The boundary or point of interaction between a network and the end user, the UNI is both a physical and logical point of demarcation. The UNI serves the technical boundary where protocol issues are resolved and as the point of division between the responsibilities of the service provider and those of the end user. In ISDN, for example, the UNI is defined as basic rate interface (BRI) for low-speed access and primary rate interface (PRI) for high-speed access, and is implemented in customer premises equipment (CPE). In frame relay, the UNI is implemented in the frame relay access device (FRAD), which is CPE, and the frame relay network device (FRND) located at the edge of the carrier network. In asynchronous transfer mode (ATM), a Private UNI is employed in a private ATM network, such as an ATM-based LAN. A Public UNI the interface between an ATM endpoint or private ATM switch and an ATM switch in a public network. See also BRI, CPE, FRAD, frame relay, FRND, ISDN, logical, physical, PRI, and protocol.