This paper presents analyses of four broad-band fiber-optic subscriber loop architectures, including active (high-speed TDM-based) and passive (dense WDM-based, dense WDM-based with an analog subcarrier-multiplexing overlay, and splitter-based) double-star topologies. The analyses focus on specific demonstrated architectures and use component cost projections based on learning curves to estimate future network costs on a per-subscriber basis. We find that the splitter-based passive loop can deliver voice and video services and that the dense WDM-based loop with a subcarrier-multiplexing overlay can deliver voice and broadcast video at lower near-term installed first costs than the other architectures. This is due to the sharing of bandwidth among a cluster of subscribers for the architectures that use splitters and to relatively lower costs for near-term analog subcarrier-multi-plexed video delivery compared to digital video delivery. However, these cost disparities are smaller in the long term. We also investigate the sensitivity of projected cost per subscriber to remote multiplexing node size and to double-star prove-in distance. The results indicate that the four architectures have very different double-star prove-in distances and that passive loop costs are minimized for much smaller remote node sizes than active loops, thus permitting cost-effective deployment of passive loops for smaller groups of subscribers. In addition, cost breakdowns for the four architectures indicate that splitter-based passive loops share electronics more effectively among subscribers than loop architectures requiring dedicated (per-subscriber) electronic interfaces, resulting in projected cost advantages for the splitter-based networks. © 1990 IEEE
