What do you mean by "their own"? There's nothing about SONET/SDH that's specific to undersea cables.
SONET has optical networking in its name. It appears to me that data not being transmitted over copper wires is a pretty crucial aspect of it... but really none of this matters as I was simply pointing out that TCP is not relevant to the speed record, in answer to the top two comments above, and not trying to make any absolute assertions about how the transport protocol works. So yes, you're right, I guess?