MDU (Multi-Dwelling Unit)
A residential building containing multiple independent housing units served by a single building demarcation, including apartments, condos, dormitories, and townhomes.
MDU stands for Multi-Dwelling Unit. In fiber access engineering, an MDU is any residential building containing multiple independent housing units served from a single building-level demarcation — apartments, condominiums, dormitories, townhomes, and senior-living complexes all qualify. MDU economics differ fundamentally from single-family residential because the in-building distribution problem is non-trivial: fiber must reach the building, then the operator must distribute service to dozens or hundreds of individual units inside the building, often through riser plant that the operator does not own or fully control.
MDUs are typically classified by unit count: small (2–24 units, garden-style apartments and small condos), medium (25–99 units, mid-rise buildings), large (100+ units, urban high-rises). Each class has different economics and different optimal in-building distribution technologies. Small MDUs often justify per-unit fiber drops (FTTH-MDU), medium MDUs typically use FTTB with in-building fiber risers, and large MDUs may require a building-level optical aggregation point with in-building PON or G.fast distribution.
In-building distribution technology choices include:
- **In-building fiber (FTTH-MDU)**: 1–2 fiber strands per unit from a building MDF to each unit's ONT. Highest performance, FTTH-class symmetric multi-gigabit. Requires significant riser pathway availability. - **G.fast over existing copper (ITU-T G.9700/G.9701)**: 1 Gbps downstream over the existing in-building twisted-pair plant. Bandwidth degrades sharply with distance (effective range ~250 ft); suitable for buildings with shorter copper risers. - **In-building PON (extension of access PON or dedicated in-building 1:8/1:16 splitters)**: shared bandwidth distributed through in-building splitters to per-unit ONTs. Reuses access PON technology and ONT inventory. - **MoCA (Multimedia over Coax Alliance)**: 1–2.5 Gbps over existing coax riser. Used when fiber and copper are both unavailable but coax is already wired.
In-building cabinet selection follows NEMA standards: NEMA 1 enclosures for indoor dry locations (the typical MDU MDF), NEMA 4 for damp/wet locations (basement utility rooms), and NEMA 4X for corrosive environments. UL 1773 (Termination Boxes) governs the enclosure used at the MDU demarcation. Cabinet sizing is driven by fiber count, ONT count, and required ventilation; a typical 200-unit MDU MDF requires a 60×30×12 inch wall cabinet with 24+ fiber drops, an MDU-grade ONT or active Ethernet switch, and battery backup for the operator-side equipment.
MDU vs SFR (Single-Family Residential): SFR deployments deliver one fiber drop per home from the nearest NAP, with the ONT/NID installed on the home's exterior wall. MDU deployments deliver a single (or few) fiber drops to the building demarcation, with internal distribution to each unit. SFR's per-passing cost is dominated by drop construction ($300–$700 per home); MDU's per-passing cost is dominated by in-building wiring ($100–$400 per unit), with the building-entry fiber drop amortized across all units. MDU service penetration tends to be higher than SFR (60–80% in well-marketed buildings versus 30–50% in SFR neighborhoods) due to single-sales-cycle building-wide commitments.
Accurate MDU modeling in the GIS captures both the building-level demarcation (location, fiber count, ONT/switch inventory) and the per-unit distribution (riser pathway, in-building technology, unit-level service status). MapItRight models MDUs as hierarchical assets — a building with N units, each unit with its own service record, all linked to the shared building demarcation — supporting both operator-side fault isolation and unit-level service activation and billing.