A three-part series on the fiber plant beneath modern railroad signalling: where the cable physically runs, how the network on it talks, and who keeps the record true. One corridor, carried through all three parts.
The physical plant: why signalling went to glass, what lives inside a 48-strand cable, how a midspan access works without touching the express path, and how a loss budget quietly fails at the far end of a fifty-mile corridor.
The logical plant: which devices may share a wire with vital equipment, an addressing schema that encodes the corridor into four octets, and the race between ring reconvergence and a vital processor's stale-data timer.
The institutional plant: why the grant that built the corridor funds nothing that keeps its records accurate, how an OTDR baseline doubles as a defensible condition assessment, and why change control is the only difference between a record and a rumor.