António Eira

Design of survivable flexible-grid DWDM networks with joint minimization of transponder cost and spectrum usage

We present a multi-objective framework to jointly optimize cost and spectrum in a survivable flexible-grid network with multiple transponder profiles. Through the use of an evolutionary algorithm, the sharing of spectral and interface resources is explored to clearly show the cost/spectrum design trade-off according to different sharing policies.

Optimized design of multistage passive optical networks

The large investments required for deploying passive optical networks (PONs) render the disposal of appropriate planning tools for designing such networks in a cost-effective way a necessity. This paper addresses the problem of finding the least costly tree topology time-division multiplexing PON (TDM-PON) deployment configurations considering equipment and installation costs (CAPEX) and operational exploration costs. With this purpose, an integer linear programing model is developed, which is capable of designing not only common single-stage PON configurations, but also PONs with multiple stages of optical splitting. In order to reduce the computation time for problems of larger size, a two-stage heuristic is also proposed. The simulation results for the cases studied reveal that an optimal multistage splitting strategy can lead to cost savings of up to 15% in CAPEX expenditures in comparison with the traditional single-stage approach. Furthermore, the heuristic procedure proposed is shown to obtain results within acceptable bounds relative to the optimum solutions, hence validating its use for larger sized networks. The results also show that the average CAPEX cost savings between the two-stage and single-stage approaches are quite dependent on the strategies used to choose candidate locations for the splitters, with values ranging from 5 to 12% depending on whether random candidate placement or k-means-based placement is used.

Multi-objective design of survivable flexible-grid DWDM networks

Emerging trends in optical transport networks aiming to support increasing data rates are reshaping the possibilities for network planning. The deployment of a flexible grid with multiple available channel bit rates and spectral widths gives way to a more clearly defined trade-off between spectrum and cost in the planning process. Furthermore, providing redundancy in these types of services is both crucial and costly. For this reason, it is important to consider all these aspects simultaneously in order to have an accurate view of the cost/spectrum trade-off in the optical backbone. This paper presents an evolutionary based multi-objective framework for optimizing network deployments with flexible-grid channel formats ranging from 40 to 400 Gbits/s with varying degrees of resilience to both link and transponder failures. The multi-objective algorithm can consider all these different aspects simultaneously and highlight the degree to which cost can be traded for spectrum, and how the protection/restoration schemes influence both parameters. After benchmarking the proposed algorithm on both objectives, we use it on two reference networks to trace the non-dominated front for multiple resilience schemes, offering different levels of protection against link and/or transponder failures. We also evaluate how the channel format selection for each demand evolves when considering single-rate or bit-rate variable transponders.

Optimal multi-period provisioning of fixed and flex-rate modular line interfaces in DWDM networks

Flex-rate transmission is seen as a core element in the realization of programmable backbone networks. The ability to adjust the channel bit rate in response to traffic changes in the network can potentially bring long-term savings by future-proofing capacity and simplifying network operations. The key issue in this topic is quantifying the degree of traffic dynamics and growth that justify the higher initial investment in flexible-rate (flex-rate) technology. In dense wavelength division multiplexing (DWDM) networks, traditionally featuring long lifespans and stable traffic growth outlooks, this question can be answered with a multi-period analysis that simulates the requirements for hardware provisioning throughout multiple planning periods with incremental traffic. In a scenario featuring sliceable bandwidth-variable transponders composed of line cards (LCs) with multiple transceiver ports, we use a multi-period planning framework to assess the advantages and drawbacks of using fixed-rate and/or flex-rate technology in the LCs and transceivers. The simulation is performed resorting to an integer linear programming (ILP) model that chooses, in each period, the routing and format selection for a set of demands that yields the minimum hardware cost, reusing any idle equipment resulting from traffic churn. The analysis of the results shows that the initial investment in flex-rate LCs and transceivers pays off for small- to medium-sized networks where the upgrade to higher bit rates does not require extra regeneration. Long and ultralong-haul scenarios benefit from the use of fixed-rate interfaces. In terms of operational issues, it is shown that flex-rate hardware provides clear benefits through reduced footprint and extended capacity due to better spectral efficiency.

Spectrum and transponder optimization in survivable translucent flexible-grid optical networks

In order to support bit-rates beyond 100 Gb/s in transport networks, flexible-grid networking was proposed as a solution to exploit the spectral efficiency of advanced modulation formats without severely impairing the transmission reach. This increase in the bit-rate highlights the critical role of survivable connectivity. Considering this, we propose a planning solution for flexible-grid translucent networks with shared restoration through an ILP model and a fast, scalable heuristic. Furthermore, we propose an algorithm to calculate the backup transponder redundancy in each node when tunable transponders are in place to restore multiple optical channels. The results show considerable spectral savings from using a shared restoration scheme instead of a dedicated one and that 18% to 30% of the backup transponders can be saved through tunable optics, depending on the tuning range used.

Optimized Design of Fixed/Flex-Rate Line-Cards and Transceivers over Multiple Planning Cycles

We present a comparison between line-card and transceiver designs based on single and multi-rate technology over multiple planning cycles. The analysis suggests multi-rate hardware is most suited to networks without significant regeneration requirements.

Impact of client- and line-side flexibility in the lifecycle of next-generation transport networks [Invited]

Fast developments in the transport network ecosystem are putting into question the foundations on which to base next-generation backbone networks. Flexibility is touted as an essential requirement to cope with traffic increasing in volume and unpredictability. Based on this principle, flexible transmission modules such as the sliceable bandwidth-variable transponder (SBVT) have been proposed to exploit the networking advantages of flexible-grid networks and more advanced modulation formats. Although the network-wide benefits of SBVTs have been the object of many studies, these do not usually consider the type of client architectures supporting them, which is critical in order to account for constraint introduced by specific architectures and emulate an operators management of its network infrastructure over time in a convincing way. The purpose of this paper is to perform a realistic techno-economic comparison between architectures based on fixed and flexible client- and line-side elements. The relevant parameters regarding cost, traffic, and equipment availability over each planning period are modeled and conveyed to a multi-period optimization framework based on integer linear programming models tailored to cost-effectively dimension the network for each client- and line-side architecture. The simulation examines the impact in each scenario of shifting client traffic patterns (from 10G/100G to 100G/400G) and the gradual introduction of higher-capacity network elements. Its results provide insight on the cost and spectrum utilization impact of deploying fixed transponders or SBVTs, coupled with fixed and flexible client-to-line interconnections, and how each of these alternatives copes with aggregated traffic increases of 400% over several years in national and pan-European backbone network topologies.

Optimized client and line hardware for multiperiod traffic in optical networks with sliceable bandwidth-variable transponders [Invited]

The sliceable bandwidth-variable transponder (SBVT) has been recently proposed as a transmission module able to combine the scalability of superchannel-based transmission with the flexibility required for highly meshed traffic. The modular nature of the SBVT implies that a large array of transmission capacity is predeployed per module, which significantly affects the planning and dimensioning of backbone optical networks. These planning methods should also account for the switching modules that are required to support the interconnection between the SBVTs on the line-side and the client signal interfaces. In this paper we study the impact of the switch capacity on the cost and flexibility of SBVT-enabled networks. Specifically, we propose a multiperiod planning simulation based on integer linear programming models to optimize incremental traffic deployments with respect to the cost of SBVTs, switches, and client cards. The results highlight the fact that switch capacity must be carefully balanced in order to avoid overprovisioning the switch capacity beyond the traffic requirements, while at the same time providing enough flexibility in the client-to-line interconnection to do efficient lightpath grooming and therefore reduce client-card- and SBVT-related costs.

Cost-optimized dimensioning of translucent WDM networks with Mixed-Line-Rate spectrum-flexible channels

In order for transport networks to cost-effectively provide higher capacity, it is expected that channel bit-rates beyond 100 Gb/s will be accomplished by resorting to a flexible WDM grid with variable channel spacing. Among the implications of this concept is the need for planning tools that fully exploit the additional degrees of freedom enabled by a flexible grid to further optimize network cost and spectral efficiency. This paper proposes an optimization framework to minimize the transponder and regenerator deployment cost in a translucent WDM network featuring channel bit-rates of 40, 100 and 400 Gb/s and multiple transmission formats per bit-rate, each characterized by its own spectral width, optical reach and cost properties. Firstly, we formulate the problem via a novel Integer Linear Programming (ILP) model, whose resolution finds the optimal (cheapest) feasible network configuration. Secondly, we propose an efficient heuristic called Narrowest First-Iterative Cost Reduction (NF-ICR) to handle network scenarios for which solving the ILP entails an unreasonable computational burden. The NF-ICR heuristic is shown to provide tight optimality bounds where the benchmark given by the ILP solution is attainable. For larger networks, we show that the use of a flexible grid and multiple format options for each bit-rate results in around 10% less cost in transponders and regenerators for metro networks, and a substantial increase in the total traffic load supported by the network. We also conclude that a distinction emerges between metro/regional scenarios and long-haul networks with long paths, wherein the shorter transparent reach of 400 Gb/s channels drives up the cost due to extra regeneration, favoring the use of parallelized solutions of lower bit-rate channels.

On the cost-effective deployment of future data services over transport networks with a flexible DWDM grid

We employ a cost-optimization procedure for the static planning of flexible-grid networks with heterogeneous interfaces spanning 40, 100 and 400 Gb/s channels. The optimization results show that the extra capacity enabled by this setup can reach 37% in a long-haul network, and more than double in a metro network. Furthermore, we evaluate different scenarios in terms of the traffic profile and the cost ratio between 100G and 400G technology. It is shown that 400G channels already have a strong case for cost-efficient deployment in the range of 2.5 to 3 times the cost of 100G, and for demands exceeding 200 Gb/s, more so in metro scenarios.