Optimization of Spectrum Resource Allocation for Multicast Services Based on Subtree Routing in Elastic Optical Networks

With the rapid development of internet applications such as video conferencing and online learning, along with the widespread adoption of bandwidth-intensive services, traditional wavelength-routed optical networks (WRONs) can no longer meet these diversified bandwidth demands. As an innovative solution, Elastic Optical Networks (EONs) dynamically allocate appropriate spectrum resources and configure corresponding modulation formats based on user requirements and traffic volumes, effectively overcoming the limitations of WRONs. However, EON transmissions must adhere to constraints including spectrum consistency, non-overlapping, and continuity. Prolonged network operation generates idle spectrum fragments that violate these constraints, resulting in spectrum resource wastage, aggravated network congestion, and degraded overall performance. To address these challenges, this study proposes the Subtree Routing Algorithm Based on Multicast Service (STMS) and the Spectrum Resource Allocation Algorithm for Multicast Services Based on Sub-Routing (SR-MSRA). The core concept of STMS involves grouping destination nodes of multicast sessions and splitting a single large light-tree into multiple subtrees, where each subtree adaptively selects optimal modulation formats according to real-time spectrum states, thereby significantly improving multicast service request success rates. Building upon STMS, SR-MSRA further enhances request success rates and mitigates spectrum fragmentation by decomposing multicast requests into sub-routes and introducing a spectrum window utilization metric to dynamically evaluate and select sub-routes. This strategy efficiently utilizes dispersed idle spectrum fragments while satisfying continuity constraints, substantially reducing multicast blocking probability. Additionally, we formulate an integer linear programming (ILP) model and design a heuristic algorithm. Extensive simulations on standard network topologies demonstrate that STMS reduces service blocking probability by 4.61\% compared to the conventional Multicast Light-Tree Protection Algorithm (MLPA). SR-MSRA exhibits superior performance in reducing blocking probability 2.43\% improvement over STMS, improving spectrum utilization, and alleviating fragmentation, proving its effectiveness in leveraging spectrum fragments. This research provides novel insights for high-speed flexible resource scheduling in EONs and offers theoretical and practical guidance for network operators to manage spectrum resources efficiently under diverse Quality of Service (QoS) requirements.