Optical Transport Network Design Research Articles

Cost minimization of multi-class demands groomed over multi-rate OTN interfaces considering WDM-layer constraints

This paper introduces a practical comprehensive approach to optimize the cost of installed Optical Transport Network (OTN) interfaces, as well as the required number of wavelengths in the substrate Wavelength Division Multiplexing (WDM) optical network. The approach assumes grooming variable-bit-rate traffic demands on multi-rate OTN interfaces. We propose an Integer Linear Programming (ILP) formulation to address the combined problem of OTN interface deployment, virtual-network formation, traffic grooming on the established distinct-capacity virtual paths, and virtual network embedding on the WDM physical substrate. The presented model focuses on mitigating the capital expenditure required to deploy OTN interfaces, usually the most costly element in the network, as well as minimizing the required number of wavelengths in the Routing and Wavelength Assignment (RWA) problem, contributing to the overall reduction in network costs and ensuring open capacity for future expansions. As the RWA problem is NP-hard and involves significant computational costs, we also propose a multi-step heuristic approach to tackle larger network instances more efficiently. In this approach, the optimization steps for the OTN design and the RWA solutions are conducted independently. For the OTN-layer planning, the optimum ILP formulation (OTN-ILP) is maintained, so that the optimum solution for the cost of installed interfaces on the OTN layer is guaranteed. The RWA problem is proposed through either an ILP formulation (RWA-ILP) or a heuristic approach. The RWA-ILP model can find the same or slightly superior number of wavelengths compared to the optimum solution of the Integrated ILP formulation, but it can provide results in reasonable times only for small networks. On the other hand, the heuristic RWA is able to run any network size, but it requires more wavelengths compared to the RWA-ILP model.

REQUIREMENTS FOR OPTICAL TRANSPORT NETWORKS FOR SUCCESSFUL IMPLEMENTATION OF 5G TECHNOLOGY

Background. The amount of data generated, transmitted and accumulated in the world is constantly growing every year. On the other hand, users need new services and information exchange capabilities. 5G technology is able to meet the requirements of subscribers to some extent. Therefore, it is important to consider the main features of fifth generation mobile networks and to determine the requirements for the design of optical transport networks that will ensure the successful implementation of 5G technology.Objective. The aim of the paper is to determine the features of design and characteristics of optical transport networks to implement the capabilities of 5G technology.Methods. The analysis of the publications devoted to modern optical networks and their optical components allowed defining the basic requirements to design of optical transport networks and their characteristics.Results. It is established that optical transport networks should provide increased bandwidth; possibility of mass optical cross-connections in ROADM/OXC nodes that support addition/removal of any wavelength from/in any direction; intelligent operation and maintenance of the network.Conclusions. The defined requirements for the design of optical transport networks and their characteristics will ensure the successful implementation of the capabilities of 5G technology, which will meet the needs of subscribers.

Optical Transport Network Design for 5G Fixed Wireless Access

The fifth generation (5G) of mobile technology, 5G is anticipated to be a significant leap in the evolution of mobile communication. 5G will be designed to attain 1000 times higher data volumes, 10 times lower latency, and 100 times more connected devices than its predecessor, 4G. Due to 5Gs ability to sustain high bandwidth per unit area, 5G is considered to be a cost-efficient solution to provide fixed wireless access (FWA) to households on a large scale. FWA is seen as an attractive alternative for fixed broadband access in scenarios where last mile access based on wired technologies is not economically viable. While approaches for enhancing user experience in a 5G FWA environment are investigated in the research community, the problem of providing cost-effective high capacity transport for FWA deployments still remains a major challenge. This is particularly challenging due to diverse transport network architectures and requirements imposed by different 5G deployment models. This paper addresses this problem by formulating a generalized joint-optimization framework to simultaneously plan wireless access and optical transport for 5G FWA networks in order to minimize the deployment cost while meeting various network requirements. We demonstrate the applicability of the proposed framework by applying it to a real scenario with a range of deployment options and where different types of optical x-haul solutions are considered. The results provide a cornerstone for deployment strategies that will be imperative for realizing a future-proof and cost-effective broadband access network.

Compact ILP formulations for the routing and wavelength assignment problem in the design of optical transport networks with regenerators

This paper addresses two variants of the routing and wavelength assignment problem arising in the context of optical transport networks. In both variants, we address the case where the physical coverage of the fiber network is such that regenerators, to be placed on intermediate nodes of the lightpaths, have to be used to reach full connectivity between network nodes. In the first variant, we aim to minimize the solution cost given by the sum of the costs of all electrical–optical–electrical converter components. In the second variant, among all minimum cost solutions, we aim to optimize the network load balancing by minimizing the highest assigned wavelength. For each problem variant, we start by defining a basic integer linear programming compact formulation. Then, we improve each formulation using variable reformulation and variable elimination techniques. Finally, we present computational results showing that the reformulated formulations with variable elimination let us obtain provable optimal solutions for problem instances of relevant size within reasonable runtimes.

A novel algorithm to integrate synchronous digital hierarchy networks into Optical Transport Network using mixed line rates

In this era of high data transfer speeds and new age technologies, Optical Transport Network (OTN) along with its newly introduced Optical Transport Hierarchy (OTH) has provided a lease of life to legacy low rate networks. It has provided a common backbone for multiple data rates to coexist on same fiber along with the enhanced transmission reach. The cost effective Optical Transport Network design has always been a complex issue due to the presence of multiple variables like number of fibers on each link, available data rates on each fiber, the wavelength count, transmission reach at each data rate, etc. In this paper an Integer Linear Programming (ILP) model has been presented to solve Routing problem for Synchronous Digital Hierarchy (SDH) over OTN over DWDM design. Optical Transport Hierarchy (OTH) has been used to integrate heterogenous SDH/SONET operating at different rates (STM-16, STM-64 and STM-256) into a single network supporting mixed line rates. These rates can coexist in a same fiber but each rate carries different cost with it. The objective function aims at finding the least cost routing solution by looking at different tradeoffs between the Capital Expenditure and the operational expenditure. Certainly different variables like the number of fibers and wavelengths, transmission reach, etc. are a factor in it. A mechanism has been put to monitor the Bit Error Rate (BER) levels as well. For evaluating the ILP model, 18 Node 38 Link European Optical Network was considered as the reference model and two ordering techniques, namely, full ILP and highest rate first (HRF) were used for deriving the results. The ILP model was designed with minimum of decision variables so in spite of big reference network it converges much faster. Under the given conditions, full ILP gave least cost network whereas HRF ordering took least time for ILP to converge.

Optimization Framework for Supporting 40 Gb/s and 100 Gb/s Services over Heterogeneous Optical Transport Networks

Continuous traffic growth and crunched profit margins are leading network operators to deploying high-capacity backbone infrastructures with minimal capital investment. However, the cost-effective design of optical transport networks (OTNs) remains a complex challenge subjected to multiple constraints, e.g., maximum bit rate per channel, electrical multiplexing capabilities, wavelength count per fiber, optical interface cost, maximum transparent reach, etc. To efficiently solve this multi-constrained dimensioning problem in presence of heterogeneous client demands and optical channel rates of 40 Gb/s and 100 Gb/s, this paper presents a novel hybrid optimization framework. The proposed approach is based on an iterative combination of linear programming and rounding algorithms for the demand routing, with graph coloring heuristics for the wavelength assignment. The performance of this framework is assessed and compared with a similar approach that resorts to an integer linear programming (ILP) model to route the demands. The results obtained show that our proposal is able to reach the same low network expenditures as the ILP while requesting less computation time. We also confirm that the most cost-effective network solutions are attained when optical line rate heterogeneity is jointly applied with diverse multiplexing capabilities at the OTN electrical layer, such as grooming and inverse-multiplexing.

Impairment-Aware Lightpath Routing and Regenerator Placement in Optical Transport Networks With Physical-Layer Heterogeneity

We develop a framework that supports impairment-aware lightpath routing and wavelength assignments in optical transport networks. Different from most existing studies, we consider a more generic optical transport network with physical-layer heterogeneity, including different fiber types, variable amplification span distances and attenuation coefficients. In addition, rather than a single amplifier type as in most of the existing studies, we consider multiple amplifier types for different amplification situations. Owing to the high cost of OEO regeneration, the total number of required regenerators is considered as the major objective for optimization. A signal-quality-aware routing algorithm is developed to find routes that are expected to require the fewest regenerators. The first-fit wavelength assignment algorithm is extended to assign wavelength(s) for lightpaths after placement of some regenerators which can freely function as wavelength converters. Simulation studies indicate that the proposed algorithm can significantly reduce the required number of regenerators compared to the simple shortest-path routing algorithm. Moreover, it is found that the signal-quality-aware algorithm shows stronger benefits when a network demonstrates higher physical-layer heterogeneity such as different fiber types and non-uniform span losses. The signal-quality-aware algorithm also demonstrates better performance when a network has a higher average nodal degree. Finally, the results indicate that multiple amplifier options are important for cost-effective optical transport network design. For a network with high physical-layer heterogeneity, multiple amplifier options can significantly reduce the required number of regenerators (up to 50%) over a single amplifier option.

Integrating optical transport quality, availability, and cost through reliability-based optical network design

The design of the optical transport network (OTN) must meet the challenges of providing a high capacity, highly dependable and reliable network and the flexibility in bandwidth management to support multi-services in a cost-effective manner. The core objective of the OTN design activity focuses on carefully balancing these design objectives. This paper presents a comprehensive design approach that integrates the OTN design with its end-to-end reliability assessment. Quantitative reliability assessment becomes an integral part of the OTN design process when considering network survivability using various protection and restoration schemes. This value-based reliability approach provides a complete set of network reliability profiles. These profiles provide a means to: 1) drive network architecture and infrastructure design by identifying both strong and vulnerable region(s); 2) provide reliability/availability cost and worth (benefit) tradeoff by quantifying the impact of various network elements and/or protection schemes; and 3) allow design of reliability-based revenue offers or service level agreements (SLAs). We will illustrate the application and benefits of using OTN reliability-based design processes in several service provider networks featuring synchronous optical network/synchronous digital hierarchy (SONET/SDH) ring and dense wavelength division multiplexing (DWDM) mesh architectures including dedicated and shared protection/restoration schemes in backbones and in metropolitan networks.

Availability design of optical transport networks

A design technique for reliable optical transport networks is presented. The network is first dimensioned in order to carry a given set of static protected optical connections, each one routed maximizing its availability. The network can be further optimized by minimizing the number of fibers to be installed, while keeping a control on connection availability, which can remain the same or decrease by a prefixed margin factor. Design and optimization algorithms are provided for networks adopting dedicated and shared path-protection. The optimization approach is heuristic. Results obtained by applying the proposed technique to two case-study networks are shown and discussed. These two case-study experiments are carried out exploiting a realistic model to evaluate terrestrial and submarine optical link availability.

Joint pricing-network design and stochastic traffic engineering to manage demand uncertainty

I will describe two networking models, together with their optimization techniques, that span several time scales. In the longest time scale, where the goal is capacity planning, I will describe the work of Bienstock, Raskina, Saniee and Wang that considers joint pricing and network design of optical transport networks. Technological innovations are yielding sharply decreasing unit costs. There is also empirical evidence that suggests that the elasticity of bandwidth demand to price is high. Integrating these features in a unified profit-maximizing model leads to a large- scale nonlinear optimization problem. In this work, efficient solution techniques are developed to maximize the carrier's net present value with respect to pricing strategies and investment decisions for technology acquisitions. In the work of Mitra and Wang the time scale is shorter, the network infrastructure is fixed, and a model for stochastic traffic engineering is given in which the optimization is with respect to bandwidth provisioning and route selection. Traffic demands are uncertain, and the objective is to maximize a risk-adjusted measure of network revenue that is generated by serving demands. Considerable attention is given to the appropriate measure of risk in the network model. Risk-mitigation strategies are also advanced. The optimization model, which is based on mean-risk analysis, enables a service provider to maximize a combined measure of mean revenue and revenue risk. The conditions under which the optimization problem is an instance of convex programming are obtained. The solution is shown to satisfy the stochastic efficiency criterion asymptotically. The efficient frontier, which is the set of Pareto optimal pairs of mean revenue and revenue risk, is obtained.

A Fiber Routing Problem in Designing Optical Transport Networks with Wavelength Division Multiplexed Systems

In this paper, we consider a fiber routing problem arising from the design of optical transport networks. The problem is to find an optimal routing of multiple rings and an optimal location of wavelength division multiplexed (WDM) systems for carrying demand traffic. This problem can be conceptualized as a Steiner (multiple) ring problem with link capacity constraints. We formulate the problem as a mixed-integer programming model and develop a new branch-and-cut procedure along with preprocessing routines and valid inequalities for optimally solving the problem. Exploiting the inherent special structures of the formulation, we focus on developing strong valid inequalities and devising an effective Tabu search heuristic for solving large-scale problems. Computational results indicate that preprocessing rules and valid inequalities provide a tight lower bound, and in turn reduce the effort required to solve the problem within the framework of the branch-and-cut procedure. Moreover, the proposed Tabu search heuristic works quite well for solving large-scale problems. Motivated by promising computational results, we provide insights into implementing the proposed branch-and-cut procedure for deploying fiber optic networks in practice.

Technology-oriented review and vision of 40-Gb/s-based optical transport networks

Research and development of 40-Gb/s-based technologies are very significant for not only increasing the total capacity of wavelength-division multiplexing transmission systems but also providing higher speed interfaces to routers and Ethernet devices in order to create new services in the twenty-first century. The technologies of digital and analog integrated circuits are progressing steadily, and the LiNbO/sub 3/ Mach-Zehnder external modulator has already reached the performance level required for practical use. Adaptive, intelligent compensation for problems such as chromatic dispersion and polarization-mode dispersion can make the design of optical transport networks more flexible. As an example, we achieved 3.5-Tb/s (43 Gb/s/spl times/88 ch) transmission over a 600-km nonzero dispersion-shifted fiber by using LiNbO/sub 3/ modulators and virtually imaged phased array variable-dispersion compensators.