(1) (Network-to-Network Interface) In ATM networking, the interface between two ATM devices (typically ATM switches). In frame relay networking, the interface between two separate frame relay networks. Contrast with UNI.
The boundary or point of interaction between network service providers.The NNI is both a physical and logical point of demarcation.The NNI serves the technical boundary where protocol issues are resolved and as the point of division between the responsibilities of the individual service providers. NNIs are defined for asynchronous transfer mode (ATM) and frame relay, as examples. See also ATM, logical, frame relay, physical, and protocol.