FTTx Network Basics

The FTTx architecture consists of a passive optical network (PON) that allows several customers to share the same connection, without any active components (i.e., components that generate or transform light through optical-electrical-optical conversion).

A feeder fiber is brought from an optical line terminal (OLT) in the CO to a fiber distribution hub (FDH) near a group of customers. From that point, a passive splitter is used to typically connect up to 32 or 64 customers to the same feeder fiber. Then, each customer premises is provided with an optical network terminal (ONT) connected to each splitter branch. This point-to-multipoint architecture dramatically reduces network installation, management, and maintenance costs as shown by the figure below.

The OLT provides voice and data downstream transmission using a 1490-nm wavelength band, while the ONT provides upstream transmission with a 1310-nm wavelength band, allowing for bidirectional transmission on the same fiber without the signals interfering with one another.

In addition, the OLT may be connected to a wavelength-division multiplexing (WDM) coupler to provide video together with voice and data (triple-play) services over a single fiber. The video is provided in the downstream direction only, usually in a 1550-nm wavelength band (traditional analog video).