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ODN

ODN is the Acronym for Optical Distribution Network

A fiber-optic telecommunications network uses unpowered devices to carry signals, typically for the last mile between Internet service providers (ISP) and their customers. In this use, a Passive Optical Network (PON) has a point-to-multipoint topology in which an ISP uses a single device to serve many end-user sites using a system such as 10G-PON or GPON. In this one-to-many topology, a single fiber serving many sites branches into multiple fibers through a passive splitter, and those fibers can each serve multiple sites through further splitters. The light from the ISP is divided through the splitters to reach all the customer sites, and light from the customer sites is combined into the single fiber. Many fiber ISPs prefer this system.

Components of an ODN

  • Feeder Fiber: The high-count trunk cable running from the Optical Line Terminal (OLT) at the exchange to a distribution point serving a neighborhood.
  • Optical Splitters: Passive glass components, typically in a street cabinet or underground closure, that divide one incoming fiber into 16, 32, 64, or 128 branches without any power.
  • Distribution Fiber: The cables that carry each split branch along streets toward individual serving areas.
  • Drop Cable: The final fiber segment from the street into the building, terminating at the wall outlet where the Optical Network Terminal (ONT) connects.

Split Ratios: The Central Design Trade-Off

Because every home on a branch shares the light from one OLT port, the choice of split ratio balances cost against capacity and reach.

  • 1:16: 16 homes per OLT port. Maximum reach and per-home capacity; common for business services.
  • 1:32: 32 homes per OLT port. The typical residential FTTH balance of cost and performance.
  • 1:64: 64 homes per OLT port. Denser urban deployments; reduced optical budget and reach.
  • 1:128: 128 homes per OLT port. Maximum density; requires short distances or higher-power optics.

Why Passive Infrastructure Matters

  • Reliability: With no electronics in the field, there is nothing between the exchange and the home that can lose power, overheat, or fail during storms, so outage rates drop accordingly.
  • Operating Cost: No street-level power feeds, batteries, or cooling means significantly lower energy and truck-roll costs per subscriber than copper or hybrid networks.
  • Future-Proofing: The glass itself is speed-agnostic. Operators have upgraded the same ODN from GPON to XGS-PON and beyond simply by changing the electronics at both ends; the buried fiber remains untouched for decades.

The Business Lens: Homes Passed vs. Homes Connected

Fiber rollout economics are measured against the ODN. A home passed is a premises the distribution network reaches; a home connected has a live drop and ONT installed. The gap between the two is the operator’s addressable market, and closing it is a marketing challenge as much as an engineering one. In open-access and wholesale-only models, a single ODN is shared by multiple competing ISPs, so the network owner’s infrastructure investment and the retail brands’ customer acquisition efforts operate as separate businesses on the same glass.