SBC Behind 1-to-1 NAT

Hi Everyone
This is my first post.

For some security reasons the SBC needs to work behind a 1-to-1 NAT environment. On its public signaling facing side, the SBC will use a private media IP address mapped to a public IP (this mapping is done on the public facing router, hence, the SBC doesn't know this public IP).

Is a there a way to tell the SBC what its External Public IP is?
If Not, then please what's the best approach here?