Giuseppe Rizzelli

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.

Scalability analysis of WSS-based ROADMs

Reconfigurable Optical Add/Drop Multiplexers (ROADMs) are becoming the industry standard for optical transparent switching in long-haul networks. ROADMs introduce new flexibility features towards full dynamic networks. In this paper, we investigate the scalability limits of the ROADM. We introduce a method to compute the number of ROADM internal subsystems (namely the wavelength selective switches) for a given traffic request. We evaluate the working and the blocking states of the ROADM with relation to its features of colorless, directionless and contentionless. We propose a method to compute the node requirements for a given set of network parameters.

On the energy consumption of IP-over-WDM architectures

Todays “green thrust” has been completely steering the evolution of our society. Therefore, since enhancements on telecommunication networks are expected to cope with the growth of traffic demand, energy consumption is becoming a crucial design metric. In this paper we focus on IP over Wavelength Division Multiplexing (IPoWDM) optical network architectures, where optical circuits (or lightpaths) interconnect IP routers. Various implementations of IPoWDM networks are possible, e.g., transparent, translucent or opaque each accounting different routing and switching constraints, in order to evolve from the classic IPoWDM approach, where only signal transmission is performed optically. Although it is a common belief that “more optical” architectures can generally guarantee a much lower total power consumption, we show that identifying the most energy-efficient IPoWDM architecture is not a trivial task. In fact we demonstrate that the most energy-efficient architecture depends on some network parameters such as number of nodes, link length and average distance between nodes. This work provide an analytical framework by which we draw guidelines to (a) assess under which conditions optical switching actually becomes more desirable than electronic switching and (b) evaluate which architecture, among those employing optical switching, is more energy-efficient under different parameter settings.

On the energy and cost trade-off of different energy-aware network design strategies

We compare different energy-aware network design strategies that adapt network resources utilization to traffic variations. We show how to achieve, without extra devices, up to 26% energy savings with respect to a 100Gb/s static network.

Impairment-aware design of translucent DWDM networks based on the k-path connectivity graph

In this paper we propose a design procedure based on comprehensive integer linear programing (ILP) for translucent optical transport networks (OTNs), exploiting an extended version of the so-called “connectivity graph.” For the first time to the best of our knowledge, we propose a mathematical approach that covers the manifold challenges of a realistic optical layer OTN design, jointly solving the regenerator placement problem (RPP) and the routing, fiber and wavelength assignment with regenerator problem (RFWA-RP). As a first contribution, we extend the concept of the connectivity graph to a k-path (k-p) connectivity graph. Second, the formulation addresses the problem of planning the number of dense wavelength division multiplexing systems, jointly solving the RPP and placing transponders. Third, we consider regeneration devices as wavelength converters also, showing the benefits arising from that aspect disregarded in the existing impairment-aware (IA) ILP formulations based on the connectivity graph. Finally we compare over different networks the results of our design procedure with those achieved by a hybrid method that combines a simplified IA-ILP formulation with a greedy heuristic. Moreover, an analytical framework to evaluate the network cost in terms of capital expenditure and operational expenditure is also presented. We show that the k-p connectivity graph represents a cost-effective tool for network design, as it allows one to greatly reduce the number of resources needed in both the protected and the unprotected scenarios.

An analysis of daily power consumption under different On-Off IP-over-WDM translucent design approaches

We compared the energy efficiency of Multi-Layer Bypass and Direct-Bypass On-Off design under daily traffic variations in 100G and 40G networks. Housing power contribution limits the energy savings achievable by On-Off dynamics.

On the energy impact of transmission reach for 100G IP-over-WDM translucent optical networks

We investigate the power consumption of IP-over-WDM networks for 100G coherent systems when varying optical reach values. Benefits of optimal reach depends on the slope of the reach-related consumption function. We also show that “greening” transponders has a linear-like impact on the reduction of network power consumption.

Translucent optical network design: A novel two-step method

We present a novel design procedure for translucent optical networks. Regenerating nodes are selected via an Impairment-Aware ILP formulation exploiting the so-called “connectivity graph”.

Complexity and Flexible Grid Networks

For the optimization of routing and spectrum allocation in a FlexiGrid Networks, we explore the tradeoff between network cost and problem complexity according to the following aspects: traffic grooming, regeneration, modulation/baud-rate assignment.

Performance of ring-resonator based optical backplane in high capacity routers

The use of architectures that implement optical switching without any need of optoelectronic conversion allows us to overcome the limits imposed by todays electronic backplane, such as power consumption and dissipation, as well as power supply and footprint requirements. We propose a ring-resonator based optical backplanes for router line-card interconnections. In particular we investigate how the feasibility of the architecture is affected by the following parameters: number of line cards, switching-element round-trip losses, frequency drifting due to thermal variations and waveguide-crossing effects. Moreover, to quantify the signal distortions introduced by filtering operations, the noiseless eye diagrams for the different parameter conditions are shown in case of an on-off keying non-return-to-zero input signal at 10 Gb/s.