ONU is divided into active optical network unit and passive optical network unit. Generally, devices equipped with network monitoring including optical receivers, upstream 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 services such as data, IPTV (i.e. interactive network television), voice (using IAD, i.e. Integrated Access Device), realizing "triple-play" applications
ONU is an optical network unit, OLT is an optical line unit, OLT+ONU forms an optical fiber access network, which is connected to the switch through V5.