A broadcast-and-select ROADM architecture to support linear hub-ended trees using point-to-multipoint coherent transceivers [Invited

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Point-to-multipoint (P2MP) coherent pluggable transceivers based on digital subcarrier multiplexing (DSCM) have been proposed as a promising technology to reduce the costs of optical transport networks. However, to establish the P2MP trees, bidirectional multicast functionality is required at the optical nodes. While conventional broadcast-and-select (B&S) wavelength selective switch (WSS)-based reconfigurable optical add/drop multiplexer (ROADM) architectures can inherently perform splitting operations, merge operations of DSCM signals face internal blocking in conventional WSSs since they require switching signals from different input ports on the same carrier wavelength (although using different subcarriers) to the common output port. In this paper, we propose an alternative ROADM architecture requiring a simple low-cost modification, which can support P2MP trees, provided that they are routed as linear chains with the hub node at one end, without requiring multicast-enabled WSSs. We evaluate the potential savings of linear hub-ended P2MP trees on a metro reference scenario using a modified tree-determination, routing, and spectrum assignment (TRSA) dimensioning algorithm. Results indicate that linear hub-ended trees can significantly reduce transceiver costs with respect to point-to-point (P2P) solutions in all considered cases, with savings ranging from 6%–28% depending on the traffic load. While these savings are somewhat less than those achievable with arbitrary P2MP trees and latency is slightly higher, spectrum waste is reduced by employing linear routing, and the trees can be supported by the proposed architecture.