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© 2016 Optical Society of America. In elastic optical networks, the success of providing high network capacity depends on the optical signal-to-noise ratio (OSNR) values of network lightpaths. As each lightpaths OSNR value defines the modulation format and capacity it can support, having high OSNRlightpaths is always beneficial. Hence, with a given set of modulation formats, service providers need to optimize their optical infrastructure, including in-line amplifiers and reconfigurable optical add-drop multiplexers (ROADMs), given the size and topology of their core networks. This also will have a direct impact on vendors who need strong insight into the requirements of service providers and their networks in terms of equipment and new technology. Therefore, in this paper a comprehensive model based on the local optimization which leads to a global network optimization (LOGON) strategy of the Gaussian noise (GN) model has been proposed, which helps in estimating the lightpath OSNR and clearly quantifies the noise contributions from in-line amplifiers and post-amplification at the ROADMs. The model introduces closed-form expressions to calculate nonlinear impairment (NLI) contributions for various span lengths while using either erbium-doped fiber amplifiers (EDFAs) or H-Raman amplifiers, which helps in optimizing the signal launch power to achieve maximum link OSNR. In addition to this, an offline strategy has been proposed that can help service providers to optimize their procurement of network equipment upfront and give insight into how much of the capacity bottleneck is alleviated in their networks if they do this. To demonstrate all of the above, the UK, Pan-European, and US Core networks have been considered, which illustrate differences in link lengths and reduced node density. It is seen that improving the OSNR conditions at the ROADM increases the network capacity when noise from in-line amplifiers is significantly reduced. Among the three networks, we found that the UK network responded the most to improved OSNR conditions at the ROADM nodes due to small link lengths and less line noise. Among the amplifiers, we found that improving ROADMs while having H-Raman in the links resulted in a maximum capacity increase. For the UK network at FG=12.5 GHz, the capacity increases by 6650 Gbps, while for the larger Pan-European and US networks, the capacity increase reduces to 4550 and 1600 Gbps due to increased link lengths and line noise. Further, following the offline strategy, we are able to accommodate 1737, 1481, and 615 100G demands using H-Raman for the UK, Pan-EU, and US networks at FG=12.5 GHz until 10%blocking is reached. Thereby, H-Raman provides 7.5%, 35.8%, and 94.9%extra capacity, respectively, for the UK, Pan-EU, and US. Finally, using H-Raman, all lightpaths in the UK network operate at PM-64QAM with maximum capacity at the end of the procedure.

Maximizing the delivered capacity of optical transponders by mining the SNR margin to a near-zero level is of critical importance for the economic viability of future optical networks. We examine this trend from the equipment design point of view and apply artificial intelligence to the problem of capacity maximization. The bottom-up approach is focused on providing the key metrics that are built on the fundamentals of network performance, whereas the top-down approach uses machine learning and policy-driven actions that have the promise to achieve an unprecedented level of control. These methods show promise in delivering a practical near-zero margin network deployment.

Centralized radio access network (C-RAN) has been considered as an architectural solution able to reduce capital and operational expenditure in dense 5G cellular networks while allowing better network performance. The C-RAN approach decouples baseband units from antenna sites and places them in selected locations, connected by the so-called fronthaul links. These links require expensive high-capacity connections, thus calling for cost-efficient deployment. This paper presents a hybrid fronthaul solution for C-RAN based on both optical fibers and free-space optics (FSO) to enhance fronthaul flexibility and minimize deployment costs. Two design strategies based on integer linear programming are proposed for both greenfield and brownfield deployments. The first strategy is referred to as joint planning (JP) and is based on the joint minimization of the number of deployed remote radio heads (RRHs) and the cost of the hybrid fiber/FSO fronthaul. The second strategy is based on two-step disjoint planning (DP) that first identifies a cost-optimal RRH placement and then finds the corresponding minimum cost deployment for the fronthaul links. Results obtained with JP and DP are compared in dense urban area scenarios (i.e., with characteristics similar to festivals or concerts), highlighting the advantage of the JP approach compared to DP, both in terms of costs and an enhanced flexibility during the network design process.

Fifth-generation (5G) systems will introduce several new requirements impacting the mobile transport network. Understanding the impact of 5G systems on trans­port networks, both wireless and fixed, is essential to the successful introduction of 5G. This paper provides an over­view of the ongoing work supporting the specification of open interfaces between the different 5G building blocks. It also presents several technologies that can facilitate ef­fective transport networks, describes the architectural challenges in designing flexible 5G transport networks, and provides dimensioning guidelines.

Quantum key distribution (QKD) has potential to provide long-term security for communications across the Internet. As security-hungry applications dramatically rise nowadays, a growing number of QKD networks are promising to be deployed in the immediate future. Nevertheless, a high-security-demand institution (e.g., a bank) needs to pay a high price to deploy its dedicated QKD network, while a cost-effective way of overcoming this challenge is to make multiple tenants share a QKD network. Each tenant represents a high-security-demand institution and can obtain secret keys on demand from the QKD network infrastructure for security purposes. Hence, how to achieve efficient and flexible multi-tenant provisioning over a QKD network becomes a crucial problem. This work introduces software defined networking (SDN) to address this problem. We experimentally demonstrate multi-tenant provisioning (including tenant establishment, adjustment, and deletion) over SDN-enabled metropolitan area QKD networks. A SDN-enabled metropolitan area QKD network architecture is introduced. We present a workflow, protocol extensions, and an on-demand secret-key resource allocation strategy for multi-tenant provisioning, which are all demonstrated by establishing an experimental testbed in the lab. Experimental results verify the effectiveness and flexibility of our SDN-based approaches for multi-tenant provisioning over metropolitan area QKD networks. Moreover, we conduct the simulation and discover the ways of improving the success probability of multi-tenant provisioning over metropolitan area QKD networks.

To accommodate the service paradigm shift driven by the now amazingly wide variety of services, telecom operators must overcome many challenges in redesigning their network infrastructure to attain system flexibility, scalability, and cost effectiveness. A key part of the solution is the recent advent of network virtualization based on commodity hardware. We propose a unique edge-server architecture that combines network virtualiza- tion with advanced digital signal processing (DSP) technology. Our architecture has the server's central processing unit running application layer functions and a generalpurpose accelerator running dissimilar physical layer functions, including advanced DSP. To elucidate the power budget capability of our coherent detection scheme, a hardware experiment demonstrates the optical power budget of 45.2 dB for quadrature phase-shift keying signals of 5 Gbit/s bit rate.

Next-generation edge nodes interfacing innovative IT clusters, 5G fronthaul, and internet of things (IoT) gateways to the optical metro/core network will require advanced and dynamic online quality of service (QoS) per-flow traffic treatment, assuring ultra-low latency requirements. However, current software-defined networking (SDN) implementations (e.g., OpenFlow) do not support forwarding procedures based on the network state, profile variations, and the history of flow statistics at the node level. Currently, such procedures require intervention by the SDN controller, leading to scalability issues and additional latency in data plane forwarding. Moreover, severe security challenges are expected to affect such nodes and threaten IT resources. Thus, increasing bandwidths will require direct deep packet inspection to avoid involvement of the SDN controller, as performed currently, or dedicated and costly security systems. This paper leverages on the potential of the programming protocol-independent packet processors (P4) open source language, recently introduced by the inventors of OpenFlow, to program the data plane structure and behavior of an SDN switch. P4 is able to instantiate custom pipelines and stateful objects, enabling complex workflows, user-defined protocols/headers, and finite state machines enforcement. Moreover, P4 allows portable implementations over different hardware targets, thus opening the way to open source fully programmable devices. Special effort is dedicated to motivate and apply P4 within a multilayer edge scenario, proposing the architecture and the applicability of an SDN P4-enabled packet-over-optical node. Moreover, three specific multilayer use cases covering dynamic traffic engineering (TE) (e.g., traffic offload and optical bypass) and cybersecurity (e.g., distributed denial of service port scan) are discussed and addressed through P4-based solutions. Experimental evaluations have been conducted over a multilayer SDN network exploiting reference P4 software switches (i.e., the behavioral model version 2, or BMV2) and field-programmable gate arrays (FPGAs) at 10 gigabit Ethernet optical interfaces. Extensive results report effective dynamic TE and cybersecurity mitigation enforcement at P4 switches without any controller intervention, showing excellent scalability performance and overall latencies practically in line with current commercial OpenFlow switches.

To quickly meet the diverse requirements imposed by emerging new services on optical access networks, we recently proposed the new concept of "flexible access system architecture" (FASA), which features the disaggregation of time-critical applications. This paper introduces our activities on FASA along with related technical trends. As our key ongoing challenge, the modularization of the dynamic bandwidth assignment function in a passive optical network is reviewed, and information on its use cases, approach, and sequences is given. Furthermore, a reference hardware implementation of FASA for mobile service is described.

Predeployment of regenerators in a selected subset of network nodes allows service providers to achieve rapid provisioning of traffic demands, high utilization, and reduced network operational costs, while still guaranteeing lightpath quality of transmission. Enabled by bandwidth-variable transceivers in flexible-grid optical networks, optical channel bandwidths are no longer fixed but constantly changing according to real-time communication requirements. Consequently, the data-rate-variable traffic together with other new network features introduced by flexible-grid networks will render the regenerator allocation very difficult due to the complicated network states. In this paper, we investigate how to allocate regenerators robustly in flexible-grid optical networks to combat physical-layer impairments when the data rates of traffic demands are random variables. The Gaussian noise model and a modified statistical network assessment process framework are used to characterize the probabilistic distributions of physical-layer impairments for each demand, based on which a heuristic algorithm is proposed to select a set of regenerator sites with minimum blocking probabilities. Our method achieves the same blocking probabilities with on average 10% less regenerator sites compared with the greedy constrained-routing regenerator allocation method, and obtains blocking probabilities two orders of magnitude lower than that of the routing and reach method with the same number of regenerator sites.

To cope with the energy inefficiency as well as the temporal uncertainty of real-world traffic in all-optical backbone networks, we explore the performance gains obtained from adaptively putting network elements into sleep mode, taking into account physical layer impairments (PLIs). Despite recent progress on link sleep mechanisms, the beneficial impacts of periodically activating and deactivating line amplifiers are seriously restricted by extra incurred operational expenditures due to accelerated aging of network equipment, which is a direct consequence of temperature fluctuations. In this paper, we revisit the problem of green PLI-constrained lightpath establishment, paying close attention to minimizing the number of on/off transitions. Toward this end, we formulate green lightpath establishment as a nonlinear multi-objective optimization problem, which addresses not only the energy efficiency, but also the grade of service and quality of service, using accurate models of a wide variety of linear/nonlinear PLIs. To tackle the developed problem under realistic scenarios, we propose the so-called green adaptive time-aware algorithm, which consists of lightpath establishment as well as wake-up/sleep procedures. The presented analysis followed by verifying simulations confirms that the proposed algorithm stands as a practical solution to the cost-efficient green impairment-constrained lightpath establishment problem under temporal uncertainly of incoming traffic.

Elastic optical networks (EONs) offer several optimization dimensions that can be harvested to increase network efficiency and survivability. More specifically, the adaptation of the modulation format to a more robust one can recover the quality of transmission (QoT) of a lightpath affected by a soft failure (i.e., a physical layer degradation resulting in QoT deterioration). In this scenario, increasing the robustness of a transmission may require a spectrum increase. Thus, the spectrum also might have to be reconfigured. In this paper, we propose spectrum sharing between lightpaths of classes requiring different rate guarantees. In the case of a soft failure, a high-priority, rate-guaranteed lightpath can expand its spectrum to recover its QoT at the expense of spectrum allocated to a lower-priority, guaranteed minimum rate lightpath. We propose an integer linear programming (ILP) routing and spectrum assignment (RSA) algorithm for the planning phase and an online RSA for the operation phase of the network that optimize spectrum sharing among lightpaths of different classes. Using these proposed techniques can effectively reduce the network costs to guarantee the rate of high-priority connections.

Breakthroughs in silicon photonics are changing the economics of network hardware and are enabling new directions in computer networking, compelling us to reexamine our previous assumptions regarding computer and network architectures. One such area that bears further study is the choice of network topology in a world where the distance between nodes is largely irrelevant, and where there is no inherent economic advantage to spatial locality. Network architects should be able to select topologies based on their merits and not merely from tradition. Combined with relaxed system-level packaging constraints, silicon photonics will likely lead to future datacenter architectures that look very different from today’s solutions. We present the design and implementation of Topanga, a packet switch optoASIC with the requisite technologies to free datacenter topologies from constraints induced by limited electrical reach. By means of our platform for integrating silicon photonics inside the package, Topanga provides optical I/O with lower energy per bit at lower cost per port than existing solutions.

We consider a unidirectional design approach to tackle the traffic asymmetry in an elastic optical network (EON). We decouple a bidirectional transponder into a pair of separate unidirectional transmitters and unidirectional receivers, and consider different multi-flow transmitters that use either an array of laser diodes or a broadband laser source with filters to generate multiple sub-carriers. To evaluate the benefit of this unidirectional design, we have considered the routing and spectrum allocation optimization problem for the EON. An integer linear programming model and an efficient heuristic algorithm based on spectrum window planes have been developed. Simulation results show that the proposed unidirectional design approach can significantly improve capacity utilization and minimize network cost compared to one based on bidirectional symmetric traffic flows. It is also efficient for network scenarios with spatial traffic asymmetry and where multi-period network planning is required.

This paper reports on the results of the design, fabrication, and experimental demonstration of a wavelength routing Thin-CLOS system based on arrayed waveguide grating routers (AWGRs) for intra-data-center applications. By using M2 W-port AWGRs, this architecture allows increasing by a factor of M the scalability provided by a wavelength router using a single W-port AWGR. The fabricated Thin-CLOS system has 64 ports and makes use of M2 = 4 AWGRs with W = 32 ports and 100 GHz channel spacing. The system fits in a 1U rack enclosure and consumes less than 10 W. We demonstrated error-free performance at 10 Gb∕s per wavelength with a power penalty of

We propose and demonstrate a four-port mode-selective optical router on a silicon-on-insulator platform. The passive routing property ensures that the router consumes no power to establish the optical links. For each port, input signals with different modes are selectively routed to the target ports through the pre-designed architecture. In general, the device intrinsically supports broadcasting of multiplexed signals from one port to the other three ports through mode division multiplexing. In some applications, the input signal from one port would only be sent to another port as in reconfigurable optical routers. The prototype is constructed by mode multiplexers/de-multiplexers and single-mode interconnect waveguides between them. The insertion losses for all optical links are lower than 8.0 dB, and the largest optical crosstalk values are lower than -18.7 dB and -22.0 dB for the broadcasting and port-to-port routing modes, respectively, at the wavelength range of 1525-1565 nm. In order to verify the routing functionality, a 40-Gbps bidirectional data transmission experiment is performed. The device offers a promising building block for passive routing by utilizing the dimension of the modes.

The nature of network services has drastically changed in recent years. New demands require new capabilities, forcing the infrastructure to dynamically adapt to new scenarios. Novel network paradigms, such as softwaredefined networking (SDN) and network functions virtualization, have appeared to provide flexibility for network management and services. The reliance on software and commoditized hardware of these new paradigms introduces new security threats and, consequently, one of the most desired capabilities is a strengthened security layer when connecting remote premises. On the other hand, traditional cryptographic protocols are based on computational complexity assumptions. They rely on certain mathematical problems (e.g., integer factorization, discrete logarithms, or elliptic curves) that cannot be efficiently solved using conventional computing. This general assumption is being revisited because of quantum computing. The creation of a quantum computer would put these protocols at risk and force a general overhaul of network security. Quantum key distribution (QKD) is a novel technique for providing synchronized sources of symmetric keys between two separated domains. Its security is based on the fundamental laws of quantum physics, which makes it impossible to copy the quantum states exchanged between both endpoints. Therefore, if implemented properly, QKD generates highly secure keys, immune to any algorithmic cryptanalysis. This work proposes a node design to provide QKD-enhanced security in end-to-end services and analyze the control plane requirements for service provisioning in transport networks. We define and demonstrate the necessary workflows and protocol extensions in different SDN scenarios, integrating the proposed solution into a virtual router providing QKD-enhanced IPsec sessions.

Network virtualization is a key technology for accommodating varying traffic demands on optical networks. Network operators construct a virtual network (VN) by slicing physical resources, and resolve traffic congestion by reconfiguring the VN in response to traffic changes. A typical approach is to configure an optimal VN using the traffic demand matrix. However, since it is difficult for this approach to reconfigure the VN following traffic changes, other methods must be explored. Previously we developed a method that observes only the service quality on the VN, i.e., link-level load information on the VN, and searches for a suitable VN by repeatedly making random changes to the current one. However, in practice this noise-induced method repeatedly reconfigures the VN, which leads to over-reconfiguration. In this paper, we propose a VN reconfiguration framework based on the Bayesian Attractor Model, which models the human behavior of making appropriate decisions by recognizing the surrounding situation. Our framework memorizes a set of VN candidates, each of which works well for a specific traffic situation, then retrieves a suitable VN candidate for the current traffic situation from this set. We use certain patterns of incoming and outgoing traffic at edge routers to characterize the traffic situation, as this information can be obtained more easily than the traffic demand matrix. By identifying the stored traffic situation that is closest to the current one and retrieving a suitable VN, our framework can reduce the over-reconfiguration. Evaluation of our method shows that it can identify the traffic situation by observing the amounts of incoming and outgoing traffic at edge routers; as a result it can decrease the number of VN reconfigurations needed to reach a VN suitable for the current traffic situation when compared to the noise-induced method.

Internet traffic is growing rapidly, driven by new applications such as the Internet of things (IoT). To overcome router scaling limitations, router bypass has been introduced. Traditional bypass is based on provisioning fixed-size bypass channels, which was shown to underutilize link capacity. In software defined networking (SDN), router bypass can be requested as a service by the application layer. This study explores the opportunity to bypass routers efficiently without the link underutilization of the traditional bypass.We combine SDN and dynamic layer provisioning to implement dynamic router bypassing and show how this leads to improved efficiency. A simulation built to compare the traditional bypass with the SDN-based bypass showed that SDN-based bypassing enhanced efficiency by 33%. When bypass traffic is increased, we show that the output capacity of a node increases up to 56%, limited by optical capacity rather than router capacity.

As optical networks become increasingly flexible and software driven, network operators need to reconsider their present mode of network planning and operation, which traditionally relies on long planning periods, performed independently for the IP edges (logical topology) and the optical transport layer (physical topology). Network planning assuming fully loaded end-of-life conditions fails to follow traffic evolution and results in capacity overprovisioning, underutilized equipment, and stranded investments. We argue that it would be beneficial to have shorter upgrade cycles and a multiperiod network planning approach that accounts jointly for the upgrade of the optical but also the IP edges of the network. We formulate the incremental multilayer planning problem of an IP over elastic optical network and propose an integer linear programming (ILP) algorithm to solve it. The ILP model leverages the reconfigurability of both network layers to delay equipment deployment and benefit from cost erosion. Our objective is, through repurposing of existing network resources, to deploy in a period the minimum additional network equipment (capital expenditures) to cope with traffic changes from the previous period but also to minimize changes in transitioning between the two periods (operational expenditures). The proposed planning approaches are validated through simulations based on realistic network scenarios, where we also study the effect of the upgrade period duration.

Network operators have deployed optical transmission systems in their production networks for several years. The transport technology for fiber-optic transmission systems in backbone networks has been a synchronous digital hierarchy. However, network operators started migrating such networks to deploy WDM systems to improve the utilization of the fibers. Network operators can migrate to 100 Gbps solutions that can cope with medium-term bandwidth needs. However, when evolving toward 400 Gbps or 1 Tbps, utilization of the optical spectrum is less efficient if the fixed-grid schemas are maintained. Elastic optical networks (EONs) are based on a flexible allocation of the spectrum and configurable transponders. There is an unprecedented flexibility at the optical layer, thanks to advances in the components to support EONs. To take advantage of such flexibility and unlock the potential of EONs, the control architecture plays a key role. This paper presents the architectural choices, including generalized multiprotocol label switching, path computation element, and software-defined networking using a transport application programming interface. Moreover, this paper presents how the open source Netphony suite enables the validation and testing of all previous control plane architectures for EONs.

In this paper, we discuss energy-efficiency improvements in core networks obtained as a result of work carried out by the GreenTouch consortium over a five-year period. A number of techniques that yield substantial energy savings in core networks were introduced, including (i) the use of improved network components with lower power consumption, (ii) putting idle components into sleep mode, (iii) optically bypassing intermediate routers, (iv) the use of mixed line rates, (v) placing resources for protection into a low power state when idle, (vi) optimization of the network physical topology, and (vii) the optimization of distributed clouds for content distribution and network equipment virtualization. These techniques are recommended as the main energy-efficiency improvement measures for 2020 core networks. A mixed integer linear programming optimization model combining all the aforementioned techniques was built to minimize energy consumption in the core network. We consider group 1 nations' traffic and place this traffic on a US continental network represented by the AT&T network topology. The projections of the 2020 equipment power consumption are based on two scenarios: a business as usual (BAU) scenario and a GreenTouch (GT) (i.e., BAU + GT) scenario. The results show that the 2020 BAU scenario improves the network energy efficiency by a factor of 4.23 x compared with the 2010 network as a result of the reduction in the network equipment power consumption. Considering the 2020 BAU + GT network, the network equipment improvements alone reduce network power by a factor of 20 x compared with the 2010 network. Including of all the BAU + GT energy-efficiency techniques yields a total energy efficiency improvement of 315×. We have also implemented an experimental demonstration that illustrates the feasibility of energy-efficient content distribution in IP/WDM networks.

As enterprises struggle to meet the demand for elastic cloud computing services in distributed data centers (DCs), a significant portion of the total expenditure is spent on the procurement and maintenance of server and network equipment. Network and server resource utilization efficiency is therefore crucial to minimize overall costs and increase return on investment. We present an adaptive and synergistic management of both network and IT resources with an autonomous control plane on a converged inter/ intra-DC network to address this issue. The control plane uses its awareness of both network and IT resource usage to provide dynamic resource allocations to meet quality of service guarantees, while also allowing for reduction in operational expenses by consolidating virtual machines to maintain high CPU usage on the active servers. We built a three-node inter-DC experimental testbed to demonstrate the feasibility of our concept and show that our algorithm successfully provisions both network resources and consolidates IT resources under various load conditions.

Due to the flexibility and adaptivity of elastic optical networks (EONs), IP-over-EON would be a promising infrastructure for next-generation backbone networks. As a backbone network usually carries massive traffic, one always needs to properly address its network survivability issue. The network survivability of an IP-over-EON can be affected not only by the fiber cuts in the EON layer but also by the router outages in the IP layer. In this work, we study how to realize the cross-layer orchestration to address IP router outages with cost-efficient multilayer restoration (MLR) in IP-over-EONs. Specifically, we consider the situation in which a single router outage happens in an IP-over-EON and propose MLR algorithms to minimize the additional operational expense (OPEX) due to MLR. We first design three MLR strategies to fully explore the flexibility and adaptivity of IP-over-EONs. Then, with the strategies, we formulate an integer linear programming (ILP) model to find the MLR scheme in which the additional OPEX due to incremental usages of sliceable bandwidth-variable transponders (SBV-Ts) and frequency slots (FSs) and lightpath reconfigurations is minimized. We also propose an auxiliary graph (AG) based heuristic algorithm to reduce the time complexity. The proposed algorithms are evaluated with extensive simulations, and the results indicate that, compared with an existing benchmark, they can effectively reduce the additional OPEX of MLR.

The data-center interconnection (DCI) market has been rising sharply for some time, leading to the development of networking solutions tailored specifically for it. On the side of the transport network, DCI devices are characterized by simple, footprint-efficient designs focused on scalability, but still leverage the benefits of flexible-rate transponders on the line-side, to extract the most from costly optical transport infrastructures. Accompanying this evolution arose the need for a technology that could provide a flexible client layer where aggregation was done outside the transport device, but flows could still be efficiently mapped to flexible-rate transponder modules. In this context, the appearance of Flex Ethernet (FlexE) is targeted at decoupling the rates of interfaces connecting routers to transport boxes, from the actual flows traversing them. Through the introduction of an additional mapping/de-mapping layer, the capacity of multiple Ethernet interfaces can be virtualized in a resource pool for different flows. This paper addresses the application of FlexE to dense wavelength division multiplexing (DWDM) transport scenarios. Specifically, it evaluates how agnostic to FlexE a transport box should be, considering the potential trade-off between its complexity and the ability to efficiently fill lightpaths. Through a network simulation handling the provisioning of Ethernet flows in a DCI scenario, we evaluate the various FlexE use cases envisioned for transport networks, and how they affect the efficiency of router port usage and transport box provisioning, as well as their effect on the capacity of the DWDM layer.

We have proposed a dynamically configurable and fast optical impairment model for the abstraction of the optical physical layer, enabling new capabilities such as indirect estimation of physical operating parameters in multivendor networks based on pre-FEC BER information and machine learning. BER is commonly reported by deployed coherent transponders; therefore, this scheme does not increase hardware cost. The estimated parameters can subsequently be used to predict optical signal quality at the receiver of not-already-established optical connections more accurately than possible based on the limited amount of information available at the time of offline system design. The higher accuracy and certainty reduce the required amount of required system margin that must be allocated to guarantee reliable optical connectivity. The remaining margin can then be applied toward increased transmission capacity, or a reduced number of regenerators in the network. We demonstrate the quality of transmission prediction experimentally in an optical mesh network with 0.6 dB Q-factor accuracy, and quantify the benefit in terms of network capacity gain in metro networks by impairment-aware network simulation.

Based on fundamental software-defined networking principles, disaggregated solutions have recently been proposed for optical transport networks. The first solution of such type takes the form of disaggregated line systems, which allow network operators to build networks using add/drop multiplexers from multiple vendors. In addition, these line systems allow any specification-compliant optical transponder to be freely connected, independent of their manufacturer. By removing the single-vendor dependency from line systems, traditional business models, based on vertically integrated solutions, are challenged and need to be rethought. Furthermore, competition between vendors is expected to increase, leading to higher innovation and differentiation. However, the development of interoperable line systems sharing a common set of specifications and capabilities may only be able to deliver suboptimal optical transmission performances when compared with proprietary solutions where line systems are fine-tuned. Hence, this paper evaluates the routing performance between disaggregated and proprietary optical line systems. Network simulations are carried out considering two different topologies with single- and multidomain proprietary deployments. The results obtained show that while proprietary line systems keep the capability of achieving the best optical performance, disaggregated solutions cannot be ignored since they have the potential to reduce the optical-electrical-optical interface count with respect to multivendor deployments while still guaranteeing minimal demand blocking.

Optical wavelength-routed networks enable parallel transmission of massive datasets on nonover-lapping wavelength channels. However, as the sizes of scientific workflows increase, the availability of multi-wavelength resources will fall short of supporting application needs. Rather, these resources must be allocated intelligently, efficiently, and flexibly to bear the burden of high-volume science. We propose lightpath-switching to support modification to the set of wavelength/route resources used to carry and transmit a lightpath signal intermittently throughout its lifetime. Lightpath-switching exposes the scheduler to flexible consumption of unused, fragmented resources during the request schedule but requires neither underlying network technology nor equipment enhancement. We explore the efficacy of lightpath-switching in terms of wavelength-switching, path-switching, and a combination of the two techniques. We prove these problems are NP-complete and develop optimization models and efficient heuristics to quantitatively and qualitatively evaluate the solution space against optimality benchmarks. Our evaluations consider cross-dimension resource consumption from the time, space, and spectrum domains, and our findings indicate great potential for increasing network-wide resource savings, particularly via wavelength-switching. Furthermore, evidence is presented to defend the claim that spectral flexibility has a greater impact on resource utilization efficiency than spatial flexibility.

Optical fiber is the required technology for radio access network (RAN) backhaul and fronthaul. We report on the evolution of RAN equipment, including the advent of virtualization and an investigation of the required architecture and optical access technologies.

Today's networks are quickly evolving toward more dynamic and flexible infrastructures and architectures. This software-based evolution has seen its peak with the development of the software-defined networking (SDN) and network functions virtualization (NFV) paradigms. These new concepts allow operators to automate the setup of services, thus reducing costs in deploying and operating the required infrastructure. On the other hand, these novel paradigms expose new vulnerabilities, as critical information travels through the infrastructure fromcentral offices, down to remote data centers and network devices. Quantum key distribution (QKD) is a state-of-the-art technology that can be seen as a source of symmetric keys in two separated domains. It is immune to any algorithmic cryptanalysis and is thus suitable for long-term security. This technology is based on the laws of physics, which forbids us from copying the quantum states exchanged between two endpoints from which a secret key can be extracted. Thus, even though it has some limitations, a correct implementation can deliver keys of the highest security. In this paper, we propose the integration of QKDsystems with well-known protocols and methodologies to secure the network’s control plane in an SDN and NFV environment. Furthermore, we experimentally demonstrate a workflow where QKD keys are used together with classically generated keys to encrypt communications between cloud and SDN platforms for setting up a service via secure shell, while showcasing the applicability to other cryptographic protocols.

The utilization of Ethernet in the cellular terrestrial cloud radio access network (C-RAN) fronthaul will potentially improve C-RAN reconfigurability and cost efficiency in terms of both capital and operational expenditures. Moreover, Common Public Radio Interface (CPRI) line bit rate dynamic reconfiguration may spare further capital expenditures by avoiding peak traffic capacity allocation. A possible solution for introducing Ethernet in the fronthaul is the encapsulation of CPRI in Ethernet. This solution is now part of the radio over Ethernet interface specified by the IEEE P1914 working group. However, it must be assured that fronthaul strict requirements on delay and jitter are still met. In this study, the combined impact of encapsulating CPRI in Ethernet and of the dynamic CPRI line bit rate reconfiguration on delay and jitter of the communication between radio equipment and a radio equipment controller is evaluated. The evaluation is both analytical and based on the presynthesis emulation of dynamic CPRI line bit rate reconfiguration. Both a size-based and a time-based encapsulation are considered. Results show that dynamic CPRI line bit rate reconfiguration can be achieved within about 1 ms. However, if a size-based encapsulation of CPRI in Ethernet is utilized, dynamic CPRI line bit rate reconfiguration might cause delay variations (i.e., jitter) up to few microseconds. Thus, to avoid jitter upon CPRI line bit rate reconfiguration, time-based encapsulation is preferable.

In this paper, a problem of rational splitter and OLT card installation in fiber-to-the-home (FTTH) networks is considered. We assume that the most tedious part of FTTH network deployment, i.e., trenching and cable installation, is completed, and the operator can start to connect customers to the network. The connecting process still requires expenditures for both passive (splitters) and active (ONUs, OLT cards) equipment. In this paper, we define the problem of rational splitter and OLT card deployment and present the multi-state optimization (MuSO) approach to handle it. MuSO minimizes the expected total cost of deployment using a stochastic model; thus, it optimizes under stochastic behavior. Finally, we compare MuSO to other rational methods, numerically validating its efficiency. We also investigate the impact of various factors—e.g., the take-up rates assumed when designing a network, delays in providing service to newly acquired customers, optimization time limits—on the final FTTH network deployment cost. The presented methodology not only can be used to minimize the deployment cost of FTTH networks, but also to assess the impact of uncertainty on network designs returned by automated methods.

The fifth generation of mobile networks (5G) is expected to introduce new services with strict end-to-end delay requirements. For this reason, service providers and network operators are increasingly relying on geographically distributed metro data centers (DCs) to bring services closer to end-users and reduce delivery time. The metro DCs frequently exchange data for different purposes, such as backup and load balancing. Some of these data transfers require guaranteed low delays. Meanwhile, efficient use of network resources is necessary to limit the cost of the network infrastructure. To address these issues, in this paper, we propose a converged intra- and inter-DC network architecture and a dynamic provisioning strategy that are able to (i) efficiently support different classes of service, (ii) offer fast data transfers among metro DCs, and (iii) enable efficient utilization of network resources. Simulation results show that the proposed network architecture and provisioning strategy achieve at least two times faster average data transfer between DCs and better network resource utilization compared with conventional solutions. We also present a prototype and an extensive set of experimental results, thus proving the implementation feasibility and effectiveness of the proposed approach.

Radio access network (RAN) cost savings are expected in future cloud RAN (C-RAN). In contrast to traditional distributed RAN architectures, in C-RAN, remote radio heads (RRHs) from different sites can share baseband processing resources from virtualized baseband unit pools placed in a few central locations (COs). Due to the stringent requirements of the several interfaces needed in C-RAN, optical networks have been proposed to support C-RAN. One of the key elements that needs to be considered are optical transponders. Specifically, sliceable bandwidth-variable transponders (SBVTs) have recently shown many advantages for core optical transport networks. In this paper, we study the connectivity requirements of C-RAN applications and conclude that dynamicity, fine granularity, and elasticity are needed. However, there is no SBVT implementation that supports those requirements, and thus, we propose and assess an SBVT architecture based on dynamic optical arbitrary generation/measurement. We consider different long-term evolution-advanced configurations and study the impact of the centralization level in terms of the capital expense and operating expense. An optimization problem is modeled to decide which COs should be equipped and which equipment, including transponders, needs to be installed. The results show noticeable cost savings from installing the proposed SBVTs compared to installing fixed transponders. Finally, compared to the maximum centralization level, remarkable cost savings are shown when a lower level of centralization is considered.

In this paper, we apply the concept of a software-defined data plane to defining new services for mobile virtual network operators (MVNOs) to empower them with the capability of tailoring fine-grained subscription plans that can meet users' demands. For this purpose, we have recently proposed the concept of application-and/ or device-specific slicing that classifies application-and/or device-specific traffic into slices and introduced various applications of our proposed system [Optical Fiber Communication Conf. (OFC), 2016, paper Th3I.4]. This paper reports the prototype implementation of the proposal into a real MVNO connecting customized smartphones so we can identify applications/devices from the given traffic with 100% accuracy. We first characterize the traffic patterns of popular applications to build a detailed understanding of how network resources are utilized for real users and applications and what their demands on different network resources are. Then, we classify traffic according to the devices and find that the flow characteristics of LTE RAN slices are very similar to those of 3G. We discover that most of the bandwidth is consumed by those flows with the duration of several hundreds of seconds, and the flow size is larger than 5 Mbytes in both LTE and 3G MVNO networks.

The growing energy footprint of communication networks has raised concern about the sustainability of future network development. The GreenTouch consortium was founded to help counter this trend by developing and integrating green network technologies from the access to the core. In order to evaluate these technologies, an end-to-end network power model was developed in the form of the Green Meter, a tool to assess the overall impact and overall energy efficiency benefits of an entire portfolio of solutions. In this paper, we describe the methodology of the Green Meter for the residential fixed access portion, which was extended to include metro aggregation. A baseline architecture for optical access and metro aggregation networks is defined, and is adapted to other scenarios integrating future technologies. The performance is evaluated each time through a mathematical model that captures the energy savings at the component level and has the ability to compute the overall system-level energy savings. We show that energy efficiency can be improved 29-fold over a decade (2010–2020) with businessas- usual trends, and with the added effort of introducing GreenTouch solutions, this could be further improved to achieve a 257-fold increase in energy efficiency. The results confirm that an emphasis on green network design can indeed have a huge impact on reducing the energy consumption of an optical access infrastructure.

We propose a network architecture consisting of long-reach passive optical network-based access and a transparent optical core network. The end users are connected to the remote node or the local exchange (LE) through an optical distribution network, and the remote node is connected by disjoint feeder fiber links to central offices located in two distinct metro/core (MC) nodes. This method of connecting a single remote node to two geographically separate MC nodes for dedicated protection in case of feeder fiber failure is referred to as dual homing. In this work, we explore the benefits of dual homing in the access in simultaneously providing better resilience and load balancing in the core network considering connections between LEs. While looking into the benefits of dual homing in terms of network resiliency, we also explore whether the path redundancies added by dual homing play a role in providing efficient distribution of load across the core network and thereby reduce the cost of provisioning capacity in terms of number of lightpaths, transponders, etc. Dual homing at both the source and destination LEs offers more options for paths between LEs through the core network. Our results show that dual-homed access proves to be advantageous over single-homed access in terms of enhancing both core network resiliency and facilitating better load balancing.

We review margins used in optical networks and review a formerly proposed margin taxonomy. For each category of margins, we review techniques that the network designer can use in order to increase the capacity of optical networks, extend their life, and decrease deployment cost (CAPEX) or total cost of ownership over their life duration. Green field (new network deployments) and brown field techniques (used after initial network deployment) are discussed. The technology needed to leverage the margins and achieve the aforementioned gains are also reviewed, along with the associated challenges.

This paper describes the experience of designing, implementing, and evaluating a carrier-grade transport network with stateful path computation element (PCE) extensions. The key concept is to develop an implementation framework for future extensions of the stateful PCE architecture to support carrier-grade transport services. The proposed framework combines a centralized provisioning controller and distributed management entities to meet the requirements both of network operators and carrier-grade transport services. To validate the feasibility of the framework, two testbeds, an emulation testbed and an integration testbed, are implemented and evaluated via functional, operational, and interoperable testing by exploiting a combinatorial testing approach. The evaluation results indicate that this combinatorial testing reduces the significant risks of protocol defects, accelerates the development cycle, improves protocol quality, and ensures interoperability in a structured and integrated manner. The evaluations of these two testbeds complement each other to build an evolving architecture. This paper describes specific lessons for a control plane developer working with a design, testbed implementation, and evaluation architecture.

Given the limited number of resources (i.e., frequency slots and transponders at optical switches) in elastic optical networks, one approach to accommodating traffic demand is for the network operator to offer a certain number of leased lightpaths in response to requests from service providers, while configuring a virtual network (VN) that accommodates the traffic demands of other consumers. It is essential to reconfigure the VN according to changes in traffic while setting aside resources for leased lightpaths and accommodating increased traffic demand on the VN. Our research group has proposed a VN reconfiguration method for traditional wavelength division multiplexing networks based on attractor selection, which is a model of the behavior by which living organisms adapt to unknown changes in their surrounding environment. However, simply adopting this method cannot make the best use of elastic optical networks since it assigns all wavelengths to accommodate the current traffic demand, which leads to a lack of resources for accommodating the future traffic demand. In this paper, we therefore propose a method for reconfiguring a VN over an elastic optical network. To set aside resources for future traffic demands, we newly define the potential bandwidth as a metric that reflects the bandwidth that can be additionally offered. Our method reconfigures a VN based on attractor selection using information about the service quality on the VN and the potential bandwidth, and it also adjusts the bandwidths of all the lightpaths that form the VN. The evaluation results show that our method can reconfigure a VN so the service quality on the VN is improved while keeping some resources unused.

To keep pace with the tremendous bandwidth growth in cloud networking, web-scale providers, such as Microsoft, have been quick to adopt elastic features of modern optical networks. In particular, colorless flexible-grid reconfigurable optical add-drop multiplexers, bandwidth-variable transceivers, and the ability to choose a variety of optical source types are integral for cloud network operators to improve network efficiency while supporting a variety of service types. We take an in-depth look at Microsoft's deployed network infrastructure and discuss the impact of elasticity on network capacity and flexibility. As a proof-of-concept, a new elastic open line system (OLS), in which the line system components and the signal sources are disaggregated, was assembled in a laboratory environment, and 4000 km of propagation over primarily nonzero dispersion-shifted fiber using multiple source types is demonstrated. Finally, the long-term goal of unifying the control plane of the OLS, DWDM signal sources, routers, and Ethernet switches under a single software-defined network controller is briefly addressed.

There is no denying the tremendous success of current optical network technologies. However, the existing optical network infrastructures are unable to support independent evolution and innovation of physical, transport, and network layer functionalities, protocols, and services. Nor can they support the increasing bandwidth demands of evolving applications and their heterogeneous resource usage and QoS requirements. This paper addresses this problem by proposing a completely softwareized optical network infrastructure and the key technology enablers, including an open and programmable optical white box, optical transport and switching technology abstractions, and a compute-aware optical network virtualization mechanism. The technology enablers are evaluated by experimental demonstration and simulation.

I present an analytical expression for the relation of the packet loss rate (PLR) with respect to the channel optical signal-to-noise ratio measured nonintrusively in an all-optical, wavelength-routed network. This closed-form expression is aimed for rapid, nonintrusive fault detection of lambda services. This relation will help achieve reliable all-optical networks with no extra optoelectrical cost due to monitoring, and yet have digital parameters such as the PLR in the service level agreements. Analytical results considering performance thresholds for triple-play services, gigabit Ethernet framing, and forward error correction are discussed. (C) 2008 Optical Society of America.

Data center interconnect with elastic optical network is a promising scenario to meet the high burstiness and high-bandwidth requirements of data center services. In our previous work, we implemented multi-stratum resilience between IP and elastic optical networks that allows to accommodate data center services. In view of this, this study extends to consider the resource integration by breaking the limit of network device, which can enhance the resource utilization. We propose a novel multi-stratum resources integration (MSRI) architecture based on network function virtualization in software defined elastic data center optical interconnect. A resource integrated mapping (RIM) scheme for MSRI is introduced in the proposed architecture. The MSRI can accommodate the data center services with resources integration when the single function or resource is relatively scarce to provision the services, and enhance globally integrated optimization of optical network and application resources. The overall feasibility and efficiency of the proposed architecture are experimentally verified on the control plane of OpenFlow-based enhanced software defined networking (eSDN) testbed. The performance of RIM scheme under heavy traffic load scenario is also quantitatively evaluated based on MSRI architecture in terms of path blocking probability, provisioning latency and resource utilization, compared with other provisioning schemes.

In this paper, we study the service provisioning schemes for dynamic advance reservation (AR) multicast requests in elastic optical networks (EONs). We first propose several algorithms that can handle the service scheduling and routing and spectrum assignment (RSA) of AR multicast requests jointly, including an integrated two-dimensional fragmentation-aware RSA (2D-FMA) that can alleviate the 2D fragmentation caused by light-tree provisioning. Then, we leverage the idea of software-defined EONs (SD-EONs) that utilizes OpenFlow (OF) in the control plane to demonstrate and evaluate the proposed algorithms. Specifically, we build an SD-EON control plane testbed, implement the algorithms in it, and perform control plane experiments on dynamic AR multicast provisioning. The results indicate that 2D-FMA achieves the best blocking performance and provides the shortest average setup delay.

The elastic lambda aggregation network (EλAN) has been presented as an access/aggregation integrated network that can accommodate multiple network services. In the EλAN, optical line terminals (OLTs) become programmable and configure logical OLTs (L-OLTs) to support network services that have different protocols and quality of service requirements. To achieve the flexible utilization of network resources and improve energy efficiency, L-OLTs are migrated between programmable OLTs like virtual machines. In this paper, an integer linear programming (ILP) model of the L-OLT placement optimization problem with optical distribution network constraints is presented. Based on this ILP model, the communication suspension time that occurs with L-OLT migration is investigated. We discuss the modification of the L-OLT migration sequence to reduce the communication suspension time. The impact of the modification on the energy saving effect of L-OLT placement optimization is evaluated in this paper.

One approach to accommodating IP traffic on a wavelength-routed network is to construct a virtual network topology (VNT) and reconfigure the VNT according to traffic changes. Our research group has proposed a VNT control method based on attractor selection, which is a model of the behavior by which living organisms adapt to unknown changes in their surrounding environment. Guided by attractors, the VNT control method searches for a solution: a VNT that can accommodate the IP traffic. Attractors are a subset of the equilibrium points in the solution space and correspond to VNT candidates. It is crucial to design the attractors properly, since they define the attractive states in the VNT control. If the VNT candidates are not designed properly, it takes a long time for the method to find a solution. This paper therefore proposes a method for designing VNT candidates. Our basic approach is to prepare VNT candidates in which the bottleneck links (lightpaths) are different from each other. However, our exhaustive algorithm based on this approach has the problem of requiring large amounts of computational time for large-scale networks. We therefore propose a method that hierarchically contracts a network topology to enable application of our algorithm to large-scale networks. Evaluation results show that the VNT control method using attractors obtained by our method achieves shorter convergence times.

Growing energy demands in the information and communication technology (ICT) sector have been recognized as a major challenge worldwide. Researchers have been actively working to address this challenge, and the major focus centers around improving the energy efficiency of access networks, which are known for consuming about three-quarters of the total network power. Among various access networks, the hybrid wireless — optical broadband access network (WOBAN), which combines a passive optical network (PON) with broadband wireless technology, is highly regarded for its enormous capacity, cost efficiency, and ease of deployment. To develop a green WOBAN, it is important to focus on reducing its power consumption, and in this work, we present an efficient resource management technique for WOBAN that reduces the power consumption of the optical line terminal (OLT) and optical network unit (ONU) by introducing sleep modes for the OLT and ONU, based on the service class and traffic load. Moreover, it considers the quality-of-service requirement of each service class. Simulation results confirm that our proposed solution can save a significant amount of power in the WOBAN network without sacrificing the quality of service of end applications.

With the rapid growth of traffic volume in telecom networks, a larger amount of network equipment with higher capacity and enhanced processing speed is required to accommodate the traffic. Therefore, expenditure due to cost and energy consumption (EC) of network equipment is also increasing. In existing research toward improving efficiency in spending, during the greenfield network design phase (i.e., the network planning phase or the phase wherein capacity is provisioned for a new network), either cost efficiency or EC efficiency is considered. However, the most cost-efficient network may not always be the most energy- efficient. Thus, during the network planning phase, the cost andECof network equipment should be considered together for cost- and energy-optimized realization of the network. In this study, an IP-over-WDM(IPoWDM) network design is explored to reduce the combined expenditure (due to cost and EC of network equipment) for setting up and operating the network over a given time period (referred to as the planning period). In this regard, we propose mixed integer linear programming-based optimization models and auxiliary matrix-based cost- and energy-efficient network design (AM-CEND) heuristic to minimize the overall expenditure. In the proposed schemes, network equipment is provisioned judiciously such that the overall expenditure is minimized. In this regard, we use a practical network setting, where all network equipment is considered to be bidirectional, and WDM equipment is considered with finite maximum transparent reach limits. It may be observed that a network designed using AM-CENDheuristic offers significant savings in the overall expenditure as illustrated by our exhaustive simulation study conducted for the example network scenario.

We present an analytical model to estimate the expected minimum numbers of network elements required to support traffic demands in a multilayer service transport network for the case where grooming of demands into channels is permitted at all nodes. This new scalable formulation expands upon earlier models and makes use of global expectation values, the concept of maximum entropy, analytical and semi-empirical models of the mean number of hops, and statistical considerations to estimate the resource requirements as a function of the total traffic, number of nodes, grooming objectives, and constraints of interest. We find that the solution provided by a routing and grooming algorithm can be described by three key variables when the cost metric is the number of transponders. Two of these variables characterize the virtual topology of the routes over which the traffic is transported, and the third characterizes the efficacy of grooming the traffic into channels over the routes. Two minor variables capture the details of the number of routes and channels of the solution when the amount of traffic and number of nodes are small. The model is applied to analyze the dimensioning of optical ring and mesh networks transporting quasi-static, uniform, and random traffic with electronic grooming and optical bypass. The analytical results are compared to special cases considered by earlier analytical models and used to understand a broad range of results obtained by numerical optimization for several routing and grooming algorithms.

In response to the need for higher-speed and affordable-cost datacenter interconnection networks, hybrid optical/electrical architectures have been proposed. Even still, a number of implementation issues remain open and little is known about the performance of real applications over such networks. To fill this gap, we present a hybrid network architecture, called HydRA, comprising commodity off-the-shelf equipment, calculate its total price using current list prices, and show its price competitiveness against fat-tree alternatives. We also report on a prototype implementation of our HydRA network that uses Ethernet switches and a custom-built software controller. We show that our HydRA network prototype manages to accelerate the execution of real parallel workloads, when compared to equal-cost electronic-only fat-tree networks.