A Passive Optical Network (PON) consists of an Optical Line Termination (OLT) on the central side of the network, to which optical splitters - splitters - are connected by a branched structure. Optical Network Units (Optical Network Unit, ONU or also ONT, Optical Network Termination) are most often connected to them in a tree, or circular or star topology. The distance between OLT and ONU can reach up to 20km.