In telecommunications, a user–network interface (UNI) is a demarcation point between the responsibility of the service provider and the responsibility of the subscriber. This is distinct from a network-to-network interface (NNI) that defines a similar interface between provider networks.
Specifications defining a UNI
Metro Ethernet Forum
The Metro Ethernet Forum's Metro Ethernet Network UNI specification defines a bidirectional Ethernet reference point for Ethernet service delivery.