optical network unit (xDSL) (ONU)

The optical network unit (ONU) is a multiplexer component of the optical access network and forms the subscriber-side interface of the optical distribution network( ODN). The optical network unit is also known as the optical line distributor( OLD) and forms the optical network termination( ONT). It receives the downstream data from the star-connected PON variants, the Ethernet Passive Optical Network( EPON) or Gigabit PON( GPON).

The ONU controls the throughput of the broadcasting. In the upstream, the data streams are collected in a common optical fiber and transmitted in a transmission window. The transmission window is assigned to the ONU by the Optical Line Termination( OLT). The ONU converts the optical signals at the ODN interface into electrical signals for the subscriber lines.

GPON network with OLT and ONUs

The ONU units differ functionally depending on whether the connection is residential or commercial and whether it is FTTB or FTTH. For businesses connected via FTTB or FTTO, for example, the termination is with a single business unit( SBU) or a multi-tenant unit( MTU). For residential customers connected via FTTH, FTTB or FTTC, with a Single Family Unit( SFU), a Home Gateway Unit( HGU), a Multi Dwelling Unit( MDU) or with an Optical Network Unit (ONU). And the Mobile Backhaul, which is connected via FTTCell, is connected via a Cellular Backhaul Unit( CBU).

Optical Network Units (ONU) are available in a wide variety of designs: As Gigabit Interface Converter( GBIC) and as SFP+ module orSFP+ module.

Optical Network Unit (ONU), Photo: Motorola

Cabling from the ONU to the subscriber is via the copper pair. With passive branching, up to 32 ONUs can be supplied simultaneously and the bandwidth distributed to the various supply areas as required. Fiber optic connections added later, for example for Fiber to the Home (FTTH), can be integrated directly.