Tii Technologies · Fiber Basics
What Is a Fiber Distribution Hub (FDH)?
A fiber distribution hub (FDH) is an enclosure in a PON/FTTH network where the feeder fiber from the central office is optically split and cross-connected to the distribution fibers that serve individual customers. It houses the PON splitters, splice provisions, and adapter panels, and gives technicians one access point to connect, test, and rearrange customer drops.
What an FDH does
In a passive optical network, one feeder fiber can serve dozens of homes because it’s divided by optical splitters (commonly 1×32). The FDH is where that division physically happens. Inside a typical hub you’ll find three functional areas: a feeder field where the incoming OSP cable is spliced or terminated, a splitter field holding the PLC splitter modules, and a distribution field of adapter panels where each output is patched to the distribution fiber heading toward a neighborhood, building, or terminal. Because customers are connected by moving patch cords rather than splicing, an FDH lets an operator light up new subscribers in minutes and audit or rearrange the network without cutting fiber.
Where it sits in the network
The FDH is the hinge point of the outside plant: central office / OLT → feeder cable → FDH (split and cross-connect) → distribution cable → entrance terminals and drop demarcation at each premise → customer connection point at the ONT. In Tii’s architecture that chain reads FDH → FET entrance terminal → FISS demarcation enclosure → CCP wall terminal.
Types and sizing
| Type | Typical use | Typical capacity |
|---|---|---|
| Wall-mount FDH | MDUs, small PON nodes, indoor/protected locations | 12–288 distribution ports (e.g., Tii FDH1/FDH2) |
| Pole/pad-mount cabinet FDH | Neighborhood serving areas, rural PON, BEAD builds | 288–864 distribution ports (e.g., Tii FDH5–FDH9) |
| Modular enclosure FDH | Wall/pole locations needing cassette-based growth | Up to 144 drops (e.g., Tii HCCH) |
Sizing an FDH means matching the distribution port count to the homes passed in the serving area (plus growth), choosing split ratio (1×32 is the common default; 1×16 for longer reaches or higher per-customer bandwidth, 1×64 for maximum density), and picking the mounting and environmental rating the site demands. Splitters are typically added on a pay-as-you-grow basis — cabinets ship with capacity for more splitter modules than day-one demand requires.
FDH vs. related enclosures
- FDH vs. fiber entrance terminal (FET): the FDH splits and cross-connects at the serving-area level; an entrance terminal transitions OSP fiber to a building or cluster of drops downstream of the hub.
- FDH vs. cross-connect cabinet: a pure cross-connect (like the Tii FDX) patches feeder to distribution without splitters; an FDH adds the PON splitting function.
- FDH vs. splice closure: a splice closure joins cables permanently; an FDH provides re-enterable, connectorized flexibility.
Specifying an FDH? See complete Tii FDH Series specifications and part-number builders (wall-mount to 864-port pad-mount cabinets), call 888-844-4720, or request a quote.