I was reading a Carrier Ethernet book from CRC Press. In it, the justification for developing Carrier Ethernet is to have a means of transporting Ethernet frames from the LAN over a MAN or WAN using another Ethernet frame format. This is suppose to lower cost, but most of all, since Ethernet is transported by Ethernet, then there is no need to convert it to another format. Conversion delay will be eliminated.
Okay, I get that part. But what I don't get is why Carrier Ethernet services is normally offered via SONET/SDH or an IP/MPLS network. The way I see it is the Carrier Ethernet frame is being converted to another format, and then re-converted back at the destination.