Domenico Siracusa

Spectrally and spatially flexible optical network planning and operations

The advent of spectrally flexible (a.k.a. elastic) optical networking is widely identified as the next generation optical network solution that permits varying bandwidth demands to be dynamically assigned over flexible spectral containers, targeting optimum use of the available network resources. Additionally, the adoption of the space dimension is identified as a promising solution for the capacity expansion of future networks, while novel spatial-spectral switching solutions show that the flexible networking concept can be further expanded over both the spatial and spectral dimensions. This article provides an overview of the latest developments and possible approaches with respect to flexible optical networking and the emerging benefits that spatially flexible networking approaches can offer. The focus is on the network planning and resource optimization functions, the main network operations related to fragmentation and IP/optical layer integration, and the control plane solutions.

Comparison of Spectral and Spatial Super-Channel Allocation Schemes for SDM Networks

We evaluate the advantages of using the extra dimension introduced by space-division multiplexing (SDM) for dynamic bandwidth-allocation purposes in a flexible optical network. In that respect, we aim to compare spectral and spatial super-channel (Sp-Ch) allocation policies in an SDM network based on bundles of SMFs (to eliminate coupling between spatial dimensions from the study) and to investigate the role of modulation format selection in the blocking probability performance with an emphasis on the spectral efficiency (SE)/reach tradeoff for different multiline-rate scenarios, created either by changing the number of sub-channels (Sb-Ch), or by employing different modulation formats. Our network-performance results show that DP-8QAM -in a multichannel (MC) single-modulation-format system assuming ITU-T 50-GHz WDM Sb-Ch spectrum occupation-offers the best compromise between SE and optical reach for both spectral and spatial Sp-Ch allocation policies. They also reveal that an MC multimodulation-format system improves the network performance, particularly for spectral Sp-Ch allocation with Sb-Ch spectrum occupation of 37.5 GHz on the 12.5-GHz grid. Additionally, as another important contribution of the paper, we investigate, for spatial Sp-Ch allocation, the performance of several SDM switching options: independent switching (InS), which offers highest flexibility, joint-switching (JoS), which routes all spatial modes as a single entity, and fractional-joint switching, which separates out the spatial modes into sub-sets of spatial modes which are routed independently. JoS is proved to offer a similar performance to that of InS for particular network load profiles, while allowing a significant reduction in the number of wavelength-selective switches.

Cognitive dynamic optical networks [invited]

The use of cognition is a promising element for the control of heterogeneous optical networks. Not only are cognitive networks able to sense current network conditions and act according to them, but they also take into account the knowledge acquired through past experiences; that is, they include learning with the aim of improving performance. In this paper, we review the fundamentals of cognitive networks and focus on their application to the optical networking area. In particular, a number of cognitive network architectures proposed so far, as well as their associated supporting technologies, are reviewed. Moreover, several applications, mainly developed in the framework of the EU FP7 Cognitive Heterogeneous Reconfigurable Optical Network (CHRON) project, are also described.

The need for a Control Orchestration Protocol in research projects on optical networking

The Control Orchestration Protocol (COP) abstracts a common set of control plane functions used by an various SDN controllers, allowing the interworking of heterogeneous control plane paradigms (i.e., OpenFlow, GMPLS/PCE). COP has been defined using YANG model language and can be transported using RESTconf, which is being incorporated by industry. COP has been defined in the scope of STRAUSS due to the need for an overarching control plane protocol for network orchestration. In this paper, several research projects describe how the COP could fit in their architecture and propose a use case for COP usage. The proposed COP use cases cover the following research projects: STRAUSS, IDEALIST, DISCUS, COMBO, INSPACE.

Next generation flexible and cognitive heterogeneous optical networks

Optical networking is the cornerstone of the Future Internet as it provides the physical infrastructure of the core backbone networks. Recent developments have enabled much better quality of service/experience for the end users, enabled through the much higher capacities that can be supported. Furthermore, optical networking developments facilitate the reduction of complexity of operations at the IP layer and therefore reduce the latency of the connections and the expenditures to deploy and operate the networks. New research directions in optical networking promise to further advance the capabilities of the Future Internet. In this book chapter, we highlight the latest activities of the optical networking community and in particular what has been the focus of EU funded research. The concepts of flexible and cognitive optical networks are introduced and their key expected benefits are highlighted. The overall framework envisioned for the future cognitive flexible optical networks are introduced and recent developments are presented.

Domain sequence protocol (DSP) for PCE-based multi-domain traffic engineering

In current multi-domain networks relying on the path computation element (PCE) architecture, domain sequence computation can be performed through mechanisms which may fail to guarantee both efficient resource utilization and an adequate level of confidentiality and scalability. In this study, we first propose a hierarchical instance of a path-vector protocol, called the domain sequence protocol (DSP), dedicated to provide the PCE with effective domain sequence information. Then we consider and evaluate through simulations the performance of the integrated DSP-PCE architecture. Results show that, compared to current routing solutions based on the border gateway protocol, significant improvements can be achieved in terms of the overall network resource utilization. In addition, this study identifies the most suitable DSP-PCE features for different network scenarios, including the announcement of single or multiple routes per domain, the advertisement of aggregate or maximum reservable inter-domain bandwidth information, the use of different PCE-based path computation procedures, and the possibility to perform additional computation attempts along different domain sequences. Finally, the experimental implementation of the proposed DSP-PCE architecture is provided to show its feasibility and its fast convergence time in the range of a few milliseconds.

Hierarchical Border Gateway Protocol (HBGP) for PCE-Based Multi-Domain Traffic Engineering

In multi-domain multi-carrier networks the effective use of network resources shall be achieved while guaranteeing an adequate level of confidentiality and scalability. A candidate solution to perform effective multi- domain Traffic Engineering (TE) is based on a combination of (i) hierarchical routing and (ii) path computation procedures. Hierarchical routing identifies the domain sequence to cross while path computation computes the strict end to end path. In this multi-domain study we first propose a hierarchical instance of BGP (HBGP) dedicated to TE information only. Then we propose and evaluate the integration of HBGP with path computation procedures based on IETF PCE architecture. Simulation results show that the hierarchical HBGP-PCE architecture, compared to current routing solutions based on BGP only, significantly improves the overall network resource utilization. In addition, this study identifies the network scenarios in which the aforementioned HBGP-PCE features provide significant advantages. Finally, the experimental implementation of the proposed HBGP-PCE architecture in a network testbed composed of commercially available routers shows the viability of the solution in real networks.

A control plane framework for future cognitive heterogeneous optical networks

Future optical networks are expected to provide an efficient infrastructure able to deliver a growing number of services, which have to meet various requirements in terms of quality of service. To achieve this objective the physical network is going through an evolution aimed at increasing its flexibility in terms of spectrum utilization and its level of heterogeneity in terms of supported services and technologies. In this context, cognitive optical networks represent a viable solution to fill the gap between the intelligence required by the future networks and the current optical technology. This paper proposes a control plane framework developed to coordinate the interactions among the elements of the future cognitive optical networks. The building blocks of the framework and the involved protocols are presented. Moreover, this paper provides an insight of the control plane issues related to the introduction of the flexible optical technology.

Virtual topology reconfiguration in optical networks by means of cognition: Evaluation and experimental validation [invited]

In optical networking, virtual topologies have been introduced mainly to provide service providers with logical connections equipped with a reserved amount of bandwidth, which can be exploited to interconnect their equipment at the edges of the transport infrastructure. Virtual topologies are thus basically an abstraction of the real substrate, created by means of a process called virtual topology design (VTD). VTD is a complex task, affected by many parameters and constraints, and among them current traffic conditions are very relevant. Indeed, it is possible that after a certain time a virtual topology becomes inappropriate to serve current traffic. In such cases, the virtual topology can be reconfigured by creating new lightpaths or modifying or deleting existing ones, thus possibly creating some service interruptions. In this paper a new virtual topology reconfiguration technique is presented. In this technique, a cognitive entity designs and reconfigures virtual topologies by exploiting traffic forecasting solutions and taking advantage of past history. Moreover, a new transition method is also proposed to reduce the impact of instable routing tables during the reconfiguration process. We demonstrate, by means of simulation, the advantages of the proposed methods, as they reduce both the operational costs and the resources in operation while maintaining low packet loss ratio. Furthermore, we validate the operation of the proposed solutions in an emulated testbed.

Cognitive dynamic optical networks

Cognitive networks are a promising solution for the control of heterogeneous optical networks. We review their fundamentals as well as a number of applications developed in the framework of the EU FP7 CHRON project.