In the IP over DWDM Wikipedia page, we see this sentence: (this link) "A true IPoDWDM solution is implemented only when the IP Routers and Switches support ITU-T G.709. In this way, IP devices can monitor the optical path and implement the transport functionality as FEC (Forward Error Correction) specified by ITU-T G.709/Y.1331".
My question is, by which actions, the abovementioned router support ITU-T G.709? As the Wikipedia page implies, we can say the OSPF on the router couldn't see the optical links' connectivity and, they are transparent to the router, ya?
And if so, Doesn't the optical layer protection and restoration mechanism (OTN or SDH/SONET protection) intervene in IP layer protocols convergence like OSPF or even STP?
What happens if a router doesn't have an OTN interface and doesn't know anything about the optical layer?