Enabling extended access aggregation with light-trees and point-to-multipoint coherent transceivers

Traditionally, traffic from the access nodes is aggregated in metro-aggregation hubs over rings or horseshoes in a fixed configuration using multiple optical point-to-point (P2P) transceivers. However, this static setup limits dynamic scalability and often leads to inefficient resource usage and high costs, especially under increasing and varying traffic conditions. Coherent optical point-to-multipoint (P2MP) transceivers offer a promising solution for aggregation at this network level. These transceivers allow a single (aggregation) node to communicate with multiple (access) nodes simultaneously via digital subcarrier multiplexing (DSCM) technology. Additionally, their long-distance transmission capabilities enable the placement of the P2MP transceiver root deeper in the hierarchy. In this paper, we propose an extended access aggregation architecture that incorporates modified reconfigurable optical add–drop multiplexers (ROADMs) to support both traditional P2P and P2MP connections. This architecture allows the creation of light-trees to enable P2MP communication and hence to boost transmission flexibility and multiplexing gains. We propose a mixed-integer linear programming (MILP) model to determine the optimal placement of P2MP transceivers and the establishment of light-trees, considering physical layer impairments (PLIs) and the required quality of transmission (QoT) for the connections. To tackle the high algorithm complexity, we also introduce a best-fit decreasing heuristic to efficiently exploit the trade-off between execution time and performance. Our simulation experiments using real network topologies showcase that our proposed architecture can greatly enhance multiplexing gains while considering the operational costs tied to network expansions and upgrades.