Paola Iovanna

Modeling and Distributed Provisioning in 10–40–100-Gb/s Multirate Wavelength Switched Optical Networks

In wavelength-switched optical networks (WSONs), quality of transmission (QoT) has to be guaranteed during lightpath provisioning. In multibit-rate WSONs, this task is complicated by the coexistence of optical connections operating at different bit-rates and modulation formats. The major issue consists in accounting for the severe impairments due to cross-phase modulation (XPM) induced by 10 Gb/s lightpaths on neighbor 40 or 100 Gb/s lightpaths. In this paper, QoT modeling is first reviewed for 10, 40, and 100 Gb/s transmission according to the adopted modulation format and detection type. In addition, a Gaussian approximation to compute the bit error rate of differential quadrature phase-shift keying (DQPSK) and QPSK signals is proposed, as well as closed formulas to compute the nonlinear phase noise variance due to XPM. Also, discussions about the XPM cumulation over spans in a WSON and how XPM can be considered in a dynamic network are provided. Then, four lightpath provisioning schemes are proposed to effectively account for QoT and, in particular, for XPM. The schemes differently exploit: 1) augmented spectral separation among lightpaths at different bit rates; 2) XPM worst-case scenario; and 3) current and novel generalized multiprotocol label switching extensions. The performance of the proposed schemes is evaluated through simulations in several multibit-rate scenarios. Results show that the proposed schemes provide effective network resource utilization while guaranteeing the adequate QoT to lightpaths at any bit rate.

Toward high-rate and flexible optical networks

The evolution of optical technologies is driving the introduction of multirate optical networks exploiting advanced transmission techniques and efficient switching devices. In the short term, optical connections operating at 10 and 100 Gb/s will coexist in the same multi-rate network infrastructure. This, however, might introduce significant issues due to detrimental inter-channels effects, which need to be considered during network planning or connection provisioning. In the long term, connections at higher bit-rates (e.g., 400 Gb/s) and based on complex modulation formats (e.g., quadrature amplitude modulation - QAM) are expected, together with the adoption of innovative and flexible bandwidth-variable optical cross-connects (BV-OXCs). BV-OXCs have the potential to significantly improve the overall network spectrum efficiency. However, critical issues might arise in the dynamic control of network operations. This article discusses the enhancements required during operation and control of future optical networks with quality of transmission guaranteed. A first network evolution scenario is considered, where 100 Gb/s lightpaths are introduced in a native 10 Gb/s network. In such a scenario, inter-channel effects between 10 and 100 Gb/s lightpaths are highlighted. Relevant methods to account for these effects are discussed and evaluated. Then, a second network evolution scenario is assumed, in which traditional OXCs are replaced with BV-OXCs, and even higher bit-rates (e.g., 400 Gb/s 16-QAM) are introduced in the network. In particular, the problem of scalability when advertising and storing spectrum resource (i.e., frequency slices) availability is presented for flex-grid optical networks (i.e., optical networks exploiting BVOXCs). Consequently, a method to efficiently handle availability information is proposed and evaluated, showing the capability to overcome scalability issues without impacting the overall network resource utilization.

Xhaul: toward an integrated fronthaul/backhaul architecture in 5G networks

The Xhaul architecture presented in this article is aimed at developing a 5G integrated backhaul and fronthaul transport network enabling flexible and software-defined reconfiguration of all networking elements in a multi-tenant and service-oriented unified management environment. The Xhaul transport network vision consists of high-capacity switches and heterogeneous transmission links (e.g., fiber or wireless optics, high-capacity copper, mmWave) interconnecting remote radio heads, 5G points of attachment (5GPoAs, e.g., macro- and small cells), centralized- processing units (mini data centers), and points of presence of the core networks of one or multiple service provider(s). This transport network shall flexibly interconnect distributed 5G radio access and core network functions, hosted on network centralized nodes, through the implementation of a control infrastructure using a unified, abstract network model for control plane integration (Xhaul Control Infrastructure, XCI); and a unified data plane encompassing innovative high-capacity transmission technologies and novel deterministic-latency switch architectures (Xhaul packet Forwarding Element, XFE). Standardization is expected to play a major role in a future 5G integrated front haul/backhaul architecture for multi-vendor interoperability reasons. To this end, we review the major relevant activities in the current standardization landscape and the potential impact on the Xhaul architecture.

5G-Crosshaul: An SDN/NFV Integrated Fronthaul/Backhaul Transport Network Architecture

This article proposes an innovative architecture design for a 5G transport solution (dubbed 5G-Crosshaul) targeting the integration of existing and new fronthaul and backhaul technologies and interfaces. At the heart of the proposed design lie an SDN/NFV-based management and orchestration entity (XCI), and an Ethernet-based packet forwarding entity (XFE) supporting various fronthaul and backhaul traffic QoS profiles. The XCI leverages widespread architectural frameworks for NFV (ETSI NFV) and SDN (Open Daylight and ONOS). It opens the 5G transport network as a service for innovative network applications on top (e.g., multi-tenancy, resource management), provisioning the required network and IT resources in a flexible, cost-effective, and abstract manner. The proposed design supports the concept of network slicing pushed by the industry for realizing a truly flexible, sharable, and cost-effective future 5G system.

Strategy for Dynamic Routing and Grooming of Data Flows into Lightpaths in New Generation Network Based on the GMPLS Paradigm

This paper reports on a novel strategy and related algorithm for realizing dynamic routing and grooming into wavelengths of data flows (label switched paths, LSPs) in new generation optical networks based on generalized MPLS (GMPLS). The method allows arbitrary granularities of LSPs. The new generation network is modeled as a multi-layer network consisting of an IP/MPLS layer and an optical layer. In particular, the proposed solution adopts a dynamic routing algorithm based on the Dijkstra algorithm, that makes use of a weight system, integrated with a suitable method for grooming LSPs into wavelengths based on the packing criterion, thus harmonizing the features of MPLS packet flows whose bandwidth vary in a continuous range of values, with the optical world, where the wavelength bandwidth ranges according to discrete values. The weight system is based on the concepts of least resistance routing that allows to evenly distribute the traffic at the MPLS layer, while packing improves the use of optical resources by favoring more filled wavelengths with respect to the emptier ones. To assess the validity of the proposed solution a simulation model has been realized. The results obtained by simulation show that the packing criterion allows reducing the refused bandwidth from two down to about four times, for a network load of 70% and 55%, respectively, when compared with the alternative method named spreading. The dependence of the proposed solution on bandwidth granularity has been also investigated. Moreover, in order to demonstrate the superior performance of the proposed routing solution, a comparison between the proposed strategy with relevant solutions known in the literature, based on either a single or multi-layer approach, is also reported. In order to perform the comparison, all the reference routing solutions that have been considered adopt the packing method for LSP grooming into the lightpaths. The results show that our solution outperforms the others in terms of amount of traffic that can be on-line accommodated. For instance, assuming a blocking probability of 10−3, the proposed solution is able to further reduce the refused bandwidth of the best routing algorithm considered in the analysis by a factor of three times, thanks to the knowledge of optical resource availability.

Packet-optical integration nodes for next generation transport networks

The development of a new generation of photonic integrated circuits and the constant progress in integrated electronics (following Moores law) made the realization of a new type of optical transport node possible, by basing it on the concept of a digital photonic switching layer working in coordination with the packet switching layer under the control of a multi-layer control plane. In this paper such a new type of optical transport node is presented, analyzed and implemented in order to better investigate its potential advantages and weaknesses if compared with the conventional all-optical transport nodes and their level of applicability. The new node concept is based on a “vertical” view of packet-opto networks able to face the challenge of growing network capacity while cutting costs and to allow an efficient combination of digital optical networks and packet-opto integrations benefits. Thanks to the use of optical-electrical-optical conversion technology, the wavelength division multiplexed (WDM) layer is provided with the traffic management flexibility and the engineering simplicity of digital transport systems (significant operational expenditures reduction) and with the network cost savings of large-scale photonic integration (capital expenditures reduction). It combines packet and WDM switching technologies where appropriate, with the ability to offload pass-through traffic from the packet layer to the lowest possible layer, so as to reduce costs and power consumption by eliminating unnecessary packet processing (total cost of ownership reduction). The main building blocks are a new digital optical transport based on an integrated packet-opto node that is scalable, flexible and low cost, and multi-layer control and management based on standard generalized multiprotocol label switching and innovative path computation element (PCE) solutions. Thanks to the flexibility of the digital reconfigurable optical add/drop multiplexer, the PCE is able to handle both layers in a very efficient way by selecting the right granularity for traffic grooming and routing. The feasibility has been assessed by a network prototype composed of four nodes produced by Ericsson Research Lab in Pisa and by a simulation analysis.

Routing Code and Spectrum Assignment (RCSA) in Elastic Optical Networks

This paper introduces the concept of code selection in RSA for EONs. Simulations show that code-adaptive time frequency packing reduces blocking probability by one order of magnitude with respect to format-adaptive Nyquist WDM.

Flexible packet-optical integration in the cloud age: Challenges and opportunities for network delayering

The telecommunication community has reached a broad consensus on the vision that future transport architecture will be dominated by optical in combination with IP. This implies a complete reassignment of the functions traditionally handled by legacy intermediate layers to packet and optical layers only. Here, current advances in photonic technologies and architectures enable the optical layer to become the ideal companion of the packet world and to unlock an effective packet offload toward flexible and dynamic optical pipes. A global crosslayer optimization is needed to minimize the misalignment between cost and revenues, and manage the rising tide of IP traffic. In this article, we describe this evolving path and explore the impact on network planning and traffic provisioning, also considering implications on the cloud scenario and sighting the software defined networks horizon.

E2E Traffic Engineering Routing for Transport SDN

The article proposes a hierarchical routing approach, validated by simulation on real network operator, based on a novel adaptive virtualization scheme, suitable for transport SDN, allowing dynamic configuration of heterogeneous multi-domain packet-optical networks.

Internet like control for MPLS based traffic engineering: performance evaluation

This paper reports a realization of a traffic engineering (TE) strategy based on a distributed control plane (Internet-like), and a performance analysis based on experiments carried out on the realized test bed and on simulations. The implementation of control plane is based on standard IP protocols, namely OSPF-TE for routing and RSVP-TE for signaling, which have been suitably extended to support the reported TE strategy. Furthermore, a threshold mechanism for limiting the information flood in the network is reported. The performance analysis assesses the validity of the proposed strategy, by reporting simulation results and measurements achieved on the test bed. In particular, the paper shows that the non-ideality due to real signaling flow and related databases updating are reasonable and in-line with real systems.