Structured cabling is building or campus telecommunications cabling infrastructure that consists of a number of standardized smaller elements (hence structured) called subsystems. Structured cabling falls into six subsystems: Entrance Facilities are where the building interfaces with the outside world. Equipment Rooms host equipment which serve the users inside the building. Telecommunications Rooms house telecommunication equipment which connect the backbone and the horizontal cabling subsystems. Backbone Cabling connect between the entrance facilities, equipment rooms and telecommunications rooms. Horizontal Cabling connect telecommunications rooms to individual outlets on the floor. Work-Area Components connect end-user equipment to outlets of the horizontal cabling system. Structured cabling design and installation is governed by a set of standards that specify wiring data centers, offices, and apartment buildings for data or voice communications, using category 5 (CAT 5E) or category 6 cable (CAT 6E) and modular sockets. These standards define how to lay the cabling in a star formation, such that all outlets terminate at a central patch panel (which is normally 19 inch rack-mounted), from where it can be determined exactly how these connections will be used. Each outlet can be ‘patched’ into a data network switch (normally also rack mounted alongside), or patched into a ‘telecoms patch panel’ which forms a bridge into a private branch exchange (PBX) telephone system, thus making the connection a voice port.