OLT density in a central office

Tags:
Networking
OLT
The text here is a little confusing. One paragraph shows: "An optical line terminal (OLT), located at the provider's central office, transmits data to users at 1310 nanometers (nm). The signal passes through splitters and can serve up to 128 customers at a range of approximately 20 kilometers, or 12.5 miles." This implies that a single OLT can serve up to 128 customers. Another sentence in the same article shows the text: "A single OLT can serve thousands of customers and can be centralized in a campus environment." Furthermore, the Fujitsu FA-2232U's data sheet shows that it can support up to 512 subscribers. No information about distance between the OLT and the ONU is visible in the data sheet. Neither 128 nor 512 seem to be a realistic density of ONU per CO. "Thousands of customers" is more realistic. Questions:
  1. Assuming one ONU per customer, how do you reconcile the estimate of thousands per OLT with the figures of 128 and 512?
  2. I would assume that one CO would be planned to host more than one OLT. Is this a reasonable assumption?
Thank you!


Software/Hardware used:
FA-2232U
1

Answer Wiki

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This pdf  seems to hold at least part of the answer.

It shows an OLT with 14 line cards; each line card has four singlemode fibre output ports. That makes a total of 56 singlemode fibres per OLT chassis.

Each fibre can be split into 32 fibres at a splitter. Each of these latter fibres goes to a customer’s ONT, supporting a total of 1792 customers (or subscriptions, at least). This matches the “thousands” referred to in the article.

What this does not answer is the context of the article’s author’s reference to 128 customers per OLT.

The other question, regarding the OLT density in a central office, would have an interesting answer but the answer is most likely going to refer to a lot of discretion in the hands of the service’s architects.

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