Annalisa Morea

Datarate Adaptation for Night-Time Energy Savings in Core Networks

We examine how datarate-adaptive transceivers can be used to follow the pronounced variations in requested bandwidth in core networks and therefore allow significant energy savings compared to static networks configured to support the peak traffic all the times. We investigate two schemes for datarate adaptation in optical transceivers: modulation-format adaptation and symbol-rate adaptation, and show how they yield comparable energy savings but through very different mechanisms. We quantify these energy savings with respect to static networks for the case of a European backbone network and find potential for up to 30% of savings when the two schemes are combined.

Impact of Inter-Channel Nonlinearities on the Planning of 25–100 Gb/s Elastic Optical Networks

In this paper, we examine how typical transmission systems can be made tunable in datarate, up to 100 Gb/s, through modulation-format versatility. We investigate through extensive numerical simulations the available reach versus datarate, taking in particular into account the nonlinear interaction between channels in this mixed-format context. We show how these versatile transmission systems can be used to design a so-called elastic optical network in which the datarate of a wavelength is adapted to both the traffic that needs to be transported and the amount of physical impairments that need to be overcome. We examine the benefits of such elastic optical networks in the case of a European backbone network, showing that elastic architectures outperform fixed-rate networks by up to 21% in terms of required number of opto-electronic interfaces.

Advantages of elasticity versus fixed data-rate schemes for restorable optical networks

We investigate link restoration in optical networks carrying multiple data-rates. We compare rate-tunable opto-electronic interfaces (elastic) versus rate-specific (fixed) technologies and show the reconfiguration ability of elastic interfaces strongly reduces the required spare resources.

Elastic optical networks: The global evolution to software configurable optical networks

Worldwide operator deployment of high-speed 100G coherent optical networks is currently underway. To ensure a competitive solution offering significant performance improvements to cope with the ever-increasing traffic demand, a novel network concept has been proposed for improved resource utilization based on “elasticity”; specifically, the ability to make a number of previously fixed transmission parameters tunable, for example optical data rate or channel spacing. The benefits are numerous, including increased network capacity, lower cost per bit, and improved energy efficiency and scalability. In this paper, we review the work carried out within the Cooperation for a Sustained European Leadership in Telecommunications (CELTIC) Elastic-Optical NETwork (EO-Net) project towards advancing the state of software-configurable optical networking. We identify the key building blocks for enabling elastic optical networks to provide desired performance improvements over static optical networks. We examine the design of elastic transponders capable of data rate adaptation, interfaces between client packet devices and transponders supporting flexible traffic aggregation, and associated algorithms for traffic grooming and routing. We also perform network cost/energy analyses. Finally, we review the experimental demonstration of such elastic functionalities.

Impact of transparent network constraints on capacity gain of elastic channel spacing

We compare fixed-grid network architectures with variable-spacing OFDM based solutions. We show that capacity gains can reach up to 50% but are strongly affected by physical and topological constraints of transparent networks and traffic statistics.

On the complexity of routing and spectrum assignment in flexible-grid ring networks [Invited]

The adoption of a flexible grid will benefit the network design and control plane of future optical networks by providing increased adaptability of spectral resources to heterogeneous network conditions. Unfortunately, this flexibility is gained at the cost of significant additional complexity in the network design and control. In this paper, we consider the optimization of routing and spectrum allocation in flexi-grid ring networks and explore the trade-off between network cost (in terms of spectrum and transponder utilization) and problem complexity (in terms of the number of variables/constraints and computational time). Such trade-offs are investigated under multiple assumptions in terms of traffic grooming, regeneration, and modulation/baud rate assignment capabilities and contrasted with the case of fixed grid.We show how in the presence of traffic grooming the additional complexity due to the flexible grid has a minor impact on problem complexity. Similarly, in all the considered scenarios, regeneration and modulation/baud rate assignment do not relevantly impact on problem complexity. We also consider two possible alternative integer linear programming (ILP) models: the slicebased and channel-based approaches. The former handles each slice individually, whereas the latter uses precomputed subsets of contiguous slices of different bandwidths. Both models are solved under several different network settings. Complexity comparison of the ILP models shows that the slice-based approach provides better performance than the channel-based approach and that the performance gap between the two models increases with the introduction of additional flexibility and dimensions.

The relevant impact of the physical parameters uncertainties when dimensioning an optical core transparent network

We illustrate the importance to consider physical uncertainties in the quality of transmission estimators used for impairment constrained based routing. Power uncertainties of 1 dB yield 80% of further regenerators.

Interest of an adaptive margin for the Quality of Transmission estimation for lightpath establishment

We justify a lightpath characteristic dependent margin when estimating the quality of transmission for the establishment of a connection by showing the resulting better prediction accuracy and eventually the reduction of the required transmission resources.

Throughput comparison between 50-GHz and 37.5-GHz grid transparent networks [Invited]

With the introduction of Nyquist pulse shaping, it is possible to transmit a channel in a spectral window close to its baud rate. To increase the overall network spectral efficiency, the most promising solution seems to be the reduction of the channel spacing. Standardization bodies have proposed a flexible grid with 12.5 GHz of granularity. Hence, 100-Gb/s signals can be transported in a 37.5-GHz grid network. While a 37.5-GHz channel spacing brings an ideal extra-throughput of 33% compared to a 50-GHz spacing, this value ignores filtering-induced impairments occurring when a narrower channel spacing is adopted. In this paper, we numerically investigate the filtering penalty stemming from optical filters and its implications on the extra-throughput provided by 37.5- versus 50-GHz grid wavelength division multiplexing (WDM) networks for two different networks with two different traffic distributions. We show fully transparent network scenarios where the ideal 33% extra-throughput of 37.5-GHz channel spacing is drastically reduced or even vanishes because of filtering penalties.

Power consumption reduction through elastic data rate adaptation in survivable multi-layer optical networks

Network survivability requires the provisioning of backup resources in order to protect active traffic against any failure scenario. Backup resources, however, can remain unused most of the time while the network is not in failure condition, inducing high power consumption wastage, if fully powered on. In this paper, we highlight the power consumption wastage of the additional resources for survivability in IP/multi-protocol label switching (MPLS) over dense wavelength division multiplexing multi-layer optical networks. We assume MPLS protection switching as the failure recovery mechanism in the network, a solution interesting for current network operators to ensure fast recovery as well as fine-grained recovery treatment per label switched path. Next, we quantitatively show how elastic optical technologies can effectively reduce such a power consumption by dynamically adjusting the data rate of the transponders to the carried amount of traffic.