Ethernet is a permanent success story, extending its reach from LAN and metro areas now also into core networks. 100 Gbit/s Ethernet will be the key enabler for a new generation of true end-to-end carrier grade Ethernet networks. This paper first focuses on functionality and standards required to enable carrier-grade Ethernet-based core networks and possible Ethernet backbone network architectures will be discussed. The second part then evaluates the CAPEX and OPEX performance of Ethernet core networks and competitive network architectures. The results propose that Ethernet will not only soon be mature enough for deployment in backbone networks but also provide huge cost advantages to providers. A novel complete, cost-effective and service-oriented infrastructure layer in the area of core networks will arise. The industry-wide efforts to cover remaining challenges also confirm this outlook.