Match topology to service, not fashion
Point-to-point active Ethernet dedicates a fiber and port per customer: maximum capacity and isolation, highest fiber count and CO space — right for business services and cell-site backhaul. Ring topologies with protection switching (sub-50 ms failover) suit metro aggregation where survivability is contractual. PON shares OLT ports and feeder fibers through passive splitters: lowest cost per home, the residential default.
Sizing the plant
Fiber counts flow from demand math: homes passed × target take rate × growth factor, plus dedicated strands for business, mobile and future nodes. Feeder segments deserve generosity — the cost of extra fibers in a cable is small; a second dig is not. Duct and pole capacity is designed for the 25-year plant, not the launch year.
Resilience by design
Classify services by availability targets; give protected services diverse physical routes (not two tubes in one cable). Document single points of failure explicitly — an honest SPOF register beats an optimistic map.
Deliverables of this phase
An architecture memo (options, costs, decision), high-level route maps, fiber count tables per segment, and the ODN class / optics selection that later budgets must obey. Every later lesson in this level fills in details under these decisions.