OC-192c/STM-64c and 10 Gigabit Ethernet WAN PHY

The introduction of 10 Gigabit Ethernet (10 GbE) WAN PHY into the IP/Ethernet networking community has led to confusion over the applicability between 10 GbE WAN PHY and OC-192c/STM-64 interfaces. Both of these interfaces support transmission at 9.6 Gbps, support SONET/SDH framing, and can be connected to SONET/SDH ADM or DWDM gear. So what is the difference? The answer can be boiled down to two things: L2/L3 protocol support, and link diagnostic and maintenance capabilities.