Long-haul Backbone Research Articles

Performance assessment of a communication infrastructure with redundant topology: A complex network approach

The physical assets within a critical infrastructure system are pivotal to its efficient performance and protection and that of other dependent systems. This is particularly the case for communication systems where network protection strategies usually involve asset redundancy. Although such redundancy is well-modelled in the literature, there is a gap in knowledge from a network science perspective in terms of its implications for network modelling and performance assessment. This paper presents a multilayer complex network framework that takes into account the heterogeneity of the redundant infrastructure for realistic network modelling and further analysis, a step change from using a single network model. Key performance indicators (KPIs) for communication networks (i.e., latency and jitter, bandwidth and throughput, queue depth and packet drops) are redefined to evaluate key important features of a long-haul backbone network such as network capacity and average use. In addition, these KPIs are adapted to deal with the aforementioned redundancy and so inform network managers with values defined over a model closer to the real system. The paper analyses the use case of a nationwide core and metro network infrastructure of one of the main UK internet service providers. The results of the analysis of KPIs showcase the advantage of the proposed multilayer complex network framework over the traditional single network model. Critical network elements within different dimensions of a communication network are identified based on their performance for prioritising network management measures.

Mitigating nonlinear penalty induced from a low-speed optical supervisory channel on coherent signals.

With the increasing signal rates of a long-haul backbone dense-wavelength-division-multiplexing (DWDM) transmission system, e.g., from 100 Gb/s to 400 Gb/s and even to 800 Gb/s, optical path impairments simultaneously become more severe. Harmful factors being formerly insignificant become noticeable, e.g., nonlinear phase noise (NPN) on main DWDM channels induced by the cross-phase modulation (XPM) from the low-speed optical supervisory channel (OSC). Field trials show that a greater than 5.13-dB penalty can be observed on the shortest channel of 400G DP-16QAM-PCS over G.654.E links, which greatly degrades the overall transmission performance and limits the maximum reach. In this paper, we propose a dual-OSC structure with opposite signals to compensate for performance degradation caused by OSC-induced NPN. This method involves no extra digital signal processing (DSP), which is not only simple but also applicable for universal signal rates. By experimental demonstration, a 1.32-dB gain in Q (dB) for 200G DP-16QAM transmission over 1618-km G.652.D can be done, almost achieving the same performance as the no OSC case.

Mining Graph-Fourier Transform Time Series for Anomaly Detection of Internet Traffic at Core and Metro Networks

This article proposes a framework to analyse traffic-data processes on a long-haul backbone infrastructure network providing internet services at a national level. This type of network requires low latency and fast speed, which means there is a large demand for research focusing on near real-time decision-making and resilience assessment. To this aim, this article proposes two innovative, complementary procedures: a multi-view approach for the topology analysis of a backbone network at a static level and a time-series mining approach of the graph signal for modelling the traffic dynamics. The combined framework provides a deeper understanding of a backbone network than classical models, allowing for backbone network optimisation operations and management at near real-time. This methodology was applied to the backbone infrastructure of a major UK internet service provider. Doing so increased accuracy and computational efficiency for detecting where and when anomalies and pattern irregularities occur in the network signal.

Optical Amplifiers for Access and Passive Optical Networks: A Tutorial

For many years, passive optical networks (PONs) have received a considerable amount of attention regarding their potential for providing broadband connectivity, especially in remote areas, to enable better life conditions for all citizens. However, it is essential to augment PONs with new features to provide high-quality connectivity without any transmission errors. For these reasons, PONs should exploit technologies for multigigabit transmission speeds and distances of tens of kilometers, which are costly features previously reserved for long-haul backbone networks only. An outline of possible optical amplification methods (2R) and electro/optical methods (3R) is provided with respect to specific conditions of deployment of PONs. We suggest that PONs can withstand such new requirements and utilize new backbone optical technologies without major flaws, such as the associated high cost of optical amplifiers. This article provides a detailed principle explanation of 3R methods (reamplification, reshaping, and retiming) to reach the extension of passive optical networks. The second part of the article focuses on optical amplifiers, their advantages and disadvantages, deployment, and principles. We suggest that PONs can satisfy such new requirements and utilize new backbone optical technologies without major flaws, such as the associated high cost.

Passive Optical Networks Progress: A Tutorial

For many years, passive optical networks (PONs) have received a considerable amount of attraction regarding their potential for providing broadband connectivity to almost every citizen, especially in remote areas where fiber optics can attract people to populate regions that have been abandoned. Error-free connectivity without dropouts can offer new opportunities to communicate, earn money and enjoy cultural events. Transmission speeds are multigigabit with distances of a few tens of kilometers; these specifications were previously reserved for high-speed and long-haul backbone networks. PONs can also support a new class of applications, such as accurate time transfer or distributed fiber sensing and follow new trends in open networking. An outline of past and current standards and standards that have been proposed for the latest generation of multigigabit PONs is provided.

Critical link analysis of a national internet backbone via dynamic perturbation

Long-haul backbone communication networks provide internet services across a region or a country. The access to internet at smaller areas and the functioning of other critical infrastructures rely on the long-haul backbone high speed services and resilience. Hence, such networks are key for the decision-making of internet service managers and providers, as well as for the management and control of other critical infrastructures. This paper proposes a critical link analysis of the physical infrastructure of the UK internet backbone network from a dynamic, complex network approach. To this end, perturbation network analyses provide a natural framework to measure the network tolerance facing structural or topological modifcations. Furthermore, there have been taken into account variations on data-traffic for the internet backbone that usually happen in a typical day. The novelty of the proposal is, then, twofold: proposing a weighted (traffic informed) Laplacian matrix to compute a perturbation centrality measure, and enhancing it by a time-dependent perturbation analysis to detect changes in link criticality within the network, coming from data traffic variation in a day. The results show which are the most critical links at every time of the day, being of main importance for protection, maintenance and mitigation plans for the UK internet backbone.

Ultrafast gain recovery in a QW-SOA and its application for 40 Gb/s regenerative format conversion from NRZ-DPSK to RZ-OOK

We propose a scheme to realize gain recovery of the order of a few picoseconds in a typical quantum well semiconductor optical amplifier (QW-SOA) using a pump signal with amplitude dips. In the scheme, the gain recovery is determined by the fast carrier density depletion and carrier temperature heating processes. The ultrafast gain recovery is numerically verified by a completed model combining the QW band structure calculation with rate equations in the QW-SOA. In practice, a pump signal with amplitude dips can be partly characterized by a non-return-to-zero differential phase-shift keying (NRZ-DPSK) signal generated by a Mach–Zehnder modulator. Therefore, we experimentally demonstrate 40 Gb/s wavelength-converting and regenerative format conversion from NRZ-DPSK to return-to-zero on–off keying (RZ-OOK), which may be a key function to connect different kinds of modulation formats at gateway nodes between long-haul backbone networks and metro area networks.

Network Planning of Broadband Wireless Networks

To deploy broadband networks, service providers, such as competing local exchange carriers, need robust plans for providing various types, amounts, and locations of services at competitive prices. Broadband networks generally consist of an access component (wireless access), a concentration component (a wireless aggregation point or hub), a service routing or distribution component (a central office or metro switch), and various combined or separate distribution components (a long-haul backbone data or voice network). Because access, aggregation, and routing or distribution vary greatly in requirements, we developed a method and platform for planning the components of fixed-wireless-broadband (FWB) systems for local loop access. We have helped various service providers to analyze and design many networking scenarios using our methods. The service providers have used these scenarios and their predicted financial outcomes to plan FWB access networks tailored to meet their marketing and financial goals. By implementing our method, one service provider has improved its planning process, achieved a competitive advantage in its markets, and increased its annual service revenues by tens of millions of dollars.

A 2.5-Gb/s clock and data recovery IC with tunable jitter characteristics for use in LANs and WANs

A 2.5-Gb/s monolithic clock and data recovery (CDR) IC using the phase-locked loop (PLL) technique is fabricated using Si bipolar technology. The output jitter characteristics of the CDR can be controlled by designing the loop-gain design and by using the switched-filter PLL technique. The CDR IC can be used in local-area networks (LANs) and in long-haul backbone networks or wide-area networks (WANs). Its power consumption is only 0.4 W. For LANs, the jitter generation of the CDR when the loop gain is optimized is 1.2 ps (0.003 UI). The jitter characteristics of the CDR optimized for WANs meet all three types of STM-I6 jitter specifications given in ITU-T Recommendation G.958. This is the first report on a CDR that can be used for both LAN's and WAN's. This paper also describes the design method of the jitter characteristics of the CDR for LANs and WANs.