ONU (Optical Network Unit) Optical Network Unit, ONU is divided into active optical network unit and passive optical network unit. Generally, equipment equipped with network monitoring devices including optical receivers, uplink optical transmitters, and multiple bridge amplifiers are called optical nodes. The PON uses a single optical fiber to connect to the OLT, and then the OLT connects to the ONU. ONU provides data, IPTV (Interactive Internet TV), voice (using IAD, Integrated Access Device) and other services, truly realizing "triple-play" applications.