-single-mode Fibers

Few-mode fibers (FMFs) with weak mode coupling which are used to transmit signals predominantly in the fundamental mode are referred to as quasi-single-mode (QSM) fibers. QSM fibers can be designed to have much larger effective areas for the fundamental propagation mode than conventional single-mode fibers (SMFs). Signal transmission over the fundamental mode of QSM fibers can reduce distortion arising from the fiber Kerr nonlinearity. Random light coupling, however, among QSM fiber modes leads to multipath interference (MPI). Simultaneous reduction of nonlinear distortion and MPI can be achieved by using hybrid fiber spans, each composed of a QSM fiber segment to restrict nonlinear distortion, followed by an ultra-low-loss, large-effective-area SMF segment to suppress MPI.In this invited paper, we review modeling and simulation tools that can be used for the design and optimization of coherent optical communication systems and networks with hybrid QSM fiber/SMF spans. We show that the precise selection of the fiber splitting ratio per span is not critical for the system performance and can be calculated with sufficient accuracy using a modified version of the nonlinear Gaussian noise model for hybrid fiber spans.

Ioannis Roudas, Xin Jiang, Luis Miranda

### Crosstalk Mitigation in Long-Reach Multicore Fiber Communication Systems Using RKHS Based Nonlinear Equalization

The transmission reach of multi-core fiber (MCF) communication systems is severely affected by inter-core crosstalk (IC-XT), which limits its application for long-reach core optical network. One of the major factors limiting the transmission reach of MCF is nonlinear IC-XT interference, which makes the overall system nonlinear, thereby resulting in a poor bit error rate (BER) performance. Conventional Volterra series based nonlinear equalizer are computationally complex, and impaired by modeling error due to the truncation of polynomial kernel. In this paper, for the first time, we propose multivariate kernel least mean square (KLMS) based adaptive nonlinear equalizer for mitigating IC-XT impairments in MCF communication systems. The proposed scheme is inspired from reproducing kernel Hilbert space (RKHS) based machine learning algorithms. Simulations are performed for different multi-core structures, fiber lengths, and modulation schemes, which show that the proposed KLMS algorithm exhibit superior BER performance over the existing Volterra series equalizer.

Sandesh Jain, Anuj Agrawal, Vimal Bhatia, Shashi Prakash

### Physical Layer Security in Optical Networks

In this paper we’ll discuss technological alternatives related to physical layer security of optical communication systems and networks. In the introduction, an overview of confidentiality and availability issues of the optical networks will be discussed, focusing mainly in the physical layer-related solutions. In the following paragraphs we’ll provide two distinct approaches for the physical layer encryption. The first is based on a One-Time-Pad implementation using synchronized true random sequences. The second uses cryptographic keys generated by Photonic Physical Unclonable Function devices for scrambling the Orthogonal Frequency Division Multiplexing subcarriers.

Dimitris Syvridis, Evangelos Pikasis, Charidimos Chaintoutis

### A Gated Service MAC Protocol for 5G Fiber-Wireless Cloud-Radio Access Networks

Next generation, i.e., fifth generation (5G), networks will leverage both fiber and wireless (FiWi) technology to meet the challenging 5G traffic demands. Moreover, a Cloud-Radio Access Network (C-RAN) architecture will be mainly adopted, which places the BaseBand Units (BBUs) at centralized locations, thus offering cost-efficient energy supply and climate control. To this end, efficient Medium Transparent-Medium Access Control (MT-MAC) protocols are needed to ensure the optimal exploitation of both media. In this paper, we propose a gated service MT-MAC protocol (gMT-MAC) for Millimeter Wave (mmWave) Analog Radio-over-Fiber (A-RoF) C-RANs. GMT-MAC grants a transmission window to each user equal to the time needed for its requested traffic to be successfully sent. A mean packet delay model is also proposed and verified by means of simulation. The performance of gMT-MAC is evaluated for different network load conditions, number of Remote Radio Heads (RRHs) and optical availability values. The provided results prove the suitability of gMT-MAC to meet the sub-ms delay requirements of latency-critical 5G services.

Agapi Mesodiakaki, Pavlos Maniotis, Georgios Kalfas, Christos Vagionas, John Vardakas, Elli Kartsakli, Angelos Antonopoulos, Eftychia Datsika, Christos Verikoukis, Nikos Pleros

### 12 Gb/s Multiband Fiber-Wireless Link Using Coherent IFoF and V-band mmWave Radio

We experimentally demonstrate two Analog Mobile Fronthaul concepts exploiting coherent optical systems technology. Single Sideband generation and coherent detection of a 12 Gb/s signal with 6 subcarriers using an IQ modulator is presented along with an extended reach Fiber-Wireless transmission concept using IQM-DD system and V-band radio.

Nikos Argyris, Giannis Giannoulis, Konstantina Kanta, Panagiotis Toumasis, Dimitrios Apostolopoulos, Hercules Avramopoulos

### System Innovations in Inter Data Center Transport Networks

We review the most important WDM DCI system innovations. State-of-the-art coherent transmission has already exceeded 6 b/s/Hz, using subcarrier modulation. The adoption of software innovations in automation and programmability, that DCI pioneered in transport networks, has also simplified operations and enables the emergence of “open” transport architectures. Combining these advancements with emerging network analytics frameworks allows exciting innovations in network design and management optimization.

Loukas Paraschis, Harald Bock, Parthiban Kandappan, Bernd Sommerkorn-Krombholz, Joao Pedro, Abhinava Sadasivarao, Sharfuddin Syed, Jeff Rahn, Paul Doolan, Biao Lu

### SDN Control of Disaggregated Optical Networks with OpenConfig and OpenROADM

Most deployed optical transport networks are proprietary, behaving as a closed, highly coupled, single-vendor managed domain. Although their control planes and management systems may export high-level and open northbound interfaces (NBI), the internal details and interfaces are not disclosed to the network operator. However, driven by the requirements of telecommunication and data-center operators and the need to keep costs down while supporting sustained traffic increase, a trend known as disaggregation has steadily emerged during the past years. It involves composing and assembling open and available components, devices and sub-systems into optical infrastructures and networks, combining “best-in-class” devices, tailored to the specific needs of the aforementioned operators. It has been motivated by factors such as an increase in hardware commoditization, a perceived different rate of innovation of the different components, a promised acceleration in service deployment, or the consequent reduction in operational and capacity expenses. In practice, disaggregation brings multiple challenges, depending on the level that applies (e.g., partial or total, down to each of the optical components) and is taking place in stages. It is commonly accepted that disaggregation implies a trade-off between: (i) the opportunities due to the new degree of flexibility provided by component migration and upgrades without vendor lock-in and (ii) the potential decrease in performance compared to fully integrated systems and the underlying complexity – including interoperability -, critical in full disaggregation scenarios. From the point of view of control and management, disaggregation heavily relies on the adoption of open interfaces exporting hardware programmability. Disaggregated optical networks are an important use case for the adoption or a unified, model-driven development. In this paper, tutorial in nature, we will introduce the main concepts behind Software Defined Networking (SDN) for disaggregated optical networks, presenting reference architectures and industry common practices related to the adoption of a unified, model driven approach. The second part will cover an overview of selected deployment models (e.g., addressing transceiver and OLS disaggregation) as well as the OpenConfig and OpenROADM optical device models and Transport API (TAPI) interfaces, which constitute the main elements of the implemented SDN control plane. Such control plane targets mainly the metro segment, as defined within the EC Metro-Haul and ONF ODTN projects.

Ramon Casellas, Ricard Vilalta, Ricardo Martínez, Raúl Muñoz

### Self-learning Routing for Optical Networks

It is generally very difficult to optimize the routing policies in optical networks with dynamic traffic. Most widely-used routing policies, e.g., shortest path routing and least congested path (LCP) routing, are heuristic policies. Although the LCP is often regarded as the best-performing adaptive routing policy, we are often eager to know whether there exist better routing policies that surpass these heuristics in performance. In this paper, we propose a framework of reinforcement learning (RL) based routing scheme, that learns routing decisions during the interactions with the environment. With a proposed self-learning method, the RL agent can improve its routing policy continuously. Simulations on a ring-topology metro optical network demonstrate that, the proposed scheme outperforms the LCP routing policy.

Yue-Cai Huang, Jie Zhang, Siyuan Yu

### Deterministic Contention Management for Low Latency Cloud RAN over an Optical Ring

The N-GREEN project has for goal the design of a low cost optical ring technology with good performance (throughput, latency$$\dots$$) without using expensive end-to-end connections. We study the compatibility of such a technology with the development of the Cloud RAN, a latency critical application which is a major aspect of 5G deployment. We show that deterministically managing Cloud RAN traffic minimizes its latency while also improving the latency of the other traffics.

Dominique Barth, Maël Guiraud, Yann Strozecki

### Resource Analysis and Cost Modeling for End-to-End 5G Mobile Networks

5G network demands massive infrastructure deployment to meet its requirements. The most cost-effective deployment solution is now a challenge. This paper identifies a cost implementation strategy for 5G by reformulating existing cost models. It analyses three geo-type scenarios and calculates the total cost of ownership (TCO) after estimating the Capex and Opex. The calculations are narrowed to specific cities for clearer understanding instead of the usual generic estimates. An end-to-end 5G network resource analysis is performed. Our result shows that by the end of first year Capex constitutes over 90% of TCO for urban scenarios. Also uniform capacity deployment across geo-types impose severe investment challenges.

Hilary Frank, Rodrigo S. Tessinari, Yuqing Zhang, Zhengguang Gao, Carlos Colman Meixner, Shuangyi Yan, Dimitra Simeonidou

### Analog IFoF/mmWave 5G Optical Fronthaul Architecture for Hot-Spots Using Multi-channel OFDM-Based WDM Signals

An analog Intermediate-Frequency-over-Fiber (IFoF) – based fronthaul 5G architecture for high traffic hot-spot environments is presented. The proposed optical fronthaul link utilizes Photonic Integrated Circuit (PIC) Wavelength Division Multiplexing (WDM) Externally Modulated Laser (EML) - based optical transmitters at a centralized Base Band Unit (BBU) and Reconfigurable Optical Add-Drop Multiplexers (ROADMs) at the Remote Radio Head (RRH) side located in the hot-spot area. By employing two WDM links, where each wavelength carries six 0.5 Gbaud IF bands of Orthogonal Frequency Division Multiplexing (OFDM) with 16 – QAM Sub-Carrier (SC) modulation, a total data rate of 96 Gb/s was achieved. Error Vector Magnitude (EVM) measurements were carried out, exhibiting acceptable performance below the EVM FEC limit of 12.5%. A power budget study was also performed, suggesting up to 9.5 km fiber lengths between the BBU and the hot-spot network. The proposed architecture complies with the high capacity and low latency requirements of the 5G vision, thus may be an efficient solution for 5G fronthauling of heavy traffic hot-spot areas.

Charoula Mitsolidou, Christos Vagionas, Agapi Mesodiakaki, Pavlos Maniotis, George Kalfas, Chris G. H. Roeloffzen, Paulus W. L. van Dijk, Ruud M. Oldenbeuving, Amalia Miliou, Nikos Pleros

### Hybrid and Optical Packet Switching Supporting Different Service Classes in Data Center Network

Optical Packet Switching is a prominent technology proposing not only a reduction of the energy consumption by the elimination of numerous optical-electrical-optical conversions in electronic switches, but also a decrease of network latencies due to the cut-through nature of packet transmission. However, it is adversely affected by packet contention, preventing its deployment. Solutions have been proposed to tackle the problem: addition of shared electronic buffers to optical switches (then called hybrid opto-electronic switches), customization of TCP protocols, and use of different service classes of packets with distinct switching criteria.In the context of data center networks we investigate a combination of said solutions and show that the hybrid switch, compared to the optical switch, boosts the performance of the data center network. Furthermore, we show that introducing a “Reliable” service class improves performance for this class not only in the case of the hybrid switch, but also brings the optical switch to performance levels comparable to that of the hybrid switch, all the while keeping other classes’ performance on the same level.

Artur Minakhmetov, Cédric Ware, Luigi Iannone

### Reduction of Delay Overfulfillment in IP-over-DWDM Transport Networks

The traffic in today’s transport networks is increasing dramatically due to more demanding applications like video on demand and improving access technologies like 5G. Additionally, the quality of service requirements are becoming more stringent while network operators are seeking new ways for revenue creation. We propose a multi-layer network reconfiguration approach that reduces the overfulfillment of service delay requirements. In that way it provides an incentive to customers with low-delay services to acquire a more expensive service class for their traffic. Additionally, it relieves highly utilized links for services with very strict delay requirements. We provide an ILP formulation that solves this multi-layer network problem by performing a cross-layer optimization. Further, we evaluate our approach for two nationwide backbone networks. We show that a reduction of service delay overfulfillment is possible and how that affects other network metrics.

Uwe Bauknecht, Tobias Enderle, Arthur Witt

### Design of a Real-Time DSP Engine on RF-SoC FPGA for 5G Networks

5G advances the wireless communications by providing a significant improvement to the data rate, capability of connected devices and data volumes compared to the previous generations. While these advantages combine along with a wider range of applications to merit the end-user, the technologies to be used are not specified. Considering this problem and in order to efficiently support the 5G deployment researchers and engineers turned their attention on FPGA base band architectures that keep the implementation cost relatively low and at the same time they are reprogramable to provide solutions to the emerging requirements and their consequent modifications. Aiming at the contribution to the 5G technologies the current paper introduces the design of a base band DSP architecture that targets the required real time performance. Moreover, the proposed architecture is scalable by efficiently parallelizing and/or pipelining the corresponding data paths. The paper presents the pilot FPGA designs of the IFFT/FFT and Sampling Frequency Offset (SFO) functions that achieve a 500 Msps performance on a RF-SoC Xilinx ZCU111 board.

Vasileios Kitsakis, Konstantina Kanta, Ioannis Stratakos, Giannis Giannoulis, Dimitrios Apostolopoulos, George Lentaris, Hercules Avramopoulos, Dimitrios Soudris, Dionysios I. Reisis

### Performance of Underwater Wireless Optical Link Under Weak Turbulence and Pointing Errors Using Heterodyne QAM Technique

Underwater optical wireless communications (UOWC) have gained attention due to the advantages they offer that can greatly alter the performance of a link. But such systems are affected by absorption and non predictable factors that may decrease the availability and the reliability of the system. In this work, the bit error rate (BER) of an underwater optical link with heterodyne detection modulated with M-QAM technique in presence of turbulence and pointing errors will be investigated. This investigation will lead to a closed form mathematical expression for the BER as a function of link parameters, that is very important in order to deploy an effective link. Various numerical results will also be presented for the reliability of the system.

Argyris N. Stassinakis, Hector E. Nistazakis, George K. Varotsos, George S. Tombras

### MCF Skew Estimation at the Receiver for ARoF Antenna Beamforming

Multicore fibers can be used for Radio over Fiber transmission of mmwave signals for phased array antennas in 5G networks. The inter-core skew of these fibers distorts the radiation pattern and has to be measured and compensated. We propose a method to accurately measure the differential delays remotely, after installation, without intervening heavily with the transmitter setup. The properties of the phase response measured at a distant receiver are exploited to acquire the differential delays among the antenna array elements.

Thomas Nikas, Evangelos Pikasis, Sotiris Karabetsos, Dimitris Syvridis

### Core Arrangement Based Spectrum-Efficient Path Selection in Core-Continuity Constrained SS-FONs

In this work, we exploit the spatial dimension of spectrally-spatially flexible optical networks (SS-FONs) to perform path selection. The existing path selection schemes in SS-FONs predominantly use k-shortest paths (KSP) method. However, in this work, we demonstrate that in SS-FONs, consideration of core selection along with link selection between source and destination nodes can significantly increase the spectrum utilization efficiency. We propose a k-core arrangement based paths (KCAP) scheme that performs path calculation and prioritization on the basis of core arrangement in different multicore fiber (MCF) structures, threshold crosstalk (XT) values, distance adaptive modulation (DAM), and the number of MCF links. The proposed KCAP achieves better spectrum utilization than the existing XT-aware and predefined core-prioritization schemes.

Anuj Agrawal, Vimal Bhatia, Shashi Prakash

### Topology and Failure Modeling for Optical Network Resilience Analysis Against Earthquakes

In this paper, we propose a stochastic failure and optical network topology (SFONT) model that can be used to comprehensively analyze the resilience of optical networks against a large number of possible earthquakes. We study an optical network densification problem, where dense network topologies are generated using the proposed SFONT model. Further, a seismic-risk aware optical network densification (SRA-OND) scheme is proposed with a view to design the future optical networks robust against earthquakes. The proposed SFONT model has been evaluated at various stages of network densification. To validate the capability of the proposed SFONT model to emulate real-world networking and failure scenario, we also perform a similar analysis based on RailTel optical network topology, seismic hazard maps, and real past earthquake data from India. Simulations indicate that the proposed SFONT model can be used to estimate and analyze the impact of network-resilience schemes on optical networks for a large number of possible earthquakes.

Anuj Agrawal, Vimal Bhatia, Shashi Prakash

### A Performance Analysis of Supervised Learning Classifiers for QoT Estimation in ROADM-Based Networks

Machine learning techniques for optimization purposes in the optical domain have been reviewed extensively in recent years. While several studies are pointing in the right direction towards building enhanced transport network control systems including estimation algorithms, the physical effects encountered in the optical domain raise several challenges that are hard to learn from and mitigate. In this paper, we provide a performance analysis of various supervised learning algorithms when predicting the Quality of Transmission (QoT), in terms of signal to noise ratio (OSNR), of lightpaths when erbium doped fiber amplifier (EDFA) power excursions and fiber nonlinearities are taken into account. The analysis considers F1-scores and computational training times as the main comparison metrics. A customized optical data network simulator was used for the generation of synthetic labeled data samples. Our results depict similar performance among groups of classifiers, and a correlation between the data sample size and the prediction accuracy.

Alan A. Díaz-Montiel, Marco Ruffini

### Programmable Flex-E and X-Ethernet Networks for Traffic Isolation in Multi-tenant Environments

In this work we investigate the coupling of Flex-E and X-Ethernet technologies as a means to realize interface slicing and fast switching respectively. Flex-E is investigated as a key technology that is able to split a physical interface into isolated sub-channels, decouple MAC rate from PHY rate and achieve hard bandwidth isolation. X-Ethernet technology introduces Ethernet PCS switching, eliminates table lookup and buffer queuing and will be investigated as a fast switching mechanism that is exploiting the PCS layer relay. We present evaluation results from implementation activities that showcase the ability of an integrated Flex-E/X-Ethernet solution to enable network slicing features in transport networks. Furthermore we present a technical approach on the way the control plane of Flex-E/X-Ethernet network can be integrated with an orchestration and management solution.

Kostas Katsalis, Rixin Li

### Q-Learning Based Joint Allocation of Fronthaul and Radio Resources in Multiwavelength-Enabled C-RAN

Multi-wavelengths passive optical networks (PONs) such as wavelength division multiplexing (WDM) and time wavelength division multiplexing (TWDM) PONs are outstanding solutions for providing a sufficient bandwidth for mobile front-haul to support C-RAN architecture in 5G mobile network. In this paper a joint allocation framework for multi-wavelength PONs mobile front-haul and C-RAN air interface uplink resources is proposed. From the principle that uplink resource allocation in mobile networks (e.g. 4G and 5G) is an NP-hard optimization problem, this paper contributes with a novel method for uplink scheduling based on a reinforcement learning (RL) algorithm known as Q-Learning. The performance of the algorithm is evaluated with numerical simulations and compared with some other relevant work from the literature such as genetic algorithm (GA) and tabu search (TS). The simulation results show that the new algorithm achieves faster convergence, higher throughput, and minimum scheduling time compared to the two other algorithms. The results also show that RL-based dynamic allocation of front-haul transport block capacity based on actual radio resource block size can greatly reduce front-haul capacity requirement and minimize total end to end uplink scheduling latency.

Ahmed Mohammed Mikaeil, Weisheng Hu

Advanced interconnect technologies play a prominent role in scaling up the performance of data center networks. Spatial Division Multiplexing (SDM) photonic interconnects have been suggested as means to overcome capacity upgrade requirements and enable disaggregation in future data centers. Here, Holographic Optical Elements (HOE) are proposed for SDM photonic interconnects. The proposed coupling scheme entails the use of holograms as fan out components for coupling light from a source to multicore fibers (MCF). The scheme is versatile and can be adopted to any SDM fiber core arrangement. Appropriate Computer-Generated Holograms (CGHs) are designed for two kind of MCF and the HOE interconnect is evaluated in terms of performance variations against system and fabrication related parameters. Furthermore, the interconnect design is optimized for loss-sensitive applications.

Christina (Tanya) Politi, Dimitris Alexandropoulos, Dimitra Simeonidou

### Supporting Diverse Customers and Prioritized Traffic in Next-Generation Passive Optical Networks

A variety of DBA (Dynamic Bandwidth Allocation) and DWBA (Dynamic Wavelength and Bandwidth Allocation) algorithms have been proposed which are based on different PONs (e.g. EPON, GPON, XG-PON, 10G-EPON, etc.). But to our knowledge, no DWBA scheme for NG-PON2 system, with diverse customers and prioritized traffic, has been proposed yet. In this work, this problem is addressed and we focus on the wavelength assignment part, assuming that the system applies conventional DBA method described in the standard ITU-T G.989. Considering this assumption, we propose five different dynamic wavelength and bandwidth allocation (DWBA) schemes. First, mixed integer linear programming (MILP) models are developed to minimize the total delay of the high priority data. Due to the MILP’s high computational complexity, heuristic algorithms are developed based on the MILP model insights. The five heuristics algorithms are: No Block-Split Heuristic (NBH), Equal Block-Split Heuristic (EBH), Priority Based No Block-Split Heuristic (P-NBH), Priority Based Equal Block-Split Heuristic (P-EBH), and Priority Based Decider Block-Split Heuristic (P-DBH). Six priority classes of requests are introduced with the goal of minimizing the total delay for the high priority data and to lessen the bandwidth wastage of the system. Finally, experiments for the performance evaluation of the five DWBA schemes are conducted. The results show that P-DBH is the most efficient among the five because this scheme offers the lowest delay for high priority data and the minimum bandwidth wastage for lower priority ones.

Naureen Hoque, Byrav Ramamurthy

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