Giulio Bottari

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.

Rethinking Optical Transport to Pave the Way for 5G and the Networked Society

The fifth generation of mobile networks (5G) is the next major phase of mobile telecommunications, which will provide the foundation for the Networked Society. To support 5G, transport will need to cater for a wide range of service requirements. It will need to support emerging 5G radio systems in terms of higher capacity and increasing number of cell sites. It must also cater for increasing need for radio interference coordination between sites as well as cost effective radio access network deployment models, and provide a flexible platform for sharing of resources where different actors through transport application programming interfaces have access to network resources and diverse transport services. In this paper, we summarize the key defining factors for 5G transport and outline a concept for programmable transport based on WDM and exploiting emerging optical devices enabled by integrated photonics.

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.

Multiplexing of Asynchronous and Independent ASK and PSK Transmissions in SDN-Controlled Intra-Data Center Network

An intra-data center architecture employing a cost-effective multi-level transmission scheme is presented. Unlike related previous works, the proposed scheme enables the optical multiplexing of two asynchronous and independent optical streams into an eight-amplitude phase-shift keying signal. The scheme is particularly suitable for intra-data center scenarios, where cost-effective solutions have to guarantee adequate bandwidth flexibility. The proposed transmitter successfully multiplexes two data streams, namely a 40 Gb/s differential quadrature phase-shift keying signal and a 10 Gb/s on-off keying one, coming from two separate (and not synchronized) apparatus. The experimental implementation, including two non-coherent receivers, reveals satisfactory performance ensuring a correct functionality (bit error rate <;10 -9) for an optical signal-to-noise ratio of about 31 dB. The design of an intra-data center switch architecture encompassing the proposed transmission scheme is then presented. Additionally, the switch includes a specifically defined Open Flow control enabling bandwidth flexibility according to application service requirements. The overall solution has been successfully implemented and demonstrated in an experimental testbed including traffic tributaries provided through off-the-shelf network elements. The overall configuration is successfully completed within a few milliseconds only.

Multi-layer grooming and routing in packet-optical networks including WSONs

A multi-layer grooming and routing method, which considers the optical layer constraints, is proposed. This method, based on a new modeling, allows significant resource saving with respect to a layer by layer approach.

Delay-Bandwidth-Aware Metric Abstraction Schemes for OIF E-NNI Multidomain Traffic Engineering

Multidomain traffic engineering (TE) has the potential not only of guaranteeing the quality of service (QoS) to connections spanning multiple domains but also of effectively utilizing intradomain resources. The hierarchical Optical Internetworking Forum (OIF) External Network-to-Network Interface (E-NNI) control plane platform has emerged as a promising candidate aiming at guaranteeing multidomain QoS provisioning. Recent efforts have been made to extend OIF E-NNI in the multicarrier scenario. However, open issues such as confidentiality, the choice of TE metric, the routing controller (RC) architecture, the path computation method, and the abstraction schemes responsible for selecting the appropriate value of the TE metric to be announced have not been addressed yet. In this study, what we believe to be a novel RC architecture integrating the path computation element (PCE) is proposed to enable the efficient provisioning of end-to-end QoS-guaranteed services. The key role of the TE metric is analyzed and discussed, together with different TE metric abstraction schemes. The end-to-end delay is here considered as the most suitable candidate and a novel family of such schemes, named delay-bandwidth aware (DBA), are proposed and evaluated by means of simulations. Results show the ability of such schemes to globally preserve control plane stability and network resource utilization while advertising a high service level.

Trade-off between power and bandwidth consumption in a reconfigurable xhaul network architecture

The increasing number of wireless devices, the high required traffic bandwidth, and power consumption will lead to a revolution of mobile access networks, which is not a simple evolution of traditional ones. Cloud radio access network technologies are seen as promising solution in order to deal with the heavy requirements defined for 5G mobile networks. The introduction of the common public radio interface (CPRI) technology allows for a centralization in BaseBand unit (BBU) of some access functions with advantages in terms of power consumption saving when switching off algorithms are implemented. Unfortunately, the advantages of the CPRI technology are to be paid with an increase in required bandwidth to carry the traffic between the BBU and the radio remote unit (RRU), in which only the radio functions are implemented. For this reason, a tradeoff solution between power and bandwidth consumption is proposed and evaluated. The proposed solution consists of: 1) handling the traffic generated by the users through both RRU and traditional radio base stations (RBS) and 2) carrying the traffic generated by the RRU and RBS (CPRI and Ethernet flows) with a reconfigurable network. The proposed solution is investigated under the lognormal spatial traffic distribution assumption. After proposing resource dimensioning analytical models validated by simulation, we show how the sum of the bandwidth and power consumption may be minimized with the deployment of a given percentage of RRU. For instance we show how in 5G traffic scenarios this percentage can vary from 30% to 50% according to total traffic amount handled by a switching node of the reconfigurable network.

Enforcing QoT via PCE in Multi Bit-Rate WSONs

Due to network upgrades, in centralized wavelength switched optical networks (WSONs), path computation element (PCE) has to guarantee the coexistence of different bit-rates in the same WSON. In particular, considering cross-phase modulation (XPM) is a challenging issue in multi bit-rate networks. In this paper, we propose three schemes based on PCE to provision lightpaths in multi bit-rate (e.g., 10-40-100-Gb/s) WSONs.

Future proof optical network infrastructure for 5G transport

The telecommunication community has reached a broad consensus that the current radio access network (RAN) and underlying transport will not be able to scale up to the traffic volume and quality expected in 5G. Thus, it is necessary to remove all the technological bottlenecks and operational rigidities to ensure a painless migration from the existing radio scenario to the 5G one. This article presents a transport architecture able to serve as a backhaul and fronthaul to convey radio traffic on the same optical infrastructure. The cornerstones of the solution are a novel photonic technology used to provide optical connectivity, complemented by a dedicated agnostic framing; a deterministic switching module; and a flexible control paradigm based on a layered scheme and on the slicing concept to facilitate optimal interactions of transport and radio resources while preserving a welldemarcated mutual independence. Simulations and experiments are presented to demonstrate the aforementioned features.