Abstract—In this paper, we focus on the design of different node architectures suitable for Few-Mode Multi-Core Fibers (FM- MCFs) based networks. Both dimensions, core and mode, open different possible ways to group spatial channels depending on the physical impairments of the Space-Division Multiplexed (SDM) optical fibers. Moreover, the channel switching across a group of cores/modes at once and the end-to-end routing are not only mandatory aspects for certain spatial channels, but also recommendable in order to reduce the node complexity/cost. Thus, we propose various SDM-capable node architectures based on versatile and homogeneous spatial group configurations. Then, a unified physical-layer-aware Quality of Transmission (QoT) estimator is formulated to not only evaluate these node architectures in a simulation tool, but also validate them in a real experimental environment using a stateful Path Computation Element (PCE) as a central controller. The obtained results disclose that the cost-efficient node design parameter, namely, the size of the spatial group  , depends on both the network and traffic profile size. Specifically, for a national optical backbone network equipped with a homogeneous and hexagonally arranged 6-weakly-coupled modes and 7-weakly-coupled cores fibers,  equals 6, while for a continental backbone network,  can raise up to 14. In any case, we demonstrate that the cost-benefit tradeoff in node design must be analyzed in detail in order to meet the huge traffic volumes of the next years. Index Terms—SDM, FM-MCFs, QoT Estimator, ROADMs, Network Design, Resource Allocation. NOMENCLATURE A/D add/drop ASE amplified spontaneous emission AoD architecture on demand BBP bandwidth blocking probability BER bit error rate BV-OXC bandwidth variable optical cross connect BVT bandwidth variable transponder R. Rumipamba-Zambrano is with the Corporación Nacional de Telecomunicaciones CNT E.P., 170518 Quito, Ecuador; Coordinación de Investigación e Innovación, ABREC, 170528 Quito, Ecuador, and with the Institute for Applied Sustainability Research, Quito, Ecuador (e-mail: ruben@rumipamba.ec) R. Muñoz and R. Casellas are with the Centre Tecnològic de Telecomunicacions de Catalunya, Barcelona 08860, Spain (e-mail: raul.munoz@cttc.es; ramon.casellas@cttc.es). J. Perelló and S. Spadaro are with the Advanced Broadband Communications Center (CCABA), Universitat Politècnica de Catalunya (UPC) – Barcelona CAPEX capital expenditures CD chromatic dispersion D nodal degree DMGD differential modal group delay DP dual-polarization DSP digital signal processing DT12 12-node deutsche telekom optical network EDFA erbium-doped fiber amplifier EON elastic optical network EROs explicit route objects FF first-fit FEC forward error correction FJoS fractional joint switching FMF few-mode fiber FM-MCFs few-mode multi-core fibers FM-SSS few-mode-based SSS FS frequency slot G group size GB guard-band GLC group lane change GN Gaussian-noise GVD group velocity dispersion HT holding time I number of connected SDM fibers in an SDM-ROADM IAT inter-arrival time ICXT inter-core crosstalk ICS inter-core skew IMXT inter-mode crosstalk InS with LC independent switching with lane change support Tech, 08034 Barcelona, Spain (e-mail: perello@ac.upc.edu; spadaro@tsc.upc.edu ). Abdulaziz E. Elfiqi is with School of Engineering, The University of Tokyo, 7- 3-1 Hongo, Bunkyo-ku, Tokyo, Japan, and with the Electronics and Electrical Communications Engineering Department, Faculty of Electronic Engineering, Menoufia University, Menouf 32952, Egypt (e-mail: abdulaziz.elfiqi@ieee.org). Copyright (c) 2020 IEEE. Rubén Rumipamba-Zambrano, Raul Muñoz, Ramon Casellas, Jordi Perelló, Salvatore Spadaro, and Abdulaziz E. Elfiqi, Member, IEEE Design and Assessment of FM-MCFs-suited SDM-ROADMs with Versatile Spatial Group Configurations and Unified QoT Estimator 1 © 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. DOI 10.1109/JLT.2020.3009413