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 operator's 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.