Line Interface Unit (LIU): The LIU is a crucial part of the fiber patch panel, serving as the interface between the network and the fiber optic cables. It is mainly used for the straight-through connection and branch connection of the indoor optical cable and the fixing of the cable terminal and functions as a pigtail storage and protection. ations in LANs at a premise location. Patch panels are Rack-mountable onto 19”, 21”and 23” rack systems, Wall Mountable, Din Rail Mountable, and Table Mountable Types. The. An LIU, or Line Interface Unit, for fiber optics is an essential component in telecommunications and data networking systems.