This Recommendation specifies the Ethernet UNI and the Ethernet NNI, where the Ethernet UNI is formed by an Ethernet interface and the Ethernet NNI by an Ethernet interface or an Ethernet over transport interface. The Ethernet over transport NNI uses the OTH server layer network. The detailed requirements applicable to these interfaces are specified in a number of ITU-T Recommendations, and in IEEE Standards that are referenced.

This Recommendation defines the interfaces of the Ethernet transport network to be used within and between subnetworks of the Ethernet network, in terms of Ethernet transport hierarchy, formats for mapping and multiplexing client signals into Ethernet connections and formats for multiplexing Ethernet connection signals into Ethernet or non-Ethernet connection signals.

This Recommendation assumes but does not specify the Ethernet component and/or equipment models to support the Ethernet UNI and NNI. Those models are specified in [ITU-T G.8021]. This Recommendation limits the specification of the Ethernet UNI and NNI to Ethernet equipment types aligned with the bridge types specified in [IEEE 802.1Q] and supporting only the untagged, prioritytagged or tagged traffic units covered in [ITU-T G.8021].