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100 Gbit/s Ethernet is foreseen in metro and access by 2014, while 1 Tbit/s Ethernet is forecasted for trunk links before 1020. This paper reviews the advantages and constraints of the optical networking and discusses how they meet the 100 Gbit/s Ethernet needs.

Continuous-variable quantum key distribution (CV-QKD) could allow QKD and classical optical signals physically sharing the same optical fibers in existing networks. However, Raman scattering imposes a limit on the optical power, which in turn impacts the network capacity for classical traffic in presence of CV-QKD. Network-planning simulations indicate that maxing out the CV-QKD capacity in an optical link can adversely impact its classical capacity. Although preliminary, these results show that designing a mixed classical and CV-QKD network will require dedicated planning heuristics and tools that specifically seek a compromise between classical and CV-QKD traffics. [ABSTRACT FROM AUTHOR]

The advanced communication networks require heterogeneous emerging technologies to be combined while enabling various future applications. The integration of 5G wireless and optical technology is considered an unavoidable approach to reach this goal. Based on 5G mobile communications and densification of cells, the upcoming idea of smart city becomes feasible and put on a lot of attention from the research community due to its effect on everyday life's improvement and modernization. The concept of a smart city should support everything from electrical grids to traffic management and requires the transmission of a huge amount of data. Smart city planning with a reliable communication infrastructure that can provide stringent network requirements is unfeasible without the joint of optical and wireless technologies. This paper aims to provide an overview of recent developments of advanced optical networking to provide 5G transport networks and their applications in connecting a huge number of devices in future smart city infrastructures. The implementation of optical technologies in 5G core networking open numerous questions of how wireless and optical can coexist to provide sophisticated future applications, such as the smart city concept. Within this research, we will provide the answers to some of the key related questions. [ABSTRACT FROM AUTHOR]

The design of a novel 1 × M fold-back type wavelength selective switch (WSS), which has fewer waveguide crossings than a conventional integrated WSS, is reported. The WSS is composed of interleavers, 1 × M optical switches, and arrayed waveguide gratings (AWGs). Switches are combined with AWGs by fold-back waveguides, and each AWG works as both a demultiplexer and multiplexer thus avoiding center wavelength mismatch caused by fabrication errors. Waveguide crossings cause excess crosstalk and loss in lightwave circuits. By using a fold-back architecture the number of crossings can be reduced to less than half that of a conventional design. We discuss the operating principle, the design method, and the scalability of the fold-back type WSS. Furthermore, the switching operation of a 200-GHz spacing, 20-channel, 1 × 2 silicon WSS in a fold-back configuration on a 5 mm × 10 mm SOI chip is demonstrated. This has 15 waveguide crossings in a path, of which six are additional crossings with monitor waveguides. The average insertion loss and average extinction ratio are 29.6 dB and 10.9 dB, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a detailed examination of a novel data center network (DCN) that can satisfy the high capacity and low latency requirements of modern cloud computing applications. This reconfigurable architecture called AgileDCN uses fast-switching optical components with a centralized control function and workload scheduler. By providing a highly flexible optical network fabric between server racks, very high network efficiencies can be achieved even under imbalanced loading patterns. Our simulation results show that, at high (70%) loads, TCP flow completion times in the AgileDCN are significantly lower than in an equivalent electronic leaf-spine network. [ABSTRACT FROM AUTHOR]

Reliable networking is an important factor in Ethernet ring mesh networks (ERMs) with ITU-T G.8032 Ethernet ring protection recommendation or with the IEC 62439-3 high-availability seamless redundancy protocol. However, there are two major challenges for this purpose: (1) Hitherto, irregular topologies are used in ERMs that it causes difficulty in analyzing and improving reliability. (2) A topology is appropriate for practical implementation, if it is low cost, simple to implement, and simple to develop for large scale-systems (i.e. scalable). However, irregular topologies are extremely difficult to implement and develop. To deal with these challenges, this paper introduces two regular topologies called chordal ring and k-cube networks, for the first time in the area of ERMs. In addition, the proposed topologies are carefully analyzed in terms of reliability. These analyzes prove that the proposed regular topologies outperform existing irregular multiple-ring networks namely shared link, shared node, complex shared link, redundant link, and 3-connected network. [ABSTRACT FROM AUTHOR]

In current dynamic optical networks with cascaded filters and amplifiers, the optical signal-to-noise ratio (OSNR) can vary significantly from channel to channel. Under such uncertainty, OSNR prediction for unestab-lished channels becomes indispensable but remains a big challenge. For protective network planning purposes such as margin threshold setting or wavelength assignment, it is desirable to evaluate the worst OSNR performance of each network link. Such exploration will unavoidably employ active monitoring probes, which may cause interruptions to the network. An efficient active monitoring strategy that optimizes the choice of probes or monitoring trials is needed. We propose a "self-learning" monitoring strategy integrated at intermediate nodes. Our method can intelligently select the channel to be monitored in order to search for the target global maxima of OSNR degradation for a specific link. Our monitoring scheme detects intermediate node OSNR in the linear regime. It is shown that our method can predict the target OSNR value with only 0.5 dB error while reducing the required monitoring data by up to 91% compared to conventional methods. [ABSTRACT FROM AUTHOR]

The NEPHELE hybrid electro-optical datacenter network (DCN) architecture is proposed as a dynamic network solution to provide high capacity, scalability, and cost efficiency in comparison to the existing DCN infrastructures. The details of the NEPHELE DCN architecture and its various key parts are introduced, and the performance of its implementation is evaluated through an end-to-end NEPHELE demonstrator, which was built at the National Technical University of Athens. Several communication scenarios are demonstrated in real time, exploiting a scalable optical data-plane architecture with a software-defined network (SDN) control plane capable of slotted operation for dynamic allocation of network resources. Real-time end-to-end functionality and integration of various software and hardware components are verified in a six-host prototype datacenter cluster.

We investigate the capacity improvement achieved by bandwidth variable transceivers (BVT) in meshed optical networks with cascaded ROADM filtering at fixed channel spacing, and then propose an artificial neural network (ANN)-aided provisioning scheme to select optimal symbol rate and modulation format for the BVTs in this scenario. Compared with a fixed symbol rate transceiver with standard QAMs, it is shown by both experiments and simulations that BVTs can increase the average capacity by more than 17%. The ANN-aided BVT provisioning method uses parameters monitored from a coherent receiver and then employs a trained ANN to transform these parameters into the desired configuration. It is verified by simulation that the BVT with the proposed provisioning method can approach the upper limit of the system capacity obtained by brute-force search under various degrees of flexibilities. [ABSTRACT FROM AUTHOR]

This work presents and analyzes experimental-based subsystem models for Erbium doped fiber amplifiers (EDFAs) and wavelength selective switches (WSSs) under operation in a metropolitan optical network testbed. Firstly, the performance of the EDFAs and two gain control types are analyzed in a heterogeneous experimental setup with lightpaths modulated at 10G/100G/200G. Secondly, the WSS optical shape filter is experimentally characterized. Subsequently, simulation models are proposed accordingly to the experimental data obtained from the experimental setups. Results of output power and spectrum shape for both amplifiers under test showed good agreement between simulation and experiment. In addition, the optical signal-to-noise ratio (OSNR) for all channels was also analyzed and it was obtained error values bellow 1 dB, which are within an acceptable error margin. The developed sub-system models will provide greater flexibility to simulate different network scenarios and enable the development and validation of future optical network intelligence algorithms.

A digital signal process enabled dual-drive Mach–Zehnder modulator (DD-MZM)-based spectral converter is proposed and extensively investigated to realize dynamically reconfigurable and high transparent spectral conversion. As another important innovation point of the paper, to optimize the converter performance, the optimum operation conditions of the proposed converter are deduced, statistically simulated, and experimentally verified. The optimum conditions supported-converter performances are verified by detail numerical simulations and experiments in intensity-modulation and direct-detection-based network in terms of frequency detuning range-dependent conversion efficiency, strict operation transparency for user signal characteristics, impact of parasitic components on the conversion performance, as well as the converted component waveform are almost nondistortion. It is also found that the converter has the high robustness to the input signal power, optical signal-to-noise ratio variations, extinction ratio, and driving signal frequency. [ABSTRACT FROM AUTHOR]

Optical data center networks (DCNs) are becoming increasingly attractive due to their technological strengths compared with the traditional electrical networks. However, existing optical DCNs are either hard to scale, vulnerable to single point of failure, or provide limited network bisection bandwidth for many practical data center workloads. To this end, we present WaveCube, a scalable, fault-tolerant, high-performance optical DCN architecture. To scale, WaveCube removes MEMS,1 a potential bottleneck, from its design. WaveCube is fault-tolerant, since it does not have single point of failure and there are multiple node-disjoint parallel paths between any pair of top-of-rack switches. WaveCube delivers high performance by exploiting multi-pathing and dynamic link bandwidth along the path. For example, our evaluation results show that, in terms of network bisection bandwidth, WaveCube outperforms prior optical DCNs by up to 400% and is 70%–85% of the ideal non-blocking network (ı.e., theoretical upper bound) under both realistic and synthetic traffic patterns. WaveCube’s performance degrades gracefully under failures—it drops 20% even with 20% links cut. WaveCube also holds promise in practice—its wiring complexity is orders of magnitude lower than Fattree, BCube, and c-Through at scale, and its power consumption is 35% of them.1

Micro-Electro-Mechanical-System–one of the most popular optical circuit switches used as the main component by many recently-proposed optical DCNs [15], [18], [39].

Traffic in the Internet backbone is expected to grow above a few Tbit/s in 2020. To cope with this, operators are moving to IP/optical network architectures, where IP is the convergence layer for all services. On the other hand, the quality of service (QoS) requirements of future applications encompasses the individualization of services and the assurance of stricter quality parameters such as latency, jitter or capacity. In other words, future optical networks will not only transport more IP data, but they will also have to offer differentiated QoS requirements to services. Finally, some emerging applications, e.g., grid computing, need greater flexibility in the usage of network resources, which involves establishing and releasing connections as if they were virtualized resources controlled by other elements or layers. In this context, traffic-driven lightpath provisioning and service-plane approaches arise as very interesting candidate solutions to solve the main challenges described above. This work reviews the concepts of service-oriented and self-managed networks and relates them to propose an integrated approach to assure QoS by offering flow-aware networking in the sense that traffic demands will be anticipated in a suitable way, lightpaths will be established taking into account QoS information (i.e., impairments) and complex services will be decomposed into optical connections so that the above techniques can be employed to assure QoS for any service.

Future flexible transceivers will be able to adjust modulation format, number of subcarriers, symbol rate, and forward error correction (FEC) scheme, according to channel and network conditions. This paper uses a combination of theoretical derivations and experimental results to recommend the best set of parameters to satisfy a specific demand to be routed along the network. In particular, for a given required transparent reach and desired net bit rate, and assuming an FEC scheme with a constant gap to capacity, the paper provides a set of modulation format, number of subcarriers, symbol rate, and code rate, which requires minimum bandwidth, while offering a conveniently low bit error rate (in optical systems, typically 10−15). We observed that optimum operating points required FEC schemes with overheads ranging from almost 0 to 145%, which is an important guideline for future flexible optical communications systems. [ABSTRACT FROM PUBLISHER]

For transmission within optical mesh networks, different signal routes acquire different impairments and are received with different signal-to-noise ratios (SNRs). The SNR can be utilized through adaptive bit- and code-rate modulation, which leads to data rates that are not multiples of the preferred 100 GbE client rate. This paper considers the use of slower 25 GbE lanes both with inverse multiplexed 100 GbE client rates and with native 25 GbE client rates and compares network blocking performance. The use of inverse multiplexed 100 GbE client data on four 25 GbE lanes accesses the lion's share of stranded capacity within the network. [ABSTRACT FROM PUBLISHER]

This work presents and analyzes experimental-based subsystem models for Erbium doped fiber amplifiers (EDFAs) and wavelength selective switches (WSSs) under operation in a metropolitan optical network testbed. Firstly, the performance of the EDFAs and two gain control types are analyzed in a heterogeneous experimental setup with lightpaths modulated at 10G/100G/200G. Secondly, the WSS optical shape filter is experimentally characterized. Subsequently, simulation models are proposed accordingly to the experimental data obtained from the experimental setups. Results of output power and spectrum shape for both amplifiers under test showed good agreement between simulation and experiment. In addition, the optical signal-to-noise ratio (OSNR) for all channels was also analyzed and it was obtained error values bellow 1 dB, which are within an acceptable error margin. The developed sub-system models will provide greater flexibility to simulate different network scenarios and enable the development and validation of future optical network intelligence algorithms. [ABSTRACT FROM AUTHOR]

In this editorial, we first set the context for the subject matter of this special issue on passive optical network (PON) supported networking. This context includes a discussion of optical networking in all segments of a global communication network and the emphasis of the importance of PONs in the access network as well as their role supporting other communication network technologies. We follow this broader context with an introduction to the articles appearing in this special issue. Lastly, we conclude this editorial with a broad outlook to the future of PONs in communication networks. [ABSTRACT FROM AUTHOR]

We evaluate the impact of variable-code-rate transceivers on cost, capacity and survivability of wavelength-routed optical networks. The transmission rate and reach trade-off is quantified for two hypothetical coded modulation schemes (aggressive and conservative) in a wavelength routing network with 50-GHz-spaced channels. The aggressive scenario assumes the 64-QAM modulation format, a small gap to capacity, and a small excess bandwidth. The conservative scenario considers the 16-QAM modulation format, and a larger capacity gap and excess bandwidth. The performance of the conservative and aggressive technologies is evaluated in three representative networks. Transparent reaches are calculated by means of an existing analytical method which assumes the AWGN hypothesis for the nonlinear noise. It is shown that variable-code-rate transceivers enable the concept of soft protection, in which the protection lightpath operates at a data rate which is lower than the corresponding working lightpath, in a way to avoid regeneration. This is specially attractive in the transport of IP traffic, where capacity reduction (in average up to 25%) may be tolerable during a repair time. It is also shown that variable-code-rate transceivers have the potential to offer significant savings in terms of transceiver usage and wavelength occupation, when compared to current fixed-rate transceivers operating at 100, 200 or 400 Gb/s. Finally, practical variable-code-rate transceivers may achieve a discrete set of N code rates, yielding a quantized capacity-versus-reach curve. The system impact of N is evaluated for several network scenarios. [ABSTRACT FROM PUBLISHER]

We propose two policies to select the route for an adaptive-alternative routing algorithm for all-optical networks. We use the NrPSR to find the Nr routes with lower cost for a given source-destination pair according to a cost function expanded in a power series (PSR) in which the coefficients are determined by a Particle Swarm Optimizer (PSO). The selected route to attend to the call request can be chosen among the Nr found routes depending on the adopted policy. In the first proposal, named NrPSR(OSNRJE), we select the route that presents the lower OSNR that attends the Quality of Transmission requirements. In the second approach, named NrPSR(OSNRMAX), we select the route that presents the higher OSNR. In our simulations we considered some physical layer effects, such as: ASE noise generation, Optical Amplifier gain and ASE saturation and OXC crosstalk. We compared the performance of our proposed policies to others previous proposed policies for the NrPSR and other well known algorithms described in the literature. NrPSR(OSNRJE) outperformed all other routing algorithms. [ABSTRACT FROM AUTHOR]

Software-defined networking (SDN) enables programmable SDN control and management functions at a number of layers, allowing applications to control network resources or information across different technology domains, e.g., Ethernet, wireless, and optical. Current cloud-based services are pushing networks to new boundaries by deploying cutting edge optical technologies to provide scalable and flexible services. SDN combined with the latest optical transport technologies, such as elastic optical networks, enables network operators and cloud service providers to customize their infrastructure dynamically to user/application requirements and therefore minimize the extra capital and operational costs required for hosting new services. In this paper a unified control plane architecture based on OpenFlow for optical SDN tailored to cloud services is introduced. Requirements for its implementation are discussed considering emerging optical transport technologies. Implementations of the architecture are proposed and demonstrated across heterogeneous state-of-the-art optical, packet, and IT resource integrated cloud infrastructure. Finally, its performance is evaluated using cloud use cases and its results are discussed. [ABSTRACT FROM PUBLISHER]

The flexibility and elasticity of the spectrum is an important topic today. As the capacity of deployed fiber-optic systems is becoming scarce, it is vital to shift towards solutions ensuring higher spectral efficiency. Working in this direction, we report an extensive experimental study on adaptive allocation of superchannels in spectrum-flexible heterogeneous optical network. In total, three superchannels were transmitted. Two 5-subcarrier 14-GHz-spaced, 14 Gbaud, polarization-division-multiplexed (PDM) quadrature-phase-shift-keyed (QPSK) superchannels were separated by a spectral gap, the band of interest (BOI). The bandwidth of the BOI was varied. The BOI was subsequently filled with another superchannel, constituted by a different number of either 14 Gbaud PDM-QPSK or PDM-16-ary quadrature amplitude modulation (16-QAM) subcarriers. The optical signal-to-noise ratio (OSNR) for transmission of the subcarriers inserted into the BOI, depending on the modulation format, subcarrier count and spacing to the neighboring superchannels, was extracted through experimental implementation of different scenarios. The obtained values were interpolated to yield the required OSNR necessary to maintain a 1×10−3 bit error rate of the central BOI subcarrier. The results provide a rule of thumb that can be exploited in resource allocation mechanisms of future spectrum-flexible optical networks. [ABSTRACT FROM PUBLISHER]

Optical networks continue to play an essential role in scaling network capacity at a dramatically reduced unit bandwidth cost, and the next generation of technology will continue this trend. Automation of optical networks has reduced operations costs and enabled customer control of high-bandwidth services. We anticipate application-driven control of optical networks to appear in the near future. This paper looks to emerging technologies, both at the physical layer and network control layer, with a goal of assessing their impact on next-generation optical network architectures. We look forward to orders of magnitude improvement both to the capacity and complexity of intelligent optical networks. [ABSTRACT FROM PUBLISHER]

We generate a single-carrier 21.4-Gbaud polarization-division-multiplexed (PDM) 64-ary quadrature-amplitude-modulated (QAM) signal (256.8-Gb/s line rate) using a single in-phase/quadrature (I/Q) optical modulator driven by 8-level electrical waveforms from a novel high-power digital-to-analog converter (DAC). We measure a required optical signal-to-noise ratio of 29.5 dB (0.1-nm reference bandwidth; 10-3 bit-error rate), 4.6-dB off the theoretical limit. Using ultra-large-area fiber, we achieve 400-km single-channel transmission. The DAC was also used to obtain excellent results with quadrature-phase-shift-keyed and 16-QAM signals at 21.4 Gbaud. [ABSTRACT FROM PUBLISHER]

Advances in photonics, silicon electronics and digital signal processing (DSP) have converged to enable highly efficient transmission across fiber optic channels. Single wavelength data rates of 112 Gb/s are sought for wide deployment based on QPSK transmission, coherent detection, and digital demodulation. Here we examine continuous phase modulation (CPM) as a means to enhance performance and reach of coherent optical links. We quantify the robustness of the constant amplitude CPM format to spectral filtering and nonlinearities in comparison to QPSK. The challenges of generating and receiving the CPM waveform are considered and a novel CPM transmitter architecture is proposed. [ABSTRACT FROM PUBLISHER]

With increasing demands for dynamic high data-rate private line services from large customers, network carriers have begun to provide flexible on-demand connections to construct these customers' networks. Advances in optical devices have greatly improved the reconfigurability of the optical layer, which makes it possible to provide optical on-demand services at wavelength granularity (10 Gbps to 40 Gbps per channel). This new dynamic wavelength service model allows a customer owning or leasing a few terminal ports in the network to connect these ports on demand. [ABSTRACT FROM PUBLISHER]

We discuss the generation, wavelength-division-multiplexed (WDM) long-haul transmission, and coherent detection of 224-Gb/s polarization-division-multiplexed (PDM) 16-ary quadrature amplitude modulation (16-QAM) at a line rate of 28 Gbaud. We measure a required optical signal-to-noise ratio of 23.4 dB (0.1-nm reference bandwidth; 10^- 3 bit-error ratio), 3.4-dB off the theoretical limit. Using ultra-large-area fiber, we achieve 2000-km single-channel transmission. We also demonstrate 1200-km WDM transmission on a 50-GHz grid (4-b/s/Hz spectral efficiency), including three passes through a wavelength-selective switch. [ABSTRACT FROM PUBLISHER]

Abstract: In all-optical networks, signals are transmitted through optical physical layer with no regeneration. Therefore, noise accumulation along lightpath can severely impair optical signal-to-noise ratio. Impairment aware routing and wavelength assignment algorithms (IA-RWA) can take into account these effects, improving the network performance. In this paper we describe a fast and high performance adaptive weight function to be used as the metric for the routing algorithm in optical networks constrained by physical impairments. The input information for this function are link availability, route length and two adjustable parameters. These two parameters provide information about the network impairments. An offline simulation must be run to adjust them prior to the online network operation. The main advantage of this approach is the use of simple network parameters during the routing process instead of a complex optical noise based formulation, which renders it a better performance in terms of both, time to find a route and blocking probability. In our simulations we considered three physical layer effects: ASE noise generation, Optical Amplifier gain and ASE saturation and OXC crosstalk. We performed a performance comparison between this new metric and other metrics previously described in the literature. [Copyright &y& Elsevier]