This Recommendation describes the functional architecture of Ethernet networks using the modelling methodology described in ITU-T Recommendations G.805, G.809 and G.800. The Ethernet network functionality is described from a network level viewpoint, taking into account an Ethernet network layered structure, client characteristic information, client/server layer associations, networking topology, and layer network functionality providing Ethernet signal transmission, multiplexing, routing, supervision, performance assessment, and network survivability. The functional architecture of the server layer networks used by the Ethernet network is not within the scope of this Recommendation. Such architectures are described in other ITU-T Recommendations or IETF RFCs. This Recommendation is based on the Ethernet specifications in IEEE Standards 802.1Q-2018 and 802.3-2018, and developments of provider bridged networks. Furthermore, the architectural aspects of provider bridges currently being defined in IEEE P802.1ad task force are taken into account. This Recommendation defines the Ethernet maintenance entities, but the specific impact on the transport functions of connection monitoring in a connectionless layer network is not addressed. Ethernet network survivability is intended for inclusion in a future version. This Recommendation is the first of a series of Ethernet and Ethernet over Transport-related Recommendations. Other Recommendations in this series will address e.g., equipment, OAM, service, performance aspects.