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Increased global traffic puts tough requirements not just on fiber communications links but on the entire network. This manifests itself in multiple ways, including how to optimize wavelength routing around the network, how to maximize the benefits arising from fine-control DSP with increasingly accurate real-time monitoring, and how to best deploy multiband or multiple fiber connectivity. This article will summarize research into all these areas to present a full picture of how future optical networks will play their role in supporting the continuing traffic demands of broadband, 5G, and associated applications. [ABSTRACT FROM AUTHOR]

Filterless Optical Networks (FONs) (i.e., optical networks where switching nodes are solely based on passive splitters and combiners) enjoy features that are highly appreciated by network operators, such as their low cost and their energy efficiency, posing them as an alternative solution to filtered Wavelength-Switched Optical Networks (WSON) based on active switching nodes. Due to FONs’ specific design criteria (the network topology must be divided into link-disjoint filterless fiber trees to avoid laser loops), traditional network problems, such as survivable virtual network mapping, shall be revisited and tackled adopting novel solutions with respect to state-of-the-art filtered WSONs. In this paper, we investigate the problem of survivable virtual network mapping (SVNM) in FONs with the aim of evaluating the cost of survivability when adopting FON technology. We first model the problem as an Integer Linear Program to establish fiber trees and provide survivable mapping of virtual networks, while minimizing cost of additional network equipment and spectrum with respect to WSON. We then propose multiple heuristic and meta-heuristic approaches to tackle large problem instances. In our numerical evaluations, we consider three scenarios: FON, WSON, and FON with pre-established fiber trees. Results show that in FON, where SVNM is jointly optimized with fiber tree establishment, the investment in additional network equipment can be largely minimized, and even avoided in some cases. In contrast, in FON with pre-established trees, amount of additional network equipment needed to guarantee survivability is significant (up to 60% with respect to WSON). [ABSTRACT FROM AUTHOR]

The recent acceleration in fiber-to-the-home deployment worldwide along with the emerging 5G communications are pressuring network operators to enhance their networks to serve these new deployments. Hence, operators are seeking new high-capacity optical-network architectures, while averting excessive capital and operational expenditures. Filterless optical networks (FONs), by replacing costly wavelength selective switches in switching nodes with passive optical power splitters/combiners, currently represent a prominent candidate for cost-effective optical-network deployment. In this tutorial, we provide an overview of the architecture and the design issues of FONs when deployed in core and in metro networks. We also perform a techno-economic study to quantify the economic benefits of FONs, comparing their cost to that of state-of-the-art filtered optical networks, and we discuss how several networking problems such as resource allocation, network slicing, and protection are tackled in the context of FONs. Finally, we present our vision of how research on FONs will evolve in the coming years. [ABSTRACT FROM AUTHOR]

Filterless Optical Networks (FONs) represent a novel cost-effective solution for metro optical networks, that allows to achieve equipment-cost savings by removing expensive optical-switching components from network nodes. In this study, we investigate how to further reduce equipment cost in FONs by minimizing amplifiers’ cost. We propose a Genetic Algorithm (GA) for placing boosters, inline amplifiers and pre-amplifiers in FONs with the objective of minimizing amplifiers cost. We provide two versions of the GA and compare their performance against a baseline amplifier placement in terms of amplifiers cost and quality-of-transmission (QoT), i.e., lightpaths OSNR and received power. Moreover, we provide a comparison between filterless and wavelength-switched architectures. Simulative results achieved over realistic network topologies show significant amplifier cost savings, up to 60% compared to baseline approaches. [ABSTRACT FROM AUTHOR]

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

5G network slicing allows partitioning of network resources to meet stringent end-to-end service requirements across multiple network segments, from access to transport. These requirements are shaping technical evolution in each of these segments. In particular, the transport segment is currently evolving in the direction of elastic optical networks (EONs), a new generation of optical networks supporting a flexible optical-spectrum grid and novel elastic transponder capabilities. In this paper, we focus on the reliability of 5G transport-network slices in EON. Specifically, we consider the problem of slicing 5G transport networks, i.e., establishing virtual networks on 5G transport, while providing dedicated protection. As dedicated protection requires a large amount of backup resources, our proposed solution incorporates two techniques to reduce backup resources: (i) bandwidth squeezing, i.e., providing a reduced protection bandwidth than the original request; and (ii) survivable multi-path provisioning. We leverage the capability of EONs to fine tune spectrum allocation and adapt modulation format and forward error correction for allocating spectrum resources. Our numerical evaluation over realistic network topologies quantifies the spectrum savings achieved by employing EON over traditional fixed-grid optical networks, and provides new insights on the impact of bandwidth squeezing and multi-path provisioning on spectrum utilization. One key takeaway from our evaluation is that multi-path provisioning can guarantee up to 40% of the bandwidth requested by a VN during failures by provisioning only 10% additional spectrum resources. This also caused VN blocking ratio for BSR up to 40% to remain very close to that of the no-backup case. [ABSTRACT FROM AUTHOR]

Failure management plays a role of capital importance in optical networks to avoid service disruptions and to satisfy customers’ service level agreements. Machine learning (ML) promises to revolutionize the (mostly manual and human-driven) approaches in which failure management in optical networks has been traditionally managed, by introducing automated methods for failure prediction, detection, localization, and identification. This tutorial provides a gentle introduction to some ML techniques that have been recently applied in the field of the optical-network failure management. It then introduces a taxonomy to classify failure-management tasks and discusses possible applications of ML for these failure management tasks. Finally, for a reader interested in more implementative details, we provide a step-by-step description of how to solve a representative example of a practical failure-management task. [ABSTRACT FROM AUTHOR]

Multicore fibers (MCFs) are one of the main technological enablers for space-division multiplexing. In principle, MCFs could scale the fiber capacity by a factor equal to the number of cores, but in practice such increase is hindered by transmission impairments due to the inter-core crosstalk between adjacent lit cores. The entity of such crosstalk depends on the number of cores and on their disposition within the fiber cladding, and also on the baud rate and modulation format used for transmission. As first MCF applications are expected over point-to-point systems, in this paper we concentrate on the resource allocation over a single link. Specifically, we study the Baud rate, Modulation format, Core and Spectrum Assignment problem in a multicore flexi-grid link, considering distance-adaptive reaches for different baud rates, modulation formats, and crosstalk impairments. We show that the problem is NP-hard and provide two integer linear programs, as well as heuristic approaches to solve it over large/practical traffic instances. Our problem formulations incorporate modeling of the exact inter-core crosstalk contributions depending on the number of lit neighbor cores. Numerical results are provided in a high-spatial-efficiency 19-core fiber considering different transmission impairment conditions. [ABSTRACT FROM AUTHOR]

Traditionally, networks operate at a small fraction of their capacities; however, recent technologies, such as software-defined networking, may let operators run their networks harder (i.e., at higher utilization levels). Higher utilization can increase the network operator’s revenue, but this gain comes at a cost: daily traffic fluctuations and failures might occasionally overload the network. We call such situations Resource Crunch. Dealing with Resource Crunch requires certain types of flexibility in the system. We focus on scenarios with flexible bandwidth requirements, e.g., some connections can tolerate reducing their bandwidth allocation. This may free capacity to provision new requests that would otherwise be blocked. For that, the network operator needs to make an informed decision, since reducing the bandwidth of a high-paying connection to allocate a low-value connection is not sensible. We propose a strategy to decide whether or not to provision a request (and which other connections to degrade) focusing on maximizing profits during Resource Crunch. To address this problem, we use an abstraction of the network state, called a connection adjacency graph (CAG). We propose an algorithm, called PROVISIONER, which integrates our CAG solution with an efficient linear program (LP). We compare our method to existing greedy approaches and to LP-only solutions, and show that our method outperforms them during Resource Crunch. [ABSTRACT FROM AUTHOR]

The fifth generation (5G) of mobile communications will target unprecedented network performance and quality of service for end users. Among the various aspects which will be addressed in 5G, advanced cell coordination is deemed as crucial to maximize network throughput. In particular, in this paper, we refer to coordinated multipoint (CoMP) techniques that allow coordinating groups of cells (i.e., clusters) through a coordination controller, namely, a radio controller coordinator (RCC), to enhance the mobile network throughput by reducing interference. We focus on the placement of RCCs in the metro optical network and on its impact on the performance of cell coordination. We provide strategies to perform an optimized placement of such controllers in metro optical networks in order to maximize network throughput via cell coordination. Several CoMP techniques have been designed, whose throughput gain is affected by various factors, e.g., gain increases with the cluster size, while it decreases for larger latencies between the RCC and cells. As current metro networks are characterized by a hierarchical architecture with different levels of central offices, the choice of where to place controllers to maximize throughput gain can be optimized according to several factors, i.e., network geographical dimension, cells density, and available technology. In addition, selection of the most appropriate CoMP technique to be used in each cluster is not trivial, as the gain provided by the various techniques is differently affected by cluster size and latency between the RCC and cells. Our results show that under certain conditions optimized placement provides up to around 10% higher coordination gain with respect to fixed controller placement. Moreover, when adopting fronthaul technology, the coordination gain provided by an optimized controller placement may increase up to 20% in comparison to fixed placement. [ABSTRACT FROM AUTHOR]

To cope with the explosion of mobile traffic demand, cloud radio access networks (C-RAN) have been recently proposed. In C-RANs, the two main elements of traditional base stations (BSs), i.e., the baseband unit (BBU) and the remote radio head (RRH), are separated, and the BBU can be virtualized and located in a remote location together with BBUs of other BSs. High-bandwidth digitized baseband signals must be exchanged between BBUs and RRHs through a large-capacity fronthaul network. Wavelength division multiplexing (WDM) technology is an efficient solution to provide sufficient fronthaul bandwidth with a large number of optical transceivers. With the fixed connections between BBUs and RRHs in the traditional C-RAN, the utilization of optical transceivers as well as BBUs is inefficient. In this paper, we propose a decomposed arrayed waveguide grating router (AWGR)-enabled passive WDM fronthaul, and we formulate the minimal energy consumption problem as integer linear programming, with the objective of minimizing the energy consumption caused by optical transceivers and BBUs, etc. We also design two dynamic lightpath adjustment heuristics by light-path reconfiguration to improve energy efficiency. In addition, we take AWGR decomposition into consideration to reduce the tuning range of tunable transceivers and free spectrum range of AWGR, hence lowering the deployment cost of transport network components. Numerical evaluation shows that our proposed schemes achieve significant energy savings compared to fixed lightpath allocation. [ABSTRACT FROM AUTHOR]

Modular design based on spatial division multiplexing switches is a promising way to improve the capacity and reduce the cabling complexity of data center networks. However, due to the coexistence of mice and elephant flows, in modular data center networks a trade-off between the blocking probability and total throughput arises. In fact, blocking elephant flows would lead to a relevant penalty on the throughput but a small penalty on the blocking probability. In this paper, we investigate the relation between the blocking and throughput in modular data center networks based on optical spatial division multiplexing. We combine the two metrics linearly by a weight factor that prioritizes them relatively. To solve the resource allocation problem, we propose both mixed integer linear programming formulations and close-to-optimal heuristics for three different spatial division multiplexing switching schemes. Simulation results demonstrate that a carefully chosen weight factor is necessary to achieve a proper balance between the blocking probability and throughput for all the schemes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Predicting the quality of transmission (QoT) of a lightpath prior to its deployment is a step of capital importance for an optimized design of optical networks. Due to the continuous advances in optical transmission, the number of design parameters available to system engineers (e.g., modulation formats, baud rate, code rate, etc.) is growing dramatically, thus significantly increasing the alternative scenarios for lightpath deployment. As of today, existing (pre-deployment) estimation techniques for light-path QoT belong to two categories: ?exact? analytical models estimating physical-layer impairments, which provide accurate results but incur heavy computational requirements, and margined formulas, which are computationally faster but typically introduce high link margins that lead to underutilization of network resources. In this paper, we explore a third option, i.e., machine learning (ML), as ML techniques have already been successfully applied for optimization and performance prediction of complex systems where analytical models are hard to derive and/ or numerical procedures impose high computational burden. We investigate a ML classifier that predicts whether the bit error rate of unestablished lightpaths meets the required system threshold based on traffic volume, desired route, and modulation format. The classifier is trained and tested on synthetic data and its performance is assessed over different network topologies and for various combinations of classification features. Results in terms of classifier accuracy are promising and motivate further investigation over real field data. [ABSTRACT FROM PUBLISHER]

Common Public Radio Interface (CPRI) is a successful industry cooperation defining the publicly available specification for the key internal interface of radio base stations between the radio equipment control (REC) and the radio equipment (RE) in the fronthaul of mobile networks. However, CPRI is expensive to deploy, consumes large bandwidth, and currently is statically configured. On the other hand, an Ethernet-based mobile fronthaul will be cost-efficient and more easily reconfigurable. Encapsulating CPRI over Ethernet (CoE) is an attractive solution, but stringent CPRI requirements such as delay and jitter are major challenges that need to be met to make CoE a reality. This study investigates whether CoE can meet delay and jitter requirements by performing FPGA-based Verilog experiments and simulations. Verilog experiments show that CoE encapsulation with fixed Ethernet frame size requires about tens of microseconds. Numerical experiments show that the proposed scheduling policy of CoE flows on Ethernet can reduce jitter when redundant Ethernet capacity is provided. The reduction in jitter can be as large as 1 μs, hence making Ethernet-based mobile fronthaul a credible technology. [ABSTRACT FROM PUBLISHER]

Modular design has recently emerged as an efficient solution to build large data center (DC) facilities. Modular DCs are based on stand-alone prefabricated modules (i.e., PODs) that can be easily installed and interconnected. PODs can generate a large amount of traffic and thus require an ultra-high-capacity interconnection network. However, current electronic and optical interconnect architectures applied to modular DCs may experience major scalability problems in terms of high energy consumption and cabling complexity. To address these problems, we investigate five optical interconnect architectures based on spatial division multiplexing (SDM), and for each architecture, we propose a resource allocation strategy. We also present an extensive comparison among the SDM architectures in terms of cost and performance (i.e., blocking probability and throughput), with the objective to find the architecture offering the best trade-off between cost and performance for given DC sizes and traffic load values. Our results demonstrate that, in small modular DCs with low traffic load, an architecture based only on SDM is the best option, while in medium DCs with medium traffic load, an architecture based on coupled SDM and flexgrid wavelength division multiplexing (WDM) with spectral flexibility is the best solution. Finally, for large DCs with high traffic load values, the best trade-off between cost and performance is achieved by an SDM architecture that is based on uncoupled SDM and flexgrid WDM. [ABSTRACT FROM PUBLISHER]

Network function virtualization is an emerging network resource utilization approach which decouples network functions from proprietary hardware and enables adaptive services to end-user requests. To accommodate the network function requests, network function instances are created and deployed at runtime. In this paper, we study a network virtualization scheme to orchestrate and manage networking and network function services. We propose an integrated design for network function instance allocation and end-to-end demand realization sharing the same physical substrate network and demonstrate that the corresponding network design problem is NP complete. A mixed-integer programming formulation is proposed first to find its optimal solution, followed by a two-player pure-strategy game model which captures the competition on physical resources between network function instance allocation and routing. We then design an algorithm based on iterative weakly dominated elimination in Game Theory. Computational results demonstrate the value of the integrated approach and its ability to allocate network function instances supporting end-to-end requests with limited physical resources in optical networks. [ABSTRACT FROM PUBLISHER]

Cloud services based on content sharing and distribution are most prevalent in today's world, and datacenter (DC) networks supporting such services manage a huge volume of data transfers, in the range of terabytes to zettabytes. Usually, contents are replicated in geographically distributed DCs for high availability and reliability, but in the case of high-impact, large-scale disasters, like weapons of mass destruction attacks, DC networks can suffer massive service disruptions and data loss. To save critical data under such circumstances, contents could be evacuated in response to an upcoming disaster alert from a likely disaster region to a safe location before the disaster occurs and causes serious data damage. Depending on the forecasted disaster scenario, content evacuation can be greatly constrained by limited available network resources and strict deadlines (evacuation times). We propose a rapid-data-evacuation (RDE) heuristic that selects the least-delay paths (considering propagation delays, network bandwidth, and congestion) through an anycast network model, and schedules critical and vulnerable contents for evacuation such that the maximum amount of contents can be evacuated within the evacuation deadline or equivalently, a given amount of contents can be evacuated in minimum time. We compare our RDE heuristic with a nearest-evacuation approach, which evacuates data only to the nearest DC using the shortest path. Our results show that, for typical scenarios considered in this study, compared to nearest evacuation, our rapid-evacuation approach provides about 64% time savings, or equivalently, about 97% more volume of evacuated contents for a given deadline. Since our algorithm is based on a greedy approach, we also present an enhanced RDE algorithm based on the simulated annealing (SA) metaheuristic as a benchmark. We show that our proposed RDE heuristic performs very close to the SA based algorithm and is much faster in computation time. Hence, it is suitable and efficient for rapid evacuation. [ABSTRACT FROM PUBLISHER]

Availability-aware service provisioning tries to satisfy the availability requirements of clients on demand and can improve the resource efficiency in optical networks. This paper studies the problem of flexible availability-aware differentiated protection (ADP) in elastic optical networks (EONs). We first consider the unique features in EONs, e.g., flexible spectrum allocation and bandwidth-squeezed protection, describe the problem of ADP, and present a theoretical analysis on service availability. Then, we develop an ADP algorithm that can change the path protection scheme to adapt to different service availability requirements. An availability-aware backup reprovisioning strategy is also proposed as a supplement of the ADP algorithm to further improve the protection efficiency. We also discuss the system design for OpenFlow-based software-defined EON (SD-EON) framework to facilitate the ADP scheme. Finally, to demonstrate the overall design, we construct an SD-EON control plane testbed that consists of 14 standalone nodes, implement the proposed algorithms in the OpenFlow controller, and perform experiments to evaluate their performance. The results indicate that the system performs well, and the proposed algorithms can reduce blocking probability effectively without sacrificing the service availability of requests. [ABSTRACT FROM PUBLISHER]

Telecommunication networks face large-scale threats, such as natural disasters (earthquake, hurricane, tsunami, etc.) and targeted attacks (weapons of mass destruction). These disasters may simultaneously destroy many network components (nodes and/or links) and cause multi-failure events. Although existing protection schemes can handle some given multi-failure scenarios, it is extremely challenging to solve all possible disaster-failure scenarios with reasonable resource costs and a 100% reliability guarantee. In this paper, we investigate postdisaster restoration strategies for telecom backbone mesh networks (such as wavelength-division multiplexed networks), whose objective is two-fold: to maintain network connectivity (i.e., guarantee a minimal degree of service for the survived connections) and to maximize the traffic flow in the post-disaster network. We study three postdisaster re-provisioning schemes employing different policies for connection rerouting and admissible bandwidth degradation (i.e., provisioning partial bandwidth). These schemes, whose services range from essential to global post-disaster re-provisioning, are the no-degradation reprovisioning (NDR) scheme, the degradation-as-needed re-provisioning (DAN) scheme, and the fairness-aware degradation re-provisioning (FAD) scheme. Corresponding mixed integer linear program models are developed and applied on two representative mesh topologies. Numerical results show that NDR can effectively decrease the connection loss ratio by rerouting some survived connections. However, both DAN and FAD can achieve optimal performance on maintaining connectivity even without rerouting any survived connections. DAN outperforms the other schemes in terms of traffic loss ratio, but it may cause a large difference between the maximum and minimum degradation ratios. FAD can improve the performance in terms of traffic loss ratio by rerouting a few survived connections. In particular, compared with DAN, FAD can provide balanced bandwidth degradation for all connections by sacrificing a certain amount of traffic flow, but avoiding extreme deterioration of the bandwidth capacity on some connections. [ABSTRACT FROM PUBLISHER]

Energy-efficiency has been widely recognized as an important target in the management of optical wavelength division multiplexing networks. A very promising power management strategy consists in putting unused transponders into a low-power state, called idle or sleep state, or even in turning them off. However, in such scenario, it should be also guaranteed that high-priority traffic, which requires short setup times, is quickly established without waiting for the long activation time of powered-off devices. A possible strategy to avoid long setup times is to reserve some idle transponders for high-priority traffic. However, reserving a large number of idle transponders for high-priority traffic will increase the blocking of low-priority traffic, since less resources are available. To analyze this tradeoff, in this paper we present a novel analytical model based on Markov chains to evaluate the blocking probability and the power savings of this transponder power management in presence of high- and low-priority traffic. The presented model can be used to estimate both power savings and blocking levels and to provide guidelines on how to dimension the number of reserved devices for high-priority traffic. [ABSTRACT FROM PUBLISHER]

Failures caused by disasters (e.g., weapons of mass destruction (WMD) attacks, earthquakes, hurricanes, etc.) can create huge amount of loss and disruptions in optical backbone networks. Due to major network disruptions in recent disasters, network operators need solutions to prevent connections from disasters, and recover them after disasters. 1) Prevention requires proactive approaches where the damage from a possible disaster should be estimated. Specifically, we propose disaster-risk-aware provisioning, which minimizes loss to a network operator in case of a disaster. 2) Recovery methods should consider that, after the initial failure, more connections might be disconnected by correlated cascading failures. Thus, we investigate a reprovisioning scheme to recover disrupted connections. Numerical examples conducted for different disaster types (WMD attack, earthquake, and tornado) show that our schemes significantly reduce the risk and loss in case of a disaster. [ABSTRACT FROM PUBLISHER]

Future passive optical networks (PONs) are expected to support much larger capacity and much wider coverage. How to jointly address these two design requirements represents one of the most challenging aspects in today's research on PONs. So far, most research efforts have been devoted to devising new architectural or technological solutionsto support such stringent requirements. In particular, the technology to be used for transmission may have diverse multiplexing techniques, types of transceivers, modulation formats, and detection techniques. However, the question of which transmission technology is the most effective considering the trade-offs in terms of complexity, offered capacity, and reach is still open. In this paper, we aim at answering this question comparing the use of time division multiplexing (TDM), wavelength division multiplexing (WDM), and hybrid TDM/WDM techniques in PONs. To achieve this goal, we first categorize the main options for transmission technologies in PONs in three families: colored dense WDM (DWDM), tunable DWDM, and colorless DWDM. Then, we propose a new optimization scheme that selects the optimal transmission technology for different operational scenarios that are defined by varying the number of users, the distance to the users, and the traffic load. The choice of the passive optical components to be used at the remote node is also part of the optimization scheme given its significant impact on the choiceof the transmission technology. As a result, we report and discuss which transmission technologies are the most suitable under different operational scenarios. [ABSTRACT FROM PUBLISHER]

This study investigates the survivable traffic grooming problem for elastic optical networks with flexible spectrum grid employing new transmission technologies. In such networks, instead of following the traditional fixed ITU-T wavelength grid, optical transponders are capable of properly tuning their rates, and consequently their spectrum occupation, by introducing the fine-granular spectrum unit, called a frequency slot. The number of contiguous frequency slots allocated to an optical path (i.e., lightpath) is adjusted to the current network flow. In this study, we propose a novel shared protection specific to elastic networks, namely, elastic separate-protection-at-connection (ESPAC). It not only provides traditional backup sharing, but also offers a new opportunity of spectrum sharing enabled by the elasticity of the transponders: 1) if the working paths of two connections are link disjoint physically, and 2) if their backup paths traverse two lightpaths which are adjacent on a fiber link, then the two backup lightpaths can share spectrum. The new opportunity of spectrum sharing is realized by using First-Fit to assign working traffic and Last-Fit to assign backup traffic, and allowing spectrum overlap between adjacent backup wavelengths. The elasticity of the transponder enables the expansion and contraction of the lightpaths, thus when a single failure occurs in the network, lightpaths carrying backup flows can be tuned to appropriate rates in such a way that the overlap spectrum is used by only one of the adjacent lightpaths. The results show ESPAC is very spectrum efficient in elastic network setting. [ABSTRACT FROM PUBLISHER]

Novel distance-adaptive optical transmission technologies have been proposed to boost transceiver datarates and to enable more flexibility in the allocation of traffic flows. The application of this new class of transceivers is being widely investigated in core networks, while their suitability in the metro area is still an open issue. On one hand, the short metro distances enable the utilization of higher spectrally efficient modulation formats, on the other hand, the lower bitrate suggests to employ lower baud rate with respect to core networks. In this letter, we perform traffic grooming and spectrum assignment using transceivers with fixed baud rate of 28 and 14 GBd and distance-adaptive modulation formats in optical metro networks. Comparisons with the wavelength-division multiplexing systems running over a fixed grid show that 1) significant savings in terms of spectrum occupation can be achieved, and that 2) such savings can be effectively achieved also using lower baud rate transceivers (e.g., 14 GBd). [ABSTRACT FROM PUBLISHER]

Hybrid circuit/packet networks where circuit and packet networks coexist are becoming attractive to support future Internet applications. They support both packet/ IP services and circuit/wavelength services. Packet services include traditional data services such as VPN, VoIP, and email, while dynamic circuit services include end-to-end bandwidth-intensive applications such as terascale science experiments. In present hybrid networks, such as ESnet, the bandwidth boundary between the circuit and packet sections of the network is fixed. However, a flexible boundary between the circuit and packet sections will enable cost-efficient bandwidth management in the network. Our study investigates two methods to dynamically migrate capacity between the circuit and packet sections, called vertical stacking and horizontal partitioning, and serves as a tutorial. In vertical stacking, the backup capacity of wavelength circuits can be dynamically exchanged between packet and wavelength services while ensuring survivability. The backup capacity can be used to protect wavelength services in the event of a failure and route packet traffic otherwise. In horizontal partitioning, the excess capacity on links in the packet section can be loaned to circuit services. We have conducted experiments using a snapshot of real traffic on ESnet with horizontal partitioning. Control mechanisms for our approaches that can be operational in ESnet are presented. [ABSTRACT FROM PUBLISHER]

A service-level agreement (SLA) typically specifies, among other metrics, the availability a service provider (SP) promises to a customer. In an optical wavelength division multiplexing (WDM) network, connection-oriented provisioning is commonly based on whether the path's statistical availability complies with the SLA-requested availability. Because of the stochastic nature of network failures, the actually provisioned availability over a specific time period is subject to uncertainty, and hence the SLA is usually at risk. We consider this uncertainty and study provisioning to minimize SLA violations. We show that the SLA Violation Risk is affected by a number of factors (e.g., failure profiles, availability target, and penalty period), and hence cannot simply be characterized by statistical path availability. We formulate the problem of risk-aware provisioning in WDM mesh networks, where path selection is dictated by SLA Violation Risk. In particular, we focus on devising an efficient scheme capable of computing path(s) that are likely to successfully accommodate the SLA-requested availability. A novel technique is applied to convert links with heterogeneous failure profiles to reference links that capture the main risk features in a relative manner. Based on the “reference link” concept, our Risk-Aware Provisioning scheme uses only limited failure information. We also extend our Risk-Aware Provisioning to use shared-path protection (SPP) for connections with strict availability requirements. We evaluate the performance and demonstrate the effectiveness of our schemes in terms of SLA violation ratio compared to the generic availability-aware approaches. [ABSTRACT FROM PUBLISHER]

Since the Internet consumes a large (and increasing) amount of energy, “green” strategies are desirable to help service providers (SP) operate their networks and provision services more energy efficiently. We focus on green provisioning strategies for optical wavelength-division multiplexing networks. A number of approaches from component layer to network layer are discussed, which should help improve the energy efficiency of the networks. Then, we consider a typical optical backbone network architecture, and minimize the operational power for provisioning. Typically, operational power depends on strategy (e.g., optical bypass versus traffic grooming), operations (e.g., electronic domain versus optical domain), and route. We analyze the constituents of operational power in various scenarios, and discuss the opportunities for energy savings. We propose a novel auxiliary graph, which can capture the power consumption of each provisioning operation. Based on the auxiliary graph, we develop a power-aware provisioning scheme to minimize the total operational power. Performance evaluation shows that our scheme always needs the least operational power, with comparison to a direct-lightpath approach and a traffic-grooming approach. The result also suggests proportional power consumption by operations (network equipment) and end-node traffic grooming to fully exploit the power-saving potential of optical networks. [ABSTRACT FROM PUBLISHER]

Protection techniques for optical networks mainly rely on preallocated backup bandwidth, which may not be able to provide full protection guarantee when multiple failures occur in a network. To protect against multiple concurrent potential failures and to utilize the available resources more efficiently, strategies such as backup reprovisioning (BR) rearrange backups of protected connections after one failure occurs or, more generally, whenever the network state changes, e.g., when a new request arrives or terminates. Recently, new solutions for automatized management in optical networks promise to allow customers to specify on-demand the terms of the service level agreement (SLA) to be guaranteed by the service provider. In this paper, we study different backup reprovisioning techniques able to further reduce the capacity requirements exploiting the knowledge, among the other service level specifications (SLSs), of the connection holding time. [ABSTRACT FROM PUBLISHER]

The ONDM 2016 Special Issue is a collection of outstanding optical networking papers, chosen among the ONDM 2016 most highly ranked papers. The papers in this special issue cover a broad range of topics including dynamic elastic optical networks, network virtualization, next-generation optical access networks, spatial division multiplexing networking, and multi-layer design. [ABSTRACT FROM PUBLISHER]